Patent Publication Number: US-6669834-B2

Title: Method for high deposition rate solder electroplating on a microelectronic workpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application No. 09/386,213, filed Aug. 31, 1999, now U.S. Pat. No. 6,334,937 which is a continuation of International Application No. PCT/US99/15850, designating the United States, filed Jul. 12, 1999, which claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/114,450, filed Dec. 31, 1998, the benefit of the filing dates of which are hereby claimed under 35 U.S.C. §119 and §119(e), and the disclosures of which are hereby incorporated by referenced in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Soldering has been a familiar technique for forming electrical and/or mechanical connections between metal surfaces and is the technique of choice for many applications in the electronics industry. Many soldering techniques have therefore been developed for applying solder to surfaces or interfaces between metals to extend soldering techniques to many diverse applications. 
     In the electronics industry, in particular, the trend toward smaller sizes of components and higher integration densities of integrated circuits has necessitated techniques for application of solder to extremely small areas and in carefully controlled volumes to avoid solder bridging between conductors. 
     High performance microelectronic devices often use solder balls or solder bumps for electrical interconnection to other microelectronic devices. For example, a very large scale integration (VLSI) chip may be electrically connected to a circuit board or other next level packaging substrate using solder balls or solder bumps. This connection technology is also referred to as “Controlled Collapse Chip Connections—C4” or “flip-chip” technology, and is often referred to as solder bumps. 
     In accordance with one type of solder bump technology developed by IBM, the solder bumps are formed by evaporation through openings in a shadow mask which is clamped to an integrated circuit wafer. For example, U.S. Pat. No. 5,234,149 entitled “Debondable Metallic Bonding Method” to Katz et al. discloses an electronic device with chip wiring terminals and metallization layers. The wiring terminals are typically primarily aluminum, and the metallization layers may include a titanium or chromium localized adhesive layer, a co-deposited localized chromium copper layer, a localized wettable copper layer, and a localized gold or tin capping layer. An evaporated localized lead-tin solder layer is located on the capping layer. 
     Solder bump technology based on an electroplating method has also been actively pursued. In this method, an “under bump metallurgy” (UBM) layer is deposited on a microelectronic substrate having contact pads thereon, typically by evaporation or sputtering. A continuous under bump metallurgy layer is typically provided on the pads and on the substrate between the pads, in order to allow current flow during solder plating. 
     An example of an electroplating method with an under bump metallurgy layer is disclosed in U.S. Pat. No. 5,162,257 entitled “Solder Bump Fabrication Method” to Yung. In this patent, the under bump metallurgy layer contains a chromium layer adjacent the substrate and pads, a top copper layer which acts as a solderable metal, and a phased chromium/copper layer between the chromium and copper layers. The base of the solder bump is preserved by converting the under bump metallurgy layer between the solder bump and contact pad into an intermetallic of the solder and the solderable component of the under bump metallurgy layer. Multiple etch cycles may, however, be needed to remove the phased chromium/copper layer and the bottom chromium layer. Even with multiple etch cycles, the under bump metallurgy layer may be difficult to remove completely, creating the risk of electrical shorts between solder bumps. U.S. Pat. No. 5,767,010, titled “Solder Bump Fabrication Methods and Structure Including a Titanium Barrier Layer”, issued Jun. 16, 1998, purports to address this problem. 
     Several technical problems are typically associated with electroplating of tin/lead solder on semiconductor wafers and other microelectronic workpieces. One problem relates to the relatively low rate at which deposition of the solder takes place. Generally, the upper deposition rate for selectively depositing solder on the surface of a microelectronic workpiece is about 1 micron/minute. Attempts to significantly increase the deposition rate have heretofore proven unsuccessful. Most such attempts are hindered by the fact that a significant amount of gas evolves during the electroplating process, particularly when traditional inert anodes are employed. The resulting gas bubbles impair the proper formation of the solder bumps and other structures formed from the solder deposit. Additionally, removal of the evolved gases can be problematic. The microelectronic fabrication industry thus has been forced to accept low deposition rate solder processes and equipment. 
     Several technical problems must be overcome in designing reactors used in the electroplating of semiconductor wafers. Utilization of a small number of discrete electrical contacts (e.g., 6 contacts) with the seed layer about the perimeter of the wafer ordinarily produces 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 solder material. 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 such non-uniformity. But such thieving techniques add to the complexity of electroplating equipment, and increase maintenance requirements. 
     Another problem with electroplating of wafers concerns efforts to prevent the electric contacts themselves from being plated during the electroplating process. Any solder plated to the electrical contacts must be removed to prevent changing contact performance. While it is possible to provide sealing mechanisms for discrete electrical contacts, such arrangements typically cover a significant area of the wafer surface, and can add complexity to the electrical contact design. 
     In addressing a further problem, it is sometimes desirable to prevent electroplating on the exposed barrier layer near the edge of the semiconductor wafer. Electroplated solder may not adhere well to the exposed barrier layer material, and is therefore prone to peeling off in subsequent wafer processing steps. Further, solder 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. 
     The specific solder to be electroplated can also complicate the electroplating process. For example, electroplating of solder may require use of a seed layer having a relatively 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. 
     Beyond the contact related problems discussed above, there are also other problems associated with electroplating reactors for solder plating. 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. 
     Still further, existing electroplating reactors are often difficult to maintain and/or reconfigure for different electroplating processes. Such difficulties must be overcome if an electroplating reactor design is to be accepted for large-scale manufacturing. 
     SUMMARY OF THE INVENTIONS 
     The present invention is accordingly directed to an improved electroplating method, chemistry, and apparatus for selectively depositing tin/lead solder bumps and other structures at a high deposition rate pursuant to manufacturing a microelectronic device from a workpiece, such as a semiconductor wafer. An apparatus for plating solder on a microelectronic workpiece in accordance with one aspect of the present invention comprises a reactor chamber containing an electroplating solution having free ions of tin and lead for plating onto the workpiece. A chemical delivery system is used to deliver the electroplating solution to the reactor chamber at a high flow rate. A workpiece support is used that includes a contact assembly for providing electroplating power to a surface at a side of the workpiece that is to be plated. The contact contacts the workpiece at a large plurality of discrete contact points that isolated from exposure to the electroplating solution. An anode, preferably a consumable anode, is spaced from the workpiece support within the reaction chamber and is in contact with the electroplating solution. In accordance with one embodiment the electroplating solution comprises a concentration of a lead compound, a concentration of a tin compound, water and methane sulfonic acid. 
     In accordance with one aspect of the present invention, the contact assembly comprises a plurality of contacts disposed to contact a peripheral edge of the surface of the workpiece. The plurality of contacts execute a wiping action against the surface of the workpiece as the workpiece is brought into engagement therewith. Further, the contact assembly includes a barrier disposed interior of the plurality of contacts that includes a member disposed to engage the surface of the workpiece to effectively isolate the plurality of contacts from the electroplating solution. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view through an electroplating reactor that is constructed in accordance with various teachings of the present invention. 
     FIG. 2 illustrates a specific construction of one embodiment of a reactor bowl suitable for use in the assembly illustrated in FIG.  1 . 
     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 . 
     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 . 
     FIGS. 11-12 illustrate two different embodiments of a “Belleville ring” contact structure. 
     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 . 
     FIGS. 16-20 illustrate various aspects of one embodiment of a quick-attach mechanism. 
     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. 
     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. 
     FIG. 23 illustrates an exploded view one embodiment of the rotor assembly. 
     FIGS. 24-26 are top plan views of integrated processing tools that may incorporate electroless plating reactors and electroplating reactors in combination. 
    
