Patent Abstract:
An electro-processing apparatus includes a rotor in a head, and a contact ring assembly on the rotor. The contact ring assembly may have one or more strips of contact fingers on a ring base, with contact fingers clamped into position on the ring base. The strips may have spaced apart projection openings, with the projections on the ring base extending into or through the projection openings. A shield ring may be attached to the ring base, to clamp the contact fingers in place, and/or to provide an electric field shield over at least part of the contact fingers. The contact fingers may be provided as a plurality of adjoining forks, with substantially each fork including at least two contact fingers.

Full Description:
TECHNICAL FIELD 
     The field of the invention is contact rings for making electrical contact to a substrate during electro processing. 
     BACKGROUND OF THE INVENTION 
     Electro processing microelectronic and similar work pieces, such as silicon wafers, typically involves immersing an electrically conductive surface on the device side of the work piece in an electrolyte. An electrical current path is established between an immersed electrode and electrical contacts touching the edges of the work piece. Metal ions in the electrolyte are deposited on the work piece (electroplating) or removed from the work piece (electro-polishing/etching). 
     As the microelectronic and other micro-scale devices are made ever smaller, the electrical contacts must meet greater performance specifications. Accordingly there is a need for improved electrical contacts in electro-processing systems. 
     SUMMARY OF THE INVENTION 
     An electro-processing apparatus includes a rotor in a head, and a contact ring assembly on the rotor. The contact ring assembly may have one or more strips of contact fingers on a ring base, with contact fingers clamped into position on the ring base. In one aspect, the strips may have spaced apart projection openings, with the projections on the ring base extending into or through the projection openings. A shield ring may be attached to the ring base, to clamp the contact fingers in place, and/or to provide an electric field shield over at least part of the contact fingers. The contact fingers may be provided as a plurality of adjoining forks, with substantially each fork including at least two contact fingers. If used, substantially each fork may have a head, a link on the head attached to an adjacent fork, and with the fingers attached to a shoulder joined to the head, or directly to the head without any shoulder on the fork. 
     The head is movable to position the contact ring assembly in the vessel and out of the vessel, to electro-plate or electro-polish a work piece, such as a silicon wafer or similar micro-scale device substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an electro-processing chamber. 
         FIG. 2  is a perspective view of the contact ring shown in  FIG. 1 . 
         FIG. 3  is an enlarged section perspective view of the contact ring shown in  FIGS. 1 and 2 . 
         FIG. 4  is an enlarged bottom perspective detail view of the contact ring. 
         FIG. 5  is an enlarged plan view of two of the side-by-side contacts shown in  FIG. 4 . 
         FIG. 6  is an enlarged plan view of a strip of contacts. 
         FIG. 7  is a further enlarged inverted view of the contact ring and shield shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , and electro processing chamber  20  has a head  22  including a rotor  24 . A motor  28  in the head  22  rotates the rotor  24 , as indicated by the arrow R in  FIG. 1 . A contact ring assembly  30  on the rotor  24  makes electrical contact with a work piece or wafer  100  held into or onto the rotor  24 . The rotor  24  may include a backing plate  26 , and ring actuators  34  for moving the contact ring assembly  30  vertically (in the direction T in  FIG. 1  between a wafer load/unload position and a processing position. The head  22  may include bellows  32  to allow for vertical or axial movement of the contact ring while sealing internal head components from process liquids and vapors. 
     Referring still to  FIG. 1 , the head  22  is engaged onto a base  36 . A vessel or bowl  38  within the base  36  holds electrolyte. One or more electrodes are positioned in the vessel. The example shown in  FIG. 1  has a center electrode  40  and a single outer electrode  42  surrounding and concentric with the center electrode  40 . The electrodes  40  and  42  may be provided in a di-electric material field shaping unit  44  to set up a desired electric field and current flow paths within the processor  20 . Various numbers, types and configurations of electrodes may be used. 
       FIG. 2  shows the contact ring assembly  30  separated from rotor  24  and  15  inverted. Accordingly, the contact fingers  82  on the contact ring assembly  30  which are shown at or near the top of the contact ring assembly  30  in  FIG. 2 , are at or near the bottom end of the contact ring assembly  30  when the contact ring assembly  30  is installed into the rotor  24 . A mounting flange  64  may be provided on the contact ring for attaching the contact ring assembly  30  to the rotor  24  with fasteners. 
