Abstract:
A reactor for electroplating a workpiece includes a vessel having a ring contact arranged to support a workpiece in a horizontal orientation. In an embodiment of the invention, an electrode is arranged below the ring contact, and a pressing member is arranged above the ring contact to press a workpiece into electrical engagement with the ring contact. The vessel may be adapted to contain an electroplating fluid between a top of the ring contact and the electrode. In one embodiment, a movable intermediate workpiece support assembly is carried by the vessel, the support assembly being actuatable to lower a workpiece carried thereby to deliver the workpiece to be supported accurately and precisely on the ring contact.

Description:
BACKGROUND  
         [0001]    In the production of semiconductor integrated circuits and other semiconductor articles from semiconductor wafers, it is often necessary to provide multiple metal layers on the wafer to serve as interconnect metallization which electrically connect the various devices on the integrated circuit to one another. Traditionally, aluminum has been used for such interconnects, however, it is now recognized that copper metallization may be preferable.  
           [0002]    The semiconductor manufacturing industry has applied copper onto semiconductor wafers by using a “damascene” electroplating process where holes, commonly called “vias”, trenches or other recesses are formed onto a substrate and into which copper is filled. 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. 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 of metal can be laid down using physical vapor deposition or chemical vapor deposition processes to produce a layer on the order of 1,000 angstroms thick. The seed layer can advantageously be formed of copper, gold, nickel, palladium, or other metals. The seed layer is formed over a surface which is convoluted by the presence of the vias, trenches, or other recessed device features.  
           [0003]    A copper layer is then electroplated onto the seed layer in the form of a blanket layer. The blanket layer is plated to an extent which forms an overlying layer, with the goal of providing a copper layer that fills the trenches and vias and extends a certain amount above these features. Such a blanket layer will typically be formed in thicknesses on the order of 10,000 to 15,000 angstroms (1-1.5 microns).  
           [0004]    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 metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed. The excess plated material can be removed, for example, using chemical mechanical planarization. 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.  
           [0005]    The electroplating of 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. Commonly, 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 cathode current to the wafer. The support system may comprise conductive fingers that secure the wafer in place and also contact the wafer in order to conduct electrical current for the plating operation.  
           [0006]    One embodiment of a reactor assembly is disclosed in U.S. Pat. No. 5,985,126, entitled “Semiconductor Plating System Workpiece Support Having Workpiece-Engaging Electrodes With Distal Contact Part And Dielectric Cover,” which is herein incorporated by reference.  
           [0007]    [0007]FIG. 1 illustrates such a reactor assembly  10  for electroplating a metal, such as copper, onto a semiconductor wafer. The assembly  10  includes a reactor vessel  11  and a processing or reactor head  12 . The vessel includes an electroplating bowl assembly  14 .  
           [0008]    As shown in FIG. 1, the electroplating bowl assembly  14  includes a cup assembly  16  which is disposed within a reservoir chamber  18 . Cup assembly  16  includes a fluid cup  20  holding the electroplating fluid for the electroplating process. The cup assembly of the illustrated embodiment also has a depending skirt  26  which extends below a cup bottom  30  and may have flutes open therethrough for fluid communication and release of any gas that might collect as the reservoir chamber fills with liquid. The cup can be made from polypropylene or other suitable material.  
           [0009]    A bottom opening in the bottom wall  30  of the cup assembly  16  receives a polypropylene riser tube  34  which is adjustable in height relative thereto by a threaded connection between the bottom wall  30  and the tube  34 . A fluid delivery tube  44  is disposed within the riser tube  34 . A first end of the delivery tube  44  is secured by a threaded connection  45  to the rear portion of an anode shield  40  which carries an anode  42 . The delivery tube  44  supports the anode within the cup. The fluid delivery tube  44  is secured to the riser tube  34  by a fitting  50 . The fitting  50  can accommodate height adjustment of the delivery tube  44  within the riser tube. As such, the connection between the fitting  50  and the riser tube  34  facilitates vertical adjustment of the delivery tube and thus the anode vertical position. The delivery tube  44  can be made from a conductive material, such as titanium, and is used to conduct electrical current to the anode  42  as well as to supply electroplating fluid to the cup.  
