US20080188162A1

US20080188162A1 - Electrochemical mechanical polishing apparatus conditioning method, and conditioning solution

Info

Publication number: US20080188162A1
Application number: US12/068,300
Authority: US
Inventors: Itsuki Kobata; Yasushi Toma; Akira Kodera; Tsukuru Suzuki; Yuji Makita; Takayuki Saito
Original assignee: Individual
Current assignee: Ebara Corp
Priority date: 2007-02-06
Filing date: 2008-02-05
Publication date: 2008-08-07

Abstract

An electrochemical mechanical polishing apparatus is for use in polishing of a conductive material (e.g., metal) on a surface of a substrate by combination of electrochemical action and mechanical action. This apparatus includes a polishing table having divided electrodes and adapted to hold a polishing pad having a polishing surface, a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface, a second electrode for supplying an electric current to the conductive film, an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface, a detecting section adapted to detect a signal corresponding to a thickness of the conductive film, a variable resistance unit having the same number of variable resistors as the number of divided electrodes, a moving mechanism for providing relative movement between the workpiece and the polishing surface, and a control section adapted to control each of the variable resistors based on the signal from the detecting section.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an electrochemical mechanical polishing apparatus, and more particularly to an electrochemical mechanical polishing apparatus for use in polishing of a conductive material (e.g., metal), formed on a surface of a substrate such as a semiconductor wafer, by combination of electrochemical action and mechanical action.
The present invention also relates to a method of conditioning a processing electrode provided in an electrochemical mechanical polishing apparatus which is for performing electrochemical mechanical polishing of a conductive material of a workpiece. The present invention also relates to a conditioning solution for use in such a conditioning method. The electrochemical mechanical polishing apparatus is used to polish a conductive film, formed on a surface of a substrate of electronic device, such as a semiconductor device and a display, and to polish a metal of, for example, a vacuum device and a high-pressure device that require a high-precision finishing.
2. Description of the Related Art
A so-called damascene process is a process of embedding an interconnect metal into interconnect recesses, such as trenches and via holes, formed on an insulating film. This damascene process is increasingly used for forming interconnects in a semiconductor device. The damascene process is performed generally as follows. First, interconnect recesses are formed on an insulating film (interlayer dielectric), which is composed of SiO₂, SiOF, SiOC, a so-called Low-k material, or the like, on a substrate. Subsequently, a barrier film of titanium, tantalum, tungsten, ruthenium, and/or their alloys is formed on a surface of the insulating film in its entirety including the interconnect recesses. Then, an interconnect metal film of aluminum, copper, silver, gold, tungsten, or their alloys is formed on a surface of the barrier film to fill the interconnect recesses with interconnect metal. Thereafter, an extra interconnect metal film and the barrier film formed on portions other than the interconnect recesses are removed. In current high-speed devices, copper or copper alloy is generally used as the interconnect metal, and the Low-k material is increasingly used for the insulating film.
In the damascene process, formation of the interconnect recesses is generally performed by dry etching or the like, and formation of the barrier film is generally performed by a dry process, such as PVD (physical vapor deposition), CVD (chemical vapor deposition), or ALD (atomic layer deposition). Formation of the interconnect metal film is performed by a wet process, such as electroplating or electroless plating, or by a dry process, such as PVD, CVD, or ALD. Recently, electroplating has been widely used to form the interconnect metal film. When the interconnect metal film is to be formed by electroplating onto the barrier film having a low electrical conductivity, a seed film, serving as an electric supply film, is typically formed in advance on the surface of the barrier film subsequent to formation of the barrier film. Generally, the excessive interconnect metal film and the barrier film are removed using a planarizing method, such as chemical mechanical polishing (CMP), or electrolytic polishing, or electrochemical mechanical polishing.
FIG. 1A through FIG. 1C are diagrams illustrating a sequence of process of forming copper interconnects for a semiconductor device. As shown in FIG. 1A, an insulating film 902, such as a film of SiO₂or Low-k material, is deposited on a conductive layer 901 a formed on a semiconductor base 901 having formed semiconductor devices. Via holes 903 and trenches 904 are formed in the insulating film 902 using a lithography etching technique, for example. Thereafter, a barrier film 905 of Ta, TaN, or the like is formed on the insulating film 902, and a seed film 906, serving as an electric supply film for electroplating, is formed on the barrier film 905 by sputtering or the like.
Then, as shown in FIG. 1B, copper plating is performed on a surface of a semiconductor substrate W to fill the via holes 903 and the trenches 904 with copper and, at the same time, to deposit a copper film 907 as an interconnect metal film on the insulating film 902. Thereafter, polishing, such as chemical mechanical polishing (CMP), is performed so as to remove the copper film 907, the seed film 906, and the barrier film 905 on the insulating film 902 until a surface of the copper film 907, filling the via holes 903 and the trenches 904, lies substantially in the same plane as a surface of the insulating film 902. Interconnects 908, composed of the seed film 906 and the copper film 907, are thus formed in the insulating film 902, as shown in FIG. 1C.
In the interconnect-formation process for the semiconductor device, the Low-k material has been introduced with a trend of low conductivity for the interlayer dielectric. Introduction of the Low-k material, on the other hand, raises an issue of how to reduce damages to the Low-k material including destruction and removal of the Low-k material during the polishing process. Lowering of polishing pressure can be one of the solutions to such an issue. In a conventional polishing process of a semiconductor wafer as typified by CMP, uniformity of a polishing rate (removal rate) within a surface of the wafer is achieved mainly by providing uniform polishing pressure over the surface of the wafer or by providing a uniform relative speed between the wafer and a polishing pad during polishing.
FIG. 2 shows a dependence of a polishing rate (removal rate) on polishing pressure in typical CMP. As shown in FIG. 2, in a low-polishing-pressure area, the polishing rate is sharply increased with an increase of the polishing pressure. However, the polishing rate has an inflection point at certain polishing pressure. In an area where the polishing pressure is beyond the inflection point, an increasing rate of the polishing rate is generally low. Under general polishing conditions (e.g., 2 to 3 psi), the polishing pressure is slightly over the inflection point shown in FIG. 2. Accordingly, polishing can be performed at a high polishing rate with uniform polishing pressure over the surface of the wafer (i.e., under the conditions of a low increasing rate of the polishing rate to the polishing pressure).
However, in the low polishing-pressure area (e.g., not more than 1.0 psi (70 hPa)), the increasing rate of the polishing rate to the polishing pressure is high. This fact raises problems including: (1) a large drop in polishing rate; and (2) a large change in polishing rate in response to a small change in polishing pressure. Therefore, solving these problems brings about realization of polishing in the low-polishing-pressure area. Electrochemical mechanical polishing, which utilizes an electrolytic action, is one of the solutions to such problems. A feature of this electrochemical mechanical polishing is that a polishing rate is increased depending on a voltage applied under constant polishing pressure. According to the electrochemical mechanical polishing, a high polishing rate with low polishing pressure can be realized.
In order to secure the uniformity of the polishing rate over the surface of the wafer, there has been proposed an electrochemical mechanical polishing apparatus having plural electrodes arranged so as to concentrically face a wafer and having power supply units (power sources) adapted to control the electrodes independently of each other, as disclosed in Japanese laid open patent publications No. 2003-193300 and No. 2003-278000, and U.S. Pat. No. 6,848,970. According to this type of apparatus, a voltage distribution can be formed within the surface of the wafer during polishing.
However, the power supply units (power sources), which are adapted to apply the voltage to the electrodes concentrically facing the wafer, are generally expensive. Moreover, an increased number of power sources incur not only an increased cost, but also complicated control mechanism.
The electrochemical mechanical polishing for removing a copper film (i.e., a conductive film) on a substrate is performed generally as follows. A substrate with a copper film formed on its surface is held by a polishing head, and a voltage is applied between the copper film and a counter electrode with the copper film serving as an anode. In this state, a polishing pad, attached to a polishing table, is brought into sliding contact with the copper film in the presence of an electrolytic solution to thereby polish the copper film. During polishing, the copper film and the counter electrode are electrically connected via the electrolytic solution. Therefore, the copper film on the surface of the substrate is required to be coupled to one of poles of a power source, and the counter electrode on the polishing table is required to be coupled to another of the poles. In addition, a number of through-holes should be formed in the polishing pad so as to provide the electrical connection between the copper film and the counter electrode via the electrolytic solution. Polyurethane having an insulation property is typically used as a material of the polishing pad.
Generally, there are two types in providing relative movement between the substrate, held by the polishing head, and the polishing pad, held by the polishing table. One is a so-called rotary type in which the polishing head and the polishing table are rotated about their own axes which are not aligned with each other, and another is a so-called orbital type in which the polishing head is rotated about its own axis while the polishing table is scrolled.
There are several ways of supplying an electric current to a conductive film (e.g., a copper film) on the surface of the substrate. For example, an electric supply contact is brought into direct contact with the conductive film, with part of the workpiece (i.e., substrate) overhanging laterally from a periphery of the polishing pad. An electric supply contact in a shape of ball or line may be provided in the polishing pad, or a polishing pad made from a conductive material (i.e., a conductive pad) may be used for supplying the current. When using the conductive pad as the polishing pad, it is a common practice that the polishing table is used as a cathode and the conductive pad is used as an anode and that an insulating material is disposed between the polishing table and the conductive pad.
Furthermore, there is proposed an apparatus having a polishing head with a retainer ring surrounding a periphery of a workpiece to be polished (e.g., a substrate) so as to hold the workpiece and to supply an electric current to a conductive film of the workpiece via the retainer ring.
However, when the electric supply contact, made from metal, is brought into direct contact with the conductive film, such as a copper film, so as to supply the electric current to the conductive film using a polishing pad made from an insulating material, a portion of the surface of the conductive film contacting the electric supply contact would be damaged. Such a damaged portion cannot be used as a semiconductor device. Furthermore, a contact area between the conductive film and the electric supply contact is relatively small, and therefore a stable contact therebetween cannot be secured. As a result, it would become difficult to reliably supply the electric current from the electric supply contact to the conductive film.
Some of the orbital- type electrochemical mechanical polishing apparatuses use the conductive pad as the polishing pad. In this orbital type, the polishing table is not rotated. Therefore, supply of the electric current to the polishing pad can be performed using a so-called stationary joint mechanism. However, in the rotary-type electrochemical mechanical polishing apparatus, the polishing pad is to be rotated together with the polishing table. Therefore, it is generally difficult to use the stationary joint mechanism for supplying the electric current to the polishing pad. Even if the stationary joint mechanism can be used to supply the electric current to the polishing pad, a very small area of the polishing pad is used for current supply to the polishing pad. Consequently, a voltage drop would occur in the polishing pad due to a relatively large electrical resistance, thus causing variations in electric potential within the surface of the conductive film. Such variations in electric potential result in variations in polishing rate within the surface of the conductive film.
In the electrochemical mechanical polishing apparatus having the retainer ring adapted to supply the electric current to the conductive film, the electrical connection between the retainer ring and the conductive film, e.g., copper film, is established by the electrolytic solution. Accordingly, “electrochemical reaction”, which converts electron current into ionic current, is required when the current is transmitted from the retainer ring to the electrolytic solution and when the current is transmitted from the electrolytic solution to the conductive film. This reaction is greatly affected by concentrations of ions in an interface between the electrolytic solution and the metal (i.e., the conductive film). Therefore, the electrochemical reaction would be rendered unstable, and stable supply of current cannot be secured. Furthermore, in the electrolytic solution, since the ions act as carriers for electric charge, the electrical resistance is high, compared with the case where electrons act as carriers for the electric charge. Accordingly, the electric current varies greatly from region to region in the surface of the conductive film, depending on a distance from a current supply point (i.e., the retainer ring). Specifically, the current is concentrated on a periphery of the conductive film, which is a closest portion to the retainer ring, and the polishing rate is thus increased at the periphery of the conductive film. Further, in this current-supply method, a large amount of electric current flows between the retainer ring and the cathode, thus lowering a current efficiency during polishing.
There has been proposed another method of supplying an electric current from a retainer ring to a conductive film, e.g., a copper film, via a seed layer formed on a side surface of a substrate (a workpiece to be polished). However, in this method, an actual contact area of a current supply point is relatively small, and this current supply point is limited to a periphery of the substrate. As a result, it is generally difficult to uniformly supply the current over a surface of the substrate. Particularly, the polishing rate would differ between a central portion and the periphery of the substrate.
Use of the pad having an electrical conductivity entails problems other than the way of current supply. For example, in the electrochemical mechanical polishing, if supply of an electric current to a copper film (i.e., a conductive film) on a surface of a substrate is performed via a polishing pad made from mainly carbon, for example, and having an electrical conductivity (i.e., a conductive pad), an electric potential is applied to the polishing pad itself This electric potential is higher than at least an electric potential of copper. As a result, oxygen would be produced as a result of an electrolytic reaction on a surface of the polishing pad. Such oxygen, produced on the surface of the polishing pad, would cause production of pits on a surface of copper, and would lower a polishing rate of copper.
Further, the above-described rotary type requires a large amount of electrolytic solution, because the apparatus of this type is designed to supply the electrolytic solution from above the polishing pad while rotating the polishing table. For example, when polishing a wafer with a diameter of 300 mm, the electrolytic solution is supplied onto the polishing surface at a flow rate of about 300 ml/min. However, most part of the electrolytic solution, which has been supplied onto the polishing surface, is scattered from the polishing table by a centrifugal force created by rotation of the polishing table, and is discarded without being used in polishing. In the electrochemical mechanical polishing, the electrolytic solution is expendable, but expensive. Therefore, it is required to reduce a cost of the electrolytic solution as low as possible.
When performing the electrochemical mechanical polishing, by-products of polishing are normally deposited on a processing electrode. If the polishing process is continued with the by-products being left on the processing electrode, an electrical resistance between a substrate and the processing electrode would be changed, thus adversely affecting control of the polishing rate within a surface of the substrate. For this reason, it is necessary to remove the by-products from a surface of the processing electrode by conditioning the processing electrode and/or the polishing pad during an interval between polishing operations.
A cleaning liquid, such as pure water, is typically used for conditioning the processing electrode and the polishing pad. However, it is difficult to remove the by-products deposited on the surface of the processing electrode, which is covered with the polishing pad, by washing the processing electrode with the cleaning liquid, e.g., pure water. Thus, chemical etching may be used to remove the by-products deposited on the surface of the processing electrode. However, in order to perform chemical etching, the electrolytic solution on the surface of the processing electrode is required to be replaced with an etching liquid (i.e., a chemical liquid). As a result, components of the etching liquid, remaining on the surface of the processing electrode after conditioning, would affect the polishing process. In order to eliminate such a problem, the etching liquid on the processing electrode and the polishing pad should be completely removed and replaced with the electrolytic solution after the conditioning process and before the subsequent polishing process. These operations require a time and a rinsing liquid.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. It is a first object of the present invention to provide an electrochemical mechanical polishing apparatus which does not have plural electrodes, can thus lower a cost, and can easily perform polishing of a workpiece, such as a wafer, in a low-polishing-pressure area at a high speed with a uniform polishing rate being secured within a surface of the workpiece in its entirety.
A second object of the present invention is to provide an electrochemical mechanical polishing apparatus which can uniformly supply an electric current to a conductive film, such as a copper film, so as to reduce variations in electric potential on a surface of the conductive film, without causing damages to the surface of the conductive film, and can achieve a highly-reliable supply of the electric current to the conductive film even if the apparatus is of a rotary type.
A third object of the present invention is to provide an electrochemical mechanical polishing apparatus which can minimize an electrolytic reaction on a surface of a polishing pad having a conductivity to thereby suppress production of pits on a surface of a conductive film, e.g., a copper film, and can polish the conductive film at a stable polishing rate.
A fourth object of the present invention is to provide an electrochemical mechanical polishing apparatus which can reduce an amount of an electrolytic solution to be used in electrochemical mechanical polishing.
A fifth object of the present invention is to provide a conditioning method which can minimize an influence of components of a conditioning solution, remaining on a surface of a processing electrode and/or a polishing pad (i.e., remaining components), on a polishing process, and can etching away by-products of polishing deposited on the surface of the processing electrode and/or the polishing pad, and to provide a conditioning solution for use in such a conditioning method.
One aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing table adapted to hold a polishing pad having a polishing surface, the polishing table having a first electrode including divided electrodes to be coupled to one of poles of a power source; a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface; a second electrode for supplying an electric current to the conductive film, the second electrode being coupled to another of the poles of the power source; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; a detecting section adapted to detect a signal corresponding to a thickness of the conductive film; a variable resistance unit having the same number of variable resistors as the number of divided electrodes, the divided electrodes being coupled to the one of the poles of the power source via the variable resistors, respectively; a moving mechanism for providing relative movement between the workpiece and the polishing surface; and a control section adapted to control each of the variable resistors based on the signal from the detecting section.
With this aspect of the present invention, currents, flowing between the divided electrodes (the first electrode) and the conductive film facing the divided electrodes (or voltages to be applied between the divided electrodes and the conductive film facing the divided electrodes), are individually controlled and adjusted during polishing by the variable resistors provided between the power source and the divided electrodes. Therefore, plural power sources are not required, and a cost can thus be lowered. Further, polishing can be performed in a low-polishing-pressure area at a high speed with a uniform polishing rate being secured over a surface of the workpiece. Moreover, controlling of the variable resistors provided between the power source and the divided electrodes is easier than controlling of plural power sources.
In a preferred aspect of the present invention, each of the divided electrodes has a ring shape, and the divided electrodes are arranged concentrically with a rotational center of the polishing table.
In a preferred aspect of the present invention, each of the variable resistors has a value of resistance that is variable in a range of 0.1 to 10 Ω.
In a preferred aspect of the present invention, the detecting section comprises an eddy current sensor.
A change in thickness of the conductive film and an exposed surface of a barrier film can be monitored by sensing a change in eddy current. This change of eddy current is fed back to the controlling section so that the controlling section individually controls the variable resistors. With this operation, a thickness of the conductive film can be controlled, and excess polishing of the conductive film (i.e., interconnect metal film) embedded in trenches, which would occur after the barrier film is exposed, can be prevented.
In a preferred aspect of the present invention, the control section is operable to control a polishing rate of the conductive film such that a barrier film, underneath the conductive film, is exposed gradually from a central portion to a peripheral portion of the workpiece.
With this aspect of the present invention, the barrier film, underneath the conductive film, is exposed without causing the conductive film to remain on the barrier film as a result of an electrical insulation.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing table adapted to hold a conductive polishing pad having a polishing surface, the polishing table having a first electrode coupled to one of poles of a power source; a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface, the polishing head having a retainer ring shaped so as to surround a periphery of the workpiece; a second electrode provided on the retainer ring so as to face the polishing pad and coupled to another of the poles of the power source, the second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; and a moving mechanism for providing relative movement between the polishing pad and the workpiece held by the polishing head.
In this apparatus with the above structures, the electric current is directly supplied from the second electrode on the retainer ring to the conductive film (e.g., a copper film) via the conductive polishing pad (i.e., a conductive pad). Specifically, electric charge is transferred by electron conduction from the second electrode to the conductive pad and to the conductive film. Therefore, the charge can be transferred uniformly and reliably to the surface of the conductive film in its entirety. As a result, a highly-uniform polishing rate of the conductive film can be maintained.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing table adapted to hold a conductive polishing pad having a polishing surface, the polishing table having a first electrode coupled to one of poles of a power source; a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface; an electric-supply section having a second electrode coupled to another of the poles of the power source and located so as not to contact the polishing head, the second electrode being brought into surface contact with the polishing surface so as to supply an electric current to the conductive film via the polishing pad; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; and a moving mechanism for providing relative movement between the polishing pad and the workpiece held by the polishing head.
In this apparatus with the above structures, the second electrode and the polishing pad are in surface contact with each other via a large contact area, and the electric current is directly supplied to the conductive film (e.g., a copper film) via the conductive polishing pad. With this structure, variations in electric potential over the surface of the conductive film can be reduced. Further, an adverse influence on the polishing surface of the polishing pad due to electric supply can be prevented. Therefore, reliability of electric supply to the conductive film can be enhanced, and deterioration of polishing performance due to electric supply can also be prevented.
In a preferred aspect of the present invention, the electrochemical mechanical polishing apparatus further includes a dresser operable to come into sliding contact with the polishing pad so as to dress the polishing pad. The electric-supply section is provided on the dresser.
Since the electric-supply section is provided on the dresser that is to dress the polishing pad, dressing of the polishing pad and supply of the electric current to the conductive film via the electric-supply section and the conductive pad can be performed in an in-situ manner. For example, when a ring-shaped dresser is used, the electric-supply section can be provided on a central portion of the dresser with an insulating material being provided between the electric-supply section and the ring-shaped dresser. In this case, this insulating material can be in a form of coil, so that a pressing force applied to the electric-supply section pressed against the polishing pad can be controlled.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing table adapted to hold a conductive polishing pad having a polishing surface, the polishing table having a first electrode coupled to one of poles of a power source; a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface; an electric-supply section having a second electrode coupled to another of the poles of the power source, the second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; and a moving mechanism for providing relative movement between the polishing pad and the workpiece held by the polishing head. The second electrode has a contact portion to be in contact with the polishing pad, and the contact portion is movable relative to the polishing pad at a relative speed of not more than 0.1 m/s.
The second electrode may have a roller as the contact portion (an electric supply contact). In this case, a rotational speed (a linear velocity of rotation) of the roller and a rotational speed of the polishing pad are adjusted such that a relative speed between the roller and the rotating pad is zero, for example. Alternatively, the roller may be rotatably supported with its rotational friction being nearly zero, so that the roller can be rotated by friction between the roller and the polishing pad. These structures can reduce the friction between the electric supply contact (roller) and the polishing pad, and can thus prevent the polishing pad from being damaged and removed from the polishing table. Because the damage to the polishing pad is prevented, reliable current supply can be secured without deteriorating polishing properties.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing table adapted to hold a conductive polishing pad having a polishing surface, the polishing table having a first electrode coupled to one of poles of a power source; a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface; a second electrode coupled to another of the poles of the power source, the second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; and a moving mechanism for providing relative movement between the polishing pad and the workpiece held by the polishing head. The polishing surface of the polishing pad has a non-contact area which does not contact the conductive film during polishing. The polishing pad has through-holes therein. The non-contact area and at least a part of inner surfaces of the through-holes have been subjected to an insulating treatment.
Since the non-contact area and the inner surface of the through-holes of the conductive polishing pad, which may be made of mainly carbon, have been subjected insulating treatment, an electrolytic reaction at the surface of the polishing pad (conductive pad) can be minimized. Therefore, formation of pits in the surface of the conductive film and a drop in polishing rate due to oxygen generated at the surface of the polishing pad can be prevented.
Usable methods of insulating part of the conductive polishing pad include an insulating coating treatment and a surface modification treatment. Examples of such an insulating coating treatment include coating of a surface with an ink, a paint, an adhesive, or the like. Examples of the surface modification treatment include modifying of a surface by means of a chemical treatment, graft polymerization, irradiation with a light, an electron beam or an ion beam, a plasma treatment, or plating.
According to the present invention, the surface of the conductive film (e.g., a copper film on a surface of a substrate) is not damaged, and reliable supply of an electric current can be performed with a uniform electric potential being provided over the surface of the conductive film, even when a rotary type is employed. Further, because the non-contact area (i.e., an area which is not used for polishing) of the conductive polishing pad is covered with the insulating material, an electrolytic reaction (production of oxygen) on the surface of the polishing pad can be minimized. As a result, production of a defect in the conductive film during polishing can be suppressed.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing pad having vertically-extending through-holes and having an upper surface serving as a polishing surface; a polishing head adapted to press a substrate against the polishing surface; a first electrode coupled to one of poles of a power source and arranged below the polishing pad; a second electrode coupled to another of the poles of the power source and adapted to supply an electric current to a conductive film on the substrate; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing pad; an electrolytic-solution path for directing an electrolytic solution, supplied from the electrolytic-solution supply section, to the through-holes from below the polishing pad; and a moving mechanism for providing relative movement between the polishing pad and the substrate held by the polishing head.
In a preferred aspect of the present invention, the electrolytic-solution path includes: an electrolytic-solution receiving section for receiving the electrolytic solution from the electrolytic-solution supply section; communication holes configured to communicate respectively with the through-holes; and communication grooves configured to communicate with the electrolytic-solution receiving section and to allow the communication holes to communicate with each other.
In a preferred aspect of the present invention, the electrolytic-solution receiving section comprises an annular groove arranged concentrically with the polishing pad; and the annular groove has a larger radius than a distance between a center of the polishing pad and a circumferential surface of the polishing head in a polishing position.
In a preferred aspect of the present invention, the electrochemical mechanical polishing apparatus further includes a weir surrounding a circumferential surface of the polishing pad. The weir has an outer wall and an inner wall, the outer wall has an upper end at a position higher than the polishing surface, and the inner wall has an upper end at a position lower than the polishing surface.
In a preferred aspect of the present invention, the electrochemical mechanical polishing apparatus further includes: a deformable liquid-permeable member surrounding a circumferential surface of the polishing pad; and a liquid recovery section provided below the liquid-permeable member. The liquid-permeable member has an upper surface at a position higher than the polishing surface.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing pad having vertically-extending through-holes and having an upper surface serving as a polishing surface; at least one liquid-retaining member embedded in the polishing surface; a polishing head adapted to press a substrate against the polishing surface; a first electrode coupled to one of poles of a power source and arranged below the polishing pad; a second electrode coupled to another of the poles of the power source and adapted to supply an electric current to a conductive film on the substrate; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing pad; and a moving mechanism for providing relative movement between the polishing pad and the substrate held by the polishing head.
In a preferred aspect of the present invention, the at least one liquid-retaining member comprises plural liquid-retaining members disposed in the through-holes.
In a preferred aspect of the present invention, the liquid-retaining member is deformable, and the liquid-retaining member has an upper surface at a position higher than the polishing surface.
Another aspect of the present invention is an electrochemical mechanical polishing apparatus including: a polishing pad having vertically-extending through-holes and having an upper surface serving as a polishing surface; a polishing head adapted to press a substrate against the polishing surface; a first electrode coupled to one of poles of a power source and arranged below the polishing pad; a second electrode coupled to another of the poles of the power source and adapted to supply an electric current to a conductive film on the substrate; an electrolytic-solution supply section for supplying an electrolytic solution to the polishing pad; and a moving mechanism for providing relative movement between the polishing pad and the substrate held by the polishing head. Each of the through-holes has an upper opening with a smaller diameter than a diameter of a lower opening thereof In a preferred aspect of the present invention, a diameter of each of the through-holes is decreased gradually from the lower opening to the upper opening.
In a preferred aspect of the present invention, each of the through-holes comprises plural holes arranged vertically in series with different diameters.
According to the present invention, the electrolytic solution can be supplied efficiently via the plural though-holes. As a result, an amount of the electrolytic solution used for polishing a substrate can be reduced. Therefore, a cost of the electrolytic solution as expendables can be reduced.
Another aspect of the present invention is a method of conditioning a processing electrode and/or a polishing pad of an electrochemical mechanical polishing apparatus. The method includes: polishing a conductive material of a workpiece by providing sliding contact between the conductive material and the polishing pad, which is arranged between the processing electrode and the conductive material, and by applying a voltage between the conductive material and the processing electrode in the presence of an electrolytic solution containing an organic acid and a corrosion inhibitor; and before or after the polishing, conditioning the processing electrode and/or the polishing pad using a conditioning solution including components of the electrolytic solution other than the corrosion inhibitor.
The conditioning solution having the essential components of the electrolytic solution, except for the corrosion inhibitor, can accelerate its etching capability by the etching function of the electrolytic solution. Therefore, performing conditioning of the processing electrode using such conditioning solution can etch away by-products of polishing deposited on the processing electrode and/or the polishing pad. Furthermore, because the basic composition of the conditioning solution is the same as the electrolytic solution used in polishing, an influence on polishing by the components (residual components) of the conditioning solution remaining after conditioning on the processing electrode and/or the polishing pad can be minimized, and the next electrolytic processing can be carried out without loss of time.
In a preferred aspect of the present invention, the conditioning solution further contains an oxidizing agent.
The conditioning solution may contain 0.1 to 5 wt % of H₂O₂as an oxidizing agent in order to promote removal of the by-products of polishing from the surface of the processing electrode.
In a preferred aspect of the present invention, the organic acid comprises at least one of acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citric acid, aconitic acid, glyoxylic acid, glycolic acid, lactic acid, gluconic acid, malic acid, and tartaric acid In a preferred aspect of the present invention, the organic acid comprises a strong acid having a sulfonic acid group.
In a preferred aspect of the present invention, the strong acid having a sulfonic acid group comprises benzenesulfonic acid, methanesulfonic acid, taurine, cysteic acid, an alkylbenzene sulfonic acid having one to six carbons in an alkyl group, trifluoromethanesulfonic acid, and fluorosulfonic acid.
Another aspect of the present invention is to provide a conditioning solution for use in conditioning a processing electrode and/or a polishing pad of an electrochemical mechanical polishing apparatus. This conditioning solution comprises: at least one organic acid or its salt; and at least one strong acid having a sulfonic acid group. The conditioning solution does not contain a corrosion inhibitor.
In a preferred aspect of the present invention, the conditioning solution further comprises an oxidizing agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A through FIG. 1C are diagrams illustrating a sequence of process of forming copper interconnects for a semiconductor device;

