Abstract:
A bladder carrier assembly having a retaining ring permanently bonded to a bladder to form a one-piece disposable bladder assembly. The retaining ring includes a rigid ring member, preferably steel, and a layer of wear resistant material, such as ultra high molecular weight polyethylene or polyether ethyl ketone, which is molded around predetermined portions of the rigid ring member. The bladder is also molded to the retaining ring and an optional template may be molded to a surface of the bladder which lies adjacent a wafer to be polished.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a disposable bladder carrier assembly for retaining workpieces such as semiconductor wafers. More particularly, the present invention relates to a one piece disposable bladder carrier assembly where a rubber bladder is molded directly to a retaining ring having a rigid ring surrounded by a bonded wear resistant plastic such as polyether ethyl ketone (PEEK) or ultra-high molecular weight polyethylene (UHMW) polyethylene. The rubber bladder is permanently bonded to the rigid ring and may also be bonded to the wear resistant plastic depending upon the particular embodiment of the bladder carrier assembly. 
     BACKGROUND OF THE INVENTION 
     Presently known chemical mechanical polishing machines typically employ either a single carrier or a plurality of carriers, each configured to hold a single semiconductor wafer firmly against a polishing surface, for example the upper surface of a rotating polishing pad. As a result of the relative motion between the semiconductor wafer surface to be polished and the polishing pad, coupled with the downward pressure applied by the wafer carrier to press the wafer against the polishing pad, even very small deviations in the uniformity of the pressure applied to the semiconductor wafer across the wafer surface can result in imperfections in the planarization process. In order to maintain a uniform pressure to the semiconductor wafer, current carriers often comprise a flexible membrane, or bladder, that covers a downward opening on the underside of a carrier thereby creating a space between the carrier and the bladder. An idealized bladder system expands or translates primarily in the axis of the wafer. When a pressurized fluid is applied to the space, the bladder applies a uniform downward pressure across the entire upper surface of a wafer that is being polished. One example of such a carrier can be found in U.S. Pat. No. 5,449,316 issued to Strasbaugh. 
     Although current carriers employing a bladder enable uniformity, carrier to carrier identicalness is a problem. Further, current carrier designs employing a bladder have a high cost of ownership due to several factors relating to lifetime of the carrier and replacement costs of the carrier such as downtime, wear on the retaining ring, ring delamination, part fatigue, assembly reproducibility and difficulty in assembling the carriers. In addition, current carriers employ adhesives and/or compressive joints which can fail as a result of too much pressure and vacuum cycling in a wet corrosive environment. 
     Accordingly, there is a need for a reliable bladder carrier that is cost efficient and time efficient. There is also a need for a method for making such a bladder carrier that further reduces cost of ownership. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, the invention relates to a one-piece bladder carrier assembly having a bladder that is permanently bonded to a retaining ring structure for retaining workpieces during processing. The bladder carrier assembly includes a rigid ring, preferably comprised of steel, a wear resistant material, such as ultra-high molecular weight (UHMW polyethylene, PEEK, polyetherketone, polyphenylene sulfide, polybutylene terthalate, and homopolymer acetal, which is formed around the rigid ring, and a bladder that is permanently bonded to the steel after or when it is cast. In another aspect of the invention, the bladder may also be permanently bonded to the wear resistant material. In addition, a cavity may be formed either within the wear resistant material, or within both the wear resistant material and the rigid ring to create a pressure wave relief space. 
     In general, in another aspect, the invention relates to a method for making a one-piece bladder carrier assembly. A rigid ring having bore holes is made and then mounted on a hardened steel plate. This assembly is then placed in a mold and a wear resistant material, such as UHMW polyethylene or PEEK, is formed around, and bonded to, the rigid ring by employing increased temperature and pressure. A bladder material such as EPDM rubber is molded concurrently with the ring structure such that the bladder is permanently bonded to either the rigid ring, or both the wear resistant material and the rigid ring. In another aspect of the invention, the bladder may be molded to the ring structure in a second step subsequent to the formation of the ring structure. 
     A main advantage of the invention is a reduced cost of ownership due to an increase in the lifetime of the carrier and a decrease in replacement costs. A further cost ownership advantage is the time and simplicity of part change procedures in a simple, one piece bolt up type assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, schematically illustrate the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. In the following Figures, like reference numbers refer to similar elements throughout the Figures. 