           [0010]    Electroplating fluid is provided to the cup through the delivery tube  44  and proceeds therefrom through fluid outlet openings  56 . Electroplating fluid fills the cup through the openings  56 , supplied from a electroplating fluid pump (not shown).  
           [0011]    An upper edge of the cup side wall  60  forms a weir which limits the level of electroplating fluid or process fluid within the cup. This level is chosen so that only the bottom surface of the wafer W is contacted by the electroplating fluid. Excess fluid pours over this top edge into the reservoir chamber  18 . The level of fluid in the chamber  18  can be maintained within a desired range for stability of operation by monitoring and controlling the fluid level with sensors and actuators. One configuration includes sensing a high level condition using an appropriate switch  63  and then draining fluid through a drain line controlled by a control valve (not shown). The out flow fluid from chamber  18  can be returned to a suitable reservoir. The fluid can then be treated with additional plating chemicals or other constituents of the plating or other process liquid, and used again.  
           [0012]    A diffusion plate  66  is provided above the anode  42  for providing a more even distribution of the fluid plating bath across the surface of wafer W. Fluid passages in the form of perforations are provided over all, or a portion of, the diffusion plate  66  to allow fluid communication therethrough. The height of the diffusion plate within the cup assembly is adjustable using threaded diffusion plate height adjustment mechanisms  70 .  
           [0013]    The anode shield  40  is secured to the underside of the consumable anode  42  using anode shield fasteners  74 . The anode shield prevents direct impingement on the anode by the plating solution as the solution passes into the processing chamber. The anode shield  40  and anode shield fasteners  74  can be made from a dielectric material, such as polyvinylidene fluoride or polypropylene. The anode shield serves to electrically isolate and physically protect the backside or the anode. It also reduces the consumption of organic plating fluid additives.  
           [0014]    The processing head  12  holds a wafer W for rotation about a vertical axis R within the processing chamber. The processing head  12  includes a rotor assembly having a plurality of wafer-engaging fingers  89  that hold the wafer against holding features of the rotor. Fingers  89  are preferably adapted to conduct current between the wafer and a plating electrical power supply and act as current thieves. Portions of the processing head  12  may mate with the processing bowl assembly  14  to provide a substantially closed processing volume  13 .  
           [0015]    The processing head  12  can be supported by a head operator. The head operator can include an upper portion which is adjustable in elevation to allow height adjustment of the processing head. The head operator also can have a head connection shaft which is operable to pivot the head  12  about a horizontal pivot axis. Pivotal action of the processing head using the operator allows the processing head to be placed in an open or face-up position (not shown) for loading and unloading wafer W with a surface-to-be-processed in a face-up orientation.  
           [0016]    Processing exhaust gas may be removed from the volume  13  through an exhaust system. FIG. 1 illustrates an outer vessel side wall  76  which extends upwardly from the vessel base plate  75  to a top end into which is nested an intermediate exhaust ring  77  having circumferentially spaced-apart slots  78  therethrough. The slots  78  communicate exhaust gas from inside the vessel  13  to a thin annular plenum  79  located between the intermediate exhaust ring  77  and the outer bowl side wall  76 . Surrounding the outer bowl side wall  76  is a vessel ring assembly  80  which forms with the side wall  76  an external, annular collection chamber  81 . Gas which is collected in the plenum  79  passes through intermittent orifices  82  and into the annular collection chamber  81 . Gas collected in the collection chamber  81  is passed through an exhaust nozzle  83  to be collected and recycled.  
           [0017]    The reactor assembly  10  of FIG. 1 can be used reliably in electroplating semiconductor wafers. However, the reactor head  12  is relatively expensive to manufacture. The reactor head  12  is adapted to move vertically, to rotate about a horizontal axis to facilitate loading and unloading wafers W, and to rotate about a vertical axis R to spin the wafer W during plating. Delivering electroplating power from an external power supply (not shown) to the fingers  89  of the reactor head  12  requires relatively complex, expensive electrical connections such as slip ring contacts. If the wafer W could be held stationary with respect to the electroplating bowl assembly  14 , the reactor head  12  could be simplified by eliminating the motor used to rotate the wafer W about the axis R. The series of spaced-apart fingers  89  deliver adequate electroplating power to the wafer W. The relatively small contact area between the fingers  89  and the wafer can lead to localized variations in the electroplating power across the surface of the wafer, though, making it more difficulty to ensure good plating uniformity.  