FIG. 2 is a graph illustrating a relationship between a polishing rate and polishing pressure in typical CMP;

FIG. 3 is a plan view showing an arrangement of a substrate processing apparatus including an electrochemical mechanical polishing apparatus according to an embodiment of the present invention;

FIG. 4 is a vertical cross-sectional front view showing an essential part of the electrochemical mechanical polishing apparatus included in the substrate processing apparatus shown in FIG. 3;

FIG. 5 is a vertical cross-sectional view showing a polishing head of the electrochemical mechanical polishing apparatus;

FIG. 6 is a bottom view showing the polishing head of the electrochemical mechanical polishing apparatus;

FIG. 7 is a vertical cross-sectional front view showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 8 is a vertical cross-sectional view showing a polishing head of the electrochemical mechanical polishing apparatus;

FIG. 9 is a bottom view showing the polishing head of the electrochemical mechanical polishing apparatus;

FIG. 10 is a vertical cross-sectional front view showing an essential part of the electrochemical mechanical polishing apparatus;

FIG. 11 is an enlarged view showing a part of the electrochemical mechanical polishing apparatus shown in FIG. 10;

FIG. 12 is a plan view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 13 is a cross-sectional view taken along line B-B shown in FIG. 12;

FIG. 14 is a view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 15 is a perspective view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 16 is a vertical cross-sectional front view showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 17 is a vertical cross-sectional view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 18 is a vertical cross-sectional view showing a modified example of an essential part of the electrochemical mechanical polishing apparatus shown in FIG. 17;

FIG. 19 is a plan view showing a part of communication grooves and communication holes formed in a lid shown in FIG. 18;

FIG. 20 is a vertical cross-sectional view showing a modified example of an essential part of the electrochemical mechanical polishing apparatus shown in FIG. 18;

FIG. 21 is a view showing an example of the communication grooves;

FIG. 22 is a view showing another example of the communication grooves;

FIG. 23 is a view showing another example of the communication grooves;

FIG. 24 is a view showing another example of the communication grooves;

FIG. 25 is a view showing another example of the communication grooves;

FIG. 26 is a view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 27 is a view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 28 is a plan view schematically showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 29 is a schematic cross-sectional view showing the electrochemical mechanical polishing apparatus shown in FIG. 28;

FIG. 30 is a plan view showing a part of a check valve provided in an annular groove;

FIG. 31 is a cross-sectional view taken along line C-C shown in FIG. 30;

FIG. 32 is a cross-sectional view showing another example of the check valve;

FIG. 33 is a cross-sectional view showing still another example of the check valve;

FIG. 34 is a schematic cross-sectional view showing an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 35 is a schematic cross-sectional view illustrating dressing of a polishing surface;

FIG. 36 is a schematic cross-sectional view showing another example of the electrochemical mechanical polishing apparatus;

FIG. 37 is a schematic cross-sectional view showing a part of a polishing pad for use in an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 38 is a schematic cross-sectional view showing a part of a polishing pad for use in an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 39 is a schematic perspective view showing an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 40 is a schematic side view showing an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 41 is a schematic side view showing another example of the electrochemical mechanical polishing apparatus shown in FIG. 40;

FIG. 42 is a schematic side view showing still another example of the electrochemical mechanical polishing apparatus shown in FIG. 40;

FIG. 43 is a schematic perspective view showing an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention;

FIG. 44 is a plan view showing an example of an electrochemical mechanical polishing apparatus; and

