US20070135024A1

US20070135024A1 - Polishing pad and polishing apparatus

Info

Publication number: US20070135024A1
Application number: US11/634,953
Authority: US
Inventors: Itsuki Kobata; Tatsuya Kohama
Original assignee: Individual
Current assignee: Ebara Corp
Priority date: 2005-12-08
Filing date: 2006-12-07
Publication date: 2007-06-14

Abstract

A polishing pad enables efficient removal of a polishing product and an “old polishing liquid” remaining on a surface (polishing surface) or in through-holes of a polishing pad. The polishing pad has a polishing surface and a plurality of through-holes extending in the thickness direction, which communicate with each other by communication grooves. The through-holes have a diameter of, e.g., 2 to 5 mm. The aperture ratio of the through-holes is, e.g., 10 to 50% of the surface area of the polishing surface of the polishing pad. The depth of the communication grooves is, e.g., 40 to 60% of the thickness of the polishing pad. The width of the communication grooves is, e.g., 10 to 50% of the diameter of the through-holes.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a polishing pad and a polishing apparatus, and more particularly to a polishing pad useful for polishing an interconnect material (metal), such as copper, deposited on a substrate, such as a semiconductor wafer, and embedded in fine interconnect recesses provided in an insulating film (interlevel dielectric film) formed on the substrate, thereby forming interconnects, and to a polishing apparatus that uses the polishing pad.
The present invention also relates to a method for conditioning a polishing pad of a polishing apparatus, and to a polishing apparatus and a polishing method which are useful for processing a film of conductive material formed on a substrate, such as a semiconductor wafer, or removing impurities adhering to the surface of the substrate.
The present invention also relates to a dresser for dressing a polishing pad of a polishing apparatus, a polishing apparatus provided with the dresser, and a method for dressing a polishing pad.
2. Description of the Related Art
A so-called damascene process, which involves embedding of an interconnect metal in interconnect recesses, such as trenches and via holes, provided in an insulating film, has been put into practical use as an interconnects-forming process for a semiconductor device. The damascene process is generally carried out by forming interconnect recesses in an insulating film (interlevel dielectric film) of SiO₂, SiOF, SiOC or a so-called low-K material, formed on a substrate, forming a barrier film of, e.g., titanium, tantalum, tungsten, ruthenium and/or an alloy thereof on an entire surface of the insulating film, including the interconnect recesses, forming a film of an interconnect metal, such as aluminum, copper, silver, gold or an alloy thereof on a surface of the barrier film while filling the interconnect recesses with the interconnect metal, and then removing an extra interconnect metal film and an extra barrier film formed outside the interconnect recesses. In current high-speed semiconductor devices, copper or copper alloy is generally employed as an interconnect material, and a so-called low-K material is increasing employed for an insulating film.
In a damascene process, the formation of interconnect recesses is most often practiced by dry etching or the like, and the formation of a barrier film is most often practiced by a dry process such as PVD, CVD or ALD. The formation of a film of interconnect metal can be carried out by a wet process, such as electroplating or electroless plating, or by a dry process, such as PVD, CVD or ALD, and is most commonly practiced by electroplating. When forming a film of interconnect metal by electroplating on a barrier film which has low electrical conductivity, it is a common practice to form in advance a seed film for electricity feeding on the barrier film subsequently to the formation of the barrier film. After the formation of a film of interconnect metal on a substrate, the metal film has surface irregularities which have been formed due to an interconnect pattern. Accordingly, the removal of an extra interconnect metal film and an extra barrier film, formed outside interconnect recesses, is generally carried out after flattening the surface irregularities of the film of interconnect metal by a flattening method, such as chemical mechanical polishing (CMP), electrolytic polishing or electrochemical mechanical polishing.
FIGS. 1A through 1C are diagrams illustrating, a sequence of process steps, an example of forming copper interconnects in a semiconductor device. As shown in FIG. 1A, an insulating film 302, such as an oxide film of SiO₂or a film of low-K material, is deposited on a conductive layer 301 a formed on a semiconductor base 301 having formed semiconductor devices. Via holes 303 and trenches 304 are formed in the insulating film 302 by performing a lithography/etching technique. Thereafter, a barrier film 305 of Ta, TaN, or the like is formed on the insulating film 302, and a seed film 306 as a feeding film for electroplating is formed on the barrier film 305 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 303 and the trenches 304 with copper and, at the same time, deposit a copper film 307 as a interconnect metal film on the insulating film 302. Thereafter, the copper film 307, the seed film 306 and the barrier film 305 on the insulating film 2 are removed by chemical mechanical polishing (CMP) or the like so as to leave copper filled in the via holes 303 and the trenches 304, and have a surface of the insulating film 302 lie substantially on the same plane as this copper. Interconnects 308 composed of the seed film 306 and the copper film 307 are thus formed in the insulating film 302 as shown in FIG. 1C.