         SUMMARY  
         [0018]    One embodiment of the present invention contemplates an electroplating reactor for electroplating workpieces or substrates having a workpiece holder which holds the workpiece, such as a wafer, with a plating side facing downwardly toward an electrode. The workpiece may be electrically coupled to a ring contact, e.g., by electrically contacting an outside region of the workpiece with the electrode. In certain applications, the workpiece holder can be non-rotating. The electrode may be submerged in an electroplating fluid. The reactor can include an improved support arrangement for supporting a diffusion plate above the electrode to improve distribution of the fluid plating bath on the workpiece surface.  
           [0019]    In another embodiment, the invention contemplates a ring contact which provides a substantially continuous contact surface around the entirety of an exclusion zone, which may include the annular outer edge of the workpiece. The ring contact can be serrated or otherwise have radial passages therethrough to allow flow through the ring contact for flow type plating.  
           [0020]    An alternative embodiment of the invention contemplates a finger support system for receiving a workpiece and for lowering a workpiece from a reactor head onto a movable intermediate support system mounted to the reactor vessel. The finger support system is pivotable to clear or move away from the workpiece after the workpiece is placed onto the movable intermediate support system. The movable intermediate support system includes supports that lower and accurately and precisely place the workpiece onto the contact surface of the ring contact. The supports of the movable intermediate support system may be slidable and/or pivotable to clear or move away from the workpiece after the workpiece is placed onto the ring contact.  
           [0021]    Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings in which details of the invention are fully and completely disclosed as part of this specification. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a sectional view of an electroplating apparatus wherein a workpiece plated thereby is rotatively held by the reactor head;  
         [0023]    [0023]FIG. 2 is a simplified, sectional view of a reactor vessel according to one embodiment of the invention;  
         [0024]    [0024]FIG. 3 is a simplified perspective sectional view of the reactor vessel of FIG. 2;  
         [0025]    [0025]FIG. 4 is a simplified, enlarged sectional view of a portion of FIG. 2;  
         [0026]    [0026]FIG. 5 is a simplified, enlarged partial sectional schematical view of a reactor vessel in accordance with an alternate embodiment of the present invention;  
         [0027]    [0027]FIG. 6 is a perspective view of an anode shield employed in the reactor vessel of FIG. 5;  
         [0028]    [0028]FIG. 7 is an exploded perspective view of a conductor pipe and inlet connector;  
         [0029]    [0029]FIG. 8 is a perspective view of an alternate ring contact assembly;  
         [0030]    [0030]FIG. 9 is an enlarged fragmentary schematical view of a further alternate embodiment ring contact of the present invention;  
         [0031]    [0031]FIG. 10 is a simplified sectional view of an alternate embodiment reactor vessel according to the invention;  
         [0032]    [0032]FIG. 11 is a sectional view of a further embodiment reactor vessel and head in a first relative position;  
         [0033]    [0033]FIG. 12 is a sectional view of the reactor vessel and head of FIG. 11 in a second relative position;  
         [0034]    [0034]FIG. 13 is a perspective view of a movable intermediate support system employed in the apparatus of FIG. 12;  
         [0035]    [0035]FIG. 14 is a sectional view of the support system shown in FIG. 13 shown in a first stage of operation;  
         [0036]    [0036]FIG. 15 is a sectional view of the support system of FIG. 14 shown in a second stage of operation;  
         [0037]    [0037]FIG. 16 is a perspective view of an operating lever of the intermediate support system of FIGS.  13 - 15 ;  
         [0038]    [0038]FIG. 17 is a simplified perspective, sectional view of a still further alternate embodiment of a reactor vessel of the invention;  
         [0039]    [0039]FIG. 18 is an enlarged, simplified fragmentary sectional view of the reactor vessel of FIG. 17; and  
         [0040]    [0040]FIGS. 19A through 19D are schematic sectional views of an additional alternate embodiment intermediate support structure, shown in four progressive stages of operation. 
