Systems and methods for electrochemically processing microfeature workpieces

Systems and methods for electrochemically processing microfeature workpieces are disclosed herein. In one embodiment, a system includes (a) a processing unit having a first flow system configured to convey a flow of a first processing fluid to a microfeature workpiece, (b) an electrode unit having an electrode and a second flow system configured to convey a flow of a second processing fluid at least proximate to the electrode, (c) a barrier between the processing unit and the electrode unit to separate the first and second processing fluids, and (d) a water balance unit for maintaining the concentration of water in the first processing fluid within a desired range.

TECHNICAL FIELD

This application relates to systems and methods for electrochemically processing microfeature workpieces having a plurality of microdevices integrated in and/or on the workpiece. The microdevices can include submicron features. Particular aspects of the present invention are directed toward electrochemical processing systems having water balance units.

BACKGROUND

Microelectronic devices, such as semiconductor devices, imagers and displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.

Tools that plate metals or other materials onto workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit copper, solder, permalloy, gold, silver, platinum, electrophoretic resist and other materials onto workpieces for forming blanket layers or patterned layers. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.

Conventional single-wafer processing stations generally include a container for receiving a flow of electroplating solution from a fluid inlet. The processing station can include an anode, a plate-type diffuser having a plurality of apertures, and a workpiece holder for carrying a workpiece. The workpiece holder can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece. When the seed layer is biased with a negative potential relative to the anode, it acts as a cathode. In operation, the electroplating fluid flows around the anode, through the apertures in the diffuser, and against the plating surface of the workpiece. The electroplating solution is an electrolyte that conducts electrical current between the anode and the cathodic seed layer on the surface of the workpiece. Therefore, ions in the electroplating solution plate the surface of the workpiece.

The plating machines used in fabricating microelectronic devices must meet many specific performance criteria. For example, many plating processes must be able to form small contacts in vias or trenches that are less than 0.5 μm wide, and often less than 0.1 μm wide. A combination of organic additives such as “accelerators,” “suppressors,” and “levelers” can be added to the electroplating solution to improve the plating process within the trenches so that the plating metal fills the trenches from the bottom up. As such, maintaining the proper concentration of organic additives in the electroplating solution is important to properly fill very small features.

One drawback of conventional plating processes is that the organic additives decompose and break down proximate to the surface of the anode. Also, as the organic additives decompose, it is difficult to control the concentration of organic additives and their associated breakdown products in the plating solution, which can result in poor feature filling and nonuniform layers. Moreover, the decomposition of organic additives produces by-products that can cause defects or other nonuniformities. To reduce the rate at which organic additives decompose near the anode, other anodes such as copper-phosphorous anodes can be used.

Another drawback of conventional plating processes is that organic additives and/or chloride ions in the electroplating solution can passivate and/or consume pure copper anodes. This alters the electrical field, which can result in inconsistent processes and nonuniform layers. Thus, there is a need to improve the plating process to reduce the adverse effects of the organic additives.

One existing approach to inhibit organic additives from contacting and passivating the anode is to place a porous barrier between the workpiece and the anode. This approach, however, only reduces the number of additives that decompose proximate to the anode surface. Furthermore, approaches that utilize a barrier to separate the workpiece from the anode can create chemical imbalances in the electroplating solution such that the concentration of one or more of the constituents in the solution is outside of the desired operating range. When the concentration of a component of the electroplating solution is not within the operating range, the plating process may be unsustainable and the processing fluid may need to be replaced. Thus, chemical imbalances can adversely affect the plating process and increase the frequency with which the electroplating solution must be replaced.

SUMMARY

The present invention is directed toward wet chemical processing systems having (a) a deposition chamber with a barrier between processing fluids to mitigate or eliminate the problems caused by organic additives, and (b) a water balance unit to maintain the concentration of water in the processing fluids within a desired range. The deposition chambers are divided into two distinct portions that interact with each other to electroplate a material onto the workpiece while controlling migration of organic additives in the processing fluids across the barrier to avoid the problems caused by the interaction between the organic additives and the anode. The water balance unit removes excess water from the processing fluids, and/or adds water to the fluids based on the composition of the fluids to maintain the concentration of water in the processing fluids within a desired operating range. By maintaining the concentration within a desired range, the life of the individual processing fluids is extended because the fluids may need to be replaced when a constituent (e.g., water) is out of specification. The increased life of the processing fluids allows the tool to operate for a longer period of time before replacing the fluids, which reduces the operating costs and tool downtime.

