Patent Publication Number: US-7211174-B2

Title: Method and system to provide electrical contacts for electrotreating processes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application Ser. No. 60/348,758, filed Oct. 26, 2001, entitled “Method and System to Provide Electrical Contacts For Electrotreating Processes” and is a continuation-in-part of U.S. application Ser. No. 09/760,757 entitled “Method and Apparatus for Electrodeposition of Uniform Film with Minimal Edge Exclusion on Substrate,” filed on Jan. 17, 2001, now U.S. Pat. No. 6,610,190 the contents of which are expressly incorporated by reference herein. 

   BACKGROUND 
   1. Field of the Invention 
   The present invention generally relates to semiconductor integrated circuit technology and, more particularly, to electrotreating techniques such as electroplating and electroetching that are applied to the entire face of a workpiece. 
   2. Background of the Related Art 
   Conventional semiconductor devices such as integrated circuits generally include a semiconductor substrate, usually a silicon substrate, and a plurality of sequentially formed dielectric interlayers such as silicon dioxide, and conductive paths or interconnects made of conductive materials. Copper and copper alloys have recently received considerable attention as interconnect materials because of their superior electromigration and low resistivity characteristics. The interconnects are usually formed by filling a conductor such as copper in features or cavities etched into the dielectric interlayers by a metallization process. The preferred method of copper metallization process is electroplating. In an integrated circuit, multiple levels of interconnect networks laterally extend with respect to the substrate surface. Interconnects formed in sequential layers can be electrically connected using features such as vias or contacts. 
   In a typical interconnect fabrication process, first an insulating layer is formed on the semiconductor substrate. Patterning and etching processes are performed to form features such as trenches, pads and vias etc. in the insulating layer. Then, copper is electroplated to fill all the features. In such electroplating processes the wafer is placed on a wafer carrier and a cathodic (−) voltage with respect to an electrode is applied to the wafer surface while the electrolyte wets both the wafer surface and the electrode. The voltage is typically applied using contacts surrounding the circumference of the wafer. The contacts are usually electrically sealed and isolated from the electrolyte by a clamp covering the circumference of the wafer surface. The clamp inhibits copper deposition on the contacts but it also inhibit copper deposition along the circumference of the wafer and causes loss of important space on the wafer. In the semiconductor industry, this unused or wasted wafer area is called edge exclusion. In the semiconductor integrated circuit industry, there is always a drive towards reducing edge exclusion on the wafers. 
   Once the plating is over, a chemical mechanical polishing (CMP) step, an electroetching (or electropolishing) or etching step, or a combination of these steps are conducted to remove the excess copper layer or copper overburden and other conductive layers that are above the top surface of the substrate. This process electrically isolates the copper deposited into various features on the wafer and thus forms the interconnect structure. The interconnect process is then repeated as many times as the number of interconnect layers desired. 
   In the electroetching process both the material to be removed and a conductive electrode are dipped into the electropolishing or electroetching solution. Typically an anodic (positive) voltage is applied to the material to be removed with respect to the conductive electrode. With the applied voltage, the material is electrochemically dissolved and removed from the wafer surface. 
   Whether a CMP process, an etching process or an electroetching process is employed, it is desirable to reduce the copper overburden thickness that needs to be removed by these processes. The importance of overcoming the copper overburden problem is evidenced by technological developments directed to the deposition of planar and thin copper layers on the wafer surfaces. Such planar deposition techniques are generally called Electrochemical Mechanical Deposition (ECMD). In such planar processes, a pad, a mask or a sweeper, which is collectively called a Workpiece Surface Influencing Device (WSID), can be used during at least a portion of the electrodeposition or electroetching processes when there is physical contact or close proximity, and relative motion between the workpiece surface and the WSID. 
