阅读说明：本技术 控制在电化学镀敷设备上的镀敷电解液浓度 (Controlling plating electrolyte concentration on electrochemical plating equipment ) 是由 何治安 尚蒂纳特·古艾迪 马权 许亨俊 奇安·斯威尼 阮光 礼萨·卡里姆 冯敬斌 于 2018-10-23 设计创作，主要内容包括：公开了在衬底用的电化学镀敷设备上控制镀电解液浓度的方法与电镀系统。一种方法包含：(a)将电镀溶液提供至电镀系统；(b)在衬底被保持于电镀系统的电镀槽的阴极室内时,将金属电镀到衬底上；(c)经由补充溶液入口,将补充溶液供应至电镀系统；以及(d)经由辅助电镀溶液入口,将辅助电镀溶液供应至电镀系统。辅助电镀溶液包含电镀溶液中的一些或全部成分。辅助电镀溶液的至少一种成分具有与其目标浓度明显偏离的浓度。(A method and electroplating system for controlling the concentration of a plating electrolyte on an electrochemical plating apparatus for a substrate is disclosed. One method comprises the following steps: (a) providing an electroplating solution to an electroplating system; (b) electroplating a metal onto a substrate while the substrate is held within a cathode chamber of an electroplating bath of an electroplating system; (c) supplying a replenishment solution to the electroplating system via a replenishment solution inlet; and (d) supplying the auxiliary plating solution to the plating system via the auxiliary plating solution inlet. The auxiliary plating solution contains some or all of the components of the plating solution. At least one component of the auxiliary plating solution has a concentration that deviates significantly from its target concentration.)

1. A method of electroplating metal onto a substrate during device fabrication, the method comprising:

(a) providing an electroplating solution to an electroplating system, the electroplating system comprising:

(i) a plating bath comprising an anode chamber and a cathode chamber and configured to hold the substrate within the cathode chamber while the metal is plated onto the substrate,

(ii) a plating solution reservoir configured to hold a portion of the plating solution while plating the metal onto the substrate,

(iii) a recirculation system for delivering the plating solution between the plating bath and the plating solution reservoir,

(iv) a replenishment solution inlet for providing a replenishment solution to the electroplating system, an

(v) An auxiliary plating solution inlet for providing an auxiliary plating solution to the plating system,

wherein the plating solution comprises a plurality of components for plating the metal onto the substrate;

(b) electroplating the metal onto the substrate while the substrate is held within the cathode chamber;

(c) supplying the replenishment solution to the electroplating system via the replenishment solution inlet, wherein the replenishment solution comprises some or all of the plurality of components, each component being at a target concentration for electroplating the metal onto the substrate, wherein supplying the replenishment solution to the electroplating system changes the composition of the electroplating solution such that at least one of the plurality of components in the electroplating solution becomes closer to its target concentration; and

(d) supplying the auxiliary plating solution to the plating system via the auxiliary plating solution inlet, wherein the auxiliary plating solution comprises some or all of the plurality of components, and wherein at least one component of the auxiliary plating solution has a concentration that substantially deviates from its target concentration.

2. The method of claim 1, further comprising repeating operations (b) - (d) to plate the metal onto a second substrate.

3. The method of claim 1, further comprising repeating operations (b) - (d) to plate the metal onto a plurality of additional substrates.

4. The method of any of the preceding claims, wherein the device is an integrated circuit.

5. The method of any one of the preceding claims, wherein the metal is copper and/or cobalt.

6. The method of any of the preceding claims, wherein the plurality of components of the electroplating solution comprise metal ions and an acid.

7. The method of claim 6, wherein the plurality of components of the electroplating solution further comprise an organic plating additive selected from the group consisting of accelerators, suppressors, levelers, and any combination thereof.

8. The method of claim 7, wherein the plurality of components of the electroplating solution further comprise chloride ions and/or borate ions.

9. The method of any of the preceding claims, wherein the plurality of components of the electroplating solution comprise copper ions, an acid, chloride ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid and the copper ions at an auxiliary concentration of copper ions that is substantially higher than the target concentration of copper ions.

10. The method of claim 9, wherein the auxiliary plating solution further comprises chloride ions at a target concentration of the chloride ions and/or wherein the auxiliary plating solution comprises an organic plating additive at a target concentration of the organic plating additive.

11. The method of claim 9, wherein the auxiliary concentration of copper ions is between about 5 and 50 times greater than the target concentration of copper ions.

12. The method of claim 1, wherein the plurality of components of the electroplating solution comprise copper ions, acid, chloride ions, and organic plating additives, and wherein the auxiliary electroplating solution comprises an acid at an acid auxiliary concentration that is lower than a target concentration of the acid and copper ions at a copper ion auxiliary concentration that is substantially higher than the target concentration.

13. The method of claim 12, wherein the auxiliary concentration of copper ions is between about 5 and 50 times greater than the target concentration of copper ions.

14. The method of claim 12, wherein the auxiliary plating solution further comprises chloride ions at a chloride ion auxiliary concentration that is higher than the target concentration of chloride ions.

15. The method of any of the preceding claims, wherein the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid, the borate ions at a target concentration of borate ions, and the cobalt ions at a cobalt ion auxiliary concentration that is substantially lower than the target concentration of cobalt ions.

16. The method of claim 15, wherein the target concentration of cobalt ions is between about 5 and 50 times greater than the auxiliary concentration of cobalt ions.

17. The method of any of the preceding claims, wherein the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid, the cobalt ions at a target concentration of the cobalt ions, and the borate ions at an auxiliary concentration of borate ions that is substantially higher than the target concentration of borate ions.

18. The method of claim 17, wherein the auxiliary concentration of borate ions is between about 1.2 and 2 times greater than the target concentration of borate ions.

19. The method of any of the preceding claims, wherein the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid, the borate ions at an auxiliary concentration of borate ions substantially higher than the target concentration of borate ions, and the cobalt ions at an auxiliary concentration of cobalt ions substantially lower than the target concentration of cobalt ions.

20. The method of any one of the preceding claims, further comprising dosing a single component solution into the electroplating solution reservoir, the single component solution comprising only one of the plurality of components for electroplating the metal onto the substrate.

