Abstract:
An apparatus for chemically-mechanically polishing a semiconductor wafer comprises a receiving surface attached with a frame; a loading mechanism in contact with the receiving surface, the loading mechanism being configured to load measured portions of a wafer-polishing member containing a fixed abrasive onto the receiving surface; a reciprocation device attached with at least a portion of the receiving surface, the reciprocation device being powered to move the receiving surface in a linear, bi-directional motion; and a wafer holder positioned to releasably hold a wafer adjacent to the receiving surface. Methods of chemically-mechanically polishing semiconductor wafers are also provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates to polishing and planarization of semiconductor wafers. More particularly, the present invention relates to method and apparatus for linearly reciprocating a portion of a continuous polishing member to process a semiconductor wafer. 
     BACKGROUND 
     Chemical mechanical planarization techniques are used to planarize and polish each layer of a semiconductor wafer. Available CMP systems, commonly called wafer polishers, often use a rotating wafer carrier that brings the wafer into contact with a polishing pad rotating in the plane of the wafer surface to be planarized. A chemical polishing agent or slurry containing microabrasives and surface modifying chemicals is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating pad and is rotated to polish and planarize the wafer. Some available wafer polishers use orbital motion, or a linear belt, rather than a rotating surface to carry the polishing head. One challenge of polishing semiconductor wafers using a disposable polishing pad on the available wafer polishers is that these polishers must be frequently stopped to replace the polishing member after a limited number of uses. Accordingly, there is a need for a method and system of performing CMP that addresses this issue. 
     SUMMARY 
     In one aspect of the invention, an apparatus for chemically-mechanically polishing a semiconductor wafer comprises a receiving surface attached with a frame; a loading mechanism in contact with the receiving surface, the loading mechanism being configured to load measured portions of a wafer-polishing member containing a fixed abrasive onto the receiving surface; a reciprocation device attached with at least a portion of the receiving surface, the reciprocation device being powered to move the receiving surface in a linear, bi-directional motion; and a wafer holder positioned to releasably hold a wafer adjacent to the receiving surface. 
     In another aspect of the invention, a loading mechanism for loading measured portions of a wafer-polishing member containing a fixed abrasive into an apparatus for the chemical-mechanical polishing of semiconductor wafers comprises a polishing member dispensing roller connected with a frame, the polishing member dispensing roller holding a supply of waferpolishing member, and a feeding device in contact with the supply of waferpolishing member, the feeding device configured to move measured portions of the wafer-polishing member onto a receiving surface in the apparatus for the chemical-mechanical polishing of semiconductor wafers. 
     In another aspect of the invention, a method of polishing semiconductor wafers comprises loading a measured portion of a wafer-polishing member containing a fixed abrasive onto the receiving surface; and reciprocating the receiving surface and wafer-polishing member in a linear, bi-directional motion against the semiconductor wafer. 
     In another aspect of the invention, an apparatus for chemically-mechanically polishing semiconductor wafers comprises a receiving surface attached to a frame; a loading mechanism in contact with the receiving surface, the loading mechanism being configured to loads discrete sheets of wafer-polishing members containing a fixed abrasive onto the receiving surface; a reciprocation device attached with at least a portion of the receiving surface, the reciprocation device being powered to move the receiving surface in a linear, bi-directional motion; and a wafer holder positioned to releasably hold a wafer adjacent to the receiving surface. 
     In another aspect of the invention, a loading mechanism for loading discreet sheets of wafer-polishing members containing a fixed abrasive into an apparatus for the chemical-mechanical polishing of semiconductor wafers comprises a supply bin in a frame, the supply bin adapted to contain a plurality of discrete sheets of wafer-polishing members; an automated sheet feeder in contact with the supply bin, the sheet feeder being configured to automatically uptake a first discrete sheet in the supply of discrete sheets and to load the first discreet sheet onto the receiving surface; and an adjustment mechanism in contact with the supply bin and the automated sheet feeder such that the adjustment mechanism adjusts the relative positioning of the automated sheet feeder and the supply of discrete sheets in the supply bin. 
     In still another aspect of the invention, a method of simultaneously conditioning a measured portion of a wafer-polishing member containing a fixed abrasive and chemically-mechanically polishing a semiconductor wafer comprises a) loading a measured portion of a wafer-polishing member containing a fixed abrasive onto the receiving surface; and b) reciprocating the receiving surface and wafer-polishing member in a linear bi-directional motion against the semiconductor wafer, c) repeating (b) and (c) until the semiconductor wafer is polished and the measured portion of the wafer-polishing member is conditioned. 
