Coupling of acoustic sensor for chemical mechanical polishing

Abstract

A chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate, an in-situ acoustic monitoring system comprising an acoustic window having a top surface to contact the substrate, and a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.

What is claimed is: 
     
         1 . A chemical mechanical polishing apparatus, comprising:
 a platen;   a polishing pad supported on the platen, the polishing pad having a polishing layer;   a carrier head to hold a surface of a substrate against the polishing pad;   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;   an in-situ acoustic monitoring system comprising an acoustic window in the polishing pad and an acoustic sensor acoustically coupled to the acoustic window, wherein the acoustic window has a lower acoustic attenuation than the polishing layer, and wherein the acoustic window has a top surface that is coplanar with the polishing surface to contact the substrate; and   a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.   
     
     
         2 . The apparatus of  claim 1 , wherein a bottom surface of the acoustic window is coplanar with a lower surface of the polishing layer. 
     
     
         3 . The apparatus of  claim 1 , wherein the polishing pad has a backing layer below the polishing pad. 
     
     
         4 . The apparatus of  claim 3 , wherein the bottom surface of the acoustic window is coplanar with a top surface of the backing layer. 
     
     
         5 . The apparatus of  claim 4 , wherein an aperture is formed through the backing layer. 
     
     
         6 . The apparatus of  claim 5 , wherein the sensor is at least partially positioned in the aperture to contact the bottom surface of the acoustic window. 
     
     
         7 . The apparatus of  claim 5 , further including an acoustically transmissive layer positioned in an aperture through the backing layer between the acoustic sensor and the acoustic window, wherein the acoustically transmissive layer has a lower acoustic attenuation than the backing layer. 
     
     
         8 . The apparatus of  claim 7 , wherein a bottom surface of the acoustically transmissive layer is coplanar with a bottom surface of the polishing pad. 
     
     
         9 . The apparatus of  claim 1 , wherein an indentation is formed in an underside of the polishing layer to form a thin portion of the polishing layer, the acoustic window is positioned in the thin portion of the polishing layer, and the sensor is at least partially positioned in the indentation. 
     
     
         10 . The apparatus of  claim 1 , wherein the acoustic window is a non-porous material. 
     
     
         11 . The apparatus of  claim 10 , wherein the polishing layer is porous and the acoustic window is solid. 
     
     
         12 . The apparatus of  claim 1 , wherein a compressibility of the acoustic window is within 20% of a compressibility of the polishing layer. 
     
     
         13 . The apparatus of  claim 1 , wherein the acoustic sensor is adhesively attached to the acoustic window to receive acoustic signals from the substrate. 
     
     
         14 . The apparatus of  claim 1 , further including an acoustically transmissive layer arranged between the acoustic sensor and the acoustic window. 
     
     
         15 . The apparatus of  claim 14 , wherein the acoustically transmissive layer is adhesively attached to the acoustic window. 
     
     
         16 . The apparatus of  claim 15 , wherein the acoustic sensor is adhesively attached to the acoustically transmissive layer. 
     
     
         17 . The apparatus of  claim 1 , wherein the in-situ acoustic monitoring system comprises a housing to support the acoustic sensor, and a spring arranged to press the housing and the acoustic sensor against a portion of the polishing layer. 
     
     
         18 . The apparatus of  claim 17 , wherein the spring comprises a strong spring or a long-travel spring. 
     
     
         19 . The apparatus of  claim 1 , wherein the controller is configured to perform frequency domain analysis to determine changes in relative power of spectral frequencies. 
     
     
         20 . A chemical mechanical polishing apparatus, comprising:
 a platen;   a polishing pad supported on the platen;   a carrier head to hold a surface of a substrate against the polishing pad;   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;   an in-situ acoustic monitoring system comprising an acoustic sensor that receives acoustic signals from the surface of the substrate, the acoustic sensor adhesively attached to a bottom surface of the polishing pad; and   a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.