   The edge exclusion problem may be overcome using deposition technologies that deposit materials across the full face of wafers. For example, U.S. application Ser. No. 09/735,546 entitled “Method and Apparatus For Making Electrical Contact To Wafer Surface for Full-Face Electroplating or Electropolishing,” filed on Dec. 14, 2000 and commonly owned by the assignee of the present invention, describes in one aspect a technique for providing full face electrotreating. It should be noted that electrotreating refers to all electrochemical processes, which are sometimes called by different names. Therefore, electrotreating includes, for example, electrodeposition or plating, electroetching or electropolishing, etc. U.S. application Ser. No. 09/760,757 entitled “Method and Apparatus for Electrodeposition of Uniform Film with Minimal Edge Exclusion on Substrate,” filed on Jan. 17, 2001 and commonly owned by the assignee of the present invention describes in one aspect a technique for forming conductive layers on a semiconductor wafer surface without losing space on the surface for electrical contacts. As exemplified in these applications, copper deposition or electroetching on a wafer surface can be achieved using electrical contacts to contact the wafer in a slidable manner, i.e. a relative motion is established between the contacts and the wafer surface during process so that material is deposited on or removed from the whole workpiece surface including the areas right under the contacts. While previously described electrical contacts are adequate, needed is an improved contact structure, which provides for even greater consistency than the established electrical contacts. 
   SUMMARY OF THE INVENTION 
   The presently preferred embodiments described herein include systems and methods for providing electrical contacts to the surface of a workpiece such as a semiconductor wafer to facilitate electrotreating processes, including electroplating and electroetching processes. The present invention provides improved contact structures, which provide for greater consistency than conventional electrical contacts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features, aspects, and advantages will become more apparent from the following detailed description when read in conjunction with the following drawings, wherein: 
       FIG. 1  is a diagram illustrating a perspective view of an exemplary electrotreating system according to a presently preferred embodiment; 
       FIGS. 2 and 3  are diagrams illustrating a bottom view and a side view, respectively, of the exemplary electrotreating system of  FIG. 1  including an exemplary pair of electrical contacts; 
       FIGS. 4A through 4C  are diagrams illustrating side views of exemplary contact members according to a first presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 ; 
       FIGS. 5A and 5B  are diagrams illustrating the interaction of the exemplary contact members of  FIGS. 4A through 4C  with the workpiece of  FIGS. 1 through 3 ; 
       FIGS. 6A through 6C  are diagrams illustrating side views of exemplary contact members according to a second presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 ; 
       FIGS. 7A through 7B  are diagrams illustrating side views of exemplary contact members according to a third presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 ; 
       FIGS. 8A through 8B  are diagrams illustrating side views of exemplary contact members according to a fourth presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 ; 
       FIG. 9A  is a diagram illustrating a side view of an exemplary contact member according to a fifth presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 ; 
       FIGS. 9B through 9D  are diagrams illustrating the interaction of the exemplary contact member of  FIGS. 9A  with the workpiece of  FIGS. 1 through 3 ; 
       FIGS. 10A and 10B  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system of  FIG. 1  including an exemplary pair of stationary contacts and a contact member mounting arrangement that includes an enclosure; 
       FIGS. 11A and 11C  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system of  FIG. 1  including an exemplary pair of laterally moving contacts and a contact member mounting arrangement that includes a guide mechanism; 
       FIG. 11B  is a diagram illustrating a detail side view of a portion of the mounting arrangement of  FIGS. 11A and 11C ; 
       FIG. 11D  illustrates an other embodiment of a curved contact member; 
       FIGS. 12A and 12B  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system of  FIG. 1  including an exemplary pair of vertically movable contact members and a contact members mounting arrangement; and 
       FIGS. 13A and 13B  are diagrams illustrating embodiments of the present invention using back-side contacts. 
   

   DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the accompanying drawings, which are provided as illustrative examples of preferred embodiments of the present invention. 
