Abstract:
Although there are several inventions disclosed herein, the present application is directed to a reactor for electrochemically processing a microelectronic workpiece. The reactor comprises a movable electrode assembly that is disposed for movement along a motion path. The motion path includes at least a portion thereof over which the electrode assembly is positioned for processing at least one surface of the microelectronic workpiece. A cleaning electrode is located along the motion path of the movable electrode assembly. In one embodiment, a programmable controller is connected to direct the movable electrode assembly to move to the cleaning electrode during a cleaning cycle. At that time, the programmable controller connects the movable electrode assembly as an anode and the cleaning electrode as a cathode for cleaning of the movable electrode assembly. The cleaning electrode may be disposed along a position of the motion path that is beyond the range of motion required to process the microelectronic workpiece so that the programmable controller may be programmed to conduct a cleaning cycle while a microelectronic workpiece is present in the reactor for processing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 09/782,216, filed Feb. 13, 2001 now U.S. Pat. No. 6,773,559, which is a a continuation-in-part of U.S. Ser. No. 09/476,526, entitled “A Microelectronic Workpiece Processing Tool Including a Processing Reactor Having a Paddle Assembly for Agitation of a Processing Fluid”, filed Jan. 3, 2000 now U.S. Pat. No. 6,547,937. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH R DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   The present invention generally relates to an apparatus for processing a microelectronic workpiece. More particularly, the present invention is directed to a processing tool that includes an improved electrochemical processing reactor that may be used to electrochernically etch one or more layers from a microelectronic workpiece. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed. Although the present invention will be described with respect to electrochemical etching, it will be recognized that many of the principles set forth herein are also applicable to other electrochemical tools and reactors. 
     FIG. 1 , labeled “prior art,” illustrates the background art of electrochemical etching. The apparatus shown is a basic electrochemical etching cell. A tank T holds liquid electrolyte E, which is typically an aqueous solution of a salt. Two electrodes, the anode A and the cathode C, are wired to a voltage source such as a battery B. When the apparatus is electrified, metal atoms in the anode A are ionized by the electricity and forced out of the metal into the solution, which, in turn, causes the metal anode A to dissolve into the aqueous solution. The rate of dissolution is proportional to the electric current, according to Faraday&#39;s law. Depending on the chemistry of the metals and salt, the metal ions from the cathode either plate the cathode, fall out as precipitate, or stay in solution. 
   Different types of electrochemical etching apparatus are described in the literature, but most are based on the foregoing principles. In conventional electrochemical etching reactors, the cathode is a shaped tool held close to the anode. The cathode is slowly moved over the face of the workpiece while electrolyte is pumped into the interstitial gap between the cathode and the workpiece, which is connected as the anode. Due to electrical field effects, the highest dissolution rates on the workpiece surface are in those places where the cathode has closely approached the anode surface. The rate falls off as the distance between the anode and the cathode increases. 
   By choosing proper electrolyte and electrical conditions electropolished surfaces can be achieved in electrochemical etching. As the name implies, electropolishing creates a very smooth mirror-like surface, said to be specular or bright, whose roughness is smaller than a wavelength of light. Unlike a mechanically polished surface, an electropolished surface has no built-up stress left by the high pressures of machining and mechanical polishing. The conductive metal may be selectively or completely etched from the surface of the workpiece. In the microelectronic industry, for example, electrochemical etching is used for through-mask patterning and for removal of continuous thin film conducting metals, such as seed layers, from the surface of a workpiece, such as a semiconductor wafer. 
   In electrochemical etching processes, the material being removed provides the conductive path for supplying a necessary portion of the processing power. As a result, the removal of material must be performed in a generally controlled manner. Attempts to concurrently remove the entire conductive surface of the workpiece may result in the etching away of portions of the conductive layer located proximate the source of processing power before areas located remote from the processing power source are removed. Remote areas would therefore become electrically isolated from the processing power prior to the completion of the electrochemical etch in those areas. By selectively applying the etching process, the likelihood of the day at a region will be electrically isolated is significantly reduced. 
   In the foregoing apparatus, material that is removed from surface of the workpiece will migrate to conductive surfaces of the electrode that is used to etch the workpiece material (“the etching electrode”). As the number of workpieces processed increases, the amount of material that collects on the etching electrode will likewise increase. This buildup of conductive material may have a significant effect on the uniformity of the surface of the etching electrode. Additionally, the buildup of material may interfere with the free-flow of electrolyte through nozzle openings of the etching electrode that are provided to supply a flow of electrolyte to the surface of the workpiece. 