The chambers include a processing unit for providing a first processing fluid to a workpiece (i.e., working electrode), an electrode unit for conveying a flow of a second processing fluid different than the first processing fluid, and an electrode (i.e., counter electrode) in the electrode unit. The chambers also include a barrier between the first processing fluid and the second processing fluid. The barrier can be a porous, permeable member that permits fluid and small molecules to flow through the barrier between the first and second processing fluids. Alternatively, the barrier can be a nonporous, semipermeable member that prevents fluid flow between the first and second processing fluids while allowing ions to pass between the fluids. In either case, the barrier separates and/or isolates components of the first and second processing fluids from each other such that the first processing fluid can have different chemical characteristics than the second processing fluid. For example, the first processing fluid can be a catholyte having organic additives and the second processing fluid can be an anolyte without organic additives or with a much lower concentration of such additives.

The barrier provides several advantages by substantially preventing the organic additives in the catholyte from migrating to the anolyte. First, because the organic additives are prevented from moving into the anolyte, the organic additives cannot flow past the anodes and decompose into products that interfere with the plating process. Second, because the organic additives do not decompose at the anodes, the anodes are consumed at a much slower rate in the catholyte so that it is less expensive and easier to control the concentration of organic additives in the catholyte. Third, less expensive anodes, such as pure copper anodes, can be used in the anolyte because the risk of passivation is reduced or eliminated.

The barrier, however, does not prevent water molecules from migrating from the anolyte to the catholyte. During electrochemical processing, water is transported across the barrier with current carrying ions in the form of a hydration sphere. As such, the concentration of water in the catholyte increases while the concentration of water in the anolyte decreases. Although water evaporates from the catholyte, the rate at which water molecules pass through the barrier exceeds the evaporation rate. Consequently, the concentration of water in the catholyte can reach undesirable levels. The water balance unit selectively removes water from the catholyte to maintain the concentration of water within a desired range. When the system is idle, water moves through the barrier from the anolyte to the catholyte by osmosis at a rate less than the rate at which the water evaporates from the catholyte. Accordingly, the water balance unit can selectively add water to the catholyte to maintain the concentration of water within a desired range when the system is idle.

The combination of having a barrier to separate the processing fluids and a water balance unit to maintain the concentration of water in the fluids within a desired range will provide a system that is more efficient and produces significantly better quality products. The system is more efficient because using one processing fluid for the workpiece and another processing fluid for the electrode allows the processing fluids to be tailored to the best use in each area without having to compromise to mitigate the adverse effects of using only a single processing solution. As such, the tool does not need to be shut down as often to adjust the fluids and it consumes less constituents. The system produces better quality products because using two different processing fluids allows better control of the concentration of important constituents in each processing fluid.

Moreover, the water balance unit maintains the concentration of water in the processing fluids within a desired operating range. This improves product quality and increases the life of the processing fluids because the fluids may need to be replaced when a constituent (e.g., water) is out of specification. The increased life of the processing fluids (a) reduces the downtime of the tool for replacing the fluids, (b) lowers the operating costs of the tool, and (c) reduces the volume of expensive organic additives that are wasted each time the processing fluid is changed.

DETAILED DESCRIPTION

As used herein, the terms “microfeature workpiece” or “workpiece” refer to substrates on and/or in which microdevices are formed. Typical microdevices include microelectronic circuits or components, thin-film recording heads, data storage elements, microfluidic devices, and other products. Micromachines or micromechanical devices are included within this definition because they are manufactured in much the same manner as integrated circuits. The substrates can be semiconductive pieces (e.g., silicon wafers or gallium arsenide wafers), nonconductive pieces (e.g., various ceramic substrates), or conductive pieces (e.g., doped wafers). Also, the term electrochemical processing or deposition includes electroplating, electro-etching, anodization, and/or electroless plating.

Several embodiments of electrochemical deposition chambers for processing microfeature workpieces are particularly useful for electrolytically depositing metals or electrophoretic resist in and/or on structures of a workpiece. The deposition chambers can accordingly be used in systems for etching, rinsing, or other types of wet chemical processes in the fabrication of microfeatures in and/or on semiconductor substrates or other types of workpieces. Several embodiments of wet chemical processing systems including electrochemical deposition chambers and water balance units are set forth inFIGS. 1-7and the corresponding text to provide a thorough understanding of particular embodiments of the invention. A person skilled in the art will understand, however, that the invention may have additional embodiments or that the invention may be practiced without several of the details of the embodiments shown inFIGS. 1-7.

A. Embodiments of Wet Chemical Processing Systems

FIG. 1schematically illustrates a system100for electrochemical deposition, electropolishing, or other wet chemical processing of microfeature workpieces. The system100includes an electrochemical deposition chamber102having a head assembly104(shown schematically) and a wet chemical vessel110(shown schematically). The head assembly104loads, unloads, and positions a workpiece W or a batch of workpieces at a processing site relative to the vessel110. The head assembly104typically includes a workpiece holder having a contact assembly with a plurality of electrical contacts configured to engage a conductive layer on the workpiece W. The workpiece holder can accordingly apply an electrical potential to the conductive layer on the workpiece W. Suitable head assemblies, workpiece holders, and contact assemblies are disclosed in U.S. Pat. Nos. 6,228,232; 6,280,583; 6,303,010; 6,309,520; 6,309,524; 6,471,913; 6,527,925; 6,569,297; 6,773,560; and 6,780,374, all of which are hereby incorporated by reference in their entirety.

