Abstract:
The present invention is directed to an improved electroplating method, chemistry, and production worthy apparatus for depositing noble metals (e.g., platinum) and their alloys onto the surface of the workpiece, such as a semiconductor wafer, pursuant to manufacturing a microelectronic device, circuit, and/or component. The reliability of the noble metal material deposited using the disclosed method, chemistry, and/or apparatus is significantly better than the reliability of noble metal structures deposited using the teachings of the prior art. This is largely attributable to the low stress of films that are deposited using the teachings disclosed herein. The metals, which can be deposited, include gold, silver, platinum, palladium, ruthenium, iridium, rhodium, osmium and alloys containing these metals.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is directed to electroplating a low-stress noble metal film onto the surface of a workpiece, such as a semiconductor wafer, in the manufacture of microelectronic devices and/or components. More particularly, the present invention is directed to a method, chemistry and apparatus for electroplating a noble metal, such as platinum, on a microelectronic workpiece.  
           [0002]    Production of semiconductor integrated circuits and other microelectronic devices from workpieces, such as semiconductor wafers, typically requires formation of one or more metal layers on the workpiece. These metal layers are used, for example, to electrically interconnect the various devices of the integrated circuit. Further, the structures formed from the metal layers may be elements of microelectronic devices such as read/write heads, etc..  
           [0003]    The microelectronic manufacturing industry has applied a wide range of metals to form such structures. These metals include, for example, nickel, tungsten, solder, and copper. Further, a wide range of processing techniques have been used to deposit such metals. These techniques include, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating, and electroless plating. Of these techniques, electroplating tends to be the most economical and, as such, the most desirable. Electroplating can be used in the deposition of blanket metal layers as well as selectively deposited or patterned metal layers.  
           [0004]    One of the process sequences used in the microelectronic manufacturing industry to form one or more metal structures on a semiconductor wafer is referred to as “damascene” or “inlaid” processing. In such processing, holes, commonly called “vias”, trenches and/or other microscopic-sized recesses are formed in a workpiece surface and filled, either entirely or only partially, with a metal. In the damascene process, the wafer is first provided with a metallic seed layer which is used to conduct electrical current during a subsequent metal electroplating step. When certain metals that readily migrate into the surface of the wafer are used, the seed layer is disposed over a barrier layer material, such as Ti, TiN, Ta, TaN, etc.  
           [0005]    The seed layer is a very thin layer of metal which can be applied using one or more of several processes. For example, the seed layer can be laid down using physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes to produce a layer on the order of 100-1,000 angstroms thick. The seed layer can be formed of copper, gold, nickel, palladium, platinum, or other metals compatible with the subsequently applied metal. The seed layer is formed over a surface which is convoluted by the presence of the vias, trenches, or other recessed device features.  
           [0006]    A metal layer may then be electroplated onto the seed layer. The layer is plated to form an overlying layer, with the goal of providing a metal layer that either entirely or partially fills the trenches and vias.  
           [0007]    After the blanket layer has been electroplated onto the semiconductor wafer, excess metal material present outside of the vias, trenches, or other recesses is removed. The excess plated material can be removed, for example, using chemical mechanical planarization, chemical etching, or plasma etching. Chemical mechanical planarization is a processing step which uses the combined action of a chemical removal agent and an abrasive which grinds and polishes the exposed metal surface to remove undesired parts of the metal layer applied in the electroplating step. The metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed.  
           [0008]    The electroplating of the semiconductor wafers takes place in a reactor assembly. In such an assembly an anode electrode is disposed in a plating bath, and the wafer with the seed layer thereon is used as a cathode. Preferably, only a lower face of the wafer contacts the surface of the plating bath. The wafer is held by a support system that also conducts the requisite electroplating power (e.g., cathode current) to the wafer. The support system may comprise conductive fingers that secure the wafer in place and also contact the wafer seed layer in order to conduct electrical current for the plating operation. One embodiment of a reactor assembly is disclosed in U.S. Ser. No. 08/988,333 filed Sep. 30, 1997 entitled “Semiconductor Plating System Workpiece Support Having Workpiece—Engaging Electrodes With Distal Contact Part and Dielectric Cover.” 
           [0009]    An efficient process for electroplating of certain noble metals is desirable in those microelectronic applications in which nickel, copper, etc. are not the optimal metal. Such components include, for example, sensors (electrochemical or micro-mechanical), capacitor structures in memory cells, and some interconnects for microelectronic devices. One application in which electroplating of a noble metal onto a workpiece is particularly useful is in the fabrication of platinum electrodes for capacitors used, for example, in semiconductor memory devices. The work function of platinum facilitates the formation of capacitor electrodes that exhibit enhanced electrical characteristics, including lower leakage currents and a higher breakdown voltage when compared to electrodes of other metals. The low leakage current minimizes the amount of charge lost between refresh cycles of, for example, dynamic memory cells including such capacitors. The higher breakdown voltage allows the capacitor to store a larger charge without significant current leakage. Consequently capacitors having smaller geometries are possible thereby allowing the formation of a greater number of capacitors upon a workpiece of a given size. Further benefits of platinum relate to the fact that it has a low propensity to react with other materials or oxidize and, as such, does not form an undesired oxide film at its surface when it is exposed to the ambient environment. This can be important where processing steps subsequent to the plating of the platinum expose the workpiece to oxygen. Such exposure is possible if subsequent processing steps, for example, try the workpiece and expose it to oxygen, such as found in the ambient air.  
           [0010]    Various platinum electroplating processes are known, though efforts have mainly been directed at development of an appropriate electroplating bath, and additives for the bath. For example, a process of electroplating a platinum-rhodium alloy on a metal substrate has been disclosed in U.S. Pat. No. 4,285,784; and a procedure for electroplating platinum and platinum alloys involving use of an organic polyamine as a platinum complexing agent has been disclosed in U.S. Pat. No. 4,427,502. Moreover, there have been some uses of platinum in semiconductor chip manufacture. For example, selective deposition of platinum on a conductive or semiconductive substrate was disclosed in U.S. Pat. No. 5,320,978, and a method for depositing a coat of platinum on the surface of a silicon substrate by dipping the substrate into an aqueous solution of chloroplatinic acid and hydrofluoric acid was disclosed in U.S. Pat. No. 3,963,523. Recently, noble metal plating on a pre-existing seed layer for the fabrication of electrodes for use in DRAM and FRAM was disclosed in U.S. Pat. No. 5,789,320.  
           [0011]    Several technical problems must be overcome in designing reactors used in the electroplating of semiconductor wafers with a noble metal, such as platinum. For example, most noble metals tend to be deposited in a state of high film stress. This film stress is generally greatest at or near the point of contact where current is applied to the seed layer during the electroplating process. This stress can be detrimental to the function and reliability of the microelectronic components produced using these materials.  
           [0012]    One factor affecting film stress is the occurrence of varying current densities that occur during the plating process while the workpiece is functioning as a cathode. In many reactors used to electroplate metals onto the surface of a semiconductor wafer, a small number of discrete electrical contacts (e.g., 6 contacts) are used to contact the seed layer about the perimeter of the wafer. Such discrete contacts ordinarily produce higher current densities near the contact points than at other portions of the wafer. This non-uniform distribution of current across the wafer, in turn, causes non-uniform deposition of the plated metallic material and, further, produces a substantial film stress near the contact locations. Such reactors are therefore not particularly well-suited for plating noble metals, such as platinum.  
           [0013]    Another problem with electroplating of noble metals onto workpieces concerns efforts to prevent the electric contacts themselves from being plated during the electroplating process. Any material plated to the electrical contacts must be removed to prevent changing contact performance. However, noble metals such as platinum, unlike metals such as copper, cannot be reverse plated from the electrical contacts. Rather, any electrical contact that is plated with the noble metal must be replaced if the plating process is to remain in a satisfactory working state.  
           [0014]    The foregoing concern also applies to the use of current thieving in the electroplating process. Current thieving, effected by the provision of electrically-conductive elements other than those which contact the seed layer, can be employed near the wafer contacts to minimize non-uniformity of the deposited noble metal. The electrically-conductive elements are generally exposed to the electroplating solution and, as such, are plated with the noble metal during the electroplating process. The elements must therefore be replaced if the plating process is to remain in a satisfactory operational state. As a result, current thieving, while desirable to increase film uniformities, can be costly to implement.  
           [0015]    When electroplating a noble metal such as platinum, it is desirable to prevent electroplating on any exposed barrier layer near the edge of the semiconductor wafer. Electroplated material may not adhere well to the exposed barrier layer material, and is therefore prone to peeling off in subsequent wafer processing steps. Further, metal that is electroplated onto the barrier layer within the reactor may flake off during the electroplating process thereby adding particulate contaminants to the electroplating bath. Such contaminants can adversely affect the overall electroplating process.  
           [0016]    The specific metal used for the seed layer can also complicate the electroplating process. For example, certain seed layer metals have a relatively high electrical resistance. Still further, some noble metals, such as platinum, have a high electrical resistance. As a consequence, use of the typical plurality of electrical wafer contacts (for example, six (6) discrete contacts) may not provide adequate uniformity of the plated metal layer on the wafer due to non-uniformities in the plating current that result from the high electrical resistance of the seed layer and/or noble metal layer (e.g., platinum).  
           [0017]    Beyond the contact related problems discussed above, there are also other problems associated with electroplating reactors. As device sizes decrease, the need for tighter control over the processing environment increases. This includes control over the contaminants that affect the electroplating process. The moving components of the reactor, which tend to generate such contaminants, should therefore be subject to strict isolation requirements. To control film stress, optimal process parameters must be determined for parameters such as electrolyte temperature, flow rate, cathode current density, current waveform and electrolyte composition. Other factors that should be considered include uniformity of deposition thickness, film resistivity, surface roughness, micro-feature throwing power and particulate contamination.  
           [0018]    Still further, existing electroplating reactors are often difficult to maintain. Such difficulties must be overcome if an electroplating reactor design is to be accepted for large-scale manufacturing.  
           [0019]    The present inventors have recognized and addressed many of the foregoing problems that exist in connection with the plating of noble metals, particularly platinum. To this end, they have developed an efficient method and production worthy apparatus for electroplating noble metals onto the surface of a workpiece, such as a semiconductor wafer. The disclosed method and apparatus provide for a suitable deposition rate, excellent film characteristics, and a reduction in the level of film stress that could otherwise result in cracking, delamination, or poor device reliability.  