    
     DETAILED DESCRIPTION OF THE INVENTIONS 
     Basic Solder Electroplating Reactor Components 
     With reference to FIGS. 1-3, there is shown a reactor assembly  20  for high deposition rate electroplating of solder on 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 metallic layer, such as a layer of solder bumps. 
     The 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. 
     The temperature of 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. These components preferably maintain the temperature of the electroplating solution in a temperature range between 20° C. and 50° C. Even more preferably, these components maintain the temperature of the electroplating solution at about 30° C. +/−5° C. As will be explained in connection with the preferred electroplating process, the preferred electroplating solution exhibits optimal deposition properties within this latter temperature range. 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 . Unlike the inert anodes used in conventional electroplating of solder to a surface of a microelectronic workpiece, anode  55  is a consumable anode formed from tin and/or lead whereby tin and lead ions of the anode are transported by the electroplating solution to the electrically-conductive surface of the workpiece, which functions as a cathode. Preferably, the consumable anode  55  has a tin/lead composition that directly corresponds to the tin/lead composition required for the solder deposit. As such, an anode used in an electroplating system for depositing high lead content solder should have a corresponding high lead-tin ratio. Similarly, an anode used in an electroplating system for depositing eutectic solder should have a corresponding low lead-tin ratio. As illustrated, the anode  55  may be provided with an anode shield  60 . 
     Electroplating solution flows at a high flow rate (i.e., 5 g/m) 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. 
     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  415 , 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. 
     Electroplating Solution 
     The preferred electroplating solution is comprised of methane sulfonic acid, a source of lead ions, a source of tin ions, one or more organic additives, and deionized water. Complementary sets of materials that are specifically designed for electroplating a tin/lead solder composition are available from LeaRonal, Enthone-OMI, Lucent, and Technic. 
     The chemical salts used for the generation of lead and tin ions are provided in a ratio that corresponds, although not necessarily directly, to the lead-to-tin ratio of the required solder deposit. Two solder deposit compositions that are typically used for attachment of semiconductor integrated circuits using flip-chip technology are eutectic solder (63% Sn, 37% Pb) and high lead solder (95% to 97% Pb, with the balance being Sn). Electroplating solutions used for electroplating a eutectic solder thus have a higher concentration of tin than of lead. Similarly, electroplating solutions used for electroplating high lead solder have a higher concentration of lead than of tin. Although there is a correspondence between the general ratios of the lead and tin used for depositing a given solder composition, this correspondence is not necessarily one-to-one. This is due to the fact that the efficiencies associated with plating lead from the solution may be significantly lower than the efficiencies associated with plating tin from the solution (i.e., it is more difficult to plate lead from the solution than it is to plate tin from the solution). 
     The overall combined concentration of the metal ions of lead and tin utilized in the electroplating solution is dependent on the requisite rate of deposition, the particular compositions of the lead and tin concentrates (which often differs between manufacturers), the composition of the consumable anode  55 , the operating temperature of the solution, cathode current density, and the desired composition of the solder deposit. The combined metal concentration should be chosen so that it is large enough to meet the requisite deposition rate while not so large as to evolve a significant amount of gas by-products that interfere with the plating process or otherwise result in unsatisfactory solder deposits. For a high rate plating of high lead content solder, the combined metal concentration is preferably between 55 g/liter and 205 g/liter. For a high rate plating of eutectic solder, lower combined metal concentrations may be used in view of the lower lead composition of the eutectic solder deposit. 
     The present inventors have found that high rate plating of about 4 microns/minute may be achieved with the following electroplating solutions, in which the particular additives are provided by the identified manufacturer. The compositions for these electroplating solutions are set forth in the following tables, and are directed to high rate plating of high lead content solder (95/5). It is believed that plating rates as high as 8 microns/minute are possible using these basic solutions and the reactor described above. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 MANUFACTURER/BRAND-NAME 
                 LeaRonal Solderon SC ™ 
               