21. The method of claim 20, wherein the single component solution is an aqueous chloride ion solution.

22. The method of claim 20, wherein the single component solution is an aqueous organic plating additive solution.

23. The method of claim 1, wherein supplying the auxiliary plating solution to the plating system comprises supplying the auxiliary plating solution to the plating solution reservoir and/or the cathode chamber of the plating cell.

24. The method of claim 1, wherein supplying the auxiliary plating solution to the plating system comprises supplying the auxiliary plating solution to an auxiliary cathode compartment of the plating cell.

25. The method of any one of the preceding claims, wherein the plating cell further comprises an ion transfer partition positioned between the anode chamber and the cathode chamber, the ion transfer partition configured to provide a path for ion transport between the plating solution in the anode chamber and the plating solution in the cathode chamber.

26. The method of claim 25, wherein the ion-transferring separator comprises a cation exchange membrane.

27. A system for electroplating metal onto a substrate during device fabrication, the system comprising:

(a) a plating bath comprising an anode chamber and a cathode chamber and configured to hold the substrate within the cathode chamber while the metal is plated onto the substrate,

(b) a plating solution reservoir configured to hold a portion of the plating solution while plating the metal onto the substrate,

(c) a recirculation system for delivering the plating solution between the plating bath and the plating solution reservoir,

(d) a replenishment solution inlet for providing a replenishment solution to the electroplating system,

(e) an auxiliary plating solution inlet for providing an auxiliary plating solution to the plating system, an

(f) A controller comprising instructions for:

(i) providing an electroplating solution to the electroplating system, wherein the electroplating solution comprises a plurality of components for electroplating the metal onto the substrate,

(ii) electroplating the metal onto the substrate while the substrate is held within the cathode chamber,

(iii) supplying the replenishment solution to the electroplating system via the replenishment solution inlet, wherein the replenishment solution comprises some or all of a plurality of components, each component being at a target concentration for electroplating the metal onto the substrate, wherein supplying the replenishment solution to the electroplating system changes the composition of the electroplating solution such that at least one of the plurality of components in the electroplating solution becomes closer to its target concentration; and

(iv) supplying the auxiliary plating solution to the plating system via the auxiliary plating solution inlet, wherein the auxiliary plating solution comprises some or all of the plurality of components, and wherein at least one component of the auxiliary plating solution has a concentration that substantially deviates from its target concentration.

28. The system of claim 27, wherein the plating cell further comprises an ion transfer partition positioned between the anode chamber and the cathode chamber, the ion transfer partition configured to provide a path for ion transport between the plating solution in the anode chamber and the plating solution in the cathode chamber.

29. The system of claim 28, wherein the ion-transferring separator comprises a cation exchange membrane.

30. The system of claim 27, wherein the plating bath further comprises one or more auxiliary electrode chambers.

31. The system of claim 30, wherein the one or more auxiliary electrode chambers are one or more cathode chambers.

32. The system of claim 27, wherein the controller further includes instructions for causing any one or more of the operations of claims 2-24.

33. A method of plating metal onto a substrate during device fabrication, the method comprising:

(a) providing a plating solution to a plating system, the plating solution for plating the metal onto the substrate and comprising a plurality of components having a target concentration;

(b) plating the metal onto the substrate; and

(c) supplying an auxiliary plating solution to the plating system, wherein the auxiliary plating solution comprises some or all of the plurality of components, and wherein at least one component of the auxiliary plating solution has a concentration that significantly deviates from its target concentration.

34. The method of claim 33, further comprising supplying a replenishment solution to the plating system, wherein the replenishment solution comprises some or all of the plurality of components, each component being at a target concentration for electroplating the metal onto the substrate, wherein supplying the replenishment solution to the electroplating system changes the composition of the electroplating solution such that at least one of the plurality of components in the electroplating solution becomes closer to its target concentration.

35. The method of claim 34, further comprising discharging some of the plating solution from the plating system to facilitate control of the composition of the plating solution via a discharge and feed procedure.

Technical Field

The present disclosure relates to control of plating solution concentration, and more particularly to such control performed on an electrochemical plating apparatus for semiconductor substrates.

Background

Electrochemical deposition processes are widely used in the semiconductor industry for metallization in integrated circuit production. One such application is copper (Cu) electrochemical deposition, which may include depositing Cu lines into trenches and/or vias previously formed in a dielectric layer. In this process, a thin adhesion metal diffusion barrier film is previously deposited on the surface by using Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD). A thin seed layer of copper is then deposited on top of the barrier layer, typically by a PVD deposition process. The features (vias and trenches) are then electrochemically filled with Cu by an electrochemical deposition process during which copper anions are electrochemically reduced to copper metal.

Disclosure of Invention

In electrochemical plating apparatuses having separate anolyte and catholyte portions, the concentration of catholyte components (e.g., acids, anions, cations, additives, etc.) may be controlled by adding an auxiliary plating solution (also sometimes referred to as an auxiliary electrolyte) to the catholyte. The composition of the auxiliary plating solution compared to the main plating solution generally depends on the chemical and/or physical reactions that occur during the plating process, but may also be designed to bring the catholyte concentration to the target concentration with only a small dosage (compared to, for example, the plating solution reservoir volume). In certain embodiments, dosing and/or adding an auxiliary plating solution to the plating solution may be on an as-needed basis or on a time-by-time basis, depending on the application. In other words, while the auxiliary plating solution is available, it may be used in small amounts, if at all. For example, it may be used only during the initial portion of the plating run during which the main plating solution changes concentration abruptly and significantly. Thereafter, many substrates can be plated in succession without the use of additional auxiliary plating solutions.