       FIG. 3  shows a section view of the contact ring assembly  30 , with the contact ring once again in the installed upright orientation shown in  FIG. 1 . In this example, the contact ring assembly  30  has a base ring  50  between an inner liner  56  and an outer shield ring  52 . Referring now also to  FIG. 4 , lines or strips of contact fingers  82  are attached to the ring base  50 . The contact fingers  82  may be positioned onto a flat angled bottom surface  70  of the ring base  50 . Consequently, the fingers  82  extend inwardly (towards the center of the contact ring assembly  30 ) and also slightly upwardly in  FIGS. 1 and 3 . Alternatively, the bottom or mounting surface  70  may be horizontal, or even inclined downwardly. 
     A shield  54 , if used, covers part of or the entire length of contact fingers  82 . In  FIG. 3 , only the innermost tips  75  of the fingers  82  are not covered or shielded by the shield  54 . The inwardly extending length of the shield  54 , relative to the length of the fingers  82 , may be adjusted to vary the current thieving effect of the fingers. In some to designs, the shield may extend inwardly past the tips of the fingers  82 , so that the fingers are completely shielded from below. Alternatively, the tips  75  of the fingers may extend radially inwardly past the inner edge of the shield  54  by 1 to 10, 2 to 5 or 2 to 8, or 3-7 mm. Rinse holes  62  may be provided in the shield  54  to better allow for cleaning and deplating of the forks  80 . If the contact ring  30  is used in a sealed ring design (a so-called dry contact ring), then the rinse holes  62  may be omitted since the electrolyte does not come into contact with the forks  80  in a sealed ring design. As shown in  FIGS. 3 and 7 , rinse holes  85  may extend inwardly through the ring section  66 , in place of, or in addition to, the rinse holes  62 . Locating the rinse holes through the outside diameter of the ring section, instead of positioning the rinse holes under the back end of the fingers, reduces the influence of the drain holes on the electric field during processing. The rinse holes  85  may optionally be located higher up on the ring section  66 , so that they remain above the plating bath at all times. 
     The shield  54  is made of a di-electric material and may be formed as part of the shield ring  52 . Alternatively, the shield  54  may be a separate ring attached to the contact ring assembly  30 . The ring base  50  may be made of metal, such as titanium. The shield ring  52  may include a ring section  66  and an attached or integral shield or shield section  54 . As shown in  FIG. 7 , the shield  54  may have an inner edge  55  oriented an acute angle to vertical, e.g., to the rotation axis T of the rotor as shown in  FIG. 1 . Also as shown in  FIG. 7 , a gap  75  may be provided between the shield  54  and the fingers in the unloaded condition. The gap  75 , if used, may close up when a wafer is loaded into the rotor  24  and the contact ring  30  is moved up (as shown in  FIGS. 1 and 3 ) to make electrical contact with the wafer and to hold the wafer in place for processing. 
     The fingers  82  are electrically connected to the processor electrical system. This electrical connection may be achieved via an electrically conductive ring base  50 , e.g., with the ring base made partially or entirely of metal. Alternatively, the ring base  50  may also be an electrically non-conductive material or dielectric material, with one or more electrical leads extending through or alongside the ring base  50 , to electrically connect with the fingers  82 . The inner liner  56  may have an outwardly tapering surface  58 , to help to guide and center a wafer  100  into the contact ring assembly  30 . The inner liner  56 , which is generally plastic or another non-conductive material, may have an outwardly extending lip  60  that extends into a slot or recess in the ring base  50 . 
     Turning to  FIGS. 4-6 , the fingers  82  may be provided on a strip  68  of connected forks  80 , with each fork  80  including two fingers, indicated as  82 A and  82 B. Lugs, pins or other protrusions  72  may be spaced apart on the angled or conical surface  70  of the ring base  50 , with the lugs  72  extending into or through a lug gap or opening  94  between adjacent forks  80 . As shown in  FIGS. 4 and 5 , each fork  80  may include a head  96  having links  92  on each side connected to adjacent forks. The fingers  82 A and  82 B of each fork  80  may be joined to a fork neck section  90  having a width about the same as the width of the head  96 . In this design as shown, the upper or outer ends of the fingers  82 A and  82 B slant or curve inwardly at a shoulder  98 . 