               
                 METHANE SULFONIC ACID 
                 120-180 g/liter-preferably, 150 
               
               
                   
                 g/liter 
               
               
                 LEAD CONCENTRATION 
                 50-100 g/liter-preferably, 75 g/ 
               
               
                   
                 liter 
               
               
                 TIN CONCENTRATION 
                 3-7 g/liter-preferably, 5 g/liter 
               
               
                 ORGANIC ADDITIVE 
                 20%-30% by volume 
               
               
                 WATER 
                 50%-60% by volume 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 MANUFACTURER/BRAND-NAME 
                 LeaRonal MHS-L ™ 
               
               
                   
                 METHANE SULFONIC ACID 
                 120-180 g/liter 
               
               
                   
                 LEAD CONCENTRATION 
                 130-170 g/liter 
               
               
                   
                 TIN CONCENTRATION 
                 15-35 g/liter 
               
               
                   
                 ORGANIC ADDITIVE 
                 20%-30% by volume 
               
               
                   
                 WATER 
                 50%-60% by volume 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
             
            
               
                 MANUFACTURER/BRAND-NAME 
                 Lucent 
               
               
                 METHANE SULFONIC ACID 
                 20%-30% by volume 
               
               
                 LEAD CONCENTRATE CONCENTRATION 
                 8%-10% by volume 
               
               
                 TIN CONCENTRATE CONCENTRATION 
                 3%-5% by volume 
               
               
                 ORGANIC ADDITIVE 
                 6%-8% by volume 
               
               
                 WATER 
                 60%-70% by volume 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 MANUFACTURER/BRAND-NAME 
                 Technic 
               