     The present invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a side view of an apparatus for chemically-mechanically polishing a semiconductor wafer. 
     FIG. 2 is a front view of the chemical-mechanical polishing apparatus of FIG.  1 . 
     FIG. 3 is a top view of the chemical-mechanical polishing apparatus of FIG.  1 . 
     FIG. 4 is a side view of a loading mechanism and the chemical-mechanical polishing apparatus for which the loading mechanism is used. 
     FIG. 5 is a side view of a loading mechanism and the chemical-mechanecal polishing apparatus for which the loading mechanism is used. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There are several preferred embodiments of the method and apparatus for chemically-mechanically polishing semiconductor wafers. 
     EMBODIMENTS HAVING A CONTINUOUS SUPPLY OF ABRASIVE MATERIAL 
     A preferred embodiment of an apparatus for chemically-mechanically polishing a semiconductor wafer is depicted in FIGS. 1,  2 , and  3 . The apparatus  2  is built about frame  4  and mounting plate  6 . 
     An abrasive belt feed roll  10  holds a supply of wafer-polishing member  12 . A preferred wafer-polishing member comprises a flexible strip having an abrasive layer fixed onto the strip. In one embodiment, the abrasive layer comprises a series of discrete cylindrical abrasive members such that as the abrasive layer becomes worn down through use, the surface area of the discrete cylindrical abrasive members remains substantially constant. The abrasive layer is preferably covered with a protective polymer layer. The polymer layer is removed before the abrasive can be used to polish a semiconductor wafer. This preferred wafer-polishing member is commercially available through the Minnesota Mining and Manufacturing Company as part numbers 3M 307EA and 3M 237AA, which are available in grades A100, A65, A45, A16, and A6. 
     In another preferred embodiment, the wafer-polishing member comprises a polishing pad adapted to receive an abrasive slurry such as the slurries disclosed in U.S. Pat. Nos. 6,007,407, 6,012,966 and 6,022,266. These patents are incorporated by reference in their entirety. A suitable polishing pad material is commercially available from the Rodel Corporation of Delaware. 
     Attached to a sidewall of abrasive belt feed roll  10  is belt tension control  14 . When belt tension control  14  is off, feed roll  10  is free to rotate. Any known belt tension control mechanism is contemplated for use with this embodiment. The preferred belt tension control  14  can be activated many ways, including but not limited to electronically, pneumatically, hydraulically or a combination. 
     Although not required, each of the above embodiments described herein may utilize a non-abrasive liquid during polishing, such as deionized water, to facilitate the polishing process. The non-abrasive liquid may be applied via nozzles  43  (See FIG. 1) to the region of the polishing strip intended for contact with a wafer. 
     Belt conditioner  20  is positioned between belt feed roll  10  and ingress rollers  22   a  and  22   b . In a preferred embodiment, belt conditioner  20  conditions the wafer-polishing member  12  before polishing member  12  is used to polish a semiconductor wafer. In a preferred embodiment, belt conditioner  20  removes the protective polymer layer from the wafer-polishing member  12 . Suitable belt conditioners  20  include, but are not limited to, the conditioners described in U.S. Pat. Nos. 6,022,266, 5,938,507, and 5,934,980, which are hereby incorporated by reference in their entirety. In another preferred embodiment, there is no belt conditioner  20  because the process of polishing occurs simultaneously with the process of conditioning. This is described in greater detail supra in this specification. 
     Ingress roller  22   a  is powered, and ingress roller  22   b  is not powered. In alternative embodiments, both rollers can be powered or roller  22   b  can be powered while  22   a  is not. Wafer-polishing member  12  is in contact with belt conditioner  20  and ingress rollers  22   a  and  22   b . In the depicted embodiment, wafer-polishing member  12  frictionally fits between ingress rollers  22   a  and  22   b . These rollers move wafer-polishing member  12  onto a receiving surface  30 . That is, through ingress rollers  22   a  and  22   b , a measured portion of wafer-polishing member  12  is pulled from feed roll  10  onto receiving surface  30 . 
