Pad-assisted electropolishing

Abstract

Pad-assisted electropolishing of the substrate is conducted by performing anodic dissolution of metal at a first portion of the substrate and simultaneously mechanically buffing a second portion of the substrate with a buffing pad. Anodic dissolution includes forming a thin liquid layer of electropolishing liquid between the anodic substrate and a cathodic electropolishing head. The location of electrical contacts between the substrate and power supply allow peripheral edge regions of the substrate to be mechanically buffed with the pad. Preferably, a substrate is further planararized using an isotropic material-removal technique. An apparatus includes an electropolishing head that is movable to a position proximate to a first portion of a substrate to form a thin gap, and a buffing pad that mechanically buffs a second portion of the substrate using minimal pressure.

1 . An apparatus for electropolishing a substrate face comprising:
 a wafer holder for holding a substrate wafer having a side edge;   an electropolishing head connected to a negative terminal of a power  5  supply, said electropolishing head capable of forming a thin gap between said electropolishing head and a first portion of a substrate face of a substrate wafer when a substrate wafer is being held in said wafer holder;   a means for providing electropolishing liquid to said first portion for making a thin liquid layer in said thin gap;   an electrical contact structure electrically connected to a positive terminal of said power supply for electrically biasing said first portion of said substrate face to generate a DC current in said electropolishing solution of said thin liquid layer in said thin gap when said substrate face comprises electrically conductive metal; and   a pad assembly for physically buffing a second portion of said substrate face.   
   
   
       2 . An apparatus for electropolishing a substrate face as in  claim 1  wherein:
 said pad assembly is capable of pressing a buffing pad against said substrate face to expel substantially said electropolishing liquid away from said second portion.   
   
   
       3 . An apparatus for electropolishing a substrate face as in  claim 1  wherein:
 said pad assembly and said second portion are substantially electrically unbiased with respect to said electropolishing liquid.   
   
   
       4 . An apparatus for electropolishing a substrate face, comprising:
 an electropolishing bath containing electropolishing liquid in a process chamber;   a wafer holder for holding a substrate wafer having a side edge, said wafer holder capable of immersing a substrate face of said substrate wafer in said electropolishing bath;   an electrode located in said electropolishing bath, said electrode being connected to a negative terminal of a power supply, and said electrode forming a space containing electropolishing liquid between said electrode and said substrate face;   an electrical contact structure electrically connected to a positive terminal of said power supply for electrically biasing a first portion of said substrate face to generate a DC current in said electropolishing liquid in said space when said substrate face comprises electrically conductive metal; and   a pad assembly located in said electropolishing bath for physically buffing a second portion of said substrate face.   
   
   
       4 . An apparatus for electropolishing a substrate face as in  claim 3  wherein said pad assembly and said second portion are substantially electrically unbiased with respect to said electropolishing liquid. 
   
   
       5 . An apparatus for electropolishing a substrate face, comprising:
 a wafer holder for holding a substrate wafer having a side edge,   a means for providing an electropolishing liquid to cover at least a first portion of said substrate face;   a means for electrically biasing said first portion positively with respect to said electropolishing liquid;   a buffing pad for physically buffing a second portion of said substrate face, a portion of said buffing pad being translatable radially outward from said side edge during said buffing to buff a periphery of said second portion contiguous to said side edge.   
   
   
       6 . An apparatus for electropolishing a substrate face, comprising:
 a wafer holder for holding a substrate wafer having a side edge,   a means for providing an electropolishing liquid to cover at least a first portion of said substrate face;   a means for electrically biasing said first portion positively with respect to said electropolishing liquid;   a buffing pad for physically buffing a second portion of said substrate face, said buffing pad being capable of reciprocating, said buffing pad having a buffing surface area that is smaller than said substrate face, said buffing surface being relatively large proximate to said side edge and relatively small distal from said side edge.