US20070158202A1

US20070158202A1 - Plating apparatus and method for controlling plating solution

Info

Publication number: US20070158202A1
Application number: US11/488,150
Authority: US
Inventors: Mizuki Nagai; Masao Hodai; Hiroyuki Kanda; Tsutomu Nakada; Takashi Kawakami
Original assignee: Individual
Current assignee: Ebara Corp
Priority date: 2005-07-19
Filing date: 2006-07-18
Publication date: 2007-07-12
Also published as: JP2007051362A

Abstract

A plating apparatus can keep concentrations of components of a plating solution constant over a long period of time and can stably form a plated film having a more uniform thickness on a surface of a substrate while minimizing an amount of the plating solution used. The plating apparatus includes a plating cell for carrying out electroplating of a surface of a substrate with a space between the surface of the substrate, serving as a cathode, and an insoluble anode filled with a plating solution, a plating solution circulation system for supplying the plating solution to the plating cell and recovering the plating solution in a circulatory manner, and a plating solution component replenishment system for supplying a replenisher solution, containing a component of the plating solution in a higher concentration than that in the plating solution, to the plating solution which circulates in the plating solution circulation system, thereby maintaining the concentration of the component in the plating solution within a predetermined range.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a plating apparatus and a method for controlling a plating solution, and more particularly to a plating apparatus useful for filling fine interconnect recesses (circuit pattern) formed in a surface of a substrate, such as a semiconductor wafer, with a metal (interconnect material), such as copper, to form interconnects, and also to a method for controlling a plating solution, which is suited for controlling the components of a plating solution for use in the plating apparatus.
2. Description of the Related Art
In recent years, as the processing speed and integration of a semiconductor chip becomes higher, there has been a growing tendency to replace aluminum or aluminum alloy with copper (Cu) having a low electric conductivity and a high electromigration resistance as metallic materials for forming interconnect circuits on the substrate such as semiconductor wafer. Copper interconnects are generally formed by filling copper into fine interconnect recesses formed in the surface of the substrate. There are known various techniques for forming such copper interconnects, including CVD, sputtering, and plating. Plating is generally used.
FIGS. 1A through 1C illustrate, in a sequence of process steps, an example of forming such a substrate having copper interconnects. First, as shown in FIG. 1A, an insulating film 2, such as an oxide film of SiO₂or a film of low-k material, is deposited on a conductive layer 1 a on a semiconductor base 1 on which semiconductor devices are formed. Contact holes 3 and trenches 4 are formed in the insulating film 2 by performing a lithography/etching technique so as to provide interconnect recesses. Thereafter, a barrier layer 5 of TaN, TiN, or the like is formed on the insulating film 2, and a seed layer 7 as an electric supply layer for electroplating is formed on the barrier layer 5 by sputtering, CVD, or the like.
Then, as shown in FIG. 1B, copper plating is performed onto a surface of the seed layer 7 of the substrate W to fill the contact holes 3 and the trenches 4 with copper and, at the same time, deposit a copper film 6 on the insulating film 2. Thereafter, the copper film 6, the seed layer 7 and the barrier layer 5 on the insulating film 2 are removed by chemical mechanical polishing (CMP) so as to make the surface of the copper film 6 filled in the contact holes 3 and the trenches 4, and the surface of the insulating film 2 lie substantially on the same plane. Interconnects composed of the copper film 6 are thus formed in the insulating film 2, as shown in FIG. 1C.
In a plating processing, as described above, a plating solution is generally used which contains three organic additives, i.e., a reaction accelerator for accelerating a plating reaction, a reaction suppressor for suppressing a plating reaction and a leveler for leveling a surface of a plated film, in addition to a salt of copper, the object metal, a supporting electrolyte, a halogen ion, such as a chlorine ion, which functions, for example, to keep an additive retained on a surface of a substrate, and water.
With the recent movement toward smaller-sized chips, printed wiring or LSI interconnects in semiconductor devices are becoming finer. Electroplating of such a fine structure necessitates enhanced embedding of a plated film in fine recesses. In order to carry out such electroplating, it is necessary to keep the concentrations of the components (a metal ion, a supporting electrolyte, a halogen ion and various additives) of a plating solution constant in the plating apparatus used over a long period of time, including the time of plating operation.
In an electroplating apparatus is generally used for an anode a metal which generates the same metal ion as that contained in a plating solution. For example, in an electroplating apparatus which uses a plating solution mainly comprising copper sulfate and sulfuric acid, and thus containing copper ions therein, phosphorus-containing copper containing a small amount of phosphorus is used for an anode. When electroplating is carried out by an electroplating apparatus that employs such an anode, the metal of the anode, for example copper, gradually dissolves in a plating solution, so that the anode gradually decreases while changing its shape. As the shape of the anode changes, variation in a thickness of a plated film formed on the cathode side becomes larger. It is therefore necessary to periodically replace the anode. Further, in the case of an anode of phosphorus-containing copper, a black sludge, called black film, is formed on a surface of the anode. The black film can adversely affect a plated film formed on the cathode side, causing a defect, e.g., in interconnects formed in interconnect recesses formed in a substrate.
An electroplating apparatus has therefore been developed which uses an insoluble anode, for example, comprising a titanium base coated with iridium oxide or the like, and performs plating of a surface of a substrate by feeding electricity between the insoluble anode and the substrate surface, serving as a cathode, while filling the space between them with a plating solution. Unlike a phosphorus-containing copper anode, an insoluble anode is free from the formation, on its surface, of a black sludge called a black film, and does not dissolve in a plating solution during plating. An insoluble anode thus has the advantage of no need for its replacement, involving less time and effort for its maintenance and management.
An automatic analysis means has recently been developed which automatically analyzes the concentration of an additive contained in a plating solution by using an electrochemical method (CVS: Cyclic Voltammetry Stripping). It is a conventional practice to analyze the concentration of an additive in a plating solution by using an automatic analysis means and, based on the analytical results, replenish the plating solution with a shortage of the component, thereby keeping the concentration of the additive in the plating solution constant.

