Patent Publication Number: US-7585398-B2

Title: Chambers, systems, and methods for electrochemically processing microfeature workpieces

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation in part of U.S. Application numbers:
         (a) Ser. No. 10/729,349, filed on Dec. 5, 2003, now U.S. Pat. No. 7,351,314;   (b) Ser. No. 10/729,357 filed on Dec. 5, 2003, now U.S. Pat. No. 7,351,315; and   (c) Ser. No. 09/872,151, filed on May 31, 2001, now U.S. Pat. No. 7,264,698, which is a continuation-in-part of U.S. application Ser. No. 09/804,697, filed on Mar. 12, 2001, now U.S. Pat. No. 6,660,137, which is a continuation of International Patent Application No. PCT/US00/10120 filed on Apr. 13, 2000 and published in the English language, which claims the benefit of U.S. Application No. 60/129,055, filed on Apr. 13, 1999. All of the foregoing are incorporated herein by reference. This application is also a continuation in part of U.S. application Ser. No. 09/875,365, filed on Jun. 5, 2001, now U.S. Pat. No. 6,916,412.       

   TECHNICAL FIELD 
   This application relates to chambers, 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 deposition chambers having nonporous barriers to separate a first processing fluid and a second processing fluid. Additional aspects of this application are directed toward electrochemical deposition chambers having (a) a barrier between a first processing fluid and a second processing fluid, and (b) a plurality of independently operable electrodes in the second processing fluid. 
   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 on the 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. 
     FIG. 1  illustrates an embodiment of a single-wafer processing station  1  that includes a container  2  for receiving a flow of electroplating solution from a fluid inlet  3  at a lower portion of the container  2 . The processing station  1  can include an anode  4 , a plate-type diffuser  6  having a plurality of apertures  7 , and a workpiece holder  9  for carrying a workpiece  5 . The workpiece holder  9  can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece  5 . When the seed layer is biased with a negative potential relative to the anode  4 , it acts as a cathode. In operation, the electroplating fluid flows around the anode  4 , through the apertures  7  in the diffuser  6 , and against the plating surface of the workpiece  5 . The electroplating solution is an electrolyte that conducts electrical current between the anode  4  and the cathodic seed layer on the surface of the workpiece  5 . Therefore, ions in the electroplating solution plate the surface of the workpiece  5 . 
   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 alter pure copper anodes. This can alter 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. 
   Still another drawback of electroplating is providing a desired electrical field at the surface of the workpiece. The distribution of electrical current in the plating solution is a function of the uniformity of the seed layer across the contact surface, the configuration/condition of the anode, the configuration of the chamber, and other factors. However, the current density profile on the plating surface can change during a plating cycle. For example, the current density profile typically changes during a plating cycle as material plates onto the seed layer. The current density profile can also change over a longer period of time because (a) the shape of consumable anodes changes as they erode, and (b) the concentration of constituents in the plating solution can change. Therefore, it can be difficult to maintain a desired current density at the surface of the workpiece. 
   SUMMARY 
   The present invention is directed, in part, toward electrochemical deposition chambers with nonporous barriers to separate processing fluids. The chambers are divided into two distinct systems that interact with each other to electroplate a material onto the workpiece while controlling migration of selected elements in the processing fluids (e.g., organic additives) from crossing the barrier to avoid the problems caused when organic additives are proximate to the anode and when bubbles or other matter get into the processing fluid. 
   The chambers include a processing unit to provide 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 nonporous barrier between the first processing fluid and the second processing fluid. The nonporous barrier allows ions to pass through the barrier but inhibits nonionic species from passing between the first and second processing fluids. As such, the nonporous barrier separates and 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 a much lower concentration of such additives. 
   The nonporous 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 being in the anolyte, they cannot flow past the anode and decompose into products that interfere with the plating process. Second, because the organic additives do not decompose at the anode, they 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 present invention is also directed toward electrochemical deposition chambers with (a) a porous and/or nonporous barrier between processing fluids to mitigate or eliminate the problems caused by organic additives, and (b) multiple independently operable electrodes to provide and maintain a desired current density at the surface of the workpiece. These chambers are also divided into two distinct systems that interact with each other to electroplate a material onto the workpiece while controlling migration of selected elements in the processing fluids (e.g., organic additives) from crossing the barrier to avoid the problems caused by the interaction between the organic additives and the anode and by bubbles or particulates in the processing fluid. Additionally, the independently operable electrodes provide better control of the electrical field at the surface of the workpiece compared to systems that have only a single electrode. 
   The chambers include a processing unit to provide 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 a plurality of electrodes (i.e., counter electrodes) 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. The barrier may also comprise a member having porous areas and nonporous areas. The barrier of these embodiments 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 multiple electrodes in this aspect of the invention can be controlled independently of one another to tailor the electrical field to the workpiece. Each electrode can have a current level such that the electrical field generated by all of the electrodes provides the desired plating profile at the surface of the workpiece. Additionally, the current applied to each electrode can be independently varied throughout a plating cycle to compensate for differences that occur at the surface of the workpiece as the thickness of the plated layer increases. 
   The combination of having multiple electrodes to control the electrical field and a barrier in the chamber will provide a system that is significantly 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 electrodes 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 (a) using two different processing fluids allows better control of the concentration of important constituents in each processing fluid, and (b) using multiple electrodes provides better control of the current density at the surface of the workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an electroplating chamber in accordance with the prior art. 
       FIG. 2A  schematically illustrates a system for electrochemical deposition, electropolishing, or other wet chemical processing of microfeature workpieces in accordance with one embodiment of the invention. 
       FIG. 2B  schematically illustrates a system for electrochemical deposition, electropolishing, or other wet chemical processing of microfeature workpieces in accordance with another embodiment of the invention. 
       FIGS. 3A-3H  graphically illustrate the relationship between the concentration of hydrogen and copper ions in an anolyte and a catholyte during a plating cycle and while the systems of  FIGS. 2A and 2B  are idle in accordance with one embodiment of the invention. 
       FIG. 4  is a schematic isometric view showing cross-sectional portions of a wet chemical vessel in accordance with another embodiment of the invention. 
       FIG. 5  is a schematic side view showing a cross-sectional, side portion of the vessel of  FIG. 4 . 
       FIG. 6  is a schematic view of a wet chemical vessel in accordance with another embodiment of the invention. 
       FIG. 7  is a schematic view of a wet chemical vessel in accordance with another embodiment of the invention. 
       FIG. 8  is a schematic view of a wet chemical vessel in accordance with another embodiment of the invention. 
       FIG. 9  is a schematic top plan view of a wet chemical processing tool in accordance with another embodiment of the invention. 