     
    
     DETAILED DESCRIPTION  
       [0041]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.  
         [0042]    FIGS.  2 - 4  illustrate a reactor vessel  200  having a surrounding vessel side wall  206  and a vessel base  208  sealed thereto. If so desired, a movable reactor head (not shown in FIGS.  2 - 4 ) may be placed over a top  207  of the vessel to close the vessel. A workpiece or substrate  209  is processed within the vessel  200 . A “substrate” is a base layer of material over which one or more metallization levels are disposed. A substrate may be, for example, a semiconductor wafer, a ceramic block, etc. A “workpiece” is an object that at least comprises a substrate, and may include further layers of material or manufactured components, such as one or more metallization levels, disposed on the substrate.  
         [0043]    Within the side wall  206  is an outer cup  210  supported on a cup support post  214 . An electrode conductor  216  is located within the support post  214  and supports the electrode  218 . (The electrode  218 , as discussed below, may have an electrical potential with respect to a surface of a workpiece  209  during plating. The electrode may have a positive charge or a negative charge relative to the workpiece, depending on the nature of the electroplating medium. For sake of convenience, in the following discussion, the electrode  218  is assumed to have a positive potential and it is, consequently, referred to as an anode.) The conductor  216  is electrically conductive and conducts electric current to the anode  218  and delivers electroplating fluid into the vessel  200  through openings  220 . An inner cup  226  is situated within the outer cup  210 . In one embodiment, the inner cup  226  is vertically adjustable with respect to the outer cup  210 . The inner cup  226  includes a top edge  228  which forms a weir for electroplating fluid held within the inner cup  226 .  
         [0044]    During electroplating, fluid flows over a bottom surface  230  of the workpiece  209 , i.e., the surface to be plated. The fluid flows over the edge  228  and into an annular space  234  between the inner and outer cups. The outer cup  210  includes plural holes  236  in a bottom thereof which allow fluid to pass into a reservoir  238  within the reactor  200 . Fluid from the reservoir exits via an outlet  240  to be collected, treated and/or recycled or disposed. Level switches  242 ,  244  maintain the fluid in the reservoir  238  at a desired level by controlling flow out of the outlet  240  via control means such as control valves or pumps (not shown).  
         [0045]    An outer cup ring portion  250  may be supported by the outer cup  210 , e.g., by mounting the outer cup ring portion  250  to a top of the outer cup  210 . The outer cup ring portion  250  may be sealed to the outer cup  210 , e.g., via an O-ring  252 . A ring contact  260  is carried by the outer cup ring portion  250 . The workpiece  209  may be urged into electrical contact with the ring contact  260 , e.g., by a resilient backing ring  264  which is carried by a backing plate  266 . The backing ring  264  and the backing plate  266  may also act to seal a top surface  268  of the workpiece  209  to prevent exposure of the top surface  268  to the process fluid. The backing ring  264  can be pressed downwardly against the workpiece  209  by a reactor head (not shown in FIGS.  2 - 4 ).  
         [0046]    The ring contact  260  may include a plurality of ring contact terminals  262 , one of which is shown in the enlarged view of FIG. 4. The terminals include a plug  262   a  and a conductor receiving socket  262   b . The plug  262   a  fits tightly into a plug socket  263  of the ring contact  260 . A sealing cover  265  may cover the exposed portions of the terminal  262  and can incorporate an O-ring  266  to seal against the ring contact  260 . A conductor (not shown) may have a casing which seals against the cover  265  and has its conducting portion fixed into the socket  262   b.    
