Optical detection of planarization, breakthrough and end-point in membrane-mediated electropolishing of metal layers

Abstract

Methods and apparatus for monitoring in situ the progress of planarization and/or removal of a thin metal layer from a substrate during membrane-mediated electropolishing processes are provided.

1 . An apparatus for use in membrane-mediated electropolishing a metal-coated workpiece comprising:
 A. a cathode half-cell comprising:
 1) a fully or partially enclosed volume, cavity or vessel; 
 2) a charge-selective ion-conducting membrane having an internal surface and an external surface, wherein the membrane forms a surface of the enclosed volume, cavity or vessel; 
 3) an electrolyte composition which at least partially fills the enclosed volume, cavity or vessel, wherein at least a portion of the internal surface of the membrane contacts the electrolyte composition and at least a portion of the external surface of the membrane contacts the work-piece during electropolishing; and 
 4) an electrode in contact with the electrolyte composition; and 
   B. an optical detection system comprising:
 1) a light source for illuminating the workpiece; and 
 2) a means for detecting light that is reflected from the workpiece. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the means for detecting light that is reflected from the workpiece is located within the enclosed volume of the cathode half-cell and the membrane and electrolyte are optically transparent. 
     
     
         3 . The apparatus of  claim 1 , wherein the means for detecting light that is reflected from the workpiece comprises an optical fiber and a photovoltaic transducer. 
     
     
         4 . The apparatus of  claim 3 , wherein the optical fiber is bifurcated. 
     
     
         5 . The apparatus of  claim 1 , wherein the membrane comprises a perfluorosulfonate ionomer. 
     
     
         6 . A process comprising:
 A. providing a light source for illuminating a workpiece being electropolished by MMEP;   B. illuminating the workpiece with light from the light source;   C. detecting light reflected from the workpiece; and   D. analyzing the reflected light to determine the topography of the workpiece.