         SUMMARY OF THE INVENTION  
         [0020]    The present invention is directed to an improved electroplating method, chemistry, and production worthy apparatus for depositing noble metals onto the surface of the workpiece, such as a semiconductor wafer, pursuant to manufacturing a microelectronic device, circuit, and/or component. The reliability of the noble metal material deposited using the disclosed method, chemistry, and/or apparatus is significantly better than the reliability of noble metal structures deposited using the teachings of the prior art. This is largely attributable to the low stress of films that are deposited using the teachings disclosed herein. The metals, which can be deposited, include gold, silver, platinum, palladium, ruthenium, iridium, rhodium, osmium and alloys containing these metals.  
           [0021]    In accordance with one aspect of the present invention, an apparatus for plating a noble metal on a microelectronic workpiece is disclosed that comprises a reactor chamber that contains an electroplating solution containing ions or complexes of the noble metal or noble metal alloy that is to be plated onto the workpiece. The apparatus also includes a workpiece support having a contact for providing electroplating power to a surface at a side of the workpiece that is to be plated. The contact electrically contacts the workpiece at a large plurality of discrete contact points and each of the contact points is isolated from exposure to the electroplating solution. To complete the electroplating cell, an anode is provided and the electroplating solution and is spaced from the workpiece support within the reaction chamber.  
           [0022]    In accordance with a further aspect of the present invention, a contact member for use in conducting electroplating power to a surface of a microelectronic workpiece that is to be electroplated with a noble metal is set forth. The contact member comprises a conductive member and a removable conductive surface material disposed about an exterior surface of the conductive member. The removable conductive surface material may be in the form of a removable conductive strip wound about the exterior surface of the conductive member. In a preferred embodiment, the conductive member and the removable conductive surface material form a single, discreet contact.  
           [0023]    In accordance with a still further aspect of the present invention, an apparatus for plating a noble metal on a microelectronic workpiece is disclosed that comprises a reactor chamber that contains an electroplating solution having ions or complexes of the noble metal or noble metal alloy that is to be plated onto the workpiece. The apparatus also includes a workpiece support including a contact assembly for providing electroplating power to a surface at a side of the workpiece that is to be plated and an anode spaced from the workpiece support within the reaction chamber and contacting the electroplating solution. A chemical delivery system is employed for supplying the electroplating solution to the reactor chamber and recirculating electroplating solution removed from the reactor chamber. To eliminate fouling of the solution, as is quite prevalent when plating a noble metal, a multi-stage filtration system is utilized. The filtration system is disposed within the chemical delivery system for filtering electroplating solution removed from the reactor chamber before it is re-supplied to the reactor chamber. It includes at least a first filter stage for filtering particles greater than or equal to a first size and a second filter stage disposed downstream of the first filter stage for filtering particles greater than or equal to a second size, the first size being greater in magnitude than the second size.  
           [0024]    It may be desirable to use a current thief in any of the foregoing electroplating apparatus. In accordance with a still further aspect of the present invention, a disposable current thief is set forth. The disposable current thief is disposed in the electroplating solution between the anode and the contact assembly and is formed from the conductive portions of a printed circuit board. The disclosed current thief is manufactured from readily available materials using simple manufacturing processes thereby significantly reducing the costs of providing current thieving in noble metal electroplating processes.  
           [0025]    A method for electroplating a noble metal onto the surface of a microelectronic workpiece is also set forth. Although the method is generally apparatus independent, any of the foregoing apparatus may be used to implement the method. Generally stated, the method involves bringing the surface of the workpiece that is to be plated into contact with an electroplating solution including ions or complexes of a noble metal or noble metal alloy that is to be plated on the surface of the workpiece. Electroplating power is applied between the surface of the workpiece and an anode using a low current for a first predetermined period of time. This is subsequently followed at a later time by application of full-scale electroplating power between the surface of the workpiece and the anode for a second predetermined period of time. In many instances, it is preferable, though not necessary, to provide the low current as the initial electroplating power and to have the full-scale electroplating power applied immediately thereafter. At a time subsequent to the end of the second predetermined period of time, electroplating power is removed and the surface of the workpiece is disengaged from the electroplating solution. Suitable parameters for electroplating the noble metal using an acidic electroplating solution as well as an alkaline electroplating solution are also set forth.  
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a cross-sectional view through an electroplating reactor that is constructed in accordance with various teachings of the present invention.  
         [0027]    [0027]FIG. 2 illustrates a specific construction of one embodiment of a reactor bowl suitable for use in the assembly illustrated in FIG. 1.  
         [0028]    [0028]FIG. 3 illustrates one embodiment of a reactor head, comprised of a stationary assembly and a rotor assembly that is suitable for use in the assembly illustrated in FIG. 1.  
         [0029]    FIGS.  4 - 10  illustrate one embodiment of a contact assembly using flexure contacts that is suitable for use in the reactor assembly illustrated in FIG. 1.  
         [0030]    FIGS.  11 - 12  illustrate two different embodiments of a “Belleville ring” contact structure.  
         [0031]    FIGS.  13 - 15  illustrate one embodiment of a contact assembly using a “Belleville ring” contact structure, such as one of those illustrated in FIGS.  11 - 12 , that is suitable for use in the reactor assembly illustrated in FIG. 1.  
         [0032]    [0032]FIG. 16A is a schematic block diagram of a flow system for supplying the plating solution to the reactor bowl.  
         [0033]    FIGS.  16 B- 20  illustrate various aspects of one embodiment of a quick-attach mechanism.  
         [0034]    [0034]FIG. 21 is a cross-sectional view of the reactor head illustrating the disposition of the reactor head in a condition in which it may accept a workpiece.  
         [0035]    [0035]FIG. 22 is a cross-sectional view of the reactor head illustrating the disposition of the reactor head in a condition in which it is ready to present the workpiece to the reactor bowl.  
         [0036]    [0036]FIG. 23 illustrates an exploded view one embodiment of the rotor assembly.  
         [0037]    [0037]FIG. 24 illustrates one embodiment of a segmented current thief suitable for noble metal plating.  
         [0038]    [0038]FIG. 25 illustrates one embodiment of a finger contact that may also function as a current thief in the plating of noble metals.  
         [0039]    FIGS.  26 - 28  are top plan views of integrated processing tools that may incorporate electroless plating reactors and electroplating reactors in combination.  
         [0040]    FIGS.  29 - 32  are various views of a further embodiment of a reactor base for providing a flow of electroplating solution to the surface of a workpiece in which the flow assists in increasing the uniformity of the electroplated noble metal layer.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     BASIC NOBLE METAL ELECTROPLATING REACTOR COMPONENTS  
       [0041]    With reference to FIGS.  1 - 3 , there is shown a reactor assembly  20  for electroplating a noble metal on the surface of a microelectronic workpiece, such as a semiconductor wafer  25 . Generally stated, the reactor assembly  20  is comprised of a reactor head  30  and a corresponding reactor bowl  35 . This type of reactor assembly is particularly suited for effecting electroplating of semiconductor wafers or like workpieces, in which an electrically conductive, thin-film seed layer of the wafer is electroplated with a blanket or patterned noble metal layer, such as a layer of platinum.  
         [0042]    A specific construction of one embodiment of a reactor bowl  35  suitable for use in the reactor assembly  20  is illustrated in FIG. 2. The electroplating reactor bowl  35  is that portion of the reactor assembly  20  that contains electroplating solution, and that directs the solution at a high flow rate against a generally downwardly facing surface of an associated workpiece  25  to be plated. To this end, electroplating solution is circulated through the reactor bowl  35 . Attendant to solution circulation, the solution flows from the reactor bowl  35 , over the weir-like periphery of the bowl, into a lower overflow chamber  40  of the reactor assembly  20 . Solution is drawn from the overflow chamber typically for re-circulation through the reactor.  
         [0043]    The temperature of the electroplating solution is monitored and maintained by a temperature sensor and heater, respectively. The sensor and heater are disposed in the circulation path of the electroplating solution. For electroplating noble metals and their alloys, particularly platinum and platinum alloys, these components maintain the temperature of the electroplating solution in a temperature range between 40° C. and 80° C. Even more preferably, these components maintain the temperature of the electroplating solution at about 65° C. 0.5. As will be explained in connection with the preferred electroplating process, the electroplating solution exhibits optimal deposition properties within this latter temperature range.  
         [0044]    The reactor bowl  35  includes a riser tube  45 , within which an inlet conduit  50  is positioned for introduction of electroplating solution into the interior portion of the reactor bowl  35 . The inlet conduit  50  is preferably conductive and makes electrical contact with and supports an electroplating anode  55 . Anode  55  is preferably an inert anode, and, in at least one of the preferred methods, a platinized titanium inert anode is used. The electrically-conductive surface of the workpiece functions as a cathode.  
         [0045]    Electroplating solution flows at a high flow rate, preferably at a rate of 5 gal/min, from the inlet conduit  50  through openings at the upper portion thereof. From there, the solution flows about the anode  55 , and through an optional diffusion plate  65  positioned in operative association with and between the cathode (workpiece) and the anode.  
         [0046]    The reactor head  30  of the electroplating reactor  20  is preferably comprised of a stationary assembly  70  and a rotor assembly  75 , diagrammatically illustrated in FIG. 3. Rotor assembly  75  is configured to receive and carry an associated wafer  25  or like workpiece, position the wafer in a process-side down orientation within reactor bowl  35 , and to rotate or spin the workpiece while joining its electrically-conductive surface in the plating circuit of the reactor assembly  20 . The reactor head  30  is typically mounted on a lift/rotate apparatus  80 , which is configured to rotate the reactor head  30  from an upwardly-facing disposition, in which it receives the wafer to be plated, to a downwardly facing disposition, in which the surface of the wafer to be plated is positioned downwardly in reactor bowl  35 , generally in confronting relationship to diffusion plate  65 . A robotic arm  418 , including an end effector, is typically employed for placing the wafer  25  in position on the rotor assembly  75 , and for removing the plated wafer from the rotor assembly.  