SUMMARY OF THE INVENTION

The amount of plating solution necessary for one plating operation is generally small with an electroplating apparatus that holds a substrate in a face-up manner, i.e., with the front surface (surface to be plated) facing upwardly. A so-called one-pass (throwaway) method, in which a plating solution is thrown away after each plating operation, is therefore employed. The one-pass method, however, involves the use of a large amount of plating solution, leading to a high running cost.
It may therefore be considered to employ a so-called circulation method in which a plating solution is recovered and reused in a circulatory manner. A plating solution circulation/recovery system adapted for such a circulation method is generally provided with a circulation tank for circulating a plating solution while recovering the plating solution after use in plating, and is designed to supply a predetermined amount of the plating solution, which has been recovered in the circulation tank, to a surface (surface to be plated) of a substrate to carry out plating of the substrate surface, and recover the plating solution, remaining on the plated surface after plating, in the circulation tank.
In order to form a good plated film stably on a surface of a substrate, it is required to keep the concentrations of the components of a plating solution constant over a long period of time, including the time of plating operation. In a plating apparatus that uses an insoluble anode, the concentrations of the components of a plating solution are known to change gradually due to consumption of a metal, such as copper, decomposition of an additive, generation of hydrogen ion, etc. with the progress of plating. Thus, when recovering a plating solution after plating in a circulation tank and reusing the plating solution, the concentrations of the components of the plating solution recovered in the circulation tank change gradually. Accordingly, in order to keep the concentration of each component of the plating solution constant over a long period of time, including the time of plating operation, it is necessary to appropriately replenish the plating solution with each component.
Replenishment of the intended metal ion in a plating apparatus that uses an insoluble anode is generally practiced by putting a powdery metal salt into a circulation tank, or by dissolving metal flakes in a separate tank before replenishing the metal ion. The supply of a powdery metal salt into a plating solution, however, increases fine particles in the plating solution, and there is a fear that the increased fine particles may cause a defect in the plated surface of a substrate. On the other hand, the method of dissolving metal flakes in a separate tank before replenishing the metal ion necessitates a complicated apparatus construction with an increased apparatus cost.
With respect to the above-described method of analyzing the concentration of an additive in a plating solution by using an automatic analysis means and, based on the analytical results, replenishing the plating solution with a shortage of the additive, thereby keeping the concentration of the additive in the plating solution constant, such an automatic analysis means generally needs a considerable time for measurement. Thus, a plating solution will be replenished with an additive after elapse of a considerable time. Further, the amount of an additive to be replenished needs to be varied depending on the plating conditions, such as a large amount when forming a thick plated film and a small amount when forming a thin plated film. There is thus a large change in the concentration of an additive in a plating solution before and after replenishment of the plating solution with the additive, and the change can vary largely depending on the plating conditions.
The present invention has been made in view of the above situations. It is therefore an object of the present invention to provide a plating apparatus which can keep the concentrations of the components of a plating solution constant over a long period of time and can stably form a plated film having a more uniform thickness on a surface of a substrate while minimizing the amount of the plating solution used, and a method for controlling a plating solution for use in the plating apparatus.
The present invention provides a plating apparatus including: a plating cell for carrying out electroplating of a surface of a substrate with a space between the surface of the substrate, serving as a cathode, and an insoluble anode filled with a plating solution; a plating solution circulation system for supplying the plating solution to the plating cell and recovering the plating solution in a circulatory manner; and a plating solution component replenishment system for supplying a replenisher solution, containing a component of the plating solution in a higher concentration than that in the plating solution, to the plating solution which circulates in the plating solution circulation system, thereby maintaining the concentration of the component in the plating solution within a predetermined range.
The amount of the plating solution used can be minimized by recovering and reusing the plating solution in a circulatory manner. Further, the use of an insoluble anode can eliminate the need for anode replacement, thus facilitating the maintenance and management of the anode. In addition, by using an insoluble anode and also by maintaining the concentration of a component of a plating solution, which concentration will change with circulation and reuse of the plating solution, within a predetermined range by replenishing the plating solution with a replenisher solution containing the component in a higher concentration than that in the plating solution, it becomes possible to prevent an increase of fine particles in the plating solution in association with the replenishment of the component of the plating solution and to avoid complication of the apparatus.
Preferably, the plating apparatus further comprises a plating solution discharge system for discharging a predetermined amount of the plating solution from the plating solution circulation system.
By discharging a predetermined amount of plating solution from the plating solution circulation system, the amount of the plating solution in the plating solution circulation system can be regulated so that the necessary amount of a replenisher solution for maintaining the concentration of a component of the plating solution within a predetermined range is secured, for example.
In a preferred aspect of the present invention, the plating solution circulation system includes a plating solution buffer tank for recovering the plating solution after its use in plating in the plating cell, a plating solution adjustment tank, connected to the plating solution buffer tank, for replenishing the plating solution with the replenisher solution, and a plating solution supply tank, connected to the plating solution adjustment tank, for storing the plating solution which has been adjusted in the plating solution adjustment tank and supplying the plating solution to the plating cell.
By sending a plating solution after its use in plating to the plating solution adjustment tank after recovering the plating solution in the plating solution buffer tank, replenishing the plating solution in the plating solution adjustment tank with a replenisher solution to adjust the concentration of a component of the plating solution, storing the plating solution containing the component in the adjusted concentration in the plating solution supply tank, and then supplying the plating solution to the plating cell for plating, it becomes possible to supply to the plating cell a plating solution having a more constant concentration of the intended component.
The component contained in the replenisher solution, supplied to the plating solution by the plating solution component replenishment system, comprises, for example, an organic additive comprising at least one of a reaction accelerator, a reaction suppressor and a leveler, a metal ion, a supporting electrolyte and a halogen ion.
For example, a plating solution for use in embedding of copper generally contains three organic additives, i.e., a reaction accelerator, a reaction suppressor and a leveler, in addition to a metal (copper) ion, a supporting electrolyte and a halogen ion. The concentrations of the components in the plating solution gradually change with the progress of plating using an insoluble anode. Thus, the concentration of each component in the plating solution can be maintained within a predetermined range by replenishing the plating solution with a replenisher solution containing the component in a higher concentration than that in the plating solution.
The replenishment quantity of the replenisher solution is determined, for example, based on a cumulative quantity of electricity taken for electroplating.
In electroplating using a plating solution in a circulatory manner, a change in the quantity of a component in the plating solution with the progress of plating (i.e., consumption of the component) is generally determined by the quantity of electricity that has been supplied for plating. Thus, the replenishment quantity of a component of the plating solution can be calculated from a cumulative quantity of electricity taken for electroplating. The calculation of the replenishment quantity of, e.g., an additive in the plating solution can be made in a shorter time than the analysis time of an automatic analysis means. This makes it possible to replenish the additive with a smaller change in the concentration of the additive in the plating solution during determination of the replenishment quantity.
Preferably, the replenisher solution contains one component of the plating solution in a higher concentration than that in the plating solution, and is supplied to the plating solution from a replenisher solution tank.
For example, in the case of maintaining the concentrations of six components, a metal ion, a supporting electrolyte, a halogen ion, a reaction accelerator, a reaction suppressor and a leveler, in a plating solution respectively within a predetermined range, the concentration of each component in the plating solution can be controlled individually by individually storing replenisher solutions each containing only one of the six components and supplying the replenisher solutions to the plating solution.
In a preferred aspect of the present invention, the plating cell has a high-resistance structure disposed between the insoluble anode and the substrate which serves as a cathode.
By disposing the high-resistance structure, which has a higher resistance than the resistance of a plating solution, between the insoluble anode and the substrate which serves as a cathode, it becomes possible to make the influence of the resistance of, e.g., a seed layer, formed in the surface (surface to be plated) of the substrate, as small as negligible, thereby reducing an in-plane difference in the current density due to the electric resistance of the substrate surface and improving the in-plane uniformity of a plated film.
The replenishment quantity of the replenisher solution may also be determined by using a consumption coefficient determined by the current density of electric current applied to carry out plating in the plating cell and by the time of application of the electric current.
There are some additives, for use in a plating solution, whose consumption will differ by a difference in the current density of electric current applied during plating and by a difference in the time of application of the electric current. Thus, if the replenishment quantity is calculated only on the basis of the cumulative quantity of electricity, a difference will be produced between the calculated replenishment quantity and the actual consumption. The consumption of such an additive can be determined more precisely by using a consumption coefficient as determined by the current density of electric current applied to carry out plating and by the time of application of the electric current.
In a preferred aspect of the present invention, the plating cell is divided into an anode chamber and a cathode side area by the high-resistance structure disposed between the insoluble anode and the substrate which serves as a cathode, and the replenishment quantity of the replenisher solution is determined individually for the anode chamber and for the cathode side area, and the respective values obtained are summed up.