       FIG. 10A  is an isometric view illustrating a portion of a wet chemical processing tool in accordance with another embodiment of the invention. 
       FIG. 10B  is a top plan view of a wet chemical processing tool arranged in accordance with another embodiment of the invention. 
       FIG. 11  is an isometric view of a mounting module for use in a wet chemical processing tool in accordance with another embodiment of the invention. 
       FIG. 12  is cross-sectional view along line  12 - 12  of  FIG. 11  of a mounting module for use in a wet chemical processing tool in accordance with another embodiment of the invention. 
       FIG. 13  is a cross-sectional view showing a portion of a deck of a mounting module in greater detail. 
   

   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 using much of the same technology as used in the fabrication of 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 or on structures of a workpiece. The electrochemical deposition chambers in accordance with the invention can accordingly be used in systems with wet chemical processing chambers 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 electrochemical deposition chambers and integrated tools in accordance with the invention are set forth in  FIGS. 2A-13  and 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 in  FIGS. 2A-13 . 
   A. Embodiments of Wet Chemical Processing Systems 
     FIG. 2A  schematically illustrates a system  100  for electrochemical deposition, electropolishing, or other wet chemical processing of microfeature workpieces. The system  100  includes an electrochemical deposition chamber  102  having a head assembly  104  (shown schematically) and a wet chemical vessel  110  (shown schematically). The head assembly  104  loads, unloads, and positions a workpiece W or a batch of workpieces at a processing site relative to the vessel  110 . The head assembly  104  typically 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; and 6,569,297; and U.S. patent application Ser. Nos. 09/733,608 and 09/823,948, all of which are hereby incorporated by reference in their entirety. 
   The illustrated vessel  110  includes a processing unit  120  (shown schematically), an electrode unit  180  (shown schematically), and a nonporous barrier  170  (shown schematically) between the processing and electrode units  120  and  180 . The processing unit  120  is configured to contain a first processing fluid for processing the microfeature workpiece W. The electrode unit  180  is configured to contain an electrode  190  and a second processing fluid at least proximate to the electrode  190 . 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 unit  120  is a catholyte and the second processing fluid in the electrode unit  180  is 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 system  100  further includes a first flow system  112  that stores and circulates the first processing fluid and a second flow system  192  that stores and circulates the second processing fluid. The first flow system  112  may include a first processing fluid reservoir  113 , a plurality of fluid conduits  114  to convey a flow of the first processing fluid between the first processing fluid reservoir  113  and the processing unit  120 , and a plurality of components  115  (shown schematically) in the processing unit  120  to convey a flow of the first processing fluid between the processing site and the nonporous barrier  170 . The second flow system  192  may include a second processing fluid reservoir  193 , a plurality of fluid conduits  185  to convey the flow of the second processing fluid between the second processing fluid reservoir  193  and the electrode unit  180 , and a plurality of components  184  (shown schematically) in the electrode unit  180  to convey the flow of the second processing fluid between the electrode  190  and the nonporous barrier  170 . The concentrations of individual constituents of the first and second processing fluids can be controlled separately in the first and second processing fluid reservoirs  113  and  193 , respectively. For example, metals, such as copper, can be added to the first and/or second processing fluid in the respective reservoir  113  or  193 . 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 systems  112  and  192 . 
   The nonporous barrier  170  is positioned between the first and second processing fluids in the region of the interface between the processing unit  120  and the electrode unit  180  to separate and/or isolate the first processing fluid from the second processing fluid. For example, the nonporous barrier  170  inhibits fluid flow between the first and second flow systems  112  and  192  while selectively allowing ions, such as cations and/or anions, to pass through the barrier  170  between the first and second processing fluids. As such, an electrical field, a charge imbalance between the processing fluids, and/or differences in the concentration of substances in the processing fluids can drive ions across the nonporous barrier  170  as described in detail below. 
   In contrast to porous barriers, such as filter media, expanded Teflon (Goretex), and fritted materials (glass, quartz, ceramic, etc.), the nonporous barrier  170  inhibits nonionic species, including small molecules and fluids, from passing through the barrier  170 . For example, the nonporous barrier  170  can be substantially free of open area. Consequently, fluid is inhibited from passing through the nonporous barrier  170  when the first and second flow systems  112  and  192  operate at typical pressures. Water, however, can be transported through the nonporous barrier  170  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  170  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. 
   Moreover, the nonporous barrier  170  can be hydrophilic so that bubbles in the processing fluids do not cause portions of the barrier  170  to dry, which reduces conductivity through the barrier  170 . Suitable nonporous barriers  170  include NAFION membranes manufactured by DuPont®, Ionac® membranes manufactured by Sybron Chemicals Inc., and NeoSepta membranes manufactured by Tokuyuma. 
   When the system  100  is used for electrochemical processing, an electrical potential can be applied to the electrode  190  and the workpiece W such that the electrode  190  is 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 electrode  190  and the workpiece W may drive positive ions through the nonporous barrier  170  from 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 the opposite direction. 
   One feature of the system  100  illustrated in  FIG. 2A  is that the nonporous barrier  170  separates and isolates the first and second processing fluids from each other, but allows ions to pass between the first and second processing fluids. As such, the fluid in the processing unit  120  can have different chemical characteristics than the fluid in the electrode unit  180 . 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 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 system  100  illustrated in  FIG. 2A  is 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 system  100  is described in more detail below. 
   To control the concentration of metal ions in the first processing solution in some electroplating applications, the system  100  illustrated in  FIG. 2A  uses characteristics of the nonporous barrier  170 , the volume of the first flow system  112 , the volume of the second flow system  192 , 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 system  100  is greater than the volume of the second processing fluid in the system  100 . 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 other wet chemical processes in other applications. 
     FIG. 2B  schematically illustrates a system  100   a  for electrochemical deposition, electropolishing, or other wet chemical processing of microfeature workpieces in accordance with another embodiment of the invention. The system  100   a  is similar to the system  100  shown in  FIG. 2A , and thus like reference numbers refer to like components in  FIGS. 2A and 2B . The system  100   a  includes an electrochemical deposition chamber  102  having a head assembly  104  (shown schematically) and a wet chemical vessel  110   a  (shown schematically). The head assembly  104  loads, unloads, and positions a workpiece W or a batch of workpieces at a processing site relative to the vessel  110   a  as described above with reference to  FIG. 2A . 