FIG. 45 is a vertical cross-sectional front view of FIG. 44.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments according to the present invention will be described below with reference to the drawings. An example, which will be described below, is a process including a step of removing a copper film (and a seed film), formed on a surface of a barrier film on a substrate as a workpiece to be polished, to thereby form an exposed surface of the barrier film. In this example, the copper film provides interconnects.
FIG. 3 is a plan view showing an arrangement of a substrate processing apparatus including an electrochemical mechanical polishing apparatus according to an embodiment of the present invention. This substrate processing apparatus is for use in a semiconductor-device fabrication process. For example, as shown in FIG. 1B, copper plating is performed beforehand on a surface of a substrate so as to fill via holes 903 and trenches 904 with copper and to deposit a copper film 907, serving as an interconnect metal film, on a surface of an insulating film 902. In this manner, a substrate (workpiece to be polished) W with the copper film is prepared. The substrate processing apparatus polishes this substrate W until the surface of the substrate W reaches a line A-A shown in FIG. 1B to thereby remove the copper film 907 (and a seed film 906) as a conductive film on the insulating film 902, thus forming an exposed surface of a barrier film 905. The substrate processing apparatus further polishes the substrate W so as to remove the barrier film 905 on the insulating film 902 to form interconnects 908, which are composed of the seed film 906 and the copper film 907, in the insulating film 902, as shown in FIG. 1C.
This substrate processing apparatus comprises a loading and unloading stage for accommodating substrate cassettes 204 adapted to store therein substrates W (see FIG. 1B) each having the copper film 907 as the interconnect metal film (i.e., conductive film). A transfer robot 202, having two hands, is provided on a moving mechanism 200 so that the hands can reach the substrate cassettes 204 in the loading and unloading stage. The moving mechanism 200 has mechanisms including a linear motor. Use of the linear motor allows the moving mechanism 200 to quickly and stably transfer a substrate having an increased diameter and an increased weight.
Two drying units 212 are provided at an opposite side of the substrate cassettes 204 with respect to the moving mechanism 200 for the transfer robot 202. These drying units 212 are arranged within reach of the hands of the transfer robot 202. A substrate station 206 having four substrate stages is provided between the drying units 212. This substrate station 206 is arranged within reach of the hands of the transfer robot 202.
Transfer robots 208 are provided in positions where hands thereof can reach the drying units 212 and the substrate station 206. Cleaning units 214 are provided next to the drying units 212, respectively. The cleaning units 214 are arranged within reach of the hands of the transfer robots 208. A rotary transporter 210 is arranged within reach of the hands of the transfer robots 208. Two electrochemical mechanical polishing apparatuses 250 according to the embodiment of the present invention are provided in positions where the substrates W can be transferred to and from the rotary transporter 210. In this embodiment, one of the two electrochemical mechanical polishing apparatuses 250 is used to perform first polishing of the copper film 907 (and the seed film 906), and another is used to perform second polishing.
The substrate processing apparatus further comprises an ITM (In-line Thickness Monitor) 224, which is a measuring section for measuring a state of a surface (e.g., a thickness of a film on the surface) of the substrate that is to be polished or that has been cleaned and dried after being polished. More specifically, as shown in FIG. 3, the ITM (measuring section) 224 lies on an extension of the moving mechanism 200, and is operable to measure a polishing state of the copper film, the barrier film, and the like on the surface of the substrate (e.g., a semiconductor wafer) before the transfer robot 202 returns a polished substrate to the substrate cassette 204 or after the transfer robot 202 removes a substrate, to be polished, from the substrate cassette 204. The ITM 224 has an optical device for emitting an optical signal to the surface of the substrate, and measures the polishing state of the surface of the substrate from the reflected optical signal from the substrate.
Each of the electrochemical mechanical polishing apparatuses 250 has a polishing table 100, a polishing head 1, an electrolytic-solution supply nozzle 102 for supplying an electrolytic solution to a polishing pad 101 (see FIG. 4) on the polishing table 100, a dresser 218 for dressing the polishing pad 101 on the polishing table 100, and a water vessel 222 for cleaning the dresser 218.
FIG. 4 shows an essential part of the electrochemical mechanical polishing apparatus 250. As shown in FIG. 4, the polishing head 1 is coupled to a polishing-head drive shaft 11 via a universal joint 10, and the polishing-head drive shaft 11 is coupled to a head air cylinder 111 secured to an arm 110. The polishing-head drive shaft 11 is moved vertically by the head air cylinder 111 to thereby move up and down the polishing head 1 in its entirety and to press a retainer ring 3, which is fixed to a lower end of a head body 2, against the polishing pad 101. The head air cylinder 111 is coupled to a compressed air source 120 via a regulator RE1. The regulator RE1 can regulate pressure of a fluid, e.g., an air, to be supplied to the head air cylinder 111, whereby pressure applied to the retainer ring 3 to press the polishing pad 101 can be adjusted.
The polishing-head drive shaft 11 is coupled to a rotational cylinder 112 via a key (not shown). The rotational cylinder 112 is provided with a timing pulley 113 on its peripheral portion. A polishing-head motor 114, serving as a rotating device, is secured to the arm 110, and a timing pulley 116 is coupled to the polishing-head motor 114. The timing pulley 113 is coupled to the timing pulley 116 via a timing belt 115. With these arrangements, by energizing the polishing-head motor 114, the rotational cylinder 112 and the polishing-head drive shaft 11 are integrally rotated via the timing pulley 116, the timing belt 115, and the timing pulley 113, whereby the polishing head 1 is rotated. The arm 110 is supported by an arm shaft 117 secured to a frame (not shown).
The polishing head 1 will now be described in more detail with reference to FIGS. 5 and 6. FIG. 5 is a vertical cross-sectional view of the polishing head 1, and FIG. 6 is a bottom view of the polishing head 1 shown in FIG. 5. As shown in FIG. 5, the polishing head 1 has the head body 2 in a shape of a cylindrical vessel having a space therein, and the retainer ring 3 fixed to the lower end of the head body 2. The head body 2 is formed of a material having a high strength and a high rigidity, such as metal or ceramic. The retainer ring 3 is formed of a resin having a high rigidity, such as PPS (polyphenylene sulfide) or ceramic.
The head body 2 includes a housing 2 a in a shape of a cylindrical vessel, an annular pressure-sheet support 2 b fitted into an inner portion of the housing 2 a, and an annular sealing member 2 c attached to a periphery of an upper surface of the housing 2 a. A lower portion of the retainer ring 3, fixed to a lower surface of the housing 2 a of the head body 2, projects inwardly. The retainer ring 3 may be formed integrally with the head body 2.
The above-described polishing-head drive shaft 11 is located above a center of the housing 2 a of the head body 2. The head body 2 and the polishing-head drive shaft 11 are coupled to each other by the universal joint 10. The universal joint 10 includes a spherical bearing mechanism and a rotation transmitting mechanism. The spherical bearing mechanism allows the head body 2 and the polishing-head drive shaft 11 to tilt with respect to each other, and the rotation transmitting mechanism transmits rotation of the polishing-head drive shaft 11 to the head body 2. With these mechanisms, the universal joint 10 transmits a pressing force and a torque of the polishing-head drive shaft 11 to the head body 2, while permitting tilting of the head body 2 with respect to the polishing-head drive shaft 11.
The spherical bearing mechanism has a spherical recess 11 a formed in a central portion of a lower surface of the polishing-head drive shaft 11, a spherical recess 2 d formed in the central portion of the upper surface of the housing 2 a, and a bearing ball 12 made from a high-hardness material, such as ceramic, interposed between the recesses 11 a and 2 d. The rotation transmitting mechanism has driving pins (not shown) fixed to the polishing-head drive shaft 11, and driven pins (not shown) fixed to the housing 2 a. The driving pins and the driven pins are vertically movable relative to each other. Accordingly, even when the head body 2 is tilted, the pins still engage each other, with contact points of the pins being shifted. The rotation transmitting mechanism thus securely transmits the torque of the polishing-head drive shaft 11 to the head body 2.
In the space formed in the head body 2 and the retainer ring 3 fixed integrally to the head body 2, there are housed an elastic pad 4 to be in contact with the substrate W, an annular holder ring 5, and a substantially disk-shaped chucking plate 6 for supporting the elastic pad 4. The elastic pad 4 is sandwiched, at its peripheral portion, between the holder ring 5 and the chucking plate 6 fixed to a lower end of the holder ring 5. The elastic pad 4 is shaped so as to cover a lower surface of the chucking plate 6. A space is thus formed between the elastic pad 4 and the chucking plate 6.
A pressure sheet 7, composed of an elastic membrane, is provided so as to stretch between the holder ring 5 and the head body 2. One end of the pressure sheet 7 is sandwiched between the housing 2 a and the pressure-sheet support 2 b of the head body 2, and another is sandwiched between an upper end portion 5 a and a stopper portion 5 b of the holder ring 5. A pressure chamber 21 is formed inside the head body 2. This pressure chamber 21 is defined by the head body 2, the chucking plate 6, the holder ring 5, and the pressure sheet 7. The pressure chamber 21 is located above the chucking plate 6. As shown in FIG. 5, a fluid passage 31, which comprises a tube and connectors, is provided so as to communicate with the pressure chamber 21. The pressure chamber 21 is coupled to the compressed air source 120 via a regulator RE2 provided in the fluid passage 31. The pressure sheet 7 is made from, for example, a rubber material having excellent strength and durability, such as ethylene-propylene rubber (EPDM), polyurethane rubber, or silicon rubber.
If the pressure sheet 7 is made from an elastic material, such as rubber, and is sandwiched between the retainer ring 3 and the head body 2, a desirable flat plane may not be obtained in the lower surface of the retainer ring 3, because of elastic deformation of the elastic pressure sheet 7. In order to avoid such a drawback, the pressure-sheet support 2 b is separately provided, according to this embodiment, so as to sandwich and fix the pressure sheet 7 between the housing 2 a and the pressure-sheet support 2 b of the head body 2.
It is possible to make the retainer ring 3 vertically movable relative to the head body 2 or to make the retainer ring 3 operable to press the polishing pad 101 independent of the head body 2, as disclosed in Japanese Patent Application No. 8-50956 (Laid-Open Publication No. 9-168964) or Japanese Patent Application No. 11-294503. In such a case, the above-described structure of fixing the pressure sheet 7 may not necessarily be employed.
A center bag (a central contact member) 8 and a ring tube (an outer contact member) 9, which are contact members to be in contact with the elastic pad 4, are provided in the space formed between the elastic pad 4 and the chucking plate 6. As shown in FIGS. 5 and 6, in this embodiment, the center bag 8 is disposed on the central portion of the lower surface of the chucking plate 6, and the ring tube 9 is disposed outside of the center bag 8 so as to surround the center bag 8. The elastic pad 4, the center bag 8, and the ring tube 9 are made from rubber having excellent strength and durability, such as ethylene-propylene rubber (EPDM), polyurethane rubber, or silicon rubber, as with the pressure sheet 7.
The space formed between the chucking plate 6 and the elastic pad 4 is divided by the center bag 8 and the ring tube 9 into plural chambers: a pressure chamber 22 formed between the center bag 8 and the ring tube 9; and a pressure chamber 23 formed outside the ring tube 9.
The center bag 8 comprises an elastic membrane 81, which is to be in contact with an upper surface of the elastic pad 4, and a center bag holder (holding member) 82 detachably holding the elastic membrane 81. The center bag holder 82 has screw holes 82 a formed therein. Screws 55 are inserted into the screw holes 82 a to thereby allow the center bag 8 to be detachably mounted on the central portion of the lower surface of the chucking plate 6. Inside the center bag 8, a central pressure chamber 24 is defined by the elastic membrane 81 and the center bag holder 82.
Similarly, the ring tube 9 comprises an elastic membrane 91, which is to be in contact with the upper surface of the elastic pad 4, and a ring tube holder (holding member) 92 detachably holding the elastic membrane 91. The ring tube holder 92 has screw holes 92 a formed therein. Screws 56 are inserted into the screw holes 92 a to thereby allow the ring tube 9 to be detachably mounted on the lower surface of the chucking plate 6. Inside the ring tube 9, an intermediate pressure chamber 25 is defined by the elastic membrane 91 and the ring tube holder 92.
Fluid passages 33, 34, 35, and 36, each including a tube and connectors, are provided so as to communicate with the pressure chambers 22 and 23, the central pressure chamber 24, and the intermediate pressure chamber 25, respectively. The pressure chambers 22 to 25 are coupled to the compressed air source 120 as a pressurized-fluid supply source via regulators RE3, RE4, RE5, and RE6 respectively provided in the fluid passages 33-36. The above-described fluid passages 31, 33-36 are coupled to the respective regulators RE2-RE6 via rotary joints (not shown) provided at an upper end of the polishing-head drive shaft 11.
A pressurized fluid (e.g., pressurized air) is to be supplied to the above-described pressure chambers 21-25, or atmospheric pressure or vacuum is to be produced in the pressure chambers 21-25 via the fluid passages 31, 33-36. As shown in FIG. 4, the pressures of pressurized fluids to be supplied to the pressure chambers 21-25 can be adjusted by the regulators RE2-RE6 provided in the fluid passages 31, 33-36. The pressures in the pressure chambers 21-25 can thus be controlled independently, or atmospheric pressure or vacuum can be produced in the pressure chambers 21-25.
In this manner, by changing the pressures in the pressure chambers 21-25 independently via the regulators RE2-RE6, the elastic pad 4 can press the substrate W against the polishing pad 101 with pressing forces adjusted for respective portions (divisional areas) of the substrate W. The pressure chambers 21-25 may be coupled to a vacuum source 121, as desired.
As shown in FIG. 4, the upper surface of the polishing table 100 of the electrochemical mechanical polishing apparatus 250 is covered with a disk-shaped insulating plate 252, and a first electrode (cathode) 256, coupled to one of poles of a power source 254, is disposed on an upper surface of the insulating plate 252. In this embodiment, the first electrode 256 is comprised of plural (three) ring-shaped divided electrodes 256 a to 256 c which are concentrically arranged. A cylindrical core 258 is disposed in a center of the divided electrodes 256 a to 256 c. Ring-shaped insulators 260 a to 260 c are disposed between the core 258 and the centrally-located divided electrode 256 a, between the divided electrode 256 a and the intermediately-located divided electrode 256 b, and between the divided electrode 256 b and the peripherally-located divided electrode 256 c, respectively. The divided electrodes 256 a to 256 c are thus electrically insulated from each other by the insulating plate 252 and the ring-shaped insulators 260 a to 260 c.
The divided electrodes 256 a to 256 c are coupled individually to feeding wires 266 a to 266 c extending from the power source 254 via electrode wires 262 a to 262 c connected respectively to the divided electrodes 256 a to 256 c and extending through an interior of the polishing table 100, and via electrode slip rings 264 a to 264 c mounted on a shaft portion 100 a of the polishing table 100. The feeding wires 266 a to 266 c extend via a variable resistance unit 270 having variable resistors 268 a to 268 c respectively provided in the feeding wires 266 a to 266 c. The variable resistors 268 a to 268 c are each capable of varying a value of resistance, e.g., in a range of 0.1 to 10 Ω. A rotary connector may be used instead of the slip rings.
During polishing, the electric currents flowing (or voltages to be applied) between the divided electrodes 256 a to 256 c, constituting the first electrode 256, and a conductive film, such as a copper film, formed on a surface of a substrate facing the divided electrodes 256 a to 256 c, can be adjusted by individually controlling the respective variable resistors 268 a to 268 c interposed between the power source 254 and the divided electrodes 256 a to 256 c. This makes it possible to carry out polishing of the substrate at a higher rate, with low polishing pressure applied (i.e., in a low-polishing-pressure area), and at a lower cost without providing plural power sources, while ensuring uniformity of a polishing rate over the surface of the substrate (a workpiece to be polished). Furthermore, controlling of the variable resistors 268 a to 268 c is easier than individually controlling of plural power sources.
Upper surfaces of the first electrode 256, the core 258, and the ring-shaped insulators 260 a to 260 c lie in the same plane, and these upper surfaces are covered with the polishing pad 101 in their entirety. An upper surface of the polishing pad 101 serves as a polishing surface. A film-thickness detection sensor (detecting section) 274, e.g., an eddy-current sensor, is provided for measuring a thickness of a conductive film, such as a copper film, formed on a surface of a substrate. A base portion of the film-thickness detection sensor (detecting section) 274 is embedded in the polishing table 100 such that an upper end surface of the film-thickness detection sensor 274 is flush with the upper surface of the first electrode 256. This film-thickness detection sensor 274 is disposed either in the first electrode 256 with an insulator being provided between the sensor 274 and the first electrode 256, or in the ring-shaped insulator, so that the sensor is electrically insulated from the first electrode 256. A signal from the film-thickness detection sensor 274 is sent to a control section 280 via a sensor wire 276, extending in the interior of the polishing table 100, and via a sensor slip ring 278 provided on a lower end of the shaft portion 100 a of the polishing table 100. The regulators RE3 to RE6 and the variable resistors 268 a to 268 c in the variable resistance unit 270 are individually controlled by an output signal from the control section 280.
A table cover 282 is disposed so as to surround the circumference of the polishing table 100. A columnar second electrode (anode) 286, coupled to the other pole of the power source 254, is supported by a support base 284 mounted on the table cover 282. This second electrode 286 is to supply an electric current to the conductive film, such as the copper film 907 (see FIG. 1B), formed on the surface of the substrate W upon contact with the substrate W. When the polishing head 1 lowers the substrate W to bring the surface (lower surface) of the substrate W into contact with the polishing surface of the polishing pad 101, a periphery of the surface (lower surface) of the substrate W is also brought into contact with an upper surface of the second electrode 286. The upper surface of the second electrode 286 is substantially flush with the upper surface (polishing surface) of the polishing pad 101. The second electrode 286 is made from an inert metal, such as Pt or C, or a metal, such as SUS or Ti, plated with, e.g., Pt. The second electrode 286 has a columnar or spherical shape, and is designed to make rotation during contact with the substrate W The second electrode 286 is supported by the support base 284 via an elastic member so that the second electrode 286 can float. The polishing head 1 is operable to hold and press the substrate against the polishing surface of the polishing pad 101 at polishing pressure of, e.g., not more than 70 hPa (about 1 psi).
In this embodiment, part of the substrate W, held by the polishing head 1 in the polishing position, lies laterally to the polishing table 100, and the upper surface of the second electrode 286 comes into contact with the lower surface of that part of the substrate. It is possible to use a ring-shaped second electrode, continuously extending around a circumference of the first electrode and insulated from the first electrode, and to rotate the second electrode together with the polishing table while allowing part of the second electrode to be in contact with part of the lower surface of the substrate W held by the polishing head 1. The second electrode 286 may be a pad-shaped conductive member.
In this embodiment, the polishing pad 101 has a large number of through-holes 101 a over the surface thereof, and is made from, for example, a foamed polyurethane resin such as IC-1000, manufactured by Nitta Haas Inc. During electrochemical mechanical polishing, an electric current flows between the surface of the substrate W, coupled to the second electrode 286, and the first electrode 254 via an electrolytic solution that has flowed into the through-holes 101 a. The polishing pad 101 may have annular grooves or lattice-patterned grooves, in addition to the through-holes 101 a provided over the polishing surface of the polishing pad 101 in its entirety. If the polishing pad 101 itself is permeable to liquid, like a PVA resin pad having continuous pores, the polishing pad 101 may not necessarily have the through-holes.
As shown in FIG. 4, the electrolytic-solution supply nozzle 102 extends in the radial direction of the polishing pad 101 and has a plurality of electrolytic-solution supply mouths arranged at regular intervals along a length direction of the electrolytic-solution supply nozzle 102.
Polishing operations of the electrochemical mechanical polishing apparatus 250 having the above structures will now be described. The substrate W is held on the lower surface of the polishing head 1, and the cylinder 111, coupled to the polishing-head drive shaft 11, is actuated to press the retainer ring 3, fixed to the lower end of the polishing head 1, against the polishing surface of the polishing pad 101 at predetermined pressure. Pressurized fluids with predetermined pressures are supplied respectively to the pressure chambers 22 and 23, the central pressure chamber 24, and the intermediate pressure chamber 25 to thereby press the substrate W against the polishing surface of the polishing pad 101. At this time, the periphery of the substrate W comes into contact with the upper surface of the second electrode 286, whereby the second electrode 286 is placed in a condition to supply the electric current to the conductive film, such as the copper film 907 (see FIG. 1B), formed on the surface of the substrate W.
Then, the voltages are applied between the divided electrodes 256 a to 256 c and the conductive film, such as the copper film 907 (see FIG. 1B), of the substrate W by the power source 254, with the voltages being individually controlled by the variable resistors 268 a to 268 c. Simultaneously, the electrolytic solution is supplied through the electrolytic-solution supply nozzle 102 to the polishing surface, whereby the electrolytic solution is held in and on the polishing pad 101. Polishing of the conductive film proceeds in the presence of the electrolytic solution between the surface of the conductive film of the substrate W and the polishing surface of the polishing pad 101, with electrical connection being provided between the first electrode 256 and the conductive film via the electrolytic solution in the through-holes 101 a of the polishing pad 101.
The portions of the substrate W, which lie underneath the pressure chambers 22 and 23, are pressed against the polishing surface of the polishing pad 101 by the pressures of the pressurized fluid supplied to the pressure chambers 22 and 23. The portion of the substrate W, which lies underneath the central pressure chamber 24, is pressed against the polishing surface, via the elastic membrane 81 of the center bag 8 and the elastic pad 4, by the pressure of the pressurized fluid supplied to the central pressure chamber 24. The portion of the substrate W, which lies underneath the intermediate pressure chamber 25, is pressed against the polishing surface, via the elastic membrane 91 of the ring tube 9 and the elastic pad 4, by the pressure of the pressurized fluid supplied to the intermediate pressure chamber 25.
Accordingly, the polishing pressure applied to the substrate W can be adjusted individually for the divisional portions, divided along a radial direction of the substrate W, by controlling the pressures of pressurized fluid to be supplied to the pressure chambers 22 to 25. In particular, a below-described controller (control section) 280 controls the pressures of pressurized fluid, to be supplied to the pressure chambers 22 to 25, independently via the regulators RE3-RE6, thereby adjusting the pressures applied to press the substrate W against the polishing pad 101 on the polishing table 100 independently for the divisional portions of the substrate W. The substrate W can thus be pressed against the polishing pad 101 with the polishing pressure being adjusted to a desired value for each divisional portion of the substrate W Similarly, the pressure of the pressurized fluid to be supplied to the head air cylinder 111 can be adjusted via the regulator RE1 so as to change the pressure applied to the retainer ring 3 pressing the polishing pad 101.
By thus appropriately adjusting, during polishing, the pressure applied to the retainer ring 3 to press the polishing pad 101 and the pressure applied to the substrate W that is pressed against the polishing pad 101, a desired distribution of polishing pressure can be obtained over the surface of the substrate W and the outside area of the substrate W, i.e., the central portion (portion C1 shown in FIG. 6), the central portion to the intermediate portion (C2), the intermediate portion (C3), the peripheral portion (C4), and the retainer ring 3 lying outside the substrate W.
In the portions of the substrate W which lie underneath the pressure chambers 22 and 23, there are a portion to which pressure is applied via the elastic pad 4 from the pressurized fluid and a portion, such as a portion corresponding to an opening 41, to which pressure of the pressurized fluid is directly applied. The pressures applied to these portions may be equal or different from each other. The elastic pad 4 around the opening 41 adheres tightly to a back surface of the substrate W during polishing. Therefore, almost no pressurized fluid leaks out of the pressure chambers 22 and 23.
The electric currents, flowing (or voltages applied) between the divided electrodes 256 a to 256 c and the conductive film on the surface of the substrate, are individually controlled and adjusted by the respective variable resistors 268 a to 268 c interposed between the power source 254 and the divided electrodes 256 a to 256 c.
As previously discussed, the substrate W is divided into four concentric circular and annular portions (C1-C4), and the respective portions (pressure areas) can be pressed at independent pressures. Further, the first electrode 256 is constituted by the divided electrodes 256 a to 256 c, and the electric currents flowing (or voltages applied) between the divided electrodes 256 a to 256 c and the conductive film, facing the divided electrodes 256 a to 256 c, can be individually adjusted. The polishing rate depends on the pressure applied to the substrate W to press the polishing surface and on the electric current flowing between the first electrode and the conductive film of the substrate W. As described above, the pressure on each divisional portion of the substrate W and the electric current flowing in each divided portion (electrode) of the first electrode can be controlled independently. Accordingly, even if there is a variation in thickness of a thin film along a radial direction of the substrate W to be polished, shortage or excess of polishing can be avoided over the surface of the substrate in its entirety.
In particular, even when a thickness of the film to be polished varies with radial positions of the substrate W, the pressure on the portion of the substrate W, having a relatively large film thickness, can be made higher than the pressure on the portion of the substrate W having a relatively small film thickness by making the pressure in the corresponding pressure chamber, which lies over the thick portion, higher than the pressures in the other pressure chambers, and/or by making the value of resistance of the corresponding variable resistor (e.g., variable resistor 268 a), connected to the feeding wire (e.g. feeding wire 266 a) that supplies the electric current to the divided electrode (e.g., divided electrode 256 a) facing the thick portion, smaller than values of the resistance of the other variable resistors (e.g., variable resistors 268 b, 268 c) so as to allow a higher current to flow into the corresponding divided electrode (e.g. divided electrode 256 a). The polishing rate of the thick portion of the substrate W can thus be selectively raised. This makes it possible to polish the surface of the substrate W without causing excess or shortage of polishing over the surface in its entirety, irrespective of a variation in thickness of the film caused by a film-formation process.
Rounded edge due to over-polishing, which could occur in an edge portion of the substrate W, can be prevented by controlling the pressure applied to the retainer ring 3 that presses the polishing pad 101. When there is a large variation in thickness of a film to be polished in the edge portion of the substrate W, the polishing rate (removal rate) of the edge portion can be controlled by making the pressure (pressing force) of the retainer ring 3 high or low. When the pressurized fluid is supplied to the pressure chambers 22 to 25, the chucking plate 6 receives an upward force. In this embodiment, the pressurized fluid is supplied via the fluid passage 31 into the pressure chamber 21 so as to prevent the chucking plate 6 from being elevated by the force applied from the pressure chambers 22 to 25.
Polishing of the substrate W is thus performed while appropriately adjusting the pressure applied by the head air cylinder 111 to press the retainer ring 3 against the polishing pad 101, the pressures applied by the pressurized airs supplied to the pressure chambers 22 to 25 to press the divisional portions of the substrate W against the polishing pad 101, and appropriately adjusting the currents flowing between the divided electrodes 256 a to 256 c (the first electrode 256) and the conductive film, e.g., copper film, on the surface of the substrate facing the divided electrodes 256 a to 256 c (or the voltages to be applied between the divided electrodes 256 a to 256 c and the conductive film on the surface of the substrate facing the divided electrodes 256 a to 256 c).