         [0047]    It will be recognized that other reactor assembly configurations may be used with the inventive aspects of the disclosed reactor head, the foregoing being merely illustrative. Another reactor assembly suitable for use in the foregoing configuration is illustrated in U.S. Ser. No. ______, entitled “Workpiece Processor Having Improved Processing Chamber”, filed Jul. 12, 1999 (Attorney Docket No. SEM4492P0831US) and further reactor assembly illustrated in U.S. Ser. No. 60/120,955, filed Apr. 13, 1999, both of which are incorporated herein by reference.  
         [0048]    ELECTROPLATING SOLUTIONS  
         [0049]    The plating bath that is used in the reactor  35  depends upon the particular noble metal or noble metal alloy that is to be plated. Examples of suitable plating solutions for plating noble metals include: 1) for gold—cyanide-based or sulfite-based baths (such as Enthone-OMI Neutronex 309); 2) for ruthenium—a sulfamate, nitrosyl sulfamate or nitroso-based bath (such as Technic&#39;s Ruthenium U, Englehard&#39;s Ru-7 and Ru-8, and LeaRonal&#39;s Decronal White 44 and Decronal Black 44); and 4) for platinum—a potassium hydroxide-based based, ammonia-sulfamate-based, or sulfate-based bath (such as Englehard&#39;s Platinum A bath or Technics Platinum S bath). The particular solution for each selected metal is partially dependent upon the particular plating process being used. For example, with respect to platinum, a potassium hydroxide-based solution, such as Englehard&#39;s Platinum A, is well suited for use in an alkaline plating process, while an ammonia-sulfamate-based solution (such as Technic&#39;s Platinum S) is particularly well suited for use in a photoresist template process. Careful control of temperature and pH of the bath is often required for optimal plating results. Such parameters are typically placed under the control of a programmable control system.  
         [0050]    Exemplary Process  
         [0051]    An exemplary process sequence for plating a noble metal or noble metal alloy, such as platinum or a platinum alloy, onto the surface of a workpiece in a reactor assembly, such as the reactor assembly illustrated in FIGS.  1 - 3 , includes the following processing steps:  
         [0052]    (Optional) Pre-wet/Pre-clean the substrate material using deionized water or acid and/or a surfactant to eliminate the dry plating surface (about 30 seconds) (the pre-wet solution may be heated to the same temperature at which electroplating will occur);  
         [0053]    Adjust and/or program (either manually or using the programmable control system) the electroplating system for the appropriate processing parameters, including electroplating solution flow rate, pH, temperature, concentration of metal or alloy to be deposited, current density and waveform of electroplating power applied, and rotation rate of workpiece;  
         [0054]    Bring the surface of the workpiece that is to be plated into contact with the noble metal or noble metal alloy electroplating solution;  
         [0055]    (Optional) Apply an initial low electroplating current for a first predetermined period of time to initiate electroplating of the workpiece;  
         [0056]    Apply full-scale electroplating current for the duration necessary to achieve the desired depth of deposited material;  
         [0057]    Halt electrolysis;  
         [0058]    Disengage the workpiece from electroplating solution;  
         [0059]    Spin the workpiece at a high spin rate (i.e., above about 200 rpm) to remove excess electroplating solution;  
         [0060]    Rinse the workpiece in a spray of deionized water (about 2 min.) and spin dry at a high rotation rate;  
         [0061]    (Optional) Subject the workpiece to a backside cleaning process to remove any backside contamination, such as potassium hydroxide contamination  
         [0062]    For an alkaline platinum plating process, the preferred processing parameters include a flow rate of about 5 gallons per minute using a plating solution having a temperature of 65° C., a pH in the range of about 11-12, preferably about 11.5, and a platinum concentration in the range of about 10-15 g/l, preferably 12.5 g/l. Electroplating power is applied having a current density between about 3 and 9 mA/cm 2 , depending on the seed layer type, with low current initiation using a pulsed waveform having a pattern of 1 ms on, 1 ms off, or DC (again, depending on the seed layer material).  
         [0063]    Low current initiation is often desirable. If a seed layer is to thin, lacks sufficient adhesion, or is too highly stressed, cracking and peeling can occur at electroplating contact points and/or structures (e.g., posts, trenches, etc.). This may be due to high localized current densities. A low current initiation step allows for a slow build-up of platinum, or other noble metal, in these areas. When the thickness has increased beyond a predetermined magnitude, the current (and plating rate) can be increased without stress cracking. The predetermined magnitude can be determined experimentally.  
         [0064]    Deposition rates in excess of 320 angstroms/min are typical using the above noted parameters. A process using the same parameters, with the exception of applying a DC waveform, can result in deposition rates that are in excess of 740 angstroms/min. The current density that is used is principally limited by the amount of hydrogen gas that evolves during the electroplating process. Hydrogen gas may then be trapped in the plated film thereby resulting in stress cracking. There is therefore a trade-off that must be made between the deposition rate and the risk of stress cracking.  
         [0065]    The alkaline platinum plating process using the above parameters has exhibited high throwing power with respect to submicron features, making it well suited for the formation of 3D plug capacitor electrodes. Such electrodes require a conformal platinum layer that is defect free, and non-porous. A For 3D plug capacitors, plating thickness in an ultra thin layer less than 500 Å is typical.  
         [0066]    The foregoing alkaline platinum plating process is generally unsuitable for use in patterned plating in which photoresist is used as the plating mask unless the photoresist has been specifically chosen and treated (e.g., deep ultraviolet bake) for use in an alkaline plating bath. Rather, an acidic plating bath is preferred for such processes. The present inventors have likewise developed an acidic platinum plating process that is suitable for use in processes employing a photoresist mask. The preferred processing parameters include a flow rate of 5 gallons per minute for a plating solution having a temperature of 65° C., a pH in the range of about 2-4, preferably about 3.0, and a platinum concentration in the range of about 2-16 g/l, preferably about 4.0 g/l. Electroplating power is applied having a current density in the range of about 20-50 mA/cm 2 , preferably about 34.5 mA/cm 2  using a pulsed waveform. The waveform may have an on time of about 1-10 ms, preferably of 1 ms, and an off time of about 1-10 ms, preferably 1 ms off. Deposition rates in excess of 550 angstroms/min are typical using the above noted acidic platinum plating parameters. The acidic platinum plating process is well suited for the formation of patterned capacitors, where a plating thickness of about 2500 angstroms is typical.  
         [0067]    As noted above, the plating process is typically applied to a workpiece having a seed layer on top of a barrier layer. Typically the seed layer is applied to the barrier layer using physical vapor deposition. The characteristics of the barrier layer and the seed layer, including the type of material and thickness, can have an impact on stress cracking and plating uniformity. Preferred barrier layer materials include TiN, Ta, TaN, Ti, and TiO2.  
         [0068]    Similar plating processes, or ones with only slight modifications, using the particular plating bath required, can be used to plate other noble metals, or noble metal alloys. As will be set forth in further detail below, the foregoing processing steps and sequence may be implemented in a single fabrication tool having a plurality of similar processing stations and a programmable robot that transfers the workpieces between such stations.  
         [0069]    There are a number of enhancements that may be made to the reactor assembly  20  described above that facilitate uniformity of the noble metal deposits over the face of the workpiece. For example, the reactor assembly  20  may use a contact assembly that reduces non-uniformities in the deposits that occur proximate the discrete contacts that are used to provide plating power to the surface at the perimeter of the workpiece, including the alternative use of a continuous or a semi-continuous ring contact. Additionally, other enhancements to the reactor assembly  20  may be added to facilitate routine service and/or configurability of the system.  
         [0070]    IMPROVED CONTACT ASSEMBLIES  
         [0071]    As noted above, the manner in which the electroplating power is supplied to the wafer at the peripheral edge thereof is very important to the overall film quality of the deposited metal. Some of the more desirable characteristics of a contact assembly used to provide such electroplating power include, for example, the following:  
         [0072]    uniform distribution of electroplating power about the periphery of the wafer to maximize the uniformity of the deposited film;  
         [0073]    consistent contact characteristics to insure wafer-to-wafer uniformity;  
         [0074]    minimal intrusion of the contact assembly on the wafer periphery to maximize the available area for device production; and  
         [0075]    minimal plating on the barrier layer about the wafer periphery to inhibit peeling and/or flaking.  
         [0076]    To meet one or more of the foregoing characteristics, reactor  20  preferably employs a ring contact assembly  85  that provides either a continuous electrical contact or a high number of discrete electrical contacts with the wafer  25 . By providing a more continuous contact with the outer peripheral edges of the semiconductor wafer  25 , in this case around the outer circumference of the semiconductor wafer, a more uniform current is supplied to the semiconductor wafer  25  that promotes more uniform current densities. The more uniform current densities enhance uniformity in the depth of the deposited material.  
         [0077]    Contact assembly  85 , in accordance with a preferred embodiment, includes contact members that provide minimal intrusion about the wafer periphery while concurrently providing consistent contact with the seed layer. Contact with the seed layer is enhanced by using a contact member structure that provides a wiping action against the seed layer as the wafer is brought into engagement with the contact assembly. This wiping action assists in removing any oxides at the seed layer surface thereby enhancing the electrical contact between the contact structure and the seed layer. As a result, uniformity of the current densities about the wafer periphery are increased and the resulting film is more uniform. Further, such consistency in the electrical contact facilitates greater consistency in the electroplating process from wafer-to-wafer thereby increasing wafer-to-wafer uniformity.  
         [0078]    Contact assembly  85 , as will be set forth in further detail below, also preferably includes one or more structures that provide a barrier, individually or in cooperation with other structures, that separates the contact/contacts, the peripheral edge portions and backside of the semiconductor wafer  25  from the plating solution. This prevents the plating of metal onto the individual contacts and, further, assists in preventing any exposed portions of the barrier layer near the edge of the semiconductor wafer  25  from being exposed to the electroplating environment. As a result, plating of the barrier layer and the appertaining potential for contamination due to flaking of any loosely adhered electroplated material is substantially limited.  
         [0079]    RING CONTACT ASSEMBLIES USING FLEXURE CONTACTS  
         [0080]    One embodiment of a contact assembly suitable for use in the assembly  20  is shown generally at  85  of FIGS.  4 - 10 . The contact assembly  85  forms part of the rotor assembly  75  and provides electrical contact between the semiconductor wafer  25  and a source of electroplating power. In the illustrated embodiment, electrical contact between the semiconductor wafer  25  and the contact assembly  85  occurs at a large plurality of discrete flexure contacts  90  that are effectively separated from the electroplating environment interior of the reactor bowl  35  when the semiconductor wafer  25  is held and supported by the rotor assembly  75 .  