   The illustrated vessel  110   a  includes a processing unit  120   a  (shown schematically), an electrode unit  180   a  (shown schematically), and a barrier  170   a  (shown schematically) between the processing and electrode units  120   a  and  180   a . The processing unit  120   a  of the illustrated embodiment includes a dielectric divider  142  projecting from the barrier  170   a  toward the processing site and a plurality of chambers  130  (identified individually as  130   a - b ) defined by the dielectric divider  142 . The chambers  130   a - b  can be arranged concentrically and have corresponding openings  144   a - b  proximate to the processing site. The chambers  130   a - b  are configured to convey a first processing fluid to/from the microfeature workpiece W. The processing unit  120   a , however, may not include the dielectric divider  142  and the chambers  130 , or the dielectric divider  142  and the chambers  130  may have other configurations. 
   The electrode unit  180   a  includes a dielectric divider  186 , a plurality of compartments  184   a - b  defined by the dielectric divider  186 , and a plurality of electrodes  190   a  and  190   b  disposed within corresponding compartments  184   a - b . The compartments  184   a - b  can be arranged concentrically and configured to convey a second processing fluid at least proximate to the electrodes  190   a - b . As noted above, 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 unit  120   a  is a catholyte and the second processing fluid in the electrode unit  180   a  is 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. Although the system  100   a  shown in  FIG. 2B  includes two concentric electrodes  190   a - b , in other embodiments, systems can include a different number of electrodes and/or the electrodes can be arranged in a different configuration. 
   The system  100   a  further includes a first flow system  112   a  that stores and circulates the first processing fluid and a second flow system  192   a  that stores and circulates the second processing fluid. The first flow system  112   a  may include (a) the first processing fluid reservoir  113 , (b) the plurality of fluid conduits  114  to convey the flow of the first processing fluid between the first processing fluid reservoir  113  and the processing unit  120   a , and (c) the chambers  130   a - b  to convey the flow of the first processing fluid between the processing site and the barrier  170   a . The second flow system  192   a  may include (a) the second processing fluid reservoir  193 , (b) the plurality of fluid conduits  185  to convey the flow of the second processing fluid between the second processing fluid reservoir  193  and the electrode unit  180   a , and (c) the compartments  184   a - b  to convey the flow of the second processing fluid between the electrodes  190   a - b  and the barrier  170   a . The concentrations of individual constituents of the first and second processing fluids can be controlled separately in the first and second processing fluid reservoirs  113  and  193 , respectively. For example, metals, such as copper, can be added to the first and/or second processing fluid in the respective reservoir  113  or  193 . 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 systems  112   a  and  192   a.    
   The barrier  170   a  is positioned between the first and second processing fluids in the region of the interface between the processing unit  120   a  and the electrode unit  180   a  to separate and/or isolate the first processing fluid from the second processing fluid. For example, the barrier  170   a  can be a porous, permeable membrane that permits fluid and small molecules to flow through the barrier  170   a  between the first and second processing fluids. Alternatively, the barrier  170   a  can be a nonporous, semipermeable membrane that prevents fluid flow between the first and second flow systems  112  and  192  while selectively allowing ions, such as cations and/or anions, to pass through the barrier  170   a  between the first and second processing fluids, as described above with respect to the nonporous barrier  170  shown in  FIG. 2A . In either case, the barrier  170   a  restricts bubbles, particles, and large molecules such as organic additives from passing between the first and second processing fluids. 
   When the system  100   a  is used for electrochemical processing, an electrical potential can be applied to the electrodes  190   a - b  and the workpiece W such that the electrodes  190   a - b  are anodes 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 electrodes  190   a - b  and the workpiece W may drive positive ions through the barrier  170   a  from 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 the opposite direction. 
   The first electrode  190   a  provides an electrical field to the workpiece W at the processing site through the portion of the second processing fluid in the first compartment  184   a  of the electrode unit  180   a  and the portion of the first processing fluid in the first chamber  130   a  of the processing unit  120   a . Accordingly, the first electrode  190   a  provides an electrical field that is effectively exposed to the processing site via the first opening  144   a . The first opening  144   a  shapes the electrical field of the first electrode  190   a  to create a “virtual electrode” at the top of the first opening  144   a . This is a “virtual electrode” because the dielectric divider  142  shapes the electrical field of the first electrode  190   a  so that the effect is as if the first electrode  190   a  were placed in the first opening  144   a . Virtual electrodes are described in detail in U.S. patent application Ser. No. 09/872,151, incorporated by reference above. Similarly, the second electrode  190   b  provides an electrical field to the workpiece W through the portion of the second processing fluid in the second compartment  184   b  of the electrode unit  180   a  and the portion of the first processing fluid in the second chamber  130   b  of the processing unit  120   a . Accordingly, the second electrode  190   b  provides an electrical field that is effectively exposed to the processing site via the second opening  144   b  to create another “virtual electrode.” 
   In operation, a first current is applied to the first electrode  190   a  and a second current is applied to the second electrode  190   b . 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 electrodes accordingly 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. 
   In addition to the benefits of having multiple independently operable electrodes, the system  100   a  is expected to have similar benefits as the system  100  described above with respect to separating the first processing fluid from the second processing fluid. As explained above, for example, 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 system  100   a  illustrated in  FIG. 2B  is also expected to be particularly efficacious in maintaining the desired concentration of copper ions or other metal ions in the first processing fluid for the reasons described in more detail below. 
   B. Operation of Electrochemical Deposition Systems 
     FIGS. 3A-3H  graphically illustrate the relationship between the concentrations of hydrogen and copper ions in the anolyte and catholyte for the systems  100  and  100   a  during a plating cycle and during an idle period. The following description regarding  FIGS. 3A-3H , more specifically, describes several embodiments of operating the system  100  shown in  FIG. 2A  for purposes of brevity. The operation of the anolyte and catholyte in the system  100   a  can be substantially similar or even identical to the operation of these features in the system  100 . As such, the following description also applies to the system  100   a  shown in  FIG. 2B . 
     FIGS. 3A and 3B  show 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 nonporous barrier  170  ( FIG. 2A ) 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 system  100  is greater than the volume of anolyte; and (b) the concentration of hydrogen ions in the catholyte is much higher than in the anolyte. 