     The fingers  82 A and  82 B of each fork  80  are parallel and spaced apart by a gap  86 , with the fingers having a width 2-5 times greater than the width of the gap  86 . For example, the fingers may a width of about 0.020 to 0.050 inches and the gap  86  may have a width of about 0.010 to 0.020 inches. Referring to  FIG. 5 , each fork  80  may have a width W of from about 0.06 to 0.120 or 0.070 to 0.100 inches. With dimensions in these ranges, far more fingers can fit onto the contact ring assembly  30  in comparison to existing designs. For example, a contact ring assembly  30  for use with a 12 inch diameter wafer may have 480 or even 720 fingers. Providing a large number of contacts may reduce adverse effects, such as current path variations and heating, when plating onto extremely thin seed layers. If desired, the fingers may be made even narrower, for example with three, four or more fingers on each fork  80 , resulting in designs having over 1000 fingers. A similar or the same gap  86  may be provided between the fingers of adjacent forks. The fingers  82 A and  82 B may be mirror images of each other, having the same size and shape. The finger thickness may vary depending on the finger material, and the finger length. The fingers shown in  FIG. 5  have a length of about 0.25 inches, measured from the inner tip to the outer root of the gap  86 . Using platinum, platinum/iridium alloy, or platinum coated titanium, finger thicknesses ranging from about 0.005 to 0.010 inch are typical. 
     Referring now to  FIG. 6 , strips or ribbons  68  of forks  80  may be made using various manufacturing techniques, such as electro discharge machining, or stamping a metal sheet, such as titanium with or without a platinum or iridium cladding. With the ring base  50  up-side down, the strips  68  are positioned on the surface  70 , with the lugs  72  positioning the strips  68 . Specifically, the outer or upper edge of the fork head  96  is positioned against a concentricity alignment rim or lip  76  of the ring base  50 , causing the fingers to align precisely concentrically on the base ring. The lugs  72  may also help to position the fingers concentrically, as well as laterally. Although a single continuous strip  68  may be used, manufacture and assembly may be simplified by using multiple shorter strips. 
     Referring to  FIG. 3 , with the strips  68  in place, shield ring  52 , including the shield  54 , is placed over the ring base  50 , with the now down-facing surface of the shield  54  in contact with the strips  68 . The shield ring  52  is then clamped onto the ring base  50  via fasteners, such as cap screws. Inner and outer rings  74  and  72  on the down-facing surface of the shield press on the shoulders  98  and head  96  of the forks  80 , clamping the forks  80  in place, largely flat against and parallel to the surface  70 . 
     The liner  56  is attached to the ring base  50  e.g., with fasteners. The liner  56  guides the wafer  100  into a processing position within the contact ring assembly  30 . Since both the liner  56  and the fingers  82  are positioned via surfaces of the ring base  50 , the fingers  82  may concentric with the wafer  100  to a high degree of precision. Holding the fingers  82  in place purely via clamping, as opposed to using known techniques such as pressing or welding, allows simplified manufacturing. It also allows the fingers to be made of precious metals, for longer contact life, because the fingers may be formed from unstressed metal sheet stock. 
     Although the strips  68  may be straight, links  92  between the forks allow the strips  68  to bend to conform to the circumference of the ring base  50 , and to the conical section of the surface  70 , if any. With this assembly, the fingers are automatically accurately and securing positioned. No positioning or bending of individual contacts is needed. The fingers are automatically positioned precisely concentric with the ring base  50 . This allows for plating highly uniform layers. The fingers may also be easily replaced when damaged or worn, as no welding, coating, or other repair steps are needed. Correspondingly, fingers made of precious metal may also be easily separated from the contact ring assembly  30  for collection. 
     The contact ring assembly  30  may be used in wet contact applications where the fingers are in contact with the electrolyte. In this type of application, the shield  54  reduces the build up of metal plated onto the fingers. This improves the performance of the plating chamber  20  and reduces the time required for contact finger de-plating. The shield  54  may be used with the finger contacts  82 , or with conventional contact fingers. The contact ring assembly  30  may also be used in sealed ring or dry contact applications. In a sealed ring design, a seal on the rotor seals the electrolyte away from the outer edges of the wafer. The fingers make electrical contact with a seed layer or other pre-existing conductive layer on the wafer, but do not come into contact with the electrolyte. 
     Thus, novel methods and designs have been shown and described. Various changes, substitutions and use of equivalents may of course be made, without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except to the following claims and equivalents of them.

Technology Classification (CPC): 2