         [0081]    The contact assembly  85  may be comprised of several discrete components. With reference to FIG. 4, when the workpiece that is to be electroplated is a circular semiconductor wafer, the discrete components of the contact assembly  85  join together to form a generally annular component having a bounded central open region  95 . It is within this bounded central open region  95  that the surface of the semiconductor wafer that is to be electroplated is exposed. With particular reference to FIG. 6, contact assembly  85  includes an outer body member  100 , an annular wedge  105 , a plurality of flexure contacts  90 , a contact mount member  110 , and an interior wafer guide  115 . Preferably, annular wedge  105 , flexure contacts  90 , and contact mount member  110  are formed from platinized titanium while wafer guide  115  and outer body member  100  are formed from a dielectric material that is compatible with the electroplating environment. Annular wedge  105 , flexure contacts  90 , mount member  110 , and wafer guide  115  join together to form a single assembly that is secured together by outer body member  100 .  
         [0082]    As shown in FIG. 6, contact mount member  110  includes a first annular groove  120  disposed about a peripheral portion thereof and a second annular groove  125  disposed radially inward of the first annular groove  120 . The second annular groove  125  opens to a plurality of flexure channels  130  that are equal in number to the number of flexure contacts  90 . As can be seen from FIG. 4, a total of  36  flexure contacts  90  are employed, each being spaced from one another by an angle of about 10 degrees.  
         [0083]    Referring again to FIG. 6, each flexure contact  90  is comprised of an upstanding portion  135 , a transverse portion  140 , a vertical transition portion  145 , and a wafer contact portion  150 . Similarly, wedge  105  includes an upstanding portion  155  and a transverse portion  160 . Upstanding portion  155  of wedge  105  and upstanding portion  135  of each flexure contact  90  are secured within the first annular groove  120  of the contact mount member  110  at the site of each flexure channel  130 . Self-adjustment of the flexure contacts  90  to their proper position within the overall contact assembly  85  is facilitated by first placing each of the individual flexure contacts  90  in its respective flexure channel  130  so that the upstanding portion  135  is disposed within the first annular groove  120  of the contact mount member  110  while the transition portion  145  and contact portion  150  proceed through the respective flexure channel  130 . The upstanding portion  155  of wedge member  105  is then urged into the first annular groove  120 . To assist in this engagement, the upper end of upstanding portion  155  is tapered. The combined width of upstanding portion  135  of the flexure contact  90  and upstanding portion  155  of wedge  105  are such that these components are firmly secured with contact mount member  110 .  
         [0084]    Transverse portion  160  of wedge  105  extends along a portion of the length of transverse portion  140  of each flexure  90 . In the illustrated embodiment, transverse portion  160  of wedge portion  105  terminates at the edge of the second annular groove  125  of contact mount member  110 . As will be more clear from the description of the flexure contact operation below, the length of transverse portion  160  of wedge  105  can be chosen to provide the desired degree of stiffness of the flexure contacts  90 .  
         [0085]    Wafer guide  115  is in the form of an annular ring having a plurality of slots  165  through which contact portions  150  of flexures  90  extend. An annular extension  170  proceeds from the exterior wall of wafer guide  115  and engages a corresponding annular groove  175  disposed in the interior wall of contact mount member  110  to thereby secure the wafer guide  115  with the contact mount member  110 . As illustrated, the wafer guide member  115  has an interior diameter that decreases from the upper portion thereof to the lower portion thereof proximate contact portions  150 . A wafer inserted into contact assembly  85  is thus guided into position with contact portions  150  by a tapered guide wall formed at the interior of wafer guide  115 . Preferably, the portion  180  of wafer guide  115  that extends below annular extension  170  is formed as a thin, compliant wall that resiliently deforms to accommodate wafers having different diameters within the tolerance range of a given wafer size. Further, such resilient deformation accommodates a range of wafer insertion tolerances occurring in the components used to bring the wafer into engagement with the contact portions  150  of the flexures  90 .  
         [0086]    Referring to FIG. 6, outer body member  100  includes an upstanding portion  185 , a transverse portion  190 , a vertical transition portion  195  and a further transverse portion  200  that terminates in an upturned lip  205 . Upstanding portion  185  includes an annular extension  210  that extends radially inward to engage a corresponding annular notch  215  disposed in an exterior wall of contact mount member  110 . A V-shaped notch  220  is formed at a lower portion of the upstanding portion  185  and circumvents the outer periphery thereof. The V-shaped notch  220  allows upstanding portion  185  to resiliently deform during assembly. To this end, upstanding portion  185  resiliently deforms as annular extension  210  slides about the exterior of contact mount member  110  to engage annular notch  215 . Once so engaged, contact mount member  110  is clamped between annular extension  210  and the interior wall of transverse portion  190  of outer body member  100 .  
         [0087]    Further transverse portion  200  extends beyond the length of contact portions  150  of the flexure contacts  90  and is dimensioned to resiliently deform as a wafer, such as at  25 , is driven against them. V-shaped notch  220  may be dimensioned and positioned to assist in the resilient deformation of transverse portion  200 . With the wafer  25  in proper engagement with the contact portions  150 , upturned lip  205  engages wafer  25  and assists in providing a barrier between the electroplating solution and the outer peripheral edge and backside of wafer  25 , including the flexure contacts  90 .  
         [0088]    As illustrated in FIG. 6, flexure contacts  90  resiliently deform as the wafer  25  is driven against them. Preferably, contact portions  150  are initially angled upward in the illustrated manner. Thus, as the wafer  25  is urged against contact portions  150 , flexures  90  resiliently deform so that contact portions  150  effectively wipe against surface  230  of wafer  25 . In the illustrated embodiment, contact portions  150  effectively wipe against surface  230  of wafer  25  a horizontal distance designated at  235 . This wiping action assists in removing and/or at penetrating any oxides from surface  230  of wafer  25  thereby providing more effective electrical contact between flexure contacts  90  and the seed layer at surface  230  of wafer  25 .  
         [0089]    With reference to FIGS. 7 and 8, contact mount member  110  is provided with one or more ports  240  that may be connected to a source of purging gas, such as a source of nitrogen. As shown in FIG. 8, purge ports  240  open to second annular groove  125  which, in turn, operates as a manifold to distribute the purging gas to all of the flexure channels  130  as shown in FIG. 6. The purging gas then proceeds through each of the flexure channels  130  and slots  165  to substantially surround the entire contact portions  150  of flexures  90 . In addition to purging the area surrounding contact portions  150 , the purge gas cooperates with the upturned lip  205  of outer body member  100  to effect a barrier to the electroplating solution. Further circulation of the purge gas is facilitated by an annular channel  250  formed between a portion of the exterior wall of wafer guide  115  and a portion of the interior wall of contact mount member  110 .  
         [0090]    As shown in FIGS. 4, 5 and  10 , contact mount member  110  is provided with one or more threaded apertures  255  that are dimensioned to accommodate a corresponding connection plug  260 . With reference to FIGS. 5 and 10, connection plugs  260  provide electroplating power to the contact assembly  85  and, preferably, are each formed from platinized titanium. In a preferred form of plugs  260 , each plug  260  includes a body  265  having a centrally disposed bore hole  270 . A first flange  275  is disposed at an upper portion of body  265  and a second flange  280  is disposed at a lower portion of body  265 . A threaded extension  285  proceeds downward from a central portion of flange  280  and secures with threaded bore hole  270 . The lower surface of flange  280  directly abuts an upper surface of contact mount member  110  to increase the integrity of the electrical connection therebetween.  
         [0091]    Although flexure contacts  90  are formed as discrete components, they may be joined with one another as an integral assembly. To this end, for example, the upstanding portions  135  of the flexure contacts  90  may be joined to one another by a web of material, such as platinized titanium, that is either formed as a separate piece or is otherwise formed with the flexures from a single piece of material. The web of material may be formed between all of the flexure contacts or between select groups of flexure contacts. For example, a first web of material may be used to join half of the flexure contacts (e.g., 18 flexure contacts in the illustrated embodiment) while a second web of material is used to join a second half of the flexure contacts (e.g., the remaining 18 flexure contacts in the illustrated embodiment). Different groupings are also possible.  
         [0092]    BELLEVILLE RING CONTACT ASSEMBLIES  
         [0093]    Alternative contact assemblies are illustrated in FIGS.  11 - 15 . In each of these contact assemblies, the contact members are integrated with a corresponding common ring and, when mounted in their corresponding assemblies, are biased upward in the direction in which the wafer or other substrate is received upon the contact members. A top view of one embodiment of such a structure is illustrated in FIG. 11 A while a perspective view thereof is illustrated in FIG. 11B. As illustrated, a ring contact, shown generally at  610 , is comprised of a common ring portion  630  that joins a plurality of contact members  655 . The common ring portion  630  and the contact members  655 , when mounted in the corresponding assemblies, are similar in appearance to half of a conventional Belleville spring. For this reason, the ring contact  610  will be hereinafter referred to as a “Bellville ring contact” and the overall contact assembly into which it is placed will be referred to as a “Bellville ring contact assembly”.  
         [0094]    The embodiment of Belleville ring contact  610  illustrated in FIGS. 11A and 11B includes  72  contact members  655  and is preferably in formed from platinized titanium. The contact members  655  may be formed by cutting arcuate sections  657  into the interior diameter of a platinized titanium ring. A predetermined number of the contact members  658  have a greater length than the remaining contact members  655  to, for example, accommodate certain flat-sided wafers.  
         [0095]    A further embodiment of a Belleville ring contact  610  is illustrated in FIG. 12. As above, this embodiment is preferably formed from platinized titanium. Unlike the embodiment of FIGS. 11A and 11B in which all of the contact members  655  extend radially inward toward the center of the structure, this embodiment includes contact members  659  that are disposed at an angle. This embodiment constitutes a single-piece design that is easy to manufacture and that provides a more compliant contact than does the embodiment of FIGS. 11A and 11B with the same footprint. This contact embodiment can be fixtured into the “Belleville” form in the contact assembly and does not require permanent forming. If the Belleville ring contact  610  of this embodiment is fixtured in place, a complete circumferential structure is not required. Rather the contact may be formed and installed in segments thereby enabling independent control/sensing of the electrical properties of the segments.  