The illustrated vessel110includes a processing unit120(shown schematically), an electrode unit180(shown schematically), and a barrier170(shown schematically) between the processing and electrode units120and180. The processing unit120is configured to contain a first processing fluid for processing the microfeature workpiece W. The electrode unit180is configured to contain an electrode190and a second processing fluid at least proximate to the electrode190. The second processing fluid is generally different than the first processing fluid, but they can be the same in some applications. In general, the first and second processing fluids have some ions in common. The first processing fluid in the processing unit120is a catholyte and the second processing fluid in the electrode unit180is an anolyte when the workpiece is cathodic. In electropolishing or other deposition processes, however, the first processing fluid can be an anolyte and the second processing fluid can be a catholyte.

The system100further includes a first flow system112that stores and circulates the first processing fluid and a second flow system192that stores and circulates the second processing fluid. The first flow system112may include (a) a first processing fluid reservoir113, (b) a plurality of fluid conduits114to convey a flow of the first processing fluid between the first processing fluid reservoir113and the processing unit120, and (c) a plurality of components115(shown schematically) in the processing unit120to convey a flow of the first processing fluid between the processing site and the barrier170. The second flow system192may include (a) a second processing fluid reservoir193, (b) a plurality of fluid conduits185to convey the flow of the second processing fluid between the second processing fluid reservoir193and the electrode unit180, and (c) a plurality of components184(shown schematically) in the electrode unit180to convey the flow of the second processing fluid between the electrode190and the barrier170. The concentrations of individual constituents of the first and second processing fluids can be controlled separately in the first and second processing fluid reservoirs113and193, respectively. For example, metals, such as copper, can be added to the first and/or second processing fluid in the respective reservoir113or193. Additionally, the temperature of the first and second processing fluids and/or removal of undesirable materials or bubbles can be controlled separately in the first and second flow systems112and192.

The barrier170is positioned between the first and second processing fluids in the region of the interface between the processing unit120and the electrode unit180to separate and/or isolate the first processing fluid from the second processing fluid. For example, the barrier170can be a porous, permeable membrane that permits fluid and small molecules to flow through the barrier170between the first and second processing fluids. Alternatively, the barrier170can be a nonporous, semipermeable membrane that prevents fluid flow between the first and second flow systems112and192while selectively allowing ions, such as cations and/or anions, to pass through the barrier170between the first and second processing fluids. In either case, the barrier170restricts bubbles, particles, and large molecules such as organic additives from passing between the first and second processing fluids. In several embodiments, the system100may not include a barrier.

Nonporous barriers, for example, can be substantially free of open area. Consequently, fluid is inhibited from passing through a nonporous barrier when the first and second flow systems112and192operate at typical pressures. Water, however, can be transported through the nonporous barrier via osmosis and/or electro-osmosis. Osmosis can occur when the molar concentrations in the first and second processing fluids are substantially different. Electro-osmosis can occur as water is carried through the nonporous barrier with current carrying ions in the form of a hydration sphere. When the first and second processing fluids have similar molar concentrations and no electrical current is passed through the processing fluids, fluid flow between the first and second processing fluids is substantially prevented.

The illustrated barrier170can also be hydrophilic so that bubbles in the processing fluids do not cause portions of the barrier170to dry, which reduces conductivity through the barrier170. Suitable materials for permeable barriers include polyethersulfone, Gore-tex, Teflon coated woven filaments, polypropylene, glass fritz, silica gels, and other porous polymeric materials. Suitable membrane type (i.e., semipermeable) barriers170include NAFION membranes manufactured by DuPont®, Ionac® membranes manufactured by Sybron Chemicals Inc., and NeoSepta membranes manufactured by Tokuyuma.

The system100further includes a water balance unit130(shown schematically) for maintaining the concentration of water molecules in the first processing fluid within a desired range. The water balance unit130can be coupled to the first processing fluid reservoir113and/or the processing unit120. As such, the first processing fluid flows from the first processing fluid reservoir113and/or the processing unit120to the water balance unit130. The water balance unit130removes or adds water to the first processing fluid to adjust the concentration of water molecules if the concentration is outside the desired range. The first processing fluid then flows from the water balance unit130to the first processing fluid reservoir113and/or the processing unit120. In the illustrated embodiment and in the following description, the water balance unit130is shown and described as being separate from the first processing fluid reservoir113. In other embodiments, however, the water balance unit and the first processing fluid reservoir can be combined such that the water balance unit includes a vessel that functions as a reservoir for the first processing fluid. Moreover, the water balance unit130can be coupled to the electrode unit180and/or the second processing fluid reservoir193to maintain the concentration of the second processing fluid within a desired range.