     FIGS. 3C and 3D  graphically 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 nonporous barrier  170  from the anolyte to the catholyte. The anode replenishes copper ions to the anolyte during the plating cycle. Thus, as shown in  FIG. 3C , the concentration of copper ions in the anolyte increases during the plating cycle. Conversely, in the catholyte cell,  FIG. 3D  shows 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. 3E-3H  graphically illustrate the concentration of hydrogen and copper ions in the anolyte and the catholyte while the system  100  of  FIG. 2A  is idle. For example,  FIGS. 3E and 3F  illustrate that the concentration of hydrogen ions increases in the anolyte and decreases in the catholyte while the system  100  is idle because the greater concentration of acid in the catholyte drives hydrogen ions across the nonporous barrier  170  to the anolyte.  FIGS. 3G and 3H  graphically illustrate that the concentration of copper ions decreases in the anolyte and increases in the catholyte while the system  100  is idle. The movement of hydrogen ions into the anolyte creates a charge imbalance that drives copper ions from the anolyte to the catholyte. Accordingly, one feature of the illustrated embodiment is that when the system  100  is 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 system  100  is idle. Another advantage of this feature is that the increased movement of copper ions across the nonporous barrier  170  prevents 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 system  100  shown in  FIG. 2A  occurs, 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 nonporous 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, a potential can be applied to the electrode and/or the workpiece. An anionic nonporous 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 system  100  also occurs by selecting suitable volumes of anolyte and catholyte. Referring back to  FIG. 2A , another feature of the illustrated system  100  is that it has a first volume of the first processing fluid and a second volume of the second processing fluid in the corresponding processing fluid reservoirs  113  and  193  and flow systems  112  and  192 . 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 to  FIGS. 3A and 3B , 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. 
   C. Embodiments of Electrochemical Deposition Vessels 
     FIG. 4  is an isometric view showing cross-sectional portions of a wet chemical vessel  210  in accordance with another embodiment of the invention. The vessel  210  is configured to be used in a system similar to the systems  100  and  100   a  ( FIGS. 2A and 2B ) for electrochemical deposition, electropolishing, anodization, or other wet chemical processing of microfeature workpieces. The vessel  210  shown in  FIG. 4  is accordingly one example of the type of vessel  110  or  110   a . As such, the vessel  210  can be coupled to a first processing fluid reservoir (not shown) so that a first flow system (partially shown as  212   a - b ) can provide a first processing fluid to a workpiece for processing. The vessel  210  can also be coupled to a second processing fluid reservoir (not shown) so that a second flow system (partially shown as  292   a - b ) can convey a second processing fluid proximate to an electrode(s). 
   The illustrated vessel  210  includes a processing unit  220 , a barrier unit  260  coupled to the processing unit  220 , and an electrode unit  280  coupled to the barrier unit  260 . The processing unit  220 , the barrier unit  260 , and the electrode unit  280  need not be separate units, but rather they can be sections or components of a single unit. The processing unit  220  includes a chassis  228  having a first portion of the first flow system  212   a  to direct the flow of the first processing fluid through the chassis  228 . The first portion of the first flow system  212   a  can include a separate component attached to the chassis  228  and/or a plurality of fluid passageways in the chassis  228 . In this embodiment, the first portion of the first flow system  212   a  includes a conduit  215 , a first flow guide  216  having a plurality of slots  217 , and an antechamber  218 . The slots  217  in the first flow guide  216  distribute the flow radially to the antechamber  218 . 
   The first portion of the first flow system  212   a  further includes a second flow guide  219  that receives the flow from the antechamber  218 . The second flow guide  219  can include a sidewall  221  having a plurality of openings  222  and a flow projector  224  having a plurality of apertures  225 . The openings  222  can be vertical slots arranged radially around the sidewall  221  to provide a plurality of flow components projecting radially inwardly toward the flow projector  224 . The apertures  225  in the flow projector  224  can be a plurality of elongated slots or other openings that are inclined upwardly and radially inwardly. The flow projector  224  receives the radial flow components from the openings  222  and redirects the flow through the apertures  225 . It will be appreciated that the openings  222  and the apertures  225  can have several different configurations. For example, the apertures  225  can project the flow radially inwardly without being canted upwardly, or the apertures  225  can be canted upwardly at a greater angle than the angle shown in  FIG. 4 . The apertures  225  can accordingly be inclined at an angle ranging from approximately 0°-45°, and in several specific embodiments the apertures  225  can be canted upwardly at an angle of approximately 5°-25°. 
   The processing unit  220  can also include a field shaping module  240  for shaping the electrical field(s) and directing the flow of the first processing fluid at the processing site. In this embodiment, the field shaping module  240  has a first partition  242   a  with a first rim  243   a , a second partition  242   b  with a second rim  243   b , and a third partition  242   c  with a third rim  243   c . The first rim  243   a  defines a first opening  244   a , the first rim  243   a  and the second rim  243   b  define a second opening  244   b , and the second rim  243   b  and the third rim  243   c  define a third opening  244   c . The processing unit  220  can further include a weir  245  having a rim  246  over which the first processing fluid can flow into a recovery channel  247 . The third rim  243   c  and the weir  245  define a fourth opening  244   d . The field shaping module  240  and the weir  245  are attached to the processing unit  220  by a plurality of bolts or screws, and a number of seals  249  are positioned between the chassis  228  and the field shaping module  240 . 
   The vessel  210  is not limited to having the field shaping unit  240  shown in  FIG. 4 . In other embodiments, field shaping units can have other configurations. For example, a field shaping unit can have a first dielectric member defining a first opening and a second dielectric member defining a second opening above the first opening. The first opening can have a first area and the second opening can have a second area different than the first area. The first and second openings may also have different shapes. 
   In the illustrated embodiment, the first portion of the first flow system  212   a  in the processing unit  220  further includes a first channel  230   a  in fluid communication with the antechamber  218 , a second channel  230   b  in fluid communication with the second opening  244   b , a third channel  230   c  in fluid communication with the third opening  244   c , and a fourth channel  230   d  in fluid communication with the fourth opening  244   d . The first portion of the first flow system  212   a  can accordingly convey the first processing fluid to the processing site to provide a desired fluid flow profile at the processing site. 
   In this particular processing unit  220 , the first processing fluid enters through an inlet  214  and passes through the conduit  215  and the first flow guide  216 . The first processing fluid flow then bifurcates with a portion of the fluid flowing up through the second flow guide  219  via the antechamber  218  and another portion of the fluid flowing down through the first channel  230   a  of the processing unit  220  and into the barrier unit  260 . The upward flow through the second flow guide  219  passes through the flow projector  224  and the first opening  244   a . A portion of the first processing fluid flow passes upwardly over the rim  243   a , through the processing site proximate to the workpiece, and then flows over the rim  246  of the weir  245 . Other portions of the first processing fluid flow downwardly through each of the channels  230   b - d  of the processing unit  220  and into the barrier unit  260 . 
   The electrode unit  280  of the illustrated vessel  210  includes a container  282  that houses an electrode assembly and a first portion of the second flow system  292   a . The illustrated container  282  includes a plurality of dividers or walls  286  that define a plurality of compartments  284  (identified individually as  284   a - d ). The walls  286  of this container  282  are concentric annular dividers that define annular compartments  284 . However, in other embodiments, the walls can have different configurations to create nonannular compartments and/or each compartment can be further divided into cells. The specific embodiment shown in  FIG. 4  has four compartments  284 , but in other embodiments, the container  282  can include any number of compartments to house the electrode(s). The compartments  284  can also define part of the first portion of the second flow system  292   a  through which the second processing fluid flows. 