Certain embodiments herein relate to methods for controlling the concentration of electroplating solutions, and more particularly to such control performed on electrochemical plating equipment for semiconductor substrates. In one aspect of embodiments herein, there is provided a method of electroplating metal onto a substrate during device fabrication, which may comprise: (a) providing an electroplating solution to an electroplating system, the electroplating system comprising: (i) a plating bath comprising an anode chamber and a cathode chamber and configured to hold the substrate within the cathode chamber while plating the metal onto the substrate, (ii) a plating solution reservoir configured to hold a portion of the plating solution while plating the metal onto the substrate, (iii) a recirculation system for delivering the plating solution between the plating bath and the plating solution reservoir, (iv) a makeup solution inlet for providing a makeup solution to the plating system, and (v) an auxiliary plating solution inlet for providing an auxiliary plating solution to the plating system, wherein the plating solution comprises a plurality of components for plating the metal onto the substrate; (b) electroplating the metal onto the substrate while the substrate is held within the cathode chamber; (c) supplying the replenishment solution to the electroplating system via the replenishment solution inlet, wherein the replenishment solution comprises some or all of the plurality of components, each component being at a target concentration for electroplating the metal onto the substrate, wherein supplying the replenishment solution to the electroplating system changes the composition of the electroplating solution such that at least one of the plurality of components in the electroplating solution becomes closer to its target concentration; and (d) supplying the auxiliary plating solution to the plating system via the auxiliary plating solution inlet, wherein the auxiliary plating solution comprises some or all of the plurality of components, and wherein at least one component of the auxiliary plating solution has a concentration that significantly deviates from its target concentration.

The method can include repeating operations (b) - (d) to plate the metal onto a second substrate.

The method may comprise repeating operations (b) - (d) to plate the metal onto a plurality of additional substrates.

In some embodiments, the apparatus may be an integrated circuit.

In some embodiments, the metal may be copper and/or cobalt.

In some embodiments, the plurality of components of the electroplating solution may comprise metal ions and an acid.

In some embodiments, the plurality of components of the electroplating solution may further comprise an organic plating additive selected from the group consisting of accelerators, suppressors, levelers, and any combination thereof.

In some embodiments, the various components of the electroplating solution may also include chloride ions and/or borate ions.

In some embodiments, the various components of the electroplating solution may also include copper ions, an acid, chloride ions, and an organic plating additive, and wherein the auxiliary electroplating solution includes the acid at a target concentration of the acid and the copper ions at an auxiliary concentration of copper ions that is substantially higher than the target concentration of copper ions. The auxiliary plating solution can also include chloride ions at a target concentration of the chloride ions and/or wherein the auxiliary plating solution includes an organic plating additive at a target concentration of the organic plating additive. The auxiliary concentration of copper ions may be between about 5 and 50 times greater than the target concentration of copper ions. The auxiliary plating solution may also include chloride ions at a chloride ion auxiliary concentration that is higher than the target concentration of chloride ions.

In some embodiments, the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid, the borate ions at a target concentration of the borate ions, and the cobalt ions at an auxiliary concentration of cobalt ions that is substantially lower than the target concentration of cobalt ions. The target concentration of cobalt ions may be between about 5 and 50 times greater than the cobalt ion auxiliary concentration.

In some embodiments, the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration of the acid, the cobalt ions at a target concentration of the cobalt ions, and the borate ions at an auxiliary concentration of borate ions that is substantially higher than the target concentration of borate ions. The borate ion secondary concentration is between about 1.2 and 2 times greater than the target concentration of borate ion.

In some embodiments, the plurality of components of the electroplating solution comprise cobalt ions, an acid, borate ions, and an organic plating additive, and wherein the auxiliary electroplating solution comprises the acid at a target concentration for the acid, borate ions at an auxiliary concentration for the borate ions that is substantially higher than the target concentration for the borate ions, and cobalt ions at an auxiliary concentration for the cobalt ions that is substantially lower than the target concentration for the cobalt ions.

The method may include dosing a single component solution into the plating solution reservoir, the single component solution including only one of the plurality of components for plating the metal onto the substrate. The single component solution may be an aqueous chloride ion solution. Additionally, in some embodiments, the single component solution may be an aqueous organic plating additive solution.

In some embodiments, supplying the auxiliary plating solution to the plating system comprises supplying the auxiliary plating solution to the plating solution reservoir and/or the cathode chamber of the plating cell.

In some embodiments, the plating cell further comprises an ion transport separator positioned between the anode chamber and the cathode chamber, the ion transport separator configured to provide a path for ion transport between the plating solution in the anode chamber and the plating solution in the cathode chamber. The ion transport separator may comprise a cation exchange membrane.

Some embodiments herein are directed to systems for electroplating metal onto a substrate during device fabrication. A system may comprise: (a) an electroplating bath comprising an anode chamber and a cathode chamber and configured to hold the substrate within the cathode chamber while electroplating the metal onto the substrate, (b) an electroplating solution reservoir configured to hold a portion of the electroplating solution while electroplating the metal onto the substrate, (c) a recirculation system for delivering the electroplating solution between the electroplating bath and the electroplating solution reservoir, (d) a makeup solution inlet for providing a makeup solution to the electroplating system, (e) an auxiliary electroplating solution inlet for providing an auxiliary electroplating solution to the electroplating system, and (f) a controller configured to execute instructions for: (i) providing an electroplating solution to the electroplating system, wherein the electroplating solution comprises a plurality of components for electroplating the metal onto the substrate, (ii) electroplating the metal onto the substrate while the substrate is held within the cathode chamber, (iii) supplying the replenishment solution to the electroplating system via the replenishment solution inlet, wherein the replenishment solution comprises some or all of a plurality of components, each component being at a target concentration for electroplating the metal onto the substrate, wherein supplying the replenishment solution to the electroplating system changes the composition of the electroplating solution such that at least one of the plurality of components in the electroplating solution becomes closer to its target concentration; and (iv) supplying the auxiliary plating solution to the plating system via the auxiliary plating solution inlet, wherein the auxiliary plating solution comprises some or all of the plurality of components, and wherein at least one component of the auxiliary plating solution has a concentration that significantly deviates from its target concentration.

In some embodiments, the plating cell further comprises an ion transport separator positioned between the anode chamber and the cathode chamber, the ion transport separator configured to provide a path for ion transport between the plating solution in the anode chamber and the plating solution in the cathode chamber. The ion transport separator may comprise a cation exchange membrane. In certain embodiments, the plating bath may further comprise one or more auxiliary electrode chambers. The one or more auxiliary electrode chambers may be one or more cathode chambers.

In some embodiments, the controller is further configured to execute instructions for causing any one or more of the above-described method operations.

In one aspect of embodiments herein, a method of plating metal onto a substrate during device fabrication is provided. The method may comprise: (a) providing a plating solution to a plating system, the plating solution for plating the metal onto the substrate and comprising a plurality of components having a target concentration; (b) plating the metal onto the substrate; and (c) supplying a secondary plating solution to the plating system, wherein the secondary plating solution comprises some or all of the plurality of components, and wherein at least one component of the secondary plating solution has a concentration that significantly deviates from its target concentration.