     Referring to FIG. 3, clamps  26   a  and  26   b  secure the measured portion of wafer-polishing member  12  onto receiving surface  30 . Clamps are merely an exemplary securing mechanism. Any securing mechanism known in the art could be used to secure wafer-polishing member  12  onto receiving surface  30 . 
     Receiving surface  30  has an ingress side and an egress side. In a preferred embodiment, belt cutter  27  is positioned above receiving surface  30  on the ingress side. In another preferred embodiment, belt cutter  27  is positioned above receiving surface  30  on the egress side. The position of the belt cutter  27  determines how much of the chemical mechanical polishing assembly oscillates with receiving surface  30  along guide rails  36   a  and  36   b  when polishing occurs. Reciprocating table  32  is attached to reciprocation drive assembly  35 . Preferred drive assemblies  35  include a crank shaft, drive motor, connecting rods, and a counter balance. A preferred drive assembly reciprocates linearly (+/−one inch) at an adjustable frequency of from about 0 to about 25 Hertz. 
     Reciprocating table  32  reciprocates in guide rails  36   a  and  36   b . It is preferred that the guide rails have linear bearings. 
     When the belt cutter  27  is on the ingress side of receiving surface  30 , as shown, the moving parts include clamps  26   a  and  26   b , egress roller  28   b , driven portions of reciprocation drive assembly  35  that impart reciprocation motion onto reciprocated table  32  and counterweight  34 . When the belt cutter is on the egress side of receiving surface  30 , the following additional parts move with receiving surface  30 : feed roll  10 , belt tension control  14 , ingress rollers  22   a  and  22   b , and egress roller  28   a.    
     Egress rollers  28   a  and  28   b  are in contact with wafer-polishing member  12  on the egress side of receiving surface  30 . Egress roller  28   a  is powered, and egress roller  28   b  is not powered. In other embodiments, both rollers may be powered or roller  28   b  may be powered while roller  28   a  is not. Belt disposal container  29  is positioned to receive spent measured portions of wafer-polishing member  12  from egress rollers  28   a  and  28   b . Any container or disposal mechanism known to those of skill in the art for disposing of spent measured portions of wafer-polishing member  12  is contemplated for use in this embodiment. 
     In a preferred embodiment, receiving surface  30  comprises reciprocating table  32  positioned above air-bearing platen assembly  34 . 
     Platen assemblies contemplated for use with this embodiment can be any known platen assembly, including but not limited to the platen assemblies disclosed in U.S. Pat. Nos. 5,558,568, 5,985,093, 6,000,997, 6,015,499 and 6,015,506, which are hereby incorporated by reference. Other acceptable platens are those commercially available from the Lam Research Corporation of Fremont, California, including the ones with the trade name TERES. Note that some of these platens are rotating platen assemblies. The platen assemblies contemplated for use with this embodiment are preferably not rotating. 
     Wafer holder  40  comprises spindle  42  and carrier head  44 . Carrier head  44  releasably holds wafer  46 . During polishing, wafer  46  is pressed against wafer-polishing member  12  by the wafer holder  40 . Spindle  42  rotates carrier head  44  and wafer  46  about an axis perpendicular to receiving surface  30  as wafer polishing member  12  reciprocates with reciprocating table  32  along guide rails  36   a  and  36   b . In another preferred embodiment, wafer holder  40  does not rotate wafer  46 , but instead holds wafer  46  stationary while polishing member  12  reciprocates with reciprocating table  32  along guide rails  36   a  and  36   b.    
     In a preferred embodiment using the apparatus described in FIGS. 1,  2 , and  3 , the method works as follows. A supply of wafer polishing member  12  is kept on belt feed roll  10 . The belt conditioner  24  conditions the wafer-polishing member  12  as it is drawn off of the feed roll so that it is ready to polish wafer  46 . After being conditioned, a measured portion of the wafer polishing member  12  is fed through ingress rollers  22   a  and  22   b , then secured to receiving surface  30  with clamps  26   a  and  26   b . This measured portion is preferably about  8  inches in length. Then, belt cutter  27  cuts the measured portion of wafer polishing member  12 , separating the wafer polishing member from the remainder of the belt feed roll  10 . Then, the reciprocation drive assembly reciprocates the receiving surface  30 , and all the parts attached therewith reciprocate along guide rails  36   a  and  36   b.    