SUMMARY OF THE INVENTION

A considerable amount of polishing product is produced during a polishing process of polishing a film of an interconnect metal, such as a copper film, to form fine interconnects. At the same time, as components of a polishing liquid are consumed, the concentrations of the components decrease gradually. If polishing is carried out using a polishing pad with such a polishing product and an “old polishing liquid”, having decreased concentrations of components, remaining on a surface (polishing surface), polishing characteristics, such as polishing rate, of the polishing apparatus used and the stabilities of the polishing characteristics would be lowered. Especially a polishing apparatus for performing electrochemical mechanical polishing uses a polishing pad disposed on a processing electrode and having a large number of through-holes so that electrical conduction can be made between the processing electrode and a surface of a substrate by filling the through-holes with a polishing liquid (electrolytic liquid). Such through-holes generally have a low efficiency of passage therethrough of a polishing liquid (electrolytic liquid), and therefore a polishing product and an “old polishing liquid” are likely to remain in the through-holes. When the polishing product remains in the through-holes and is accumulated on the surface of the processing electrode, the electrical conduction between a substrate and the processing electrode will be impeded by the polishing product, which would cause lowering of polishing characteristics of the polishing apparatus and the stabilities of the characteristics. It is thus a problem in maintaining the polishing characteristics of the polishing apparatus how to efficiently remove the polishing product and the “old polishing liquid” remaining on the surface of the polishing pad.
Dishing or erosion, which can occur in a substrate surface in a polishing process for the formation of fine interconnects, decreases the cross-sectional area of the interconnects and raises the resistance of the interconnects. Dishing or erosion is therefore required to be minimized, especially when forming very fine interconnects of the 65-nm or later generation.
One of the factors, which affect dishing or erosion, is surface conditions (surface roughness, etc.) of a polishing pad used in a polishing process. The surface conditions of a polishing pad are usually determined by conditioning of the surface, e.g., with a dresser. The use of a polishing pad having a large surface roughness increases the polishing rate. Such a polishing pad, however, may contact recessed portions in a surface of a film of interconnect metal or interconnect recesses whereby the recessed portions will be polished, which would cause dishing or erosion. A large surface roughness of a polishing pad thus lowers the flattening property of the polishing pad. A polishing pad having a small surface roughness, on the other hand, is poor in the capability of holding a polishing agent (slurry) used in a polishing process. In addition, the mechanical action of the polishing pad on a substrate decreases. Thus, a small surface roughness of polishing pad decreases the polishing rate and adversely affects the uniformity of the polishing rate in a surface of a substrate. It is therefore a significant problem how to condition a surface of a polishing pad in order to polish a substrate without dishing or erosion while maintaining the intended polishing rate and its uniformity in the surface of the substrate.
When processing a fragile material, such as a low-K material, in a semiconductor device manufacturing process, there is a fear of breakage of the material, for example, due to buckling. In electrochemical mechanical polishing which generally performs polishing of a conductive film of a substrate by rubbing a polishing pad against the conductive film while applying a voltage between the conductive film and a counter electrode, there is a possibility of breakage of a material due to a load applied by contact between the conductive film of the substrate and the polishing pad and also to a load applied by contact between the substrate and a feeding electrode for feeding electricity to the conductive film of the substrate. Therefore, application of a high load to the substrate should be avoided.
Feeding of electricity to the conductive film of the substrate by contact of the film with the feeding electrode may be carried out invarious manners, including a manner of utilizing pin contact and a manner of using a conductive pad. When the degree of contact between the conductive film of the substrate and the feeding electrode is adjusted by using an elastic body, such as a leaf spring or a coil spring, it is generally difficult to arbitrarily adjust a very low contact pressure.
The present invention has been made in view of the above situation. It is therefore a first object of the present invention to provide a polishing pad which enables efficient removal of a polishing product and an “old polishing liquid” remaining on a surface (polishing surface) or in through-holes of the polishing pad, and a polishing apparatus which employs the polishing pad.
It is a second object of the present invention to provide a method for conditioning a polishing pad, which makes it possible to polish an extra metal film or an extra barrier film formed on a surface of a substrate while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion even when the substrate is for the manufacturing of a semiconductor device having a very fine interconnect structure of the 65-nm or later generation.
It is a third object of the present invention to provide a polishing apparatus and method which enables control of a contact pressure, especially for a very low pressure, thus making it possible to polish a substrate without damage to devices formed in the substrate even when processing a fragile material.
It is a fourth object of the present invention to provide a dresser which can easily and securely remove foreign matter, such as a polishing product, remaining on a surface or in through-holes of a polishing pad, a polishing apparatus provided with the dresser, and a method for dressing a polishing pad.
In order to achieve the above objects, the present invention provides a polishing pad having a polishing surface and having a plurality of through-holes extending in the thickness direction, said through-holes communicating with each other by communication grooves. The through-holes have a diameter of, for example, 2 to 5 mm.
During conditioning of the polishing pad, a polishing product and an “old polishing liquid, remaining on the surface (polishing surface) or in the through-holes of the polishing pad, can be forced out of the polishing pad by a liquid which is applied to the polishing pad upon the conditioning. Conditioning of the polishing pad can thus be carried out while efficiently removing such foreign matters.
The aperture ratio of the through-holes is preferably 10 to 50%, more preferably 20 to 40% of the surface area of the polishing surface of the polishing pad. This can ensure a sufficient area of the polishing surface which is to make contact with a surface of a substrate and actually polish the surface, thus avoiding lowering of the polishing efficiency.
The depth of the communication grooves is preferably 40 to 60%, more preferably 40 to 50% of the thickness of the polishing pad. This can avoid significant lowering of the strength of the polishing pad due to the presence of the communication grooves.
The communication grooves are preferably formed in the reverse surface of the polishing pad from the polishing surface. This can avoid a decrease in the area of the polishing surface, which is to make contact with a surface of a substrate and actually polish the surface, due to the presence of the communication grooves.
The width of the communication grooves is preferably 10 to 50% of the diameter of the through-holes. This can ensure a sufficient flow passage area of the communication grooves, so that a polishing product and an “old polishing liquid”, remaining on the surface (polishing surface) or in the through-holes of the polishing pad, can be more efficiently forced out by a liquid which is applied to the polishing pad upon its conditioning.
In a preferred aspect of the present invention, the communication grooves are arranged in a concentric pattern, a lattice pattern, an arc pattern, a radial pattern or a spiral pattern, or a combination thereof.
Preferably, at least one flow passage groove is provided between the communication grooves. Such a flow passage groove can further facilitate passage of a fluid through the polishing pad.
In a preferred aspect of the present invention, the polishing pad has a hardness (Asker-C) of 60 to 95.
Preferably, the polishing pad has a support layer, having a lower hardness than the polishing pad, in the reverse surface of the polishing pad from the polishing surface. Preferably, the communication grooves are formed in the support layer.
At least part of the polishing surface of the polishing pad may have conducting properties. This enables feeding of electricity to a surface conductive film of a substrate via the polishing surface of the polishing pad during contact between the conductive film and the polishing surface upon polishing.
The present invention provides a polishing apparatus, comprising: a polishing table having a polishing pad and a first electrode which is connected to one pole of a power source and whose surface is covered with the polishing pad, said polishing pad having a plurality of through-holes extending in the thickness direction and communicating with each other by communication grooves; a top ring for holding a substrate and pressing the substrate against a polishing surface of the polishing pad; a second electrode, connected to the other pole of the power source, for feeding electricity to the substrate; a liquid supply section for supplying a liquid to the polishing surface of the polishing pad; a conditioning section for conditioning the polishing surface of the polishing pad; and a relative movement mechanical for moving the substrate held by the top ring and the polishing pad relative to each other.
The present invention provides a method for conditioning a polishing pad of a polishing apparatus for polishing and removing a metal film and/or a barrier film formed outside interconnect recesses provided in an insulating film formed on a surface of a substrate, comprising carrying out initial conditioning of the polishing pad in the following two steps: the first conditioning step comprising rubbing the polishing pad with a dresser at a pressure of not more than 0.6 psi; and the second conditioning step comprising polishing a dummy substrate with the polishing pad at a polishing pressure which is higher than a polishing pressure upon polishing of a substrate.
Excessive initial conditioning of a polishing pad can be prevented by carrying out initial conditioning of the polishing pad, e.g., after replacement of the polishing pad, in the following two steps: the first conditioning (dressing) step comprising rubbing the polishing pad with a dresser at a pressure of not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa); and the second conditioning (pad-leveling polishing) step comprising polishing a dummy substrate at a polishing pressure which is higher, preferably at least twice, more preferably at least three times higher than a polishing pressure upon polishing of a substrate. The dummy substrate polishing step can remove undulation on the polishing pad. By carrying out polishing of a substrate using a polishing pad which has undergone the optimal initial conditioning and the dummy substrate polishing, it becomes possible to polish, e.g., a metal film while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion. The pressure of the dresser is calculated from a load applied on the dresser and the contact area of the dresser with the polishing surface.
The dummy substrate is a test substrate which is prepared in the same shape as a device wafer (substrate) to become a product and is used in a test operation of a polishing apparatus prior to polishing of a device wafer. The dummy substrate is formed of, for example, SiC and, in some cases, has a copper film, an insulating film, etc. formed on the surface, as with a device wafer. Conventional test polishing of a dummy substrate is generally carried out under the same conditions as in polishing of a device wafer. On the other hand, the pad-leveling polishing (the second conditioning) of a dummy substrate according to the present invention is carried out at a pressure of not less than 1.5 psi (about 10.3 kPa), which is higher, preferably at least twice, more preferably at least three times higher than a polishing pressure to be used in polishing of a device wafer. By thus carrying out the pad-leveling polishing at a high pressure, a surface of a polishing pad, which has been excessively roughened by the first conditioning, can be leveled. This can enhance the in-plane uniformity of a polished device wafer and, in addition, can improve the polishing rate. The above-described numerical values are determined experimentally.
The polishing pad is used, for example, in chemical mechanical polishing.
A polishing pad composed of, e.g., a closed-or open-cell foamed polyurethane or a polyester non-woven fabric is generally used in chemical mechanical polishing. Excessive conditioning of such a polishing pad for use in chemical mechanical polishing can be prevented by carrying out initial conditioning of the polishing pad in the following two steps: the first conditioning (dressing) step of conditioning (dressing) the polishing pad at a low load; and the second conditioning (pad-leveling polishing) step of polishing a dummy substrate at a polishing pressure which is higher, preferably at least twice higher than a polishing pressure upon polishing of a substrate. This makes it possible to carry out chemical mechanical polishing of a substrate while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion.
The polishing pad may be used in electrochemical mechanical polishing.
Electrochemical mechanical polishing is a polishing method which performs polishing by both an electrochemical removal action and a mechanical polishing action. Electrochemical mechanical polishing includes a method which involves rubbing a substrate against a polishing pad to polish the substrate with the aid of a scrubbing action and a method which involves the use of abrasive grains.
Also in electrochemical mechanical polishing, a polishing pad is generally employed which is composed of, for example, a closed-or open-cell foamed polyurethane, a polyester non-woven fabric, a PVA sponge or a conductive pad. By initially conditioning such a polishing pad for use in electrochemical mechanical polishing into the optimum conditions, electrochemical mechanical polishing of a substrate can be carried out while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion.
Polishing and removal of a metal film, for the most part, may preferably be carried out by electrolytic polishing which performs polishing only by an electrolytic action without using abrasive grains, thus without causing significant damage to a polishing object. This can materially reduce damage to the interconnect structure of the substrate upon polishing of the metal film. An electrolytic polishing (electrochemical mechanical polishing) process is frequently employed in combination with other polishing process, such as followed by chemical mechanical polishing. By initially conditioning a polishing pad, e.g., for use in subsequent chemical mechanical polishing, into the optimum conditions, the intended polishing rate and its uniformity in a surface of a substrate can be maintained in the subsequent polishing process while preventing the occurrence of dishing or erosion.
Ultrapure water electrolytic polishing, which uses ultrapure water as an electrolytic liquid, may be employed when carrying out electrolytic polishing. Ultrapure electrolytic polishing is a polishing method in which a catalytic material (e.g., ion exchanger), which promotes electrolysis of water, is disposed on an electrode, and polishing of a material is effected by an electrochemical interaction between the material and OH⁻ ions or H⁺ ions generated by electrolysis of water. Since processing of a substrate can be performed by solely using pure water (ultrapure water), adhesion of extraneous impurities, such as an electrolyte, to the surface of the substrate can be avoided. This can simplify a cleaning process after the electrolytic polishing and significantly reduce the burden of waste liquid disposal.
The polishing pressure of the polishing pad upon polishing of a substrate is preferably not more than 1.5 psi (about 10.3 kPa).
Especially, the lower the polishing pressure applied to a substrate upon its polishing is, the more the state of contact between a polishing pad and the substrate affects the polishing characteristics. By using a polishing pad which has been initially conditioned into the optimum conditioned in the above-described manner, it becomes possible to carry out polishing of a substrate at a polishing pressure of the polishing pad of not more than 1.5 psi (about 10.3 kPa) while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion.
Preferably, during polishing of a substrate or during an interval between polishing operations, the polishing pad is further conditioned by rubbing the polishing pad with a dresser at a pressure of not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa).
This makes it possible to maintain the optimum conditions of the surface of the polishing pad, which has been optimized by the initial conditioning, over a longer period of time.
In a preferred aspect of the present invention, the first conditioning of the polishing pad with the dresser is carried out at a dressing speed of not more than 50 μm/h.
A common dresser has diamond abrasive grains fixed to a dressing surface, e.g., by electrodeposition or molding. Methods for decreasing the dressing speed of such a dresser include: (1) using blocky abrasive grains in the dressing surface; (2) using abrasive grains with a high grain count (e.g., #200 or higher); (3) decreasing the pressure of the dresser; and (4) decreasing the relative speed between the dresser and a polishing pad.