In this embodiment, the polishing head 1 has the pressure chambers 21 to 25 whose internal pressures can be changed independently via the regulators RE2 to RE6 for fine polishing control. Alternatively, it is possible to use a polishing head which is not provide with pressure chambers whose internal pressures are independently variable, but is designed to hold (e.g., attract) a substrate and press the substrate against the polishing surface of the polishing pad 101 uniformly e.g., at polishing pressure of not more than 70 hPa (about 1 psi).
The operations of the substrate processing apparatus will now be described.
First, the substrate cassette 204, which stores a large number of substrates W shown in FIG. 1B each having the copper film 907 formed on the surface, is mounted on the loading and unloading stage. One substrate is removed from the substrate cassette 204 by the transfer robot 202 and placed onto the substrate station 206. The transfer robot 208 receives the substrate from the substrate station 206 and, after reversing the substrate as necessary, transfers the substrate to the rotary transporter 210. The rotary transporter 210 is then rotated horizontally, and the substrate, supported by the rotary transporter 210, is held by the polishing head 1 of one of the two electrochemical mechanical polishing apparatuses 250.
Thereafter, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. The polishing head 1 is then lowered to press the substrate against the polishing surface of the polishing pad 101 at predetermined pressure of not more than 70 hPa (1 psi). While supplying an electrolytic solution to the polishing pad 101, the voltages are applied by the power source 254 between the divided electrodes 256 a to 256 c (the first electrode 256) and the conductive film of the substrate, i.e. the copper film 907, facing the divided electrodes 256 a to 256 c to perform polishing (first polishing) of the conductive film. Holding of the substrate, e.g., by vacuum attraction, may be released during polishing of the substrate with the polishing pad 101.
In the electrochemical mechanical polishing apparatus 250, the first polishing is performed so as to remove the conductive film, e.g., the copper film 907 (and the seed film 906), until an average thickness of the remaining conductive film is not more than 300 nm and a variation in thickness of the remaining conductive film falls within not more than 150 nm. During polishing of the copper film 907 (and the seed film 906), the film-thickness detection sensor 274, such as an eddy-current sensor, detects an in-plane distribution of the thickness of the copper film 907 (and the seed film 906), and the control section 280 controls and adjusts the polishing pressures to be applied to the divisional portions (press areas) C1 to C4 shown in FIG. 6. The control section 280 also adjusts the electric currents flowing (or voltages applied) between the divided electrodes 256 a to 256 c and the conductive film, via the variable resistors 268 a to 268 c of the variable resistance unit 270. The electrochemical mechanical polishing generally causes little damage to interconnects. Therefore, use of the electrochemical mechanical polishing can significantly reduce damage to an interconnect structure of the substrate. For example, the electrochemical mechanical polishing can be used for removing most part of an interconnect metal film formed outside interconnect recesses. Since a portion of the film outside of the interconnect recesses constitutes a major part of a total amount of the film to be removed, use of the electrochemical mechanical polishing can significantly reduce damage to the interconnect structure.
A speed of relative movement between the polishing pad 101 and the substrate W may also be controlled. A rotational speed of the polishing pad 101 may be controlled, e.g., in a range of 20 to 40 rpm, and a rotational speed of the substrate W may be controlled, e.g., in a range of 50 to 100 rpm. It is possible to rotate the substrate W in an opposite direction to a rotational direction of the polishing pad 101, if necessity. It is also possible to move the substrate W repeatedly in the radial direction of the polishing pad 101, if necessity.
After completion of the first polishing in one of the electrochemical mechanical polishing apparatuses 250, the polished surface and the back surface of the substrate are cleaned (rinsed) with a cleaning liquid, e.g., pure water, and then dried, if necessary. The substrate is then transported via the rotary transporter 210 to another of the electrochemical mechanical polishing apparatuses 250, and held by the polishing head 1. In the electrochemical mechanical polishing apparatus 250 which performed the first polishing, on the other hand, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
In the second polishing, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. The polishing head 1 is then lowered to press the substrate against the polishing surface of the polishing pad 101. While supplying an electrolytic solution to the polishing pad 101, voltages are applied by the power source 254 between the divided electrodes 256 a to 256 c (the first electrode 256) and the conductive film of the substrate to perform the second polishing of the conductive film which has not been removed by the first polishing. Specifically, the second polishing is performed so as to remove the copper film 907 (and the seed film 906) remaining on the barrier film 905 to thereby expose the barrier film 905.
The electrochemical mechanical polishing apparatus 250 performs the second polishing under a condition such that the polishing rate of the conductive film is decreased from the center to the periphery of the substrate. With this operation, the barrier film 905, underlying the conductive film, i.e., the copper film 907 (and seed film 906), is gradually exposed from the center toward the periphery of the substrate W. Finally, the conductive film on the barrier film 905 is completely polished away. Performing of the second polishing in this manner can prevent the conductive film from remaining on the barrier film 905 during polishing as a result of an electrical insulation of the conductive film. If the conductive film remains on the barrier film 905 with the electrical insulation of the conductive film being established, such conductive film cannot be removed by electrochemical mechanical polishing. The second polishing, performed in a manner as discussed above, does not cause the electrical insulation of the conductive film, and can thus completely remove the conductive film. The distribution of the thickness of the conductive film during the second polishing can be monitored based on a change with time in eddy current generated by an eddy-current sensor and a change in rotational speed of the polishing table 100. When a difference is produced between the monitoring results and the intended film thickness distribution, the monitoring results may be fed back to the values of resistance of the variable resistors 268 a to 268 c and the polishing pressures, so that the present film thickness distribution can be adjusted to the intended distribution.
After completion of the second polishing in the electrochemical mechanical polishing apparatus 250, the substrate is transported to the cleaning unit 214, via the rotary transporter 210 and the transfer robot 208. If necessary, the substrate may be reversed prior to transfer to the cleaning unit 214. In the electrochemical mechanical polishing apparatus 250 after the second polishing, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
The substrate surface is cleaned (rinsed) in the cleaning unit 214, and the cleaned substrate is transported by the transfer robot 208 to the substrate station 206 and placed onto it. The transfer robot 202 (or 208) removes the substrate from the substrate station 206, and transports the substrate to the drying unit 212, which has a pen sponge for cleaning of the upper surface and a spin-drying function, for example. In the drying unit 212, the substrate is cleaned and dried. Thereafter, the cleaned and dried substrate is returned to the substrate cassette 204 by the transfer robot 202.
Whether the conductive film, such as the copper film 907 (and seed film 906), on the barrier film 905 is completely removed or not can be detected by monitoring a change in eddy current generated by an eddy-current sensor, whereby an end point of polishing can be detected. The end point of polishing can also be detected by utilizing a difference in electrode potential between the conductive film and the barrier film, and by monitoring a change in electrode potential using a reference electrode. The reference electrode is preferably present near a substrate (a workpiece to be polished), and may be disposed in the retainer ring or on a circumferential surface of the retainer ring, or may be operable to approach a substrate from the polishing table through the through-hole of the polishing pad.
In this embodiment, the substrate processing apparatus includes the two electrochemical mechanical polishing apparatuses, and the first polishing and the second polishing are carried out separately in the two electrochemical mechanical polishing apparatuses. Alternatively, in a case where the first polishing and the second polishing can be carried out, for example, using the same electrolytic solution in a single electrochemical mechanical polishing apparatus by changing the polishing pressure and/or the voltage applied between the first electrode and the second electrode (conductive film), it is possible to perform the first polishing and the second polishing successively in the single electrochemical mechanical polishing apparatus. In this case, shifting from the first polishing to the second polishing may be made based on a measurement result of a film-thickness detector, for example, a change in eddy current detected by an eddy-current sensor.
Although a substrate, such as a semiconductor wafer, is used as a workpiece to be polished in this embodiment, it should be noted the workpiece to be polished is not limited to the substrate such as the semiconductor wafer.
Further, although in this embodiment an insulating pad is used as the polishing pad, it is possible to use a conductive polishing pad. In this case, the conductive pad may be coupled to the pole of the power source either directly or indirectly, e.g., via an electric-supply contact, so as to supply an electric current to the conductive film via the conductive pad.
Other embodiments of the present invention will now be described with reference to FIG. 7 through FIG. 16. In the following description, elements identical to those in the above-described embodiment are given the same reference numerals, and a duplicate description thereof is herein omitted. Further, structures and operations which will not be particularly described are identical to those in the above-described embodiment.
As shown in FIG. 7, a sensor coil 328 of an ITM 326, e.g., an eddy-current sensor, for measuring a thickness of a conductive film, e.g., a copper film, formed on a surface of a substrate, is embedded in polishing table 100 of an electrochemical mechanical polishing apparatus 250. A signal from the ITM 326 is input into a control section 310, and the regulators RE3 to RE6 are controlled by output signals from the control section 310. As shown in FIG. 8, a ring-shaped second electrode 364, made of e.g., platinum, is mounted on a lower surface of retainer ring 3. This second electrode 364 is shaped so as to cover the lower surface of the retainer ring 3 in its entirety.
As shown in FIG. 10, a disk-shaped first electrode (cathode) 354, coupled to one of poles of a power source 352, is provided on an upper surface of the polishing table 100, and an insulating platen 356 is disposed on the first electrode 354 so as to cover an upper surface of the first electrode 354. A surface of the insulating platen 356 in its entirety is covered with polishing pad 101, and an upper surface of the polishing pad 101 serves as a polishing surface. The insulating paten 356 has a large number of vertical through-holes 356 a into which an electrolytic solution flows.
The polishing pad 101 is made of a conductive material, e.g., a material composed of carbon as a main component, so that the polishing pad 101 has an electrical conductivity. The polishing pad (conductive pad) 101 has a large number of vertical through-holes 101 a. A second electrode 364 is mounted on a lower surface of retainer ring 3 and is to be brought into contact with an electric-supply contact 362, as described below. An electric current is supplied from the second electrode 364, contacting the electric-supply contact 362, via the polishing pad (conductive pad) 101 to a conductive film, such as copper film 907, of a substrate W held by the polishing head 1. The first electrode 354 and the conductive film are electrically connected via an electrolytic solution. This electrolytic solution is supplied from electrolytic-solution supply nozzle 102 to the polishing surface of the polishing pad 101 and flows into the through-holes 101 a provided in the polishing pad 101 and into the through-holes 356 a provided in the conductive platen 356.
In this embodiment, a conductive sheet 358, composed of, for example, platinum, is provided between the insulating platen 356 and the polishing pad 101 in order to reduce a variation in electric potential on the polishing pad 101 and to thus reduce a variation in electric potential on the surface of the conductive film, such as the copper film 907, of the substrate W Through-holes 358 a for the electrolytic solution are provided in the conductive sheet 358 at positions facing the through-holes 356 a provided in the insulating platen 356.
A support base 360 is disposed laterally to the polishing table 100. The polishing head 1 is operable to hold the substrate W with part of the retainer ring 3 lying laterally to the polishing table 100. The electric-supply contact 362, coupled to the other pole of the power source 352, is mounted on the support base 360 at a position facing the retainer ring 3 of the polishing head 1. An upper surface of the electric-supply contact 362 is substantially flush with the upper surface (polishing surface) of the polishing pad 101. The ring-shaped second electrode 364, formed of, e.g., platinum, is provided on the entire lower surface of the retainer ring 3. It is possible to provide a ring-shaped second electrode on part of the lower surface of the retainer ring 3.
When the polishing head 1, holding the substrate W, is lowered, part of the second electrode 364 on the lower surface of the retainer ring 3 comes into contact with the upper surface of the electric-supply contact 362, while most of the other part of the second electrode 364 comes into contact with the upper surface of the polishing pad 101. At the same time, the conductive film, such as the copper film 907, of the substrate W also comes into contact with the upper surface of the polishing pad 101. Accordingly, as shown in FIG. 11, the electric current is supplied from the electric-supply contact 362 and the second electrode 364 to the conductive film of the substrate W directly via the polishing pad (conductive pad) 101 having the electrical conductivity. Thus, electric charges are transferred to the conductive film as a result of electron conduction via: the electric-supply contact 362; the second electrode 364 provided on the retainer ring 3; and the conductive pad 101. Therefore, the electric charges can be conveyed uniformly to the entire surface of the conductive film, thus making it possible to maintain in-plane uniformity of the processing rate of the conductive film. In addition, the polishing pad 101 is not damaged by the electric-supply contact 362, because the polishing pad 101 and the electric-supply contact 362 are not in direct contact.
Although the substrate W shown in FIG. 10 partly lies laterally to the polishing pad 101, it is possible to bring the entire surface of the substrate W into contact with the polishing pad 101. Although in this embodiment the electric-supply contact 362 is provided, and the electric-supply contact 362 is brought into contact with the second electrode 364 on the retainer ring 3 to supply the electric current, it is also possible to provide a wire in the interior of the polishing head 1 and to electrically connect the other pole of the power source 352 directly to the second electrode 364 on the retainer ring 3 via the wire and a rotary joint. In this case, it is not necessary for the polishing head 1 to hold the substrate W with part of the retainer ring 3 lying laterally to the polishing table 100.
In this embodiment, the conductive sheet 358, formed of, e.g., platinum, is provided between the polishing pad 101 and the insulating platen 356 so as to reduce the variation in electrical potential on the polishing pad 101. In particular, the electric charges are transferred from the electric-supply contact 362 to the second electrode 364 and then to the polishing pad 101, and are then transferred through the conductive sheet 358 and are supplied again more uniformly to the entire surface of the polishing pad 101.
The conductive sheet 358 has the through-holes 358 a at positions facing the through-holes 101 a of the polishing pad 101. A size of each through-hole 358 a is preferably larger than a size of each through-hole 101 a of the polishing pad 101, and a contact area between the conductive sheet 358 and the electrolytic solution is preferably small. This is because, if the size of the through-hole 358 a of the conductive sheet 358 is small, an electrolytic reaction is likely to occur at a surface of the through-hole 358 a, resulting in reduction of a current efficiency of polishing (i.e., proportion of electric current used in polishing to the total electric current applied).
Although the material of the conductive sheet 358 is not limited to platinum, an electric resistance of the conductive sheet 358 is preferably as low as possible. When a copper film is to be polished, it is preferred for the conductive sheet 358 to use a material which has a higher standard electrode potential than that of copper (i.e., a nobler material or a lower ionization tendency than copper). This is because, if the standard electrode potential of the material of the conductive sheet 358, underlying the polishing pad 101, is lower than copper (i.e., if the ionization tendency is higher than that of copper), the conductive sheet would be oxidized to form an oxide film prior to reaction of the copper film, and loss of electrical conductivity or dissolution of the conductive sheet would occur.
It is most preferable that the conductive sheet 358 have a sheet shape. However, the conductive sheet 358 may have a structure of numerous fine wires or a net-like structure. The conductive sheet 358 may be simply sandwiched between the polishing pad 101 and the insulating platen 356. It is preferred to cover a portion of the conductive sheet 358, which is to be in contact with the electrolytic solution, with an insulating material to avoid contact of the conductive sheet 358 with the electrolytic solution, in order to prevent an anodic reaction on the conductive sheet 358. In a case where the conductive sheet 358 is of a structure having no contact portion with the electrolytic solution, there is no fear of anodic dissolution by anodic polarization on the conductive sheet 358. Therefore, it is possible to form the conductive sheet of a material (baser material) having a lower electrode potential than a conductive film (an object to be polished), such as a copper film. The polishing pad 101 and the conductive sheet 358 may be bonded with a conductive adhesive.
The second electrode 364, provided on the lower surface of the retainer ring 3, is preferably formed of a conductive material which will not dissolve upon anodic polarization, and at least has a higher standard electrode potential than a conductive film (polishing object), such as a copper film. Therefore, the second electrode 364 is preferably platinum. Because platinum is harder than copper, when polishing the copper film 907 as a conductive film using the second electrode 364 formed of platinum, the second electrode 364 is hardly scratched. Even if the second electrode 364 is scratched, the scratch would not significantly affect a polishing performance.
As shown in FIG. 7, the electrolytic-solution supply nozzle 102 extends in the radial direction of the polishing pad 101 and has a plurality of electrolytic-solution supply mouths 140 arranged at regular intervals along the length direction of the nozzle 102.
Polishing operations of the electrochemical mechanical polishing apparatus 250 having the above structures will now be described. When carrying out polishing of a substrate W, the substrate W is held on the lower surface of the polishing head 1, with the retainer 3 surrounding a circumference of the substrate W The cylinder 111, coupled to the polishing head drive shaft 11, is then actuated to lower the polishing head 1, thereby bringing part of the second electrode 364, provided on the lower surface of the retainer 3, into contact with the electric-supply contact 362 and bringing most of the other part of the second electrode 364 into contact with the polishing pad 101. In this state, pressurized fluids at predetermined pressures are supplied respectively to the pressure chambers 22 and 23, the central pressure chamber 24, and the intermediate pressure chamber 25 to thereby press the substrate W, held by the polishing head 1, against the polishing surface of the polishing pad 101.
While a voltage is applied by the power source 352 between the first electrode 354 and the conductive film, such as the copper film 907, formed on the surface of the substrate W, an electrolytic solution is supplied from the electrolytic-solution supply nozzle 102 to the polishing surface. Simultaneously, the polishing head 1 and the polishing table 100 are rotated, whereby the electrolytic solution is held in the through-holes 101 a of the polishing pad 101 and in the through-holes 356 a of the insulating platen 356, and polishing of the conductive film proceeds in the presence of the electrolytic solution between a lower surface of the conductive film of the substrate W and the upper surface of the first electrode 354.
Upon contact between the electric-supply contact 362 and the second electrode 364, an electric current is supplied from the second electrode 364 to the conductive film, such as the copper film 907, of the substrate W held by the polishing head 1 directly via the polishing pad (conductive pad) 101 having the electrical conductivity. The electrolytic solution is held in the through-holes 101 a of the polishing pad 101 and in the through-holes 356 a of the insulating platen 356, and the electric current flows between the surface of the substrate W and the first electrode 356, whereby electrochemical mechanical polishing of the conductive film is performed. The conductive sheet 358 has the through-holes 358 a so as not to obstruct flowing of the electrolytic solution. The polishing pad 101 may have annular grooves or lattice-patterned grooves, in addition to the through-holes 101 a provided over the polishing surface of the polishing pad 101 in its entirety. If the polishing pad 101 itself is permeable to liquid, like a pad having continuous pores, the polishing pad 101 may not necessarily have the through-holes.
In this embodiment also, the substrate W is divided into four concentric circular and annular portions (C1-C4), and those portions (areas) can be pressed at different pressures (see FIG. 6). The polishing rate (removal rate) depends on the pressure on the substrate W pressed against the polishing surface. Since the pressures on the divisional portions of the substrate W can be controlled independently as described above, the polishing rates of the four portions (C1-C4) of the substrate W can be controlled independently. Accordingly, even when there is a variation in thickness of a thin film along a radial direction of the substrate W, shortage or excess of polishing can be avoided over the surface of the substrate W.
In particular, even when a thickness of a film on the surface of the substrate W varies with radial positions of the substrate W, the pressure on the portion of the substrate W, having a relatively large film thickness, can be made higher than the pressure on the portion of the substrate W having a relatively small film thickness by making the pressure in the corresponding pressure chamber, which lies over the thick portion, higher than the pressures in the other pressure chambers, or by making the pressures in the pressure chambers, which lie over the thin portions, lower than the pressure in the other pressure chamber. The polishing rate of the thick portion of the substrate W can thus be selectively raised. This makes it possible to polish the surface of the substrate W without causing excess or shortage of polishing over the surface in its entirety, irrespective of a variation in thickness of the film caused by a film-formation process.
Polishing of the substrate W is thus performed with the pressure, applied to the retainer ring 3, being appropriately adjusted by the head air cylinder 111 and with the pressures, applied to the divisional portions of the substrate W, being appropriately adjusted by the pressurized air supplied to the pressure chambers 22 to 25.
As described above, the pressure on the substrate W can be controlled by independently controlling the pressures in the pressure chambers 22 and 23, the pressure chamber 24 in the center bag 8, and the pressure chamber 25 in the ring tube 9. Further according to this embodiment, pressure-controllable areas of the substrate W can be easily changed by changing position and size of the center bag 8 and the ring tube 9.
A thickness distribution of a film formed on a surface of a substrate may vary depending on a type of film-forming method or film-forming apparatus used. According to this embodiment, the position and the size of the pressure chambers for applying pressure to the substrate can be changed simply by replacing the center bag 8 and the center bag holder 82, or the ring tube 9 and the ring tube holder 92. Therefore, the position and range of pressure control on the substrate can be easily changed according to a thickness distribution of a film, to be polished, at a low cost simply by changing only a part of the polishing head 1. In other words, this makes it possible to deal with a change in thickness distribution of a film on the surface of the substrate easily at a low cost. Changing the shape and position of the center bag 8 or the ring tube 9 results in a change in size of the pressure chamber 22, lying between the center bag 8 and the ring tube 9, and a change in size of the pressure chamber 23 surrounding the ring tube 9.
The operations of the substrate processing apparatus according to this embodiment will now be described with reference to FIG. 3.
First, the substrate cassette 204, which stores a large number of substrates W shown in FIG. 1B each having the copper film 907 formed on the surface, is mounted on the loading and unloading stage. One substrate is removed from the substrate cassette 204 by the transfer robot 202 and placed onto the substrate station 206. The transfer robot 208 receives the substrate from the substrate station 206 and, after reversing the substrate as necessary, transfers the substrate to the rotary transporter 210. The rotary transporter 210 is then rotated horizontally, and the substrate, supported by the rotary transporter 210, is held by the polishing head 1 of one of the two electrochemical mechanical polishing apparatuses 250.
Thereafter, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. The polishing head 1 and the polishing table 100 are rotated together about their own axes. In this state, the polishing head 1 is lowered to bring a part of the second electrode 364 on the retainer ring 3 into contact with the electric-supply contact 362 and to bring most of the other part of the second electrode 364 into contact with the polishing surface of the polishing pad 101. At the same time, the polishing head 1 presses the substrate against the polishing surface of the polishing pad 101 at predetermined pressure of not more than 70 hPa (1 psi). While the electrolytic solution is supplied to the polishing pad 101, the voltage is applied by the power source 352 between the first electrode 354 and the conductive film of the substrate W to thereby perform polishing (first polishing) of the conductive film. Holding of the substrate, e.g., by vacuum attraction, may be released during polishing of the substrate with the polishing pad 101.
In the electrochemical mechanical polishing apparatus 250, the first polishing is performed so as to remove the conductive film, e.g., the copper film 907 (and the seed film 906), until an average thickness of the remaining conductive film is not more than 300 nm and a variation in thickness of the remaining conductive film falls within not more than 150 nm. During polishing of the copper film 907 (and the seed film 906), the ITM 326, such as an eddy-current sensor, detects an in-plane distribution of the thickness of the copper film 907 (and the seed film 906), and the control section 310 controls and adjusts the polishing pressures to be applied to the divisional portions (press areas) C1 to C4 shown in FIG. 9. The electrochemical mechanical polishing generally causes little damage to interconnects. Therefore, use of the electrochemical mechanical polishing can significantly reduce damage to an interconnect structure of the substrate. For example, the electrochemical mechanical polishing can be used for removing most part of an interconnect metal film formed outside interconnect recesses. Since the film outside of the interconnect recesses constitutes a major part of a total amount of the film to be removed, use of the electrochemical mechanical polishing can significantly reduce damage to the interconnect structure.
After completion of the first polishing in one of the electrochemical mechanical polishing apparatuses 250, the polished surface and the back surface of the substrate are cleaned (rinsed) with a cleaning liquid, e.g., pure water, and then dried, if necessary. The substrate is then transported via the rotary transporter 210 to another of the electrochemical mechanical polishing apparatuses 250, and held by the polishing head 1. In the electrochemical mechanical polishing apparatus 250 which performed the first polishing, on the other hand, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
In the second polishing, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. Then, as with the first polishing, the polishing head 1 and the polishing table 100 are rotated about their own axes, and the polishing head 1 is lowered to press the substrate against the polishing surface of the polishing pad 101. Simultaneously, the electrolytic solution is supplied to the polishing pad 101, and the voltage is applied by the power source 352 between the first electrode 354 and the conductive film of the substrate, i.e. the copper film 907, to perform the second polishing of the conductive film which has not been removed by the first polishing. Specifically, the second polishing is performed so as to remove the copper film 907 (and the seed film 906) remaining on the barrier film 905, thereby exposing the barrier film 905.
After completion of the second polishing in the electrochemical mechanical polishing apparatus 250, the substrate is transported to the cleaning unit 214, via the rotary transporter 210 and the transfer robot 208. If necessary, the substrate may be reversed prior to transfer to the cleaning unit 214. In the electrochemical mechanical polishing apparatus 250 after the second polishing, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
The substrate surface is cleaned (rinsed) in the cleaning unit 214, and the cleaned substrate is transported by the transfer robot 208 to the substrate station 206 and placed onto it. The transfer robot 202 (or 208) removes the substrate from the substrate station 206, and transports the substrate to the drying unit 212, which has a pen sponge for cleaning of the upper surface and a spin-drying function, for example. In the drying unit 212, the substrate is cleaned and dried. Thereafter, the cleaned and dried substrate is returned to the substrate cassette 204 by the transfer robot 202.
