Polishing pad with controlled abrasion rate

Abstract

A polishing pad is provided, having its face shaped to produce controlled nonuniform removal of material from a workpiece. Non-uniformity is produced as a function of distance from the pad's rotational axis (the working radius). The pad face is configured with both raised, contact regions and voided, non-contact regions such that arcuate abrasive contact varies nonuniformly as a function of distance from the pad's rotational axis. Void density at any distance may be produced by several techniques such as varying void size as a function of working radius or varying the number of voids per unit area as a function of working radius. Either technique produces variation in voided area per total unit area for rings of pad surface concentric with the rotational axis having infintesimally small width.

I claim:  
     
       1. A polishing pad rotatable about a central axis, said pad having a circular, planar face perpendicular to said central axis, said face to be brought in spinning contact with a workpiece during a polishing operation, said face extending from said central axis to an outer, continuous, circular periphery and comprising both raised and voided regions, wherein at least one of said raised regions is disposed immediately proximate said central axis, said raised and voided regions being configured so as to produce a controlled nonuniform rate of material removal from said workpiece, said rate of material removal being a non-linear function of distance from the pad's rotational axis to a working radius. 
     
     
       2. The polishing pad of  claim 1 , wherein high material removal rates correspond to bands of low void density on said face and low removal rates correspond to bands of high void density on said face. 
     
     
       3. The polishing pad of  claim 2 , wherein said voids are recessed regions within said face. 
     
     
       4. The polishing pad of  claim 2 , wherein said voids are holes which extend entirely through the pad. 
     
     
       5. The apparatus of  claim 2 , wherein said voids are circular. 
     
     
       6. A rotatable polishing pad having a central axis and a substantially planar contact surface extending substantially continuously from said central axis to an outer, continuous, circular periphery for polishing a workpiece, comprising: 
       
         at least two perceptibly different substantially arcuate regions on said contact surface;  
       
       
         at least one of said contact surface regions including a first density of voided area opening onto said contact surface; and  
       
       
         at least another of said contact surface regions including a second density of voided area opening onto said contact surface, said second density of voided area being not equal to said first density of voided area. 
       
     
     
       7. The polishing pad of  claim 6 , wherein said at least two contact surface regions are substantially contiguous. 
     
     
       8. The polishing pad of  claim 6 , wherein said at least two contact surface regions together extend radially from said central axis to said periphery of said polishing pad. 
     
     
       9. The polishing pad of  claim 6 , further including at least a third substantially arcuate region on said contact surface including a third density of voided area, opening onto said contact surface, wherein said at least three contact surface regions are arranged substantially coaxially, and wherein at least one of said substantially coaxial contact surface regions is interposed between at least two other contact surface regions having either greater or lesser voided area density. 
     
     
       10. The polishing pad of  claim 9 , wherein at least one of said arcuate contact surface regions comprises a substantially circular region extending radially from said central axis, and two others of said at least three contact surface regions each comprises an annular band lying on a larger radius than said circular region. 
     
     
       11. The polishing pad of  claim 9 , wherein said at least three contact surface regions are substantially contiguous. 
     
     
       12. The polishing pad of  claim 9 , wherein said at least three contact surface regions together extend radially from said central axis to said periphery of said polishing pad. 
     
     
       13. The polishing pad of  claim 6 , wherein said differing voided area densities are substantially a function of the number of voids per unit area in a region, the size of the voids in a region, or a combination thereof. 
     
     
       14. A rotatable polishing pad having a central axis and a substantially planar contact surface extending substantially continuously from said central axis to an outer, continuous, circular periphery for polishing a workpiece, comprising: 
       
         at least two perceptibly different, substantially arcuate regions on said contact surface, each of said regions lying at least partially on different radii with respect to said central axis;  
       
       
         at least one of said contact surface regions including a first contact area per unit surface area on said contact surface; and  
       
       
         at least another of said contact surface regions including a second contact area per unit surface area on said contact surface, said second contact area per unit surface area being not equal to said first contact area per unit surface area. 
       
     
     
       15. The polishing pad of  claim 14 , wherein said at least two contact surface regions are substantially contiguous. 
     
     
       16. The polishing pad of  claim 14 , wherein said at least two contact surface regions extend radially from said central axis to said periphery of said polishing pad. 
     
     
       17. The polishing pad of  claim 14 , further including at least a third substantially arcuate region on said contact surface including a third density of voided area, opening onto said contact surface, wherein said at least three contact surface regions are arranged substantially coaxially, and wherein at least one of said substantially coaxial contact surface regions is interposed between at least two other contact surface regions having either greater or lesser contact area per unit surface area. 
     
     
       18. The polishing pad of  claim 17 , wherein at least one of said arcuate contact surface regions comprises a substantially circular region extending radially from said central axis, and at least two others of said at least three contact surface regions each comprises an annular band lying on a larger radius than said circular region. 
     
     
       19. The polishing pad of  claim 17 , wherein said at least three contact surface regions are substantially contiguous. 
     
     
       20. The polishing pad of  claim 17 , wherein said at least three contact surface regions together extend radially from said central axis to said periphery of said polishing pad. 
     
     
       21. The polishing pad of  claim 14 , wherein said contact surface includes a plurality of apertures therein, and said differing contact area per unit surface area in said at least two contact surface regions is substantially a function of the number of apertures opening onto said contact surface per unit area in a region, the size of the apertures in a region, or a combination thereof. 
     
     
       22. A rotatable polishing pad having a central axis and a contact surface extending substantially continuously from said central axis to an outer, continuous, circular periphery for polishing a workpiece, comprising: 
       
         a plurality of perceptibly different substantially concentric contact regions on said contact surface;  
       
       
         each of said regions providing a different contact area per unit surface area than the contact area per unit surface area of any radially adjacent region; and  
       
       
         wherein the contact area per unit surface area of a region lying between two radially adjacent regions is either less than or greater than the contact area per unit surface area of both of said radially adjacent regions. 
       
     
     
       23. The polishing pad of  claim 22 , wherein at least one of said regionsare  is defined by at least one distinct radial boundary. 
     
     
       24. The polishing pad of  claim 22 , wherein at least two of said regions are mutually contiguous and a transition therebetween is indistinct. 
     
     
       25. The polishing pad of  claim 22 , wherein said contact surface includes a plurality of apertures therein, and said differing contact area per unit surface area is substantially a function of the number of apertures opening onto said contact surface per unit area, the size of the apertures, or a combination thereof. 
     
     
       26. A rotatable polishing pad having a central axis and a contact surface extending substantially continuously from said central axis to an outer, continuous, circular periphery for polishing a workpiece, said contact surface comprising at least two regions of differing contact area per unit surface area, wherein said contact surface includes a contact area per unit surface area varying non-linearly as a function of distance extending from said central axis to said periphery of said pad. 
     
     
       27. The polishing pad of  claim 26 , wherein said contact surface is marked by a distinct boundary lying at a given radius from said central axis between said at least two regions of differing contact area per unit surface area. 
     
     
       28. The polishing pad of  claim 26 , wherein said contact surface is defined by a gradual transition lying generally proximate a given radius from said central axis between said at least two regions of differing contact area per unit surface area. 
     
     
       29. A rotatable polishing pad having a central axis and a contact surface extending substantially continuously from said central axis to an outer, continuous, circular periphery for polishing a workpiece, wherein said contact surface provides a continuous variation in contact area per unit surface area as a non-linear function of radius from said central axis.