   The non-uniformity resulting from the material build-up alters the gap distance between the anode, formed by the surface of the workpiece, and the cathode formed by the etching electrode. These non-uniformities, in turn, result in a corresponding non-uniformity in the electric field between the workpiece and etching electrode. The electric field variations give rise to uneven etch rates. As the variations in the uniformity of the etch rate increase, so does the chance that portions of the workpiece surface may become electrically isolated from the source of processing power prior to completion of the etching process in those areas. Further, such variations cannot be tolerated in processes that require highly uniform etched surfaces, such as in electrochemical planarization. 
   Another factor that can affect the uniformity of the current density and, consequently, the uniformity of the etching rate, is the change in the area of the workpiece that is exposed to the etching electrode as the etching electrode is swept across the workpiece. The degree to which this changing area affects the etching rate is dependent on the relative shape of both the workpiece and etching electrode. For example, this etching rate dependency occurs when a circular wafer is swept by a paddle-shaped etching electrode assembly having a rectangular etching electrode. Initially, as the rectangular etching electrode begins to move across the surface of the workpiece, it intersects a first edge of the wafer. In most reactors, the rectangular etching electrode assembly intersects the workpiece at a point that is approximately at the center of the rectangular electrode. As the rectangular etching electrode moves toward the center of the workpiece, the area over which the etching electrode and the workpiece surface are exposed to one another increases. When the rectangular etching electrode is positioned proximate the center of the workpiece, the area of exposure is typically at its maximum value. As the etching electrode continues to move across the workpiece, away from the center of the workpiece, the area of exposure again begins to decrease until the etching electrode completes it movement to the opposite edge of the workpiece. The varying area of exposure between the workpiece and the etching electrode can have a significant detrimental effect on current densities and etch rates and, thus, have a corresponding detrimental effect on the desired results of the etching process. 
   The present inventors have recognized many of the problems associated with electrochemical etching reactors and processes employing existing microfabrication facilities. One or more of these problems are addressed in the exemplary processing tool set forth herein that includes an improved electrochemical etching reactor. 
   BRIEF SUMMARY OF THE INVENTION 
   Although there are several inventions disclosed herein, the present application is directed to a reactor for electrochemically processing a microelectronic workpiece. The reactor comprises a movable electrode assembly that is disposed for movement along a motion path. The motion path includes at least a portion thereof over which the electrode assembly is positioned for processing at least one surface of the microelectronic workpiece. A cleaning electrode is located along the motion path of the movable electrode assembly. In one embodiment, a programmable controller is connected to direct the movable electrode assembly to move to the cleaning electrode during a cleaning cycle. At that time, the programmable controller connects the movable electrode assembly as an anode and the cleaning electrode as a cathode for cleaning of the movable electrode assembly. The cleaning electrode may be disposed along a position of the motion path that is beyond the range of motion required to process the microelectronic workpiece so that the programmable controller may be programmed to conduct a cleaning cycle while a microelectronic workpiece is present in the reactor for processing. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of the components of the basic electrolytic cell that may be used to electrochemically etch a surface layer of a workpiece. 
       FIG. 2  is a basic cross-sectional view of an electrochemical etching reactor constructed in accordance with one embodiment of the present invention. 
       FIG. 3A  used and exploded view of one embodiment of the head engagement assembly used in the reactor of  FIG. 2 . 
       FIG. 3B  is a perspective view of one embodiment of an etching assembly constructed in accordance with the present invention. 
       FIG. 3C  is a bottom plan view of the etching assembly shown in  FIG. 3B . 
       FIG. 4A  is a perspective view of the components of one embodiment of an electrode assembly that may be used in the etch assembly of  FIGS. 3A-3C . 
       FIGS. 4B ,  4 C and  4 D are further views of the electrode assembly shown in  FIG. 4A . 
       FIG. 5  illustrates operation of the etching assembly of the foregoing figures as it is moved adjacent to the surface of a workpiece that is under process. 
       FIG. 6  is a plan view illustrating a silhouette of a circular workpiece superimposed upon multiple electrode assembly positions, where the positions represent movement of the electrode assembly along the length of the workpiece during processing. 
       FIGS. 7A and 7B  illustrate one embodiment of a gap adjustment mechanism that may be used in the reactor of  FIG. 2 . 
       FIGS. 8A and 8B  illustrate one embodiment of a spring float assembly that may be used in the compliant mounting used in the reactor base of all of the reactor shown in  FIG. 2 . 
       FIG. 9  illustrates a first embodiment of a contact assembly that may be used in the reactor head of the reactor shown in  FIG. 2 . 
       FIG. 10  illustrates a second embodiment of a contact assembly that may be used in the reactor head of the reactor shown in  FIG. 2  million 
       FIG. 11  is a schematic block diagram of a circuit that may be used to detect the resistance across the contacts and workpiece in a multi-segment contact assembly, such as the one shown in  FIG. 10 . 
       FIG. 12  illustrates an embodiment of the contact portion of the reactor head assembly shown in  FIG. 2 , wherein the contact portion is adapted to accept a tray that holds the workpiece. 