FIGS. 12 and 13 show a main portion of an electrochemical mechanical polishing apparatus according to yet another embodiment of the present invention. This embodiment differs from the embodiment shown in FIGS. 7 through 11 in the following respects. Instead of the electric-supply contact 362 in the embodiment shown in FIGS. 7 through 11, the electrochemical mechanical polishing apparatus of this embodiment has an electric-supply section 370 having a similar structure to the polishing head 1. Further, a circular second electrode 372 is provided, not on the lower surface of the retainer ring 3, but on a lower surface of the electric-supply section 370.
In the electrochemical mechanical polishing apparatus shown in FIGS. 12 and 13, a second electrode is not provided on the lower surface of the retainer ring 3 of the polishing head 1, and an electric-supply contact is not provided laterally to polishing table 100. The electric-supply section 370, having approximately the same size as the polishing head 1, is coupled to a lower end of a rotatable and vertically-movable electric-supply section drive shaft 374. The electric-supply section 370 is arranged at a position where the electric-supply section 370 and the polishing head 1 do not interfere with each other. The lower surface of the electric-supply section 370 is flat, and the second electrode 372, formed of, e.g., platinum, is provided on the flat lower surface of the electric-supply section 370. The second electrode 372 is directly coupled via a rotary joint 376 to a wire 375 extending from one of poles of power source 352. Other structures of the apparatus according to this embodiment are substantially the same as those of the embodiment shown in FIGS. 7 through 11.
In operations, the polishing head 1, holding a substrate W, is lowered to press the substrate W against the polishing surface of the polishing pad 101 of the polishing table 100. At the same time, the electric-supply section 370 is lowered to bring the second electrode 372 into surface contact with the polishing surface of the polishing pad 101. While a voltage is applied by the power source 352 between the first electrode 354 and a conductive film, such as the copper film 907, formed on a surface of the substrate W, an electrolytic solution is supplied from the electrolytic-solution supply nozzle 102 (see FIG. 7) to the polishing surface. Simultaneously, the polishing head 1, the polishing table 100, and the electric-supply section 370 are rotated about their own axes, whereby the electrolytic solution is held in the through-holes 101 a of the polishing pad 101 and in the through-holes 356 a of the insulating platen 356. Polishing of the conductive film thus proceeds in the presence of the electrolytic solution between a lower surface of the conductive film of the substrate W and the upper surface of the first electrode 354.
In this embodiment, the electric current is supplied from the second electrode 372 directly to the conductive film of the substrate W, held by the polishing head 1, via the polishing pad (conductive pad) 101 which is in direct surface contact with the second electrode 372. As described above, the electric-supply section 370 is arranged such that it does not contact the polishing head 1, and the second electrode 372 is brought into surface contact with the polishing surface of the polishing pad 101, so that the electric current is supplied to the conductive film of the substrate W via the polishing pad 101. With these arrangements, a sufficient contact area can be secured between the second electrode 372 and the polishing pad 101, thereby reducing variation in electrical potential on the conductive film, such as the copper film 907. Furthermore, reliability of electric supply to the conductive film can be enhanced. In addition, an adverse influence on the polishing surface of the polishing pad due to electric supply can be prevented. Therefore, deterioration of polishing performance due to electric supply can be prevented.
It is generally desirable to arrange an electrolytic-solution supply nozzle immediately upstream of the polishing head 1, in order to fully fill numerous holes of the polishing pad with the electrolytic solution. On the other hand, it is desirable that those holes of the polishing pad 101 which lie under the electric-supply section 370 are not filled with the electrolytic solution and that the electric current flows as little as possible between the second electrode (i.e., an electric-supply electrode) 372 and the first electrode 354. It is therefore desirable that the electric-supply section 370 be located most downstream of the electrolytic-solution supply nozzle 102 or near a rotational center of the polishing table 100.
The polishing surface of the polishing pad 101 has a non-contact area which never contacts the conductive film of the substrate W during polishing. In FIGS. 12 and 13, such a non-contact area is illustrated as a central area S which is a concentric circular area of the polishing surface of the polishing pad 101. The central area S and inner surfaces of the through-holes 101 a of the polishing pad 101 have been subjected to an insulating treatment. In this embodiment, as shown in FIG. 13, insulating films 378 are formed so as to cover the central area S and the inner surfaces of the through-holes 101 a.
Since the non-contact area (the central area S) and the inner surface of the through-holes 101 a of the conductive polishing pad 101, which may be made of mainly carbon, are covered with the insulating films 378, an electrolytic reaction at the surface of the polishing pad (conductive pad) 101 can be minimized. Therefore, formation of pits in the surface of the conductive film and a drop in polishing rate due to oxygen generated at the surface of the polishing pad 101 can be prevented.
Usable methods of insulating part of the conductive polishing pad 101 include an insulating coating treatment and a surface modification treatment. Examples of such an insulating coating treatment include coating of a surface with an ink, a paint, an adhesive, or the like. Examples of the surface modification treatment include modifying of a surface by means of a chemical treatment, graft polymerization, irradiation with a light, an electron beam or an ion beam, a plasma treatment, or plating.
FIG. 14 shows a main portion of an electrochemical mechanical polishing apparatus according to yet another embodiment of the present invention. This embodiment differs from the embodiment shown in FIGS. 12 and 13 in that the electric-supply section in the embodiment shown in FIGS. 12 and 13 is provided in a dresser. In particular, this embodiment uses a dresser 380 including a cylindrical main body 382 and a number of circular dressing sections 384 provided on a periphery of a lower surface of the main body 382. The dressing sections 384 are arranged at regular intervals along a circumferential direction of the lower surface of the main body 382.
An electric-supply section 386 is provided centrally on a lower surface of a support portion 396 surrounded by the main body 382 of the dresser 380. Diamond particles, for example, are attached by electro-deposition (plating) to a lower surface of each dressing section 384.
The electric-supply section 386 has a circular second electrode 388 formed of, e.g., platinum. This second electrode 388 constitutes a lower end of the electric-supply section 386. A wire 390, extending from one of poles of power source 352, is directly connected to the second electrode 388 via a rotary joint 392. A lower surface of the second electrode 388 lies at a slightly lower level than the lower surfaces of the dressing sections 384, and the second electrode 388 is flexibly supported by the support portion 396 connected to the main body 382. A compression spring 394, made of an insulating material, is interposed between the support portion 396 and the second electrode 388.
When performing dressing of the polishing pad 101, the dressing sections 384 are brought into contact with the polishing surface of the polishing pad 101, and the dresser 380 and the polishing pad 101 are rotated together about their own axes. During dressing, the second electrode 388 of the electric-supply section 386 is in contact with the polishing surface of the polishing pad 101, so that an electric current is supplied via the polishing pad 101 to a conductive film, such as the conductive film 907, of the substrate held by the polishing head 1 shown in FIG. 13.
Since the electric-supply section 386 is provided on the dresser 380, dressing of the polishing pad 101 by the dresser 380 and supply of the electric current to the conductive film via the electric-supply section 386 and the polishing pad 101 can be performed simultaneously in an in-situ manner. Further, a pressing force that presses the second electrode 388 against the polishing pad 101 can be controlled by the compression spring 394 made of an insulating material. Control of the pressing force can be performed in the following manner. The compression spring 394 is fixed by, e.g., a screw, to the support portion 396 separated from the main body 382. The main body 382 and the support portion 396 are designed such that their vertical relative positions are adjustable. The pressing force to be applied to the second electrode 388 against the polishing pad 101 is thus adjusted. The dressing sections 384 need to be electrically insulated from the second electrode 388, and therefore the compression spring 394 is formed of an insulating material in this embodiment. If at least one of the support portion 396 and the main body 382 is formed of an insulating material, however, it is possible to use a conductive compression spring. It is also possible to provide an insulating material between the second electrode 388 and a compression spring.
FIG. 15 shows a main portion of an electrochemical mechanical polishing apparatus according to yet another embodiment of the present invention. The electrochemical mechanical polishing apparatus of this embodiment includes a polishing table 400, a rotatable and vertically-movable polishing head 402 disposed above the polishing table 400, and a dresser 404. A circular first electrode 408, made of, e.g., platinum, and coupled to one of poles of a power source 406, is provided on an upper surface of the polishing table 400. An insulating platen 410 is disposed on the first electrode 408 so as to cover an upper surface of the first electrode 408. An upper surface of the insulating platen 410 in its entirety is covered with a polishing pad 412, and an upper surface of the polishing pad 412 serves as a polishing surface. The polishing table 400, the first electrode 408, and the insulating paten 410 are rotatable integrally about an axis.
As with the above-described embodiment, the insulating paten 410 has a large number of vertical through-holes, and the polishing pad 412 also has a large number of vertical through-holes 412 a. As with the above-described embodiment, the polishing pad 412 is made of a conductive material so as to exhibit an electrical conductivity. The conductive material may contain carbon as a main component. Although not shown diagrammatically, above the polishing table 400 is disposed an electrolytic-solution supply nozzle for supplying an electrolytic solution to the upper surface (polishing surface) of the polishing pad 412.
An electric-supply section 414 is provided so as to be in contact with the upper surface of the polishing pad 412. This electric-supply section 414 covers the upper surface of the polishing pad 412, and is fixed in position. The electric-supply section 414 has a second electrode 416 coupled to another of the poles of the power source 406. The second electrode 416 is made of platinum, for example. A surface of the second electrode 416, except for a connection with a wire extending from the power source 406, is covered with an insulator 418. The electric-supply section 414 has openings 414 a and 414 b at positions facing the polishing head 402 and the dresser 404, respectively. These openings 414 a and 414 b have sizes matching sizes of the polishing head 402 and the dresser 404, respectively.
In operations, the polishing head 402, holding a substrate W, is lowered through the opening 414 a of the electric-supply section 414 to press the substrate W against the polishing surface of the polishing pad 412. If necessary, the dresser 404 is lowered through the opening 414 b of the electric-supply section 414 to press the polishing surface of the polishing pad 412. While a voltage is applied by the power source 406 between the first electrode 408 and a conductive film, such as the copper film 907, formed on the surface of the substrate W, an electrolytic solution is supplied from the electrolytic-solution supply nozzle to the polishing surface. Simultaneously, the polishing head 402 and the polishing table 400 are rotated about their own axes, whereby the electrolytic solution is held in the through-holes 412 a of the polishing pad 412 and in the through-holes of the insulating platen 410. Polishing of the conductive film thus proceeds in the presence of the electrolytic solution between a lower surface of the conductive film of the substrate W and the upper surface of the first electrode 408.
In this embodiment, the electric current is supplied from the second electrode 416 directly to the conductive film of the substrate W, held by the polishing head 412, via the polishing pad (conductive pad) 412 which is in direct surface contact with the second electrode 416. With these arrangements, a sufficient contact area can be secured between the second electrode 416 and the polishing pad 412, thereby reducing a variation in electrical potential on the conductive film, such as the copper film 907. Furthermore, reliability of electric supply to the conductive film can be enhanced. In addition, because an adverse influence on the polishing surface of the polishing pad 412 is prevented, deterioration of polishing performance due to electric supply can be prevented. Moreover, the electrolytic solution is prevented from scattering. Therefore, an amount of the electrolytic solution can thus be reduced and a cost can also be reduced.
FIG. 16 shows a main portion of an electrochemical mechanical polishing apparatus according to yet another embodiment of the present invention. The electrochemical mechanical polishing apparatus of this embodiment includes a polishing table 500, and a rotatable and vertically-movable polishing head 502 disposed above the polishing table 500. A circular first electrode 508, made of, e.g., platinum, and coupled to one of poles of a power source 506, is provided on an upper surface of the polishing table 500. An insulating platen 510 is disposed on the first electrode 508 so as to cover an upper surface of the first electrode 508. An upper surface of the insulating platen 510 in its entirety is covered with a conductive polishing pad 512, and an upper surface of the polishing pad 512 serves as a polishing surface.
As with the above-described embodiment, the insulating paten 510 has a large number of vertical through-holes 510 a, and the polishing pad 512 also has a large number of vertical through-holes 512 a. A second electrode (conductive sheet) 514, e.g., formed from a platinum foil, is disposed between the insulating platen 510 and the polishing pad 512. This second electrode 514 has through-holes 514 a at positions corresponding to the through-holes 512 a of the polishing pad 512. Although not shown diagrammatically, an electrolytic-solution supply nozzle for supplying an electrolytic solution to the upper surface (polishing surface) of the polishing pad 512 and a dresser are disposed above the polishing table 500.
An electric-supply contact 516 is disposed above the polishing table 500. This electric-supply contact 516 is coupled to another of the poles of the power source 506 and is operable to come into contact with the polishing surface of the polishing pad 512 to thereby supply an electric current to the second electrode 514. The electric-supply contact 516 is in a form of a rotatable roller with a cylindrical shape. The rotational speeds (linear velocity of rotation) of the electric-supply contact (roller) 516 and the rotating polishing pad 512 are regulated so that a relative speed between the electric-supply contact (roller) 516 and the rotating polishing pad 512 at their contact point is not more than 0.1 m/s, preferably zero. It is possible to rotatably support the electric-supply contact (roller) 516 with its rotational friction being nearly zero so that the electric-supply contact (roller) 516 is allowed to rotate together with the rotating polishing pad 512 by the friction between the polishing pad 512 and the surface of the electric-supply contact (roller) 516.
The above-described control of the relative speed can minimize a frictional force generated between the polishing pad 512 and the electric-supply contact (roller) 516, thereby preventing scratching on the polishing pad 512 and peel-off of the polishing pad 512 or the second electrode 514 from the polishing table 500. By preventing scratching on the polishing pad 512, the electric current can be supplied to the conductive film without impairing the polishing properties of the polishing pad 512.
Although in this embodiment a single roller-type electric-supply contact 516 is provided, it is possible to provide a plurality of roller-type electric-supply contacts. This arrangement can increase a contact area between the electric-supply contacts and the polishing pad, thereby enhancing the reliability of electric supply. Instead of a roller-type electric-supply contact, an electric-supply contact in a form of a brush may also be used.
FIG. 17 is a vertical cross-sectional front view showing an essential part of an electrochemical mechanical polishing apparatus according to still another embodiment of the present invention, and FIG. 18 is a vertical cross-sectional view schematically showing a part of an essential part of the electrochemical mechanical polishing apparatus shown in FIG. 17. The polishing head according to this embodiment are basically identical to the polishing head according to the above embodiment shown in FIG. 5 and FIG. 6. Further, elements of this embodiment, which are identical to those of the above embodiment, are denoted by the same reference numerals, and will not be described repetitively.
As shown in FIG. 17, a circular support member 654 is fixed to an upper surface of polishing table 100. Polishing pad 101 is attached to an upper surface of the support member 654, and an upper surface of the polishing pad 101 provides a polishing surface. The support member 654 comprises a circular base 654 b and a lid 654 a covering an upper surface of the base 654 b. Vertically extending through-holes 101 a are formed in the polishing pad 101. The polishing table 100 is coupled to a non-illustrated rotating mechanism, so that the polishing table 100 is rotated together with the support member 654 and the polishing pad 101.
Electrolytic-solution supply nozzle 102 is provided so as to extend along a radial direction of the polishing pad 101, and has a supply mouth 102 a at a tip end thereof This supply mouth 102 a is located above a central portion of the polishing pad 101. An electrolytic solution is supplied from a non-illustrated electrolytic-solution supply source onto the central portion of the polishing pad 101 through the electrolytic-solution supply nozzle 102.
The support member 654 is coupled to one of poles of power source 352, and serves as a first electrode (cathode). An electrical contact, such as a roller or brush, is provided between a wire extending from the power source 352 and the support member (cathode) 654. For example, as shown in FIG. 18, an electrical contact 662 is provided so as to contact a side surface of the support member 654. The electrical contact 662 is preferably made from soft metal having a low specific resistance, such as gold, silver, copper, platinum, or palladium.
The lid 654 a has communication holes 655 in the same positions as those of the above-described through-holes 101 a of the polishing pad 101. Further, communication grooves 656 are formed on a lower surface of the lid 654 a so as to allow the communication holes 655 to communicate with each other. Communication grooves may be formed on an upper surface of the base 654 b. A first electrolytic-solution receiving port 658A, vertically extending through the polishing pad 101, is formed at the central portion of the polishing pad 101. Further, a second electrolytic-solution receiving port 658B is formed in the lid 654 a in the same position as that of the first electrolytic-solution receiving port 658A. This second electrolytic-solution receiving port 658B communicates with the plural communication grooves 656. The first electrolytic-solution receiving port 658A and the second electrolytic-solution receiving port 658B serve as an electrolytic-solution receiving section.
With these arrangements, the electrolytic solution, supplied through the supply mouth 102 a of the nozzle 102, flows through the first electrolytic-solution receiving port 658A, the second electrolytic-solution receiving port 658B, the communication grooves 656, and the communication holes 655 in this order to reach the through-holes 101 a. Upward flow of the electrolytic solution toward the polishing surface is formed in each of the through-holes 101 a, and the electrolytic solution is thus supplied to the polishing surface. In this embodiment, the first electrolytic-solution receiving port 658A, the second electrolytic-solution receiving port 658B, the communication grooves 656, and the communication holes 655 serve as an electrolytic-solution path for directing the electrolytic solution to the through-holes 101 a from below the polishing pad 101.
FIG. 19 is a plan view showing a part of the communication grooves 656 and the communication holes 655 formed in the lid 654 a shown in FIG. 18. It is preferable that the communication groove 656 have a width w in a range of 1 mm to 30 mm, and it is preferable that the communication hole 655 (and the through-hole 101 a) have a diameter r in a range of 1 mm to 30 mm. The width w of the communication groove 656 is preferably smaller than the diameter r of the communication hole 655 (and the through-hole 101 a). It is preferable that the communication groove 656 have a depth in a range of 1 mm to 5 mm.
The lid 654 a and the base 654 b are fixed to each other by a non-illustrated clamp. An O-ring 657 is provided between a periphery of the lower surface of the lid 654 a and the base 654 b. This O-ring 657 is made from a material which is hard to react with the electrolytic solution. An engagement portion may be provided so as not to allow the lid 654 a and the base 654 b to slide relative to each other in a rotational direction. The support member 654 is detachably mounted on the polishing table 100 by non-illustrated bolts.
The lid 654 a has a rigidity and a strength high enough to hold the polishing pad 101. Examples of a material forming the lid 654 a include a dielectric, such as PEEK (polyetheretherketone resin) or fluororesin, or a conductive material (e.g., metal, alloy, conductive plastic). It is preferable that the base 654 b be made from the same material as the lid 654 a. In this embodiment, because the support member 654 serves as the cathode (first electrode), at least one of the lid 654 a and the base 654 b is made from a conductive material. Both the lid 654 a and the base 654 b can be made from dielectric. In this case, a cathode is provided, in addition to the support member 654. For example, a cathode may be provided between the lid 654 a and the base 654 b so as to be in contact with the electrolytic solution flowing through the above-described electrolytic-solution path.
The polishing pad 101 is attached to the upper surface of the lid 654 a with an adhesive. It is preferable that a surface roughness of the upper surface of the lid 654 a be small. This is for the following reasons. The through-holes 101 a are uniformly formed over the polishing pad 101, and therefore a contact area between the lid 654 a and the polishing pad 101 is relatively small. Moreover, an adhesive strength would be lowered due to the electrolytic solution that soaks into a contact surface through the through-holes 101 a. Thus, from a viewpoint of preventing removal of the polishing pad 101, it is preferable that the surface roughness of the upper surface of the lid 654 a be small. For example, the surface roughness (Ra) of the upper surface of the lid 654 a is preferably at most 1 μm.
FIG. 20 is a vertical cross-sectional view showing a modified example of an essential part of the electrochemical mechanical polishing apparatus 250 shown in FIG. 18. In this example shown in FIG. 20, a rotary joint 658C, serving as an electrolytic-solution receiving section, is provided in the central portions of the polishing pad 101 and the lid 654 a. An upper end of the rotary joint 658C is connected to the electrolytic-solution supply nozzle 102, and a lower end of the rotary joint 658C communicates with the communication grooves 656. Therefore, the electrolytic solution, supplied through the electrolytic-solution supply nozzle 102, flows through the rotary joint 658C into the communication grooves 656 of the support member 654. In this example also, the electrolytic solution is supplied to the support member 654 from above the polishing surface, flows under the polishing pad 101, and is supplied to the through-holes 101 from below the polishing pad 101. In this embodiment, the rotary joint 658C, the communication grooves 656, and the communication holes 655 serve as the electrolytic-solution path.
FIG. 21 through FIG. 25 are views each showing an example of the communication grooves 656. In FIG. 21, the communication grooves 656 extend radially, and are preferably arranged at equal intervals (e.g., at intervals ranging from 10 to 120°) in a circumferential direction. In FIG. 22, the communication grooves 656 comprise radially-extending grooves shown in FIG. 21 and concentric circular grooves extending in a circumferential direction. In FIG. 23, the communication grooves 656 comprise radially-extending grooves shown in FIG. 21 and zigzag branch grooves extending in a circumferential direction. An interval in a radial direction between the branch grooves is preferably in a range of 1 mm to 200 mm. In FIG. 24, the communication grooves 656 comprise grid grooves. An interval between adjacent two of the grid grooves is in a range of 1 mm to 200 mm. In FIG. 25, the communication grooves 656 extend spirally, and are preferably arranged at equal intervals (e.g., at intervals ranging from 10 to 90°) in a circumferential direction. A radius of curvature of the communication grooves 656 is preferably half to five times a radius of the polishing pad 101.
A second electrode (an electric supply electrode) 664 is disposed laterally to the polishing pad 101. This second electrode 664 is coupled to another of the poles of the power source 352. An upper surface of the second electrode 664 and the upper surface (i.e., polishing surface) of the polishing pad 101 lie in substantially the same horizontal plane. The polishing head 1 is operable to bring the substrate W into contact with the polishing surface, with part of the substrate W lying laterally to the periphery of the polishing pad 101, so that a lower surface of the substrate W is in contact with the second electrode 664. In this state, the second electrode 664 supplies an electric current to the conductive film, e.g., copper film 307, on the substrate W held by the polishing head 1. In this manner, the support member 654, as a cathode, and the conductive film, as an anode, on the substrate W are electrically connected to each other via the electrolytic solution flowing through the support member 654 and the through-holes 101 a.
During electrochemical mechanical polishing, the polishing head 1 rotates the substrate W with the conductive film (e.g., the copper film) on the substrate W being in contact with the second electrode 664 (details of operations will be described later). As a result, a surface of the conductive film would be damaged by the second electrode 664. In addition, wear of the second electrode 664 is also likely to occur due to contact with the conductive film, and would result in unstable supply of the electric current. In view of such drawbacks, the second electrode (current supply electrode) 664 is preferably made from a conductive resin which is softer than metal of the conductive film and has a high wear resistance.
Examples of such a conductive resin include a resin having a conductivity itself, and a resin with a conductive material dispersed therein. Instead of the conductive resin, a conductive fiber may be used. Preferred examples of the conductive material include graphite, carbon nanotube, carbon nanohorn, carbon nanocoil, fullerene, conductive carbon black. In order to enhance the wear resistance of the second electrode 664, it is preferable to use a resin with carbon nanotube, which is a carbon material having a high wear resistance, dispersed in the resin. The second electrode 664 is preferably made from a composite resin, which contains the above conductive material, in a shape of sheet or foam formed by injection molding or cast molding. An amount of the conductive material added to the resin is preferably not less than 1% by mass, more preferably not less than 10% by mass. This is because, if the amount of the conductive material is less than 1% by mass, the conductivity is low and, as a result, the resin cannot exhibit sufficient electrical characteristic for use as the electric supply electrode.
Generally, electrical conduction is classified into two types: electron conduction; and ionic conduction. The above-described conductive material is an electron-conductive material. Instead, a material having ionic conduction can be used for the second electrode 664. Ion exchange resin or ion exchange fiber may be used as such a material having ionic conduction. Specific examples of the ion exchange resin include a ball-shaped ion exchange resin and an ion exchange membrane. Specific examples of the ion exchange fiber include a fiber, such as polyethylene nonwoven fabric, with ion-exchange groups introduced thereto by graft polymerization.
When the above-described ion exchange resin or the ion exchange fiber (which will be hereinafter referred to as ion exchange material) is used for the electric supply electrode, it is necessary to consider the following two respects.
First, it is necessary to keep the ion exchange material wet, otherwise the ion exchange material does not exhibit the ion conductivity. In view of this respect, at least a part of the ion exchange material is required to be immersed in pure water or the like at all times. For example, a nozzle may be provided so as to supply pure water to the ion exchange material at all times, or the ion exchange material in a shape of film may be wound around a roller with a lower part of the roller being immersed in pure water retained in a tank.
Second, electrical connection between the cathode (first electrode) and the ion exchange material via the electrolytic solution should be avoided. If the cathode and the ion exchange material are electrically connected via the electrolytic solution, an electric current does not flow through the conductive film on the surface (i.e., a short circuit is formed). As a result, the conductive film would not be polished. In order to avoid such a short circuit, it is preferable to provide a partition plate between the ion exchange material and the cathode (the support member 654 in this embodiment), or to supply an air to blow away the electrolytic solution so as not to allow the electrolytic solution to contact the ion exchange material.
The conductive resin or conductive fiber may be directly connected to a wire from the power source 352, or may be coupled via a metal block, metal plate, metal sheet, or the like. For example, the conductive fiber may be disposed on a metal plate connected to a wire from the power source 352, so that the conductive fiber is brought into contact with the conductive film on the substrate W to supply the electric current. In this case, platinum, which is stable against anodic polarization, is preferably used as the metal.