         [0047]    [0047]FIG. 5 illustrates schematically an alternate configuration of an inner cup  227  which includes a diffusion plate  320  arranged above the anode  218 . Additionally, the anode  218  is carried on an anode shield  322 . The anode shield is fastened to the anode by a plurality of screws  324 . The anode and the anode shield are supported by the conductor  216  (shown in FIG. 2). The diffusion plate  320  is supported on a ledge  325  of the cup  227  via a support ring  326 . The diffusion plate  320  is retained by a hold down ring  328  which is fixed to the cup  227  by a plurality of fasteners  329 . The support ring  326  can be a sealing and/or elevation adjustment element. The support ring  326  assists in preventing fluid bypass around the diffusion plate to the wafer surface, i.e., the support ring helps seal between the diffusion plate and the surrounding cup or ring wall to force fluid through the diffusion plate. The diffusion plate supporting arrangement can be incorporated into any of the embodiments described herein. For example, the ledge  325  and the rings  326 ,  328  as needed, can be incorporated into the cups  16 ,  226  (FIGS. 1 and 2), or into the cup ring portion  250  or cups  211 ,  431  (FIGS. 10, 11,  12  and  17 ).  
         [0048]    [0048]FIG. 6 illustrates an alternate anode shield  330  which is fastened to the anode by fasteners via four apertures  332   a ,  332   b ,  332   c ,  332   d . Additionally, the anode shield  330  includes four engagement formations which comprise four extending plates  336  each formed with an end stop  338  and a rib  340 . When the anode is placed over the shield  330  and fastened thereto, each plate  336  forms a slot beneath the anode. A hook (e.g., hook  358  in FIG. 7, discussed below) which enters the slot is forced past the rib  340  to be trapped between the rib  340  and the end stop  338 .  
         [0049]    [0049]FIG. 7 illustrates an inlet connector  348  that includes a central aperture  350  for flow connection to an open flanged end of a conductor pipe  351 . Additionally, a separate conductor  354  (shown schematically) can be inserted through the conductor pipe  351  and the aperture  350 , and electrically connected to the anode by a plug  355 . An exemplary conductor arrangement is described in U.S. Pat. No. 6,228,232, entitled “Reactor Vessel Having Improved Cup, Anode and Conductor Assembly,” and herein incorporated by reference.  
         [0050]    A plurality of fastener holes  352  are available for receiving screws  353  (only one shown) to attach the connector  348  to a flange  349  of the conductor pipe  351 . The flange  349  includes threaded holes  359  for threadedly receiving the screws  353 . The connector includes rectangular openings  356  for distributing fluid into the cup.  
         [0051]    Between adjacent openings  356 , is one of four engagement hooks  358  each having a head or hook portion  360 . Each one of the hook portions  360  enters one of the slots formed by the engagement formations of the anode-shield.  
         [0052]    The connector  348  may support the anode and anode shield from the conductor pipe  351 . By utilizing a bayonet-type arrangement as described, the anode can easily be removed for maintenance by turning and lifting from a top side only of the reactor vessel. This simplifies assembly and reassembly and reduces maintenance costs. Additional benefits of using a bayonet connection to support the anode are described in the aforementioned U.S. Pat. No. 6,228,232.  
         [0053]    [0053]FIG. 8 illustrates an alternate ring contact  276 , having a serrated or discontinuous top edge  276   a . The top edge  276   a  is configured to provide sufficient electrical contact area with a workpiece to deliver sufficient power for plating, yet provide sufficient passages to allow fluid to pass through the ring contact. This type of ring contact may be utilized, for example, in the reactor vessel  200  of FIGS.  2 - 4  or in the alternative reactor vessels described below with respect to FIGS.  10 - 12 .  
         [0054]    [0054]FIG. 9 illustrates an alternate ring contact assembly  279 . A compliant overmolded seal lip  277  extends from the outer plating cup ring portion  250  upwardly to the wafer  209 . When the wafer is moved downwardly to engage the upper edge  279   a  of the ring contact assembly  279 , the seal lip  277  may substantially seal the ring contact  260  from exposure to the plating fluid. The seal lip  277  ideally contacts on a photoresist layer of the workpiece, while the ring contact  260  contacts the plating seed layer.  