       FIGS. 13A and 13B  illustrate one embodiment of a tray that may be used with the contact portion shown in  FIG. 2 . 
       FIGS. 14   a  through  14 C illustrate one embodiment of a handle that may be used with the tray of  FIGS. 13A and 13B . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  illustrates an electrochemical etching reactor constructed in accordance with one embodiment of the present invention. The reactor, shown generally at  1 , includes a reactor head assembly  345  and a reactor base  315 . The reactor my be incorporated in an integrated tool with other reactors that execute the same or ancillary processes used in the microfabrication of micro-sized devices and/or components. For example, the reactor may be included in a multiple station tool such as the LT-210C™ or EquinoX™ tools available from Semitool, Inc. of Kalsipell, Mont. 
   The reactor head assembly  345  may be connected to a lift mechanism  703  to drive the reactor head vertically in the directions noted by the arrows  704 . For example, lift mechanism  3  may drive the reactor head assembly  345  between a first position (not illustrated) in which it cooperates with the reactor base assembly  345  to define the controlled processing environment and a second position (illustrated in  FIG. 2 ) in which the reactor head assembly  345  is separated from the reactor base assembly  315 . In the second position, a workpiece that is to be processed or that has been processed may be loaded or unloaded from the reactor head assembly  345 . To facilitate the loading and/or unloading process, the lift mechanism  703  may also include one or more actuators that rotate the reactor head assembly  345  in the directions noted by arrows  706  about the horizontal axis illustrated at arrows  705 . 
   In the illustrated embodiment, the reactor head assembly  345  includes the principal components that are used to load and unload the workpiece as well as those components that are used to provide processing power to the workpiece. To this end, reactor head assembly  345  includes an actuator section  710  and a workpiece contact section  715 . As will be set forth in further detail below, the actuator section  710  includes those components that are used to open and close the components of the contact section  715  for loading and unloading the workpiece, while workpiece contact section  715  includes those components that are used to support the workpiece and conduct electrical power to it during processing. The actuator section  710  may also include electrical circuits used to test the resistance of the surface that is to be electrochemically etched to either set the electrical parameters that are to be used for the processing and/or to insure that the workpiece meets certain parameters before it is processed. 
   Depending on the particular process requirements, reactor base  315  may serve as a reservoir that is filled with an electrolyte. In such instances, the reactor head assembly  345  is driven to a processing position in which at least one surface of the workpiece makes contact with the fluid surface of the electrolyte. In the embodiment shown here, however, reactor base  315  is not filled with electrolyte. Rather, it cooperates with the reactor head assembly  345  to provide a controlled processing environment in which electrochemical etching may take place. It may also include a drain to remove the electrolyte after it has been utilized in the etching process. 
   Generally stated, the reactor base assembly  315  of the illustrated embodiment comprised of a chamber portion  720  and a head engagement portion  725 . The head engagement portion  725  includes an etch assembly, shown generally at  10 , having an electrode assembly  20  that is driven linearly in the directions noted by arrows  721 . As will be set forth in further detail below, the electrode assembly  20  includes at least one conductive plate that serves as the cathode during electrochemical etching. Further, the electrode assembly  20  of the disclosed embodiment serves to provide a flow of electrolyte that spans the interstitial region between the conductive plate and the workpiece. In this arrangement, the surface of the workpiece that is to be electrochemically etched serves as the anode. 
   As noted above in connection with known electrochemical etching reactors, the spacing between the cathode and the surface of the workpiece is often critical to the uniformity of the etching process. As such, the etch assembly  10  is provided with one or more gap adjustment mechanisms, shown generally at  200 . In operation, the contact portion  715  of the reactor head assembly  345  includes structures that align with end portions of the gap adjustment mechanisms  200  so that the contact portion  715  and the etch assembly  10  properly register with one another. Since the workpiece is carried by the contact portion  715  and the electrode assembly  20  is carried by the etch assembly  10 , the gap adjustment mechanisms  200  serve to initially provide and thereafter maintain the electrode of the electrode assembly  20  and the surface of the workpiece at a predetermined distance from one another. 
   To ensure that the gap adjustment mechanisms  200  do not deviate to any substantial degree from their predetermined positions when the etch assembly  10  and the reactor head assembly  345  are registered with one another, head engagement portion  725  of the reactor base assembly  315  is compliantly mounted to the chamber portion  720 . In the illustrated embodiment, this compliant mounting is provided by cooperating float mechanism/pin pairs. With reference to  FIG. 2 , the reactor includes one or more float mechanisms  260  in fixed engagement with the chamber portion  720  that engage respective pins  255  that are in fixed engagement with the head engagement portion  725 . The specific details relating to one embodiment of a float mechanism  260  and corresponding pin  255  are set forth below. 