The present invention provides another polishing apparatus, comprising: a polishing table having a first electrode connected to one pole of a power source and holding a polishing pad having a polishing surface of a larger size than a surface to be polished of a substrate; a top ring for holding the substrate and pressing the substrate against the polishing surface of the polishing pad at a pressure of not more than 1 psi; a second electrode including at least one electrode member, connected to the other pole of the power source, which is to make contact with a conductive film of the substrate, held by the top ring and being pressed against the polishing surface of the polishing pad, to feed electricity to the conductive film, and a supporting base for floatingly supporting the electrode member by a floating mechanism; a liquid supply section for supplying a liquid to the polishing surface of the polishing pad; a conditioning section for conditioning the polishing surface of the polishing pad; and a relative movement mechanism for moving the substrate held by the top ring and the polishing pad relative to each other.
By thus fixing the first electrode (processing electrode), having a larger area than a substrate, to the table, and floatingly supporting the electrode member of the second electrode (feeding electrode), which generally is not required to have such a large area as that of the first electrode and is generally provided at one or two feeding sites, and bringing the electrode member into contact with a conductive film of the substrate, it becomes possible to control the contact pressure of the electrode member on the conductive film of the substrate, especially for a very low pressure, while ensuring feeding of electricity from the second electrode to the conductive film. This makes it possible carry out polishing of the substrate without damage to devices formed on the substrate even when processing a fragile material
In a preferred aspect of the present invention, the electrode member is supported by an electrode base.
When an electrode member having low rigidity, such as a conductive pad, is used, such an electrode member can be sufficiently reinforced by supporting it with an electrode base having high rigidity.
In a preferred aspect of the present invention, the floating mechanism is adapted to floatingly support the electrode member by the fluid pressure of a fluid which has been filled into a pressure chamber formed between the electrode member and the supporting base and surrounded by an elastic membrane.
Preferably, the floating mechanism is adapted to supply the fluid at a predetermined pressure to the pressure chamber.
The contact pressure of the electrode member on a conductive film of a substrate can be arbitrarily controlled by adjusting the pressure of the fluid to be supplied to the pressure chamber. Thus, the pressure between the substrate and the electrode member can be controlled such that it is lower than a pressure which may cause damage to a semiconductor device, and the substrate can be processed without damage to a fragile material.
In a preferred aspect of the present invention, the second electrode is provided with a stopper for limiting the movement of the electrode member in a direction away from the supporting base and in a direction parallel to the supporting base.
This can prevent the electrode member from lying far away from the supporting base during a non-processing time when the electrode member is not in contact with a substrate and can also prevent the electrode member from moving in a direction parallel to the supporting base due to a frictional force generated between the electrode member and a substrate during processing.
The present invention provides a polishing method comprising: applying a voltage between a first electrode, connected to one pole of a power source and disposed in a polishing table, and a conductive film, formed on a surface of a substrate, to which electricity is fed from an electrode member connected to the other pole of the power source and supported floatingly; and polishing the conductive film by rubbing it with a polishing surface of a polishing pad mounted to the polishing table while filling the space between the first electrode and the conductive film of the substrate with a liquid.
The present invention also provides a dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein first brush bristles and second brush bristles having lower rigidity than the first brush bristles are implanted in the dressing surface.
According to the dresser of the present invention, dressing of a polishing surface of a polishing pad with the dresser can be performed by rubbing the polishing surface chiefly with the first brush bristles while allowing the tips chiefly of the second brush bristles, having low rigidity, to easily enter, e.g., numerous through-holes formed in the polishing pad and scraping out a processing product remaining in the through-holes with the second brush bristles. This enables easy and secure removal of foreign matter, such as a polishing product, remaining on the surface (polishing surface) or in the through-holes of the polishing pad.
The second brush bristles are preferably longer than the first brush bristles.
This makes it possible to dress a polishing surface of a polishing pad with the dresser while allowing the tips of the second brush bristles to more easily enter, e.g., numerous through-holes formed in the polishing pad and more securely scraping out a processing product remaining in the through-holes.
The present invention provides another dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein first brush bristles and second brush bristles, both having the same rigidity but having different lengths, are implanted in the dressing surface.
In a preferred aspect of the present invention, one of the first brush bristles and the second brush bristles are arranged in a concentric pattern, a lattice pattern, a radial pattern or a spot-like pattern, or a combination thereof, with the other brush bristles in the background.
The present invention provides yet another dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein the dressing surface comprises a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher and a brush dressing section provided with brush bristles.
According to the dresser of the present invention, dressing of a polishing surface of a polishing pad with the dresser can be performed by rubbing the polishing surface with the surface of the diamond dressing section while allowing the tips of the brush bristles provided in the brush dressing section to easily enter, e g., numerous through-holes formed in the polishing pad and scraping out a processing product remaining in the through-holes with the brush bristles. This enables easy and secure removal of foreign matter, such as a polishing product, remaining on the surface (polishing surface) or in the through-holes of the polishing pad.
Preferably, the diamond dressing section is disposed circumferentially outside the brush dressing section.
The brush dressing section may be disposed in a concentric pattern, a lattice pattern, a radial pattern or a spot-like pattern, or a combination thereof, inside the diamond dressing section.
The present invention provides yet another polishing apparatus, comprising: a polishing table having a first electrode connected to one pole of a power source, and a polishing pad covering a surface of the first electrode; a top ring for holding a substrate and pressing the substrate against a polishing surface of the polishing pad; a second electrode, connected to the other pole of the power source, for feeding electricity to the substrate; a liquid supply section for supplying a liquid to the polishing surface of the polishing pad; a dresser having first brush bristles and second brush bristles having lower rigidity than the first brush bristles, for dressing the polishing surface of the polishing pad by bringing the brush bristles into sliding contact with the polishing surface; and a relative movement mechanism for moving the substrate held by the top ring and the polishing pad relative to each other.
The present invention provides yet another polishing apparatus, comprising: a polishing table having a first electrode connected to one pole of a power source, and a polishing pad covering a surface of the first electrode; a top ring for holding a substrate and pressing the substrate against a polishing surface of the polishing pad; a second electrode, connected to the other pole of the power source, for feeding electricity to the substrate; a liquid supply section for supplying a liquid to the polishing surface of the polishing pad; a dresser having first brush bristles and second brush bristles, both having the same rigidity but having different lengths, for dressing the polishing surface of the polishing pad by bringing the brush bristles into sliding contact with the polishing surface; and a relative movement mechanism for moving the substrate held by the top ring and the polishing pad relative to each other.
The present invention provides yet another polishing apparatus, comprising: a polishing table having a first electrode connected to one pole of a power source, and a polishing pad covering a surface of the first electrode; a top ring for holding a substrate and pressing the substrate against a polishing surface of the polishing pad; a second electrode, connected to the other pole of the power source, for feeding electricity to the substrate; a liquid supply section for supplying a liquid to the polishing surface of the polishing pad; a dresser having a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher and a brush dressing section provided with brush bristles, for dressing the polishing surface of the polishing pad by bringing the diamond dressing section and the brush dressing section into sliding contact with the polishing surface; and a relative movement mechanism for moving the substrate held by the top ring and the polishing pad relative to each other.
The present invention also provides a method for dressing a polishing pad comprising: carrying out dressing of a polishing surface of a new polishing pad, at the start-up of a polishing apparatus having the new polishing pad, by bringing a dresser, having a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher and a brush dressing section provided with brush bristles, into sliding contact with the polishing surface; and carrying out dressing of the polishing surface of the polishing pad, during polishing of a substrate or during an interval between polishing operations, by bringing a dresser, having first brush bristles and second brush bristles having lower rigidity than the first brush bristles, into sliding contact with the polishing surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are diagrams illustrating, in a sequence of process steps, an example of forming copper interconnects in a semiconductor device;
FIG. 2 is a layout plan view of a polishing system incorporating a polishing apparatus (electrochemical mechanical polishing apparatus) according to an embodiment of the present invention;
FIG. 3 is a plan view showing the main portion of the polishing apparatus shown in FIG. 2;
FIG. 4 is a cross-sectional view showing the main portion of the polishing apparatus shown in FIG. 2;
FIG. 5 is a rear view of a polishing pad of the polishing apparatus shown in FIG. 2;
FIG. 6 is a cross-sectional view of the polishing pad of the polishing apparatus shown in FIG. 2;
FIG. 7 is a rear view of another polishing pad;
FIG. 8 is a perspective rear view of yet another polishing pad;
FIG. 9 is a cross-sectional diagram showing a second electrode shown in FIGS. 3 and 4;
FIG. 10 is a cross-sectional diagram showing another second electrode;
FIG. 11 is a vertical sectional view showing a top ring of the polishing apparatus shown in FIGS. 3 and 4;
FIG. 12 is a bottom view of the top ring of FIG. 11;
FIG. 13 is a front view showing the main portion of a CMP (chemical mechanical polishing) apparatus provided in the polishing system shown in FIG. 2;
FIG. 14 is a graph showing the relationship between polishing amount and residual surface level difference obtained in Experimental Example;
FIG. 15 is a cross-sectional diagram showing yet another polishing pad;
FIG. 16 is a cross-sectional diagram showing the main portion of a polishing apparatus according to another embodiment of the present invention;
FIG. 17 is a cross-sectional diagram showing the main portion of a polishing apparatus according to yet another embodiment of the present invention;
FIG. 18 is an enlarged view of a portion of the polishing apparatus shown in FIG. 17;
FIG. 19 is a rear view of a dresser of the polishing apparatus shown in FIG. 17;
FIG. 20 is a rear view of another dresser;
FIG. 21 is a cross-sectional diagram showing the main portion of a polishing apparatus according to yet another embodiment of the present invention; and
FIG. 22 is a plan view showing the main portion of a polishing apparatus according to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the drawings.
FIG. 2 is a layout plan view of a polishing system incorporating a polishing apparatus according to an embodiment of the present invention. This polishing system is used to carry out polishing of a surface of, e.g., a substrate W as shown in FIG. 1B, which has undergone copper plating to fill via holes 303 and trenches 304 with copper and deposit a copper film 307 as an interconnect metal film on an insulating film 302, to remove the copper film 307, a seed film 306 and a barrier film 305 on the insulating film 302, thereby forming interconnects 308 composed of the seed film 306 and the copper film 307 in the insulating film 302, as shown in FIG. 1C.
This polishing system comprises four load-unload stages 2 each for placing a substrate cassette 1 that accommodates a plurality of substrates W (shown in FIG. 1B), each having a copper film 307 as an interconnect metal film. A transfer robot 4 having two hands is provided on a travel mechanism 3 so that the transfer robot 4 can move along the travel mechanism 3 and access the respective substrate cassettes 1 on the respective load-unload stages 2. The travel mechanism 3 employs a linear motor system. The use of linear motor system enables a stable high-speed transfer of a substrate even when the substrate has large size and weight.
According to the polishing system shown in FIG. 1, an external SMIF (Standard Manufacturing Interface) pod or FOUP (Front opening Unified Pod) is used as the load-unload stage 2 for mounting the substrate cassette 1. The SMIF and FOUP are closed vessels each of which can house the substrate cassette therein and, by covering with a partition, can keep the internal environment independent of the external space. When the SMIF or FOUP is set as the load-unload stage 2 of the polishing system, a shutter 52 on the polishing apparatus side, provided in a housing 46, and a shutter on the SMIF or FOUP side are opened, whereby the polishing system and the substrate cassette 1 become integrated. After completion of substrate polishing process, the shutters are closed to separate the SHIF or FOUP from the polishing system, and the SMIF or FOUP is transferred automatically or manually to another processing process. It is therefore necessary to keep the internal atmosphere of the SMIF or FOUP clean.
For that purpose, there is a down flow of clean air through a chemical filter in the upper space of an area A, which a substrate passes through right before returning to the substrate cassette 1. Further, since the linear motor is employed for traveling of the transfer robot 4, scattering of dust can be reduced and the atmosphere in the area A can be kept clean.
In order to keep substrate in the substrate cassette 1 clean, it is possible to use a clean box that may be a closed vessel, such as a SMIF or FOUP, having a built-in chemical filter and a fan, and can maintain its cleanness by itself.
Two drying units 5, 6 are disposed at the opposite side of the substrate cassettes 1 with respect to the travel mechanism 3 of the transfer robot 4. The drying units 5, 6 are disposed at positions that can be accessed by the hands of the transfer robot 4. Between the two drying units 5, 6 and at a position that can be accessed by the transfer robot 4, there is provided a substrate station 50 having four substrate supports 7, 8, 9 and 10.
An area B, in which the drying units 5, 6 and the substrate station 50 are disposed, and an area A, in which the substrate cassettes land the transfer robot 4 are disposed, are partitioned by a partition wall 14 so that the cleanliness of the area B and the area A can be separated. The partition wall 14 has an opening for allowing substrates to pass therethrough, and a shutter 11 is provided at the opening of the partition wall 14. A transfer robot 20 is disposed at a position where the transfer robot 20 can access the drying unit 5 and the three substrate supports 7, 9 and 10, and a transfer robot 21 is disposed at a position where the transfer robot 21 can access the drying unit 6 and the three substrate supports 8, 9 and 10.
A cleaning unit 22 is disposed at a position adjacent to the drying unit 5 and accessible by the hands of the transfer robot 20, and another cleaning unit 23 is disposed at a position adjacent to the drying unit 6 and accessible by the hands of the transfer robot 21.
The drying units 5 and 6, the cleaning units 22 and 23, the substrate supports 7, 8, 9 and 10 of the substrate station 50, and the transfer robots 20, 21 are all placed in the area B. The pressure in the area B is adjusted so as to be lower than the pressure in the area A.
The polishing system has a housing 46 for enclosing various components therein. The interior of the housing 46 is partitioned into a plurality of compartments or chambers (including the areas A and B) by partition wall 14 and partition walls 24A, 24B.
Thus, two areas C and D, constituting two polishing chamber, are divided from the area B by the partition walls 24A, 24B. In one areas C, there is provided a first polishing apparatus composed of a polishing apparatus (electrochemical mechanical polishing apparatus) 54 according to the present invention, and in another area D, there is provided a second polishing apparatus composed of a CMP (chemical mechanical polishing) apparatus 56.