   The vessel  210  can further include at least one electrode disposed in the electrode unit  280 . The vessel  210  shown in  FIG. 4  includes a first electrode  290   a  in a first compartment  284   a , a second electrode  290   b  in a second compartment  284   b , a third electrode  290   c  in a third compartment  284   c , and a fourth electrode  290   d  in a fourth compartment  284   d . The electrodes  290   a - d  can be annular or circular conductive elements arranged concentrically with one another. In other embodiments, the electrodes can be arcuate segments or have other shapes and arrangements. Although four electrodes  290  are shown in the illustrated embodiment, other embodiments can include a different number of electrodes, including a single electrode, two electrodes, etc. 
   In this embodiment, the electrodes  290  are coupled to an electrical connector system  291  that extends through the container  282  of the electrode unit  280  to couple the electrodes  290  to a power supply. The electrodes  290  can provide a constant current throughout a plating cycle, or the current through one or more of the electrodes  290  can be changed during a plating cycle according to the particular parameters of the workpiece. Moreover, each electrode  290  can have a unique current that is different than the current of the other electrodes  290 . The electrodes  290  can be operated in DC, pulsed, and pulse reverse waveforms. Suitable processes for operating the electrodes are set forth in U.S. patent application Ser. Nos. 09/849,505; 09/866,391; and 09/866,463, all of which are hereby incorporated by reference in their entirety. 
   The first portion of the second flow system  292   a  conveys the second processing fluid through the electrode unit  280 . More specifically, the second processing fluid enters the electrode unit  280  through an inlet  285  and then the flow is divided as portions of the second processing fluid flow into each of the compartments  284 . The portions of the second processing fluid flow across corresponding electrodes  290  as the fluid flows through the compartments  284  and into the barrier unit  260 . 
   The illustrated barrier unit  260  is between the processing unit  220  and the electrode unit  280  to separate the first processing fluid from the second processing fluid while allowing individual electrical fields from the electrodes  290  to act through the openings  244   a - d . The barrier unit  260  includes a second portion of the first flow system  212   b , a second portion of the second flow system  292   b , and a nonporous barrier  270  separating the first processing fluid in the first flow system  212  from the second processing fluid in the second flow system  292 . The second portion of the first flow system  212   b  is in fluid communication with the first portion of the first flow system  212   a  in the processing unit  220 . The second portion of the first flow system  212   b  includes a plurality of annular openings  265  (identified individually as  265   a - d ): adjacent to the nonporous barrier  270 , a plurality of channels  264  (identified individually as  264   a - d ) extending between corresponding annular openings  265  and corresponding channels  230  in the processing unit  220 , and a plurality of passageways  272  extending between corresponding annular openings  265  and a first outlet  273 . As such, the first processing fluid flows from the channels  230   a - d  of the processing unit  220  to corresponding channels  264   a - d  of the barrier unit  260 . After flowing through the channels  264   a - d  in the barrier unit  260 , the first processing fluid flows in a direction generally parallel to the nonporous barrier  270  through the corresponding annular openings  265  to corresponding passageways  272 . The first processing fluid flows through the passageways  272  and exits the vessel  210  via the first outlet  273 . 
   The second portion of the second flow system  292   b  is in fluid communication with the first portion of the second flow system  292   a  in the electrode unit  280 . The second portion of the second flow system  292   b  includes a plurality of channels  266  (identified individually as  266   a - d ) extending between the barrier  270  and corresponding compartments  284  in the electrode unit  280  and a plurality of passageways  274  extending between the nonporous barrier  270  and a second outlet  275 . As such, the second processing fluid flows from the compartments  284   a - d  to corresponding channels  266   a - d  and against the nonporous barrier  270 . The second processing fluid flow flexes the nonporous barrier  270  toward the processing unit  220  so that the fluid can flow in a direction generally parallel to the barrier  270  between the barrier  270  and a surface  263  of the barrier unit  260  to the corresponding passageways  274 . The second processing fluid flows through the passageways  274  and exits the vessel  210  via the second outlet  275 . 
   The nonporous barrier  270  is disposed between the second portion of the first flow system  212   b  and the second portion of the second flow system  292   b  to separate the first and second processing fluids. The nonporous barrier  270  can be a semipermeable membrane to inhibit fluid flow between the first and second flow systems  212  and  292  while allowing ions to pass through the barrier  270  between the first and second processing fluids. As explained above, the nonporous barrier  270  can also be cation or anion selective and accordingly permit only the selected ions to pass through the barrier  270 . Because fluids are inhibited from flowing through the nonporous barrier  270 , the barrier  270  is not subject to clogging. 
   Electrical current can flow through the nonporous barrier  270  in either direction in the presence of an electrolyte. For example, electrical current can flow from the second processing fluid in the channels  266  to the first processing fluid in the annular openings  265 . Furthermore, the nonporous barrier  270  can be hydrophilic so that bubbles in the processing fluids do not cause portions of the barrier  270  to become dry and block electrical current. The nonporous barrier  270  shown in  FIG. 4  is also flexible to permit the second processing fluid to flow from the channels  266  laterally (e.g., annularly) between the barrier  270  and the surface  263  of the barrier unit  260  to the corresponding passageway  274 . The nonporous barrier  270  can flex upwardly when the second processing fluid exerts a greater pressure against the barrier  270  than the first processing fluid. 
   The vessel  210  also controls bubbles that are formed at the electrodes  290  or elsewhere in the system. For example, the nonporous barrier  270 , a lower portion of the barrier unit  260 , and the electrode unit  280  are canted relative to the processing unit  220  to prevent bubbles in the second processing fluid from becoming trapped against the barrier  270 . As bubbles in the second processing fluid move upward through the compartments  284  and the channels  266 , the angled orientation of the nonporous barrier  270  and the bow of the barrier  270  above each channel  266  causes the bubbles to move laterally under the barrier  270  toward the upper side of the surface  263  corresponding to each channel  266 . The passageways  274  carry the bubbles out to the second outlet  275  for removal. The illustrated nonporous barrier  270  is oriented at an angle α of approximately 5°. In additional embodiments, the barrier  270  can be oriented at an angle greater than or less than 5° that is sufficient to remove bubbles. The angle α, accordingly, is not limited to 5°. In general, the angle α should be large enough to cause bubbles to migrate to the high side, but not so large that it adversely affects the electrical field. 