   During electrochemical etching, the etch material may build-up on the cathode thereby altering the desired distance between the cathode and the surface of the workpiece. This becomes a particularly onerous problem when the reactor is used to electrochemically etch, large volumes of workpieces in a production environment. Accordingly, etch assembly  10  is provided with a cleaning electrode  35  and may be programmed to execute a cleaning cycle after processing a single workpiece, after processing a predetermined number of workpieces, or during a single processing cycle. During a cleaning cycle, electrode assembly  20  is driven to a position in which the conductive plate thereof is adjacent the cleaning electrode  35 . Electrical power is then provided between the conductive plate and the cleaning electrode while a flow of electrolyte or other electrically conductive solution is maintained between them. The electrical power is provided during this cleaning cycle so that the cleaning electrode  35  operates as a cathode and the conductive plate of the electrode assembly  20  operates as an anode. In this operation, the material at the surface of the conductive plate is removed thereby leaving the conductive plate in a state in which workpiece-to-workpiece processing is substantially uniform and is not generally dependent on the total number of workpieces processed by the reactor. The cleaning electrode may, for example, be formed from platinum plated titanium or some other inert material. 
     FIG. 3A  is an exploded view of one embodiment of the head engagement portion  725  of the reactor base assembly  315  that is suitable for use in the reactor of  FIG. 2 . As shown in  FIG. 3A , the head engagement portion  725  includes a top cover  740  having a rectangular flange  742  and an upstanding circular rim  744  that defines a central aperture. The rim  744  and central aperture has a diameter that is large enough to allow at least the contact portion  715  of the reactor head  345  to extend therethrough so that the workpiece may be placed proximate the electrode assembly  20  for processing. 
   The top cover  740  is secured to an upper surface of an intermediate cover  746 . The intermediate cover  746  includes a plurality of downward depending sidewalls  748  that extend into engagement with a bottom cover  752 . Together, the intermediate cover  746  and bottom cover  752  cooperate to define one or more chambers that hold the components used to drive the electrode assembly  20 . Such an arrangement assists in isolating the components from the reactive chemicals that are typically used for processing. Further, this arrangement assists in preventing contaminants generated by the drive components from entering and fouling the processing of the workpiece. 
     FIG. 3B  is a perspective view of one embodiment of an etch assembly  10 , the components of which are also shown in an expanded form in  FIG. 3A . 
   In the illustrated embodiment, the etch assembly  10  includes an electrode assembly  20  having a rectangular plan surface  730  that faces a lower surface of a microelectronic workpiece  25 , shown here by dashed lines as a disk-shaped semiconductor wafer. Although reference is made to one particular shape of workpiece, one skilled in the art will readily appreciate, that workpieces having alternative shapes could also be used without departing from the teachings of the present invention. 
   As shown in both  FIGS. 3A and 3B , three gap adjustment mechanisms  200  are spaced at equal angular distances with respect to the workpiece  25 . When the contact portion  715  of the reactor head assembly  345  engages the gap adjustment mechanisms  200 , the workpiece  25  rests along a plane that is parallel to the plane defined by these three points of engagement. Alternatively, the contact portion  715  may be designed so that the portions thereof that are engaged by the gap adjustment mechanisms  200  are recessed a sufficient distance so that the workpiece rests directly along the plane defined by these three points of engagement. In either instance, this ensures that the planar face of the electrode assembly  20  and the lower surface of the workpiece  25  are properly spaced from one another. 
   The electrode assembly  20  may be driven across the surface of the workpiece in a variety of manners. Here, the electrode assembly is driven linearly along the entire diameter of the workpiece  25  in order to process substantially the entire workpiece surface. With reference to  FIGS. 3A ,  3 B and  3 C, the electrode assembly  20  of the illustrated embodiment includes one or more connection tabs  30  that are connected to the drive mechanism. A first portion of each of the connection tabs  30  is connected to a corresponding drive belt  185 , the details of which will be discussed below. A second portion of each of the connection tabs  30  engages a corresponding guide rod  195  along which the electrode assembly  20  is driven during processing. In operation, the guide rods  195  assist in ensuring fluid and accurate motion of the electrode assembly  20  along its motion path. The guide rods  195  additionally help to maintain a consistent relative spacing between the surface of an electrode assembly  20  and the nearby workpiece  25 . 
   With particular reference to  FIG. 3C , the electrode assembly  20  is driven along guide rods  195  by a drive mechanism that includes a set of four pulleys  170   a - b , each pulley being located at a respective corner of the etch assembly  10 . The pulleys  170   a - c  ride upon corresponding pulley rods  175   a  and  175   b , with pulleys  170   a  and  170   b  sharing common pulley  175   a . Pulley  170  is connected so that it is directly driven by a motor  180 . 
   The pulleys  170   b  and  170   d  are coupled to one another by drive belt  185   a  while pulleys  170   a  and  170   c  are coupled to one another by drive belt  185   b . As such, the rotational motion imposed on pulley  170   d  by motor  180  is imparted to all of the remaining pulleys  170   a - c . This motion, in turn, is imparted as a linear movement of the electrode assembly  20  since it is attached at connection tabs  30  to the drive belts  185 . In the illustrated embodiment, the gear ratios of the pulleys are one to one with respect to one another. As such, the relative rates of movement of the pulleys  170   a - d  and the corresponding movement of the drive belts  185   a  and  185   b  are substantially identical. 