These and other features are described below with reference to the associated drawings.

Drawings

Exemplary embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary plating electrolyte or electroplating solution recirculation and/or dosing system.

FIG. 2 illustrates the relationship of the bath-side to the metal ion distribution effect, which shows, for example, the selective movement of metal ions through a semi-permeable membrane.

Fig. 3A-3D show various graphs illustrating plating bath concentration drift due to plating performed in accordance with one or more embodiments disclosed herein.

Fig. 4 illustrates the relatively low plating current efficiency case shown in fig. 2.

FIGS. 5A-5C show various graphs illustrating the plating bath concentration trends shown in FIG. 4 without supplemental or auxiliary plating solution introduced into the system.

FIGS. 6A-6C show various graphs illustrating dosing of acid, e.g., to supplement acid, and dosing of Deionized (DI) water to control cobalt ion concentration Co²⁺]In the case of (2), FIG. 4 shows the plating bath concentration trend.

Fig. 7 shows a configuration of the electroplating system shown in fig. 1, in which an auxiliary electrolyte for copper (Cu) plating, or an electroplating solution, is introduced.

Fig. 8A-8B show various graphs illustrating bath concentration results with dosing of an auxiliary replenishment solution (MS) for copper (Cu) plating electrolytes.

Fig. 9 shows a configuration of the electroplating system shown in fig. 1, in which an auxiliary electrolyte for cobalt (Co) plating, or an electroplating solution, is introduced.

Fig. 10A-C show various graphs illustrating expected bath performance with dosing of the auxiliary electrolyte for cobalt (Co) plating.

FIG. 11A shows a configuration of the electroplating system shown in FIG. 1 in which an auxiliary electrolyte, or plating solution, is introduced into the cathode side of the electroplating cell.

FIG. 11B shows a graph of assist current as a function of cation concentration in the electroplating solution.

FIG. 12 shows an arrangement of the electroplating system shown in FIG. 1 in which an auxiliary electrolyte, or electroplating solution, is introduced into the anode side of the electroplating cell.

FIGS. 13A-13E show various graphs illustrating the effect of cobalt (Co)²⁺) In the case of dosing into the anode compartment of an electroplating cell, the main electroplating solution and anolyte concentration trends.

Fig. 14 shows a schematic top view of an exemplary electrodeposition apparatus.

Fig. 15 shows a schematic top view of an alternative exemplary electrodeposition apparatus.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to obscure the disclosed embodiments. Although the disclosed embodiments will be described in conjunction with specific embodiments, it will be understood that they are not intended to limit the disclosed embodiments.

Introduction and background

Control of the composition and concentration of the electroplating solution used in the electroplating system may be important to the performance of the electrochemical deposition process. Generally, there are multiple components in a given electroplating solution. For example,the electrolyte composition used to deposit copper on the wafer may vary, but may include sulfuric acid, copper salts (e.g., CuSO)₄) Chloride ions, and organic additives. The composition of the plating solution is selected to optimize the rate and uniformity of plating within features of the wafer, or within field regions of the wafer (e.g., regions without features formed on or within the wafer). During the electroplating process, the copper salt acts as a source of copper cations and also provides conductivity to the electroplating solution: additionally, in certain embodiments, sulfuric acid enhances electroplating solution conductivity by providing hydrogen ions as charge carriers. In addition, organic additives, which are generally recognized in the art as promoters, suppressors, or levelers, are capable of selectively enhancing or suppressing the rate of copper (Cu) deposition on various surfaces and wafer features. The chlorine (C1) ions help to moderate the effects of organic additives and may be added to the electroplating bath for this purpose. In some implementations, an additional halogen (e.g., bromine or iodine) is used instead of or in addition to chlorine.

In general, since the chemical processes occurring at the anode during electroplating may not be necessarily compatible with the chemical processes occurring at the cathode, it may be desirable to separate the anode region from the cathode region of the electroplating bath by a semi-permeable membrane. For example, during operation, insoluble particles may form on the anode. It is generally desirable to protect the wafer from such insoluble particles to avoid such particles from interfering with subsequent metal deposition processes performed on the wafer. In addition, it may also be desirable to confine the organic additives to the cathodic portion of the plating bath to prevent such additives from contacting and/or reacting with the anode. For example, a suitable separator may allow ions to flow between the anode and cathode regions of the plating cell, and thus allow current to flow between the anode and cathode regions of the plating cell, but will still limit unwanted particles and/or organic additives from permeating through the separator. Thus, during electrodeposition, the use of a separator will allow the creation of different chemical environments in the cathodic area and in the anodic area of a plating tank equipped with a separator. The electrolyte contained within the anode region of the plating tank may be referred to as "anolyte". Likewise, the electrolyte contained within the cathode region of the plating tank may be referred to as "catholyte".

Electroplating Apparatus having a membrane for separating the anode region from the cathode region is described in more detail in U.S. patent No.6,527,920 entitled "coater Electroplating Apparatus" by Mayer et al, and is incorporated herein by reference in its entirety. As described above, such a separator allows current to flow between the anode region and the cathode region, but may be further configured to selectively restrict current flow depending on the type of ions. That is, a membrane separating the catholyte from the anolyte may exhibit selectivity for different types of ions. For example, for Cu plating applications, the separator may allow for hydrogen ion (H)⁺) To compare copper ions (e.g. Cu)²⁺And/or Cu⁺) At a faster rate. According to the selectivity of the membrane, in e.g. Cu²⁺And H⁺The movement or current of a particular type of ion, more generally, may be primarily carried by hydrogen ions before a certain molar ratio is reached between concentrations. After this ratio is reached, the copper ions and hydrogen ions may begin to carry current across the membrane in proportion to the Cu in the anode portion of the electrochemical cell²⁺And the concentration of the acid is stable. Thus, the acid component of the anolyte can be continuously consumed until a certain molar ratio between copper ions and hydrogen ions is reached, since hydrogen ions are the main current carrier under these conditions. The concentration of copper salts is increased at the same time as the acid component of the anolyte is consumed, especially when using copper-containing anodes. Since the acid is consumed in the anode over a period of time, the above-described effects (e.g., consumption of the acid of the anolyte with a commensurate increase in copper salts) may be referred to in the art as an "acid/metal ion partitioning effect" or an "anode chamber consumption effect" that occurs inside the anode chamber.