In particular, the electrochemical mechanical polishing apparatus (first polishing apparatus) 54, disposed in the area C, includes polishing tables 34 and 36, a top ring 32, a polishing liquid supply nozzle 40 as a liquid supply section for supplying a polishing liquid (electrolytic liquid) to a polishing pad 66 (see FIGS. 3 and 4) of the polishing table 34, a dresser (conditioning section) 38 for dressing the polishing pad 66 of the polishing table 34, and a dresser 48 for dressing the polishing pad of the polishing table 36. The CMP apparatus (second polishing apparatus) 56, disposed in the area D, on the other hand, includes polishing tables 35 and 37, a top ring 33, a polishing liquid supply nozzle 41 for supplying a polishing liquid to a polishing pad of the polishing table 35, a dresser 39 for dressing the polishing pad of the polishing table 35, and a dresser 49 for dressing the polishing pad of the polishing table 37.
Though in this embodiment both the electrochemical mechanical polishing apparatus 54 and the CMP apparatus 56 have two polishing tables so as to perform more multi-polishing processes, one polishing tables 36, 37 of each of two polishing tables may be omitted.
The electrochemical mechanical polishing apparatus 54 includes, besides the mechanical dresser 38, an atomizer (conditioning section) 44 as a fluid-pressure dresser, and the CMP apparatus 56 includes, besides the mechanical dresser 39, an atomizer 45 as a fluid-pressure dresser. An atomizer is designed to jet a mixed fluid of a liquid (e.g., pure water) and a gas (e.g., nitrogen) in the form of a mist from a plurality of nozzles to the polishing surface. The main purpose of the atomizer is to rinse away polished scraping sand slurry particles deposited on and clogging the polishing surface. Cleaning of the polishing surface by the fluid pressure of the atomizer (atomizing) and setting of the polishing surface by the mechanical contact of the dresser (dressing) 38, 39 can effect a more desirable conditioning, i.e., regeneration of the polishing surface.
FIGS. 3 and 4 show the main portion of the electrochemical mechanical polishing apparatus 54. The polishing table 34 of the electrochemical mechanical polishing apparatus 54 is formed of a material having a low ionization tendency, such as platinum, in particular a material having a lower ionization tendency than a polishing object, such as copper. In an upper surface of the polishing table 34 are disposed a disk-shaped first electrode (cathode) 62 connected to one pole of a power source 60, and a rod-like second electrode (anode) 64 connected to the other pole of the power source 60, the electrodes 62, 64 being electrically insulated from each other. An entire upper surface of the first electrode 62 is integrally covered with a polishing pad 66 whose upper surface constitutes a polishing surface 66 a.
The second electrode 64 is so designed that when a substrate W held by the top ring 32 is lowered and the front surface (lower surface) of the substrate W is brought into contact with the polishing surface 66 a of the polishing pad 66, the upper end surface of the second electrode 64 comes into contact with the surface of the substrate W whereby electricity can be fed from the second electrode 64 to an electrical conductor, such as the copper film 307 (see FIG. 1B), formed on the surface of the substrate W. The top ring 32 is designed to press a substrate held by the top ring 32 against the polishing surface 66 a of the polishing pad 66, e.g., at a pressure of not more than 1 psi (about 70 hPa).
As shown in detail in FIGS. 5 and 6, the polishing pad 66 according to this embodiment is comprised of, e.g., IC 1000, manufactured by Nitta Haas Inc., having a large number of vertical through-holes 66 b having a diameter “d” of 2 to 5 mm, opening to the first electrode (processing electrode) 62. During electrochemical polishing, electric current flows between the first electrode (processing electrode) 62 and the surface of the substrate W connected to the second electrode (feeding electrode) 64 via a polishing liquid that has flowed into the through-holes 66 b.
The through-holes 66 b are disposed in a matrix-like pattern in the polishing pad 66. The aperture ratio of the through-holes 66 b is 10 to 50%, preferably 20 to 40% of the surface area of the polishing surface 66 a of the polishing pad 66. This can ensure a sufficient area of the polishing surface 66 a which is to make contact with the surface (surface to be polished) of a substrate and actually polish the surface, thus avoiding lowering of the polishing efficiency.
Communication grooves 66 c, connecting the through-holes 66 b with each other and arranged in a lattice pattern, are provided in the reverse surface of the polishing pad 66 from the polishing surface 66 a. By thus connecting the through-holes 66 b with the communication grooves 66C, it becomes possible to carry out conditioning of the polishing pad 66 while efficiently removing a polishing product and an “old polishing liquid”, remaining on the polishing surface (front surface) 66 a or in the through-holes 66 b of the polishing pad 66, by forcing them out of the polishing pad 66 through the communication grooves 66 c with a liquid which is applied to the polishing pad 66 during the conditioning. The provision of the communication grooves 66 c in the reverse surface of the polishing pad 66 from the polishing surface 66 a can avoid a decrease in the area of the polishing surface, which is to make contact with the surface of a substrate and actually polish the surface, due to the presence of communication grooves.
The depth “h” of the communication grooves 66 c is preferably 40 to 60%, more preferably 40 to 50% of a thickness “t” of the polishing pad 66. This can avoid significant lowering of the strength of the polishing pad 66 due to the presence of the communication grooves 66 c. The width “S” of the communication grooves 66 c is preferably 10 to 50% of the diameter “d” of the through-holes 66 b. This can ensure a sufficient flow passage area of the communication grooves 66 c, so that a polishing product and an “old polishing liquid”, remaining on the polishing surface (front surface) or in the through-holes 66 b of the polishing pad 66, can be more efficiently forced out by a liquid which is applied to the polishing pad 66 during its conditioning.
As shown in FIG. 7, it is also possible to dispose the through-holes 66 b such that they are positioned at the vortices of triangles and connect the through-holes 66 b with each other with the communication grooves 66 c arranged in a parallelogram pattern. Further, as shown in FIG. 8, it is also possible to disposed the through-holes 66 b along concentric circles and connect the through-holes 66 b with each other with the communication grooves 66 c arranged in a concentric pattern. In this case, a flow passage groove 66 d may be formed between the concentric communication grooves 66 c so as to further facilitate passage of a fluid through the polishing pad 66.
FIG. 9 shows the second electrode 64 in detail. As shown in FIG. 9, the second electrode 64 includes an electrode member 102 electrically connected to a conducting wire 100 extending from the anode of the power source 60 (see FIG. 4), and a supporting base 106 which floating supports the electrode member 102 by a floating mechanism 104. The floating mechanism 104 includes a pressure chamber 110 formed between the electrode member 102 and the supporting base 106 and surrounded by a stretchable, bellows-like elastic membrane 108, and a fluid introduction inlet 106 a for introducing a fluid at a controlled pressure into the pressure chamber 110 is provided in the supporting base 106, so that the electrode member 102 is floatingly supported by the fluid pressure of the fluid that has been filled into the presence chamber 110.
By thus floatingly supporting the electrode member 102 on the supporting base 106 by the floating mechanism 104, an upper surface of the electrode member 102 can be securely brought into contact with a conductive film, such as the copper film 307 (see FIG. 1B), formed on the surface of the substrate W at a more uniform contact pressure to feed electricity to the conductive film. Further, the contact pressure of the electrode member 102 on the substrate W can be arbitrarily controlled by adjusting the pressure of the fluid to be supplied into the pressure chamber 110. Thus, the pressure between the electrode member 102 and the substrate W can be controlled at a lower pressure than a pressure at which a semiconductor device will be damaged, enabling processing of the substrate without damage to a fragile material.
On a peripheral portion of the supporting base 106 is vertically mounted a stopper 112 for limiting the upward movement and the horizontal movement of the electrode member 102. In particular, the stopper 112 has at its upper end an inwardly-expanding expanded portion 112 a, while the electrode member 102 has a step portion 102 a. The upward movement of the electrode member 102 is limited by engagement between the expanded portion 112 a and the step portion 102 a. On the other hand, by sliding contact between the inner circumferential surface of the expanded portion 112 a and the outer circumferential surface of the smaller-diameter portion, positioned above the step portion 102 a, of the electrode member 102, the horizontal movement of the electrode member 102 is limited without the tilting movement of the electrode member 102 being impeded.
Such limitation of the upward movement of the electrode member 102 can prevent the electrode member 102 from lying far away from the supporting base 106 in a non-processing time when the electrode member 102 is not in contact with the substrate W, and can also prevent the electrode member 102 from moving, together with the substrate W, in a direction parallel to the supporting base 106 due to a fictional force generated between the electrode member 102 and the substrate W during processing.
In this embodiment the electrode member 102 is formed of a material having high rigidity, such as a metal or a conductive oxide. In case the electrode member 102 is formed of a material having low rigidity, such as a conductive pad, the weak electrode member 102 can be sufficiently reinforced by supporting it with an electrode base 114 having high rigidity so that the floating mechanism 104 lies between the supporting base 106 and the electrode base 114, as shown in FIG. 10. The electrode base 114 may either be an electrical conductor or an insulator.
The top ring 32 is coupled to the lower end of a top ring-driving shaft 68 which is rotatable and is movable between a predetermined polishing position above the polishing table 34 and a position above a pusher 30 (see FIG. 2). The dresser 38 has, in the peripheral region of the lower surface, a plurality of circular protrusions 38 a arranged in a ring and each comprised of, for example, a member (e.g., diamond pellet) with diamond grains embedded in the lower surface, a hard material such as a ceramic material, or a brush, and is coupled to the lower end of a dresser-driving shaft 70 which is rotatable and is movable between a predetermined dressing position above the polishing table 34 and a retreat position beside the dressing position.
The polishing liquid supply nozzle (liquid supply section) 40 has a number of polishing liquid supply orifices 40 a disposed along the length direction, and is disposed such that it extends radially above the polishing table 34. Similarly, the atomizer 44 has a number of supply orifices disposed along the length direction, and is disposed such that it extends radially above the polishing table 34. The polishing liquid supply nozzle 40 is designed to make either one of a linear movement, a reciprocating movement, a pivoting movement and a rotational movement, or a combination of two or more movements.
Further, though not shown diagrammatically, a pure water supply nozzle for supplying pure water to the polishing pad 66 and a dressing liquid supply nozzle for supplying a dressing liquid to the polishing pad 66 may be disposed above the polishing table 34, according to necessity.
In operation of the electrochemical mechanical polishing apparatus 54, the top ring 32 holding a substrate W is moved to a predetermined polishing position above the polishing table 34. Thereafter, while rotating the top ring 32, the top ring 32 is lowered to press the surface (lower surface) of the substrate W against the polishing surface 66 a of the rotating polishing pad 66 at a predetermined polishing pressure which is, for example, not more than 1 psi (about 70 hPa) and, at the same time, a predetermined voltage is applied from the power source 60 to between the first electrode 62 and the second electrode 64 while supplying a polishing liquid from the polishing liquid supply nozzle 40 to the polishing surface 66 a of the polishing pad 66, thereby polishing a conductive film, such as the copper film 307 (see FIG. 1B), formed on the surface of the substrate W. During the polishing, the polishing liquid supply nozzle 40 is allowed to make either one of a linear movement, a reciprocating movement, a pivoting movement and a rotational movement, or a combination of two or more movements, according to necessity.
After completion of the electrochemical mechanical polishing, the supply of the polishing liquid to the polishing pad 66 is stopped, and the first electrode 62 and the second electrode 64 are disconnected from the power source 60. Thereafter, a so-called water polishing is carried out by rotating the substrate W while pressing it against the polishing surface 66 a of the polishing pad 66 at a low pressure and, at the same time, supplying pure water to the polishing pad 66, thereby cleaning the surface of the substrate W. Thereafter, the top ring 32 is raised, and the substrate W after cleaning is sent to the next process.
After cleaning of the substrate, conditioning (dressing) of the polishing surface 66 a of the polishing pad 66 with the dresser 38 is carried out in the following manner: First, the dresser 38 is moved from the retreat position to a position above the polishing pad 66. Thereafter, the lower surface (dressing surface) of the dresser 38 is pressed against the polishing surface (front surface) 66 a of the polishing pad 66 at a predetermined pressure which is not more than 0.5 psi (about 35 hPa), preferably not more than 0.3 psi (about 20 hPa) while moving them relative to each other and supplying a dressing liquid to the polishing surface 66 a of the polishing pad 66.
A considerable amount of polishing product is produced during electrochemical mechanical polishing of a surface conductive film, such as the copper film 307, of a substrate with the use of the polishing pad 66. The polishing pad 66 has, almost over its entirety, a large number of vertical through-holes 66 b so that electrical conduction can be made between the first electrode (processing electrode) 62 and a surface conductive film, such as the copper film 307, of a substrate by filling the through-holes 66 b with a polishing liquid (electrolytic liquid). The through-holes 66 b generally have a low efficiency of passage therethrough of a polishing liquid (electrolytic liquid), and therefore a polishing product and an “old polishing liquid”, having decreased concentrations of components, are likely to remain in the through-holes 66 b. When the polishing product remains in the through-holes 66 b and is accumulated on the surface of the first electrode 62, the electrical conduction between the first electrode 62 and a surface conductive film, such as the copper film 307, of a substrate will be impeded by the polishing product, which would cause lowering of polishing characteristics of the polishing apparatus and the stabilities of the characteristics.
According to this embodiment, in carrying out dressing (conditioning) of the polishing pad 66 with the dresser 38, the polishing product and the “old polishing liquid”, remaining on the polishing surface (front surface) 66 a or in the through-holes 66 b of the polishing pad 66, can be efficiently removed by forcing them out of the polishing pad 66 through the communication grooves 66 c with a liquid which is applied to the polishing pad 66 during the dressing. The polishing product and the “old polishing liquid”, remaining on the polishing surface (front surface) 66 a or in the through-holes 66 b of the polishing pad 66, can thus be removed easily and securely.
Further, according to necessity, pressurized pure water or a pressurized chemical for promoting removal of the polishing liquid is supplied (atomized) from the atomizer 44 to the polishing pad 66 to remove foreign matter, such as the polishing product, and the “old polishing liquid”, adhering to the surface of the polishing pad 66. At this time, foreign matter, such as the reaction product, adhering to the through-holes 66 b of the polishing pad 66 or to the surface of the first electrode 62 exposed in the communication grooves 66 c, can also be removed. The atomizing (conditioning) with the atomizer 44 is preferably carried out simultaneously with or shortly after the dressing (conditioning) with the dresser 38.
Thereafter, according to necessity, the polishing table 34 is rotated at a rotational speed of 50 to 100 rpm, which is higher than that for conditioning, for several seconds for draining.
The top ring 32 will now be described in more detail with reference to FIGS. 11 and 12. As shown in FIG. 11, the top ring 32 includes a top ring body 202 in the shape of a cylindrical vessel having an internal space therein, and the retainer ring 203 fixed to the lower end of the top ring body 202. The top ring body 202 is formed of, for example, a material having high strength and high rigidity, such as a metal or a ceramic. The retainer ring 203 is formed of, for example, a resin having high rigidity or a ceramic.
The top ring body 202 includes a housing portion 202 a in the shape of a cylindrical vessel, an annular pressure sheet support portion 202 b fitted in the cylindrical portion of the housing portion 202 a, and an annular sealing portion 202 c fitted into a peripheral portion of the upper surface of the housing portion 202 a. The lower portion of the retainer ring 203, fixed to the lower surface of the housing portion 202 a of the top ring body 202, projects inwardly. The retainer ring 203 maybe formed integrally with the top ring body 202.