   Referring now to  FIG. 1 , it is a diagram illustrating a perspective view of an exemplary electrotreating system  100  according to a presently preferred embodiment.  FIG. 1  schematically shows an exemplary electrotreating system  100  which is capable of performing both electroplating and electroetching processes. The exemplary electrotreating system of the present invention may be one having the capability of planar electroplating and planar electroetching such as an Electrochemical Mechanical Deposition (ECMD) or Electrochemical Mechanical Etching (ECME) system. It should be noted that these systems are collectively referred to as Electrochemical Mechanical Processing (ECMPR) systems. The exemplary ECMPR system  100  includes an electrode  102 , a workpiece  104 , and a workpiece surface influencing device (WSID)  106 . The WSID  106  may be, for example, a mask, a mask plate, a pad, a sweeper, or other suitable surface influencing device. The WSID  106  may be over a cavity or a cup  107 . A solution  108  fills the cup  107  and touches the electrode  102  and the work piece  104 . If plating is to be performed, or both plating and electropolishing are to be performed, the solution  108  will typically contain the ionic species of the metal to be deposited and additives for good quality film formation. For plating or plating and etching, an exemplary copper plating solution may be, for example, a copper sulfate solution with additives that are commonly used in the industry. If only electropolishing is to be performed, however, the solution  108  used may be a typical electroetching/polishing solution, which does not contain ionic species of the material to be etched. For copper electroetching, solutions containing an acid, such as phosphoric acid are common. The workpiece  104  may be, for example, a silicon wafer to be plated with a conductor metal, preferably copper or copper alloy. The wafer  104  includes a front surface  109  to be plated with copper and a bottom surface  110  to be held by a carrier head  111 . The carrier head  111  is rotated by a shaft  112  or spindle. The shaft  112  is placed through a non-rotating shaft housing  113 , which is movably attached to a support structure (not shown). The shaft housing can be simultaneously moved with the shaft  112  and the carrier head  111  when the shaft  112  and the carrier head  111  are moved along the z or x directions. The WSID  106  includes a top surface  114 , a bottom surface  115 , and channels  118  or openings extending between the top and the bottom surfaces  114 ,  115 . The channels  118  may have any form, size, or may form any pattern on the WSID  106  for better film uniformity. Any channel  118  shape that allows fluid communication between the wafer  104  and the electrode  102  through the WSID  106  can be used. Although in  FIG. 1  the WSID  106  has a rectangular shape, it may be shaped in any geometrical form. In U.S. application Ser. No. 09/960,236 entitled “Mask Plate Design,” filed on Sep. 20, 2001, also assigned to the same assignee as the present invention, discloses various mask plate embodiments. 
   As previously mentioned, the exemplary electrotreating system  100  is capable of performing planar or non-planar electroplating as well as planar or non-planar electroetching. In this respect, if a non-planar process approach is chosen, the front surface  109  of the wafer  104  is brought into proximity of the top surface  114  of the WSID  106 , but it does not touch it, so that non-planar metal deposition can be performed. Further, if a planar process approach is chosen, the front surface  109  of the wafer  104  contacts the top surface  114  of the WSID  106  in one aspect of the invention. As the plating solution, depicted by arrows  108 , is delivered through the channels  118 , the wafer  104  is moved while either the front surface  109  contacts the top surface  114  or is in close proximity of the top surface  114  of the WSID  106 . The wafer  104  may be moved rotationally which may be clockwise or counter clockwise, or it can be moved laterally along the x-axis of the WSID  106 , or it can be both rotated and moved laterally. Under an applied potential between the wafer  104  and the electrode  102 , and in the presence of the solution  108  that fills the channels  118 , the metal such as copper, is plated on or etched off the front surface  109  of the wafer  104 . It is noted, however, that the above description described rotation and movement of the wafer  104 , while assuming that the WSID  106  was stationary. It is understood that the system  100 , as described above, will allow for either the wafer or the WSID to move, or for both of them to move, thereby creating the same relative motion effect. For ease of description, however, the invention was above-described and will continue to be described in terms of movement of the wafer. 