               
                 TECHNI ACID NF 
                 15% by volume 
               
               
                 TECHNI LEAD NF 500 CONCENTRATION 
                 5% by volume 
               
               
                 TECHNI TIN NF 300 CONCENTRATION 
                 13.3% by volume 
               
               
                 TECHNI NF 820 HS MAKEUP 
                 5% by volume 
               
               
                 TECHNI NF 820 HS SECONDARY 
                 0.3% by volume 
               
               
                 ADDITIVE 
               
               
                 WATER 
                 balance of remaining 
               
               
                   
                 volume % 
               
               
                   
               
            
           
         
       
     
     The foregoing solution compositions can also be adjusted with respect to the lead and tin concentrations to optimize those solutions for depositing eutectic solder. For example, the solution compositions set forth in TABLE 5 below may be used to deposit eutectic solder at a high plating rate of about 2 microns/minute with excellent results. It is expected that a solution in which the tin and lead additive concentrations are doubled will produce a eutectic solder deposit at a high plating rate of about 4 microns/minute. 
     
       
         
           
               
               
             
               
                 TABLE 5 
               
               
                   
               
             
            
               
                 MANUFACTURER/BRAND-NAME 
                 LeaRonal Solderon SC ™ 
               
               
                 METHANE SULFONIC ACID 
                 120-180 g/liter-preferably, 150 
               
               
                   
                 g/liter 
               
               
                 LEAD CONCENTRATION 
                 about 10 g/liter 
               
               
                 TIN CONCENTRATION 
                 about 23.5 g/liter 
               
               
                 ORGANIC ADDITIVE 
                 20%-30% by volume 
               
               
                 WATER 
                 50%-60% by volume 
               
               
                   
               
            
           
         
       
     