         [0096]    A first embodiment of a Bellville ring contact assembly is illustrated generally at  600  in in FIGS.  13 - 15 . As illustrated, the contact assembly  600  comprises a conductive contact mount member  605 , a Bellville ring contact  610 , a dielectric wafer guide ring  615 , and an outer body member  625 . The outer, common portion  630  of the Bellville ring contact  610  includes a first side that is engaged within a notch  675  of the conductive base ring  605 . In many respects, the Belleville ring contact assembly of this embodiment is similar in construction with the flexure contact assembly  85  described above. For that reason, the functionality of many of the structures of the contact assembly  600  will be apparent and will not be repeated here.  
         [0097]    Preferably, the wafer guide ring  615  is formed from a dielectric material while contact mount member  605  is formed from a single, integral piece of conductive material or from a dielectric or other material that is coated with a conductive material at its exterior. Even more preferably, the conductive ring  605  and Bellville ring contact  610  are formed from platinized titanium or are otherwise coated with a layer of platinum.  
         [0098]    The wafer guide ring  615  is dimensioned to fit within the interior diameter of the contact mount member  605 . Wafer guide ring  615  has substantially the same structure as wafer guides  115  and  115   b  described above in connection with contact assemblies  85  and  85   b , respectively. Preferably, the wafer guide ring  615  includes an annular extension  645  about its periphery that engages a corresponding annular slot  650  of the conductive base ring  605  to allow the wafer guide ring  615  and the contact mount member  605  to snap together.  
         [0099]    The outer body member  625  includes an upstanding portion  627 , a transverse portion  629 , a vertical transition portion  632  and a further transverse portion  725  that extends radially and terminates at an upturned lip  730 . Upturned lip  730  assists in forming a barrier to the electroplating environment when it engages the surface of the side of workpiece  25  that is being processed. In the illustrated embodiment, the engagement between the lip  730  and the surface of workpiece  25  is the only mechanical seal that is formed to protect the Bellville ring contact  610 .  
         [0100]    The area proximate the contacts  655  of the Belleville ring contact  610  is preferably purged with an inert fluid, such as nitrogen gas, which cooperates with lip  730  to effect a barrier between the Bellville ring contact  610 , peripheral portions and the backside of wafer  25 , and the electroplating environment. As particularly shown set forth in FIGS. 19 and 20, the outer body member  625  and contact mount member  605  are spaced from one another to form an annular cavity  765 . The annular cavity  765  is provided with an inert fluid, such as nitrogen, through one or more purge ports  770  disposed through the contact mount member  605 . The purged ports  770  open to the annular cavity  765 , which functions as a manifold to distribute to the inert gas about the periphery of the contact assembly. A given number of slots, such as at  780 , corresponding to the number of contact members  655  are provided and form passages that route the inert fluid from the annular cavity  765  to the area proximate contact members  655 .  
         [0101]    [0101]FIGS. 14 and 15 also illustrate the flow of a purging fluid in this embodiment of Bellville ring contact assembly. As illustrated by arrows, the purge gas enters purge port  770  and is distributed about the circumference of the assembly  600  within annular cavity  765 . The purged gas then flows through slots  780  and below the lower end of contact mount member  605  to the area proximate Bellville contact  610 . At this point, the gas flows to substantially surround the contact members  655  and, further, may proceed above the periphery of the wafer to the backside thereof. The purging gas may also proceed through an annular channel  712  defined by the contact mount member  605  and the interior of the compliant wall formed at the lower portion of wafer guide ring  615 . Additionally, the gas flow about contact members  655  cooperates with upturned lip  730  effect a barrier at lip  730  that prevents electroplating solution from proceeding therethrough.  
         [0102]    When a wafer or other workpiece  25  is urged into engagement with the contact assembly  600 , the workpiece  25  first makes contact with the contact members  655 . As the workpiece is urged further into position, the contact members  655  deflect and effectively wipe the surface of workpiece  25  until the workpiece  25  is pressed against the upturned lip  730 . This mechanical engagement, along with the flow of purging gas, effectively isolates the outer periphery and backside of the workpiece  25  as well as the Bellville ring contact  610  from contact with the plating solution.  
         [0103]    Other similar contact assembly designs that have a large number of contacts and that isolate the contacts from the electroplating environment are likewise suitable for use in the disclosed reactor assembly. Such additional contact assembly designs are set forth, for example, in PCT Application ______, filed Jul. 9, 1999 (Attorney Docket No. SEM4492P0571PC), which is hereby incorporated by reference.  
         [0104]    PLATING BATH FILTRATION SYSTEM  
         [0105]    While platinum will plate over the barrier layer the platinum will not readily adhere to materials preferably used for the barrier layer (i.e. Ti, Ta, TaN, TiO 2 , TIAlN). As a result, the plated platinum tends to flake off of the barrier layer and pollute the electroplating solution. By limiting the formation of plated platinum on the barrier layer, a significant source of platinum flakes is substantially reduced.  
         [0106]    Prior to supplying the recirculated solution to the plating module, the solution is filtered so as to limit pollutants in the solution, like platinum flakes. The filtered particles will eventually clog the filter and the filter will need to be replaced. By limiting the flaking of plated material the operational life of the filter is extended. So as to further extend the operational life of the filter, and/or in instances where platinum is allowed to form on the barrier layer, the use of a cascaded filter  201  has been determined to be beneficial. As illustrated in FIG. 16A, preferably a three-stage filter is used between the electroplating reactor  20  and the plating solution source tank  22 . In the illustrated embodiment, the first stage  202  provides filtration of particles of a first predetermined size or larger, the second stage  203  provides filtration of particles of a second predetermined size or larger, and the third stage  204  provides filtration of particles of a third predetermined size or larger. In the preferred embodiment, the first stage  202  provides filtration of particles 4.5 μm or larger, the second stage  203  provides filtration of particles 1.0 μm or larger, and the third stage  204  provides filtration of particles 0.1 μm or larger.  
         [0107]    ROTOR CONTACT CONNECTION ASSEMBLY  
         [0108]    In many instances, it may be desirable to have a given reactor assembly  20  function to execute a wide range of noble metal electroplating recipes. Execution of a wide range of electroplating recipes may be difficult, however, if the process designer is limited to using a single contact assembly construction. Further, the plating contacts used in a given contact assembly construction must be frequently inspected and, sometimes, replaced. This is often difficult to do in existing electroplating reactor tools, frequently involving numerous operations to remove and/or inspect the contact assembly. This problem may be addressed by providing a mechanism by which the contact assembly  85  is readily attached and detached from the other components of the rotor assembly  75 . Further, a given contact assembly type can be replaced with the same contact assembly type without re-calibration or readjustment of the system.  
         [0109]    To be viable for operation in a manufacturing environment, such a mechanism must accomplish several functions including:  
         [0110]    1. Provide secure, fail-safe mechanical attachment of the contact assembly to other portions of the rotor assembly;  
         [0111]    2. Provide electrical interconnection between the contacts of the contact assembly and a source of electroplating power;  
         [0112]    3. Provide a seal at the electrical interconnect interface to protect against the processing environment (e.g., wet chemical environment);  
         [0113]    4. Provide a sealed path for the purge gas that is provided to the contact assembly; and  
         [0114]    5. Minimize use of tools or fasteners which can be lost, misplaced, or used in a manner that damages the electroplating equipment.  
         [0115]    [0115]FIGS. 16B and 17 illustrate one embodiment of a quick-attach mechanism that meets the foregoing requirements. For simplicity, only those portions of the rotor assembly  75  necessary to understanding the various aspects of the quick-attach mechanism are illustrated in these figures.  
         [0116]    As illustrated, the rotor assembly  75  may be comprised of a rotor base member  1205  and a removable contact assembly  1210 . Preferably, the removable contact assembly  1210  is constructed in the manner set forth above in connection with contact assembly  85 . The illustrated embodiment, however, employs a continuous ring contact. It will be recognized that both contact assembly constructions are suitable for use with the quick-attachment mechanism set forth herein.  
         [0117]    The rotor base member  1205  is preferably annular in shape to match the shape of the semiconductor wafer  25 . A pair of latching mechanisms  1215  are disposed at opposite sides of the rotor base member  205 . Each of the latching mechanisms  1215  includes an aperture  1220  disposed through an upper portion thereof that is dimensioned to receive a corresponding electrically conductive shaft  1225  that extends downward from the removable contact assembly  1210 .  
         [0118]    The removable contact assembly  1210  is shown in a detached state in FIG. 16B. To secure the removable contact assembly  1210  to the rotor base member  1205 , an operator aligns the electrically conductive shafts  1225  with the corresponding apertures  1220  of the latching mechanisms  1215 . With the shafts  1225  aligned in this manner, the operator urges the removable contact assembly  1210  toward the rotor base member  1205  so that the shafts  1225  engage the corresponding apertures  1220 . Once the removable contact assembly  1210  is placed on the rotor base member  1205 , latch arms  1230  are pivoted about a latch arm axis  1235  so that latch arm channels  1240  of the latch arms  1230  engage the shaft portions  1245  of the conductive shafts  1235  while concurrently applying a downward pressure against flange portions  1247 . This downward pressure secures the removable contact assembly  1210  with the rotor base assembly  1205 . Additionally, as will be explained in further detail below, this engagement results in the creation of an electrically conductive path between electrically conductive portions of the rotor base assembly  1205  and the electroplating contacts of the contact assembly  1210 . It is through this path that the electroplating contacts of the contact assembly  1210  are connected to receive power from a plating power supply.  
         [0119]    [0119]FIGS. 18A and 18B illustrate further details of the latching mechanisms  1215  and the electrically conductive shafts  1225 . As illustrated, each latching mechanism  1215  is comprised of a latch body  1250  having aperture  1220 , a latch arm  1230  disposed for pivotal movement about a latch arm pivot post  1255 , and a safety latch  1260  secured for relatively minor pivotal movement about a safety latch pivot post  1265 . The latch body  1250  may also have a purge port  270  disposed therein to conduct a flow of purging fluid to corresponding apertures of the removable contact assembly  210 . An O-ring  275  is disposed at the bottom of the flange portions of the conductive shafts  1225   
         [0120]    FIGS.  19 A- 19 C are cross-sectional views illustrating operation of the latching mechanisms  1215 . As illustrated, latch arm channels  1240  are dimensioned to engage the shaft portions  1245  of the conductive shafts  1225 . As the latch arm  1230  is rotated to engage the shaft portions  1245 , a nose portion  1280  of the latch arm  1230  cams against the surface  1285  of safety latch  1260  until it mates with channel  1290 . With the nose portion  1280  and corresponding channel  1290  in a mating relationship, latch arm  1230  is secured against inadvertent pivotal movement that would otherwise release removable contact assembly  1210  from secure engagement with the rotor base member  1205 .  