     FIGS. 2 and 3  are diagrams illustrating a bottom view and a side view, respectively, of the exemplary electrotreating system  100  of  FIG. 1  including an exemplary pair of electrical contacts  116 . As shown in  FIGS. 2 and 3 , during electroplating or electroetching processes, cathodic or anodic potentials can be applied through the electrical contacts  116  that touch an exposed edge  120  of the front surface  109  of the wafer  104  as the wafer  104  is moved, i.e., moved laterally, rotated, or both rotated and moved laterally. The electrical contacts  116  are connected to a power source terminal (not shown) through electrical lines  121 . In accordance with the principles of the present invention, electrical contacts  116  may include unidirectional or bi-directional contact members. As exemplified in  FIGS. 4A through 5B , the contact members preferably used for cases when the wafer is rotated either in clockwise direction or counter clockwise direction. However, as exemplified in  FIGS. 6A through 9D , there are shown contact members preferably used for rotation in both directions. Referring also to  FIGS. 10A through 12A  and as will be described more fully below, the electrical contacts  116  of the system  100  can also be made stationary, laterally movable and vertically movable. 
     FIGS. 4A through 4C  are diagrams illustrating side views of exemplary contact members  122 A,  122 B according to a first presently preferred embodiment and according to the exemplary electrotreating system  100  of  FIGS. 1 through 3 . As illustrated in  FIGS. 4A and 4B , the contact members  122 A,  122 B include a base  124  and one or more contact elements  126 . In this embodiment the contact elements  126  are brushes that are made of bundles of conductive bristles  128  or wires. Bristles  128  may, for example, be made of flexible alloy wires, Pt alloy wires or stainless steel wires or the like. The base  124  may be made of copper, stainless steel, titanium or the like or may be coated as the brushes described below. The brushes  126  are preferably made from, or coated with, conductive materials that do not react with the solutions used, and if used for deposition, resist Cu plating. Materials or coatings such as platinum, platinum alloys, Ta, TaN, Ti, TiN and the like can be used. These conductive materials and considerations are preferably used for the other embodiments described below. 
   The brush  126  can have a length in the range of 1 to 4 cm, preferably 2–3 cm., although any suitable length may be used. The length of the brush and the distance pushed by the wafer surface against the bristles determine the force that is applied on the wafer surface by the brush  126 . As a rule of thumb, the longer the brush, the milder the force that is applied on the wafer, and the lesser the chance of having scratches along the exposed edge  120  shown in  FIG. 2 . Each contact element is made up of a number of bundles, preferably 5 to 20, and most preferably at least 10, with each bundle having a number of individual wires, such as between 20 to 300, preferably in the range of 50 to 200, if 0.002 inch thick wire is used, but will vary as needed. In this embodiment, because the brushes  126  are slanted to the right, the contact member  122 A is preferably used when the wafer  104  is rotated in way that it travels to the right over the contact elements  126 . Similarly, the contact member  122 B is preferably used when the wafer  104  is moving to the left over the brushes. 
   As shown in  FIG. 4C , the angle of slant, depicted by ‘A’, for brushes  126  in both contact members  122 A and  122 B is about 45 degrees, so that the angle of slant is preferably between 30 to 60 degrees, although any suitable angle may be used. The angle of slant ‘A’ is the angle measured between an upper surface  130  of the base  124  and a slant axis  132  that is symmetrically crossing the center of the brush  126 . The angle of slant allows the brushes  126  to flex easily and uniformly as the wafer  104  makes contact with the contact members  122 A or  122 B. 
     FIGS. 5A and 5B  are diagrams illustrating the interaction of the exemplary contact members of  FIGS. 4A through 4C  with the workpiece  104  of  FIGS. 1 through 3 . In operation, as shown in  FIGS. 5A and 5B , as a wafer  104  moves from a first position ‘A’ to a second position ‘B’ along a distance d, the brush  126  is pressed down by the same distance d. As the distance d gets longer, the force applied on the wafer  104 , as well as the chance of scratching the wafer  104 , increase. However, as the angle “A” gets smaller ( FIG. 4C ), the force gets lower, and there is less chance of scratching the wafer  104 . 