         [0055]    [0055]FIG. 10 illustrates a reactor vessel  201  in accordance with an alternative embodiment of the invention. The reactor vessel  201  may share many components in common with the reactor vessel  200  of FIG. 2 and like reference numbers are used in both drawings to refer to like components. One difference between the reactor vessels  200  and  201  is that the inner cup  226  and the outer cup  210  of the reactor vessel  200  are eliminated and replaced in the reactor vessel  201  by a single cup  211 . The electroplating fluid flows upwardly from the conductor  216 , and over the workpiece  209 . The process electroplating fluid flows through the serrations of the alternate ring contact  276  (shown in FIG. 8) to an annular area  278  between the single cup  211  and the vessel side wall  206 . The single cup  211  is supported on the support post  214 . The single cup  211  does not include the apertures  236  associated with the outer cup  210  shown in FIGS. 2 and 3. The fluid that is collected in the reservoir  238  passes out of the outlet  240  and is recycled or disposed as per the previously described embodiment.  
         [0056]    One advantage of the flow-through configuration of FIGS. 8 and 10, wherein the ring contact  276  serves as an overflow weir, is that the ring contact  276  may be immersed with overflowing plating solution when the wafer is not present. This condition allows the contact  276  to be plated and/or de-plated between wafers without decreasing throughput, i.e., automation for wafer cycling, moving wafers into and out of the vessel, can happen simultaneously with contact conditioning.  
         [0057]    [0057]FIG. 11 illustrates a reactor head and vessel assembly  400  including a reactor head  402  and a reactor vessel  406  supported on a frame or deck  408 . The reactor head  402  includes a mechanism  410  for activating workpiece gripping fingers  412  to grip or release a workpiece  209 . An exemplary embodiment of a mechanism for gripping and releasing a workpiece with gripping fingers, and pivoting the fingers to release the workpiece, is disclosed in U.S. Pat. No. 5,377,708, issued Jan. 3, 1995, and herein incorporated by reference.  
         [0058]    A top side backing plate  416  may be arranged to press, and sealingly isolate, the top side  268  of the workpiece as described for example with respect to the previously described embodiment of FIG. 2. In this view, the backing ring  264  is either not shown for simplicity of depiction, or is not needed based on the resilient characteristics of the materials chosen for the backing plate  416 .  
         [0059]    The vessel  406  includes an outer vessel side wall  420  sealed to a base  422 . A fluid conduit conductor  426  delivers fluid into the vessel  406  through openings  428 , and conducts electricity to an electrode  430 . in this embodiment, a consumable anode is not used, i.e., the electroplating metal is introduced via the electroplating fluid.  
         [0060]    A cup  431  is arranged within the vessel  406  and surrounds the electrode  430 . A diffusion plate  434  is carried by the cup  431  above the electrode  430 . An upper cup portion  436  includes top weir edge  438 .  
         [0061]    Surrounding the upper cup portion is a ring contact assembly  444  which includes a support ring  446  and a ring contact  448 . The ring contact assembly  444  may be carried by the vessel  406 , e.g., by being mounted on a top flange  450  of the cup  431 . The support ring  446  includes passageways  454 , aligned with passages  456  through the top flange  450 , to drain fluid from above the support ring to a reservoir  457 , and to vent reservoir gases through slots (not shown) to an exhaust plenum  460  for collection and recycling. Passages  464  through the flange  450  allow fluid passing over the weir edge  438  to return to the reservoir  457 .  
         [0062]    A movable intermediate support assembly  470  for supporting a workpiece is located above the ring contact assembly  444 . The support assembly  470  is operative to receive a workpiece  209  from the fingers  412  and to deliver the workpiece downwardly to a position resting on the ring contact  448 . The support assembly  470  includes workpiece positioning supports  474  spaced around a workpiece positioning ring  476 . The ring  476  is raised and lowered, e.g., by pivoting levers  478 , and is guided for precise positioning of workpieces onto the ring contact  448 . Each pivoting lever  478  has a base end  480  which may be spring-loaded, as shown in FIGS. 14 and 15.  
         [0063]    [0063]FIG. 12 illustrates the reactor head  402  coupled to the vessel  406 . The intermediate support assembly  470  is still in a raised position. The fingers  412  have lowered the workpiece  209  onto the supports  474 . Pivoting the lever  478  of FIG. 12 in a clockwise direction will lower the support assembly  470  to a position where the workpiece is supported by the ring contact  448 , the supports  474  dropping to a retracted position below the workpiece  209 .  