         [0121]    FIGS.  20 A- 20 D are cross-sectional views of the rotor base member  1205  and removable contact assembly  1210  in an engaged state. As can be seen in these cross-sectional views, the electrically conductive shafts  1225  include a centrally disposed bore  1295  that receives a corresponding electrically conductive quick-connect pin  1300 . It is through this engagement that an electrically conductive path is established between the rotor base member  1205  and the removable contact assembly  1210 .  
         [0122]    As also apparent from these cross-sectional views, the lower, interior portion of each latch arm  1230  includes a corresponding channel  1305  that is shaped to engage the flange portions  1247  of the shafts  1225 . Edge portions of channel  1305  cam against corresponding surfaces of the flange portions  1247  to drive the shafts  1225  against surface  1310  which, in turn, effects a seal with O-ring  1275 .  
         [0123]    ROTOR CONTACT DRIVE  
         [0124]    As illustrated in FIGS. 21, 22 and  23 , the rotor assembly  75  includes an actuation arrangement whereby the wafer or other workpiece  25  is received in the rotor assembly by movement in a first direction, and is thereafter urged into electrical contact with the contact assembly by movement of a backing member  310  toward the contact assembly, in a direction perpendicular to the first direction.  
         [0125]    As illustrated, the stationary assembly  70  of the reactor head  30  includes a motor assembly  1315  that cooperates with shaft  1320  of rotor assembly  75 . Rotor assembly  75  includes a generally annular housing assembly, including rotor base member  1205  and an inner housing  1320 . As described above, the contact assembly is secured to rotor base member  1205 . By this arrangement, the housing assembly and the contact assembly  1210  together define an opening  1325  through which the workpiece  25  is transversely movable, in a first direction, for positioning the workpiece in the rotor assembly  75 . The rotor base member  1205  preferably defines a clearance opening for the robotic arm as well as a plurality of workpiece supports  3130  upon which the workpiece is positioned by the robotic arm after the workpiece is moved transversely into the rotor assembly by movement through opening  1325 . The supports  1330  thus support the workpiece  25  between the contact assembly  1210  and the backing member  1310  before the backing member engages the workpiece and urges it against the contact ring.  
         [0126]    Reciprocal movement of the backing member  1310  relative to the contact assembly  1210  is effected by at least one spring which biases the backing member toward the contact assembly, and at least one actuator for moving the backing member in opposition to the spring. In the illustrated embodiment, the actuation arrangement includes an actuation ring  1335  which is operatively connected with the backing member  1310 , and which is biased by a plurality of springs, and moved in opposition to the springs by a plurality of actuators.  
         [0127]    With particular reference to FIG. 21, actuation ring  1335  is operatively connected to the backing member  1310  by a plurality (three) of shafts  1340 . The actuation ring, in turn, is biased toward the housing assembly by three compression coil springs  1345  which are each held captive between the actuation ring and a respective retainer cap  350 . By this arrangement, the action of the biasing springs  1345  urges the actuation ring  1335  in a direction toward the housing, with the action of the biasing springs thus acting through shafts  1340  to urge the backing member  1335  in a direction toward the contact assembly  1210 . The drive shaft  1360  is operatively connected to inner housing  1320  for effecting rotation of workpiece  25 , as it is held between contact assembly  210  and backing member  310 , during plating processing. The drive shaft  360 , in turn, is driven by motor  315  that is disposed in the stationary portion of the reactor head  30 .  
         [0128]    Rotor assembly  75  is preferably detachable from the stationary portion of the reactor head  30  to facilitate maintenance and the like. Thus, drive shaft  1360  is detachably coupled with the motor  1315 . In accordance with the preferred embodiment, the arrangement for actuating the backing member  1310  also includes a detachable coupling, whereby actuation ring  1335  can be coupled and uncoupled from associated actuators which act in opposition to biasing springs  1345 .  
         [0129]    Actuation ring  1335  includes an inner, interrupted coupling flange  1365 . Actuation of the actuation ring  1335  is effected by an actuation coupling  1370  of the stationary assembly  70 , which can be selectively coupled and uncoupled from the actuation ring  1335 . The actuation coupling  1370  includes a pair of flange portions  1375  which can be interengaged with coupling flange  1365  of the actuation ring  1335  by limited relative rotation therebetween. By this arrangement, the actuation ring  1335  of the rotor assembly  75  can be coupled to, and uncoupled from, the actuation coupling  1370  of the stationary assembly  70  of the reactor head  30 .  
         [0130]    Actuation coupling  370  is movable in a direction in opposition to the biasing springs  1345  by a plurality of pneumatic actuators  1380  mounted on a frame of the stationary assembly  70 . Each actuator  1380  is operatively connected with the actuation coupling  1370  by a respective drive member  1385 , each of which extends generally through the frame of the stationary assembly  70 .  
         [0131]    There is a need to isolate the foregoing mechanical components from other portions of the reactor assembly  20 . A failure to do so will result in contamination of the processing environment (here, a wet chemical electroplating environment). Additionally, depending on the particular process implemented in the reactor  20 , the foregoing components can be adversely affected by the processing environment.  
         [0132]    To effect such isolation, a bellows assembly  1390  is disposed to surround the foregoing components. The bellows assembly  1390  comprises a bellows member  1395 , preferably made from Teflon, having a first end thereof secured at  1400  and a second end thereof secured at  1405 . Such securement is preferably implemented using the illustrated liquid-tight, tongue-and-groove sealing arrangement. The convolutes  1410  of the bellows member  1395  flex during actuation of the backing plate  1310 .  
         [0133]    WAFER LOADING/PROCESSING OPERATIONS  
         [0134]    Operation of the reactor head  30  will be appreciated from the above description. Loading of workpiece  25  into the rotor assembly  75  is effected with the rotor assembly in a generally upwardly facing orientation, such as illustrated in FIG. 3. Workpiece  25  is moved transversely through the opening  325  defined by the rotor assembly  75  to a position wherein the workpiece is positioned in spaced relationship generally above supports  1330 . A robotic arm  418  is then lowered (with clearance opening  325  accommodating such movement), whereby the workpiece is positioned upon the supports  1330 . The robotic arm  418  can then be withdrawn from within the rotor assembly  75 .  
         [0135]    The workpiece  25  is now moved perpendicularly to the first direction in which it was moved into the rotor assembly. Such movement is effected by movement of backing member  1310  generally toward contact assembly  1210 . It is presently preferred that pneumatic actuators  1380  act in opposition to biasing springs  1345  which are operatively connected by actuation ring  1335  and shafts  1340  to the backing member  1310 . Thus, actuators  1380  are operated to permit springs  1345  to bias and urge actuation ring  1335  and, thus, backing member  1310 , toward contact  210 . FIG. 22 illustrates the disposition of the reactor head  30  in a condition in which it may accept a workpiece, while FIG. 21 illustrates the disposition of the reactor head in a condition in which it is ready to present the workpiece to the reactor bowl  35 .  
         [0136]    In the preferred form, the connection between actuation ring  1335  and backing member  1310  by shafts  1340  permits some “float”. That is, the actuation ring and backing member are not rigidly joined to each other. This preferred arrangement accommodates the common tendency of the pneumatic actuators  1380  to move at slightly different speeds, thus assuring that the workpiece is urged into substantial uniform contact with the electroplating contacts of the contact assembly  1210  while avoiding excessive stressing of the workpiece, or binding of the actuation mechanism.  
         [0137]    With the workpiece  25  firmly held between the backing member  1310  and the contact assembly  1210 , lift and rotate apparatus  80  rotates the reactor head  30  and lowers the reactor head into a cooperative relationship with reactor bowl  35  so that the surface of the workpiece is placed in contact with the surface of the plating solution (i.e., the meniscus of the plating solution) within the reactor vessel. FIG. 1 illustrates the apparatus in this condition. If a contact assembly such as contact assembly  85  is used in the reactor  20 , the contact assembly  85  seals the entire peripheral region of the workpiece. Depending on the particular electroplating process implemented, it may be useful to insure that any gas which accumulates on the surface of the workpiece is permitted to vent and escape. Accordingly, the surface of the workpiece may be disposed at an acute angle, such as on the order of two degrees from horizontal, with respect to the surface of the solution in the reactor vessel. This facilitates venting of gas from the surface of the workpiece during the plating process as the workpiece, and associated backing and contact members, are rotated during processing. Circulation of plating solution within the reactor bowl  35 , as electrical current is passed through the workpiece and the plating solution, effects the desired electroplating of the noble metal or noble metal alloy on the surface of the workpiece.  
         [0138]    A number of features of the present reactor facilitate efficient and cost-effective electroplating of a noble metal or noble metal alloy on workpieces such as semiconductor wafers. By use of a contact assembly having substantially continuous contact in the form of a large number of sealed, compliant discrete contact regions, a high number of plating contacts are provided while minimizing the required number of components. The actuation of the backing member  1310  is desirably effected by a simple linear motion, thus facilitating precise positioning of the workpiece, and uniformity of contact with the contact ring. The isolation of the moving components using a bellows seal arrangement further increases the integrity of the electroplating process.  
         [0139]    Maintenance and configuration changes are easily facilitated through the use of the detachable contact assembly  1210 . Further, maintenance is also facilitated by the detachable configuration of the rotor assembly  75  from the stationary assembly  70  of the reactor head. The contact assembly provides excellent distribution of electroplating power to the surface of the workpiece, while the preferred provision of the peripheral isolation region protects the contacts from the plating environment (e.g., contact with the plating solution), thereby desirably preventing build-up of noble metal onto the electrical contacts. The perimeter seal also desirably prevents plating onto the peripheral portion of the workpiece.  