The acid/metal dispensing procedure described above may also inadvertently cause several undesirable side effects to the plating system. Several such side effects are described in U.S. patent No.8,128,791 entitled "Control of electrokinetic in a coater electrokinetic Apparatus," issued to Buckalew et al (referred to herein as the' 791 patent), the entire contents of which are incorporated herein by reference. Undesirable side effects include potential crystallization or precipitation of excess salt from the electroplating solution onto the anode surface inside the anode chamber. In addition, water may leak across the membrane due to electro-osmotic effects (electro-osmotic effects) caused by the pressure gradient created between the anode and cathode portions of the device, which ultimately leads to membrane damage and failure. U.S. patent No.8,128,791 describes a method of controlling the composition of the anolyte by frequently replenishing the anode chamber with plating electrolyte. This process may be referred to in the art as "bleed and feed". Instead of tapping and feeding, diluted electrolyte may be added into the anode chamber of the plating tank.

The above-described acid and anion distribution effects may also produce undesirable fluctuations in the concentration of the plating solution on the cathode side of the plating cell, which in turn may affect the performance of the plating process. Several examples are described below.

To understand the above phenomena, a typical electrolyte management system is illustrated in fig. 1. As shown, there are several primary sections in the electrolyte management system 100, such as the anolyte loop 132 and/or the catholyte loop 118. Generally, there is a central bath 102 that provides plating solution to the plating tank 148 and the main cathode chamber 122. The central bath 102 contains a solution recirculation loop (not shown in fig. 1). Furthermore, in certain embodiments or configurations, the central bath may also have temperature control devices and dosing systems, such as dosing systems for additive dosing, deionized water (DI) dosing, and other active bath ingredient dosing. Additionally, in some embodiments, the central bath 102 may be equipped with a drain or overflow line 146 leading away from the central bath 102 to remove unnecessary plating solution at the appropriate time. Furthermore, in an electroplating apparatus (e.g., plating tank 148) having separate anode and cathode sections, the anode section (e.g., primary anode chamber 126) may have a dedicated recirculation loop 132, as well as dosing lines (not shown in fig. 1), and overflow and/or drain lines (not shown in fig. 1). In such a configuration, the main cathode chamber 122 may be configured to receive plating electrolyte from the central bath 102, circulate electrolyte through the feed line 112 to the plating tank 148, and direct overflow back to the central plating bath 102 through the tank and/or overflow drain line 142. Those skilled in the art will appreciate that the configuration shown in fig. 1 is exemplary and that many other suitable configurations may exist without departing from the scope of the present disclosure. In addition, certain variations and/or configurations of the system 100 shown in fig. 1, 7,9, 11A, and 12 are merely representative schematics and should not be understood as an actual arrangement or configuration of the system 100.

The electrolyte management system 100 shown in fig. 1 will be used to illustrate variations of the system 100 with respect to supplying auxiliary, or supplemental, electrolyte to components of each system 100 to adjust for undesirable fluctuations in plating solution concentration on either the cathode side or the anode side of the plating tank 148. These variants are shown in fig. 7,9, 11A and 12 and are described in further detail below. Generally, the system 100 shown in fig. 1 includes a cathodic solution circuit 118 and an anodic solution circuit 132, which in certain embodiments may be in fluid communication with each other through a bath 102 contained within an electroplating solution reservoir 150. During normal operation of the system 100, a feed plating electrolyte (sometimes referred to as a make-up solution) having a defined concentration of metal ions in an acid-containing solution is provided to the system 100 via line 108. Various set points 110 (e.g., valves, pressures, and/or flow controllers) may be installed on line 108 and/or other lines similar thereto to adjust the flow of fluid through the line on which the set point 110 is installed. Likewise, mixing point 112 may receive a fluid flow from feed line 108. Mixing points 112 may also be installed throughout the system 100 as needed to adjust the delivery and quantity of fluids flowing through the lines 108, etc.

Thus, the feed plating electrolyte may flow through the set point 110 into the bath 102 to accumulate in the sump 150 used to house the bath 102. In certain embodiments, the organic additive flows into bath 102 via line 104. Likewise, Deionized (DI) water may be flowed into bath 102 via line 106 to adjust the concentration levels of various components or feedstocks of bath 102. Operation of the system 100 can include directing bath 102 fluid to the cathode side 12 of the plating tank 148 via line 1162 pumped to accumulate therein. In certain embodiments, a cathode 128 may be at least partially immersed in the cathode side 122 and electrically connected with an anode 130, which may also be immersed in the anode side 126, to complete an electrical circuit 134. Additionally, the current (or more precisely, the electrons carrying the current) is generally in a direction 136, for example, from the negatively charged anode 130 to the positively charged cathode 128. This current drives metal ions (e.g., copper ions, Cu) in the acid-containing solution in the cathode side or compartment 122²⁺) To allow such copper metal to be electroplated onto the wafer 200 disposed within the cathode side 122 of the plating bath 148 as shown in figure 2.

The solution on the cathode side 122 can be pumped back to the bath 102 through a cell overflow or drain line 138 as desired. Likewise, the solution on anode side 126 may also be pumped to bath 102 through anode discharge line 142 as needed. Overflow from bath 102 may be intermittently pumped out of system 100 through a bath overflow or drain line 146 (which may be more generally referred to as a bath dosing and overflow control loop 144). In certain embodiments, the bath dosing and overflow control loop may include a recirculation pump (not shown), a dosing line (not shown), a bath overflow line 146, and temperature control devices and/or mechanisms (not shown). The supply of make-up solution via line 108 is used in conjunction with dumping electrolyte from a reservoir 150 containing the main electroplating solution or bath 102 as a bleed and feed sequence.