When the system100is used for electrochemical processing, an electrical potential can be applied to the electrode190and the workpiece W such that the electrode190is an anode and the workpiece W is a cathode. The first and second processing fluids are accordingly a catholyte and an anolyte, respectively, and each fluid can include a solution of metal ions to be plated onto the workpiece W. The electrical field between the electrode190and the workpiece W may drive positive ions through the barrier170from the anolyte to the catholyte, or drive negative ions in the opposite direction. In plating applications, an electrochemical reaction occurs at the microfeature workpiece W in which metal ions are reduced to form a solid layer of metal on the microfeature workpiece W. In electrochemical etching and other electrochemical applications, the electrical field may drive ions in the opposite direction.

During electrochemical processing, water is transported across the barrier170with current carrying ions in the form of a hydration sphere. As such, the concentration of water in the catholyte increases while the concentration of water in the anolyte decreases. Although water evaporates from the catholyte, the rate at which water molecules pass through the barrier170exceeds the evaporation rate. Consequently, the concentration of water in the catholyte can reach undesirable levels. The water balance unit130selectively removes water from the catholyte to maintain the concentration of water in the catholyte within a desired range. The water balance unit130may also add water to the anolyte to maintain the concentration of water in the anolyte within a desired range. When the system100is idle, water moves through the barrier170from the anolyte to the catholyte by osmosis at a rate less than the rate at which the water evaporates from the catholyte. Accordingly, the water balance unit130can selectively add water to the catholyte and/or the anolyte to maintain the concentration of water within a desired range when the system100is idle.

One feature of the system100illustrated inFIG. 1is that the water balance unit130maintains the concentration of water in the first and second processing fluids within a desired operating range. An advantage of this feature is that by maintaining the concentration of water in the processing fluids within a desired range, the life of the individual processing fluids is extended because the fluids may need to be replaced when the constituents (e.g., water) are out of specification. The increased life of the processing fluids (a) reduces the downtime of the system100for replacing the fluids, (b) lowers the operating cost of the system100, and (c) reduces the volume of expensive organic additives that are wasted each time the processing fluid is changed.

Another feature of the system100illustrated inFIG. 1is that the barrier170separates the first processing fluid in the first flow system112and the second processing fluid in the second flow system192from each other, but allows ions and/or small molecules, depending on the type of barrier170, to pass between the first and second processing fluids. As such, the fluid in the processing unit120can have different chemical and/or physical characteristics than the fluid in the electrode unit180. For example, the first processing fluid can be a catholyte having organic additives and the second processing fluid can be an anolyte without organic additives or with a much lower concentration of such additives. As explained above in the summary section, the lack of organic additives in the anolyte provides the following advantages: (a) reduces by-products of decomposed organics in the catholyte; (b) reduces consumption of the organic additives; (c) reduces passivation of the anode; and (d) enables efficient use of pure copper anodes.

The system100illustrated inFIG. 1is also particularly efficacious in maintaining the desired concentration of copper ions or other metal ions in the first processing fluid. During the electroplating process, it is desirable to accurately control the concentration of materials in the first processing fluid to ensure consistent, repeatable depositions on a large number of individual microfeature workpieces. For example, when copper is deposited on the workpiece W, it is desirable to maintain the concentration of copper in the first processing fluid (e.g., the catholyte) within a desired range to deposit a suitable layer of copper on the workpiece W. This aspect of the system100is described in more detail below.

To control the concentration of metal ions in the first processing solution in some electroplating applications, the system100illustrated inFIG. 1uses characteristics of the barrier170, the volume of the first flow system112, the volume of the second flow system192, and the different acid concentrations in the first and second processing solutions. In general, the concentration of acid in the first processing fluid is greater than the concentration of acid in the second processing fluid, and the volume of the first processing fluid in the system100is greater than the volume of the second processing fluid in the system100. As explained in more detail below, these features work together to maintain the concentration of the constituents in the first processing fluid within a desired range to ensure consistent and uniform deposition on the workpiece W. For purposes of illustration, the effect of increasing the concentration of acid in the first processing fluid will be described with reference to an embodiment in which copper is electroplated onto a workpiece. One skilled in the art will recognize that different metals can be electroplated and/or the principles can be applied to different wet chemical processes in other applications. In additional embodiments, however, the concentration of acid in the first processing fluid may not be greater than the concentration of acid in the second processing fluid, and/or the volume of the first processing fluid may not be greater than the volume of the second processing fluid.

