Apparatus and Method for In-Situ Endpoint Detection for Chemical Mechanical Polishing Operations

Abstract

An apparatus and method of chemical mechanical polishing (CMP) of a wafer employing a device for determining, in-situ, during the CMP process, an endpoint where the process is to be terminated. This device includes a laser interferometer capable of generating a laser beam directed towards the wafer and detecting light reflected from the wafer, and a window disposed adjacent to a hole formed through a platen. The window provides a pathway for the laser beam during at least part of the time the wafer overlies the window.

1 . A method for chemical mechanical polishing (CMP) a wafer on a polishing system, the method comprising the steps of: 
 supporting a polishing pad over a platen, the polishing pad having a polishing surface, a bottom surface and a window from the polishing surface to the bottom surface;    holding the wafer on a polishing head against the polishing surface;    supplying a polishing liquid to the polishing surface;    polishing a surface layer on the wafer to remove an increasing amount thereof;    during at least a part of the polishing operation, directing a light beam through a solid light transmissive element so that the light beam impinges the wafer and reflects back through the light-transmitting material to an optical detector, wherein the light-transmitting element is secured to the polishing pad so as to prevent the polishing liquid from passing through the polishing pad, the solid light transmissive element being more transmissive to light than the polishing surface; and    determining a point to end polishing based on a signal from the detector.    
   
   
       2 . The method of  claim 1 , further comprising rotating the platen and the polishing pad.  
   
   
       3 . The method of  claim 1 , wherein the light transmissive element has a top surface substantially flush with the polishing surface.  
   
   
       4 . The method of  claim 1 , wherein the polishing pad includes a polishing layer including the light transmissive element and a backing layer having an aperture aligned with the light transmissive element.  
   
   
       5 . A method of endpoint detection during polishing of a wafer using a polishing pad, said method comprising, 
 polishing the wafer with a polishing pad that has a polishing surface, a bottom surface and a window from the polishing surface to the bottom surface;    transmitting detection light through a solid light transmissive element secured to the polishing pad to a surface of the wafer being polished, wherein the solid light transmissive element is secured so as to prevent the polishing liquid from passing through the polishing pad, the solid light transmissive element being more transmissive to light than the polishing surface; and    receiving a reflection of said light reflecting off of said wafer surface and passing through said transparent portion of said polishing pad.    
   
   
       6 . The method of  claim 5 , further comprising rotating the platen and the polishing pad.  
   
   
       7 . The method of  claim 5 , wherein the light transmissive element has a top surface substantially flush with the polishing surface.  
   
   
       8 . The method of  claim 5 , wherein the polishing pad includes a polishing layer including the light transmissive element and a backing layer having an aperture aligned with the light transmissive element.