CMP pad platen with viewport

Abstract

A viewport used by an end point detection system for chemical mechanical polishing (CMP) is attached to a platen that holds a CMP pad. During a CMP operation to polish a semiconductor wafer, the viewport is aligned with a hole in the CMP pad to permit optical access to the wafer by the end point detection system. The viewport shields optical components of the end point detection system from byproducts of the polishing, while also permitting the use of optical techniques to determine how much material has been polished from the surface of the wafer during the CMP operation.

I claim:  
     
         1 . An apparatus, comprising: 
 a platen to hold a pad to be used in a chemical mechanical polishing operation on a wafer; and    a viewport attached to the platen to permit optical measurement of the wafer through the pad during the chemical mechanical polishing operation.    
     
     
         2 . The apparatus of  claim 1 , wherein: 
 the viewport is to fit within an opening through the pad.    
     
     
         3 . The apparatus of  claim 1 , wherein: 
 the viewport is removably attached to the platen.    
     
     
         4 . The apparatus of  claim 1 , wherein: 
 the viewport is attached to the platen with a threaded fastener.    
     
     
         5 . The apparatus of  claim 1 , wherein: 
 the viewport is attached to the platen with an adhesive.    
     
     
         6 . The apparatus of  claim 1 , further comprising: 
 an O-ring seal between the platen and the viewport.    
     
     
         7 . The apparatus of  claim 1 , wherein: 
 the viewport has a compressibility substantially equivalent to a compressibility of the pad.    
     
     
         8 . The apparatus of  claim 1 , wherein: 
 the viewport includes a material that is at least partially transparent at a wavelength of light used in the optical measurement.    
     
     
         9 . A system, comprising: 
 a pad to polish a wafer in a chemical mechanical polishing operation, the pad having an opening therethrough;    a platen coupled to the pad;    a viewport attached to the platen and disposed at least partially within the opening; and    a light emitter coupled to the platen to direct light to the wafer through the viewport and through the opening during the chemical mechanical polishing operation.    
     
     
         10 . The system of  claim 9 , wherein: 
 the light emitter is a laser light emitter.    
     
     
         11 . The system of  claim 9 , wherein: 
 the viewport is at least partially transparent to the light.    
     
     
         12 . The system of  claim 9 , wherein: 
 the viewport is removably attached to the platen.    
     
     
         13 . The system of  claim 9 , wherein: 
 the viewport is attached to the platen with a threaded fastener.    
     
     
         14 . A method, comprising: 
 polishing a wafer with a pad coupled to a platen during a chemical mechanical polishing operation; and    directing light to the wafer through a viewport attached to the platen to determine a thickness of a surface material on the wafer.    
     
     
         15 . The method of  claim 14 , wherein: 
 said directing includes directing the light through an opening in the pad.    
     
     
         16 . The method of  claim 14 , wherein: 
 said directing includes directing the light through an opening in the pad in which the viewport is disposed.    
     
     
         17 . The method of  claim 14 , wherein: 
 said polishing includes at least one of removing a first predetermined thickness of surface material and removing the surface material until a second predetermined thickness of surface material remains.    
     
     
         18 . A machine-readable medium that provides instructions, which when executed by a set of one or more processors, cause said set of processors to perform operations comprising: 
 directing light to a wafer through a viewport attached to a platen to determine a thickness of a surface material on the wafer as the surface material is being polished by a pad in a chemical mechanical polishing operation;    and    determining when to end the chemical mechanical polishing operation based on the thickness of the surface material.    
     
     
         19 . The medium of  claim 18 , wherein: 
 said directing includes directing the light through an opening in the pad in which the viewport is disposed.    
     
     
         20 . The medium of  claim 18 , wherein: 
 said directing includes directing the light through the viewport attached to the platen with a mechanical fastener.