   An advantage of the illustrated barrier unit  260  is that the angle α of the nonporous barrier  270  prevents bubbles from being trapped against portions of the barrier  270  and creating dielectric areas on the barrier  270 , which would adversely affect the electrical field. In other embodiments, other devices can be used to degas the processing fluids in lieu of or in addition to canting the barrier  270 . As such, the nonporous barrier  270  need not be canted relative to the processing unit  220  in all applications. 
   The spacing between the electrodes  290  and the nonporous barrier  270  is another design criteria for the vessel  210 . In the illustrated vessel  210 , the distance between the nonporous barrier  270  and each electrode  290  is approximately the same. For example, the distance between the nonporous barrier  270  and the first electrode  290   a  is approximately the same as the distance between the nonporous barrier  270  and the second electrode  290   b . Alternatively, the distance between the nonporous barrier  270  and each electrode  290  can be different. In either case, the distance between the nonporous barrier  270  and each arcuate section of a single electrode  290  is approximately the same. The uniform spacing between each section of a single electrode  290  and the nonporous barrier  270  is expected to provide more accurate control over the electrical field compared to having different spacings between sections of an electrode  290  and the barrier  270 . Because the second processing fluid has less acid, and is thus less conductive, a difference in the distance between the nonporous barrier  270  and separate sections of an individual electrode  290  has a greater affect on the electrical field at the workpiece than a difference in the distance between the workpiece and the barrier  270 . 
   In operation, the processing unit  220 , the barrier unit  260 , and the electrode unit  280  operate together to provide a desired electrical field profile (e.g., current density) at the workpiece. The first electrode  290   a  provides an electrical field to the workpiece through the portions of the first and second processing fluids that flow in the first channels  230   a ,  264   a , and  266   a , and the first compartment  284   a . Accordingly, the first electrode  290   a  provides an electrical field that is effectively exposed to the processing site via the first opening  244   a . The first opening  244   a  shapes the electrical field of the first electrode  290   a  according to the configuration of the rim  243   a  of the first partition  242   a  to create a “virtual electrode” at the top of the first opening  244   a . This is a “virtual electrode” because the field shaping module  240  shapes the electrical field of the first electrode  290   a  so that the effect is as if the first electrode  290   a  were placed in the first opening  244   a . Virtual electrodes are described in detail in U.S. patent application Ser. No. 09/872,151, which is hereby incorporated by reference. Similarly, the second, third, and fourth electrodes  290   b - d  provide electrical fields to the processing site through the portions of the first and second processing fluids that flow in the second channels  230   b ,  264   b , and  266   b , the third channels  230   c ,  264   c , and  266   c , and the fourth channels  230   d ,  264   d , and  266   d , respectively. Accordingly, the second, third, and fourth electrodes  290   b - d  provide electrical fields that are effectively exposed to the processing site via the second, third, and fourth openings  244   b - d , respectively, to create corresponding virtual electrodes. 
     FIG. 5  is a schematic side view showing a cross-sectional side portion of the wet chemical vessel  210  of  FIG. 4 . The illustrated vessel  210  further includes a first interface element  250  between the processing unit  220  and the barrier unit  260  and a second interface element  252  between the barrier unit  260  and the electrode unit  280 . In this embodiment, the first interface element  250  is a seal having a plurality of openings  251  to allow fluid communication between the channels  230  of the processing unit  220  and the corresponding channels  264  of the barrier unit  260 . The seal is a dielectric material that electrically insulates the electrical fields within the corresponding channels  230  and  264 . Similarly, the second interface element  252  is a seal having a plurality of openings  253  to allow fluid communication between the channels  266  of the barrier unit  260  and the corresponding compartments  284  of the electrode unit  280 . 
   The illustrated vessel  210  further includes a first attachment assembly  254   a  for attaching the barrier unit  260  to the processing unit  220  and a second attachment assembly  254   b  for attaching the electrode unit  280  to the barrier unit  260 . The first and second attachment assemblies  254   a - b  can be quick-release devices to securely hold the corresponding units together. For example, the first and second attachment assemblies  254   a - b  can include clamp rings  255   a - b  and latches  256   a - b  that move the clamp rings  255   a - b  between a first position and a second position. As the latches  256   a - b  move the clamp rings  255   a - b  from the first position to the second position, the diameter of the clamp rings  255   a - b  decreases to clamp the corresponding units together. Optionally, as the first and second attachment assemblies  254   a - b  move from the first position to the second position, the attachment assemblies  254   a - b  drive the corresponding units together to compress the interface elements  250  and  252  and properly position the units relative to each other. Suitable attachment assemblies of this type are disclosed in detail in U.S. Patent Application No. 60/476,881, filed Jun. 6, 2003, which is hereby incorporated by reference in its entirety. In other embodiments, the attachment assemblies  254   a - b  may not be quick-release devices and can include a plurality of clamp rings, a plurality of latches, a plurality of bolts, or other types of fasteners. 
   One advantage of the vessel  210  illustrated in  FIGS. 4 and 5  is that worn components in the barrier unit  260  and/or the electrode unit  280  can be replaced without shutting down the processing unit  220  for a significant period of time. The barrier unit  260  and/or the electrode unit  280  can be quickly removed from the processing unit  220  and then a replacement barrier and/or electrode unit can be attached in only a matter of minutes. This significantly reduces the downtime for repairing electrodes or other processing components compared to conventional systems that require the components to be repaired in situ on the vessel or require the entire chamber to be removed from the vessel. 
   An alternate embodiment of the barrier unit  260  can include a porous barrier instead of the nonporous barrier  270  shown and described above with reference to  FIGS. 4 and 5 . Such a porous barrier can generally separate the first and second flow systems, but the porous barrier generally allows some fluid to flow between the first and second flow systems. 
   D. Additional Embodiments of Electrochemical Deposition Vessels 
     FIG. 6  is a schematic view of a wet chemical vessel  310  in accordance with another embodiment of the invention. The vessel  310  includes a processing unit  320  (shown schematically), an electrode unit  380  (shown schematically), and a barrier  370  (shown schematically) separating the processing and electrode units  320  and  380 . The processing unit  320  and the electrode unit  380  can be generally similar to the processing and electrode units  220  and  280  described above with reference to  FIGS. 4 and 5 . For example, the processing unit  320  can include a portion of a first flow system to convey a flow of a first processing fluid toward the workpiece at a processing site, and the electrode unit  380  can include at least one electrode  390  and a portion of a second flow system to convey a flow of a second processing fluid at least proximate to the electrode  390 . The barrier  370  can be a nonporous barrier or a porous barrier. 