     FIGS. 6A through 8B  illustrate contact members that are preferably for use irrespective of the direction that the wafer is moved. Rotational direction of the wafer can be changed any time during the process.  FIGS. 6A through 6C  are diagrams illustrating side views of exemplary contact members  136  according to a second presently preferred embodiment and according to the exemplary electrotreating system  100  of  FIGS. 1 through 3 . As shown in  FIG. 6A , in one embodiment, the contact member  136  includes a series of contact elements  138  that are assembled into a base  140 , preferably a base frame. In this embodiment, the contact elements  138 A are rollers. Further, as shown in  FIG. 6B , the rollers  138 A are preferably disk shaped with a flat contact surface  139  that enable the rollers  138 A to roll over the wafer  104  surface while establishing electrical contact. Because of the flat surface  139  of the rollers  138 A, the rollers  138 A of the contact member  136  are held in a perpendicular posture on the wafer  104  when the member  136  makes contact to the wafer  104 . The base frame  140  may have a first frame halve  142  and a second frame halve  144 . The rollers  138 A are movably held between the first and the second halves  142 ,  144  by pins  146  which are placed through the centers of the rollers  138 A and secured to the halves  142 ,  144  from both ends of the pins  146 . 
     FIG. 6C  shows an alternative roller design, with rollers  138 B, having a round contact surface  150 . Similar to the rollers  138 A described above, the rollers  138 B are held between the first and second halves  142 ,  144  of the base frame  140  by a number of pins  146 . The round contact surface  150  of the rollers  138 B enables them to contact the wafer  104  surface at an angle. In both designs, the rollers  138 A,  138 B may be furnished with suitable mechanical biasing mechanisms to enhance their contact ability with the wafer  104  surface. Such biasing mechanisms can be, but not limited to, springs that are placed adjacent the pins  146  and biasing the rollers  138 A,  138 B towards the wafer  104 . Such biasing mechanisms may also assist the rollers  138 A,  138 B to move smoothly on the surface of the wafer  104 . 
     FIGS. 7A through 7B  are diagrams illustrating side views of exemplary contact members  152  according to a third presently preferred embodiment and according to the exemplary electrotreating system  100  of  FIGS. 1 through 3 .  FIGS. 7A and 7B  show the contact member  152  having a base  154  and a contact element  156 . In this embodiment the contact element  156  is a loop contact having a loop-shape configuration. The loop contact  156  may be attached to the base  154  through a lower portion  158  of the contact  156 . In this embodiment, an upper portion  160  of the contact  156  may preferably be made flat. The loop contact makes physical and electrical contact with the wafer surface through the upper portion  160  when it is placed on the wafer. The loop shape of the loop contact  156  enhances the contact that occurs during its placement on the wafer by creating a spring action against the wafer. As shown in  FIG. 7B , in another design, the loop contact  156  may have an upper portion  162  with curved or convex shape. The loop contact may be made of conductive wires, strips or flat pieces. The base  154  is preferably made of a conductive material. It should be noted that the loops in  FIG. 7A  or  7 B may be empty loops, or there may be a compressible material such as a foam material inside the loop to support the upper portion  160  better. 
     FIGS. 8A through 8B  are diagrams illustrating side views of exemplary contact members  166  according to a fourth presently preferred embodiment and according to the exemplary electrotreating system of  FIGS. 1 through 3 .  FIG. 8A  shows the contact member  166  having a base  168  and a contact element  170 . The contact element  170  may be a conductive bar attached to the base  168  by at least a pair of flexible members  172 , such as leaf springs. As shown in  FIG. 8B  in a side view, the bar  170  may have a round upper portion  174  allowing the contact member to be placed on the wafer at an angle. The flexible members  172  push the bar  170  against the wafer and thereby enhance electrical contact between the wafer and the contact member. The base and the flexible members are all preferably made of conductive materials. It should be noted that the contact element  170  may be a thin conductive foil such as a 25–1000 micron thick metallic foil. In this case, to support this thin foil, the flexible members  172  are replaced by a compressible member (not shown) such as a foam material that is placed between the contact element  170  and the base  168 . 