   The position of the electrode assembly  20  along its motion path may be detected and controlled in a variety of manners. In the illustrated embodiment, a position sensor  190  is attached to one of the connection tabs  30  so that it moves linearly along the motion path with the electrode assembly  20 . As the electrode assembly is driven along the motion path, the position sensor  190  provides an encoded signal whose value corresponds to the electrode assembly&#39;s absolute position. By decoding the signal received from the position sensor  190 , the position of the electrode assembly  20  can be tracked. Such decoding may be accomplished by providing the encoded signal to a programmable control system, shown generally at  780  of  FIG. 3B . A programmable control system  780 , in turn, may be connected to drive the motor  180  in response to the decoded position of the electrode assembly.  20 . 
   The cleaning electrode  35  of the illustrated embodiment is disposed along the motion path of the electrode assembly  20  and is positioned beyond the range of movement required to process the workpiece  25 . This allows the electrode assembly  20  to be cleaned even when a workpiece  25  is present. Further, depending on the processing requirements, the programmable control system  780  may be programmed so that cleaning operations are conducted as part of the processing of a single workpiece. For example, if the material that is electrochemically etched from the surface of the workpiece builds up quickly as a single workpiece is processed, a cleaning cycle may be scheduled mid-way (or at some other predetermined point) through the processing of the single workpiece. 
   The particular construction of one embodiment of an electrode assembly  20  suitable for use in the reactor of  FIG. 2  is illustrated in  FIGS. 4A through 4D . As shown, the electrode assembly  20  includes a top portion  45  and a bottom portion  50 . The top portion  45  includes a top surface having one or more conductive segments  40 . The bottom portion  50  is adapted for coupling to one or more fluid and/or electrical supply lines. For example, the bottom portion  50  may be coupled to one or more fluid sources or drains, electrical sources for receiving processing power, and/or vacuum sources for inducing pressure differentials at the surface of the electrode assembly  20 . In the illustrated embodiment, a number of different lines are provided to the bottom portion  50 . A first source of fluid is supplied to the electrode assembly  20  via a flexible tube  55  that is coupled proximate the center of the bottom portion  50 . A second source of fluid is provided by a pair of fluid supply lines  60  located near a first end of the electrode assembly  20 . A source of vacuum is coupled to a second end of the electrode assembly  20  by a pair of vacuum supply lines  65 . Finally, an electrical source providing processing power is coupled to the electrode assembly  20  via an electrical connection  70  located proximate the vacuum supply lines  65 . 
   The flexible tube  55  is connected to a reservoir containing processing fluid through a pump for supplying the processing fluid to the surface of the electrode assembly  20 . Processing fluid provided through the flexible tube  55  is received by a central chamber  75  located within the bottom portion  50  of the electrode assembly  20 . The central chamber  75  distributes the fluid lengthwise across the electrode assembly  20 . From the central chamber  75 , the fluid enters the top portion  45  of the electrode assembly  20  through a diffuser plate  80  ( FIGS. 4C and 4D ). As particularly shown in  FIG. 4D , the top portion  45  includes a protrusion  85 , sized and shaped to correspond to the top opening of the central chamber  75 , that is received by the central chamber, and upon which the diffuser plate  80  is connected. A gasket  90  located around the periphery of the protrusion  85  seals against the internal sidewall surface of the central chamber  75 , thereby effectively restricting fluid flow between the peripheral surface of the protrusion  85  and the sidewall surface of the central chamber  75 . 
   In the illustrated embodiment, the diffuser plate  80 , as shown in  FIG. 4D , includes a series of openings that span the length of the electrode assembly  20 . These openings are smaller proximate the center of the electrode assembly  20  compared to the size of the openings at the end portions thereof. As such, the fluid flow from the bottom portion  50  to the top portion  45  is more restricted proximate the point where the fluid is supplied to the electrode assembly  20  (here, the point of connection with flexible tube  55 ) and less restricted further away from the initial source of the fluid. This assists in ensuring a generally uniform fluid pressure through chamber  75  thereby providing for an even distribution of the fluid flow to the workpiece across the entire length of the electrode assembly  20 . 
   After the fluid flows through the diffuser plate  80 , it enters one of the supply channels  100  located within a distribution portion  105  of the electrode assembly  20 . From the supply channel  100 , the fluid travels through openings  120  in a gasket  110  and exits the electrode assembly  20  through one or more fluid delivery ports  115  located at the upper surface of the electrode assembly  20 . 
   A source of de-ionized water and a source of vacuum pressure are also provided through openings at the surface of the electrode assembly  20  in a manner that is somewhat similar to that described above for the processing fluid. The fluid supply lines  60  supply the de-ionized water and are connected to a pump that, in turn, is coupled to a reservoir containing de-ionized water. The supply lines  65  are connected to a source of vacuum pressure. For example, the supply lines  65  may be connected to an air aspirator through a fluid separator. In this manner, the fluids and the gases that are drawn in through the electrode assembly  20  from the processing environment may be separated from one another. 
