Multifunctional endpoint detection window

Abstract

A polishing pad for chemical mechanical polishing includes a top window material, which is transparent to light, which forms a seal with polishing material, with subpad material, or both; a bottom window material, having a void space inward from a peripheral surface if the bottom window material. The void space is aligned to allow light passing through the top window portion to and the void space enabling optical end-point detection. Vibrational signals can be transmitted through the top window material or the polishing material and through the bottom window material enabling acoustic end-point detection.

What is claimed is: 
     
         1 . A polishing pad for chemical mechanical polishing comprising:
 a polishing layer having a polishing surface and a polishing layer interface surface opposite the polishing surface, the polishing layer comprising a polishing material,   a subpad layer having a subpad interface surface adjacent to the polishing layer interface surface and a bottom surface opposite the subpad interface surface, the subpad layer comprising a subpad material,   a top window material, which is transparent to light, the top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, wherein the top window peripheral surface forms a seal with the polishing material, with the subpad interface surface, or both,   a bottom window portion, wherein the bottom window portion comprises a bottom window material having a bottom window interface surface adjacent the top window interface surface or the polishing layer interface surface, a bottom window peripheral surface, a bottom window bottom surface and a void space inward from the bottom window peripheral surface,   wherein the void space is aligned to allow light passing through the top window portion to pass through the polishing pad via the void space enabling optical end-point detection and vibrational signals can be transmitted through the top window material or the polishing material and through the bottom window material enabling acoustic end-point detection.   
     
     
         2 . The polishing pad of  claim 1  wherein the top window polishing face surface is recessed below the polishing surface. 
     
     
         3 . The polishing pad of  claim 1  wherein the pad comprises an encapsulating layer adjacent to the bottom window bottom surface. 
     
     
         4 . The polishing pad of  claim 1  wherein there is a gap between the bottom window peripheral surface and the subpad material. 
     
     
         5 . The polishing pad of  claim 3  wherein the encapsulating layer extends across the subpad bottom surface. 
     
     
         6 . The polishing pad of  claim 3  wherein the encapsulating layer defines a bottom surface coplanar with the subpad bottom surface. 
     
     
         7 . The polishing pad of  claim 3  wherein the encapsulating layer is transparent to light and encloses the void. 
     
     
         8 . The polishing pad of  claim 1  wherein the bottom window material is elastomeric. 
     
     
         9 . The polishing pad of  claim 1  wherein the subpad material is different from the bottom window material. 
     
     
         10 . A method of polishing comprising:
 providing a substrate to be polished;   providing the polishing pad as in  claim 1 ;   providing a slurry on the polishing pad;   polishing by moving the substrate relative to the polishing pad; and   monitoring polishing by (a) transmitting a light wave through the top window material and the void and detecting the light wave reflected from the substrate (b) transmitting a vibrational signal through the top window material, the polishing layer material or both and through the bottom window material, or both (a) and (b).