In the case where the plating cell is divided into the anode chamber and the cathode side area, an additive, which is contained in a plating solution and whose consumption is affected by the current density, is consumed differently in the anode chamber and in the cathode side area. Therefore, the consumption of the additive can be determined more precisely by individually determining the consumptions in the anode chamber and in the cathode side area, and summing up the determined consumptions.
The component of the plating solution, contained in the replenisher solution whose replenishment quantity is determined by using the consumption coefficient determined by the current density and the time of application of the electric current, is, for example, a reaction accelerator.
The concentration in a plating solution of a reaction accelerator, whose consumption is affected by the current density, can thus be controlled more strictly. This enables uniform copper plating or the like, thereby producing highly-reliable copper interconnects or the like.
In a preferred aspect of the present invention, the plating solution adjustment tank has a liquid level sensor for measuring a liquid level of the plating solution in the plating solution adjustment tank.
By measuring the liquid level of the plating solution stored in the plating solution adjustment tank, the amount of the plating solution stored in the plating solution adjustment tank can be maintained in a certain range.
Preferably, the plating apparatus further comprises a plating solution analyzer for sampling the plating solution to be supplied to the plating cell, and analyzing the concentrations of the components of the plating solution.
By sampling the plating solution at specified time intervals and analyzing the concentrations of the components in the plating solution by the plating solution analyzer, and replenishing the plating solution with deficient components, it becomes possible to deal with a case in which the consumptions of the components of the plating solution become imbalanced, e.g., due to a change in the plating conditions with time.
The present invention provides a method for controlling a plating solution comprising replenishing a plating solution, to be used in plating, with a replenisher solution containing a component of the plating solution in a higher concentration than that in the plating solution, thereby maintaining the concentration of the component in the plating solution within a predetermined range
The present invention provides another method for controlling a plating solution comprising recovering a plating solution, which has been used in plating in a plating cell, in a plating solution buffer tank, sending the plating solution in the plating solution buffer tank to a plating solution adjustment tank, and replenishing the plating solution in the plating solution adjustment tank with a replenisher solution containing a component of the plating solution in a higher concentration than that in the plating solution, thereby maintaining the concentration of the component in the plating solution within a predetermined range, sending the plating solution in the plating solution adjustment tank to a plating solution supply tank, and supplying the plating solution in the plating solution supply tank to the plating cell.
In a preferred aspect of the present invention, a plating metal is copper, and the plating solution having a copper ion concentration of 20-60 g/Lis replenished with an aqueous solution of copper sulfate having a copper sulfate concentration of 200 g/L to saturation concentration, thereby maintaining the concentration of copper ion in the plating solution within a predetermined.
In a preferred aspect of the present invention, the plating solution contains sulfuric acid as a supporting electrolyte, and the plating solution having a sulfuric acid concentration of 10-100 g/L is replenished with sulfuric acid having a concentration of 20-98 wt %, thereby maintaining the concentration of sulfuric acid in the plating solution within a predetermined range.
In a preferred aspect of the present invention, the plating solution contains chlorine as a halogen ion, and the plating solution having a chlorine concentration of 30-90 mg/L is replenished with hydrochloric acid having a concentration of 1-36 wt %, thereby maintaining the concentration of chlorine in the plating solution within a predetermined range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A through 1C are diagrams illustrating, in a sequence of steps, an example for forming copper interconnects by plating process;
FIG. 2 is an overall plan view of a substrate processing apparatus provided with a plating apparatus according an embodiment of the present invention;
FIG. 3 is a plan view of a plating cell of the plating apparatus shown in FIG. 2;
FIG. 4 is an enlarged sectional view of a substrate holder and a cathode portion of the plating cell of the plating apparatus shown in FIG. 2;
FIG. 5 is a front view of a pre-coating/recovering arm of the plating cell of the plating apparatus shown in FIG. 2;
FIG. 6 is a plan view of the substrate holder of the plating cell of the plating apparatus shown in FIG. 2;
FIG. 7 is a cross-sectional view taken along line B-B of FIG. 6;
FIG. 8 is a cross-sectional view taken along line C-C of FIG. 6;
FIG. 9 is a plan view of a cathode portion of the plating cell of the plating apparatus shown in FIG. 2;
FIG. 10 is a cross-sectional view taken along line D-D of FIG. 9;
FIG. 11 is a plan view of an electrode arm section of the plating cell of the plating apparatus shown in FIG. 2;
FIG. 12 is a cross-sectional diagram schematically showing an electrode head and the substrate holder of the plating cell of the plating apparatus shown in FIG. 2 upon electroplating;
FIG. 13 is a diagram schematically showing the plating apparatus shown in FIG. 2 upon plating;
FIG. 14 is a diagram schematically showing the plating apparatus shown in FIG. 2 upon replacement of a plating solution in the electrode head;
FIG. 15 is a diagram schematically showing a plating apparatus according to another embodiment of the present invention upon plating;
FIG. 16 is a diagram schematically showing the plating apparatus according to another embodiment of the present invention upon replacement of a plating solution in an electrode head;
FIG. 17 is a diagram schematically showing a plating apparatus according to yet another embodiment of the present invention upon plating;
FIG. 18 is a diagram schematically showing the plating apparatus according to yet another embodiment of the present invention upon replacement of a plating solution in an electrode head;
FIG. 19 is a graph showing a change in the consumption rate (consumption coefficient) of a reaction accelerator with current density and with the time of application of electric current;
FIGS. 20A and 20B are graphs showing the relationship between the number of wafers processed and the concentrations of the components of a plating solution in Example 2;
FIGS. 21A and 21B are graphs showing the relationship between the number of wafers processed and the concentrations of the components of a plating solution in Example 3; and
FIG. 22 is a graph showing the relationship between the number of wafers processed and the concentration of a reaction accelerator in a plating solution in Example 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the drawings. The following embodiments show examples in which copper is embedded in fine interconnect recesses formed in a surface of a semiconductor substrate so as to form interconnects composed of copper.
FIG. 2 is a plan view showing a substrate processing apparatus incorporating a plating apparatus according to an embodiment of the present invention. As shown in FIG. 2, this substrate processing apparatus houses therein two loading/unloading units 10 for housing a plurality of substrates W therein, two plating cells 12 for performing plating process, a transfer robot 14 for transferring substrates W between the loading/unloading units 10 and the plating cells 12, and plating solution supply facility 18, having a plating solution adjustment tank 16, for supplying a plating solution to the plating cells 12.
The plating cell 12, as shown in FIG. 3, is provided with a substrate processing section 20 for performing plating process and processing incidental thereto, and a plating solution tray 22 for storing a plating solution is disposed adjacent to the substrate processing section 20. There is also provided an electrode arm portion 30 having an electrode head 28 which is held at the front end of a swing arm 26 swingable about a rotating shaft 24 and which is swung between the substrate processing section 20 and the plating solution tray 22. Furthermore, a pre-coating/recovering arm 32, and fixed nozzles 34 for ejecting pure water or a chemical liquid such as ion water, and also a gas or the like toward a substrate are disposed laterally of the substrate processing section 20. In this embodiment, three of the fixed nozzles 34 are disposed, and one of them is used for supplying pure water.
The substrate processing section 20, as shown in FIG. 4, has a substrate holder 36 for holding a substrate W with its surface (surface to be plated) facing upwardly, and a cathode portion 38 located above the substrate holder 36 so as to surround a peripheral portion of the substrate holder 36. Further, a substantially cylindrical bottomed cup 40 surrounding the periphery of the substrate holder 36, for preventing scatter of various chemical liquids used during processing, is provided so as to be vertically movable by an air cylinder (not shown).
The substrate holder 36 is adapted to be raised and lowered by the air cylinder 44 to and from a lower substrate transfer position A, an upper plating position B, and a pretreatment/cleaning position C that is intermediate positions A and B. The substrate holder 36 is also adapted to rotate at an arbitrary acceleration and an arbitrary velocity, integrally with the cathode portion 38 by a rotating motor and a belt (not shown). Substrate carry-in and carry-out openings (not shown) are provided in confrontation with substrate transfer position A in a side panel of the plating cell 12 facing the transfer robot 14. When the substrate holder 36 is raised to plating position B, a sealing member 90 and cathode electrodes 88 (to be described below) of the cathode portion 38 are brought into contact with the peripheral portion of the substrate W held by the substrate holder 36. On the other hand, the cup 40 has an upper end located below the substrate carry-in and carry-out openings, and when the cup 40 ascends, the upper end of the cup 40 reaches a position above the cathode portion 38 closing the substrate carry-in and carry-out openings, as shown by imaginary lines in FIG. 4.
The plating solution tray 22 serves to replace part of the plating solution in the electrode head 28 with a new plating solution while positioning the electrode head 28 in the plating solution tray 22, when plating has not been performed. The plating solution tray 22 is set at a size in which the high-resistance structure 110 can be accommodated, and the plating solution tray 22 has a plating solution supply port and a plating solution drainage port (not shown). A photo-sensor, for measuring a liquid level of the plating solution, is attached to the plating solution tray 22.
The electrode arm portion 30 is vertically movable by a vertical movement motor (not shown), which is a servomotor, and a ball screw, and swingable between the plating solution tray 22 and the substrate processing section 20 by a swing motor (not shown) in this example. A pneumatic actuator may be used instead of the motor.
As shown in FIG. 5, the pre-coating/recovering arm 32 is coupled to an upper end of a vertical support shaft 58. The pre-coating/recovering arm 32 is swingable by a rotary actuator 60 and is also vertically moveable by an air cylinder (not shown) The pre-coating/recovering arm 32 supports a pre-coating nozzle 64 for discharging a pre-coating liquid, on its free end side, and a plating solution recovery nozzle 66 for recovering the plating solution, on a portion closer to its proximal end. The pre-coating nozzle 64 is connected to a syringe that is actuatable by an air cylinder, for example, for intermittently discharging a pre-coating liquid from the pre-coating nozzle 64. The plating solution recovery nozzle 66 is connected to a pump 134 (see FIG. 13) provided in a plating solution recovery pipe 130 to draw the plating solution on the substrate from the plating solution recovery nozzle 66 by actuation of the pump 134.