The top ring-drying shaft 68 is provided above the center of the housing portion 202 a of the top ring body 202. The top ring body 202 and the top ring-driving shaft 68 are coupled by a universal joint portion 210. The universal joint portion 210 includes a spherical bearing mechanism which allows the top ring body 202 and the top ring-driving shaft 68 to tilt with respect to each other, and a rotation transmitting mechanism which transmits the rotation of the top ring-driving shaft 68 to the top ring body 202. Thus, the universal joint portion 210, while permitting tilting of the top ring body 202 with respect to the top ring-driving shaft 68, transmits the pressure and the torque of the top ring-driving shaft 68 to the top ring body 202.
The spherical bearing mechanism is comprised of a spherical recess 68 a formed in the center of the lower surface of the top ring-driving shaft 68, a spherical recess 202 d formed in the center of the upper surface of the housing portion 202 a, and a bearing ball 212 of a high-hardness material, such as a ceramic, interposed between the recesses 68 a, 202 d. The rotation transmitting mechanism is comprised of a driving pin (not shown) fixed to the top ring-driving shaft 68, and a driven pin (not shown) fixed to the housing portion 202 a. The driving pin and the driven pin are vertically movable relative to each other. Accordingly, even when the top ring body 202 is tilted, the pins still engage each other each at a shifted contact point. The rotation transmitting mechanism thus securely transmits the rotary torque of the top ring-driving shaft 68 to the top ring body 202.
In the interior space defined by the top ring body 202 and the retainer ring 203 fixed integrally to the top ring body 202, there are housed an elastic pad 204 to be in contact with a substrate W, such as a semiconductor wafer, held by the top ring 32, an annular holder ring 205, and a generally disk-shaped chucking plate 206 for supporting the elastic pad 204. The elastic pad 204 is nipped, at its peripheral portion, between the holder ring 205 and the chucking plate 206 fixed to the lower end of the holder ring 205, and covers the lower surface of the chucking plate 206. A space is thus formed between the elastic pad 204 and the chucking plate 206.
A pressure sheet 207, composed of an elastic film, is stretched between the holder ring 205 and the top ring body 202. The pressure sheet 207 is fixed with its one end nipped between the housing portion 202 a and the pressure sheet support portion 202 of the top ring body 202, and the other end nipped between an upper end portion 205 a and a stopper portion 205 b of the holder ring 205. A pressure chamber 221 is formed inside the top ring body 202 by the top ring body 202, the chucking plate 206, the holder ring 205 and the pressure sheet 207. As shown in FIG. 11, a fluid passage 231, e.g., comprised of a tube and a connector, communicates with the pressure chamber 221. The pressure chamber 221 is connected to the compressed air source via a regulator provided in the fluid passage 231. The pressure sheet 207 is formed of, for example, a rubber material having excellent strength and durability, such as ethylene-propylene rubber (EPDM), polyurethane rubber, or silicon rubber.
In case the pressure sheet 207 is formed of an elastic material, such as a rubber, and is fixed by nipping it between the retainer ring 203 and the top ring body 202, because of the elastic deformation of the elastic pressure sheet 207, a desirable flat plane may not be obtained in the lower surface of the retainer ring 203. In view of this, the pressure sheet support portion 202 b is separately provided, according to this embodiment, so as to nip and fix the pressure sheet 207 between the housing portion 202 a and the pressure sheet support portion 202 b of the top ring body 202.
A center bag 208 (central contact member) and a ring tube 209 (outer contact member), which are contact members to be in contact with the elastic pad 204, are provided in the space formed between the elastic pad 204 and the chucking plate 206. As shown in FIGS. 11 and 12, in this embodiment, the center bag 208 is disposed in the center of the lower surface of the chucking plate 206, and the ring tube 209 is disposed outside of the center bag 208 such that it surrounds the center bag 208. As with the pressure sheet 207, the elastic pad 204, the center bag 208 and the ring tube 209 are formed of, for example, a rubber material having excellent strength and durability, such as ethylene-propylene rubber (EPDM), polyurethane rubber, or silicon rubber.
The space formed between the chucking plate 206 and the elastic pad 204 is divided by the center bag 208 and the ring tube 209 into the following chambers: a pressure chamber 222 formed between the center bag 8 and the ring tube 209; and a pressure chamber 223 formed outside the ring tube 209.
The center bag 208 is comprised of an elastic film 281, which is in contact with the upper surface of the elastic pad 204, and a center bag holder 282 (holding portion) detachably holding the elastic film 281. The center bag holder 282 has screw holes 282 a, and the center bag 208 is detachably mounted to the center of the lower surface of the chucking plate 206 by screwing screws 255 into the screw holes 282 a. The center bag 208 internally has a central pressure chamber 224 defined by the elastic film 281 and the center bag holder 282.
Similarly, the ring tube 209 is comprised of an elastic film 291, which is in contact with the upper surface of the elastic pad 204, and a ring tube holder 292 (holding portion) detachably holding the elastic film 291. The ring tube holder 292 has screw holes 292 a, and the ring tube 209 is detachably mounted to the lower surface of the chucking plate 206 by screwing screws 256 into the screw holes 292 a. The ring tube 209 internally has an intermediate pressure chamber 225 defined by the elastic film 291 and the ring tube holder 292.
Fluid passages 233, 234, 235, 236, each comprised of, e.g., a tube and a connector, communicate with the pressure chambers 222, 223, the central pressure chamber 224 and the intermediate pressure chamber 225, respectively. The pressure chambers 222-225 are connected to the compressed air source as a supply source via regulators respectively provided in the fluid passages 233-236. The above-described fluid passages 231, 233-236 are connected to the respective regulators RE2-RE6 via rotary joints (not shown) provided at the upper end of the top ring-driving shaft 68.
A pressurized fluid, such as pressurized air, or atmospheric pressure or vacuum is supplied to the above-described pressure chamber 221, lying over the chucking plate 206, and to the pressure chambers 222-225 through the fluid passages 231, 233-236 communicating with the pressure chambers. By thus making the pressures in the pressure chambers 221-225 independently variable by the regulators, it becomes possible to adjust the pressure of the elastic pad 204 on the substrate W, and thus the pressure of the substrate W on the polishing pad 204, independently for divisional portions (divisional areas) of the substrate W.
The operation of the top ring 32 having the above construction upon polishing will now be described. When carrying out polishing of a substrate W, the substrate W is held on the lower surface of the top ring 32 while a cylinder, coupled to the top ring-driving shaft 68, is actuated to press the retainer ring 203, fixed to the lower end of the top ring 32, against the polishing surface 66 a of the polishing pad 66 of the polishing table 34 at a predetermined pressure. Pressurized fluids at predetermined pressures are respectively supplied to the pressure chambers 222, 223, the central pressure chamber 224 and the intermediate pressure chamber 225 to press the substrate W against the polishing surface 66 a of the polishing pad 66 of the polishing table 34.
At this time, the substrate W comes into contact with the electrode member 102 of the second electrode 64, which is floatingly supported by the floating mechanism 104, whereby feeding of electricity to a conductive film, such as the copper film 307 (see FIG. 1B), provided on the surface of the substrate W, becomes possible. Especially with this embodiment in which the substrate W is floatingly supported by the top ring 32, owing to the synergistic effect with the floating supporting of the electrode member 102 of the second electrode 64 by the floating mechanism 104, the electrode member 102 can be securely brought into contact with the substrate W at a more uniform contact pressure.
While applying a voltage from the power source 60 to between the first electrode 62 and the surface conductive film, such as the copper film 307 (see FIG. 1B), provided on the surface of the substrate W, a polishing liquid is supplied from the polishing liquid supply nozzle 40 to the polishing surface 66 a, whereby the polishing liquid is held in and on the polishing pad 66, so that polishing of the lower surface of the substrate W is carried out in the presence of the polishing liquid between the surface (lower surface) to be polished of the substrate W and the polishing surface 66 a of the polishing pad 66.
By appropriately adjusting, during polishing, the pressure of the retainer ring 203 on the polishing pad 66 and the pressure of the substrate W on the polishing pad 66, a desired distribution of polishing pressure can be obtained over the center portion of the substrate W (portion C1 shown in FIG. 12), the center to intermediate portion (C2), the intermediate portion (C3) and the peripheral portion (C4), and the retainer ring 203 lying outside the substrate W.
In the electrochemical mechanical polishing apparatus 54, initial conditioning of the polishing pad 66 is carried out, for example, after replacement of the polishing pad 66, in the following manner: First, the dresser 38 is moved from the retreat position to a position above the polishing pad 66. Thereafter, the lower surface (dressing surface) of the dresser 38 is pressed against the polishing surface (front surface) 66 a of the polishing pad 66 at a predetermined pressure which is not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa) while moving them relative to each other and supplying a dressing liquid to the polishing surface 66 a of the polishing pad 66, thereby carrying out first conditioning (dressing) of the polishing surface 66 a of the polishing pad 66. The first conditioning time is preferably 5 to 30 minutes in order to flatten the polishing surface 66 a of the polishing pad 66 to such an extent that it can be used for polishing and to sufficiently dress the polishing surface 66 a uniformly over the entire surface.
In this embodiment, the dresser 38 performs the first conditioning (dressing) of the polishing pad 66 at a dressing speed of not more than 50 μm/h. A common dresser has diamond abrasive grains fixed to a dressing surface, e.g., by electrodeposition or molding. Methods for decreasing the dressing speed of such a dresser include: (1) using blocky abrasive grains in the dressing surface; (2) using abrasive grains with a high grain count (e.g., #200 or higher); (3) decreasing the pressure of the dresser; and (4) decreasing the relative speed between the dresser and a polishing pad.
Thereafter, a dummy substrate, which has been carried into the polishing system, is held by the top ring 32, and the dummy substrate is moved to a predetermined polishing position above the polishing table 34. Thereafter, while rotating the top ring 32, it is lowered to press the surface (lower surface) of the dummy substrate against the polishing surface 66 a of the rotating polishing pad 66 at a predetermined polishing pressure which is higher, preferably at least twice, more preferably at least three times higher than a polishing pressure during polishing of a substrate. In practice, polishing of the dummy substrate is carried out at a pressure of not less than 1.5 psi (10.3 kPa). At the same time, while supplying a polishing liquid from the polishing liquid supply nozzle 40 to the polishing surface 66 a of the polishing pad 66, a predetermined voltage is applied from the power source 60 to between the first electrode 62 and the second electrode 64, thereby carrying out second conditioning of the polishing pad 66 for leveling of the polishing surface 66 a. The second conditioning is preferably carried out for at least 5 minutes in order to level or settle the polishing surface 66 a which has been excessively roughened.
The above two-step initial conditioning can prevent excessive initial conditioning of the polishing pad 66 and bring the polishing surface 66 a of the polishing pad 66 into the optimum conditions. The use in polishing of the polishing pad 66, which has undergone such initial polishing, makes it possible to polish, e.g., a metal film while maintaining the intended polishing rate and its uniformity in the surface of a substrate and preventing the occurrence of dishing or erosion.
When carrying out polishing of a real substrate, the top ring 32 holding a substrate W is first moved to a predetermined polishing position above the polishing table 34. Thereafter, while rotating the top ring 32, it is lowered to press the surface (lower surface) of the substrate W against the polishing surface 66 a of the rotating polishing pad 66 at a predetermined polishing pressure which is, for example, not more than 1 psi (about 7 kPa). At the same time, while supplying a polishing liquid from the polishing liquid supply nozzle 40 to the polishing surface 66 a of the polishing pad 66, a predetermined voltage is applied from the power source 60 to between the first electrode 62 and the second electrode 64, thereby polishing a conductive film, such as the copper film 307 (see FIG. 1B), formed on the surface of the substrate W.
The lower the polishing pressure applied to a substrate W upon its polishing is, the more the state of contact between the polishing pad 66 and the substrate W affects the polishing characteristics. By using the polishing pad 66 which has been initially conditioned into the optimum conditions in the above-described manner, it becomes possible to carry out polishing of the substrate W at a polishing pressure of the polishing pad 66 of not more than 1.5 psi (about 10.3 kPa) while maintaining the intended polishing rage and its uniformity in the surface of the substrate W and preventing the occurrence of dishing or erosion.
After completion of the electrochemical mechanical polishing, the supply of the polishing liquid to the polishing pad 66 is stopped, and the first electrode 62 and the second electrode 64 are disconnected from the power source 60. Thereafter, a so-called water polishing is carried out by rotating the substrate W while pressing it against the polishing surface 66 a of the polishing pad 66 at a low pressure and, at the same time, supplying pure water to the polishing pad 66, thereby cleaning the surface of the substrate W. Thereafter, the top ring 32 is raised, and the substrate W after cleaning is sent to the next process.
After completion of the water polishing of the substrate W, conditioning (dressing) of the polishing surface 66 a of the polishing pad 66 with the dresser 38 is carried out. In particular, the lower surface (dressing surface) of the dresser 38 is pressed against the polishing pad 66 at a predetermined pressure which is, for example, not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa) while moving them relative to each other and supplying a dressing liquid to the polishing surface 66 a of the polishing pad 66, thereby carrying out dressing of the polishing surface 66 a of the polishing pad 66. By thus further conditioning the polishing pad 66 during polishing of a substrate or during an interval between polishing operations, the optimum conditions of the polishing surface 66 a of the polishing pad 66, which has been optimized by the initial conditioning, can be maintained over a longer period of time.
FIG. 13 shows the main portion of the CMP apparatus 56. As shown in FIG. 13, the upper surface of the polishing table 35 of the CMP apparatus 56 is almost entirely covered with a polishing pad 80 whose upper surface constitutes a polishing surface 80 a. As with the above-described polishing pad 66 of the electrochemical mechanical polishing apparatus 54, the polishing pad 80 is composed of, e.g., IC-1000, manufactured by Nitta Haas Inc. The top ring 33 is designed to press a substrate, held by the top ring 33, against the polishing surface 80 a of the polishing pad 80, e.g., at a pressure of not more than 1.5 psi (about 10.3 kPa), and is coupled to the lower end of a top ring-driving shaft 82 which is rotatable and movable between a predetermined polishing position above the polishing table 35 and a position above a pusher 30′ (see FIG. 2).
The dresser 39 has, in the peripheral region of the lower surface, a plurality of protrusions 39 a arranged in a ring and each comprised of, for example, a member (e.g., diamond pellet) with diamond grains embedded in the lower surface, a hard material such as a ceramic material, or a brush, and is coupled to the lower end of a dresser-driving shaft 84 which is rotatable and is movable between a predetermined dressing position above the polishing table 35 and a retreat position beside the dressing position.
In this embodiment, the dresser-driving shaft 84 is coupled to a low-friction type pneumatic cylinder 86 with a dynamic frictional resistance of, e.g., 0.44 kg, disposed vertically and oriented downwardly. The pneumatic cylinder 86 is designed to lower the dresser 39 when air is supplied via a controller 88 to the upper internal space above the piston, and raise the dresser 39 when air is supplied via a regulator 90 to the lower internal space underneath the piston.
The dresser-driving shaft 84 and the dresser 39 rotate together via a transfer pin 92 and are coupled via a pole bearing 94 such that they are tiltable to each other.
