Cmp system having an eddy current sensor of reduced height

Abstract

By providing an eddy current sensor element in a polishing tool at a reduced height level in combination with a corresponding optical endpoint detection system, standard polishing pads may be used, thereby enhancing the lifetime of the polishing pad and increasing tool utilization.

1 . A polishing tool, comprising:
 a polishing platen having a surface configured to receive a sub pad and a top pad, said top pad having a polishing surface and a lower surface in contact with said sub pad, said sub pad having a first opening covered by a portion of said top pad; and   an inductive sensor positioned in said first opening, said inductive sensor having a sensing surface that is positioned at a height level that is less than a height level of said lower surface of said top pad.   
     
     
         2 . The polishing tool of  claim 1 , wherein said top pad comprises a substantially transparent window. 
     
     
         3 . The polishing tool of  claim 2 , wherein said window is positioned above said first opening in said sub pad. 
     
     
         4 . The polishing tool of  claim 2 , wherein said window is positioned above a second opening formed in said sub pad. 
     
     
         5 . The polishing tool of  claim 1 , wherein said sensing surface is substantially flush with a surface of said sub pad that is in contact with said top pad. 
     
     
         6 . The polishing tool of  claim 1 , further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material above said top pad. 
     
     
         7 . The polishing tool of  claim 2 , further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said top pad. 
     
     
         8 . The polishing tool of  claim 1 , wherein said top pad comprises a magnetic material at a portion located above said sensing surface. 
     
     
         9 . The polishing tool of  claim 1 , further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface. 
     
     
         10 . The polishing tool of  claim 1 , wherein a thickness of said top pad is substantially uniform across said polishing platen. 
     
     
         11 . A polishing tool, comprising:
 a polishing platen having a surface configured to receive a polishing pad having a substantially uniform thickness; and   an inductive sensor comprising a sensing surface positioned to extend from said surface of said platen and to support said polishing pad.   
     
     
         12 . The polishing tool of  claim 11 , further comprising a sub pad provided below said polishing pad, said sub pad having at least one opening for receiving said sensing surface. 
     
     
         13 . The polishing tool of  claim 11 , wherein said sensing surface is covered by a window portion of said polishing pad. 
     
     
         14 . The polishing tool of  claim 11 , further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material provided above said polishing pad. 
     
     
         15 . The polishing tool of  claim 13 , further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said polishing pad. 
     
     
         16 . The polishing tool of  claim 11 , wherein said polishing pad comprises a magnetic material at a portion supported by said sensing surface. 
     
     
         17 . The polishing tool of  claim 11 , further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface. 
     
     
         18 . A polishing pad for a polishing tool, comprising:
 a base material configured to be mounted on a polishing platen, said base material comprising laterally restricted areas having included therein a magnetic material; and   a surface for polishing a substrate.   
     
     
         19 . The polishing pad of  claim 18 , wherein said magnetic material is comprised of ferrite particles.