As shown in FIGS. 6 through 8, the substrate holder 36 has a disk-shaped substrate stage 68 and six vertical support arms 70 disposed at spaced intervals on the circumferential edge of the substrate stage 68 for holding a substrate W in a horizontal plane on respective upper surfaces of the support arms 70. A positioning plate 72 is mounted on an upper end one of the support arms 70 for positioning the substrate by contacting the end face of the substrate. A pressing finger 74 is rotatably mounted on an upper end of the support arm 70, which is positioned opposite to the support arm 70 having the positioning plate 72, for abutting against an end face of the substrate W and pressing the substrate W to the positioning plate 72 when rotated. Chucking fingers 76 are rotatably mounted on upper ends of the remaining four support arms 70 for pressing the substrate W downwardly and gripping the circumferential edge of the substrate W.
The pressing finger 74 and the chucking fingers 76 have respective lower ends coupled to upper ends of pressing pins 80 that are normally urged to move downwardly by coil springs 78. When the pressing pins 80 are moved downwardly, the pressing finger 74 and the chucking fingers 76 are rotated radially inwardly into a closed position. A support plate 82 is disposed below the substrate stage 68 for engaging lower ends of the opening pins 80 and pushing them upwardly.
When the substrate holder 36 is located in substrate transfer position A shown in FIG. 4, the pressing pins 80 are engaged and pushed upwardly by the support plate 82, so that the pressing finger 74 and the chucking fingers 76 rotate outwardly and open. When the substrate stage 68 is elevated, the opening pins 80 are lowered under the resiliency of the coil springs 78, so that the pressing finger 74 and the chucking fingers 76 rotate inwardly and close.
As shown in FIGS. 9 and 10, the cathode portion 38 comprises an annular frame 86 fixed to upper ends of vertical support columns 84 mounted on the peripheral edge of the support plate 82 (see FIG. 8), a plurality of, six in this embodiment, cathode electrodes 88 attached to a lower surface of the annular frame 86 and projecting inwardly, and an annular sealing member 90 mounted on an upper surface of the annular frame 86 in covering relation to upper surfaces of the cathode electrodes 88. The sealing member 90 is adapted to have an inner peripheral edge portion inclined inwardly downwardly and progressively thin-walled, and to have an inner peripheral end suspending downwardly.
When the substrate holder 36 has ascended to plating position B, as shown FIG. 4, the cathode electrodes 88 are pressed against the peripheral portion of the substrate W held by the substrate holder 36 for thereby allowing electric current to pass through the substrate W. At the same time, an inner peripheral end portion of the sealing member 90 is brought into contact with an upper surface of the peripheral portion of the substrate W under pressure to seal its contact portion in a watertight manner. As a result, the plating solution supplied onto the upper surface (surface to be plated) of the substrate W is prevented from seeping from the end portion of the substrate W, and the plating solution is prevented from contaminating the cathode electrodes 88.
In this embodiment, the cathode portion 38 is vertically immovable, but rotatable in a body with the substrate holder 36. However, the cathode portion 38 may be arranged such that it is vertically movable and the sealing member 90 is pressed against the surface to be plated of the substrate W when the cathode portion 38 is lowered.
As shown in FIGS. 11 and 12, the electrode head 28 of the electrode arm section 30 includes a electrode holder 94 which is coupled via a ball bearing 92 to the free end of the swing arm 26, and a high-resistance structure 110 of porous material, which is disposed such that it closes the bottom opening of the electrode holder 94. The electrode holder 94 has a downward-open and cup-like bottomed configuration having at its lower inside an recess portion 94 a, while the high-resistance structure 110 has at its top a flange portion 110 a. The flange portion 110 a is inserted into the recess portion 94 a. Thus, the plating cell 12 is divided into an anode chamber 100 and a cathode side area 101 in the electrode holder 94 by the high-resistance structure 110.
The high-resistance structure 110 is composed of porous ceramics such as alumina, SiC, mullite, zirconia, titania or cordierite, or a hard porous material such as a sintered compact of polypropylene or polyethylene, or a composite material comprising these materials. The high-resistance structure 110 may be composed of a woven fabric or a non-woven fabric. In case of the alumina-based ceramics, for example, the ceramics with a pore diameter of 30 to 200 μm is used. In case of the SiC, SiC with a pore diameter of not more than 30 μm, a porosity of 20 to 95%, and a thickness of about 1 to 20 mm, preferably 5 to 20 mm, more preferably 8 to 15 mm, issued. The high-resistance structure 110, in this embodiment, is constituted of porous ceramics of alumina having a porosity of 30%, and an average pore diameter of 100 μm. The porous ceramic plate per se is an insulator, but the high resistance structure is constituted to have lower electric conductivity than that of the plating solution by causing the plating solution to enter its interior complicatedly and follow a considerably long path in the thickness direction.
The high-resistance structure 110, which has the high resistance, is thus disposed between the anode chamber 100 and the cathode side area 101. Hence, the influence of the resistance of the seed layer 7 (see FIG. 1) becomes a negligible degree. Consequently, the difference in current density over the surface of the substrate due to electrical resistance on the surface of the substrate W becomes small, and the uniformity of the plated film over the surface of the substrate can be improved.
In the anode chamber 100 and located above the high-resistance structure 110 is disposed an insoluble anode 98 having a large number of vertically-extending through-holes 98 a therein. The electrode holder 94 has a plating solution discharge outlet 103 for discharging by suction a plating solution in the anode chamber 100. The plating solution discharge outlet 103 is connected to a plating solution discharge pipe 106 connecting with a waste liquid tank 160. Further, a plating solution supply inlet 104, positioned beside the insoluble anode 98 and the high-resistance structure 110 and vertically penetrating the peripheral wall of the electrode holder 94, is provided within the peripheral wall of the electrode holder 94. The plating solution supply inlet 104 is connected to a plating solution supply pipe 102 extending from the plating solution adjustment tank 16.
The plating solution supply inlet 104 is to supply a plating solution from the side of the insoluble anode 98 and the high-resistance structure 110 into the cathode side area 101 between the substrate W and the high-resistance structure 110 when the substrate holder 36 is in the plating position B (see FIG. 4) and the electrode head 28 is in such a lowered position that the distance between the substrate W held by the substrate holder 36 and the high-resistance structure 110 is, for example, about 0.5 to 3 mm. The lower-end nozzle portion of the plating solution supply inlet 104 opens to the cathode side area 101 between the sealing member 90 and the high-resistance structure 110. A rubber shielding ring 112 for electrical shielding is attached to the circumferential surface of the high-resistance structure 110.
The plating solution, supplied from the plating solution supply inlet 104, flows in one direction along the surface of the substrate W, and by the flow of the plating solution, air in the cathode side area 101 between the substrate W and the high-resistance structure 110 is forced out of the area. The cathode side area 101 defined by the substrate W and the sealing member 90 is thus filled with the fresh, composition-adjusted plating solution supplied from the plating solution supply inlet 104, and the plating solution is stored in the cathode side area 101 defined by the substrate W and the sealing member 90.
The insoluble anode 98 is composed of an insoluble metal, such as platinum, titanium, etc. or a material comprising a base of such a metal and a coating of iridium oxide. The insoluble anode 98 is free from the formation on its surface of a black sludge called black film and will not dissolve in a plating solution during plating. The use of the insoluble anode 98 can thus eliminate the need for anode replacement. For reasons of easy passage of plating solution, etc., the insoluble anode 98 may have a net-like structure.
As shown in FIG. 13, the plating solution supply facility 18 includes a plating solution supply pipe 102 extending from the plating solution adjustment tank 16 and connected to the plating solution supply inlet 104 (see FIG. 12), and a plating solution recovery pipe 130 extending from the plating solution adjustment tank 16 and connected to the plating solution recovery nozzle 66 (see FIG. 5). The plating solution supply pipe 102 and the plating solution recovery pipe 130 are provided with pumps 132, 134, respectively. A plating solution circulation system 136 is thus constructed. In particular, the pump 132 provided in the plating solution supply pipe 102 is driven to supply a predetermined amount of the plating solution in the plating solution adjustment tank 16 to that area of the surface (surface to be plated) of the substrate W, held by the substrate holder 36, which is surrounded by the sealing member 90. After the completion of plating, the pump 134 provided in the plating solution recovery pipe 130 is driven to suck the plating solution, remaining on the surface of the substrate W, by the plating solution recovery nozzle 66 and recover the plating solution in the plating solution adjustment tank 16 for reuse of the plating solution.
The plating solution supply facility 18 also includes a plating solution component replenishment system 138 for supplying replenisher solutions, each containing a component of the plating solution in a higher concentration than that in the plating solution, to the plating solution in the plating solution adjustment tank 16 so as to maintain the concentration of the component in the plating solution within a predetermined range. In particular, the plating solution in this embodiment contains three organic additives, a reaction accelerator, a reaction suppressor and a leveler, in addition to copper ions in a concentration of 20-60 g/L, sulfuric acid as a supporting electrolyte in a concentration of 10-100 g/L, and chlorine as a halogen ion in a concentration of 30-90 mg/L.
The replenishment system 138 includes a replenisher solution tank 140 storing an aqueous solution of copper sulfate having a copper sulfate concentration of 200 g/L to saturation concentration, a replenisher solution tank 142 storing sulfuric acid having a concentration of 20-98 wt %, a replenisher solution tank 144 storing hydrochloric acid having a concentration of 1-36 wt %, a replenisher solution tank 146 storing a reaction accelerator solution of a commercial concentration, a replenisher solution tank 148 storing a reaction suppressor solution of a commercial concentration, and a replenisher solution tank 150 storing a leveler solution of a commercial concentration. The replenisher solutions are supplied from the replenisher solution tanks 140-150 to the plating solution in the plating solution adjustment tank 16, and pure water (DIW) is also supplied through a pure water replenishment pipe 152 to the plating solution, thereby maintaining the concentrations of the components of the plating solution recovered in the plating solution adjustment tank 16 each within a predetermined range before reusing the plating solution. The plating solution adjustment tank 16 is provided with a liquid level sensor 154 for measuring a liquid level of the plating solution stored therein.
The concentration of copper sulfate in the replenishing aqueous solution of copper surface is preferably in the range of 250-300 g/L, the concentration of the replenishing sulfuric acid is preferably in the range of 50-98 wt % from the viewpoint of reducing the replenishment quantity, and the concentration of the replenishing chlorine is preferably in the range of 5-20 wt % because of easier handling.
Though the plating solution used in this embodiment contains the three organic additives, a reaction accelerator, a reaction suppressor and a leveler, it is also possible to use a plating solution containing one or two of the organic additives and replenish the component(s) of the plating solution with the replenisher solution(s).
The plating solution supply facility 18 also includes a plating solution discharge system 162 for discharging the plating solution, which circulates in the plating solution circulation system 136, into the waste liquid tank 160. In particular, a branching three-way valve 164 is provided in the plating solution recovery pipe 130, and a waste liquid pipe 166, branched by the three-way valve 164, is connected to the waste liquid tank 160.