In the CMP apparatus 56 the total weight of the dresser 39 and the dresser-driving shaft 84 is preset in the regulator 90, and air in an amount, which cancels out the weight, has previously been supplied via the regulator 90 to the pneumatic cylinder 86. Accordingly, the pressure of the dresser 39 on the polishing pad 80 is zero unless air is supplied via the controller 88 to the pneumatic cylinder 86. Thus, the pressure of the dresser 39 can be adjusted from zero to any higher value by adjusting the amount of air to be supplied via the controller 88. Especially by using the low-friction type pneumatic cylinder 86 that operates with a dynamic frictional resistance of 0.4 kg, it becomes possible to set the pressure even at such a low value as 10N (Newton).
It is, of course, possible to provide the above construction to the dresser-driving shaft 70 of the electrochemical mechanical polishing apparatus 54.
The polishing liquid supply nozzle 41 has a number of polishing liquid supply orifices disposed along the length direction, and is disposed such that it extends radially above the polishing table 35. Similarly, the atomizer 45 has a number of supply orifices disposed along the length direction, and is disposed such that it extends radially above the polishing table 35.
Further, though not shown diagrammatically, a pure water supply nozzle for supplying pure water to the polishing pad 80 and a dressing liquid supply nozzle for supplying a dressing liquid to the polishing pad 80 maybe disposed above the polishing table 35, according to necessity.
Also in the CMP apparatus 56, initial conditioning of the polishing pad 80 is carried out, for example, after replacement of the polishing pad 80, in the following manner: First, the dresser 39 is moved from the retreat position to a position above the polishing pad 80. Thereafter, the lower surface (dressing surface) of the dresser 39 is pressed against the polishing surface (front surface) 80 a of the polishing pad 80 at a predetermined pressure which is not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa) while moving them relative to each other and supplying a dressing liquid to the polishing surface 80 a of the polishing pad 80, thereby carrying out first conditioning (dressing) of the polishing surface 80 a of the polishing pad 80. The first conditioning time is preferably 5 to 30 minutes in order to flatten the polishing surface 80 a of the polishing pad 80 to such an extent that it can be used for polishing and to sufficiently dress the polishing surface 80 a uniformly over the entire surface. In this embodiment, the dresser 39 performs the first conditioning (dressing) of the polishing pad 80 at a dressing speed of not more than 50 μm/h.
Thereafter, a dummy substrate, which has been carried into the polishing system, is held by the top ring 33, and the dummy substrate is moved to a predetermined polishing position above the polishing table 35. Thereafter, while rotating the top ring 33, it is lowered to press the surface (lower surface) of the dunmy substrate against the polishing surface 80 a of the rotating polishing pad 80 at a predetermined polishing pressure which is higher, preferably at least twice, more preferably at least three times higher than a polishing pressure upon polishing of a substrate while a polishing liquid is supplied from the polishing liquid supply nozzle 41 to the polishing surface 80 a of the polishing pad 80, thereby carrying out second conditioning of the polishing pad 80 for leveling of the polishing surface 80 a. The second conditioning is preferably carried out for at least 5 minutes in order to level or settle the polishing surface 80 a which has been excessively roughened.
The above two-step initial conditioning can prevent excessive initial conditioning of the polishing pad 80 and bring the polishing surface 80 a of the polishing pad 80 into the optimum conditions. The use in polishing of the polishing pad 80, which has undergone such initial polishing, makes it possible to polish, e.g., a metal film while maintaining the intended polishing rate and its uniformity in the surface of a substrate and preventing the occurrence of dishing or erosion.
When carrying out polishing of a real substrate, the top ring 33 holding a substrate W is first moved to a predetermined polishing position above the polishing table 35. Thereafter, while rotating the top ring 33 in the B direction, it is lowered to press the surface (lower surface) of the substrate W against the polishing surface 80 a of the polishing pad 80, rotating in the A direction, at a predetermined polishing pressure which is, for example, not more than 1.5 psi (about 10.3 kPa), while a polishing liquid is supplied from the polishing liquid supply nozzle 41 to the polishing surface 80 a of the polishing pad 80, thereby polishing a conductive film, such as the copper film 307 (see FIG. 1B), formed on the surface of the substrate W.
The lower the polishing pressure applied to a substrate w upon its polishing is, the more the state of contact between the polishing pad 80 and the substrate W affects the polishing characteristics. By using the polishing pad 80 which has been initially conditioned into the optimum conditions in the above-described manner, it becomes possible to carry out polishing of the substrate W at a polishing pressure of the polishing pad 80 of not more than 1.5 psi (about 10.3 kPa) while maintaining the intended polishing rage and its uniformity in the surface of the substrate W and preventing the occurrence of dishing or erosion.
After completion of the chemical mechanical polishing, the supply of the polishing liquid to the polishing pad 80 is stopped. Thereafter, a so-called water polishing is carried out by rotating the substrate W while pressing it against the polishing surface 80 a of the polishing pad 80 at a low pressure and, at the same time, supplying pure water to the polishing pad 80, thereby cleaning the surface of the substrate W. Thereafter, the top ring 33 is raised, and the substrate W after cleaning is sent to the next process.
After the cleaning of the substrate W, conditioning (dressing) of the polishing surface 80 a of the polishing pad 80 with the dresser 39 is carried out. In particular, the lower surface (dressing surface) of the dresser 39 is pressed against the polishing pad 80 at a predetermined pressure which is, for example, not more than 0.6 psi (about 4.1 kPa), preferably not more than 0.35 psi (about 2.4 kPa) while moving them relative to each other and supplying a dressing liquid to the polishing surface 80 a of the polishing pad 80, thereby carrying out dressing of the polishing surface 80 a of the polishing pad 80. Such conditioning of the polishing pad 80 can maintain the optimum conditions of the polishing surface 80 a, which has been optimized by the initial conditioning, over a longer period of time.
Further, according to necessity, pressurized pure water or a pressurized chemical for promoting removal of the polishing liquid is supplied (atomized) from the atomizer 45 to the polishing pad 80 to remove foreign matter, such as a polishing product, and the “old polishing liquid”, adhering to the surface of the polishing pad 80. The atomizing with the atomizer 45 is preferably carried out simultaneously with or shortly after the dressing with the dresser 39.
Thereafter, according to necessity, the polishing table 35 is rotated at a rotational speed of 50 to 100 rpm, which is higher than that for conditioning, for several seconds for draining.
As shown in FIG. 2, in the area C separated from the area B by the partition wall 24A and at a position that can be accessed by the hands of the transfer robot 20, there is provided a reversing device 28 for reversing a substrate. In the area D separated from the area B by the partition wall 24B and at a position that can be accessed by the hands of the transfer robot 21, there is provided a reversing device 28′ for reversing a substrate. The partition walls 24A, 24B between the area B and the areas C, D has two openings each for allowing substrates to pass therethrough. Shutters 25, 26 are provided at the respective openings only for reversing devices 28, 28′.
The reversing devices 28, 28′ have a chuck mechanism for chucking a substrate, a reversing mechanism for reversing a substrate, and a substrate detecting sensor for detecting whether the chuck mechanism chucks a substrate or not, respectively. The transfer robot 20 transfers a substrate to the reversing device 28, and the transfer robot 21 transfers a substrate to the reversing device 28′.
In the area C constituting one of the polishing chambers, there is provided a linear transporter 27A constituting a transport mechanism for transporting a substrate between the reversing device 28 and the top ring 32 of the electrochemical mechanical polishing apparatus 54. In the area D constituting the other of the polishing chambers, there is provided a linear transporter 27B constituting a transport mechanism for transporting a substrate between the reversing device 28′ and the top ring 33 of the CHP apparatus 56. The linear transporter 27A comprises two stages linearly movable between a lifter 29 and the pusher 30 in a reciprocating fashion. Similarly, the linear transporter 27B comprises two stages linearly movable between a lifter 29′ and the pusher 30′ in a reciprocating fashion.
The operation of the polishing system will now be described.
First, initial conditioning of the polishing pad 66 or 80 is carried out in the above-described manner, for example, after the polishing pad 66 mounted on the surface of the polishing table 34 of the electrochemical mechanical polishing apparatus 54 or the polishing pad 80 mounted on the surface of the polishing table 35 of the CHP apparatus 56 is replaced with a new one.
Thereafter, a substrate cassette 1 in which a number of substrates W such as shown in FIG. 1B, having a copper film 307 formed on the surface, are housed, is placed in the load-unload stage 2. One substrate is taken by the transfer robot 4 out of the substrate cassette 1, and the substrate is transported to the substrate station 50 and placed on it. The transfer robot 20 receives the substrate from the substrate station 50, and transports the substrate to the reversing machine 28 in the area C, where the substrate is reversed. The lifter 29 receives the reversed substrate from the reversing machine 28, and passes the substrate to the linear transporter 27A. The linear transporter 27A moves horizontally and places the substrate on the pusher 30. The top ring 32 of the electrochemical mechanical polishing apparatus 54 is then moved to above the pusher 30.
The top ring 32 receives the substrate from the pusher 30 and, while holding the substrate inside the retainer ring 203 by vacuum attraction, moves the substrate from above the pusher 30 to a polishing position above the polishing table 34. Thereafter, the top ring 32 is lowered to press the substrate against the polishing surface 66 a of the polishing pad 66 at a predetermined polishing pressure which is not more than 1.5 psi (about 10.3 kPa) and, at the same time, a voltage is applied from the power source 60 to between the first electrode 62 and a surface conductive film, such as the copper film 307 (see FIG. LB), provided on the surface of the substrate W while supplying a polishing liquid to the polishing pad 66, thereby polishing the conductive film. The vacuum attraction of the substrate in the top ring 32 may be released during polishing of the substrate with the polishing pad 66.
Polishing of the copper film 307 (and the seed film 306) by the electrochemical mechanical polishing apparatus 54 is carried out, for example, until the surface of the barrier film 305 becomes exposed, as shown by line A-A in FIG. 1B. Damage to an interconnect structure due to polishing can be significantly reduced by thus employing electrochemical mechanical polishing, which generally causes little damage to interconnects, etc., at least partly in a polishing process and carrying out polishing and removal of the substantial portion of a film of interconnect material formed outside interconnect recesses, amounting to the majority of the total polishing amount, by electrochemical mechanical polishing.
After completion of the polishing by the electrochemical mechanical polishing apparatus 54, conditioning of the polishing surface 66 a of the polishing pad 66 with the dresser 38 and conditioning of the polishing surface 66 a with the atomizer 44 are carried out in the above-described manners to prepare for the next polishing.
The substrate after the polishing by the electrochemical mechanical polishing apparatus 54 is again moved to the pusher 30 and placed on it. The polished surface and the back surface of the substrate, which has been released from the top ring 32 by the pusher 30, are cleaned by a cleaning water supplied from the nozzle provided in the pusher 30. The substrate is then moved via the linear transporter 27A and the lifter 29 to the reversing machine 28, where the substrate is reversed. The reversed substrate is transported by the transfer robot 20 to the cleaning unit 22, where the surface of the substrate is cleaned by rinsing. The substrate after cleaning is transported by the transfer robot 20 to the substrate station 50 and placed on it.
The transfer robot 21 receives the substrate on the substrate station 50 and transports it to the reversing machine 28′ in the area D, where the substrate is reversed. The lifter 29′ receives the reversed substrate from the reversing machine 28′ and passes the substrate to the linear transporter 27B. The linear transporter 27B moves horizontally, and places the substrate on the pusher 30′. The top ring 33 of the CMP apparatus 56 is then moved to above the pusher 30′.
The top ring 33 receives the substrate from the pusher 30′ and, while holding the substrate inside the retainer ring by vacuum attraction, moves the substrate from above the pusher 30′ to a polishing position above the polishing table 35. Thereafter, the top ring 33 is lowered to press the substrate against the polishing surface 80 a of the polishing pad 80, mounted on the upper surface of the polishing table 35, at a predetermined polishing pressure which is, for example, not more than 1 psi (about 7 kPa) and, at the same time, a polishing liquid is supplied from the polishing liquid supply nozzle 41 to the polishing pad 80 while rotating the top ring 33 and the polishing table 35, thereby further polishing the surface of the substrate. The vacuum attraction of the substrate in the top ring 33 may be released during polishing of the substrate with the polishing pad 80.
The polishing by the CMP apparatus 56 may polish, for example, the copper film 307 (and the seed film 306) remaining on the surface of the substrate on which the barrier film 305 has been exposed upon the polishing by the electrochemical mechanical polishing apparatus 54 to thereby completely remove the unnecessary copper film 307 (and the seed film 306), and may further polish the barrier film 305, thereby forming the interconnects 308 in the insulating film 302, as shown in FIG. 1C.
By thus polishing and removing the majority of a film of interconnect material by electrochemical mechanical polishing, and subsequently polishing and removing the remainder of the film of interconnect material by using CMP, which has a high capability of eliminating a surface level difference, the flatness of the substrate surface after polishing can be enhanced. Further, by switching from electrochemical mechanical polishing to CMP when a barrier film has become exposed, the remainder of the film of interconnect material and the underlying barrier film can be securely polished and removed.
After completion of the polishing by the CMP apparatus 56, as in the case of the electrochemical mechanical polishing apparatus 54, conditioning of the polishing surface 80 a of the polishing pad 80 of the CMP apparatus 56 with the dresser 39 and conditioning of the polishing surface 80 a with the atomizer 45 are carried out to prepare for the next polishing.
The substrate after the polishing by the CMP apparatus 56, on the other hand, is again moved to the pusher 30′ and placed on it. The substrate is then moved via the linear transporter 27B and the lifter 29′ to the reversing machine 28′, where the substrate is reversed. The reversed substrate is transported by the transfer robot 21 to the cleaning unit 23, where the surface of the substrate is cleaned by rinsing. The substrate after cleaning is transported by the transfer robot 21 to the substrate station 50 and placed on it.
The transfer robot 20 (or 21) takes the cleaned substrate out of the substrate station 50, and transports the substrate to the drying unit 5 (or 6), for example, including a pen sponge for cleaning of the upper surface of a substrate and having a spin-drying function, where the substrate is cleaned and dried. The substrate after cleaning/drying is returned by the transfer robot 4 to the substrate cassette 1.
Though in this embodiment a semiconductor wafer is used as a substrate to be polished, the present invention is of course not limited to polishing of a semiconductor wafer. Besides a polishing cloth usable as the polishing pad 66 of the electrochemical mechanical polishing apparatus 54 and/or the polishing pad 80 of the CMP apparatus 56, it is also possible to use a fixed-abrasive pad impregnated with abrasive grains which, if its fairly hard polishing surface collapsed, can self-regenerate the polishing surface, or to use various types of abrasive-free polishing pads.
Though in this embodiment a barrier film and a copper film (and a seed film) formed on a surface of a substrate W is polished in two steps, it is of course possible to polish the substrate surface in three or more steps, as by polishing the copper film (and the seed film) by ultrapure water electrolytic polishing using ultrapure water as an electrolytic liquid, followed by polishing by CMP, or carrying out the final polishing of the copper film (and the seed film) and polishing of the barrier film by two-step CMP.
Various types of dressers, including a diamond dresser and a brush dresser, may be used in the present invention. Further, various shapes of dressers, including a ring-shaped dresser, a disk-shaped dresser and a pellet-type dresser, may be employed. An appropriate type or shape of dresser maybe selected depending on the processing conditions such as the dresser material, the substrate to be polished, the material of the polishing pad, etc.