When a copper film is to be polished, a surface of the cathode (the support member 654 in this embodiment) is preferably made from a material which is likely to produce hydrogen during the electrochemical mechanical polishing. This is because the following reason. When performing the electrochemical mechanical polishing of the copper film, copper ions are dissolved into the electrolytic solution. These copper ions receive electrons from the cathode to form copper, which is deposited on the surface of the cathode (i.e., the surface of the cathode is plated with copper). If the surface of the cathode is plated with copper, a processing speed (i.e., a removal rate) would be changed or would differ from area to area. Thus, by forming the surface of the cathode with metal which is likely to produce hydrogen, a reaction of producing the hydrogen becomes dominant over the reaction of copper deposition on the surface of the cathode. As a result, the surface of the cathode is prevented from being plated with copper.
In view of this reason, the material of forming the cathode is preferably selected from ruthenium, platinum, palladium, stainless steel, and the like. Alternatively, foil of metal which is likely to produce hydrogen may be attached to the cathode, or the cathode may be plated with metal which is likely to produce hydrogen. For example, when using platinum, the cathode is made from titanium which is suitable for platinum plating, and a liquid-contact portion (e.g., the surface) of the cathode is plated with platinum. In this case, a sufficient thickness of a plated layer is about 1 μm. Palladium can also be used for plating.
Next, operations of the electrochemical mechanical polishing apparatus 250 having the above structures will be described. When polishing, the retainer ring 3 surrounds the periphery of the substrate W, and the lower surface of the polishing head 1 holds the substrate W. The head air cylinder 111, coupled to the polishing-head drive shaft 11, is operated so as to move the polishing head 1 downwardly, whereby part of the substrate W is brought into contact with the second electrode 664, and most of the other part of the substrate W is brought into contact with the polishing surface of the polishing pad 101. In this state, the pressurized fluids with predetermined pressures are supplied into the pressure chambers 22 and 23, the central pressure chamber 24, and the intermediate pressure chamber 25 (see FIG. 5) to thereby press the substrate W, held by the polishing head 1, against the polishing surface of the polishing pad 101 on the polishing table 100.
The electrolytic solution is supplied through the electrolytic-solution supply nozzle 102, while a voltage is applied between the support member 654 and the conductive film (e.g., the copper film 307) on the surface of the substrate W by the power source 352. The electrolytic solution flows through the first electrolytic-solution receiving port 658A, the second electrolytic-solution receiving port 658B, the communication grooves 656, the communication holes 655, and the through-holes 101 a onto the polishing surface. Simultaneously, the polishing head 1 and the polishing table 100 are rotated together to thereby polish the conductive film on the substrate W in the presence of the electrolytic solution between the conductive film and the support member (cathode) 654.
Polishing of the substrate W is thus performed while appropriately adjusting the pressure applied by the head air cylinder 111 to the retainer ring 3 pressing the polishing pad 101 and the pressures, applied by the pressurized air in the pressure chambers 22 to 25, to press the divisional portions of the substrate W against the polishing pad 101.
As described above, the pressure on the substrate W can be controlled by independently controlling the pressures in the pressure chambers 22 and 23, the pressure chamber 24 in the center bag 8, and the pressure chamber 25 in the ring tube 9. Further according to this embodiment, pressure-controllable areas of the substrate can be easily changed by changing position and size of the center bag 8 and the ring tube 9.
A thickness distribution of a film formed on a surface of a substrate may vary depending on a type of film-forming method or film-forming apparatus used. According to this embodiment, the position and the size of the pressure chambers for applying pressure on the substrate can be changed simply by replacing the center bag 8 and the center bag holder 82, or the ring tube 9 and the ring tube holder 92. Therefore, the position and range of pressure control on the substrate can be easily changed according to a thickness distribution of a film, to be polished, at a low cost simply by changing only a part of the polishing head 1. In other words, this makes it possible to deal with a change in thickness distribution of a film on the surface of the substrate easily at a low cost. Changing the shape and the position of the center bag 8 or the ring tube 9 results in a change in size of the pressure chamber 22, lying between the center bag 8 and the ring tube 9, and a change in size of the pressure chamber 23 surrounding the ring tube 9.
The operations of the substrate processing apparatus according to this embodiment will now be described with reference to FIG. 3.
First, the substrate cassette 204, which stores a large number of substrates W shown in FIG. 1B each having the copper film 907 formed on the surface, is mounted on the loading and unloading stage. One substrate is removed from the substrate cassette 204 by the transfer robot 202 and placed onto the substrate station 206. The transfer robot 208 receives the substrate from the substrate station 206 and, after reversing the substrate as necessary, transfers the substrate to the rotary transporter 210. The rotary transporter 210 is then rotated horizontally, and the substrate, supported by the rotary transporter 210, is held by the polishing head 1 of one of the two electrochemical mechanical polishing apparatuses 250.
Thereafter, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. The polishing head 1 and the polishing table 100 are rotated together about their own axes. In this state, the polishing head 1 is lowered to bring a part of the conductive film of the substrate into contact with the second electrode 664 and to press most of the other part of the conductive film into contact with the polishing surface of the polishing pad 101 at predetermined pressure of not more than 70 hPa (1 psi). While the electrolytic solution is supplied from the electric-solution supply nozzle 102, the voltage is applied by the power source 352 between the support member (cathode) 654 and the conductive film of the substrate W to thereby perform polishing (first polishing) of the conductive film. Holding of the substrate, e.g., by vacuum attraction, may be released during polishing of the conductive film.
In the electrochemical mechanical polishing apparatus 250, the first polishing is performed so as to remove the conductive film, e.g., the copper film 907 (and the seed film 906), until an average thickness of the remaining conductive film is not more than 300 nm and a variation in thickness of the remaining conductive film falls within not more than 150 nm. During polishing of the copper film 907 (and the seed film 906), the ITM 326, such as an eddy-current sensor, detects an in-plane distribution of the thickness of the copper film 907 (and the seed film 906), and the control section 310 controls and adjusts the polishing pressures to be applied to the divisional portions (pressure areas) C1 to C4 shown in FIG. 5. The electrochemical mechanical polishing generally causes little damage to interconnects. Therefore, use of the electrochemical mechanical polishing can significantly reduce damage to an interconnect structure of the substrate. For example, the electrochemical mechanical polishing can be used for removing most part of an interconnect metal film formed outside interconnect recesses. Since the film outside of the interconnect recesses constitutes a major part of a total amount of the film to be removed, use of the electrochemical mechanical polishing can significantly reduce damage to the interconnect structure.
After completion of the first polishing in one of the electrochemical mechanical polishing apparatuses 250, the polished surface and the back surface of the substrate are cleaned (rinsed) with a cleaning liquid, e.g., pure water, and then dried, if necessary. The substrate is then transported via the rotary transporter 210 to another of the electrochemical mechanical polishing apparatuses 250, and held by the polishing head 1. In the electrochemical mechanical polishing apparatus 250 which performed the first polishing, on the other hand, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
In the second polishing, the substrate, held by the polishing head 1, is moved to a polishing position above the polishing table 100. Then, as with the first polishing, the polishing head 1 and the polishing table 100 are rotated about their own axes, and the polishing head 1 is lowered to press the substrate against the polishing surface of the polishing pad 101. Simultaneously, the electrolytic solution is supplied from the electric-solution supply nozzle 102, and the voltage is applied by the power source 352 between the support member 654 and the conductive film of the substrate, i.e. the copper film 907, to perform the second polishing of the conductive film which has not been removed by the first polishing. Specifically, the second polishing is performed so as to remove the copper film 907 (and the seed film 906) remaining on the barrier film 905, thereby exposing the barrier film 905.
After completion of the second polishing in the electrochemical mechanical polishing apparatus 250, the substrate is transported to the cleaning unit 214, via the rotary transporter 210 and the transfer robot 208. If necessary, the substrate may be reversed prior to transfer to the cleaning unit 214. In the electrochemical mechanical polishing apparatus 250 after the second polishing, conditioning of the polishing surface of the polishing pad 101 with the dresser 218 is performed so as to prepare for the next polishing.
The substrate surface is cleaned (rinsed) in the cleaning unit 214, and the cleaned substrate is transported by the transfer robot 208 to the substrate station 206 and placed onto it. The transfer robot 202 (or 208) removes the substrate from the substrate station 206, and transports the substrate to the drying unit 212, which has a pen sponge for cleaning of the upper surface and a spin-drying function, for example. In the drying unit 212, the substrate is cleaned and dried. Thereafter, the cleaned and dried substrate is returned to the substrate cassette 204 by the transfer robot 202.
FIG. 26 is a view schematically showing an essential part of an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 26, a weir 670 is provided so as to surround circumferential surfaces of polishing pad 101 and polishing table 100. This weir 670 is fixed to plural support rods 674. The weir 670 has an outer wall 670 a, an inner wall 670 b, and a bottom portion 670 c. A small gap is formed between the inner wall 670 b and the polishing table 100, so that the polishing table 100 does not come into contact with the weir 670 during rotation. An upper end of the outer wall 670 a is at a higher position than the polishing surface, and an upper end of the inner wall 670 b is at a lower position than the polishing surface. With these arrangements, the electrolytic solution flows out from the polishing surface via a centrifugal force into the weir 670.
The electrolytic solution, received by the weir 670, is discharged through a liquid-recovery line 671, and is reused after passing through a non-illustrated filter. A flow-rate regulating valve 672 is provided in the liquid-recovery line 671, so that a flow rate of the electrolytic solution, flowing through the liquid-recovery line 671, can be regulated. This flow-rate regulating valve 672 is operated so as to keep a liquid level of the electrolytic solution on the polishing surface constant, based on an amount of the electrolytic solution supplied from the electrolytic-solution supply nozzle 102 (see FIG. 18). With this flow-rate control, polishing can be performed with the electrolytic solution being retained on the polishing surface (i.e., with the liquid level of the electrolytic solution being higher than at least the polishing surface).
Second electrode (electric supply electrode) 664 is covered with an insulating cover 673 so as not to contact the electrolytic solution stored in the weir 670. Support member (cathode) 654 is coupled to the power source 352 via a wire extending through a rotational shaft of the polishing table 100. The polishing pad 101 may be a conductive pad (a polishing pad having a conductivity), so that the electric current can be supplied to the conductive film on the substrate W via the conductive pad by bringing the second electrode 664 into contact with the conductive pad. With this arrangement, polishing can be performed without holding the substrate W in the overhanging position. In this embodiment, the electrolytic solution may be supplied directly onto the polishing surface from above the polishing pad 101 without providing the above-described electrolytic-solution path.
FIG. 27 is a view schematically showing an essential part of an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 27, a deformable sponge member (liquid-permeable member) 680 is arranged so as to surround polishing pad 101, support member 654, and polishing table 100. A liquid-recovery section 681 is provided below the sponge member 680. The sponge member 680 is fixed to the liquid-recovery section 681, which is fixed to plural support rods 674. A circumferential surface of the polishing pad 101 and an inner surface of the sponge member 680 are in contact with each other. An upper end of the sponge member 680 is at a higher position than the polishing surface. With this arrangement, the electrolytic solution is moved by a centrifugal force to a periphery of the polishing pad 101, and is then absorbed into the sponge member 680. The electrolytic solution flows downwardly in the sponge member 680 into the liquid-recovery section 681. The electrolytic solution, stored in the liquid-recovery section 681, is delivered through liquid-recovery line 671 for reuse. In this embodiment, the flow-rate regulating valve is not provided.
During polishing, a part of an upper portion of the sponge member 680 is deformed by the polishing head 1, whereby the conductive film on the substrate W, held by the polishing head 1, is brought into contact with the second electrode 664. In this embodiment also, a conductive pad can be used so that polishing can be performed without holding the substrate W in the overhanging position.
FIG. 28 is a plan view schematically showing an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. FIG. 29 is a schematic cross-sectional view of the electrochemical mechanical polishing apparatus 250 shown in FIG. 28. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 28, the substrate W, held by polishing head 1, is located within polishing surface (i.e., not in the overhanging position), and part of the substrate W is located on a central portion of polishing pad 101 during polishing. With these arrangements, the polishing pad 101 can be small in size, compared with the above embodiments, and as a result, an amount of the electrolytic solution to be used in polishing can be reduced.
In this embodiment, a conductive pad is used as the polishing pad 101. Second electrode 664 is arranged so as to contact the polishing pad 101, so that an electric current is supplied from the second electrode 664 to the conductive film on the substrate W via the conductive polishing pad 101. An annular groove (an electrolytic-solution receiving section) 682 is formed in the polishing pad 101 and lid 654 a. The annular groove 682 and the polishing pad 101 are concentrically arranged. This annular groove 682 has a larger radius than a distance between the center of the polishing pad 101 and a circumferential surface of the polishing head 1 in a polishing position, so that part of the annular groove 682 is positioned radially outwardly of the polishing head 1 at all times during polishing.
Electrolytic-solution supply nozzle 102 is provided so as to extend along the radial direction of the polishing pad 101, and has supply mouth 102 a at a tip end thereof This supply mouth 102 a is located in the annular groove 682. As with the above embodiments, communication grooves 656, communicating with the annular groove 682, are formed on the lid 654 a of support member 654. With these arrangements, the electrolytic solution is supplied through the electrolytic-solution supply nozzle 102 into the annular groove 682, and flows through the communication grooves 656, communication holes 655, and through-holes 101 a onto the polishing surface. The annular groove 682 is required to have a larger width than an outer diameter of the electrolytic-solution supply nozzle 102. On the other hand, from a viewpoint of preventing the electrolytic solution from scattering, it is preferable that the width of the annular groove 682 be as small as possible. In order to prevent the electrolytic solution from scattering from the annular groove 682, a simple check valve may be provided on the lid 654 a. FIG. 30 through FIG. 33 show examples of such a check valve.
FIG. 30 is a plan view showing part of a check valve provided in the annular groove 682. FIG. 31 is a cross-sectional view taken along line C-C in FIG. 30. As shown in FIG. 30 and FIG. 31, an annular check valve 683 is provided so as to cover an upper portion of the annular groove 682. This check valve 683 is made from an elastic material, such as a sponge. A slit 683 a is formed in the check valve 683. This slit 683 a extends in a circumferential direction of the check valve 683. The electrolytic-solution supply nozzle 102 is inserted into the slit 683 a. Although a part of the slit 683 a is opened by the electrolytic-solution supply nozzle 102 inserted in the slit 683 a, most part of the slit 683 a is closed. Therefore, the check valve 683 can prevent the electrolytic solution from flowing out from the annular groove 682. As shown in FIG. 30 and FIG. 31, a gap cover 684 is preferably provided so as to fill a gap between the electrolytic-solution supply nozzle 102 and the check valve 683.
FIG. 32 and FIG. 33 are cross-sectional views each showing another example of the check valve 683. In the example shown in FIG. 32, check valve 683 is made from a thin rubber sheet. This check valve 683 is bent upwardly upon contact with the electrolytic-solution supply nozzle 102. In the example shown in FIG. 33, check valve 683 is made from a hollow rubber tube. This check valve 683 is compressed upon contact with the electrolytic-solution supply nozzle 102.
The annular groove 682 is not necessarily concentric with the polishing pad 101. The annular groove 682 may be an orbital groove or may be an annular groove whose center is not on a central axis of the polishing pad 101. In this case, in order to allow the electrolytic-solution supply nozzle 102 to follow the rotating annular groove, the electrolytic-solution supply nozzle 102 is configured to be movable in a radial direction of the polishing pad 101. For example, the electrolytic-solution supply nozzle 102 may be fixed to a slider which is freely movable in the radial direction of the polishing pad 101.
FIG. 34 and FIG. 35 are cross-sectional views each schematically showing an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 34, sponges 687, each serving as a liquid-retaining member, are provided in through-holes 101 a of polishing pad 101. These sponges 687 have lower ends contacting base 654 b of support member 654, and have upper ends positioned above polishing surface of the polishing pad 101. The sponges 687 are made from a deformable material, so that polishing head 1, holding the substrate W, can compress the sponges 687 via the substrate W to allow the substrate W to contact the polishing surface during polishing. With this structure, the electrolytic solution is retained by the sponges 687 during polishing. Hence, an amount of the electrolytic solution scattering off the polishing surface due to a centrifugal force can be reduced.
On the other hand, when dressing the polishing surface, the above-described clamp is removed, and as shown in FIG. 35, lid 654 a is elevated so that the upper ends of the sponges 687 are positioned below the polishing surface. In this state, the lid 654 a and the base 654 b are fixed in position. Then, while a pure-water supply nozzle 688 supplies pure water onto the polishing surface, the dresser 218 dresses the polishing surface. Because the dresser 218 does not contact the sponges 687 during dressing, the sponges 687 are not damaged by the dresser 218.
Other than the sponge, a fibrous member or an open-cell foam may be used for the liquid-retaining member. An example of a method of forming the open-cell foam includes the steps of mixing fine particles of calcium carbonate with a base material, injection-molding the base material mixed with the calcium carbonate particles to form an injection-molded product, and immersing the injection-molded product into hydrochloric acid water to decompose and dissolve the calcium carbonate particles. In this case, an amount of the calcium carbonate particles, filling the base material, is required to be large enough to allow the calcium carbonate particles to be in contact with each other. As the base material, polyurethane, polyolefin, or rubber can be used.
FIG. 36 is a schematic cross-sectional view showing another example of this embodiment. As shown in FIG. 36, in this example, the electrolytic-solution path for directing the electrolytic solution to the through-holes 101 a from below the polishing pad 101 is not provided. Instead, the electrolytic solution is supplied directly onto the polishing surface from the electrolytic-solution supply nozzle 102. Sponges 687, each serving as the liquid-retaining member, are provided in the through-holes 101 a, respectively, so that the electrolytic solution, supplied from the electrolytic-solution supply nozzle 102, is retained by the sponges 687.
In this example, it is preferable that the upper ends of the sponges 687 be positioned below the polishing surface so as not to interfere with dressing of the polishing surface. An arrangement of the liquid-retaining members is not limited to the above examples in which the liquid-retaining members are disposed in the through-holes 101 a which are uniformly distributed over the polishing surface. For example, the polishing surface may have grooves on its upper surface (i.e., polishing surface), and the liquid-retaining members may be disposed in these grooves. In this case, the arrangements of the liquid-retaining members as viewed from above include a linear arrangement, a concentric circular arrangement, and a fan-shaped arrangement.
FIG. 37 and FIG. 38 are cross-sectional views each schematically showing an example of a polishing pad 101 used in an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
In this embodiment, each of through-holes 101 a has an upper opening with a smaller diameter than a diameter of a lower opening thereof More specifically, in the example shown in FIG. 37, the diameter of each of the through-holes 101 a is gradually decreased from the lower opening to the upper opening. In the example shown in FIG. 38, each of the through-holes 101 a has two holes arranged vertically in series with different diameters. Because the upper opening is smaller than the lower opening, the electrolytic solution retained in the through-holes 101 a is prevented from scattering due to a centrifugal force. In this embodiment, the electrolytic-solution path for directing the electrolytic solution to the through-holes 101 a from below polishing pad 101 may not be provided. Instead, the electrolytic solution may be supplied directly onto the polishing surface from electrolytic-solution supply nozzle 102 so that the through-holes 101 a retain the electrolytic solution therein.
FIG. 39 is a schematic cross-sectional view showing an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 39, an annular gas passage 690 is provided so as to surround polishing pad 101. This gas passage 690 has a slit (i.e., gas ejection opening) 691 in an inner circumferential surface thereof, so that a gas, flowing through the gas passage 690, is ejected through the slit 691 toward a center of polishing surface of the polishing pad 101. With this gas passage 690, the gas can push back the electrolytic solution that is about to flow out from the polishing surface by a centrifugal force. The gas ejection opening is not limited to the slit. Plural holes (each having a diameter of not more than 1 mm, for example) may be provided as the gas ejection opening. In this embodiment, the electrolytic-solution path for directing the electrolytic solution to the through-holes 101 a from below the polishing pad 101 may not be provided. Instead, the electrolytic solution may be supplied directly onto the polishing surface from electrolytic-solution supply nozzle 102. Further, a conductive pad may be used for the polishing pad 101, and the second electrode (electric supply electrode) may be in contact with the conductive pad so as to supply an electric current to the conductive film on the substrate via the conductive pad.
FIG. 40 is a schematic side view showing an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
As shown in FIG. 40, two cylindrical rollers 693 and 694, each rotatable about its own axis, are provided laterally to polishing pad 101. These rollers 693 and 694 are operable to sandwich the overhanging polishing head 1 during polishing, and the lower roller 694 is placed in contact with a lower surface of the substrate W. This roller 694 is electrically connected to power source 352 to serve as the second electrode (electric supply electrode). A surface of the roller 694, to be brought into contact with the substrate W, is preferably made from metal that is inactive for anodic polarization, or a conductive resin, or a conductive fiber.
A rotational speed (a linear velocity of rotation) of the roller 694 and a rotational speed of the substrate W are adjusted such that a relative speed between the roller 694 and the rotating substrate W is not more than 0.1 m/s, preferably zero. The roller 694 may be rotatably supported with its rotational friction being nearly zero, so that the roller 694 can be rotated by friction between the roller 694 and the substrate W. These structures can reduce the friction between the roller 694 and the substrate W, and can thus prevent the conductive film on the substrate W from being damaged and removed. Although one pair of rollers 693 and 694 is provided so as to sandwich the polishing head 1, plural pairs of rollers may be provided in parallel. Providing the plural pairs of rollers can increase a contact area between the rollers and the substrate W, and can thus enhance a reliability of current supply.
FIG. 41 is a schematic side view showing another example of the electrochemical mechanical polishing apparatus 250 according to the embodiment of the present invention. In this example, a single roller 694 is provided as the second electrode (electric supply electrode), and is arranged so as to contact the lower surface of the substrate W held by the overhanging polishing head 1. In this example also, plural rollers, which are to be in contact with the lower surface of the substrate W, may be provided. Other operations and structures of the roller 694 are the same as those of the example shown in FIG. 40.
FIG. 42 is a schematic side view showing still another example of the electrochemical mechanical polishing apparatus 250 according to the embodiment of the present invention. In this example, a roller 695, having a vertical cross-sectional shape with a thin central portion and thick end portions, is provided as the second electrode (electric supply electrode). This roller 695 is rotatable about a vertical axis, and is arranged such that a circumferential surface thereof is in contact with a circumferential surface of the overhanging polishing head 1. The substrate W, held by the polishing head 1, is brought into contact with the circumferential surface of the roller 695, whereby the conductive film on the substrate W and the roller 695 are electrically connected. Other operations and structures of the roller 695 are the same as those of the example shown in FIG. 40. According to this example, the roller 695 is not required to press the substrate W from a direction perpendicular to a surface of the substrate W. Therefore, a good contact is maintained between the conductive film on the substrate W and the polishing surface, thus resulting in uniform polishing.
FIG. 43 is a schematic perspective view showing an electrochemical mechanical polishing apparatus 250 according to still another embodiment of the present invention. Components and operations of this embodiment, which will not be described below, are identical to those of the previously-described embodiment shown in FIG. 18, and will not be described repetitively.
In this embodiment, a belt-shaped ring member 696 is provided so as to surround polishing pad 101. This ring member 696 has an upper surface lying in the same horizontal plane as polishing surface of the polishing pad 101, so that part of the substrate W, held by the overhanging polishing head 1, is placed in contact with the upper surface of the ring member 696. The ring member 696 is electrically connected to power source 352, and thus serves as the second electrode (electric supply electrode). The upper surface of the ring member 696 can be made from metal that is inactive for anodic polarization, or a conductive resin, or a conductive fiber.
A gap is formed between the polishing pad 101 and the ring member 696, and the ring member 696 is rotatable independently of the polishing pad 101. A rotational speed (a linear velocity of rotation) of the ring member 696 and a rotational speed of the substrate W are adjusted such that a relative speed between the ring member 696 and the rotating substrate W is not more than 0.1 m/s, preferably zero. The ring member 696 may be rotatably supported with its rotational friction being nearly zero, so that the ring member 696 can be rotated by friction between the ring member 696 and the substrate W.
FIG. 44 is a plan view of an electrochemical mechanical polishing apparatus according to yet another embodiment of the present invention, and FIG. 45 is a vertical sectional front view of the apparatus of FIG. 44. The electrochemical mechanical polishing apparatus can be used to carry out polishing of, e.g., a substrate (workpiece to be polished) W as shown in FIG. 1B, which has been subjected to copper plating that fills via holes 903 and trenches 904 with copper and deposits a copper film 907 as an interconnect metal film on an insulating film 902. Polishing is performed until a polished surface reaches a level shown by line A-A in FIG. 1B, thus removing the copper film 907 (and a seed film 906) as a conductive film (conductive material) on the insulating film 902 and exposing the barrier film 905. Polishing is further performed so as to remove the barrier film 905 on the insulating film 902, whereby interconnects 908, composed of the seed film 906 and the copper film 907, are formed in the insulating film 902 as shown in FIG. 1C.
As shown in FIGS. 44 and 45, the electrochemical mechanical polishing apparatus includes a rotatable processing table (turntable) 710, a vertically-movable and rotatable substrate holder (polishing head) 712 for detachably holding the substrate W with its front surface (having the copper film 907) downwardly, and a cylindrical processing chamber 714 having a bottom portion. The processing chamber 714 is shaped so as to surround the processing table 710 and the substrate holder 712 to prevent scattering of an electrolytic solution, which is supplied to an upper surface of the processing table 710 during polishing, and a conditioning solution and pure water, which are supplied to the upper surface of the processing table 710 after polishing. The processing chamber 714 has in its sidewall a discharge outlet 714 a for discharging the liquid, such as the electrolytic solution, stored in the processing chamber 714. The substrate holder 712 is designed to move between a predetermined polishing position above the processing table 710 and a substrate transferring and receiving position lateral to the polishing position.