As previously mentioned, one factor to consider during the supply of the plating electrolyte to the cathode side 122 to perform electroplating on a wafer housed therein is the acid metal anion partitioning effect. This effect can be observed in copper electroplating processes and can be applied to other similar electroplating systems. On the anode, as illustrated in FIG. 2, for example, shown as metal ions or Me⁺The Cu ions pass through an oxidation reaction Cu4 → Cu due to the passing of a direct current²⁺+2e is deplated (de-plated) into the anodic solution. On the cathode side 122, by reacting Cu²⁺+2e → Cu, extraction of Cu from solution²⁺Ions. Similarly, at the entire membrane 124 on the anode side 126, the anolyte, which has become rich in metal ions, slowly carries the acid or the plating current over time, since the acid carries most of the plating currentH⁺The ions are consumed. At the cathode side 122, the solution flowing through the membrane (from the anode chamber to the cathode chamber) is rich in acid due to the removal of metal ions (e.g., copper ions for Cu plating) from the solution when plating or electrodeposition is performed on the wafer 200 housed therein. As mentioned, ion transport through the membrane favors hydrogen ions over copper ions. Thus, the copper ion concentration in the cathode side 122 will decrease over time, while the acid concentration therein will increase, as illustrated in fig. 3B, which, for example, shows an initial spike in acid concentration followed by a final gradual decrease in acid concentration as the concentration level approaches a steady state condition. As described elsewhere, the acid metal ion partitioning effect can be eliminated by employing a high electrolyte replenishment rate on the anode side 126 and/or on the bath 102 in fluid communication with the cathode side 122 in many configurations. However, high replenishment rates may unnecessarily waste plating solution and increase the operating costs of the plating equipment.

The acid/metal ion partitioning effect can have a substantial effect on electroplating solutions having relatively low metal ion concentrations (e.g., about 5g/l or less). In such solutions, variations in concentration as little as a few tenths of a gram per liter can greatly affect the overall concentration of metal ions in the solution and, therefore, the overall plating performance. For example, if the target copper ion concentration is about 2g/l and the concentration drift consumes about 0.6g/l of copper of the catholyte, the concentration drops by 30% and the plating performance may therefore suffer significantly negatively.

Other changes observed with electroplating with metals other than copper are shown in fig. 6A-D. More specifically, cobalt (Co) may be selected for use as the metal for such electroplating process. As in the copper plating electrolyte, the cobalt plating electrolyte may be configured to contain a cobalt salt, sulfuric acid, an organic additive, and boric acid as a buffer solution.

In this plating process, as in the previous Cu electroplating example, the following reactions are performed: me-e → Me +, which causes metal ions to be extracted from the anode. Meanwhile, at the cathode surface, the plating current efficiency (current efficiency is defined herein as metal plating (Me) because of less than 100% of metal plating⁺+ e → Me) current is delivered to the anodePercent of total current), so two reduction reactions occur simultaneously: co²⁺+2e → Co and 2H⁺+2e→H₂. The amount of current consumed by each reaction varies between plating process settings. The net effect of this plating process on the plating bath electrolyte over time is: (1) the metal ion concentration increases because more metal ions are released from the anode than are consumed at the cathode; (2) the acid concentration is reduced because the acid is consumed only at the cathode side and is not supplied from the anode; (3) boric acid (H)₃BO₃) The concentration is unchanged because boric acid is not actively involved in the reaction. This is illustrated in fig. 5. Note that the acid metal ion partitioning effect occurring in the anode side can further shift the metal ions from the acid concentration if the amount of charge carried by the acid through the membrane is significant. However, in some applications, the partitioning effect becomes negligible because the acid concentration is much lower than the metal ion concentration. The partitioning effect on catholyte concentration in such electroplating processes is not included in order to make the description herein straightforward.

Dosing of acid to the plating bath may be performed in the above-described system (e.g., electrolyte management system 100) with net consumption of acid by the plating electrolyte. The Co ion concentration also needs to be controlled by adding Deionized (DI) water to the plating electrolyte in view of process performance. Since both acid and DI were dosed to the bath, the boric acid concentration would decline over time without any dosing mechanism. This is illustrated in fig. 6. Since boric acid (any other component that performs a similar function in other metal plating processes) may be important to the Co plating process, the boric acid concentration also needs to be addressed.

On plating equipment, it is sometimes desirable to have an auxiliary cathode, as disclosed in U.S. patent No.8,308,931 (entitled "Method and Apparatus for Electroplating") by Reid et al and U.S. patent No.8,475,644 (entitled "Method and Apparatus for Electroplating") by Mayer et al, the entire contents of which are incorporated herein by reference. Supplementing the auxiliary cathode or auxiliary anode in the electrolyte management system provides certain advantages. The auxiliary cathode is typically housed in a small compartment to avoid contact with the main cathode (wafer substrate in the plating apparatus) and it typically has a smaller size than the main cathode (wafer substrate). It is sometimes desirable to have different electrolyte concentrations in the auxiliary cathode chamber. For example, it is sometimes preferable to have a higher anion concentration in the auxiliary cathode chamber (than in the plating electrolyte of the main cathode) so that a higher current can be applied to the auxiliary cathode.

Definition of

The following terms are used intermittently throughout this disclosure:

"substrate" -in this application, the terms "semiconductor wafer," "substrate," "wafer substrate," and "partially fabricated integrated circuit" are used interchangeably. Those skilled in the art will appreciate that the term "partially fabricated integrated circuit" may refer to a silicon wafer during any of a number of stages on which integrated circuit fabrication is performed. Wafers or substrates used in the semiconductor device industry typically have a diameter of 200mm, or 300mm, or 450 mm. In addition, the terms "electrolyte," "electroplating bath," "plating bath," "plating solution," and "plating solution" are used interchangeably. The following detailed description assumes that the embodiments are implemented on a wafer. However, these embodiments are not so limited. The workpiece may have various shapes, sizes, and materials. In addition to semiconductor wafers, other workpieces that can utilize the disclosed embodiments include various items such as printed circuit boards, magnetic recording media, magnetic recording sensors, mirrors (mirrors), optical components, micromechanical devices, and the like.

"Metal" -a material (element, compound, or alloy) that is desired to be plated onto a substrate or wafer for purposes of this disclosure. Examples include copper, cobalt, tin, silver, nickel, and alloys or combinations of any of these.