     In the meantime, wafer holder  40 , which is holding wafer  46 , is brought into contact with the measured portion of polishing member  12 . Wafer holder  40  spins about an axis perpendicular to receiving surface  30  while polishing member  12  reciprocates with the receiving surface. Wafer  46  is polished by the combination of spinning and reciprocating. When polishing is complete, the measured portion of polishing member  12  is taken through egress rollers  28   a  and  28   b , and is discarded into disposal container  29 . 
     In the alternative preferred embodiment wherein the belt cutter is on the egress side of receiving surface  30 , belt conditioner  20  is omitted. The alternative apparatus works as follows. A supply of wafer polishing member  12  is kept on belt feed roll  10 . A measured portion of the wafer polishing member  12  is fed through ingress rollers  22   a  and  22   b , then secured to receiving surface  30  with clamps  26   a  and  26   b . This measured portion is small, preferably less than one inch in length, more preferably less than one-half inch, and most preferably about ¼ inch. Then, the receiving surface  30  and all the parts attached therewith reciprocate along guide rails  36   a  and  36   b . Wafer holder  40 , which is holding wafer  46 , is in contact with the measured portion of polishing member  12 . Wafer holder  40  spins about an axis perpendicular to receiving surface  30  while polishing member  12  reciprocates with the receiving surface. Wafer  46  is polished at the same time the wafer is conditioned by the combination of spinning and reciprocating. When the first small measured portion is complete, the next small measured portion is pulled onto receiving surface  30  and the reciprocation process is repeated. This occurs until the entire wafer  46  is polished and the polishing member  12  is conditioned. Once a measured portion of polishing member  12  has been conditioned, small or otherwise, it is preferably used to polish more than one wafer  46 . 
     When polishing and conditioning of a wafer  46  is complete, the belt cutter  27  cuts off the spent portion of polishing member  12 . Then, the measured portion of polishing member  12  is taken through egress rollers  28   a  and  28   b , and is discarded into disposal container  29 . Any mechanism for disposing of spent polishing member is within the scope of the described embodiment. Such mechanisms include but are not limited to take-up rollers. 
     EMBODIMENTS USING DISCREET SHEETS OF ABRASIVE MATERIAL 
     In another preferred embodiment, an apparatus for chemically-mechanically polishing semiconductor wafers has an improved loading mechanism for loading discrete sheets of polishing member  12  onto a receiving surface  30 . 
     Referring to FIGS. 4 and 5, two embodiments of a loading mechanism are shown. In FIGS. 4 and 5, loading mechanism  100  is shown. Supply bin  105  contains a supply of discrete sheets of polishing member  12 . Feed roll  110  makes a first discrete sheet available to a web pick up vacuum member  115 . In the embodiment depicted in FIG. 4, there is only one web pick up vacuum member  115 . In the embodiment depicted in FIG. 5, there are two web pick up vacuum members  115 . 
     Vacuum member  115  is attached to a frame at a pivot point  120 . Vacuum member  115  makes contact with a discreet sheet of polishing member  12 , rotates about the pivot point  120 , and delivers the discreet sheet of polishing member  12  to transfer rollers  125   a  and  125   b . Then, in FIG. 4, the discreet sheet of polishing member  12  is slid along web transfer guide  126  where it is fed to ingress rollers  128   a  and  128   b . In FIG. 5, no transfer guide  126  is shown, but such a guide is optional and can be included in the assembly. 
     After the first discreet sheet of polishing member  12  is removed from the supply bin  105 , the supply bin&#39;s position is adjusted using any indexing mechanism known to those of skill in the art. Exemplary non-limiting indexing mechanisms are disclosed in U.S. Pat. Nos. 4,248,413, 4,807,868, and 5,013,026. These patents are hereby incorporated by reference. 
     In these embodiments, it is preferred that the discreet sheets of polishing member  12  be durable enough to remain undamaged while being stacked in a pile and being handled by several sets of rollers and a vacuum member  115 . To achieve such a durable set of discreet sheets of polishing member  12 , it is preferred that the abrasive be a fixed abrasive as described above. 
     SCOPE 
     It should be appreciated that the apparatus of the present invention is capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described above. The invention may be embodied in other forms without departing from its spirit or essential characteristics. For example, the embodiments of the present invention may be modified to include a linear motor drive. The described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is therefore indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are embraced to be within their scope.