A disk-shaped processing electrode 716, covering the upper surface the processing table 710 in its entirety, is provided on the upper surface of the processing table 710. An upper surface of the processing electrode 716 is entirely covered with a polishing pad 718 whose upper surface serves as a polishing surface. The polishing pad 718 has a large number of vertical through-holes 718 a so that the liquid, such as the electrolytic solution supplied to the upper surface of the processing table 710, is held within the polishing pad 718. During polishing, the processing electrode 716 is electrically connected to a conductive film, such as the copper film 907, formed on the surface of the substrate W via the electrolytic solution held in the through-holes 718 a of the polishing pad 718. In this embodiment, the polishing pad 718 is composed of IC-1000, manufactured by Nitta Haas Inc., having a large number of through-holes all over the body.
The polishing pad 718 may have annular grooves or lattice-patterned grooves, in addition to the through-holes provided over the polishing surface of the polishing pad 718 in its entirety. If the polishing pad 718 itself is permeable to liquid, the polishing pad 718 may not necessarily have through-holes.
Above the processing table 710 is disposed an electrolytic-solution supply nozzle 720 for supplying the electrolytic solution to the upper surface of the processing table 710 during polishing. The electrolytic-solution supply nozzle 720 is connected to an electrolytic-solution supply line 726 which extends from an electrolytic-solution storage tank 724 for temporary storage of the electrolytic solution 722. The electrolytic-solution supply line 726 has a not-shown electrolytic-solution supply mechanism, such as a tube pump, a diaphragm pump, or a bellows pump. As shown in FIG. 44, the electrolytic-solution supply nozzle 720 has a number of electrolytic-solution supply mouths 720 a, and is disposed above the processing table 710 such that it extends in a radial direction of the processing table 710.
An example of the electrolytic solution 722 to be used is, as will be discussed later, an aqueous solution comprising an organic acid, such as malonic acid, a strong acid having a sulfonic acid group, such as methanesulfonic acid, and a corrosion inhibitor, such as benzotriazole, as main components, and optionally containing additives such as a water-soluble polymeric compound, abrasive particles, and a surfactant.
A conditioning-solution supply nozzle 730 and a pure-water supply nozzle 732 are disposed above the processing table 710. The conditioning-solution supply nozzle 730 is for supplying the conditioning solution to the upper surface of the processing table 710 after polishing, and the pure-water supply nozzle 732 is for supplying pure water (i.e., a rinsing liquid) to the upper surface of the processing table 710. The conditioning-solution supply nozzle 730 is connected to a conditioning-solution supply line 738 which extends from a conditioning-solution storage tank 736 for temporary storage of a conditioning solution 734. The conditioning-solution storage tank 736 has a not-shown conditioning-solution supply mechanism, such as a tube pump, a diaphragm pump, or a bellows pump. As shown in FIG. 44, the conditioning-solution supply nozzle 730 has a number of conditioning-solution supply mouths 730 a, and is disposed above the processing table 710 such that it extends in the radial direction of the processing table 710.
An example of the conditioning solution 734 to be used is an aqueous solution comprising the main components of the electrolytic solution 722, but excluding the corrosion inhibitor from them, i.e., comprising the organic acid, such as malonic acid, and the strong acid having a sulfonic acid group, such as methanesulfonic acid, as main components and optionally containing an oxidizing agent, such as H₂O₂, as an additive.
A columnar electric-supply electrode 740 is provided laterally to the processing table 710 in the processing chamber 714. The electric-supply electrode 740 has an upper surface that is substantially flush with the polishing surface of the polishing pad 718. With these arrangements, when the substrate holder 712, holding the substrate W, is lowered to press the substrate W against the polishing surface of the polishing pad 718 at predetermined pressure, the upper surface of the electric-supply electrode 740 comes into contact with a peripheral portion of a surface (lower surface) of the conductive film, such as the copper film 907, of the substrate W, whereby an electric current is supplied to the conductive film. When carrying out polishing, the processing electrode 716 is electrically connected to a cathode of a power source 742, and the electric-supply electrode 740 is electrically connected to an anode of the power source 742.
A rotatable and vertically-movable dresser 744 is provided at a position lateral to the substrate holder 712. This dresser 744 is operable to contact the polishing pad 718 so as to perform mechanical dressing of the polishing pad 718. The dresser 744 is movable between a dressing position above the processing table 710 and a waiting position lateral to the dressing position. In this embodiment, the dresser 744 has circular brushes 746 in a ring-like arrangement at a peripheral portion of a lower surface of the dresser 744.
Operations of electrochemical mechanical polishing using this electrochemical mechanical polishing apparatus will now be described. First, the substrate holder 712, holding the substrate W with its front surface downwardly, is moved to a predetermined position above the processing table 710. Next, the electrolytic solution 722 is supplied from the electrolytic-solution supply nozzle 720 to the upper surface of the processing table 710, while the processing table 710 is rotated. At the same time, while rotating the substrate W, the substrate holder 712 is lowered to press the substrate W against the polishing surface of the polishing pad 718 at a pressure of, e.g., not more than 70 hPa (about 1 psi). When the electric-supply electrode 740 comes into contact with the conductive film, such as the copper film 907, of the substrate W, the electric-supply electrode 740 is electrically connected to the anode of the power source 742 and the processing electrode 716 is electrically connected to the cathode of the power source 742 to thereby apply a predetermined voltage between the processing electrode 716 and the conductive film of the substrate W. As a result, an electrolytic reaction occurs at the surface of the conductive film as an anode, and the conductive film is thus polished. During polishing, the processing electrode 716 and the conductive film of the substrate W are electrically connected via the electrolytic solution 722 held in the through-holes 718 a of the polishing pad 718.
During polishing, the surface of the copper film 907 of the substrate W, serving as an anode, is anodically oxidized, and simultaneously a protective film is formed on the surface of the copper film 907 by the corrosion inhibitor in the electrolytic solution 722 and by the water-soluble polymeric compound which is optionally added to the electrolytic solution 722. Simultaneously, the copper film 907 of the substrate W, which is being pressed against the polishing pad 718, is moved relative to the polishing pad 718 by the rotational movement of the substrate W and the rotational movement of the processing table 710, and is thus mechanically polished. On the other hand, the protective film, formed on recessed portions present in the surface of the copper film 907, is not removed, and electrochemical mechanical polishing proceeds only on the protective film formed on raised portions present in the surface of the copper film 907. By thus selectively removing only the protective film on the raised portions of the surface irregularities of the copper film 907 of the substrate W, the surface of the copper film 907 is polished and planarized.
After completion of electrochemical mechanical polishing, supply of the electrolytic solution 722 to the polishing pad 718 is stopped, and the processing electrode 716 and the electric-supply electrode 740 are electrically disconnected from the power source 742. Thereafter, so-called water polishing is carried out by rotating the substrate W while pressing it against the polishing surface of the polishing pad 718 at low pressure and, at the same time, supplying pure water to the polishing pad 718, thereby cleaning the surface of the substrate W Thereafter, the substrate holder 712 is elevated, and the cleaned substrate W is then transported for the next process.
After cleaning of the substrate, conditioning of the processing electrode 716 and the polishing pad 718 using the conditioning solution 734 and dressing of the polishing surface of the polishing pad 718 with the dresser 744 are performed. Although in this embodiment dressing with the dresser 744 is performed simultaneously, it is of course possible to perform only conditioning of the processing electrode 716 and the polishing pad 718 using the conditioning solution 734.
Operations of conditioning and dressing are performed as follows. The processing table 710 is rotated at a rotational speed of, e.g., 30 rpm, and simultaneously the conditioning solution 734 is supplied from the conditioning-solution supply nozzle 730 to the polishing pad 718 at a flow rate of, e.g., 200 ml/ min. The conditioning solution 734 supplied flows into the through-holes 718 a of the polishing pad 718 and comes into contact with the surface of the processing electrode 716 and the surface of the polishing pad 718, including inner surfaces of the through-holes 718 a. At the same time, lower surfaces (dressing surfaces) of the brushes 746 of the dresser 744 press the polishing pad 718 at predetermined pressure, while the dresser 744 is rotated at a predetermined rotational speed, thereby dressing the surface of the polishing pad 718.
An aqueous solution comprising the main components of the electrolytic solution 722, but excluding the corrosion inhibitor therefrom, is used as the conditioning solution 734, which has the same etching action as the electrolytic solution 734. Thus, use of such conditioning solution 734 promotes etching, and can thus etch away by-products of polishing deposited on the surface of the processing electrode 716 and also by-products of polishing deposited on the surface of the polishing pad 718, including the inner surfaces of the through-holes 718 a. Furthermore, because the basic composition of the conditioning solution is the same as the electrolytic solution used in polishing, an influence on polishing by the components (residual components) of the conditioning solution remaining after conditioning on the processing electrode 716 and the surface, including the inner surfaces of the through-holes 718 a, of the polishing pad 718 can be minimized, and the next electrolytic processing can be carried out without loss of time.
When performing the electrochemical mechanical polishing, by-products of polishing are normally deposited on the processing electrode 716. If the polishing process is continued with the by-products being left on the processing electrode 716, an electrical resistance between the conductive film, such as the copper film 907, of the substrate and the processing electrode 716 would be changed, thus adversely affecting control of the polishing rate on the surface of the substrate W. For this reason, it is necessary to remove the by-products from the surface of the processing electrode 716 by conditioning the processing electrode 716 and the polishing pad 718 during an interval between polishing operations.
At least a polishing-pad-side surface of the dresser 744 may be made of a conductive material, and a reverse voltage from a voltage in polishing may be applied to the processing electrode 716 so as to perform conditioning in the same manner as described above. For example, a voltage is applied such that the processing electrode 716 serves as an anode and the dresser 744 serves as a cathode. Application of the voltage in this manner can enhance a conditioning effect. In the case of applying a voltage during conditioning, it is also possible to provide a counter electrode, instead of the dresser 744, on the upper surface (polishing surface) of the polishing pad 718, and to carry out conditioning only with a brush or a conditioning solution while applying a voltage with the processing electrode serving as an anode and the counter electrode serving as a cathode.
After completion of conditioning, the processing table 710 is rotated at a higher rotational speed than that in conditioning, for example at 50 to 100 rpm. While the processing table 710 is in rotation, pure water, preferably ultrapure water, is supplied from the pure-water supply nozzle 732 to the polishing pad 718, so that the processing electrode 716 and the surface of the polishing pad 718, including the inner surfaces of the through-holes 718 a, are rinsed with pure water, preferably ultrapure water, to thereby prepare for the next polishing.
A description will now be made of the electrolytic solution 722 for use in electrochemical mechanical polishing by the electrochemical mechanical polishing apparatus, and the conditioning solution 734 for use in conditioning of the processing electrode 716 and the polishing pad 718.
The electrolytic solution 722 contains: (1) at least one organic acid or its salt; (2) at least one strong acid having a sulfonic acid group; and (3) a corrosion inhibitor (nitrogen-containing heterocyclic compound) as main components. The electrolytic solution 722 may optionally contain: (4) a water-soluble polymeric compound; (5) a pH adjustor; (6) abrasive particles; and (7) a surfactant as additives. The electrolytic solution 722 may also contain, as a starting component, (8) a conductive material which is identical to a material of the conductive film to be polished, e.g., copper.
The conditioning solution 734 contains the main components of the electrolytic solution 722, except for the corrosion inhibitor. More specifically, the conditioning solution 734 contains: (1) the at least one organic acid or its salt; and (2) the at least one strong acid having a sulfonic acid group, both contained in the electrolytic solution 722. The conditioning solution 734 may further contain an oxidizing agent, e.g., 0.1 to 5 wt % of H₂O₂, as an additive in order to promote removal of the by-products of polishing from the surface of the processing electrode 716 during conditioning.
Although copper is a material to be polished in this embodiment, other conductive materials may, of course, be an object of polishing. Examples of such conductive materials include a copper alloy, silver or its alloy, gold or its alloy, aluminum or its alloy, tungsten or its alloy or its nitride or its carbide or its nitrogen carbide, titanium or its alloy or its nitride or its carbide or its nitrogen carbide, tantalum or its alloy or its nitride or its carbide or its nitrogen carbide, ruthenium or its alloy, and a combination thereof.
The organic acid, contained in both the electrolytic solution 722 and the conditioning solution 734, is required to form a soluble complex with a metal (conductive material), such as copper, as a polishing object. In particular, the organic acid needs to make a coordinate bond with a metal, such as copper, to form a complex which is soluble in the aqueous solution. At least the organic acid itself must be water-soluble. The organic acid preferably has at least one carboxyl group (—COOH) in the molecule, or has at least one hydroxyl group (—OH) together with a carboxyl group(s) in the molecule. Such organic acid also has a pH buffering ability to stabilize a pH of the liquid.
Examples of usable carboxylic acid having one carboxyl group include formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, isovaleric acid, sorbic acid, glyoxylic acid, pyruvic acid, levulinic acid, benzoic acid, m-toluic acid, and acetylsalicylic acid. Examples of usable carboxylic acid having two or more carboxyl groups include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, α-ketoglutaric acid, aconitic acid, phthalic acid, and pyromellitic acid. Examples of usable carboxylic acid having at least one carboxyl group and at least one hydroxyl group include citric acid, glycolic acid, lactic acid, gluconic acid, malic acid, tartaric acid, oxalacetic acid, salicylic acid, m-hydroxybenzoic acid, gentisic acid, protocatechuic acid, gallic acid, glucuronic acid, sialic acid, and ascorbic acid.
Examples of carboxylic acid salt include a potassium salt, an ammonium salt, an alkylamine salt, and a hydroxylamine salt. These salts may be used singly or as a mixture of two or more in the liquid.
Of the above-listed organic acids, malonic acid, succinic acid, citric acid, glycolic acid, lactic acid, gluconic acid, malic acid, and tartaric acid are preferably used. Results of polishing experiment confirmed that use of the electrolytic solution containing any one of these organic acids resulted in a flat polished surface at a relatively high processing rate.
A concentration of the organic acid in the solution should be not more than a saturation solubility at a solution temperature during polishing. If the concentration exceeds the saturation solubility, the organic acid will precipitate in the solution whereby stable processing cannot be performed. For example, the solubility of maleic acid is 78% by weight (25° C.). If the concentration of the organic acid is lower than 0.1%, on the other hand, a smaller amount of the organic acid than required. for a coordinate bond with a metal to be dissolved is supplied to a surface of the metal to be processed, thus causing problems including a low processing rate and surface roughening. In addition, the organic acid in such a low concentration will not have a sufficient pH buffering action. For the above reasons, the concentration of the organic acid is preferably 0.1 to 80% by weight, more preferably 1 to 50% by weight.
The strong acid having a sulfonic group, contained both in the electrolytic solution 722 and the conditioning solution 734, is for accelerating an etching action of the solution and for increasing the electric conductivity of the solution in order to facilitate passage of an electric current. The strong acid herein refers to an acid having a pKa value of not more than three. The pKa is a logarithm of an inverse number of a first dissociation constant indicative of an intensity of an acid.
In general, use of a strong acid decreases an electric potential at which dissolution of copper begins. In other words, copper can be processed at a lower voltage applied. However, use of sulfuric acid, nitric acid, or perchloric acid considerably roughen a surface of a metal to be processed due to etching of the metal, e.g., copper. Further, phosphoric acid is highly viscous in a concentration range in which surface gloss can be obtained, and therefore requires a relatively high voltage for processing of copper. On the other hand, test results confirmed that use of methanesulfonic acid allowed a low voltage for processing of copper and resulted in a relatively flat surface processed and good processing characteristics.
Preferred examples of the strong acid having a sulfonic acid group include methanesulfonic acid, benzenesulfonic acid, taurine, cysteic acid, an alkylbenzene sulfonic acid having one to six carbons in an alkyl group, trifluoromethanesulfonic acid, and fluorosulfonic acid. These acids may be used singly or as a mixture of two or more. The concentration of the strong acid having a sulfonic acid group is preferably 0.1 to 20% by weight, more preferably 5 to 20% by weight. If the concentration of the strong acid is too low, the electric conductivity of the solution is so low that less electric current is allowed to pass through the solution. Therefore, the concentration of the strong acid having a sulfonic acid group is preferably not less than 5% by weight. On the other hand, if the concentration of the strong acid exceeds 20% by weight, the saturation solubility of the organic acid and other components in the liquid will decrease, causing precipitation of the components.
The corrosion inhibitor contained in the electrolytic solution 722 is preferably a nitrogen-containing heterocyclic compound and may be one which is known to form a compound with a metal, such as copper, to be processed and form a protective film on the metal surface to prevent corrosion of the metal. Such corrosion inhibitor can prevent excessive processing and can thus prevent dishing. Therefore, use of such corrosion inhibitor can promote planarization of a surface processed.
Benzotriazole, which is well known as a corrosion inhibitor for copper, or its derivatives can be preferably used as a corrosion inhibitor. Examples of other usable corrosion inhibitors, having the effect of promoting planarization, include indole, 2-ethylimidazole, benzimidazole, 2-mercaptobenzimidazole, 3-amino-1,2,4-triazole, 3-amino-5-methyl-4H-1,2,4-triazole, 5-amino-1H-tetrazole, 2-mercaptobenzothiazole, sodium 2-mercaptobenzothiazole, 2-methylbenzothiazole, (2-benzothiazolylthio)acetic acid, 3-(2-benzothiazolylthio) propionic acid, 2-mercapto-2-thiazolin, 2-mercaptobenzoxazole, 2,5-dimercapto-1,3,4-thiadiazole, 5-methyl-1,3,4-thiadiazole-2-thiol, 5-amino-1,3,4-thiadiazole-2-thiol, pyridine, phenazine, acridine, 1-hydroxypyridine-2-thione, 2-aminopyridine, 2-aminopyrimidine, trithiocyanuric acid, 2-dibutylamino-4,6-dimercapto-s-triazine, 2-anilino-4,6-dimercapto-s-triazine, 6-aminopurine, and 6-thioguanine. These compounds may be used either singly or as a mixture of two or more.
If the concentration of the corrosion inhibitor in the electrolytic solution is too low, formation of a protective film is insufficient. As a result, excessive etching of a metal, such as copper, will occur and a flat processed surface will not be obtained. On the other hand, if the concentration of the corrosion inhibitor is too high, although not exceeding the saturation solubility, an excessive protective film will be formed on the surface of the metal, such as copper, thus lowering a processing rate. Furthermore, formation of such an excessive protective film will result in non-uniform processing, which causes surface roughening and formation of pits in the processed surface. Thus, the concentration of the corrosion inhibitor is preferably 0.001 to 5% by weight, more preferably 0.02 to 2% by weight.
The water-soluble polymeric compound contained in the electrolytic solution 722, together with the corrosion inhibitor, forms a protective film, which prevents excessive etching and is thus effective in planarizing a surface of a metal, such as copper. Further, a viscosity of the electrolytic solution, containing the water-soluble polymeric compound, is high in the vicinity of the surface (to be processed) of the metal. As a result, a viscous film is formed on recessed portions of fine irregularities present on the surface of the metal, and the fine irregularities are polished and removed. Consequently, a glossy surface is obtained.
Preferred examples of the water-soluble polymeric compound, having the above effect, include polyacrylic acid or a salt thereof, polymethacrylic acid or a salt thereof, polyethylene glycol, polyisopropyl acrylamide, polydimethyl acrylamide, polymethacrylamide, polymethoxyethylene, polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylpyrrolidone. These compounds may be used either singly or as a mixture of two or more.
A water-soluble polymeric compound having a weight-average molecular weight of 1,000 to 500,000 can be used as the above water-soluble polymeric compound. A polymeric compound having a weight-average molecular weight of more than 500,000 will not dissolve into the electrolytic solution, causing coagulation with the corrosion inhibitor or abrasive particles. On the other hand, a polymeric compound having a weight-average molecular weight of less than 1,000 cannot form a sufficient protective film on a surface of a metal, such as copper, thus lowering planarizing performance. For these reasons, the weight-average molecular weight of the water-soluble polymeric compound, contained in the electrolytic solution, is preferably 1,000 to 100,000, more preferably 2,000 to 25,000.
In order not to lower the processing rate in electrochemical mechanical polishing and to prevent excessive processing, the concentration of the water-soluble polymeric compound is preferably 0.005 to 5% by weight, more preferably 0.01 to 2% by weight.
A pH adjustor may be added to the electrolytic solution 722 in order to adjust the pH of the electrolytic solution 722. A preferred example of the pH adjustor is an alkali, such as ammonia, alkylamine, hydroxylamine, polyamine, an alkali metal compound (e.g. potassium hydroxide) or an alkaline earth metal compound, or a mixture thereof. A concentration of the alkali is generally 0.1 to 20% by weight, and may be appropriately determined in accordance with an application and a material of the workpiece, the concentration of the organic acid or its salt, the concentration of the strong acid, and an intended pH.
The pH of the electrolytic solution 722 is preferably 2 to 10. When the pH of the electrolytic solution 722 is low, materials to be used to constitute an electrochemical mechanical polishing apparatus should be selected from those having a high corrosion resistance. In addition, on one hand the processing rate may increase when the pH of the electrolytic solution 722 is low, but on the other hand a surface processed is rough and excessive etching of a metal, such as copper, will proceed. A flat processed surface can therefore be hardly obtained. When the pH of the electrolytic solution 722 is high, formation of a protective film between copper and the corrosion inhibitor and/or the water-soluble polymeric compound can be insufficient, whereby planarizing action may be lowered. The electrolytic solution 722 has most preferably a pH of 3 to 6 when it is used for a polishing process in formation of copper interconnects of a semiconductor substrate which requires a high processing rate and a highly-flat and glossy surface.
The electrolytic solution 722 preferably contains abrasive particles. The abrasive particles have an effect of mechanically polishing away a metal, such as copper. Besides, in the present invention, the abrasive particles have an effect of mechanically polishing away the metal-protective film formed by the corrosion inhibitor and the water-soluble polymeric compound. An extra protective film can be removed by the action of the abrasive particles during electrochemical mechanical polishing, whereby a sufficiently high processing rate can be obtained.
Examples of preferred abrasive particles for use in the electrolytic solution 722 include those of alumina, colloidal silica, fumed silica, zirconium oxide, cerium oxide, titanium oxide, and manganese oxide. These materials may be used either singly or as a mixture of two or more. Of these, alumina, colloidal silica, and fumed silica are preferably used.
A concentration of abrasive particles in the electrolytic solution 722 is preferably not more than 10% by weight in order to allow electrochemical mechanical polishing to function effectively. On the other hand, the concentration of abrasive particles needs to be not less than 0.01% by weight in order to allow the abrasive particles to exhibit their own function as abrasive particles. When a fixed abrasive, such as a polishing pad, is used, the protective film can be effectively removed by bringing the fixed abrasive into contact with a surface of a metal, such as copper. In this case, it is not necessary to use the abrasive particles in the electrolytic solution 722. It is also possible to use both the fixed abrasive and the abrasive particles. Use of the abrasive particles in a concentration of more than 10% by weight can cause a considerable agglomeration of the particles, leading to an extremely high viscosity of the electrolytic solution. In such a case, deposited abrasive particles would impede electrochemical mechanical polishing and cause scratches on the surface of the metal. Therefore, an optimal concentration of the abrasive particles is 0.05 to 2% by weight.
The electrolytic solution 722 may contain a surfactant. Any type of surfactant can be used so long as it can improve dispersion of the abrasive particles. For example, cationic, anionic, amphoteric and non-ionic surfactants can be used. Examples of the anionic surfactant include alkyl ether carboxylate, alkyl sulfate, alkyl sulfonate, amide sulfonate, alkylaryl sulfonate, naphthalenesulfonate, and their formalin condensates. Examples of the cationic surfactant include aliphatic amine salts and aliphatic ammonium salts. The surfactant to be used is appropriately selected according to the concentration of abrasive particles and the pH of the electrolytic solution 722. Preferred surfactant is the anionic surfactant. In particular, alkyl sulfonate and a formalin condensate of naphthalenesulfonate are preferred.
The electric conductivity of the electrolytic solution 722 is preferably 5 to 200 mS/cm. When the electric conductivity of the electrolytic solution 722 is low, a higher voltage or current needs to be applied so as to increase a processing rate. Application of a higher voltage or current will cause adverse effects, including reduction of current efficiency during polishing due to generation of oxygen, formation of pits in a processed surface, and a lowered planarizing capability due to breakage of the protective film. Thus, electrochemical mechanical polishing is desirably performed at a low voltage. To this end, the electric conductivity of the electrolytic solution 722 is preferably 5 to 200 mS/cm.
In order to increase the polishing rate in electrochemical mechanical polishing and to prevent surface roughening, the electrolytic solution 722 preferably contains a conductive material that is identical to a material to be polished, e.g., copper. A concentration of such a conductive material, e.g., copper, contained in the electrolytic solution 722 is not less than 0.001% by weight, preferably not less than 0.005% by weight, more preferably not less than 0.01% by weight. Such a conductive material contained in the electrolytic solution 722 can accelerate diffusion of the same conductive material, e.g., copper, or the by-products of polishing including the conductive material, from the surface of the polishing object (the material to be polished) into the electrolytic solution 722 during polishing. On the other hand, the concentration of the conductive material, e.g., copper, in the electrolytic solution 722 is not more than 10% by weight, preferably not more than 1% by weight. This is because, if the concentration of the conductive material contained in the electrolytic solution 722 is more than 1% by weight, the conductive material is likely to consume other component(s) of the electrolytic solution 722. When the conductive material to be polished is a compound, respective components of the conductive material may be contained in the electrolytic solution 722 in accordance with a component ratio of the compound.
An example of the electrolytic solution 722 contains: (1) 2 to 80% by weight of an organic acid; (2) 2 to 20% by weight of a strong acid having a sulfonic acid group; (3) 0.01 to 1% by weight of a corrosion inhibitor; (4) 0.01 to 1% by weight of a water-soluble polymeric compound; (5) 0.01 to 2% by weight of abrasive particles; and (6) 0.01 to 1% by weight of a surfactant. A pH of the electrolytic solution 722 of this example is adjusted so that it has a pH of 2 to 10. The aqueous solvent may be deionized water, preferably ultrapure water.
An example of the conditioning solution 734 contains: (1) 2 to 80% by weight of an organic acid; (2) 2 to 20% by weight of a strong acid having a sulfonic acid group; and (3) 0.1 to 5% by weight of an oxidizing agent (e.g., H₂O₂).