Thus, when sucking the plating solution remaining on the surface (surface to be plated) of the substrate W by the plating solution recovery nozzle 66 and recovering the plating solution in the plating solution adjustment tank 16 by driving the pump 134, provided in the plating solution recovery pipe 130, after the completion of plating, part of the plating solution is discharged through the waste liquid pipe 166 to the waste liquid tank 160.
As shown in FIG. 14, the plating solution discharge pipe 106, connected to the plating solution discharge outlet 103 (see FIG. 12), is connected to the waste liquid tank 160, and the plating solution discharge pipe 106 is provided with a pump 170. When the high-resistance structure 100 of the electrode head 28 is immersed in the plating solution in the plating solution tray 22, the pump 132 provided in the plating solution supply pipe 102 is driven to supply the plating solution in the plating solution adjustment tank 16 into the plating solution tray 22 while the pump 170 provided in the plating solution discharge pipe 106 is driven to draw the plating solution from the anode chamber 100, thereby carrying out replacement of the plating solution, with which the high-resistance structure 110 is impregnated, with a new plating solution and discharge of the old plating solution.
When carrying out plating, the cathode electrodes 88 are electrically connected to the cathode of the plating power source 114, and the insoluble anode 98 to the anode of the plating power source 114. The plating power source 114 may be one which can change the direction of electric current so that the plating apparatus has an etching function of etching a plated film.
The operation of the substrate processing apparatus incorporating the plating apparatus according to an embodiment of the present invention will now be described.
First, a substrate W to be plated is taken out from one of the loading/unloading units 10 by the transfer robot 14, and transferred, with the surface (surface to be plated) facing upwardly, through the substrate carry-in and carry-out opening defined in the side panel of a frame, into one of the plating cell 12. At this time, the substrate holder 36 is in lower substrate transfer position A. After the hand of the transfer robot 14 has reached a position directly above the substrate stage 68, the hand of the transfer robot 14 is lowered to place the substrate W on the support arms 70. The hand of the transfer robot 14 is then retracted through the substrate carry-in and carry-out opening.
After the hand of the transfer robot 14 is retracted, the cup 40 is elevated. Then, the substrate holder 36 is lifted from substrate transfer position A to pretreatment/cleaning position C. As the substrate holder 36 ascends, the substrate W placed on the support arms 70 is positioned by the positioning plate 72 and the pressing finger 74, and then reliably gripped by the chucking fingers 76. When the ascending movement of the cup 40 is completed, the substrate carry-in and carry-out opening in the side panel is closed by the cup 40, isolating the atmosphere in the side panel and the atmosphere outside of the side panel from each other.
Meanwhile, the electrode head 28 of the electrode arm portion 30 is in a normal position over the plating solution tray 22 now as shown in FIG. 14, and the high-resistance structure 110 is immersed in the plating solution in the plating solution tray 22. In this state, replacement of the plating solution, with which the high-resistance structure 110 is impregnated, with a new plating solution is carried out by supplying a plating solution into the plating solution tray 22 and discharging the plating solution in the anode chamber 100.
When the cup 4 is elevated, the pre-coating step is initiated. Specifically, the substrate holder 36 that has received the substrate W is rotated, and the pre-coating/recovering arm 32 is moved from the retracted position to a position confronting the substrate W. When the rotational speed of the substrate holder 36 reaches a preset value, the pre-coating nozzle 64 mounted on the tip end of the pre-coating/recovering arm 32 intermittently discharges a pre-coating liquid which comprises a surfactant, for example, toward the surface of the substrate W. At this time, since the substrate holder 36 is rotating, the pre-coating liquid spreads all over the surface of the substrate W. Then, the pre-coating/recovering arm 32 is returned to the retracted position, and the rotational speed of the substrate holder 36 is increased to spin the pre-coating liquid off and dry the surface of the substrate W.
After the completion of the pre-coating step, the plating step is initiated. First, the substrate holder 36 is stopped against rotation, or the rotational speed thereof is reduced to a preset rotational speed for plating. In this state, the substrate holder 36 is lifted to plating position B. Then, the peripheral portion of the substrate W is brought into contact with the cathode electrodes 88, when it is possible to pass an electric current, and at the same time, the sealing member 90 is pressed against the upper surface of the peripheral portion of the substrate W, thus sealing the peripheral portion of the substrate W in a watertight manner.
Based on a signal indicating that the pre-coating step for the loaded substrate W is completed, the electrode arm portion 30 is swung in a horizontal direction to displace the electrode head 28 from a position over the plating solution tray 22 to a position over the plating processing position. After the electrode head 28 reaches this position, the electrode head 28 is lowered toward the cathode portion 38. The electrode head is stopped when the high-resistance structure 110 does not contact with the surface of the substrate W but is held closely to the surface of the substrate W at a distance ranging from 0.1 mm to 3 mm. Next, the cathode side area 101 between the substrate W and the high-resistance structure 110 and surrounded by the sealing member 90 is filled with the plating solution by supplying a predetermined amount of plating solution from the plating solution supply pipe 102, as shown in FIG. 13.
Then, the cathode electrodes 88 are connected to the cathode of the plating power source 114 and the insoluble anode 98 is connected to the anode of the plating power source 114 to carry out plating onto the surface (surface of the seed layer 7) of the substrate W while integrating the quantity of electricity taken for plating. After the completion of plating, the plating power source 114 is disconnected from the cathode electrodes 88 and the insoluble anode 98, and the electrode arm section 30 is raised and pivoted to return the electrode head 28 to above the plating solution tray 22 and is then lowered to the normal position.
Next, the pre-coating/recovery arm 32 is moved from the retreat position to the position opposite to the substrate W and lowered. The pump 134 provided in the plating solution recovery pipe 130 is then driven to recover most of the plating solution on the substrate W from the plating solution recovery nozzle 66 into the plating solution adjustment tank 16 while discharging part of the plating solution into the waste liquid tank 160. After completion of the recovery of the plating solution, the pre-coating/recovery arm 32 is returned to the retreat position. The plated surface of the substrate W is then rinsed by spraying pure water from the fixed nozzle 34 for spraying pure water onto the center of the substrate W while rotating the substrate holder 36 at an increased speed, thereby replacing the plating solution on the surface of the substrate W with pure water. By thus carrying out rinsing of the substrate W, the cathode electrodes 88 of the cathode section 38 can be prevented from being contaminated with the plating solution due to splashing of the plating solution upon lowering of the substrate holder 36 from the plating position B.
After completion of the rinsing, the washing with water step is initiated. That is, the substrate holder 36 is lowered from plating position B to pretreatment/cleaning position C. Then, while pure water is supplied from the fixed nozzle 34 for supplying pure water, the substrate holder 36 and the cathode portion 38 are rotated to perform washing with water. At this time, the sealing member 90 and the cathode electrodes 88 can also be cleaned, simultaneously with the substrate W, by pure water directly supplied to the electrode potion 38, or pure water scattered from the surface of the substrate W.
After washing with water is completed, the drying step is initiated. That is, supply of pure water from the fixed nozzle 34 is stopped, and the rotational speed of the substrate holder 36 and the cathode portion 38 is further increased to remove pure water on the surface of the substrate W by centrifugal force and to dry the surface of the substrate W. The sealing member 90 and the cathode electrodes 88 are also dried at the same time. Upon completion of the drying, the rotation of the substrate holder 36 and the cathode portion 38 is stopped, and the substrate holder 36 is lowered to substrate transfer position A. Thus, the gripping of the substrate W by the chucking fingers 76 is released, and the substrate W is just placed on the upper surfaces of the support arms 70. At the same time, the cup 40 is also lowered.
All the steps for one substrate including the plating step, the pretreatment step accompanying to the plating step, the cleaning step, and the drying step are now finished. The transfer robot 14 inserts its hand through the substrate carry-in and carry-out opening into the position beneath the substrate W, and raises the hand to receive the plated substrate W from the substrate holder 36. Then, the transfer robot 14 returns the plated substrate W received from the substrate holder 36 to one of the loading/unloading units 10.
When the insoluble anode 98 is used and the plating solution is recovered and reused in a circulatory manner, as described above, the concentrations of the components in the plating solution recovered in the plating solution adjustment tank 16 change gradually. According to this embodiment, therefore, the replenisher solutions, each containing a component of the plating solution in a higher concentration than that in the plating solution, are supplied from the plating solution component replenishment system 138 into the plating solution adjustment tank 16 when, after having processed a plurality of substrates, a cumulative quantity of electricity taken for plating has reached to a predetermined value, for example, 50 Ah. In particular, the plating solution in the plating solution adjustment tank 16 is replenished with: an aqueous solution of copper sulfate having a copper sulfate concentration of 200 g/L to saturation concentration, supplied from the replenisher solution tank 140; sulfuric acid having a concentration of 20-98 wt %, supplied from the replenisher solution tank 142; hydrochloric acid having a concentration of 1-36 wt %, supplied from the replenisher solution tank 144; a reaction accelerator solution of a commercial concentration, supplied from the replenisher solution tank 146; a reaction suppressor solution of a commercial concentration, supplied from the replenisher solution tank 148; a leveler solution of a commercial concentration, supplied from the replenisher solution tank 150; and pure water (DIW), supplied through the pure water replenishment pipe 152. The concentrations of the components of the plating solution recovered in the plating solution adjustment tank 16 are thus maintained each within a predetermined range, and the concentration-controlled plating solution is reused in a circulatory manner.
The amount of the plating solution used can be minimized by recovering and reusing the plating solution in a circulatory manner through the plating solution circulation system 136. Further, the use of the insoluble anode 98, which needs no replacement, can facilitate the maintenance and management of the anode. In addition, by using the insoluble anode 98 and also by maintaining the concentrations of the components of the plating solution, which concentrations will change with circulation and reuse of the plating solution, each within a predetermined range by replenishing the plating solution with the replenisher solutions, each containing one of the components in a higher concentration than that in the plating solution, by the plating solution component replenishment system 138, it becomes possible to prevent an increase of fine particles in the plating solution in association with the replenishment of the components of the plating solution and to avoid complication of the apparatus.