   With reference to  FIGS. 4A and 4C , the de-ionized water and the vacuum pressure are supplied through vertical passageways  125  and  130 , respectively. As shown, the vertical passageways  125  and  130  are disposed at opposite ends of the electrode assembly  20 . The passageways  125 ,  130  each begin where the respective supply lines  60  and  65  connect to the electrode assembly  20  and extend through the bottom portion  50 , into the top portion  45  where they open to a corresponding manifold channel  103 ,  107  in the fluid distribution portion  105  of the electrode assembly  20 . At the point where passageways  125 ,  130  transition between the bottom portion  50  and the top portion  45 , O-ring seals  135  are provided to limit leakage outside of the passageways  125 ,  130  prior to opening into the corresponding manifold channel  103 ,  107 . 
   The manifold channels  103 ,  107  distribute the de-ionized water and the vacuum supply respectively to one or more fluid delivery ports  140  and one or more fluid recovery ports  145 . In the illustrated embodiment, the electrode assembly  20  includes two sets of fluid delivery ports  140  for de-ionized water, and two sets of fluid recovery ports  145 . 
   The surface of the electrode assembly  20  may be in the form of a single, continuous electrode. However, the surface of the electrode assembly  20  of the illustrated embodiment is comprised of a plurality of individual conductive segments  40 A through  40 E that are electrically isolated from one another (in the absence of an electrolyte or other conductive liquid). Electrical power is provided from an external power supply to these segments through respective conductive rods  150 A through  150 E. As will be explained in further detail below, electrical power to these individual segments may be controlled during processing based on the area of the electrode assembly  20  surface that is exposed to the surface of the workpiece under process. 
     FIG. 5  illustrates operation of the electrode assembly  20  when it is proximate a surface, such as the surface of the workpiece  25  or the surface of the cleaning electrode  35 . As shown, a fluid  155  is provided from the electrode assembly  20  and fills the interstitial region between the workpiece  25  and the surface of the electrode assembly  20 . This fluid  155  may be, for example, electrolyte (used in an electrochemical etch process or electrochemical deposition), de-ionized water, etc. 
   The fluid  155  may be handled in a variety of different manners after it has contacted the surface of the workpiece  25  or the surface of the cleaning electrode  35 . For example, the fluid may be allowed to enter the chamber of the base assembly  315 . Alternatively, the fluid may be recovered via the suction force provided by the fluid recovery ports  145 . This can be especially useful where multiple types of fluids are employed for processing and/or contact cleaning. In such instances, mixing of the various fluid types in the base assembly  315  may be undesirable. Further, it may be desirable to recover the fluid through ports  145  for replenishment, recycling, etc. 
   Given the manner in which the operation of the electrode assembly  20  is shown in  FIG. 5 , it is clear that the electrode assembly is in motion and proceeding to the right hand side of the drawing. However, arrows  160  indicate the potential for bi-directional movement of the electrode assembly  20  during processing. In order to facilitate fluid recovery regardless of the direction in which the electrode assembly  20  travels, two sets of fluid recovery ports  145  are employed in the illustrated embodiment. The fluid recovery port sets are located exterior to and on opposite sides of the fluid delivery ports  140 . 
   Generally stated, the fluid is retained within the gap between the surface of the electrode assembly  20  and the corresponding surface of the workpiece or cleaning electrode when the volume of processing fluid provided to the surface does not exceed the volume of fluid that can be supported by the surface tension forces. With this in mind, it will be recognized that the rate at which the de-ionized water, or any other fluid, is recovered through the fluid recovery ports  145  should take account of the rate at which the de-ionized water is provided through the fluid delivery ports  140 . 
     FIG. 6  illustrates the relative area of engagement between electrode assembly  20  and a disk-shaped microelectronic workpiece  25  as the electrode assembly  20  is moved during workpiece processing. At each position, designated by the electrode assembly positions  20 A- 20 C, it can be seen that the area of the electrode assembly  20  that overlies the surface of the workpiece  25  varies as the electrode assembly  20  is moved along the length of the workpiece. If a single, continuous conductive element is used at the surface of the electrode assembly  20 , processing power is provided across the entire length of the assembly regardless of the area of exposure. This can create electric field fringe effects that vary as the electrode assembly  20  is moved across the workpiece during processing. Depending on the processing requirements, such fringe effect may have a detrimental effect on the overall uniformity of the process. To avoid or otherwise control these fringe effects, each of the conductive segments  40 A through  40 E may be connected to individually controlled outputs of a power control system, shown schematically at  792 . Power control system  792  may take any number of forms. For example, power control system  792  may include a programmable controller, a standard power supply, and a power distribution circuit that is controlled by the programmable controller. Other configurations are likewise suitable. 
   The manner in which power is controlled for each of the segments  40 A through  40 E is process dependent. However, some of the ways in which power may be controlled are set forth in Table 1 below. 
   
