Smoothing pad for bare semiconductor wafers

Abstract

One embodiment of the present invention is a smoothing pad for bare semiconductor wafers the smoothing pad for bare semiconductor wafers. The smoothing pad comprises a smoothing body having a closed-cell thermoplastic foam comprising an ethylene vinyl acetate block copolymer comprising a vinyl acetate content ranging from about 1 to about 18 wt %. The smoothing body is substantially free of particles having an average size of greater than about 1 micron. Other aspects of the invention comprise a method of preparing a bare semiconductor wafer and a method of manufacturing a pad for smoothing bare semiconductor wafers.

1 . A smoothing pad for bare semiconductor wafers, comprising: 
 a smoothing body including: 
 a closed-cell thermoplastic foam comprising an ethylene vinyl acetate block copolymer having a vinyl acetate content ranging from about 1 to about 18 wt %, 
 wherein said smoothing body is substantially free of particles having an average size of greater than about 1 micron.  
 
   
     
     
         2 . The pad as recited in  claim 1 , wherein a surface of said smoothing body is free of grooves.  
     
     
         3 . The pad as recited in  claim 1 , wherein said smoothing body is substantially free of particles having an average size of about 0.3 microns or greater.  
     
     
         4 . The pad as recited in  claim 1 , wherein an interior of said closed-cell thermoplastic foam smoothing body comprise cells having an average size ranging from about 50 to about 300 microns, and a smoothing surface of said closed-cell thermoplastic comprises concave cells having said average size.  
     
     
         5 . The pad as recited in  claim 1 , wherein said ethylene vinyl acetate block copolymer has a vinyl acetate content ranging from about 6 to about 12 wt %.  
     
     
         6 . The pad as recited in  claim 1 , wherein said ethylene vinyl acetate block copolymer has a melt index ranging from 0.2 to about 25 dg/min (ASTM D1238).  
     
     
         7 . The pad as recited in  claim 1 , wherein said closed-cell thermoplastic foam smoothing body has a hardness ranging from about 20 to about 75 Shore A.  
     
     
         8 . The pad as recited in  claim 1 , wherein said closed-cell thermoplastic foam smoothing body has a gel fraction ranging from about 60 to about 90 percent.  
     
     
         9 . The pad as recited in  claim 1 , wherein said thermoplastic foam smoothing body has a density ranging from about 0.1 to about 0.4 g/cm 3 .  
     
     
         10 . The pad as recited in  claim 1 , further including a backing film coupled to said smoothing body by a thermal weld.  
     
     
         11 . The pad as recited in  claim 10 , wherein said backing film has a thickness of about 2 mil or less.  
     
     
         12 . The pad as recited in  claim 10 , wherein said backing film comprises a condensed ethylene vinyl acetate polymer.  
     
     
         13 . The pad as recited in  claim 1 , wherein a ratio of a thickness of said smoothing body to a thickness of a backing film coupled to said smoothing body is about 35:1 or greater.  
     
     
         14 . A method of preparing a bare semiconductor wafer, comprising: 
 smoothing a bare semiconductor wafer including: 
 situating a smoothing pad adjacent to a surface of said bare semiconductor wafer; and  
 moving said smoothing pad relative to said bare semiconductor wafer until said surface has a roughness of less than or equal to about 20 Angstroms, wherein said smoothing pad includes a smoothing body having: 
 a closed-cell thermoplastic foam composed of an ethylene vinyl acetate block copolymer having a vinyl acetate content ranging from about 1 to about 18 wt % and said smoothing body is substantially free of particles having an average size of greater than about 1 micron.  
 
   
     
     
         15 . The method as recited in  claim 14 , wherein said surface roughness after said smoothing ranges from about 2 to about 20 Angstroms.  
     
     
         16 . The method as recited in  claim 14 , wherein less than about 1.5 microns/min of said bare semiconductor wafer is removed during said smoothing and a planarity of said bare semiconductor wafer after said smoothing has a TIR of about 0.15 microns.  
     
     
         17 . The method as recited in  claim 14 , further comprising polishing said bare semiconductor wafer, including: 
 situating a polishing pad adjacent to said surface of said bare semiconductor wafer; and    moving said polishing pad relative to said bare semiconductor, 
 wherein said polishing pad is different than said smoothing pad.  
   
     
     
         18 . A method of manufacturing a pad for smoothing bare semiconductor wafers, comprising: 
 placing an ethylene vinyl acetate block copolymer and a foaming agent into a container, wherein said ethylene vinyl acetate block copolymer having a vinyl acetate content ranging from about 1 to about 18 wt % and said ethylene vinyl acetate block copolymer is substantially free of particles having an average size of about 1 micron or greater;    mixing said ethylene vinyl acetate block copolymer and said foaming agent together; and then forming closed cells throughout said ethylene vinyl acetate block copolymer to thereby produce a closed-cell thermoplastic smoothing body.    
     
     
         19 . The method as recited in  claim 18 , further comprising thermally welding said closed-cell thermoplastic foam smoothing body to a backing film.  
     
     
         20 . The method as recited in  claim 19 , wherein said backing film is composed of a non-foamed ethylene vinyl acetate polymer and has a thickness of about 2 mil or less.