     FIGS. 9B through 9D  are diagrams illustrating the interaction of the exemplary contact member  176  of  FIGS. 9A  with the workpiece  104  of  FIGS. 1 through 3 .  FIGS. 9A through 9D  show the contact member  176 , which can be used as a bi-directional contact. As shown in  FIG. 9A , the contact member  176  includes a base  178  and one or more contact elements  180 . In this embodiment, the contact elements  180  are brushes that are made of bundles of conductive bristles  182  or wires. Bristles  182  may, for example, be made of flexible alloywires, such as stainless steel wires or the like. The base  178  is preferably made of a conductive material. The brush  180  can have a length in the range of 1 to 5 cm., preferably 2 to 3 cm., although any suitable length may be used. The length of the brush  180  determines the force that can be applied on the brush  180 . As a rule of thumb, the longer the brush, the milder the force that is applied on the wafer  104 , and the lesser the chance of having scratches along the exposed edge  120  shown in  FIG. 2 . Each contact member is made up of a number of bundles, preferably 5 to 20, and most preferably at least 10, with each bundle having a number of individual wires, such as between 20 to 300, preferably in the range of 100 to 200, if 0.002 inch thick wire is used, but will vary as needed. The brushes are preferably slanted at angles of between 30 and 60 degrees, preferably 45 degrees, as shown in  FIGS. 4A and 4B , but could also be are placed perpendicular to an upper surface  184  of the base  178  as shown in  FIG. 9A . 
   As shown in  FIGS. 9B through 9D , the contact member  176  can be used with a wafer that is moving in either direction. As shown in  FIG. 9B , as the wafer  104 , which is rotating in the counter clockwise direction, is approached and contacted with the brush  180  the brush flexes over the right side. At this point, if the rotational direction of the wafer  104  needs to be changed, the wafer is first raised above the brush  180  as shown in  FIG. 9C . And, the wafer  104  is rotated in the clockwise direction while the wafer  104  is approached to the brush  180  so that the brush can be flexed over the left side. 
   Referring back to  FIGS. 1 through 3 , as previously mentioned, the system  100  may include stationary, laterally movable, or vertically movable electrical contact structures. Again, as previously mentioned, each such electrical contact structure may include the above described contact member embodiments. 
     FIGS. 10A and 10B  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system  100  of  FIG. 1  including an exemplary pair of stationary contacts  182  and a contact member mounting arrangement that includes an enclosure  188 . As illustrated in  FIGS. 10A and 10B , the stationary contacts  182  can be integrated with the system  100 . The stationary contacts  182  can be any of the specific contact members described in detail above with regard to the above described embodiments. An exemplary brace portion  184  of the stationary contact  182  connects the stationary contact  182  to the enclosure  188  that contains the system  100 , or it may be simply fixed onto the cup  107  (not shown). It is understood that, in this embodiment, the stationary contacts  182  are stationary with respect to the WSID  106 . The stationary contacts  182  can be positioned adjacent the WSID  106 . The stationary contacts  182  may be biased toward the wafer  104  with a biasing mechanism (not shown), such as a spring, to provide better contact between the contacts  182  and the wafer  104 .  FIG. 10B  shows the position of the stationary contacts  182  with respect to the WSID  106  and the wafer from a partial bottom view. As the wafer  104  is rotated in clockwise or counter clockwise directions as well as laterally moved in the x-direction, the stationary contacts  182  touch the exposed edge  120  of the wafer  104 . For clarity of illustration, electrical connections to the contact elements have not been shown in any of the figures. Commonly known means and techniques can be used to provide electrical power to the contact elements. In this embodiment, the stationary contacts may have a predetermined length that is based on the size of the wafer, size and shape of the WSID  106  and the amount of the lateral motion of the wafer on the WSID. The length of the stationary contacts should be such adjusted that the exposed edge  120  is continuously contacted by at least some of the stationary contacts. In addition, as illustrated in  FIG. 10A , the height of the stationary contacts may preferably be above the level of any solution directly above the WSID so that the wafer  104  touches the contacts and voltage can be applied to the wafer  104  via the contacts prior to any contact between the wafer  104  and the solution from the cup  107 . 