     FIG. 1 is a perspective view of the backside of the bladder carrier assembly of the present invention shown from the top of the assembly; 
     FIG. 2 is a perspective view of the front or wafer side of the bladder carrier assembly of the present invention shown from the bottom of the assembly; 
     FIG. 3A is a top plan view of a first exemplary embodiment of the present invention; 
     FIG. 3B is a cross-sectional view of the first exemplary embodiment of the present invention taken along line A—A of FIG. 3A; 
     FIG. 3C is an enlarged view of area Z in FIG. 3B; 
     FIG. 4A is a top plan view of a second exemplary embodiment of the present invention showing torroidal bending element; 
     FIG. 4B s a cross-sectional view of the second exemplary embodiment of the present invention taken along line A—A of FIG. 4A; 
     FIG. 4C is an enlarged view of area Z in FIG. 4B; 
     FIG. 5A is a top plan view of a third exemplary embodiment of the present invention showing the wafer loaded into a wafer carrier assembly having a stepped horizontal suspension bending element; 
     FIG. 5B is a cross-sectional view of the third exemplary embodiment of the present invention ken along line A—A of FIG. 5A; 
     FIG. 5C is a enlarged view of area Z in FIG. 5B; and 
     FIG. 6 is a flowchart showing a method for making the bladder carrier assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention is directed to a one-piece, disposable bladder-retaining ring assembly (also known throughout the specification and claims herein as a disposable bladder carrier assembly) for use in chemical mechanical polishing (CMP) of workpieces that has a built in low cost of ownership. The bladder-retaining ring assembly is designed to extend the lifetime of a carrier and as a result, can process many more wafers than current carrier designs. When the bladder-retaining ring assembly has completed its useful lifetime, the assembly is simply thrown away and replaced with another one-piece bladder-retaining ring assembly. 
     FIG. 1 is a perspective view of the disposable bladder carrier assembly  10  shown from the top of the assembly which is known as the backside of the assembly during use. The disposable bladder carrier assembly includes a retaining ring assembly  12  that is permanently bonded to a bladder  14 . A top surface  16  of retaining ring assembly  12  has a plurality of bore holes  18  which extend into retaining ring assembly  12  to enable the disposable bladder carrier assembly  10  to be secured to a CMP apparatus. The carrier retains a wafer while the CMP apparatus rotates and moves the wafer across a polishing surface. Another perspective view of the disposable bladder carrier assembly  10  shown from the bottom of the assembly which is known as the front or wafer retaining side of the assembly during use is shown in FIG.  2 . The bladder  14  is permanently bonded to the retaining ring assembly  12  near a bottom surface  20  of the bladder carrier assembly  10 . It is this side of the bladder carrier assembly  10  which retains a recessed wafer and comes into contact with a polishing surface. 
     Turning now to FIG. 3A, there is shown a top plan view of a first exemplary embodiment of the disposable bladder carrier assembly  10  of the present invention. A retaining ring assembly  12  (later described in detail with reference to FIGS. 3B and 3C) is permanently bonded to a bladder  14 . The top surface of the retaining ring assembly  12  includes bore holes  18  for removably connecting retaining ring assembly  12  to a CMP apparatus which rotates and moves wafers contained in the retaining ring assembly  12  during chemical mechanical polishing. A top surface  22  of bladder  14  is covered by the CMP apparatus when the retaining ring assembly  12  is connected to the CMP apparatus. The bladder  14  is permanently attached near a bottom surface (not shown) of retaining ring assembly  12  such that a wafer (not shown) will lie adjacent to a bottom surface (not shown) of bladder  14  during processing of the wafer. 
     FIG. 3B is a cross-sectional view taken along line A—A of FIG.  3 A. Bladder  14  is permanently bonded to retaining ring  12  by molding with a suspension device so that the bladder  14  can float independently from the retaining ring  12  The permanent bonding of bladder  14  to retaining ring  12  is preferably achieved by molding but may also be achieved with the use of permanent adhesives or the like which are suitable for bonding to rubber. FIG. 3B also shows that retaining ring  12  is comprised of a rigid ring member  30 , preferably comprised of steel, having a plurality of bore holes  18  contained therein and a layer of a wear resistant material  32 , such as UHMW polyethylene, PEEK polyetherketone, polyphenylene sulfide ,polybutylene terthalate, and homopolymer acetal, for example, which surrounds a substantial portion of steel ring member  30 . It is well known that use of inexpensive UHMW polyethylene in carriers could extend the life of the carriers. However, by itself, UHMW polyethylene does not hold shape and dimension well under load. The disposable bladder carrier assembly of the present invention overcomes this limitation by using a steel reinforcement that is locked into the structure with chemical bonding and by casting the structure in a shape that stearically hinders delamination. 
     An enlarged view of area Z shown in FIG. 3B is illustrated in detail in FIG. 3C. A layer of wear resistant material  32 , preferably PEEK or UHMW polyethylene, is molded around an adhesive coated rigid ring member  30  having bore holes  18  such that the material layer  32  covers a substantial portion of the outer surface of rigid ring member  30  with the exception of the top surface  34  of rigid ring member  30  which contains the openings for bore holes  18 . The material layer  32  forms a continuous layer covering the outer circumference of rigid ring member  30  and the bottom surface of rigid ring member  30 . In the embodiment shown in FIG. 3C, bladder  14  is molded to a top surface of material layer  32  where it extends beyond the bottom surface of rigid ring member  30  and a portion of the inner circumference of ring member  30 . In use, a bottom surface of wafer  36  lies adjacent bladder  14 . Bladder  14  is preferably comprised of rubber which is raw prior to molding the bladder  14  to material layer  32  and ring member  30 . Bladder  14  may also be comprised of soft urethanes and the like. Bladder  14  may be molded with a suspension device to allow the bladder  14  to float independently of retaining ring  12 . 