     Exemplary Process 
     The reactor system and electroplating solutions described above can be used to implement a process for depositing lead-tin solder at a high rate of deposition in excess of about 2 microns/minute and potentially as high as 8 microns/minute. An exemplary process sequence preferably includes the following processing steps: 
     1. Pre-wet 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 also include an amount of MSA and be heated to the same temperature at which electroplating will occur); 
     2. Adjust and/or program the electroplating system for the following processing parameters: electroplating flow set-point at nominal 5 gpm (or other high flow rate of comparable magnitude), electroplating bath temperature about 20° C.-50° C. (preferably, about 30° C.), rotate workpiece at a rotation rate between about 1 and 100 rpm (preferably, about 20 rpm), change the direction of the rotation at intervals between about 5 and 60 seconds; 
     3. Bring the surface of the workpiece that is to be plated into contact with the electroplating solution without application of electroplating power thereby inducing an acid etch of the substrate (about 30 seconds); 
     4. Apply electroplating power at a current set-point that is between about 50 and 200 milliamps/cm 2  (time duration dependent on desired vertical plate height or bump volume); 
     5. Halt electrolysis; 
     6. Disengage workpiece from electroplating solution; 
     7. Spin the workpiece at a high spin rate (i.e., above about 200 rpm) to remove excess electroplating solution; 
     8. Rinse the workpiece in a spray of deionized water (about 2 min.) and spin dry at a high rotation rate. 
     Other processing sequences may also be used to provide high-quality solder deposits that are deposited at a high deposition rate, the foregoing processing steps and sequence being illustrative. 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. 
     There are a number of enhancements that may be made to the reactor assembly  20  described above that facilitate uniformity of the solder deposits over the face of the workpiece. For example, the reactor assembly  20  may use a contact assembly that reduces non-uniformities in the deposit that occur proximate the discrete contacts that are used to provide plating power to the surface at the perimeter of the workpiece. Additionally, other enhancements to the reactor assembly  20  may be added to facilitate routine service and/or configurability of the system. 
     Improved Contact Assemblies for Electroplating Solder 
     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 solder. Some of the more desirable characteristics of a contact assembly used to provide such electroplating power include, for example, the following: 
     uniform distribution of electroplating power about the periphery of the wafer to maximize the uniformity of the deposited film; 
     consistent contact characteristics to insure wafer-to-wafer uniformity; 
     minimal intrusion of the contact assembly on the wafer periphery to maximize the available area for device production; and 
     minimal plating on the barrier layer about the wafer periphery to inhibit peeling and/or flaking. 
     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. 
     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. 
     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. 
     Ring Contact Assemblies Using Flexure Contact 
     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 . 
     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 . 
     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. 
     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 . 
     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 . 
     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 . 
     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 . 
     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 . 
     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 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 . 
     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 . 
     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. 
     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. 
     Belleville Ring Contact Assemblies 
     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. 11A while a perspective view thereof is illustrated in FIG.  11 B. 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 “Belleville ring contact” and the overall contact assembly into which it is placed will be referred to as a “Belleville ring contact assembly”. 
     The embodiment of Belleville ring contact  610  illustrated in FIGS. 16A and 16B 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. 
     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. 
     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. 
     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. 
     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. 
     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 . 
     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. 14 and 15, 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 . 
     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. 
     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. 
     Rotor Contact Connection Assembly 
     In many instances, it may be desirable to have a given reactor assembly  20  function to execute a wide range of solder 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. 
     To be viable for operation in a manufacturing environment, such a mechanism must accomplish several functions including: 
     1. Provide secure, fail-safe mechanical attachment of the contact assembly to other portions of the rotor assembly; 
     2. Provide electrical interconnection between the contacts of the contact assembly and a source of electroplating power; 
     3. Provide a seal at the electrical interconnect interface to protect against the processing environment (e.g., wet chemical environment); 
     4. Provide a sealed path for the purge gas that is provided to the contact assembly; and 
     5. Minimize use of tools or fasteners which can be lost, misplaced, or used in a manner that damages the electroplating equipment. 
     FIGS. 16 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. 
     As illustrated, the rotor assembly  75  may be comprised of a rotor base member  205  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. 
     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 . 
     The removable contact assembly  1210  is shown in a detached state in FIG.  16 . 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. 
     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 . 
     FIGS. 19A-19C 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 . 
     FIGS. 20A-20D 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 . 
     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 . 
     Rotor Contact Drive 
     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. 
     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. 
     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. 
     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 . 
     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 . 
     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 . 
     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 . 
     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. 
     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 . 
     Wafer Loading/Processing Operations 
     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  415  is then lowered (with clearance opening  325  accommodating such movement), whereby the workpiece is positioned upon the supports  1330 . The robotic arm  415  can then be withdrawn from within the rotor assembly  75 . 
     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. 12 illustrates the disposition of the reactor head  30  in a condition in which it may accept a workpiece, while FIG. 22 illustrates the disposition of the reactor head and a condition in which it is ready to present though workpiece to the reactor bowl  35 . 
     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. 
     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 solder on the surface of the workpiece. 
     A number of features of the present reactor facilitate efficient and cost-effective electroplating of of solder 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. 
     Maintenance and configuration changes are easily facilitated through the use of a 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 seal protects the contacts from the plating environment (e.g., contact with the plating solution), thereby desirably preventing build-up of solder onto the electrical contacts. The perimeter seal also desirably prevents plating onto the peripheral portion of the workpiece. 
     Integrated Plating Tool 
     FIGS. 24 through 26 are top plan views of integrated processing tools, shown generally at  1450 ,  1455 , and  1500  that may incorporate electroless plating reactors and electroplating reactors as a combination for plating on 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  450  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 ,  4155 , and  1500  are computer programmable to implement user entered processing recipes. 
     Each of the processing tools  1145 ,  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 . 
     One or more of the processing stations  1475  are configured as electroplating assemblies, such as the electroplating assembly described above, for electroplating solder onto the semiconductor wafers. For example, each of the processing tools  1450  and  1455  may include eight solder plating reactors and a single pre-wet/rinse station. The pre-wet/rinse station is preferably one of the type available from Semitool, Inc. Alternatively, each of the processing tools  1450  and  1455  may be configured to plate copper studs onto the semiconductor wafers and plate solder, such as eutectic solder, over the copper studs. In such instances, for example, five of the processing stations  1475  may be configured to plate eutectic solder, one of the stations may be configured to plate the copper studs, 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). Still further, each of the processing tools  1450  and  1455  may be configured to plate two different types of solder (e.g., eutectic solder and high lead solder). 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-solder electroplating and post-solder electroplating processes. As such, the foregoing configurations are merely illustrative of the variations that may be used. 
     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.