     FIGS. 11A and 11C  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system  100  of  FIG. 1  including an exemplary pair of laterally moving contacts  190  and a contact member mounting arrangement which includes a guide mechanism. The laterally moving contacts  190  can be any of the specific contact members described in detail above with regard to the above-described embodiments.  FIG. 11B  is a diagram illustrating a detailed side view of a portion of the mounting arrangement of  FIGS. 11A and 11C . As illustrated in  FIGS. 11A through 11C , a laterally moving contact  190  can be integrated with the system  100 . A brace portion  192  connects the laterally moving contact  190  to a guide mechanism  194 . As shown in  FIG. 11B  in cross section, the guide mechanism  194  can be a rail that accommodates an end of the brace portion  192  and allows the end of the brace portion  192  to move along the rail  194 . The lateral motion of the contact  190  is provided by motion rods  195  that are permanently attached to the shaft housing  113 . The lower end of the rods  195  can be removably inserted into a hole in the end of the brace  192  when the carrier head is lowered down. As the carrier head  111  moves laterally in the x-direction during the process, the rods  195  move the brace  192  in the rail  194  and thereby the contacts  190  are moved along with the wafer laterally. Alternatively, the contacts  190  can be connected to a moving mechanism (not shown) that is controlled by a controller (not shown) that causes the movement of the contacts  190  to correspond to the lateral motion of the carrier head  111 . The contacts  190  may be biased toward the wafer  104  with a spring (not shown) for better conductivity between the contacts  190  and the wafer  104 .  FIG. 11C  shows the position of the contacts  190  with respect to the WSID  106  and the wafer from a partial bottom view. As the wafer  104  is rotated in clockwise or counter clockwise directions as well as laterally moved in the x-direction, the contacts  190  continue making contact with the exposed edge  120  of the wafer  104  by moving with the wafer  104 . Therefore, they do not have to be as long as those in the case of stationary contacts of  FIG. 10B , and they do not necessarily be straight. As illustrated by the embodiment illustrated in  FIG. 11D  that shows contacts  190 A, the contacts  190 A can have a curved shape that follows the contour of the wafer edge. As also illustrated in  FIG. 11B , the height of the stationary contacts can preferably be above the level of any solution directly above the WSID so that the wafer  104  touches the contacts and voltage can be applied to the wafer  104  via the contacts prior to any contact between the wafer  104  and the solution from the cup  107 . 
     FIGS. 12A and 12B  are diagrams illustrating a side view and a bottom view, respectively, of the exemplary electrotreating system  100  of  FIG. 1  including an exemplary pair of vertically and laterally movable contacts  196  and a contact members mounting arrangement. As illustrated in  FIGS. 12A and 12B , a vertically movable contact  196  can be integrated with the system  100 . The vertically moving contacts  196  can be any of the specific contact members described in detail above with regard to the above described embodiments. A brace portion  198  of the vertically movable contact  196  may be attached to the shaft housing  113 . As mentioned above the shaft housing  113  can move vertically with the carrier head in the z direction as well as laterally in the x direction. As the carrier head  111  moves vertically in the z-direction during the process, the contacts  196  keep their position along the exposed edge  120 . In this embodiment, since the only relative motion between the contacts  196  and the wafer is rotational, this design allows an operator to adjust the pressure between the contacts  202  and the wafer to a desired fixed level before the process and consequently keep the pressure at that desired level. Lack of relative lateral motion between the contacts  196  and the wafer  104  reduces mechanical abrasion that may be caused by the contacts  196  over the exposed edge  120 . Alternatively, the contacts  196  can be connected to a moving mechanism (not shown) that is controlled by a controller (not shown) that causes the movement of the contacts  196  to correspond to the vertical motion of the carrier head  111 . The contacts  196  may be biased toward the wafer  104  with a spring (not shown) for better conductivity between the contacts  196  and the wafer  104 .  FIG. 12B  shows the position of the contacts  196  with respect to the WSID  106  and the wafer from a partial bottom view. As the wafer  104  is rotated in clockwise or counter clockwise directions as well as laterally moved in the x-direction, the contacts  196  continue making contact with the exposed edge  120  of the wafer  104 . In this embodiment the contacts  196  need to be moved out of the way by a mechanism (not shown) during the loading of the wafer  104  on the carrier head  111 . After loading the wafer contacts make physical contact to its surface and the process is initiated. Similar to the case discussed with respect to  FIGS. 11A and 11C , as the wafer  104  is rotated in clockwise or counter clockwise directions as, well as laterally moved in the x-direction, the contacts  196  continue making contact with the exposed edge  120  of the wafer  104  by moving with the wafer  104 . Therefore, they do not have to be as long as those in the case of stationary contacts of  FIG. 10B , and they do not necessarily be straight. They can have a curved shape that follows the contour of the wafer edge. 