FIGS. 2A-2Hgraphically illustrate the relationship between the concentrations of hydrogen and copper ions in the anolyte and catholyte during a plating cycle and while the system100is idle.FIGS. 2A and 2Bshow the concentration of hydrogen ions in the second processing fluid (anolyte) and the first processing fluid (catholyte), respectively, during a plating cycle. The electrical field readily drives hydrogen ions across the barrier170(FIG. 1) from the anolyte to the catholyte during the plating cycle. Consequently, the concentration of hydrogen ions decreases in the anolyte and increases in the catholyte. As measured by percent concentration change or molarity, the decrease in the concentration of hydrogen ions in the anolyte is generally significantly greater than the corresponding increase in the concentration of hydrogen ions in the catholyte because: (a) the volume of catholyte in the illustrated system100is greater than the volume of anolyte; and (b) the concentration of hydrogen ions in the catholyte is much higher than in the anolyte.

FIGS. 2C and 2Dgraphically illustrate the concentration of copper ions in the anolyte and catholyte during the plating cycle. During the plating cycle, the anode replenishes copper ions in the anolyte and the electrical field drives the copper ions across the barrier170from the anolyte to the catholyte. Thus, as shown inFIG. 2C, the concentration of copper ions in the anolyte increases during the plating cycle. Conversely, in the catholyte cell,FIG. 2Dshows that the concentration of copper ions in the catholyte initially decreases during the plating cycle as the copper ions are consumed to form a layer on the microfeature workpiece W.

FIGS. 2E-2Hgraphically illustrate the concentration of hydrogen and copper ions in the anolyte and the catholyte while the system100ofFIG. 1is idle. For example,FIGS. 2E and 2Fillustrate that the concentration of hydrogen ions increases in the anolyte and decreases in the catholyte while the system100is idle because the greater concentration of acid in the catholyte drives hydrogen ions across the barrier170to the anolyte.FIGS. 2G and 2Hgraphically illustrate that the concentration of copper ions decreases in the anolyte and increases in the catholyte while the system100is idle. The movement of hydrogen ions into the anolyte creates a charge imbalance that drives copper ions from the anolyte to the catholyte.

One feature of the illustrated embodiment is that when the system100is idle, the catholyte is replenished with copper because of the difference in the concentration of acid in the anolyte and catholyte. An advantage of this feature is that the desired concentration of copper in the catholyte can be maintained while the system100is idle. Another advantage of this feature is that the increased movement of copper ions across the barrier170prevents saturation of the anolyte with copper, which can cause passivation of the anode and/or the formation of salt crystals.

The foregoing operation of the system100shown inFIG. 1occurs, in part, by selecting suitable concentrations of hydrogen ions (i.e., acid protons) and copper. In several useful processes for depositing copper, the acid concentration in the first processing fluid can be approximately 10 g/l to approximately 200 g/l, and the acid concentration in the second processing fluid can be approximately 0.1 g/l to approximately 1.0 g/l. Alternatively, the acid concentration of the first and/or second processing fluids can be outside of these ranges. For example, the first processing fluid can have a first concentration of acid and the second processing fluid can have a second concentration of acid less than the first concentration. The ratio of the first concentration of acid to the second concentration of acid, for example, can be approximately 10:1 to approximately 20,000:1. The concentration of copper is also a parameter. For example, in many copper plating applications, the first and second processing fluids can have a copper concentration of between approximately 10 g/l and approximately 50 g/l. Although the foregoing ranges are useful for many applications, it will be appreciated that the first and second processing fluids can have other concentrations of copper and/or acid.

In other embodiments, the barrier can be anionic and the electrode can be an inert anode (i.e. platinum or iridium oxide) to prevent the accumulation of sulfate ions in the first processing fluid. In this embodiment, the acid concentration or pH in the first and second processing fluids can be similar. Alternatively, the second processing fluid may have a higher concentration of acid to increase the conductivity of the fluid. Copper salt (copper sulfate) can be added to the first processing fluid to replenish the copper in the fluid. Electrical current can be carried through the barrier by the passage of sulfate anions from the first processing fluid to the second processing fluid. Therefore, sulfate ions are less likely to accumulate in the first processing fluid where they can adversely affect the deposited film.

In other embodiments, the system can electrochemically etch copper from the workpiece. In these embodiments, the first processing solution (the anolyte) contains an electrolyte that may include copper ions. During electrochemical etching, an electrical potential can be applied to the electrode and/or the workpiece. An anionic barrier can be used to prevent positive ions (such as copper) from passing into the second processing fluid (catholyte). Consequently, the current is carried by anions, and copper ions are inhibited from flowing proximate to and being deposited on the electrode.

The foregoing operation of the illustrated system100also occurs by selecting suitable volumes of anolyte and catholyte. Referring back toFIG. 1, another feature of the illustrated embodiment is that the system100has (a) a first volume of the first processing fluid in the first flow system112, the first processing fluid reservoir113, and the water balance unit130, and (b) a second volume of the second processing fluid in the second flow system192and the second processing fluid reservoir193. The ratio between the first volume and the second volume can be approximately 1.5:1 to 20:1, and in many applications is approximately 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1. The difference in volume in the first and second processing fluids moderates the change in the concentration of materials in the first processing fluid. For example, as described above with reference toFIGS. 2A and 2B, when hydrogen ions move from the anolyte to the catholyte, the percentage change in the concentration of hydrogen ions in the catholyte is less than the change in the concentration of hydrogen ions in the anolyte because the volume of catholyte is greater than the volume of anolyte. In other embodiments, the first and second volumes can be approximately the same.