         [0140]    CURRENT THIEVING IN NOBLE METAL PLATING REACTORS  
         [0141]    [0141]FIG. 24 illustrates an embodiment of a current thief that may be used in the plating of noble metals, such as platinum, to enhance the uniformity of the plated film. The embodiment of the current thief illustrated here may be exposed to the electroplating solution and may be used in conjunction with one or more of the contact assemblies described above or with a plurality of discrete figure contacts such as those described below. Current thieving can be particularly useful where a large number of discrete electrical contacts is not practical. Beneficial features of current thieving are discussed in connection with U.S. patent application Ser. No. 08/933,450, similarly assigned to Semitool, Inc., the disclosure of which is incorporated herein by reference.  
         [0142]    However, in an electroplating environment providing for the deposition of noble metals, certain difficulties associated with the use of current thieves are experienced. One such difficulty is that certain noble metals, like platinum, once plated cannot be readily deplated. The present inventors have addressed this problem and have developed a segmented current thief  415 , illustrated in FIG. 24, that is suitable for use in the plating of noble metals, such as platinum. The segmented current thief  415  provides for multiple pads  420  located about the periphery of the semiconductor wafer  25 . Each of the pads  420  can be individually provided with a controlled amount of electroplating power to promote uniform current densities and/or uniform deposition of plated material.  
         [0143]    In operation, current thief  415  is a contact with the noble metal plating solution. Plating material will therefore plate the pads  420 . As a result, the current thief  415  has a limited useful life before the plating material accumulates to a degree in which it begins to interfere with the optimal plating process parameters. Accordingly, the current thief  415  is designed to be readily manufactured from inexpensive materials and, as such, is disposable. To this end, current thief  415  is comprised of a printed circuit board with the individual pads separately formed on the printed circuit substrate. Such a current thief  415  could be produced relatively inexpensively, and changed as necessary as part of the regular maintenance. The lower costs of the current thief would help mitigate the expense of more frequent replacement.  
         [0144]    In instances where discrete finger contacts are used, current thieving may be provided by a portion of the discrete finger contact. FIG. 25 shows an example of a discrete finger contact  425 . Portions  430  of the finger  425  may have exposed metal for performing a current thieving function.  
         [0145]    Because the finger contact  425  often may not be readily replaced with an inexpensive alternative, the finger contacts  425  includes multiple separate conductive wrap layers  435 , only one of which will be exposed at any given time. After sufficient build up of deposited material has accumulated one of the conductive wrap layers  435  may be individually removed, exposing a fresh wrap layer underneath. As the individual wrap layers  435  are removed, the accumulation of deposited material is removed with it. In this way the useful life of the finger contact  425  is recycled or renewed.  
         [0146]    INTEGRATED NOBLE METAL PLATING TOOL  
         [0147]    [0147]FIGS. 26 through 28 are top plan views of integrated processing tools, shown generally at  1450 ,  1455 , and  1500  that may be used to deposit a noble metal on the surface of a microelectronic workpiece, such as a semiconductor wafer. Processing tools  1450  and  1455  are each based on tool platforms developed by Semitool, Inc., of Kalispell, Mont. The processing tool platform of the tool  1450  is sold under the trademark LT-210™, the processing tool platform of the tool  1455  is sold under the trademark LT-210C™, and the processing tool  1500  is sold under the trademark EQUINOX™. The principal difference between the tools  1450 ,  1455  is in the footprints required for each. The platform on which tool  1455  is based has a smaller footprint than the platform on which tool  1455  is based. Additionally, the platform on which tool  1450  is based is modularized and may be readily expanded. Each of the processing tools  1450 ,  1455 , and  1500  are computer programmable to implement user entered processing recipes.  
         [0148]    Each of the processing tools  1450 ,  1455 , and  1500  include an input/output section  1460 , a processing section  1465 , and one or more robots  1470 . The robots  1470  for the tools  1450 ,  1455  move along a linear track. The robot  1470  for the tool  1500  is centrally mounted and rotates to access the input/output section  1460  and the processing section  1465 . Each input/output section  1460  is adapted to hold a plurality of workpieces, such as semiconductor wafers, in one or more workpiece cassettes. Processing section  1465  includes a plurality of processing stations  1475  that are used to perform one or more fabrication processes on the semiconductor wafers. The robots  1470  are used to transfer individual wafers from the workpiece cassettes at the input/output section  1460  to the processing stations  1475 , as well as between the processing stations  1475 .  
         [0149]    One or more of the processing stations  1475  are configured as electroplating assemblies, such as the electroplating assembly described above, for electroplating a noble metal, such as platinum, onto the semiconductor wafers. For example, each of the processing tools  1450  and  1455  may include eight noble metal plating reactors and a single pre-wet/rinse station. The prewet/rinse station is preferably one of the type available from Semitool, Inc. Preferably, one of the stations may be configured to execute a pre-wet/rinse process, and one of the stations may be configured as a spin rinser/dryer (SRD). Further, one or more of the processing chambers can be configured as an annealing station that can be used to anneal the noble metal layer. It will now be recognized that a wide variation of processing station configurations may be used in each of the individual processing tools  1450 ,  1455  and  1500  to execute pre-noble metal electroplating and post-noble metal electroplating processes. As such, the foregoing configurations are merely illustrative of the variations that may be used.  
         [0150]    ALTERNATIVE PROCESSING CONTAINER  
         [0151]    [0151]FIG. 29 illustrates the basic construction of an alternative processing container  35  and the corresponding flow velocity contour pattern resulting from the processing container construction. As illustrated, the processing container  35  generally comprises a main fluid flow chamber  2505 , an antechamber  2510 , a fluid inlet  2515 , a plenum  2520 , a flow guide  2525  separating the plenum  2520  from the antechamber  2510 , and a nozzle/slot assembly  2530  separating the plenum  2520  from the main chamber  2505 . These components cooperate to provide a flow (here, of the electroplating solution) at the wafer  25  with a substantially radially independent normal component. In the illustrated embodiment, the impinging flow is centered about central axis  2535  and possesses a nearly uniform component normal to the surface of the wafer  25 . This results in a substantially uniform mass flux to the wafer surface that, in turn, enables substantially uniform processing thereof.  
         [0152]    Electroplating solution is provided through inlet  2515  disposed at the bottom of the container  35 . The fluid from the inlet  2515  is directed therefrom at a relatively high velocity through antechamber  2510 . In the illustrated embodiment, antechamber  2510  includes an accelerated region  2540  through which the electroplating solution flows radially from the fluid inlet  2515  toward fluid flow region  2545  of antechamber  2510 . Fluid flow region  2545  has a generally inverted U-shaped cross-section that is substantially wider at its outlet region proximate flow guide  2525  than at its inlet region proximate region  2540 . This variation in the cross-section assists in removing any gas bubbles from the electroplating solution before the electroplating solution is allowed to enter the main chamber  2505 . Gas bubbles that would otherwise enter the main chamber  2505  are allowed to exit the processing container  35  through a gas outlet (not illustrated in FIG. 29, but illustrated in the embodiment shown in FIGS.  30 - 32 ) disposed at an upper portion of the antechamber  2510 .  
         [0153]    Electroplating solution within antechamber  2510  is ultimately supplied to main chamber  2505 . To this end, the electroplating solution is first directed to flow from a relatively high-pressure region  2550  of the antechamber  2510  to the comparatively lower-pressure plenum  2520  through flow guide  2525 . Nozzle assembly  2530  includes a plurality of nozzles or slots  2555  that are disposed at a slight angle with respect to horizontal. Electroplating solution exits plenum  2520  through nozzles  2555  with fluid velocity components in the horizontal, vertical and radial directions.  
         [0154]    Main chamber  2505  is defined at its upper region by a contoured sidewall  2560  and a slanted sidewall  2565 . The contoured sidewall  2560  assists in preventing fluid flow separation as the electroplating solution exits nozzles  2555  (particularly the uppermost nozzle(s)) and turns upward toward the surface of wafer  25 . Beyond breakpoint  2570 , fluid flow separation will not substantially affect the uniformity of the normal flow. As such, sidewall  2565  can generally have any shape, including a continuation of the shape of contoured sidewall  2560 . In the specific embodiment disclosed here, sidewall  2565  is slanted and, as will be explained in further detail below, is used to support one or more anodes.  
         [0155]    Electroplating solution exits from main chamber  2505  through a generally annular outlet  2570 . Fluid exiting outlet  2570  may be provided to a further exterior chamber for disposal or may be replenished for re-circulation through the electroplating solution supply system.  
         [0156]    In those instances in which the processing container  35  forms part of an electroplating reactor, the processing container  35  is provided with one or more anodes. In the illustrated embodiment, a principal anode  2580  is disposed in the lower portion of the main chamber  2505 . If the peripheral edges of the surface of the wafer  25  extend radially beyond the extent of contoured sidewall  2560 , then the peripheral edges are electrically shielded from principal anode  2580  and reduced plating will take place in those regions. However, if plating is desired in the peripheral regions, one or more further anodes may be employed proximate the peripheral regions. Here, a plurality of annular anodes  2585  are disposed in a generally concentric manner on slanted sidewall  2565  to provide a flow of electroplating current to the peripheral regions. An alternative embodiment would include a single anode or multiple anodes with no shielding from the contoured walls to the edge of the wafer.  
         [0157]    The anodes  2580 ,  2585  may be provided with electroplating power in a variety of manners. For example, the same or different levels of electroplating power may be multiplexed to the anodes  2580 ,  2585 . Alternatively, all of the anodes  2580 ,  2585  may be connected to receive the same level of electroplating power from the same power source. Still further, each of the anodes  2580 ,  2585  may be connected to receive different levels of electroplating power to compensate for the variations in the resistance of the plated film. An advantage of the close proximity of the anodes  2585  to the wafer  25  is that it provides a high degree of control of the radial film growth resulting from each anode.  