The replenishment quantity of each replenisher solution is determined, for example, based on a cumulative quantity of electricity taken for plating. In electroplating using a plating solution in a circulatory manner, a change in the quantity of a component in the plating solution with the progress of plating is generally determined by the quantity of electricity that has been supplied for plating. Thus, on the basis of a predetermined experimental data for consumption or increase of a component, the replenishment quantity of the component of the plating solution can be calculated from a cumulative quantity of electricity taken for electroplating.
The calculation of the replenishment quantity of a component of a plating solution from a cumulative quantity of electricity can be made in a shorter time than the analysis time of an automatic analysis means. This makes it possible to replenish, e.g., an additive with a smaller change in the concentration of the additive in the plating solution during determination of the replenishment quantity.
The plating solution adjustment tank 16 is provided with a liquid level sensor 154 for measuring a liquid level of the plating solution stored in the tank 16, so that the plating solution in a constant amount can be stored in the plating solution adjustment tank 16 by stopping supply of the replenisher solutions and pure water when the liquid level of the plating solution in the plating solution adjustment tank 16 has come up to a predetermined position by the supply of the replenisher solutions and pure water. When the plating solution is recovered in the plating solution adjustment tank 16, part of the plating solution is discharged into the waste liquid tank 160 by the plating solution discharge system 162. The amount of the plating solution recovered and reused in the plating solution circulation system 136 can thus be adjusted, making it possible to supply the replenisher solutions and pure water in amounts sufficient for bringing the concentrations of the components in the plating solution in the plating solution adjustment tank 16 each into a predetermined range.
FIGS. 15 and 16 schematically show a plating apparatus according to another embodiment of the present invention. This plating apparatus differs from the above-described plating apparatus in the following respects: The plating solution circulation system 136 includes a plating solution buffer tank 200 and a plating solution supply tank 202 respectively located on the upstream side and on the downstream side of the plating solution adjustment tank 16. The plating solution recovery pipe 130 extending from the plating solution recovery nozzle 66 is connected to the plating solution buffer tank 200, while the plating solution supply pipe 102 for supplying a plating solution through the plating solution supply inlet 114 to the plating cell 12 is connected to the plating solution supply tank 202. The plating solution buffer tank 200 is connected to the plating solution adjustment tank 16 via a communication pipe 206 provided with a pump 204, and the plating solution adjustment tank 16 is connected to the plating solution supply tank 202 via a communication pipe 210 provided with a pump 208. To the bottom of the plating solution adjustment tank 16 is connected one end of a plating solution withdrawing pipe 214 provided with a pump 212, while the other end of the plating solution withdrawing pipe 214 is connected to the waste liquid tank 160. The plating solution discharge system 162 is thus constructed.
Further, as shown in FIG. 16, in carrying out replacement of the plating solution, with which the high-resistance structure 110 of the electrode head 28 is impregnated, with a new plating solution and discharge of the old plating solution when the high-resistance structure 110 is immersed in the plating solution in the plating solution tray 22, the plating solution can be selectively introduced into the waste liquid tank 160 and disposed of, or can be introduced into the plating solution buffer tank 200 for recovery and reuse of the plating solution, by a three-way valve 215.
The plating apparatus of this embodiment is also provided with a plating solution analyzer 216 for sampling the plating solution in the plating solution supply tank 202 and analyzing the components, and returning the sampled solution after analysis to the plating solution adjustment tank 16. Further, pure water is stored in a pure water tank 218 and supplied into the plating solution adjustment tank 16. The plating solution buffer tank 200 is provided with a liquid level sensor 220 for measuring a liquid level of the plating solution stored in the plating solution buffer tank 200.
According to this embodiment, the plating solution is recovered in the plating solution buffer tank 200 every time one substrate is processed in the plating cell 12, and the plating solution in the plating solution buffer tank 200 is sent to the plating solution adjustment tank 16 when the amount of the plating solution recovered in the plating solution buffer tank 200 has reached a predetermined amount. Part of the plating solution received by the plating solution adjustment tank 16 is discharged by the plating solution discharge system 162. Simultaneously with or after the discharge of the plating solution, as with the preceding embodiment, the replenisher solutions each containing a component of the plating solution, in a higher concentration than that in the plating solution, i.e., an aqueous solution of copper sulfate, sulfuric acid, hydrochloric acid, a reaction accelerator solution, a reaction suppressor solution, a leveler solution and pure water (DIW), are supplied from the plating solution replenishment system 138 to the plating solution in the plating solution adjustment tank 16 so that the concentrations of the components of the plating solution in the plating solution adjustment tank 16 are kept constant.
The plating solution, having the adjusted concentrations of components, is sent from the plating solution adjustment tank 16 to the plating solution supply tank 202, and a predetermined amount of the plating solution is sent from the plating solution supply tank 202 to the plating cell 12. In particular, as shown in FIG. 15, a predetermined amount of the plating solution is sent from the plating solution supply tank 202 to the area between the substrate W and the insoluble anode 98 and surrounded by the sealing member 90, and a voltage is applied from the plating power source 114 to between the insoluble anode 98 and the cathode electrodes 88 to carry out plating of the surface of the substrate W. Further, as shown in FIG. 16, a predetermined amount of the plating solution is sent from the plating solution supply tank 202 into the plating solution tray 22 while discharging the plating solution in the anode chamber 100 of the electrode head 28 through the plating solution discharge pipe 106, thereby carrying out replacement of the plating solution with which the high-resistance structure 110 is impregnated.
By thus sending a plating solution after its use in plating to the plating solution adjustment tank 16 after recovering the plating solution in the plating solution buffer tank 200, replenishing the plating solution in the plating solution adjustment tank 16 with replenisher solutions to adjust the concentrations of the components of the plating solution, storing the plating solution containing the components in the adjusted concentrations in the plating solution supply tank 202, and then supplying the plating solution to the plating cell 12 for plating, it becomes possible to supply to the plating cell 12 a plating solution having a more constant concentration of each component.
Further according to this embodiment, the plating solution in the plating solution supply tank 202 is sampled at specified time intervals to analyze the concentrations of the components in the plating solution by the plating solution analyzer 216, and the plating solution in the plating solution adjustment tank 16 is replenished with deficient components by the plating solution component replenishment system 138. This makes it possible to deal with a case in which the consumptions of the components of the plating solution become imbalanced, e.g., due to a change in the plating conditions with time.
As shown in FIGS. 17 and 18, it is possible to omit the plating solution buffer tank 200 and the plating solution supply tank 202, and to connect the plating solution recovery pipe 130 extending from the plating solution recovery nozzle 66, and the plating solution supply pipe 102 for supplying the plating solution through the plating solution supply inlet 104 to the plating cell 12, both to the plating solution adjustment tank 16, thereby simplifying the apparatus.
In the preceding embodiment, the replenishment quantity of a component of plating solution is calculated from a cumulative quantity of electricity taken for plating, based on the fact that the consumption of a plating solution component is generally determined by the quantity of electricity during plating. There are, however, some additives, such as a reaction accelerator, whose consumption in a plating solution will differ by a difference in the current density of electric current applied upon plating and by a difference in the time of application of the electric current. Thus, if the replenishment quantity is calculated only on the basis of a cumulative quantity of electricity, a difference will be produced between the calculated replenishment quantity and the actual consumption.
FIG. 19 shows the consumption rate (consumption coefficient) of a reaction accelerator contained in a plating solution present in the cathode side area 101 between the substrate W and the high-resistance structure 110 and surrounded by the sealing member 90, as determined when plating of the substrate surface is carried out by bringing the electrode head 28 close to the surface of the substrate W, filling the cathode side area 101 with the plating solution, and connecting the cathode electrodes 88 and the insoluble anode 98 respectively to the cathode and the anode of the plating power source 114, as shown in FIG. 15, and when such plating is carried out with various current densities and various times of application of electric current.
The consumption of such an additive as a reaction accelerator, whose consumption will differ by a difference in the current density of electric current applied upon plating and by a difference in the time of application of the electric current, can be determined more precisely by predetermining a consumption coefficient (consumption rate) as shown in FIG. 19, determined by the current density of electric current applied to carry out plating and the time of application of the electric current, and determining the consumption of the reaction accelerator based on the current density of electric current applied upon actual plating and the time of application of the electric current.
By thus more precisely determining the consumption of a reaction accelerator, and supplying a reaction accelerator solution in such an amount as to compensate for that consumption from the replenisher solution tank 146 of the plating solution component replenishment system 138 to the plating solution in the plating solution adjustment tank 16, it becomes possible to more strictly control the concentration in a plating solution of a reaction promoter whose concentration will be affected by the current density. This enables uniform copper plating or the like, thereby producing highly-reliable copper interconnects or the like.
When recovering part of the plating solution from the anode chamber 100 to reuse it, as shown in FIG. 16, the plating solution, in which an additive, e.g., a reaction accelerator, has been consumed in the anode chamber 100, is returned to the plating solution buffer tank 200. An additive such as a reaction accelerator is consumed differently in the anode chamber 100 and in the cathode side area 101. Thus, the consumption of such an additive can be determined more precisely by predetermining the consumption rate (consumption coefficient) of the additive, such as a reaction accelerator, contained in the plating solution in the anode chamber 110, as determined when carrying out plating of the surface of a substrate with various current densities and various times of application of electric current, determining the consumption, by plating, of the additive contained in the plating solution in the anode chamber 100 by using the consumption coefficient, and adding the thus-determined consumption to the consumption, by plating, of the additive in the cathode side area 101 as determined in the above-described manner.

