Method for forming interconnects on thin wafers

Abstract

A method of forming a semiconductor interconnect including, in the order recited: (a) providing a semiconductor wafer; (b) forming bonding pads in a terminal wiring level on the frontside of the wafer; (c) reducing the thickness of the wafer; (d) forming solder bumps on the bonding pads; and (e) dicing the wafer into bumped semiconductor chips.

1 . A fixture for holding a wafer and an evaporative mask comprising: 
 a bottom ring having a inner periphery and an outer periphery, said bottom ring having a raised inner lip formed along said inner periphery and a raised outer lip formed along said outer periphery, the height of said inner lip above a surface of said bottom ring being greater than a height of said outer lip above said surface of said bottom ring;    a shim having a inner and an outer periphery, the outer periphery of said shim fitting inside and in proximity to said outer lip of said bottom ring, a bottom surface of said shim proximate to said inner periphery of said shim contacting an upper surface of said inner lip of said bottom ring; and    a top ring having an inner periphery and an outer periphery, said top ring having a lower raised lip formed along said inner periphery of said bottom ring and extending below a bottom surface of said top ring.    
   
   
       2 . The fixture of  claim 1 , wherein said bottom ring and said top ring are adapted to press a bottom surface of said wafer against an upper surface of said shim and to press a top surface of said wafer against a bottom surface of said evaporative mask and to press a top surface of said evaporative mask proximate to said periphery of said evaporative mask against a lower surface of said lower raised lip of said top ring.  
   
   
       3 . The fixture of  claim 1 , wherein the combined thicknesses of said wafer and said shim are substantially equal to a thickness of a thicker wafer, said fixture designed to hold said thicker wafer without said shim being present.  
   
   
       4 . The fixture of  claim 1 , wherein said shim has thickness such that said wafer is bowed substantially a same amount as a thicker wafer would be bowed without said shim being present, said fixture designed to hold said thicker wafer.  
   
   
       5 . A fixture, comprising: 
 a bottom ring having opposite top and bottom surfaces and inner and outer raised lips on said top surface;    a shim having a circular opening and opposite top and bottom surfaces;    a top ring having opposite top and bottom surface surfaces; and    said bottom ring and said top ring adapted to press said bottom surface of said shim adjacent to said circular opening against said inner raised lip, to press a bottom surface of a wafer against said upper surface of said shim, to press a top surface of said wafer against a bottom surface of a mask and to press a top surface of said mask proximate to a periphery of said mask against said lower surface of said top ring.    
   
   
       6 . The fixture of  claim 5 , wherein said shim, said top ring and said bottom ring are adapted to impart a bow to said wafer and said mask, a central part of said wafer and a central part of said mask bowed away from said bottom ring and peripheral portions of said wafer and said mask bowed toward said bottom ring.  
   
   
       7 . The fixture of  claim 5 , wherein the combined thicknesses of said wafer and said shim are substantially equal to a thickness of a thicker wafer said fixture is designed to hold without said shim being present.  
   
   
       8 . The fixture of  claim 5 , wherein said shim has thickness such that said wafer is bowed substantially a same amount as a thicker wafer would be bowed without said shim being present, said fixture designed to hold said thicker wafer.  
   
   
       9 . The fixture of  claim 5 , wherein said inner raised lip extends a first distance above said top surface of said bottom ring, said outer raised lip extends a second distance above said top surface of said bottom ring, said first distance is greater than said second distance.  
   
   
       10 . A fixture, comprising: 
 a bottom ring having a inner periphery and an outer periphery, said bottom ring having a raised inner lip formed along said inner periphery and a raised outer lip formed along said outer periphery;    a shim having a inner and an outer periphery, the outer periphery of said shim fitting inside and in proximity to said outer lip of said bottom ring, a bottom surface of said shim proximate to said inner periphery of said shim contacting an upper surface of said inner lip of said bottom ring; and    a top ring having an inner periphery and an outer periphery, said top ring having a lower raised lip formed along said inner periphery of said bottom ring and extending below a bottom surface of said top ring.    
   
   
       11 . The fixture of  claim 10 , wherein the height of said inner lip above a surface of said bottom ring being greater than a height of said outer lip above said surface of said bottom ring.  
   
   
       12 . The fixture of  claim 11 , wherein said height of said inner lip is about 0.080 inches and said height of said outer lip is about 0.073 inches.  
   
   
       13 . The fixture of  claim 10 , wherein said bottom ring includes openings extending between said surface and an opposite surface of said bottom ring, said opening located between said inner and outer lips.  
   
   
       14 . The fixture of  claim 10 , wherein a thickness of said shim is substantially equal to a difference between a thickness of said wafer and a thickness of a thicker wafer after said thicker wafer has been thinned, said fixture designed to hold said thicker wafer.