   Unlike the vessel  210 , the vessel  310  does not include a separate barrier unit but rather the barrier  370  is attached directly between the processing unit  320  and the electrode unit  380 . The barrier  370  otherwise separates the first processing fluid in the processing unit  320  and the second processing fluid in the electrode unit  380  in much the same manner as the nonporous barrier  270 . Another difference with the vessel  210  is that the barrier  370  and the electrode unit  380  are not canted relative to the processing unit  320 . 
   The first and second processing fluids can flow in the vessel  310  in a direction that is opposite to the flow direction described above with reference to the vessel  210  of  FIGS. 4 and 5 . More specifically, the first processing fluid can flow along a path F 1  from the barrier  370  toward the workpiece and exit the vessel  310  proximate to the processing site. The second processing fluid can flow along a path F 2  from the barrier  370  toward the electrode  390  and then exit the vessel  310 . In other embodiments, the vessel  310  can include a device to degas the first and/or second processing fluids. 
     FIG. 7  schematically illustrates a vessel  410  having a processing unit  420 , an electrode unit  480 , and a barrier  470  canted relative to the processing and electrode units  420  and  480 . This embodiment is similar to the vessel  310  in that it does not have a separate barrier unit and the barrier  470  can be nonporous or porous, but the vessel  410  differs from the vessel  310  in that the barrier  470  is canted at an angle. Alternatively,  FIG. 8  schematically illustrates a vessel  510  including a processing unit  520 , an electrode unit  580 , and a barrier  570  between the processing and electrode units  520  and  580 . The vessel  510  is similar to the vessel  410 , but the barrier  570  and the electrode unit  580  are both canted relative to the processing unit  520  in the vessel  510 . 
   E. Embodiments of Integrated Tools with Mounting Modules 
     FIG. 9  schematically illustrates an integrated tool  600  that can perform one or more wet chemical processes. The tool  600  includes a housing or cabinet  602  that encloses a deck  664 , a plurality of wet chemical processing stations  601 , and a transport system  605 . Each processing station  601  includes a vessel, chamber, or reactor  610  and a workpiece support (for example, a lift-rotate unit)  613  for transferring microfeature workpieces W into and out of the reactor  610 . The vessel, chamber, or reactor  610  can be generally similar to any one of the vessels described above with reference to  FIGS. 2A-8 . The stations  601  can include spin-rinse-dry chambers, seed layer repair chambers, cleaning capsules, etching capsules, electrochemical deposition chambers, and/or other types of wet chemical processing vessels. The transport system  605  includes a linear track  604  and a robot  603  that moves along the track  604  to transport individual workpieces W within the tool  600 . The integrated tool  600  further includes a workpiece load/unload unit  608  having a plurality of containers  607  for holding the workpieces W. In operation, the robot  603  transports workpieces W to/from the containers  607  and the processing stations  601  according to a predetermined workflow schedule within the tool  600 . For example, individual workpieces W can pass through a seed layer repair process, a plating process, a spin-rinse-dry process, and an annealing process. Alternatively, individual workpieces W may not pass through a seed layer repair process or may otherwise be processed differently. 
     FIG. 10A  is an isometric view showing a portion of an integrated tool  600  in accordance with an embodiment, of the invention. The integrated tool  600  includes a frame  662 , a dimensionally stable mounting module  660  mounted to the frame  662 , a plurality of wet chemical processing chambers  610 , and a plurality of workpiece supports  613 . The tool  600  can also include a transport system  605 . The mounting module  660  carries the processing chambers  610 , the workpiece supports  613 , and the transport system  605 . 
   The frame  662  has a plurality of posts  663  and cross-bars  661  that are welded together in a manner known in the art. A plurality of outer panels and doors (not shown in  FIG. 10A ) are generally attached to the frame  662  to form an enclosed cabinet  602  ( FIG. 9 ). The mounting module  660  is at least partially housed within the frame  662 . In one embodiment, the mounting module  660  is carried by the cross-bars  661  of the frame  662 , but the mounting module  660  can alternatively stand directly on the floor of the facility or other structures. 
   The mounting module  660  is a rigid, stable structure that maintains the relative positions between the wet chemical processing chambers  610 , the workpiece supports  613 , and the transport system  605 . One aspect of the mounting module  660  is that it is much more rigid and has a significantly greater structural integrity compared to the frame  662  so that the relative positions between the wet chemical processing chambers  610 , the workpiece supports  613 , and the transport system  605  do not change over time. Another aspect of the mounting module  660  is that it includes a dimensionally stable deck  664  with positioning elements at precise locations for positioning the processing chambers  610  and the workpiece supports  613  at known locations on the deck  664 . In one embodiment (not shown), the transport system  605  is mounted directly to the deck  664 . In an arrangement shown in  FIG. 10A , the mounting module  660  also has a dimensionally stable platform  665  and the transport system  605  is mounted to the platform  665 . The deck  664  and the platform  665  are fixedly positioned relative to each other so that positioning elements on the deck  664  and positioning elements on the platform  665  do not move relative to each other. The mounting module  660  accordingly provides a system in which wet chemical processing chambers  610  and workpiece supports  613  can be removed and replaced with interchangeable components in a manner that accurately positions the replacement components at precise locations on the deck  664 . 
   The tool  600  is particularly suitable for applications that have demanding specifications which require frequent maintenance of the wet chemical processing chambers  610 , the workpiece support  613 , or the transport system  605 . A wet chemical processing chamber  610  can be repaired or maintained by simply detaching the chamber from the processing deck  664  and replacing the chamber  610  with an interchangeable chamber having mounting hardware configured to interface with the positioning elements on the deck  664 . Because the mounting module  660  is dimensionally stable and the mounting hardware of the replacement processing chamber  610  interfaces with the deck  664 , the chambers  610  can be interchanged on the deck  664  without having to recalibrate the transport system  605 . This is expected to significantly reduce the downtime associated with repairing or maintaining the processing chambers  610  so that the tool  600  can maintain a high throughput in applications that have stringent performance specifications. 
     FIG. 10B  is a top plan view of the tool  600  illustrating the transport system  605  and the load/unload unit  608  attached to the mounting module  660 . Referring to  FIGS. 10A and 10B  together, the track  604  is mounted to the platform  665  and in particular, interfaces with positioning elements on the platform  665  so that it is accurately positioned relative to the chambers  610  and the workpiece supports  613  attached to the deck  664 . The robot  603  (which includes end-effectors  606  for grasping the workpiece W) can accordingly move the workpiece W in a fixed, dimensionally stable reference frame established by the mounting module  660 . Referring to  FIG. 10B , the tool  600  can further include a plurality of panels  666  attached to the frame  662  to enclose the mounting module  660 , the wet chemical processing chambers  610 , the workpiece supports  613 , and the transport system  605  in the cabinet  602 . Alternatively, the panels  666  on one or both sides of the tool  600  can be removed in the region above the processing deck  664  to provide an open tool. 