"electroplating cell" -a cell generally used to house an anode and a cathode positioned opposite each other. Electroplating (which occurs on the cathode in a plating bath) refers to the use of an electric current to reduce dissolved metal cations to form thin adherent gold on the electrodeBelongs to a plating process. In certain embodiments, the plating cell has two compartments, one for housing the anode and the other for housing the cathode. In certain embodiments, the anode compartment is separated from the cathode compartment by a semi-permeable membrane that allows for selective migration of the concentration of ionic species therethrough. The membrane may be an ion exchange membrane, such as a cation exchange membrane. For some implementations, Nafion^TMA model number (e.g., Nafion 324) is suitable.

"Anode compartment" -a compartment within the plating cell that is designed to house an anode. The anode chamber may include a support for holding the anode and/or providing one or more electrical connections to the anode. The anode compartment may be separated from the cathode compartment by a semi-permeable membrane. The electrolyte in the anode chamber is sometimes referred to as anolyte.

"cathode compartment" -a compartment within the plating bath designed to house a cathode. Generally in the context of the present disclosure, the cathode is a substrate, e.g., a wafer, such as a silicon wafer having a plurality of partially fabricated semiconductor devices. The electrolyte in the cathode chamber is sometimes referred to as catholyte.

"electroplating solution (or electroplating bath, plating electrolyte, or main electrolyte)" — a liquid typically having dissociated metal ions in solution, with a conductivity enhancing component such as an acid or base. The dissolved cations and anions are uniformly dispersed in the solvent. This solution is electrically neutral. If a potential is applied to such a solution, cations of the solution are attracted to the electron-rich electrode, while anions are attracted to the electron-poor electrode.

"make-up solution" -a plating solution that generally contains all or almost all of the components of the main plating solution. The replenishment solution is provided to the plating solution to maintain the concentration of the solution components within a desired range, and is selected to maintain good plating performance. This approach is used because the concentration of the components can change during the drift of the solution or over time due to any of several factors as described below. Make-up solution is typically provided as a "feed" in the tapping and feeding system. Typically, the concentration of the components in the replenishment solution is similar or identical to the target concentration of those components. Some make-up solutions do not contain organic plating additives.

"Recirculation System" -the supply of fluid material back into the central sump for subsequent reuse. The recirculation system may be configured to efficiently reuse the electroplating solution and also configured to control and/or maintain the concentration level of metal ions within the solution as desired. The recirculation system may include piping or other fluid conduits along with a pump or other mechanism for driving recirculation.

"target concentration" -the concentration level of metal ions and/or other constituents in the plating solution that is used to achieve the desired plating performance. In various embodiments, the components of the replenishment solution are provided at target concentrations.

"auxiliary plating solution (or auxiliary electrolyte)" -an additional plating solution that is similar to the replenishment solution but has a metal ion or other component concentration that substantially deviates from the target concentration of the plating solution. In certain embodiments, an auxiliary plating solution is applied to correct for an undesirable concentration drift of one or more components in the plating solution.

The concentrations described in g/l refer to the total mass (grams) of the ingredients contained per liter of solution. For example, a concentration of 10g/l of component A means that 10g of component A are present in one liter volume of solution containing component A. When the concentration of an ion (e.g., copper ion or cobalt ion) is specified in g/l, the concentration value refers only to the mass of the ion (not the ion-generating salt or salts) contained per unit volume of the solution. For example, a copper ion concentration of 2g/l corresponds to 2g of copper ions per liter of solution in which the copper ions are dissolved. It does not refer to the presence of 2 grams of copper salt (e.g. copper sulfate) per liter of solution, nor to the mass of anions. However, when referring to the concentration of an acid (e.g., sulfuric acid, a pythonic acid, or boric acid), the concentration value refers to the mass of the total acid (hydrogen and anions) contained per unit volume. For example, a solution with 10g/l sulphuric acid corresponds to 10g of H per litre of solution₂SO₄。

Electroplating system using auxiliary electrolyte

Methods and apparatus that allow such methods to be implemented are included in the present disclosure to control the concentration of plating electrolyte provided to the plating apparatus (primarily for the cathode side of the apparatus). In certain embodiments, similar methods may be used to control the electrolyte concentration in the anode portion of the electroplating apparatus, which may in turn affect the electrolyte concentration on the cathode side.

The method disclosed herein comprises adding a supplemental or supplemental plating electrolyte to a plating apparatus that can contain and use a target concentration of plating electrolyte to plate onto a primary cathode (wafer substrate).

The secondary electrolyte typically has a different composition or has its target concentration than the primary plating electrolyte. Examples of the characteristics of the auxiliary electrolyte include:

(1) the secondary electrolyte contains most or all of the components contained in the primary electrolyte. In certain embodiments, the secondary electrolyte lacks an organic plating additive, while the primary electrolyte contains such an additive. In various embodiments, the secondary electrolyte comprises all of the components of the primary electrolyte except for one or both of the components. For example, in a copper-acid electroplating system, the secondary electrolyte may lack chloride ions and/or organic plating additives, but otherwise have all of the remaining components of the copper-acid primary electrolyte. In another example, a cobalt-acid electroplating system may use an auxiliary electrolyte that lacks cobalt ions and/or organic plating additives, but otherwise has all of the remaining components of the cobalt-acid main electrolyte.

(2) Most (but not all) of the components of the secondary electrolyte may have the same or substantially the same concentrations as those in the primary electrolyte, particularly the target concentrations of these components in the primary electrolyte. In some cases, these components of the auxiliary electrolyte have the same or substantially the same composition as the make-up solution (MS). For example, in an acid-copper electroplating system, the auxiliary electrolyte may contain acid and chloride ions at substantially the same concentrations as the acid and chloride ions in the main electrolyte. In another example, in an acid-cobalt electroplating system, the electrolyte may contain acid and cobalt ions at substantially the same concentrations as the acid and cobalt ions in the main electrolyte.

(3) At least one of the components in the secondary electrolyte has a concentration that is significantly different from the target concentration of the primary electrolyte. For example, in an acid-copper electroplating system, the target concentration of copper ions in the main electrolyte may be about 2g/l, while the concentration of copper ions in the auxiliary electrolyte may be about 40 g/l. For example, in an acid-cobalt electroplating system, the target concentration of borate ions in the main electrolyte may be about 33g/l, while the concentration of borate ions in the auxiliary electrolyte may be about 45g/l (e.g., the solubility limit of borate).