EXAMPLE 1

A 300-mm silicon wafer, having in a surface a barrier layer and a copper seed layer formed by PVD, was prepared. Using the plating apparatus shown in FIGS. 2 through 14, a copper plated film having a thickness of 1 μm was formed on the surface of the silicon wafer. The same plating operations were carried out consecutively. The composition of the plating solution used and the plating conditions are shown below. The quantity of electricity used for plating was integrated and, every time the cumulative quantity of electricity has reached 50 Ah, the plating solution was replenished with the below-described replenisher solutions (concentration adjustment solutions) so as to adjust the concentrations of the components of the plating solution in the plating solution adjustment tank to the initial concentrations. The replenishment quantity of each replenisher solution containing one of the components was calculated based on a consumption or an increase as predetermined experimentally for the component.
Composition of Plating Solution

- Copper sulfate pentahydrate: 200 g/L
- Sulfuric acid: 80 g/L
- Chlorine: 50 mg/L
- Organic additives (reaction accelerator, reaction suppressor, leveler): predetermined amounts
  Plating Conditions
- Amount of plating solution: 50±5 L
- Amount of plating solution replaced in the electrode head: 10 ml for each operation
- Amount of plating solution supplied: 100 ml for each operation
- Amount of plating solution recovered: 90 ml for each operation
  Replenisher Solutions (Concentration Adjustment Solutions)
- Aqueous solution of copper sulfate pentahydrate: copper ion concentration 73 g/L
- 96 wt % sulfuric acid
- 10 wt % hydrochloric acid
- Organic additives (reaction accelerator, reaction suppressor, leveler): commercial concentrations

COMPARATIVE EXAMPLE 1

The consecutive plating operations, each forming the plated film on the surface of the silicon wafer, were carried out in the same manner as in Example 1, but without replenishing the plating solution with a replenisher solution.

COMPARATIVE EXAMPLE 2

The consecutive plating operations, each forming the plated film on the surface of the silicon wafer, were carried out in the same manner as in Example 1, except that the plating solution remaining on the silicon wafer after plating was discharged without recovering it in the plating solution adjustment tank.

Table 1 shows a change in the concentration of each component of the plating solution and the amount of the plating solution discharged, as observed after carrying out consecutive plating operations in the respective manners of Example 1 and Comp. EXAMPLES 1 AND 2.

	TABLE 1


		Amount of
	Change in concentration	plating

Plating		Sulfuric					solution
conditions	Copper	acid	Chlorine	Accelerator	Suppressor	Leveler	discharged

Ex. 1	∘	∘	∘	∘	∘	∘	∘ (small)
Comp. Ex. 1	x	x	□	x	□	□	∘ (small)
Comp. Ex. 2	∘	∘	∘	∘	∘	∘	x (large)

As will be appreciated from the data in Table 1, the concentrations of the components of the plating solution can be maintained each in a predetermined range in Example 1, and the amount of the plating solution discharged is small. In contrast, the data for Comp. Example 1 shows a large change in the concentration of each component of the plating solution. The concentration of each component decreases or increases with an increase in the number of the wafers processed, and thus the initial plating performance cannot be maintained. Though, in Comp. Example 2 the concentrations of the components of the plating solution can be maintained each in a predetermined range, the amount of the plating solution discharged is large and thus is uneconomical.

EXAMPLE 2

A 300-mm silicon wafer, having in a surface a barrier layer and a copper seed layer formed by PVD, was prepared. Using the plating apparatus shown in FIGS. 15 and 16, a copper plated film having a thickness of 1 μm was formed on the surface of the silicon wafer. The same plating operations were carried out consecutively. The composition of the plating solution used is the same as in Example 1, and the plating conditions are shown below. The replenishment quantity of each of the same replenisher solutions (concentration adjustment solutions) as used in Example 1 was calculated based on a cumulative quantity of electricity and on a consumption or an increase predetermined experimentally for each component of the plating solution. The plating solution in the plating solution adjustment tank was replenished with the replenisher solutions in the calculated amounts so as to adjust the concentration of each component of the plating solution to a predetermined concentration.
Plating Conditions
Amount of plating solution: 50±5 L Amount of plating solution replaced in the electrode head: 20 ml for each operation

- Amount of plating solution supplied: 100 ml for each operation

FIGS. 20A and 20B show the concentrations of the components of the plating solution in the plating solution supply tank. The concentration data shows a constant concentration of each component of the plating solution in the plating solution supply tank, indicating constancy of the concentrations of the components of the plating solution supplied to the plating cell.

EXAMPLE 3

Plating of wafers was carried out in the same manner as in Example 1, but using the plating apparatus shown in FIGS. 17 and 18. FIGS. 21A and 21B show the concentrations of the components of the plating solution in the plating solution adjustment tank. As will be appreciated from the data, though the concentrations of the components of the plating solution in the plating solution adjustment tank, i.e., the plating solution to be supplied to the plating cell, change respectively, the concentrations can be adjusted and maintained each in a predetermined range.