     Turning now to FIG. 4A, there is shown a top plan view of a second exemplary embodiment of the present invention. The disposable bladder carrier assembly  50  includes retaining ring  52  which is permanently bonded, preferably by molding, to bladder  54 . A plurality of bore holes  58  are contained within a top surface of retaining ring  52  for connection to a CMP apparatus. Disposable bladder  54  is molded to retaining ring  52  near the bottom of the inner circumference of the retaining ring  52  such that a top surface  62  of bladder  54  is recessed within the inner circumference of retaining ring  52 . Bore holes  58  are used to secure the bladder/retaining ring assembly to the CMP apparats used for CMP. During polishing, a wafer will lie adjacent to the bottom surface (not shown) of bladder  54 . 
     FIG. 4B shows a cross-sectional view of FIG. 4A taken along line A—A of FIG.  4 B. Bladder  54  is shown molded to retaining ring  52 . In FIG. 4C, an enlarged drawing of area Z in FIG. 4B shows the connection of bladder  54  to retaining ring  52  in detail. In this embodiment of the present invention, retaining ring  52  comprises a rigid ring member  70  having a channel  71  formed therein about an outside circumference of rigid ring member  70 , and a plurality of bore holes  58  formed within a top surface of rigid ring member  70 . A wear resistant material layer  72 , such as UHMW polyethylene or PEEK, is molded around the bottom and side surfaces of rigid ring member  70 . An optional relief space  73  may be formed within either the material layer  72 , or both the material layer  72  and rigid ring member  70  during molding of the material layer  72  to the rigid ring member  70 . If relief space  73  is formed within a portion of rigid ring member  70 , then rigid ring member  70  would be formed to include relief space  73  before molding material layer  72  to rigid ring member  70 . Bladder  54  is then molded to material layer  72  of retaining ring  52 . In order to achieve this permanent bond, a recess is formed within material layer  72  while molding material layer  72  to rigid ring member  70  and bladder  54  fills this recess when bladder  54  is molded to material layer  72 . This embodiment of the present invention may also include a pressure relief space  77  which is formed within bladder  54  when bladder  54  is molded to material layer  72  in order to produce a flat torroidal bending element. 
     A third exemplary embodiment  80  of the present invention is shown in FIGS. 5A-5C. FIG. 5A shows retaining ring  82  molded to bladder  84  where a top surface  92  of bladder  84  is recessed within an inner circumference of retaining ring  82  as a result of molding bladder  84  to a bottom inner circumference of retaining ring  82 . A top surface of retaining ring  82  has a plurality of bore holes  88  formed therein in order to connect the retaining ring and bladder assembly of the present invention to a CMP apparatus that is used to rotate and move workpieces across a polishing surface during CMP. FIG. 5B shows a cross-sectional view taken along line A—A of FIG.  5 B and FIG. 5C shows an enlarged view of area Z identified in FIG.  5 B. This third exemplary embodiment  80  of the present invention is identical to the previously described second exemplary embodiment  50  of the present invention with the exception of a machined layer  89  of wear resistant material, such as UHMW polyethylene or PEEK, which is formed over an outer circumference and bottom surface of material layer  82  to produce a stepped horizontal suspension bending element. During polishing, wafer  92  lies adjacent a bottom surface of bladder  84  and machined layer  89  extends beyond the thickness of wafer  92 . 
     A flow chart showing the method of the present invention for making a bladder and retaining ring assembly for retaining workpieces during CMP is shown in FIG.  6 . In step  120 , a rigid ring member is formed which is preferably made of steel. An optional channel may be formed within the outer circumference of the ring member. A layer of wear resistant material, such as UHMW polyethylene or PEEK, is then bonded to specific predetermined areas of the outer surface of the rigid ring member in step  122 . The metal surface of the ring member which is coated with adhesive and the material layer, which preferably comprises raw rubber, is then molded to the material layer and/or the rigid ring member in step  124  so that a permanent bond is formed between the bladder and the retaining ring which comprises the rigid ring member and material layer. Pressure and heat vulcanize the rubber and cure the adhesive Alternatively, the material layer is molded and bonded in one step as in step  126 . During step  126 , one or more recesses may be formed within the material layer by the use of spacers during molding to facilitate permanent bonding of the material layer to the rigid ring member and/or to create a pressure relief space. Finally, in step  128 , an optional template, preferably comprised of fiberglass, is bonded to the surface of the bladder which lies adjacent a workpiece during polishing. 
     The present invention comprises a quick disconnect bladder assembly which is suitable for horizontal suspension of wafers. The permanent adhesion and/or compressive joints in the bladder carrier of the present invention improves reliability and reduces cost of ownership as a result of a decrease in required manpower and assembly time. Further, the process for making the disposable bladder assembly of the present invention further reduces cost of ownership because it creates high part identicality from various features such as CNC machining of molds and inserts, rigid positioning of devices during casting, CNC finish machining of the assembly, and minimal utilization of manpower. 
     The present invention has been described above with reference to exemplary embodiments. These embodiments are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the present invention in any way. Those skilled in the art having read this disclosure will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope of the present invention. These and other changes and modifications are intended to be included within the scope of the present invention, as expressed in the following claims.