(4) In view of the normal process without the use of an auxiliary electrolyte, the composition of the auxiliary electrolyte, which is significantly different in concentration, is the same as the composition in the main electrolyte that will experience the greatest composition or concentration shift, e.g., copper ions and acid in fig. 3A-D and borate ions in fig. 6C. In some cases, especially those involving a pronounced acid/metal ion partitioning effect, the pronounced drift is temporary (i.e., it occurs only temporarily and not permanently). See fig. 3B-D. For example, drift may only be evident at the start of operation after replacement of a large amount or all of the electrolyte. As an example, the temporary drift may exist for a duration corresponding to plating of approximately 300-1,000 wafers, or for a period of approximately one day. In some implementations, the use of an auxiliary electrolyte is only required during a temporary period of significant drift.

(5) The components in the secondary electrolyte have a significantly higher or lower concentration depending on the drift direction of the concentration of the components in the main electrolyte during use. For example, in view of the positive "drift" in acid concentration in the catholyte as shown in fig. 3D, the auxiliary electrolyte may contain a significantly reduced acid concentration. The concept of "drift" as understood in the art and referred to herein may be considered a perturbation of the target concentration value. For example, the drift may be a perturbation of about 2-3% greater than the specified target value. In another example, the auxiliary electrolyte may contain a significantly increased copper ion concentration in view of the negative drift of the copper ion concentration in the catholyte shown in fig. 3C. In yet another example, in view of the negative drift in borate concentration in the catholyte shown in fig. 6C, the auxiliary electrolyte may contain a significantly increased borate ion concentration.

(6) The volume of the auxiliary electrolyte used may be relatively small compared to the volume of the central plating bath (the primary plating solution) or the tank holding the bath (e.g., tank 150 shown in fig. 1, 7,9, 11A, and 12). This has the following benefits: reduces reliance on consumable raw materials and, thus, may allow for a design or configuration that does not increase, or significantly increase, the footprint of the plating equipment. In one example, the amount of auxiliary electrolyte used in a one day continuous plating operation (e.g., plating about 1,000 wafers) is no greater than 5% of the volume of the electroplating solution reservoir.

(7) The use of a secondary electrolyte may significantly reduce the bleed and feed rate (fed rate) required to maintain the primary electrolyte within controlled specifications. The amount of reduction in the bleed and feed rates depends on the particular electroplating system application. In an example where the make-up solution has a copper ion concentration of about 2g/l, the rate of draw-off and feed required to control the copper ion concentration to within 5% to achieve the target may be greater than about 150%. For the same application but using an auxiliary plating solution as described herein, the bleed and feed rates can be reduced to only 15%, but still have similar or even better control over the copper concentration in the solution. Bleed-to-feed ratio refers to the percentage of the volume of fluid in the plating solution reservoir that is replaced (bled off or fed in) during the continuous plating period of the day. For example, if the tank holds 150 liters of plating solution, a 15% bleed and feed rate would require 22.5 liters of plating solution to be replaced during a day of continuous plating.

(8) The addition of the main electrolyte or the auxiliary electrolyte to the auxiliary cathode compartment is based on the main electrolyte composition and may not always be required. For example, auxiliary electrolyte addition may not always be required, except for temporary concentration deviations due to the effects of acid/metal ion partitioning.

(9) In certain embodiments, the auxiliary electrolyte may be supplied to the electroplating apparatus through a small container attached to the electroplating apparatus. Further, in certain embodiments, the supply of the auxiliary electrolyte may be accomplished through an overall facility supply (e.g., available to multiple tools in a manufacturing facility and possibly through the entire facility's source).

(10) In some embodiments, the secondary electrolyte is introduced into the primary plating solution reservoir. Additionally, in certain embodiments, an auxiliary electrolyte is introduced into the cathode chamber of the plating tank and/or the auxiliary cathode chamber of the plating tank. In some applications, an auxiliary electrolyte is introduced into the anode compartment of the plating tank. This latter application may help to maintain the catholyte concentration within specifications. Various orientations and/or configurations of auxiliary electrolyte supplies for the components of the electrolyte management system 100 shown in fig. 1 are shown in fig. 7,9, 11A, and 12 and will be described in more detail below.

When a concentration value is specified, "substantially the same" means within +/-5% of the specified target value. For example, a concentration substantially the same as 2g/l may be in the range of about 1.9 to 2.1 g/l. Unless otherwise specified, when a concentration value is specifically indicated, "substantially deviated," "substantially different," and the like, mean that the more concentrated component has a concentration between about 1.3 and 50 times the concentration of the less concentrated component. In some cases, the difference in the target concentration or replenishment solution of the components in (a) the auxiliary plating solution and (b) the main plating solution is between about 5 and 50 times. For example, the concentration of component a in the secondary plating solution is about 5 to 50 times greater than in the primary plating solution, and vice versa. In another example, the concentration of component a in the auxiliary plating solution is about 5 to 20 times greater than in the main plating solution, and vice versa. In yet another example, the concentration of component a in the auxiliary plating solution is about 15 to 30 times greater than in the main plating solution, and vice versa.

As previously mentioned, component concentration shifts in the plating electrolyte may be prevalent. This is particularly true for plating equipment having separate anode and cathode portions, but may not necessarily be limited to such designs. In order to maintain both the catholyte and anolyte concentrations at acceptable levels to ensure acceptable electrochemical plating performance, a common method of controlling the electrolyte concentration is to employ high electrolyte make-up (e.g., "bleed and feed") rates. However, doing so can significantly increase the operating cost of running the plating process and sometimes make the plating process prohibitively expensive. Furthermore, in some cases, the application and/or use of high bleed and feed rate alone may not be sufficient to address issues related to electrochemical plating performance. A second method that can be used is to dose each of the components of the electrolyte independently. However, doing so may make the dosing algorithm extremely complex. In addition, dosing of each component of the plating electrolyte will have a diluting effect on all other components in the plating electrolyte. Therefore, the electroplating apparatus will eventually be in a dosed/calculated state at all times. Therefore, this approach is generally avoided.

By using a "complementary" auxiliary plating solution, the replenishment rate can be significantly reduced and, at the same time, the concentration drift in the main plating electrolyte can be significantly reduced. By properly designing the auxiliary electrolyte, the amount of auxiliary electrolyte used can be minimized so that the use of the auxiliary electrolyte does not cause substantial additional costs for the setup and operation of the electroplating apparatus.