     
       
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               POSITION 
               POWER 
             
             
                 
             
           
           
             
               20A 
               Segment 40A and Segment 40E have no exposure to the 
             
             
                 
               workpiece. No processing power to these segments. 
             
             
               20B 
               Segment 40B and Segment 40D have minimal exposure 
             
             
                 
               to the workpiece. At least three possible alternatives exist: 
             
             
                 
               1 - No processing power is provided to segments 40B 
             
             
                 
               and 40D, as the amount of exposure is very limited. 
             
             
                 
               2 - Full processing power is provided to segments 40B 
             
             
                 
               and 40D since they at least partially overlie the workpiece. 
             
             
                 
               3 - A limited level of processing power is provided to 
             
             
                 
               segments 40D and 40B to account for the limited exposure 
             
             
                 
               that these segments have with the workpiece 25. 
             
             
               20C 
               Segment 40C, similar to Segments 40B and 40D, is only 
             
             
                 
               partially exposed, consequently the specific level of 
             
             
                 
               processing power which would be most beneficial may 
             
             
                 
               similarly vary 
             
             
                 
             
           
        
       
     
   
   As opposed to altering the amount of electroplating power provided to the electrode of the court to assembly, it may be possible to compensate for the electric field variations by altering the motion profile that is used by the electrode assembly as it moves across the face of the workpiece. For example, the electrode assembly may be moved quickly along the end portions of its motion path when compared to its motion as it traverses the middle portions of the workpiece. 
   A specific embodiment of the gap adjustment mechanisms  200  is illustrated in  FIGS. 7A and 7B . As shown, the gap adjustment mechanisms  200  each include a base portion  205  having a pair of mounting holes  210  for attachment to the etch assembly  10 . Each gap adjustment assembly  200  further includes an arm  215  that has a first end attached to an axle  22 , and a second end connected to a pin  240  that terminates at a spherical head  245 . It is the spherical head  245  advance in cages the appropriate portion of the contact portion of the reactor head assembly  345 . As such, the particular shape and size of arm  215  is dependent on where and how far it must span to engage the corresponding section of the contact portion  715  of the reactor head assembly  345 . 
   Axle  220  cooperates with the base portion  205  to form a fulcrum about which arm  215  may pivot. The other end of the axle  220  is coupled to a first end of a lever arm  225 . Lever arm  225  is engaged at a second end thereof by an adjustable tip of a micrometer  230 . The micrometer  230  is adjusted to pivot the lever arm  225  about axle  220  and thereby produce a corresponding raising and lowering of the spherical head  245 . This allows the position of the contact portion  715  of the head assembly  345  (and, thus, the workpiece) to be spaced from the upper surface of the electrode assembly  20  with a high degree of accuracy. 
   A specific embodiment of the float assemblies  260  is illustrated in FIGS.  8 A and  8 B. As shown, each float assembly  260  includes a housing  265  having a central passageway  270 , within which a spring float shaft  275  is received. One end of the spring float shaft  275  terminates at a flange  280  that is wider than the upper portion of the central passageway  270  thereby restricting motion of the shaft  275  past point  285 . The shaft  275  is biased toward this point  285  by a spring  290  similarly located within the central passageway  270  of the housing  265 . The end of the spring  290  opposite the point of contact with the shaft  275  is fixed with respect to the housing  265  by a retainer  295 . In some instances a second retainer  295  can be used to further increase the compression of the spring  290 . 
   The retainer  295 , in turn, is held in place by a snap ring  300 . The snap ring  300  is a discontinuous circular ring that may be squeezed to reduce its diameter. When deformed in this manner, the snap ring  300  can slide into the bottom opening  305  of the housing  265  past the more restrictive shaft diameter, and expand and fit within a groove  310  located in the wall of the central passageway  270  having a larger diameter, which is proximate to the opening  305 . 
   While the spring float assembly  260  can be a separate assembly, as illustrated in connection with  FIGS. 8A and 8B , the spring float assembly  260  can also be integrated as part of the reactor base assembly  315  or as part of the base plate of the processing station (not shown). Various other configurations can also be employed to provide a compliant connection between the head engagement portion  725  and the base portion  720  of the reactor base assembly  315 . 
     FIG. 9  illustrates one embodiment of a contact assembly  910  that may be used in the contact portion  715  apparatus of  FIG. 2 . Generally stated, contact assembly  910  includes an exteriorly disposed dielectric rim  915  and an interiorly disposed conductive ring  920  having a plurality of sawtooth-shaped contact  925 . The contact assembly  910  may also inclu de one or more connection members  930  that a used to secure the contact ring assembly  910  to the other components of the contact portion  715 . Further details of this exemplary interconnection as well as of the contact assembly construction can be found in U.S. Ser. No. ______ filed Nov. 20, 2000, entitled “______”, which is hereby incorporated by reference. 
   Dielectric rim  915  includes a plurality of cut-out section  935  that are disposed for alignment with the spherical heads  245  of the gap adjustment mechanisms  200 . Each cut-out section  935  is provided with a corresponding insert  940 . It is the inserts  940  that are used to directly engage the spherical heads  245 . Since the inserts  940  are formed as pieces that are separate from the rim  915 , it is possible to form the dielectric rim  915  from a material that is less durable than would otherwise be required to sustain the wear and tear associated with frequent engagement of the gap adjustment mechanisms  200 . 
     FIG. 10  illustrates a further contact assembly, shown generally at  340 , that may be used in the contact portion  715  of the reactor head assembly  345 . As illustrated, the contact assembly  340  includes a plurality of contacts  350  that are used to supply processing power to the surface of the workpiece  25 . Unlike contact assembly  910 , however, the contacts  350  of contact assembly  340  are formed as two groups  355  and  360  that are electrically isolated from one another (in the absence of an electrolyte). By electrically isolating the contact groups, it becomes possible to check the resistance across the workpiece  25 . 