         [0064]    The support assembly  470  is centered and guided within an upper vessel ring  482 . Each of the levers  478  is guided for pivoting by a guide formation of the upper vessel ring  482 . Preferably, three levers  478  are provided and are spaced at 120° separation around the ring. Additionally, a plurality of guide rods  486  may be fixed to the vessel ring  487  and guided in slots (not shown) of the positioning ring  476  to set the horizontal positioning of the ring  476 .  
         [0065]    As illustrated in FIG. 13, the upper vessel ring  482  includes circular openings  488 , one at each lever  478 . A cover  490  is mounted into each opening  488  and held to the vessel ring  482  by one or more screws, recessed within one or more screw holes  491 .  
         [0066]    As illustrated in FIGS. 14 and 15, each lever  478  pivots about a trunnion  494 . An opposite rounded end  493  of each lever presses against a top  500  of a guide slot  502  formed in the positioning ring  476 . The base end  480  of the lever is connected by a spring  504  to a connection  506  on a respective cover  490 .  
         [0067]    [0067]FIG. 15 shows the support assembly  470  in the lowered position. Each lever  478  has pivoted about its respective trunnion  494  against the urging of a respective spring  504 . The head ( 402  in FIGS. 11 and 12) may force the support assembly  470  downwardly to overcome the upward biasing force of the springs  504  on their levers  478 .  
         [0068]    [0068]FIG. 16 illustrates an embodiment of the lever  478  having an activation shaft  492 , a trunnion  494 , and an effecter arm  496  which carries the rounded end  493 . The effecter arm  496  lifts or lowers the ring  476 . The activation shaft includes a hole  492   a  for receiving an end of one spring  504 .  
         [0069]    [0069]FIGS. 17 and 18 illustrate an alternate movable intermediate support assembly  570 . The assembly includes a plurality of workpiece supports  574 . The supports  574  are actuated to be translated or slid downwardly, and are returned upwardly by spring tension from respective springs  577 , each spring acting between an elevated fixture  590  on the vessel ring  591  and a lug  593  on the support  574 . There are preferably three supports  574  spaced at 120° around a circumference of the vessel. Each support includes an inclined surface  578  for centering the workpiece between the supports  574 . In operation, the workpiece fingers  412  deliver a workpiece to the assembly  570  and then tilt outwardly to release the workpiece onto the surfaces  578  to be guided to a ledge  579  of the supports. The location of the fingers  412  and the supports  574  are staggered circumferentially of the workpiece  209  to avoid interference.  
         [0070]    As illustrated in FIG. 18, the supports  574  can be retracted upwardly to a position  574   a  to receive the workpiece  209  from the fingers  412  without any significant vertical drop of the workpiece. The supports are then lowered through the position marked  574   b  to the position marked  574   c  wherein the workpiece  209  rests on the ring contact  260  in position  209   c  and the supports are spaced below the edge of the workpiece. The workpiece moves through the positions marked  209   a ,  209   b ,  209   c . To translate the supports, the lugs  593  can be lowered against spring tension of the springs  577  by an external actuator (not shown).  
         [0071]    Alternatively, a finger plate  602  which carries the fingers  412  has a push surface  604  which can be lowered to press a contact surface  606  of the supports  574  downwardly against the urging of the springs  577  to deliver the workpiece  209  onto the ring contact  260 .  
         [0072]    As a further alternative, the head  402  can include a mechanism (not shown) attached thereto which depresses the supports  574  downwardly, and later releases the supports for upward movement, conjointly with the lowering and raising of the head  402  to the reactor vessel  406 . The supports  574  are moved downwardly to deliver the workpiece  209  onto the ring contact  260 .  
         [0073]    As shown in FIG. 18, the supports  574  include two pins  584  which can vertically pass through a slot  586  formed into structure of the vessel such as in the vessel ring  591 . The slot  586  guides the vertical movement of the support  574  to place and then later remove a workpiece  209  onto/from the ring contact  260 .  
         [0074]    Additionally, it is also readily derived from this invention disclosure that the supports  574  could be reconfigured to sweep outwardly about a pivot point which is rotationally fixed to the vessel, such as a pin placed substantially at the elevation shown for the pin  584  in FIG. 18. The clockwise rotation of the support  574 , for example, would lower a workpiece onto a contact ring.  