EXPERIMENTAL EXAMPLE

A 100 mm-diameter dresser A with diamond abrasive grains electrodeposited on a surface and a 100 mm-diameter dresser B with diamond abrasive grains, having a higher grain count (smaller size) than the abrasive grains of the dresser A, electrodeposited on a surface, were prepared. A polishing pad composed of IC-1000, manufactured by Nitta Haas Inc., was dressed (conditioned) with the dresser A at a pressure of 3.2 psi. The same polishing pad was dressed with the dresser B at a pressure of 0.64 psi. Dressing of the same polishing with the dresser B was also carried out but at a different pressure of 0.4 psi. Polishing of a surface of a substrate (semiconductor wafer) was carried out using each of the dressed polishing pads, and a change in a surface level difference with the progress of polishing was measured on each of the test substrates to examine a difference in the fattening characteristic between the substrates. In the experiment a load of 25 N (including the own weight of the dresser) was applied to the polishing pad to produce a pressure of 0.4 psi. The results of the measurement are shown in FIG. 14.
As will be appreciated from the data in FIG. 14, better flattening (elimination of surface level difference) of the substrate surface can be attained when polishing of the substrate is carried out using the polishing pad which has been dressed with the dresser B having the diamond abrasive gains of a higher grain count. The grain count of diamond abrasive grains is preferably not lower than #100, more preferably not lower than #200. Further, it is apparent from the comparative data for the different pressures (0.4 psi vs. 0.64 psi) of the same dresser B upon dressing that the use of the lower dressing pressure (0.4 psi) results in enhanced elimination of the surface level difference of the substrate, and that the use of a dressing pressure of not more than 0.6 psi will attain sufficient elimination of surface level difference and in-plane uniformity of a substrate in polishing of the substrate using a thus-dressed polishing pad.
Various shapes of diamond abrasive grains, including blocky grains (regularly-shapedones) and irregular grains, can be used in a diamond dresser. A uniformly-conditioned surface is easily obtainable especially when using a dresser having blocky diamond grains. It is desirable that in a diamond dresser, part of each diamond abrasive grain, preferably at least 50% and more preferably at least 70% of the grain size, be embedded in the dressing surface.
Though the use of IC-1000, manufactured by Nitta Haas Inc., as a polishing pad has been particularly described above, the advantages of the present invention described above with reference to the present dressing (conditioning) method can be obtained also when any other polishing pad is used. Thus, it is possible with any polishing pad to polish, e.g., a metal film of a substrate while maintaining the intended polishing rate and its uniformity in the substrate surface and preventing the occurrence of dishing or erosion.
According to the method for conditioning a polishing pad of the present invention, a polishing pad can be initially conditioned into the optimum conditions. The use of the polishing pad, which has undergone such initial conditioning, makes it possible to polish an extra metal film or an extra barrier film formed on a surface of a substrate while maintaining the intended polishing rate and its uniformity in the surface of the substrate and preventing the occurrence of dishing or erosion even when the substrate is for the manufacturing of a semiconductor device having a very fine interconnect structure of the 65-nm or later generation.
According to the polishing method and the polishing apparatus of the present invention, a contact pressure, especially a very low contact pressures, between a feeding electrode (second electrode) and a conductive film of a substrate can be controlled while ensuring feeding of electricity from the electrode to the conductive film. This makes it possible to carry out polishing of a surface of a substrate without damage to devices formed in the substrate even when processing a fragile material.
FIG. 15 shows another polishing pad 180. The polishing pad 180 has a two-layer structure consisting of a pad body 182 of the same construction as the above-described polishing pad 66, having a hardness (Asker-C) of 60 to 95 and the front surface (upper surface) constituting a polishing surface 182 a, and a support layer 184 having a lower hardness than the pad body 182. The pad body 182 has a large number of vertical through-holes 182 b, which communicate with each other by communication grooves 182 c provided in the back surface of the pad body 182, and the support layer 184 is superimposed on the back surface of the pad body 182. In this embodiment, the support layer 184 is composed of a material having conducting properties.
According to the polishing pad 180 of this embodiment, the pad body 182 (polishing pad 66) having a large number of through-holes 182 b can be mounted on the surface of the first electrode (processing electrode) 62 with support of the support layer 184.
Though in this embodiment the communication grooves 182 c are provided in the back surface of the polishing pad 182, it is also possible to provide the communication grooves in the surface of the support layer 184.
FIG. 16 shows the main portion of a polishing apparatus (electrochemical mechanical polishing apparatus) 54 a having yet another polishing pad 190, according to another embodiment of the present invention. The electrochemical mechanical polishing apparatus 54 a shown in FIG. 16 differs from the electrochemical mechanical polishing apparatus 54 shown in FIGS. 3 and 4 in the following respects: The electrochemical mechanical polishing apparatus 54 a shown in FIG. 6 uses a polishing pad 190 basically having the same construction as the polishing pad 66 shown in FIGS. 5 and 6 but having a conducting portion 192 in at least part, in this embodiment in a ring-shaped continuous peripheral portion which is to make contact with a substrate W during polishing, of the polishing surface 66 a. Further, a second electrode (anode) 194, which is to make contact with the conducting portion 192 of the polishing pad 190, is disposed above the polishing table 34. Thus, in carrying out electrochemical polishing, electricity is fed from the second electrode 194 via the conducting portion 192 of the polishing pad 190 to an electrical conductor, such as the copper film 307 (see FIG. 1B), formed on a surface (lower surface) of a substrate W, and electric current flows between the surface of the substrate W and the first electrode (processing electrode) 62 via a polishing liquid that has flowed into the through-holes 66 b of the polishing pad 190.
As a method for feeding electricity to a substrate is generally employed a so-called contact method which involves bringing a feeding electrode, formed of a simple substance such as copper, platinum or carbon, an alloy such as a stainless steel, or a conductive oxide such as IrO₂, into direct contact with a substrate. It is a conventional practice with such feeding method to provide a feeding electrode with a substrate-contact surface having a curvature, such as a spherical surface, or reduce a contact pressure between a feeding electrode and a substrate surface in order to prevent the formation of scratches in a substrate surface due to direct contact with a feeding electrode. On the other hand, it is also a conventional practice to provide a feeding electrode with a plurality of substrate-contact points or increase the contact area of a feeding electrode with a substrate surface in order to ensure stable feeding of electricity to a substrate surface. These countermeasures, however, would have an adverse effect on prevention of the formation of scratches in a substrate surface.
According to this embodiment, the contact area between a substrate W and the conducting portion 192 can be increased so as to ensure stable and defect-free electricity feeding to an electrical conductor, such as the copper film 307, in the surface of the substrate W. Further, the formation of defects in a surface of a substrate W can be prevented more securely by utilizing the flexibility of the polishing pad 190 and eliminating direct contact of a feeding electrode with the substrate surface. In addition, by connecting the through-holes 66 b of the polishing pad 190 with the communication grooves 66 c, it becomes possible to uniformly supply a liquid (polishing liquid) to the through-holes 66 b, enabling more uniform polishing of an electrical conductor, such as the copper film 307, in a surface of a substrate W.
Usable materials for the conducting portion 192 are exemplified by carbon as s simple substance and a sheet, fibers or a textile containing a carbon material. When a sheet or the like containing a carbon material is used as a material for the conducting portion 192, it is necessary to incorporate the carbon material into the sheet or the like in such a manner as to ensure continuous electrical conduction for a certain area of the polishing surface of the polishing pad.
Though in this embodiment the continuous conducting portion 192 is provided in a peripheral portion of the polishing surface 66 a of the polishing pad 190, it may be sufficient to make at least part of the polishing surface 66 a have conducting properties. It is possible to use a polishing pad composed of a single conductive layer or a polishing pad composed of a multilayer of a conductive layer and an insulating layer. The use of such a multilayer polishing pad can easily ensure good contact with a substrate surface, thus facilitating polishing of the substrate surface. Further, it is possible to make an entire polishing surface of a polishing pad have conducting properties or to make an entire surface of a polishing pad have both conducting properties and insulating properties. For example,by disposing an electrical conductor in a mosaic pattern in a surface of a common polyester polishing pad to form a hybrid structure, the entire polishing surface of the polishing pad can be made to have both conducting properties and insulating properties.
Also in the electrochemical mechanical polishing apparatus 54 a shown in FIG. 16, as with the electrochemical mechanical polishing apparatus 54 shown in FIGS. 3 and 4, a liquid (polishing liquid) is supplied to the polishing surface 66 a of the polishing pad 190 upon polishing. During polishing, it is necessary to uniformly feed electricity via the second electrode 194 and the conducting portion 192 of the polishing pad 190 to an electrical conductor, such as the conductive film 307, in a surface of a substrates This requires the through-holes 66 b of the polishing pad 190 to be filled with the liquid. The provision of the communication grooves 66 c can facilitate filling of the liquid into the through-holes 66 b of the polishing pad 190.
According to the present invention, a polishing product and an “old polishing liquid”, remaining on the surface (polishing surface) or in the through-holes of a polishing pad, can be forced out of the polishing pad through the communication grooves by a liquid which is applied to the polishing pad upon its conditioning. This enables efficient removal of the polishing product and the “old polishing liquid”, making it possible to maintain the polishing characteristics and their stabilities of a polishing apparatus having the polishing pad.
FIG. 17 shows the main portion of a polishing apparatus (electrochemical mechanical polishing apparatus) 54 b provided with another dresser 38 b, according to yet another embodiment of the present invention, FIG. 18 shows an enlarged view of a portion of FIG. 17, and FIG. 19 shows a rear view of the dresser 38 b. As shown in FIGS. 17 through 19, the dresser 38 b of this embodiment comprises a disk-shaped support plate 380 and two types of brush bristles 386, i.e., first brush bristles 382 which are short and have high rigidity (as compared to second brush bristles 384) and second brush bristles 384 which are long and have low rigidity (as compared to first brush bristles 382), both implanted in a dressing surface (lower surface) of the support plate 380. In particular, the dressing surface (lower surface) of the support plate 380 is divided into a plurality of areas, e.g., four areas E1 to E4 as shown in FIG. 19, and the second and first brush bristles 384, 382 are implanted alternately, i.e., the second brush bristles 384 are implanted in the areas E1, E3 and the first brush bristles 382 are implanted in the areas E2, E4. The brush bristles 386 are formed of, for example, nylon, PVA or polyester.
The length of the second brush bristles 384 is preferably not more than the sum of the length of the first brush bristles 382, a thickness of the polishing pad 66 and 5 mm. It is also possible to use first brush bristles 382 and second brush bristles 384 both having the same rigidity.
The support plate 380 is coupled to the lower end of a dresser-driving shaft 70 which is rotatable and movable between a predetermined dressing position above the polishing table 34 and a retreat position beside the dressing position.
As shown in FIG. 20, it is also possible to provide scattered areas E5 of a circular or any other shape in the dressing surface of the support plate 380, and implant the long second brush bristles 384 having low rigidity (as compared to the first brush bristles 382) in the areas E5 and the short brush bristles 382 having high rigidity (as compared to the second brush bristles 384) in the other area, so that the second brush bristles 384 are present in a spot-like pattern in the dressing surface with the first brush bristles 382 in the background.
When the second brush bristles 384 are thus provided in a spot-like pattern with the first brush bristles 382 in the background, the diameter of each spot of the second brush bristles 384 is preferably smaller than the diameter of the through-holes 66 b provided in the polishing pad 66.
It is also possible to dispose the second brush bristles 384 in a lattice pattern or a radial pattern, or in any combination of concentric, lattice, radial and spot-like patterns with the first brush bristles 382 in the background. Further, it is possible to dispose the first brush bristles 382 in any one of the above-described patterns or in any combination of the patterns with the second brush bristles 384 in the background.
According to this embodiment, dressing of the polishing surface 66 a of the polishing pad 66 with the dresser 38 b is carried out after cleaning of a substrate or at the start-of the apparatus after the polishing pad 66 is replaced with a new one. In particular, the dresser 38 b is first moved from the retreat position to a position above the polishing pad 66. Thereafter, the dresser 38 b is lowered to press the brush bristles 386 of the dressing surface (lower surface) of the dresser 38 b against the polishing surface (front surface) 66 a of the polishing pad 66 at a predetermined pressure while moving the brush bristles 386 and the polishing surface 66 a relative to each other and supplying a dressing liquid to the polishing surface 66 a of the polishing pad 66.
As described above, a considerable amount of polishing product is produced during electrochemical mechanical polishing of a surface conductive film, such as the copper film 307, of a substrate with the use of the polishing pad 66. The polishing pad 66 has, almost over its entirely, a large number of vertical through-holes 66 b so that electrical conduction can be made between the first electrode (processing electrode) 62 and a surface conductive film, such as the copper film 307, of a substrate by filling the through-holes 66 b with a polishing liquid (electrolytic liquid). The through-holes 66 b generally have a low efficiency of passage therethrough of a polishing liquid (electrolytic liquid), and therefore a polishing product is likely to remain in the through-holes 66 b. When the polishing product remains in the through-holes 66 b and is accumulated on the surface of the first electrode 62, the electrical conduction between the first electrode 62 and a surface conductive film, such as the copper film 307, of a substrate will be impeded by the polishing product, which would cause lowering of polishing characteristics of the polishing apparatus and the stabilities of the characteristics.
According to this embodiment, dressing of the polishing surface 66 a of the polishing pad 66 with the dresser 38 b can be performed by rubbing the polishing surface 66 a chiefly with the first brush bristles 382 while allowing the tips chiefly of the second brush bristles 384, having low rigidity, to easily enter the numerous through-holes 66 b formed in the polishing pad 66 and scraping out foreign matter, such as a processing product, remaining in the through-holes 66 b with the second brush bristles 384. This enables easy and secure removal of foreign matter, such as a polishing product, remaining on the surface (polishing surface) 66 a or in the through-holes 66 b of the polishing pad 66.
FIG. 21 shows the main portion of a polishing apparatus (electrochemical mechanical polishing apparatus) 54 c according to yet another embodiment of the present invention. The polishing apparatus 54 c of this embodiment includes a dresser 400 retreatably disposed above the polishing pad 66, having a large number of through-holes 66 b, mounted on the upper surface of the first electrode (processing electrode) 62. The dresser 400 includes a disk-shaped support plate 402 having a dressing surface (lower surface) which comprises a diamond dressing section 406 provided with diamond abrasive grains 404 having a grain count of #100 or higher, and a brush dressing section 410 provided with brush bristles 408. The diamond dressing section 406 is disposed in a ring outside the brush dressing section 410. The brush bristles 408 of the brush dressing section 410 have low rigidity, for example approximately the same rigidity as the above-described second brush bristles 384 shown in FIGS. 18 and 19, which is lower than that of brush bristles generally used for dressers. The lower portions of the brush bristles 408 project downwardly from the surface (lower surface) of the diamond dressing section 406.
It is also possible to dispose the brush dressing section 410 in a concentric pattern, a lattice pattern, a radial pattern or a spot-like pattern, or a combination thereof, inside the diamond dressing section 406.
In operation, the dresser 400 in the retreat position is moved to a position above the polishing pad 66. Thereafter, the dresser 400 is lowered to press the diamond dressing section 406 and the brush dressing section 410 of the dressing surface (lower surface) of the support plate 402 against the polishing surface (front surface) 66 a of the polishing pad 66 at a predetermined pressure which is preferably not more than 0.5 psi (about 35 hPa), more preferably not more than 0.3 psi (about 20 hPa) while moving the dressing surface and the polishing surface 66 a relative to each other and supplying a dressing liquid to the polishing surface 66 a, thereby dressing the polishing surface 66 a of the polishing pad 66.
According to this embodiment, dressing of the polishing surface 66 a of the polishing pad 66 with the dresser 400 can be performed by rubbing the polishing surface 66 a with the diamond abrasive grains 404 of the diamond dressing section 406 while allowing the tips of the brush bristles 408, having low rigidity, to easily enter the numerous through-holes 66 b formed in the polishing pad 66 and scraping out foreign matter, such as a processing product, remaining in the through-holes 66 b with the brush bristles 408. This enables easy and secure removal of foreign matter, such as a polishing product, remaining on the surface (polishing surface) 66 a or in the through-holes 66 b of the polishing pad 66.
It has been confirmed experimentally that a substrate can be polished with good flattening characteristics when the substrate surface is polished using a polishing pad, IC-1000 manufactured by Nitta Haas Inc., which has dressed with a dresser with diamond abrasive grains, having a grain count of #100 or higher, electrodeposited on the dressing surface at a dressing pressure of not more than 0.5 psi (about 35 hPa). The grain count of the diamond abrasive grains is preferably #200 or higher.
FIG. 22 shows a polishing apparatus (electrochemical mechanical polishing apparatus) 54 d according to yet another embodiment of the present invention. The electrochemical mechanical polishing apparatus 54 d of this embodiment adds the dresser 400 provided in the electrochemical mechanical polishing apparatus 54 c shown in FIG. 21 to the electrochemical mechanical polishing apparatus 54 b shown in FIG. 17 so that one of the dressers 38 b, 400 can be chosen when carrying out dressing of the polishing pad 66.
According to the electrochemical mechanical polishing apparatus) 54 d of this embodiment, at the start-up of the electrochemical mechanical polishing apparatus 54 d, for example, after replacement of the polishing pad 66 with a new one, dressing (initial dressing) of the polishing surface 66 a of the polishing pad 66 is carried out by using the dresser 400, having the diamond dressing section 406 provided with the diamond abrasive grains 404 having a grain count of #100 or higher and the brush dressing section 410 provided with the brush bristles 408, and rubbing the polishing pad 66 with the dresser 400 preferably at a pressure of not more than 0.5 psi (about 35 hPa), more preferably not more than 0.3 psi (about 20 hPa). The initial dressing of the polishing pad 66 can thus be carried out without dressing the pad excessively.
Further, during polishing of a substrate or during an interval between polishing operations, dressing of the polishing surface 66 a of the polishing pad 66 is carried out by bringing the dresser 38 b, having the first brush bristles 382 and the second brush bristles 384 having lower rigidity than the first brush bristles 382, into sliding contact with the polishing surface 66 a. The dressing can securely remove foreign matter, such as a polishing product, which has entered the through-holes 66 b of the polishing pad 66 during polishing, out of the through-holes 66 b.
The present invention makes it possible to carry out dressing of a polishing pad having through-holes while easily and securely removing foreign matter, such as a polishing product, remaining on the surface or in the through-holes of the polishing pad. The use of the thus-dressed polishing pad in a polishing apparatus makes it possible to carry out polishing of a substrate while maintaining the polishing characteristics and their stabilities of the polishing apparatus.
While the present invention has been described with reference to the embodiments thereof, it will be understood by those skilled in the art that the present invention is not limited to the embodiments, but changes could be made to the embodiments within the inventive concept that will be appreciated from the claims, the specification and the drawings.