EXAMPLE 4

Plating of wafers was carried out using a plating solution comprising a copper sulfate solution (Cu: 40 g/L, H₂SO₄: 80 g/L, Cl⁻: 50 ppm) and additives (reaction suppressor: 6 ml/L, reaction accelerator: 10 ml/L, leveler: 2 ml/L). After carrying out plating at a current density of 40 mA/cm²for one hour, plating was further carried out at a current density of 20 mA/cm²for one hour. At intervals of 20 minutes, the consumption of the reaction accelerator was determined by using a consumption coefficient as determined by the current density and the time of application of electric current, and the reaction accelerator in such an amount as to compensate for the consumption was added to the plating solution. FIG. 22 shows the concentration of the reaction accelerator in the plating solution during plating. The data in FIG. 22 demonstrates that the concentration of the reaction accelerator in the plating solution is kept constant during plating.
According to the present invention, a system for recovering and reusing a plating solution in a circulatory manner is established, whereby the amount of the plating solution used can be reduced. Further, the use of an insoluble anode, which needs no replacement and whose maintenance and management can be made with ease, can prevent an increase of fine particles in a plating solution and can avoid complication of the apparatus. In addition, it becomes possible with the present invention to keep the concentrations of the components of a plating solution constant over a long period of time, thus stabilizing the plating properties of the plating solution.

Claims

1. A plating apparatus comprising:

a plating cell for carrying out electroplating of a surface of a substrate with a space between the surface of the substrate, serving as a cathode, and an insoluble anode filled with a plating solution;

a plating solution circulation system for supplying the plating solution to the plating cell and recovering the plating solution in a circulatory manner; and

a plating solution component replenishment system for supplying a replenisher solution, containing a component of the plating solution in a higher concentration than that in the plating solution, to the plating solution which circulates in the plating solution circulation system, thereby maintaining the concentration of the component in the plating solution within a predetermined range.

2. The plating apparatus according to claim 1, further comprising a plating solution discharge system for discharging a predetermined amount of the plating solution from the plating solution circulation system.

3. The plating apparatus according to claim 1, wherein the plating solution circulation system includes a plating solution buffer tank for recovering the plating solution after its use in plating in the plating cell, a plating solution adjustment tank, connected to the plating solution buffer tank, for replenishing the plating solution with the replenisher solution, and a plating solution supply tank, connected to the plating solution adjustment tank, for storing the plating solution which has been adjusted in the plating solution adjustment tank and supplying the plating solution to the plating cell.

4. The plating apparatus according to claim 1, wherein the component contained in the replenisher solution, supplied to the plating solution by the plating solution component replenishment system, comprises an organic additive comprising at least one of a reaction accelerator, a reaction suppressor and a leveler, a metal ion, a supporting electrolyte and a halogen ion.

5. The plating apparatus according to claim 1, wherein the replenishment quantity of the replenisher solution is determined based on a cumulative quantity of electricity taken for electroplating.

6. The plating apparatus according to claim 1, wherein the replenisher solution contains one component of the plating solution in a higher concentration than that in the plating solution, and is supplied to the plating solution from a replenisher solution tank.

7. The plating apparatus according to claim 1, wherein the plating cell has a high-resistance structure disposed between the insoluble anode and the substrate which serves as a cathode.

8. The plating apparatus according to claim 1, wherein the replenishment quantity of the replenisher solution is determined by using a consumption coefficient determined by the current density of electric current applied to carry out plating in the plating cell and by the time of application of the electric current.

9. The plating apparatus according to claim 8, wherein the plating cell is divided into an anode chamber and a cathode side area by the high-resistance structure disposed between the insoluble anode and the substrate which serves as a cathode, and the replenishment quantity of the replenisher solution is determined individually for the anode chamber and for the cathode side area, and the respective values obtained are summed up.

10. The plating apparatus according to claim 8, wherein the component of the plating solution, contained in the replenisher solution whose replenishment quantity is determined by using the consumption coefficient determined by the current density and the time of application of the electric current, is a reaction accelerator.

11. The plating apparatus according to claim 3, wherein the plating solution adjustment tank has a liquid level sensor for measuring a liquid level of the plating solution in the plating solution adjustment tank.

12. The plating apparatus according to claim 1, further comprising a plating solution analyzer for sampling the plating solution to be supplied to the plating cell, and analyzing the concentrations of the components of the plating solution.

13. A method for controlling a plating solution, comprising:

replenishing a plating solution, to be used in plating, with a replenisher solution containing a component of the plating solution in a higher concentration than that in the plating solution, thereby maintaining the concentration of the component in the plating solution within a predetermined range.

14. The method for controlling a plating solution according to claim 13, wherein the replenishment quantity of the replenisher solution is determined based on a cumulative quantity of electricity taken for electroplating.

15. The method for controlling a plating solution according to claim 13, wherein the replenishment quantity of the replenisher solution is determined by using a consumption coefficient determined by the current density of electric current applied to carry out plating in the plating cell and by the time of application of the electric current.

16. The method, for controlling a plating solution according to claim 15, wherein the plating cell is divided into an anode chamber and a cathode side area by a high-resistance structure disposed between an insoluble anode and a substrate which serves as a cathode, and the replenishment quantity of the replenisher solution is determined individually for the anode chamber and for the cathode side area, and the respective values obtained are summed up.

17. The method for controlling a plating solution according to claim 15, where in the replenishment quantity of the replenisher solution is determined based on a cumulative quantity of electricity taken for electroplating.

18. The method for controlling a plating solution according to claim 13, wherein a plating metal is copper, and the plating solution having a copper ion concentration of 20-60 g/L is replenished with an aqueous solution of copper sulfate having a copper sulfate concentration of 200 g/L to saturation concentration, thereby maintaining the concentration of copper ion in the plating solution within a predetermined range.

19. The method for controlling a plating solution according to claim 13, wherein the plating solution contains sulfuric acid as a supporting electrolyte, and the plating solution having a sulfuric acid concentration of 10-100 g/L is replenished with sulfuric acid having a concentration of 20-98 wt %, thereby maintaining the concentration of sulfuric acid in the plating solution within a predetermined range.

20. The method for controlling a plating solution according to claim 13, wherein the plating solution contains chlorine as a halogen ion, and the plating solution having a chlorine concentration of 30-90 mg/L is replenished with hydrochloric acid having a concentration of 1-36 wt %, thereby maintaining the concentration of chlorine in the plating solution within a predetermined range.

21. A method for controlling a plating solution, comprising:

recovering a plating solution, which has been used in plating in a plating cell, in a plating solution buffer tank;

sending the plating solution in the plating solution buffer tank to a plating solution adjustment tank, and replenishing the plating solution in the plating solution adjustment tank with a replenisher solution containing a component of the plating solution in a higher concentration than that in the plating solution, thereby maintaining the concentration of the component in the plating solution within a predetermined range;

sending the plating solution in the plating solution adjustment tank to a plating solution supply tank; and

supplying the plating solution in the plating solution supply tank to the plating cell.

22. The method for controlling a plating solution according to claim 21, where in the replenishment quantity of the replenisher solution is determined based on a cumulative quantity of electricity taken for electroplating.

23. The method for controlling a plating solution according to claim 21, where in the replenishment quantity of the replenisher solution is determined by using a consumption coefficient determined by the current density of electric current applied to carry out plating in the plating cell and by the time of application of the electric current.

24. The method for controlling a plating solution according to claim 23, wherein the plating cell is divided into an anode chamber and a cathode side area by a high-resistance structure disposed between an insoluble anode and a substrate which serves as a cathode, and the replenishment quantity of the replenisher solution is determined individually for the anode chamber and for the cathode side area, and the respective values obtained are summed up.

25. The method for controlling a plating solution according to claim 23, wherein the component of the plating solution, contained in the replenisher solution whose replenishment quantity is determined by using the consumption coefficient determined by the current density and the time of application of the electric current, is a reaction accelerator.

26. The method for controlling a plating solution according to claim 21, wherein a plating metal is copper, and the plating solution having a copper ion concentration of 20-60 g/L is replenished with an aqueous solution of copper sulfate having a copper sulfate concentration of 200 g/L to saturation concentration, thereby maintaining the concentration of copper ion in the plating solution within a predetermined range.

27. The method for controlling a plating solution according to claim 21, wherein the plating solution contains sulfuric acid as a supporting electrolyte, and the plating solution having a sulfuric acid concentration of 10-100 g/L is replenished with sulfuric acid having a concentration of 20-98 wt %, thereby maintaining the concentration of sulfuric acid in the plating solution within a predetermined range.

28. The method for controlling a plating solution according to claim 21, wherein the plating solution contains chlorine as a halogen ion, and the plating solution having a chlorine concentration of 30-90 mg/L is replenished with hydrochloric acid having a concentration of 1-36 wt %, thereby maintaining the concentration of chlorine in the plating solution within a predetermined range.