B. Additional Embodiments of Wet Chemical Processing Systems

FIG. 3schematically illustrates a system200for wet chemical processing of microfeature workpieces in accordance with another embodiment of the invention. The system200is generally similar to the system100described above with reference toFIG. 1. For example, the illustrated system200includes an electrochemical deposition chamber202, a first processing fluid reservoir113, a second processing fluid reservoir193, and a water balance unit130in fluid communication with the first reservoir113and/or chamber202for maintaining the concentration of water in the first processing fluid within a desired range.

The deposition chamber202has a wet chemical vessel210(shown schematically) with a processing unit220(shown schematically), an electrode unit280(shown schematically), and a barrier170(shown schematically) between the processing and electrode units220and280. The processing unit220of the illustrated embodiment includes a dielectric divider242projecting from the barrier170toward the processing site and a plurality of chambers215(identified individually as215a-b) defined by the dielectric divider242. The chambers215a-bcan be arranged concentrically and have corresponding openings244a-bproximate to the processing site. The chambers215a-bare configured to convey the first processing fluid to/from the microfeature workpiece W. In other embodiments, the processing unit220may not include the dielectric divider242and the chambers215, or the dielectric divider242and the chambers215may have other configurations.

The illustrated electrode unit280includes a dielectric divider286, a plurality of compartments284(identified individually as284a-b) defined by the dielectric divider286, and a plurality of electrodes290(identified individually as290a-b) disposed within corresponding compartments284. The compartments284can be arranged concentrically and configured to convey the second processing fluid at least proximate to the electrodes290. Although the illustrated system200includes two concentric electrodes290, in other embodiments, systems can include a different number of electrodes and/or the electrodes can be arranged in a different configuration.

When the system200is used for electrochemical processing, an electrical potential can be applied to the electrodes290and the workpiece W such that the electrodes290are anodes and the workpiece W is a cathode. The first electrode290aprovides an electrical field to the workpiece W at the processing site through the portion of the second processing fluid in the first compartment284aof the electrode unit280and the portion of the first processing fluid in the first chamber230aof the processing unit220. Accordingly, the first electrode290aprovides an electrical field that is effectively exposed to the processing site via the first opening244a. The first opening244ashapes the electrical field of the first electrode290ato create a “virtual electrode” at the top of the first opening244a. This is a “virtual electrode” because the dielectric divider242shapes the electrical field of the first electrode290aso that the effect is as if the first electrode290awere placed in the first opening244a. Virtual electrodes are described in detail in U.S. patent application Ser. No. 09/872,151, which is hereby incorporated by reference in its entirety. Similarly, the second electrode290bprovides an electrical field to the workpiece W through the portion of the second processing fluid in the second compartment284bof the electrode unit280and the portion of the first processing fluid in the second chamber230bof the processing unit220. Accordingly, the second electrode290bprovides an electrical field that is effectively exposed to the processing site via the second opening244bto create another “virtual electrode.”

In operation, a first current is applied to the first electrode290aand a second current is applied to the second electrode290b. The first and second electrical currents are controlled independently of each other such that they can be the same or different than each other at any given time. Additionally, the first and second electrical currents can be dynamically varied throughout a plating cycle. The first and second electrodes290a-baccordingly provide a highly controlled electrical field to compensate for inconsistent or non-uniform seed layers as well as changes in the plated layer during a plating cycle.

C. Embodiments of Water Balance Units

FIG. 4is a schematic view of a water balance unit130in accordance with one embodiment of the invention. The illustrated water balance unit130includes a vessel132for containing a first processing fluid160, a gas source140(shown schematically) for providing gas to the vessel132to vaporize water in the first processing fluid160, and a vacuum pump146(shown schematically) for exhausting the gas and vaporized water from the vessel132. The vessel132has an interior volume configured to receive the first processing fluid160with a headspace134above the fluid160. The vessel132further includes a plurality of inlets136coupled to the gas source140by gas lines142. The inlets136are positioned for flowing gas into the first processing fluid160to increase the surface area of the first processing fluid160exposed to a gas. Because the exposed surface area of the first processing fluid160is generally proportional to the rate at which the water in the first processing fluid160vaporizes, flowing gas into the first processing fluid160increases the vaporization rate of the water in the fluid160.