   F. Embodiments of Dimensionally Stable Mounting Modules 
     FIG. 11  is an isometric view of a mounting module  660  configured in accordance with an embodiment of the invention for use in the tool  600  ( FIGS. 9-10B ). The deck  664  includes a rigid first panel  666   a  and a rigid second panel  666   b  superimposed underneath the first panel  666   a . The first panel  666   a  is an outer member and the second panel  666   b  is an interior member juxtaposed to the outer member. Alternatively, the first and second panels  666   a  and  666   b  can have different configurations than the one shown in  FIG. 11 . A plurality of chamber receptacles  667  are disposed in the first and second panels  666   a  and  666   b  to receive the wet chemical processing chambers  610  ( FIG. 10A ). 
   The deck  664  further includes a plurality of positioning elements  668  and attachment elements  669  arranged in a precise pattern across the first panel  666   a . The positioning elements  668  include holes machined in the first panel  666   a  at precise locations, and/or dowels or pins received in the holes. The dowels are also configured to interface with the wet chemical processing chambers  610  ( FIG. 10A ). For example, the dowels can be received in corresponding holes or other interface members of the processing chambers  610 . In other embodiments, the positioning elements  668  include pins, such as cylindrical pins or conical pins, that project upwardly from the first panel  666   a  without being positioned in holes in the first panel  666   a . The deck  664  has a set of first chamber positioning elements  668   a  located at each chamber receptacle  667  to accurately position the individual wet chemical processing chambers at precise locations on the mounting module  660 . The deck  664  can also include a set of first support positioning elements  668   b  near each receptacle  667  to accurately position individual workpiece supports  613  ( FIG. 10A ) at precise locations on the mounting module  660 . The first support positioning elements  668   b  are positioned and configured to mate with corresponding positioning elements of the workpiece supports  613 . The attachment elements  669  can be threaded holes in the first panel  666   a  that receive bolts to secure the chambers  610  and the workpiece supports  613  to the deck  664 . 
   The mounting module  660  also includes exterior side plates  670   a  along longitudinal outer edges of the deck  664 , interior side plates  670   b  along longitudinal inner edges of the deck  664 , and endplates  670   c  attached to the ends of the deck  664 . The transport platform  665  is attached to the interior side plates  670   b  and the end plates  670   c . The transport platform  665  includes track positioning elements  668   c  for accurately positioning the track  604  ( FIGS. 10A and 10B ) of the transport system  605  ( FIGS. 10A and 10B ) on the mounting module  660 . For example, the track positioning elements  668   c  can include pins or holes that mate with corresponding holes, pins or other interface members of the track  604 . The transport platform  665  can further include attachment elements  669 , such as tapped holes, that receive bolts to secure the track  604  to the platform  665 . 
     FIG. 12  is a cross-sectional view illustrating one suitable embodiment of the internal structure of the deck  664 , and  FIG. 13  is a detailed view of a portion of the deck  664  shown in  FIG. 12 . The deck  664  includes bracing  671 , such as joists, extending laterally between the exterior side plates  670   a  and the interior side plates  670   b . The first panel  666   a  is attached to the upper side of the bracing  671 , and the second panel  666   b  is attached to the lower side of the bracing  671 . The deck  664  can further include a plurality of throughbolts  672  and nuts  673  that secure the first and second panels  666   a  and  666   b  to the bracing  671 . As best shown in  FIG. 13 , the bracing  671  has a plurality of holes  674  through which the throughbolts  672  extend. The nuts  673  can be welded to the bolts  672  to enhance the connection between these components. 
   The panels and bracing of the deck  664  can be made from stainless steel, other metal alloys, solid cast materials, or fiber-reinforced composites. For example, the panels and plates can be made from Nitronic 50 stainless steel, Hastelloy 625 steel alloys, or a solid cast epoxy filled with mica. The fiber-reinforced composites can include a carbon-fiber or Kevlar® mesh in a hardened resin. The material for the panels  666   a  and  666   b  should be highly rigid and compatible with the chemicals used in the wet chemical processes. Stainless steel is well-suited for many applications because it is strong but not affected by many of the electrolytic solutions or cleaning solutions used in wet chemical processes. In one embodiment, the panels and plates  666   a - b  and  670   a - c  are 0.125 to 0.375 inch thick stainless-steel, and more specifically they can be 0.250 inch thick stainless steel. The panels and plates, however, can have different thicknesses in other embodiments. 
   The bracing  671  can also be stainless steel, fiber-reinforced composite materials, other metal alloys, and/or solid cast materials. In one embodiment, the bracing can be 0.5 to 2.0 inch wide stainless steel joists, and more specifically 1.0 inch wide by 2.0 inches tall stainless steel joists. In other embodiments the bracing  671  can be a honey-comb core or other structures made from metal (e.g., stainless steel, aluminum, titanium, etc.), polymers, fiber glass or other materials. 
   The mounting module  660  is constructed by assembling the sections of the deck  664 , and then welding or otherwise adhering the end plates  670   c  to the sections of the deck  664 . The components of the deck  664  are generally secured together by the throughbolts  672  without welds. The outer side plates  670   a  and the interior side plates  670   b  are attached to the deck  664  and the end plates  670   c  using welds and/or fasteners. The platform  665  is then securely attached to the end plates  670   c , and the interior side plates  670   b . The order in which the mounting module  660  is assembled can be varied and is not limited to the procedure explained above. 
   The mounting module  660  provides a heavy-duty, dimensionally stable structure that maintains the relative positions between the positioning elements  668   a - b  on the deck  664  and the positioning elements  668   c  on the platform  665  within a range that does not require the transport system  605  to be recalibrated each time a replacement processing chamber  610  or workpiece support  613  is mounted to the deck  664 . The mounting module  660  is generally a rigid structure that is sufficiently strong to maintain the relative positions between the positioning elements  668   a - b  and  668   c  when the wet chemical processing chambers  610 , the workpiece supports  613 , and the transport system  605  are mounted to the mounting module  660 . In several embodiments, the mounting module  660  is configured to maintain the relative positions between the positioning elements  668   a - b  and  668   c  to within 0.025 inch. In other embodiments, the mounting module is configured to maintain the relative positions between the positioning elements  668   a - b  and  668   c  to within approximately 0.005 to 0.015 inch. As such, the deck  664  often maintains a uniformly flat surface to within approximately 0.025 inch, and in more specific embodiments to approximately 0.005-0.015 inch. 
   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, various aspects of any of the foregoing embodiments can be combined in different combinations, or features such as the sizes, material types, and/or fluid flows can be different. Accordingly, the invention is not limited except as by the appended claims.