         [0075]    [0075]FIGS. 19A through 19D illustrate a further alternative embodiment for delivering a workpiece to a ring contact. Supports  774  can be guided for translation to lower the workpiece from the gripping fingers  412  to the ring contact  260  and then guided to rotate outwardly at an end of downward translation, to clear or move away from the workpiece  209 . To provide for this movement, each support  774  has a guide plate  777  with top and bottom pins  780 ,  782  respectively. The pins are guided by a guide bracket  784  outside of the vessel  406 . The guide bracket  784  includes a cam slot  786  having a vertical portion  788  and an oblique portion  790  extending from the vertical portion  788 . The oblique portion  790  extends downwardly and radially outwardly relative to a centerline of the vessel  406 . Thus, the support  774  will travel vertically while the pins  780 ,  782  are both within the vertical portion  788 , but will rotate about the top pin  780  when the bottom pin  782  moves radially outwardly within the oblique portion  790  of the cam slot  786 .  
         [0076]    In FIG. 19A, the head  402  is illustrated at an elevated position above the ring contact  260 . The workpiece  209  is held by the fingers  412  above the supports  774  which extend from outside the vessel into the vessel. Each support  774  includes a workpiece supporting surface  775  adjacent to an inclined workpiece guiding surface  773 . The guiding surfaces  773  will locate the workpiece at a correct position within a horizontal plane. The head may also include a backing plate  416  such as shown in FIG. 11 or a backing plate  266  with a resilient backing ring  264  as shown in FIG. 2.  
         [0077]    In FIG. 19B the head  402  has been lowered to deliver the workpiece  209  onto the support surfaces  775  of the supports  774 . At this point in time and location within the vessel, the fingers  412  will rotate outwardly to clear the workpiece  209 . At this point the workpiece is supported entirely on the support surfaces  775 . Further downward movement of the head then moves the supports  774  downwardly (by a mechanism not shown) with the pins  780 ,  782  moving down the vertical portion  788  of each of the cam slots  786 .  
         [0078]    [0078]FIG. 19C illustrates that the supports have completed a purely vertical travel, and the workpiece rests on the ring contact  260 .  
         [0079]    As illustrated in FIG. 19D, further vertical movement of the guide plates  777 , particularly movement of the bottom pin  782  within the oblique slot portion  790 , causes the support  774  to vertically descend and also to pivot about the top pin  780 . This movement rotates the workpiece supporting surfaces  775  away from the workpiece  209 .  
         [0080]    The reactor head  402  further descends to press the resilient backing ring  264  against a top side of the workpiece as described above with respect to the embodiment of FIG. 2.  
         [0081]    When the processing of the workpiece  209  is completed, the steps of FIGS.  19 A- 19 D are reversed. The backing ring  264  is raised from the workpiece  209 . The support  774  are lifted and rotated inwardly to pick up the workpiece. The workpiece is elevated within the vessel by vertical lifting of the supports  774 . The fingers  412  are tilted inwardly to engage edges of the workpiece. The fingers  412  and the head  402  are lifted from the reactor vessel  406 . The workpiece can then be removed and a new workpiece engaged by the fingers.  
         [0082]    The ring contact of the present invention provides widely distributed electrical contact with the workpiece. This enhances electroplating uniformity and contact reliability. The assembly may provide back side protection of the workpiece. The contact can be constantly wetted to ensure contact quality. The contact construction can be more robust than prior known contact fingers.  
         [0083]    Utilizing a fixed, i.e., non rotating, ring contact in accordance with embodiments of the invention increases reliability of plating power fed to the contact. Select embodiments automate workpiece delivery to the ring contact, utilizing the movable intermediate support system, which facilitates accurate contact placement relative to the workpiece exclusion zone. Non-rotation of the contact and the use of an intermediate support assembly can simplify the reactor head design by eliminating the motor necessary to rotate the workpiece and providing electroplating power connections in the vessel itself rather than in the vessel and the reactor head.  
         [0084]    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.  
         [0085]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.