In the illustrated water balance unit130, the inlets136are positioned at the bottom of the vessel132so that gas bubbles144flow from the bottom of the first processing fluid160to the top of the fluid160. This arrangement increases the surface area of the first processing fluid160exposed to the gas because the gas bubbles144travel the entire height of the fluid160. In additional embodiments, however, the vessel may include a different number of inlets, and/or the inlets can be positioned in a different arrangement to flow gas into the first processing fluid160in the vessel. For example, the inlets can be positioned in the sidewalls of the vessel below a surface of the first processing fluid. The type of gas can also be selected to further increase the rate at which water in the first processing fluid vaporizes. For example, the gas can be a dehumidified gas and/or a heated gas, such as nitrogen or other suitable gases.

The headspace134of the vessel132fills with gas and water vapor162as the gas bubbles144travel through the first processing fluid160. The water molecules at a surface161of the first processing fluid160are exposed to the gas in the headspace134, which also increases the vaporization rate of the water. The vacuum pump146exhausts the gas and water vapor162from the headspace134via an outlet138in the vessel132. In doing so, the vacuum pump140may create a negative pressure in the headspace134to further increase the vaporization rate of the water molecules at the surface161of the first processing fluid160. The water balance unit130may also include a condenser147(shown schematically in broken lines) to condense the water vapor and separate the water from the gas.

The illustrated water balance unit130further includes a sensor148(shown schematically) for detecting the concentration of water in the first processing fluid160and a controller150(shown schematically) operably coupled to the sensor148, gas source140, and vacuum pump146for maintaining the concentration of water in the first processing fluid160within a desired range. After the sensor148detects the concentration of water in the first processing fluid160, the controller150can transmit signals to (a) the gas source140for controlling the flow of gas into the vessel132, and/or (b) the vacuum pump146for controlling the flow of water vapor162out of the headspace134. By adjusting the flow of gas into the vessel132and/or the flow of gas and water vapor162out of the vessel132, the controller150can adjust the concentration of water in the first processing fluid160. For example, if the sensor148detects a concentration of water that exceeds the desired range, the controller150directs (a) the gas source140to increase the flow of gas into vessel132and/or (b) the vacuum pump146to increase the flow of gas and water vapor162out of the vessel132to reduce the concentration of water in the first processing fluid160. In contrast, if the sensor148detects a concentration of water less than the desired range, the controller150directs (a) the gas source140to decrease or stop the flow of gas into vessel132and/or (b) the vacuum pump146to decrease or stop the flow of gas and water vapor162out of the vessel132to increase the concentration of water in the first processing fluid160. Although in the illustrated embodiment the sensor148is positioned in the vessel132, in other embodiments, the sensor148can be positioned in the processing unit120(FIG. 1), the first processing fluid reservoir113(FIG. 1), and/or any of the fluid conduits that convey the first processing fluid160.

The water balance unit130may optionally include a water source164(shown schematically) for adding make-up water to the vessel132when the concentration of water in the first processing fluid160is below the desired range. In other embodiments, the water source164can be coupled to the first processing fluid reservoir113(FIG. 1) and/or the processing unit120(FIG. 1) for adding water directly to the reservoir113and/or the processing unit120. The system100(FIG. 1) may also include a degassing device (not shown) to remove bubbles from the first processing fluid160before the fluid160flows into the processing unit120.

One feature of the water balance unit130illustrated inFIG. 4is that the inlets136flow gas into the first processing fluid160to increase the surface area of the fluid160exposed to the gas. Because the gas flows through the first processing fluid160, the surface area of the fluid160exposed to the gas is greater than the transverse cross-sectional area of the vessel132. An advantage of this feature is the vaporization rate of water molecules in the first processing fluid160is increased because the vaporization rate is generally proportional to the exposed surface area of the first processing fluid160. As such, by controlling the flow of gas into the vessel132, the concentration of water in the first processing fluid160can be maintained within a desired range.

FIG. 5is a schematic view of a water balance unit330in accordance with another embodiment of the invention. The water balance unit330is generally similar to the water balance unit130described above with reference toFIG. 4. For example, the water balance unit330includes a vessel332having an interior volume configured to contain a first processing fluid160and a headspace134above the fluid160. The illustrated water balance unit330, however, includes a heating element336positioned in the vessel332to heat the first processing fluid160. Heating the first processing fluid160increases the vaporization rate of water molecules in the fluid160.

In the illustrated embodiment, the controller150is operably coupled to the heating element336, the vacuum pump146, and the sensor148for maintaining the concentration of water molecules in the first processing fluid160within a desired range. For example, when the sensor148detects a water concentration that exceeds the desired range, the controller150transmits signals to (a) the heating element336to increase the temperature of the first processing fluid160and/or (b) the vacuum pump140to increase the flow of gas and water vapor162out of the headspace134. Similarly, when the sensor148detects a water concentration less than the desired range, the controller150transmits signals for (a) reducing the heat generated by the heating element336and/or (b) reducing the flow of gas and water vapor162from the headspace134. As such, the illustrated water balance unit330maintains the concentration of water molecules in the first processing fluid160within a desired range.