     FIG. 13A  illustrates a side view of the exemplary electrotreating system  100  of  FIG. 1  including an exemplary back-side contacts  202  and a contact member mounting arrangement associated therewith. As illustrated in  FIG. 13A , the back-side contact  202  can be integrated with the system  100 . The back-side contacts  202  can be any of the specific contact members described in detail above with regard to the above described embodiments. In this embodiment, the wafer  204  will have a conductive layer  206 , typically a seed layer, that extends from the frontside  208 , around the bevel portion  210 , to the backside  212 , so that electrical contact can be 
   maintained between the wafer  204  and the back-side contact  202  from the back-side of the wafer. In this embodiment, the contact member that holds the contacts  202  can be attached. A brace portion  198  of the back-side contact  202  may be attached to the shaft housing  113 . As mentioned above the shaft housing  113  can move vertically with the carrier head in the z direction as well as laterally in the x direction. As the carrier head  111  moves vertically in the z-direction during the process, the contacts  196  keep their position along the exposed backside edge. In this embodiment, since the only relative motion between the contacts  202  and the wafer is rotational, this design allows an operator to adjust the pressure between the contacts and the wafer to a desired fixed level before the process and consequently keep the pressure at that desired level. Lack of relative lateral motion between the contacts  202  and the wafer  204  reduces mechanical abrasion. Alternatively, the contacts  202  can be connected to a moving mechanism (not shown) that is controlled by a controller (not shown) that controls the vertical motion of the carrier head  111 . The contacts  202  may be biased toward the wafer  204  with a spring (not shown) for better conductivity between the contacts  202  and the wafer  204 . Alternatively, the contact member and back-side contacts  202  can be disposed within the carrier head  111 , such that electrical contact is established once the wafer  204  is placed onto the carrier head  111 , as shown by the dotted line in  FIG. 13A  within the carrier head  111 . It should be noted that contact may also be made right at the edge (bevel) of the wafer. 
     FIG. 13B  illustrates another embodiment of a system that provides backside contacts. As illustrated, the WSID  106 A has dimensions that are larger than the wafer in all dimensions, such that the entire wafer is exposed to the WSID  106 A and the process solution during processing. 
   Cleaning of the contacts is also a consideration. In one aspect, conventional contacts are, in many instances coated with Cu, Pt, Pd or other materials to ensure repeatability. In time, however, they deteriorate due to corrosion and the like. Such corrosion will change uniformity if the contact is stationery with respect to the wafer, but the uniformity will average out if the contact moves with respect to the wafer, as it will with the present invention. In another aspect, actual cleaning of the contacts can extend their life and increase the uniformity of the contact. Methods of cleaning include electropolishing during the processing of a wafer, while electropolishing the wafer, usage of a conditioning wafer after processing some number of wafers, either with our without electropolishing occurring, or removal of the contacts from the system and cleaning them using conditioning pads, electropolishing, or other conventional cleaning operations. 
   Although the present invention has been particularly described with reference to the preferred embodiments, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims include such changes and modifications.