   A schematic diagram of one embodiment of a contact resistance sensing circuit that may be used to check the resistance across the workpiece  25  is shown generally at  485  in  FIG. 11 . Circuit  485  is based on precise generation of a constant current by current source  487 . As illustrated, precision current source  487  is referenced to a precision bandgap voltage reference  489 . Bandgap voltage reference  489  also serves as a reference for the generation of upper and lower threshold voltages by circuits  491  and  493 , respectively. The upper and lower threshold voltages are used to determine whether the current from the constant current source  487  is within a predetermined range before a measurement of the contact and workpiece resistance is conducted. During this pre-measurement cycle, current source  487  is switched to drive a constant current through a series-connected circuit including low resistance resistor  495  (i.e., 2 ohm), the workpiece  25  and contacts  350  and, optionally, a pair of switching circuits  497  and  499  that are used to enable current flow through the workpiece and contacts. The voltage drop across the resistor  495  is proportional to the current flowing through it. Accordingly, this voltage drop is used to determine whether the current provided by the current source  487  falls within a predetermined acceptable range. As shown, the voltage drop across resistor  495  is provided to a pair of individual amplifier circuits  501  and  503 . The output signals of the amplifier circuits  501  and  503 , in turn, are each provided to the input of a respective comparator circuit  507  and  509 . Comparator circuit  507  compares the output voltage provided from amplifier  501  with a high current threshold reference voltage provided by reference circuit  491 . Similarly, comparator circuit  509  compares the output voltage provided from amplifier  503  with a low current threshold reference voltage provided by reference circuit  493 . The output signals from the competitors  507  and  509  are connected together in a wired-OR configuration. The output of this wired-OR configuration is used to determine whether the constant current flow provided by current source  487  is within a predetermined acceptable range, and is labeled as “current source okay” reflecting its function. As noted above, circuits  491  and  493  generate their respective threshold voltages with reference to the precision bandgap voltage reference  489  and, as such, these threshold values are highly stable. Each of circuits  491  and  493 , as well as the voltage reference  492  that generates threshold voltage Vmax, may include adjustable precision resistors or the like to set the minimum and maximum threshold values manually. Alternatively, these values may be set using a precision digital-to-analog converter that is connected to receive voltage data values from a programmable control circuit or the like. 
   Provided that the current measurement falls within the predetermined range as indicated by the output of comparator circuits  507  and  509 , the voltage drop across the contacts and workpiece is indicative of the resistance of the workpiece and contacts and, as such, may be measured. In the illustrated embodiment, the voltage across the contacts and workpiece is provided to a pair of amplifier circuits  511  and  513 . The output signals of the amplifier circuits  511  and  513  are provided as input signals to a differential amplifier  515 , which may also provide for some amplification of the signal. The output of the differential amplifier  515 , in turn, is provided for comparison to an upper voltage threshold value at comparator circuit  517 . Since the upper voltage threshold value is generated with respect to the precision bandgap voltage reference  489 , it is highly stable and accurate. If the voltage provided at the output of differential amplifier  515  exceeds the voltage Vmax, the output of comparator  517  will be at a corresponding logic state and processing of the workpiece will not continue. However, if the voltage provided at the output of differential amplifier  515  is below the voltage Vmax, electrochemical processing of the workpiece may proceed. 
   Given the low resistances and high currents that must necessarily be used in the foregoing circuit, circuit stability and measurement repeatability, although strongly desired, are difficult to obtain. To overcome many of the problems associated with this stability and repeatability of circuit  485 , one or more precision bandgap voltage references are used to generate the constant current as noted above. Further, current flow through the current source  487  is maintained at all times, even when no measurements are being made. This is done to insure the thermal stability of the measurement circuits, including the precision bandgap voltage reference  489 . To accomplish this, a switch (either mechanical or semiconductor) may be used to switch the constant current source between a first circuit that includes the contacts and workpiece and a second circuit that directs the current into a current sink. 
   The embodiment of the contact portion  715  illustrated in  FIG. 12  is adapted to load and unload the workpiece  25  using a workpiece tray. To this end, the contact portion  715  includes a tray slot  365  through which a tray  370  may be inserted and extracted. Tray  370 , is shown, is adapted for receiving a workpiece  25 , and provides a degree of protection for the workpiece as it is loaded onto the contact portion  711  of the head assembly  345  through the tray slot  365 . Once inserted into the tray slot  365 , the workpiece  25  can make a connection with the contacts  350  of the contact assembly  340  for processing. 
     FIGS. 13A and 13B  illustrate both top and bottom isometric views of a tray  370  adapted for receiving such a workpiece  25 . As shown in  FIG. 13A , the top of the tray  370  includes a circular depression  375  corresponding to the shape of the workpiece  25  to be received. At one end of the tray is a slot  380  through which a vacuum wand (not shown) may be inserted or removed, to facilitate placement and removal of a workpiece  25  onto the tray  370 . The top of the tray further includes a series of markings  385  located around the periphery of the workpiece depression  375  that enable the operator to visually verify the proper angular positioning of the workpiece as it is loaded onto the tray  370 . 
   The tray  370  may be manually loaded and removed from the head assembly  345 . As shown in  FIG. 13B , the bottom of the tray  370  includes a depression  390  for facilitating gripping the tray  370  with a handle assembly  400  ( FIGS. 14A , B and C) proximate the slot  380  through which an air wand, or similar instrument, can be inserted. 
   As can be seen in  FIGS. 14A-14C , the handle assembly  400  includes both a first piece  405  and second piece  410 . The first piece  405  and the second piece  410  are coupled together by a pair of screws  415  and slide pins  420 . The slide pins  420  reside within a pair of slots  425  located within the first piece  405 . This construction allows the first piece  405  to slide with respect to the second piece  410 . The handle assembly  400  further includes a plunger pin  430 . The plunger pin  430  is adapted for moving within a slot  435  formed within the second piece  410 . The plunger pin  430  is further adapted for engaging a detent  440  at one end of the slot  435 . Once engaged plunger pin  430  and detent  440  provide a slight retaining force. 
   When the top piece  405  is shifted forward with respect to the second piece  410 , a protrusion  445  at the front of the handle located at the second of the top piece is exposed. The protrusion  445  is sized and shaped to correspond to depression  390  included in the bottom of tray  370 . By sliding the first piece  405  even with the second piece  410 , the front  450  of the second piece  410  extends over the protrusion  445 . If the protrusion  445  of the top piece  405  of handle assembly  400  has been received into the depression  390  of tray  370 , the engagement serves to fix the handle assembly  400  to the tray  370 . The tray  370  may then be carried by the handle assembly  400  and readily inserted into the tray slot  365 . By subsequently sliding the first piece  405  forward with respect to the bottom piece  410 , the handle assembly  400  may be disengaged from the tray  370 . The first piece  405  and second piece  410  each include a corresponding indentation  455 ,  460 , which can be gripped by the operator to facilitate movement of the first piece  405  with respect to the second piece  410 . 
   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 wart 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.