In several applications, while maintaining the concentration of the water molecules in the first processing fluid160within the desired range, the heating element336heats the first processing fluid160to a desired operating temperature for electrochemical processing in the processing unit120(FIG. 1). In other applications, however, the heating element336may heat the first processing fluid160to a temperature that exceeds the desired operating temperature. As such, the system100(FIG. 1) can include a temperature control unit168(shown schematically inFIG. 5) in the fluid conduits114(FIG. 1) and/or the first processing fluid reservoir113(FIG. 1) to adjust the temperature of the first processing fluid160to the desired operating temperature before the fluid160enters the processing unit120.

FIG. 6is a schematic view of a water balance unit430in accordance with another embodiment of the invention. The water balance unit430can be generally similar to the water balance unit130described above with reference toFIG. 3. For example, the water balance unit430can include a vessel432having an interior volume configured to receive the first processing fluid160with a headspace134above the fluid160. The illustrated vessel432, however, includes an inlet436positioned in the headspace134and operably coupled to the gas source142for flowing gas over the surface161of the first processing fluid160. Flowing gas over the surface161of the first processing fluid160increases the vaporization rate of the water molecules at the surface161of the fluid160.

The illustrated vessel432further includes an outlet438positioned in the headspace134and operably coupled to the vacuum pump146for exhausting the gas and water vapor162from the headspace134. As such, the gas flows over the surface161of the first processing fluid160and through the headspace134in a direction D. The controller150is operably coupled to the gas source142to vary the flow of gas across the surface161of the processing fluid160for maintaining the concentration of water within a desired range. For example, when the sensor148detects a water concentration that exceeds the desired range, the controller150transmits signals to the gas source142to increase the flow of gas across the surface161of the first processing fluid160. In contrast, when the sensor148detects a water concentration less than the desired range, the controller150transmits signals to (a) the gas source142to reduce or stop the flow of gas across the surface161of the first processing fluid160and/or (b) the water source164to add water to the first processing fluid160. As such, the illustrated water balance unit430maintains the concentration of water molecules in the first processing fluid160within a desired range.

One feature of the water balance unit430illustrated inFIG. 6is that the gas flows over the surface161of the first processing fluid160and does not flow through the fluid160. An advantage of this feature is that the water balance unit430does not introduce bubbles into the first processing fluid160that must be removed by degassing the fluid160before processing. Bubbles in the first processing fluid160can adversely affect the plating process because a bubble may become trapped against the workpiece and impede deposition on that portion of the workpiece.

In other embodiments, vessels may have several inlets and/or outlets arranged in different configurations for flowing gas across the surface161of the first processing fluid160. For example, in several embodiments, a vessel can include a plurality of inlets positioned around the perimeter of the headspace and an outlet positioned proximate to the center of the headspace such that gas flows inward from the inlets toward the outlet. Alternatively, a vessel can include a plurality of outlets positioned around the perimeter of the headspace and an inlet positioned at the center of the headspace such that gas flows outward from the inlet toward the outlets. In additional embodiments, the water balance unit430may not include the gas source142and/or the vacuum pump146. In such embodiments, the exposure of the surface161of the first processing fluid160to ambient air may increase the vaporization rate of water sufficiently such that there is no need to flow gas through the vessel.

FIG. 7is a schematic view of a water balance unit530in accordance with another embodiment of the invention. The illustrated water balance unit530includes a vessel532for receiving the first processing fluid160, a filter540for removing water molecules from the first processing fluid160, and a pump542for driving the first processing fluid160through the filter540. The filter540can be a reverse osmosis filter to remove water from the first processing fluid160. The controller150is operably coupled to the pump542to vary the flow of the first processing fluid160through the filter540for maintaining the concentration of water within a desired range. For example, when the sensor148detects a water concentration that exceeds the desired range, the controller150transmits signals to the pump542to increase the flow of the first processing fluid160through the filter540, which increases the volume of water removed from the fluid160. In contrast, when the sensor148detects a water concentration less than the desired range, the controller150transmits signals to the pump542to decrease or stop the flow of the first processing fluid160through the filter540, which reduces or stops the removal of water from the fluid160. As such, the illustrated water balance unit530maintains the concentration of water molecules in the first processing fluid160within a desired range.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, in several embodiments, the components of one water balance unit described above with reference toFIGS. 4-7can be combined with one or more of the components of another water balance unit. In one such embodiment, the water balance unit430illustrated inFIG. 6can further include the heating element336illustrated inFIG. 5in the vessel432. In other embodiments, the water balance unit130illustrated inFIG. 4can also include one or more inlets, such as the inlet436illustrated inFIG. 6, positioned to flow gas over the surface161of the first processing fluid160. Accordingly, the invention is not limited except as by the appended claims.