Claims

1. A polishing pad having a polishing surface and having a plurality of through-holes extending in the thickness direction, said through-holes communicating with each other by communication grooves.

2. The polishing pad according to claim 1, wherein the through-holes have a diameter of 2 to 5 mm.

3. The polishing pad according to claim 1, wherein the aperture ratio of the through-holes is 10 to 50% of the surface area of the polishing surface of the polishing pad.

4. The polishing pad according to claim 1, wherein the depth of the communication grooves is 40 to 60% of the thickness of the polishing pad.

5. The polishing pad according to claim 1, wherein the communication grooves are formed in the reverse surface of the polishing pad from the polishing surface.

6. The polishing pad according to claim 1, wherein the width of the communication grooves is 10 to 50% of the diameter of the through-holes.

7. The polishing pad according to claim 1, wherein the communication grooves are arranged in a concentric pattern, a lattice pattern, an arc pattern, a radial pattern or a spiral pattern, or a combination thereof.

8. The polishing pad according to claim 1, wherein at least one flow passage groove is provided between the communication grooves.

9. The polishing pad according to claim 1, wherein the polishing pad has a hardness (Asker-C) of 60 to 95.

10. The polishing pad according to claim 9, wherein a support layer, having a lower hardness than the polishing pad, is provided on the reverse surface of the polishing pad from the polishing surface.

11. The polishing pad according to claim 10, wherein communication grooves are formed in the support layer.

12. The polishing pad according to claim 1, wherein at least part of the polishing surface has conducting properties.

13. A polishing apparatus, comprising:

a polishing table having a polishing pad and a first electrode which is connected to one pole of a power source and whose surface is covered with the polishing pad, said polishing pad having a plurality of through-holes extending in the thickness direction and communicating with each other by communication grooves;

a top ring for holding a substrate and pressing the substrate against a polishing surface of the polishing pad;

a second electrode, connected to the other pole of the power source, for feeding electricity to the substrate;

a liquid supply section for supplying a liquid to the polishing surface of the polishing pad;

a conditioning section for conditioning the polishing surface of the polishing pad; and

a relative movement mechanical for moving the substrate held by the top ring and the polishing pad relative to each other.

14. The polishing apparatus according to claim 13, wherein the liquid supply section has a plurality of liquid supply orifices.

15. The polishing apparatus according to claim 13, wherein the liquid supply section makes either one of a linear movement, a reciprocating movement, a pivoting movement and a rotational movement or a combination of two or more movements.

16. A method for conditioning a polishing pad of a polishing apparatus for polishing and removing a metal film and/or a barrier film formed outside interconnect recesses provided in an insulating film formed on a surface of a substrate, comprising carrying out initial conditioning of the polishing pad in the following two steps:

the first conditioning step comprising rubbing the polishing pad with a dresser at a pressure of not more than 0.6 psi; and

the second conditioning step comprising polishing a dummy substrate with the polishing pad at a polishing pressure which is higher than a polishing pressure upon polishing of a substrate.

17. The method for conditioning a polishing pad according to claim 16, wherein the polishing pad is used in chemical mechanical polishing.

18. The method for conditioning a polishing pad according to claim 16, wherein the polishing pad is used in electrochemical mechanical polishing.

19. The method for conditioning a polishing pad according to claim 16, wherein the polishing pressure of the polishing pad upon polishing of a substrate is not more than 1.5 psi.

20. The method for conditioning a polishing pad according to claim 16, wherein during polishing of a substrate or during an interval between polishing operations, the polishing pad is further conditioned by rubbing the polishing pad with a dresser at a pressure of not more than 0.6 psi.

21. The method for conditioning a polishing pad according to claim 16, wherein the first conditioning of the polishing pad with the dresser is carried out at a dressing speed of not more than 50 μm/h.

22. A polishing apparatus, comprising:

a polishing table having a first electrode connected to one pole of a power source and holding a polishing pad having a polishing surface of a larger size than a surface to be polished of a substrate;

a top ring for holding the substrate and pressing the substrate against the polishing surface of the polishing pad at a pressure of not more than 1 psi;

a second electrode including at least one electrode member, connected to the other pole of the power source, which is to make contact with a conductive film of the substrate, held by the top ring and being pressed against the polishing surface of the polishing pad, to feed electricity to the conductive film, and a supporting base for floatingly supporting the electrode member by a floating mechanism;

a relative movement mechanism for moving the substrate held by the top ring and the polishing pad relative to each other.

23. The polishing apparatus according to claim 22, wherein the electrode member is supported by an electrode base.

24. The polishing apparatus according to claim 22, wherein the floating mechanism is adapted to floatingly support the electrode member by the fluid pressure of a fluid which has been filled into a pressure chamber formed between the electrode member and the supporting base and surrounded by an elastic membrane.

25. The polishing apparatus according to claim 24, wherein the floating mechanism is adapted to supply the fluid at a predetermined pressure to the pressure chamber.

26. The polishing apparatus according to claim 22, wherein the second electrode is provided with a stopper for limiting the movement of the electrode member in a direction away from the supporting base and in a direction parallel to the supporting base.

27. A polishing method comprising:

applying a voltage between a first electrode, connected to one pole of a power source and disposed in a polishing table, and a conductive film, formed on a surface of a substrate, to which electricity is fed from an electrode member connected to the other pole of the power source and supported floatingly; and

polishing the conductive film by rubbing it with a polishing surface of a polishing pad mounted to the polishing table while filling the space between the first electrode and the conductive film of the substrate with a liquid.

28. A dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein first brush bristles and second brush bristles having lower rigidity than the first brush bristles are implanted in the dressing surface.

29. The dresser according to claim 28, wherein the second brush bristles are longer than the first brush bristles.

30. The dresser according to claim 28, wherein one of the first brush bristles and the second brush bristles are arranged in a concentric pattern, a lattice pattern, a radial pattern or a spot-like pattern, or a combination thereof, with the other brush bristles in the background.

31. A dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein first brush bristles and second brush bristles, both having the same rigidity but having different lengths, are implanted in the dressing surface.

32. The dresser according to claim 31, wherein one of the first brush bristles and the second brush bristles are arranged in a concentric pattern, a lattice pattern, a radial pattern or a spot-like pattern, or a combination thereof, with the other brush bristles in the background.

33. A dresser having a dressing surface which is to face a polishing surface of a polishing pad and to make sliding contact with the polishing surface for dressing of the polishing surface, wherein the dressing surface comprises a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher, and a brush dressing section provided with brush bristles.

34. The dresser according to claim 33, wherein the diamond dressing section is disposed circumferentially outside the brush dressing section.

35. A polishing apparatus, comprising;

a polishing table having a first electrode connected to one pole of a power source, and a polishing pad covering a surface of the first electrode;

a dresser having first brush bristles and second brush bristles having lower rigidity than the first brush bristles, for dressing the polishing surface of the polishing pad by bringing the brush bristles into sliding contact with the polishing surface; and

36. A polishing apparatus, comprising:

a dresser having first brush bristles and second brush bristles, both having the same rigidity but having different lengths, for dressing the polishing surface of the polishing pad by bringing the brush bristles into sliding contact with the polishing surface; and

37. A polishing apparatus, comprising:

a dresser having a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher and a brush dressing section provided with brush bristles, for dressing the polishing surface of the polishing pad by bringing the diamond dressing section and the brush dressing section into sliding contact with the polishing surface; and

38. A method for dressing a polishing pad comprising:

carrying out dressing of a polishing surface of a new polishing pad, at the start-up of a polishing apparatus having the new polishing pad, by bringing a dresser, having a diamond dressing section provided with diamond abrasive grains having a grain count of #100 or higher and a brush dressing section provided with brush bristles, into sliding contact with the polishing surface; and

carrying out dressing of the polishing surface of the polishing pad, during polishing of a substrate or during an interval between polishing operations, by bringing a dresser, having first brush bristles and second brush bristles having lower rigidity than the first brush bristles, into sliding contact with the polishing surface.