EXAMPLE 1

An electrolytic solution containing malonic acid, methanesulfonic acid, and benzotriazole (corrosion inhibitor) as main components, and polyacrylic acid (molecular weight: 5000), methanol, a surfactant, and abrasive particles as additives was prepared. A conditioning solution containing malonic acid, methanesulfonic acid, and hydrogen peroxide (H₂O₂) was prepared. Using the electrochemical mechanical apparatus shown in FIGS. 44 and 45, conditioning was performed as follows. While the processing table 710 was rotated at a rotational speed of 30 rpm, the conditioning solution was supplied to the upper surface of the processing table 710 at a flow rate of 200 ml/min to perform conditioning of the processing electrode 716 and the polishing pad 718 for two minutes.
Next, while the processing table 710 was rotated at a rotational speed of 60 rpm, ultrapure water was supplied to the upper surface of the processing table 710 at a flow rate of 200 ml/min to perform rinsing of the processing electrode 716 and the polishing pad 718 for two minutes. Thereafter, while the processing table 710 was rotated at a rotational speed of 100 rpm, the electrolytic solution was supplied to the upper surface of the processing table 710 at a flow rate of 100 ml/min to polish a copper film, formed on a surface of a semiconductor wafer, for one minute.
After polishing, no surface roughening was observed on the surface (polished surface) of the copper film of the semiconductor wafer. Further, good polishing results were obtained in the gloss of the polished surface and in the elimination of initial surface irregularities of the wafer.

COMPARATIVE EXAMPLE 1

Conditioning and rinsing of the processing electrode 716 and the polishing pad 718 were performed using a mixed solution of sulfuric acid and hydrogen peroxide solution as a conditioning solution. Other conditions were the same as those of Example 1. Thereafter, the surface copper film of the semiconductor wafer was polished in the same manner as in Example 1.
After polishing, surface roughening was observed on the surface (polished surface) of the copper film of the semiconductor wafer. Further, elimination of initial surface irregularities of the wafer was found to be poor.
After performing the comparative conditioning of the processing electrode 716 and the polishing pad 718, rinsing of the processing electrode 716 and the polishing pad 718 was performed by supplying ultrapure water to the upper surface of the processing table 710 at a flow rate of 200 ml/min. During rinsing, a relationship between the pH at the surface (or in the through-holes 718 a) of the polishing pad 718, the rinsing time, and the rotational speed of the processing table 710 was studied. The results are shown in Table 1.

TABLE 1

	Rotational speed:	Rotational speed:
Rinsing time	60 rpm	120 rpm

2 min	acidic	weakly acidic
5 min	weakly acidic	neutral
10 min	neutral	neutral

This Table 1 shows the following facts. As in Example 1, when carrying out the rinsing for two minutes by supplying ultrapure water to the upper surface of the processing table 710 at a flow rate of 200 ml/min while rotating the processing table 710 at a rotational speed of 60 rpm, rinsing can be completed without affecting the subsequent electrochemical mechanical polishing. On the other hand, as can be seen in Comparative Example 1, when the rinsing is carried out under the same conditions as those of Example 1, it takes ten minutes, which is five times the rinsing time in Example 1, to complete rinsing so as not to affect the subsequent electrochemical mechanical polishing. This means that an amount of the ultrapure water used is five times that used in Example 1. Although rinsing can be completed in five minutes in Comparative Example 1 by increasing the rotational speed of the processing table to 120 rpm, the high rotational speed of the processing table will pose the problem of scattering of the conditioning solution (chemical solution).
Conditioning solutions that can be used in the present invention are not limited to the particular electrolytic solutions described hereinabove. Thus, any conditioning solution can be used so long as it contains the same main components as those of an electrolytic solution for use in electrolytic processing, except for a component (e.g., corrosion inhibitor) which hinders removal of by-products of electrolytic processing.
The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims and equivalents.

Claims

1. An electrochemical mechanical polishing apparatus, comprising:

a polishing table adapted to hold a polishing pad having a polishing surface, said polishing table having a first electrode including divided electrodes to be coupled to one of poles of a power source;

a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface;

a second electrode for supplying an electric current to the conductive film, said second electrode being coupled to another of the poles of the power source;

an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface;

a detecting section adapted to detect a signal corresponding to a thickness of the conductive film;

a variable resistance unit having the same number of variable resistors as the number of divided electrodes, said divided electrodes being coupled to the one of the poles of the power source via said variable resistors, respectively;

a moving mechanism for providing relative movement between the workpiece and the polishing surface; and

a control section adapted to control each of said variable resistors based on the signal from said detecting section.

2. The electrochemical mechanical polishing apparatus according to claim 1, wherein

each of said divided electrodes has a ring shape, and

said divided electrodes are arranged concentrically with a rotational center of said polishing table.

3. The electrochemical mechanical polishing apparatus according to claim 1, wherein each of said variable resistors has a value of resistance that is variable in a range of 0.1 to 10 Ω.

4. The electrochemical mechanical polishing apparatus according to claim 1, wherein said detecting section comprises an eddy current sensor.

5. The electrochemical mechanical polishing apparatus according to claim 1, wherein said control section is operable to control a polishing rate of the conductive film such that a barrier film, underneath the conductive film, is exposed gradually from a central portion to a peripheral portion of the workpiece.

6. An electrochemical mechanical polishing apparatus, comprising:

a polishing table adapted to hold a conductive polishing pad having a polishing surface, said polishing table having a first electrode coupled to one of poles of a power source;

a polishing head adapted to hold a workpiece having a conductive film and to press the workpiece against the polishing surface, said polishing head having a retainer ring shaped so as to surround a periphery of the workpiece;

a second electrode provided on said retainer ring so as to face the polishing pad and coupled to another of the poles of the power source, said second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad;

an electrolytic-solution supply section for supplying an electrolytic solution to the polishing surface; and

a moving mechanism for providing relative movement between the polishing pad and the workpiece held by said polishing head.

7. An electrochemical mechanical polishing apparatus, comprising:

an electric-supply section having a second electrode coupled to another of the poles of the power source and arranged so as not to contact said polishing head, said second electrode being brought into surface contact with the polishing surface so as to supply an electric current to the conductive film via the polishing pad;

8. The electrochemical mechanical polishing apparatus according to claim 7, further comprising a dresser operable to come into sliding contact with the polishing pad so as to dress the polishing pad, said electric-supply section being provided on said dresser.

9. An electrochemical mechanical polishing apparatus, comprising:

an electric-supply section having a second electrode coupled to another of the poles of the power source, said second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad;

a moving mechanism for providing relative movement between the polishing pad and the workpiece held by said polishing head,

wherein said second electrode has a contact portion to be in contact with the polishing pad, and

the contact portion is movable relative to the polishing pad at a relative speed of not more than 0.1 m/s.

10. An electrochemical mechanical polishing apparatus, comprising:

a second electrode coupled to another of the poles of the power source, said second electrode being brought into contact with the polishing pad so as to supply an electric current to the conductive film via the polishing pad;

wherein the polishing surface of the polishing pad has a non-contact area which does not contact the conductive film during polishing,

the polishing pad has through-holes therein, and

the non-contact area and at least a part of inner surfaces of the through-holes have been subjected to an insulating treatment.

11. An electrochemical mechanical polishing apparatus, comprising:

a polishing pad having vertically-extending through-holes and having an upper surface serving as a polishing surface;

a polishing head adapted to press a substrate against said polishing surface;

a first electrode coupled to one of poles of a power source and arranged below said polishing pad;

a second electrode coupled to another of the poles of the power source and adapted to supply an electric current to a conductive film on the substrate;

an electrolytic-solution supply section for supplying an electrolytic solution to said polishing pad;

an electrolytic-solution path for directing an electrolytic solution, supplied from said electrolytic-solution supply section, to said through-holes from below said polishing pad; and

a moving mechanism for providing relative movement between said polishing pad and the substrate held by said polishing head.

12. The electrochemical mechanical polishing apparatus according to claim 11, wherein

said electrolytic-solution path includes:

an electrolytic-solution receiving section for receiving the electrolytic solution from said electrolytic-solution supply section;

communication holes configured to communicate respectively with said through-holes; and

communication grooves configured to communicate with said electrolytic-solution receiving section and to allow said communication holes to communicate with each other.

13. The electrochemical mechanical polishing apparatus according to claim 12, wherein:

said electrolytic-solution receiving section comprises an annular groove arranged concentrically with said polishing pad; and

said annular groove has a larger radius than a distance between a center of, said polishing pad and a circumferential surface of said polishing head in a polishing position.

14. The electrochemical mechanical polishing apparatus according to claim 11, further comprising:

a weir surrounding a circumferential surface of said polishing pad,

wherein said weir has an outer wall and an inner wall,

said outer wall has an upper end at a position higher than said polishing surface, and

said inner wall has an upper end at a position lower than said polishing surface.

15. The electrochemical mechanical polishing apparatus according to claim 11, further comprising:

a deformable liquid-permeable member surrounding a circumferential surface of said polishing pad; and

a liquid recovery section provided below said liquid-permeable member,

wherein said liquid-permeable member has an upper surface at a position higher than said polishing surface.

16. An electrochemical mechanical polishing apparatus, comprising:

at least one liquid-retaining member embedded in said polishing surface;

a polishing head adapted to press a substrate against said polishing surface;

an electrolytic-solution supply section for supplying an electrolytic solution to said polishing pad; and

17. The electrochemical mechanical polishing apparatus according to claim 16, wherein

said at least one liquid-retaining member comprises plural liquid-retaining members disposed in said through-holes.

18. The electrochemical mechanical polishing apparatus according to claim 16, wherein

said liquid-retaining member is deformable, and

said liquid-retaining member has an upper surface at a position higher than said polishing surface.

19. An electrochemical mechanical polishing apparatus, comprising:

a polishing head adapted to press a substrate against said polishing surface;

a moving mechanism for providing relative movement between said polishing pad and the substrate held by said polishing head,

wherein each of said through-holes has an upper opening with a smaller diameter than a diameter of a lower opening thereof.

20. The electrochemical mechanical polishing apparatus according to claim 19, wherein

a diameter of each of said through-holes is decreased gradually from said lower opening to said upper opening.

21. The electrochemical mechanical polishing apparatus according to claim 19, wherein

each of said through-holes comprises plural holes arranged vertically in series with different diameters.

22. A method of conditioning a processing electrode and/or a polishing pad of an electrochemical mechanical polishing apparatus, said method comprising:

polishing a conductive material of a workpiece by providing sliding contact between the conductive material and the polishing pad, which is arranged between the processing electrode and the conductive material, and by applying a voltage between the conductive material and the processing electrode in the presence of an electrolytic solution containing an organic acid and a corrosion inhibitor; and

before or after said polishing, conditioning the processing electrode and/or the polishing pad using a conditioning solution including components of the electrolytic solution other than the corrosion inhibitor.

23. The method according to claim 22, wherein the conditioning solution further containing an oxidizing agent.

24. The method according to claim 22, wherein the organic acid comprises at least one of acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citric acid, aconitic acid, glyoxylic acid, glycolic acid, lactic acid, gluconic acid, malic acid, and tartaric acid.

25. The method according to claim 22, wherein the organic acid comprises a strong acid having a sulfonic acid group.

26. The method according to claim 22, wherein the strong acid having a sulfonic acid group comprises benzenesulfonic acid, methanesulfonic acid, taurine, cysteic acid, an alkylbenzene sulfonic acid having one to six carbons in an alkyl group, trifluoromethanesulfonic acid, and fluorosulfonic acid.

27. A conditioning solution for use in conditioning a processing electrode and/or a polishing pad of an electrochemical mechanical polishing apparatus, said conditioning solution comprising:

at least one organic acid or its salt; and

at least one strong acid having a sulfonic acid group,

wherein said conditioning solution does not contain a corrosion inhibitor.

28. The conditioning solution according to claim 27, further comprising an oxidizing agent.