         [0158]    Anodes  2580 ,  2585  may be consumable, but are preferably inert and formed from platinized titanium or some other inert conductive material. However, as noted above, inert anodes tend to evolve gases that can impair the uniformity of the plated film. To reduce this problem, as well as to reduce the likelihood of the entry of bubbles into the main processing chamber  2505 , processing container  35  includes several unique features. With respect to anode  2580 , a small fluid flow path  2590  is provided between the underside of anode  2580  and antechamber  2510 . This results in a Venturi effect that causes the electroplating solution proximate the surfaces of anode  2580  to be drawn into antechamber  2510  and, further, provides a suction flow that affects the uniformity of the impinging flow at the central portion of the surface of the wafer. Gas bubbles forming at the surfaces of anode  2580  are thus swept into antechamber  2510  and are prevented from entering main chamber  2505 . Rather than entering main chamber  2505  where they would disturb the boundary layer conditions at the surface of wafer  25 , the gas bubbles enter antechamber  2510  and exit the gas outlet at the upper region of antechamber  2510 . The Venturi flow path  2590  may be shielded to prevent any large bubbles originating from outside the chamber from rising through region  2590 . Instead, such bubbles enter the bubble-trapping region of the antechamber  2510 . Similarly, electroplating solution sweeps across the surfaces of anodes  2585  in a radial direction toward fluid outlet  2570  to remove gas bubbles forming at their surfaces. Further, the radial components of the fluid flow at the surface of the wafer assists and sweeping gas bubbles therefrom.  
         [0159]    The foregoing reactor design effectively de-couples the fluid flow from adjustments to the electric field. This occurs due to the absence of a diffuser disposed between the anode and the cathode (workpiece). Further, the use of multiple anodes contributes to this result as well. An advantage of this approach is that a chamber with nearly ideal flow for electroplating and other processes (i.e., a design which provide substantial uniform diffusion layer across the wafer) may be designed that will not be degraded when electroplating or other process applications require significant changes to the electric field.  
         [0160]    There are numerous processing advantages with respect to the illustrated flow through the reactor chamber. As illustrated, the flow through the various system components is directed away from the wafer surface and, as such, there are no jets of fluid created to disturb the uniformity of the diffusion layer. Although the diffusion layer may not be perfectly uniform, any non-uniformity will be relatively gradual as a result.  
         [0161]    As is also evident from the foregoing reactor design, the flow that is normal to the wafer has greater a magnitude near the center of the wafer and creates a dome-shaped meniscus. The dome-shaped meniscus assists in minimizing bubble entrapment as the wafer or other workpiece is lowered into the processing solution (here, the electroplating solution). The flow pattern resulting in the dome-shaped meniscus is influenced by the Venturi flow at the bottom of the chamber  2505 . This flow at the bottom of the main chamber  2505  influences the flow at the centerline thereof. The centerline flow velocity is otherwise difficult to implement and control. However, the strength of the Venturi flow provides a non-intrusive design variable that may be used to affect this aspect of the flow.  
         [0162]    A still further advantage of the foregoing reactor design is that it assists in preventing bubbles that find their way into the main chamber from reaching the wafer. To this end, the flow pattern is such that the solution travels downward just before entering the main chamber. As such, bubbles remain in the antechamber and escape through holes at the top thereof. Further, bubbles are prevented from entering the main chamber through the Venturi flow path through the use of the shield that covers the Venturi flow path (see description of the embodiment of the reactor illustrated in FIGS.  30 - 32 ). Still further, the upward sloping inlet path (see FIG.  32  and appertaining description) to the antechamber prevents bubbles from entering the main chamber through the Venturi flow path.  
         [0163]    There are also advantages associated with the electric field in the foregoing reactor design. Multiple concentric anodes are used so that a uniform film can be plated by making adjustments to the current passing through each anode. Generally, the more resistive the plated film, the more the magnitude of the current at the central anodes should be increased to yield a uniform film. Some further reasons for adjusting the electric field include changes to the following:  
         [0164]    seed layer thickness;  
         [0165]    open area of plating surface (pattern wafers, edge exclusion);  
         [0166]    final plated thickness;  
         [0167]    bath conductivity, metal concentration; and  
         [0168]    plating rate.  
         [0169]    The particular reactor embodiment disclosed herein is readily adapted to compensate for the foregoing changes.  
         [0170]    FIGS.  30 - 32  illustrate a specific construction of a complete processing chamber assembly  2610 . As illustrated, assembly  2610  is comprised of the processing container  35  shown in FIG. 29 along with a corresponding exterior cup  2605 . Processing container  35  is disposed within exterior cup  2605  to allow exterior cup  2605  to receive spent electroplating solution that overflows from the processing container  35 . A flange  2615  extends about the assembly  2610  for securement with, for example, the frame of the corresponding tool.  
         [0171]    With particular reference to FIGS. 31 and 32, the flange of the exterior cup assembly  2605  is formed to engage or otherwise accept rotor portion  75  of head assembly  25  and allow contact between the wafer  25  and the processing solution, such as electroplating solution, in the main chamber  2505 . The exterior cup assembly  2605  also includes a main cylindrical housing  2625  into which a drain cup member  2627  is disposed. The drain cup member  2627  includes an outer surface having channels  2629  that, together with the interior wall of housing  2625 , form one or more helical flow chambers  2640  that serve as an outlet for the processing solution. Electroplating solution overflowing a weir member  2739  at the top of processing cup  35  drains through the helical flow chambers  2640  and exits an outlet (not illustrated) where it is either disposed of or replenished and re-circulated. This configuration is particularly suitable for systems that include fluid re-circulation since it assists in reducing the mixing of gases with the processing solution thereby further reducing the likelihood that gas bubbles will interfere with the uniformity of the diffusion layer at the workpiece surface.  
         [0172]    In the illustrated embodiment, antechamber  2550  is defined by the walls of a plurality of separate components. More particularly, antechamber  2550  is defined by the interior walls of drain cup member  2627 , an anode support member  2697 , the interior and exterior walls of a mid-chamber member  2690 , and the exterior walls of flow guide  2550 .  
         [0173]    [0173]FIG. 31 illustrates the manner in which the foregoing components are brought together to form the reactor. To this end, the mid-chamber member  2690  is disposed interior of the drain cup member  2627  and includes a plurality of leg supports  2692  that sit upon a bottom wall thereof. The anode support member  2697  includes an outer wall that engages a flange  630  that is disposed about the interior of drain cup member  2627 . The anode support member  2697  a also includes a channel  2705  that sits upon and engages an upper portion of flow guide  2550 , and a further channel  2710  that sits upon and engages an upper rim of nozzle assembly  2530 . Midchamber member  2690  also includes a centrally disposed annular receptacle  2715  that is dimensioned to accept the lower portion of nozzle assembly  2530 . Likewise, an annular channel  2725  is disposed radially exterior of the annular receptacle  2715  to engage a lower portion of flow guide  550 .  
         [0174]    In the illustrated embodiment, the flow guide  2550  is formed as a single piece and includes a plurality of vertically oriented slots  2670 . Similarly, the nozzle assembly  2530  is formed as a single piece and includes a plurality of horizontally oriented slots that constitute the nozzles  2555 .  
         [0175]    The anode support assembly  2697  includes a plurality of annular grooves that are dimensioned to accept corresponding annular anode assemblies  2785 . Each anode assembly  2785  includes an anode  2585  (preferably formed from platinized titanium or in other inert metal) and a conduit  2730  extending from a central portion of the anode  2585  through which a metal conductor may be disposed to electrically connect the anode  2585  of the assembly  2785  to an external source of electrical power. Conduit  2730  is shown to extend entirely through the reactor assembly  2610  and is secured at the bottom thereof by a respective fitting  2733 . In this manner, anode assemblies  2785  effectively urge the anode support member  2697  downward to clamp the flow guide  2550 , nozzle member  2530 , mid-chamber member  2690 , and drain cup member  2627  against the bottom portion  2737  of the housing assembly  2605 . This allows for easy assembly and disassembly of the reactor  2610 .  
         [0176]    The illustrated embodiment also includes a weir member  2739  that detachably snaps or otherwise easily secures to the upper exterior portion of anode support member  2697 . As shown, weir member  2739  includes a rim  2742  that forms a weir over which the processing solution flows into the helical flow chamber  2640 . Weir member  2739  also includes a transversely extending flange  2744  that extends radially inward and forms an electric field shield over all or portions of one or more of the anodes  2585 . Since the weir member  2739  may be easily removed and replaced, the reactor assembly  2610  may be readily reconfigured and adapted to provide different electric field shapes. Such differing electrical field shapes are particularly useful in those instances in which the reactor must be configured to process more than one size or shape of a workpiece.  
         [0177]    The anode support member  2697 , with the anodes  2727  in place, forms the contoured wall  2560  and slanted wall  2565  that is illustrated in FIG. 29. As noted above, the lower region of anode support member  2697  is contoured to define the upper interior wall of antechamber  2510  and preferably includes one or more gas outlets  2665  that are disposed therethrough to allow gas bubbles to exit from the antechamber  2510  to the exterior environment.  
         [0178]    With particular reference to FIG. 32, inlet  2515  is defined by an inlet fluid guide, shown generally at  2810 , that is secured to the floor of drain cup member  2627  by one or more fasteners  2815 . Inlet fluid guide  2810  includes a plurality of open channels  2817  that guide fluid received at inlet  2515  to an area beneath mid-chamber member  2690 . Channels  2817  of the illustrated embodiment are defined by upwardly angled walls  2819 . Electroplating solution exiting channels  2817  flows therefrom to one or more further channels  2821  that are likewise defined by walls that angle upward.  
         [0179]    Central anode  2580  includes an electrical connection rod  2581  that proceeds to the exterior of the reactor assembly  2610  through central apertures formed in nozzle member  2550 , drain cup member  2627  and inlet fluid guide  2810 . The small fluid regions shown at  2590  in FIG. 29 are formed in FIG. 32 by vertical channels  2823  that proceed through drain cup member  2627  and the bottom wall of nozzle member  2550 . The vertical channels  2823  of the drain cup member  2627  are separated from the vertical channels  2823  at the bottom wall  2825  of nozzles member  2550  by an intermediate chamber  2827  that is defined by the exterior portion of bottom wall  2825  and the interior wall at the bottom of drain cup member  2627 . As illustrated, the exterior portion of bottom wall  2825  extends at a downward angle from a central region thereof. This construction assists in preventing bubbles from entering the main chamber  2505  since any bubbles reaching vertical channel  2823  of drain cup member  2627  will proceed into chamber  2827  and flow to the upper portions thereof proximate connection rod  2581  without entering main chamber  2505 .  
         [0180]    Numerous modifications may be made to the foregoing system without departing from the basic teachings thereof. Although the present invention has been described in substantial detail with reference to one or more specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention as set forth in the appended claims.