Carrier head acoustic monitoring with sensor in platen

Abstract

A chemical mechanical polishing apparatus has a platen to support a polishing pad, the platen having a recess, a carrier head to hold a surface of a substrate against the polishing pad and comprising a retaining ring to retain the substrate below the carrier head, a motor to generate relative motion between the platen and the carrier head so as to polish the substrate, an in-situ acoustic monitoring system comprising an acoustic sensor arranged in the recess that receives acoustic energy from friction between the substrate and the polishing pad and from friction between the retaining ring and the polishing pad, and a controller configured to generate a value for a carrier head status parameter based on received acoustic signals from the in-situ acoustic monitoring system, and change or polishing parameter or generate an alert based on the carrier head status parameter.

1 . A chemical mechanical polishing apparatus, comprising:
 a platen to support a polishing pad, the platen having a recess;   a carrier head to hold a surface of a substrate against the polishing pad, wherein the carrier head comprising a retaining ring to retain the substrate below the carrier head;   a motor to generate relative motion between the platen and the carrier head so as to polish the substrate;   an in-situ acoustic monitoring system comprising an acoustic sensor arranged in the recess that receives acoustic energy from friction between the substrate and the polishing pad, and from friction between the retaining ring and the polishing pad; and   a controller configured to
 generate a value for a carrier head status parameter based on received acoustic signals from the in-situ acoustic monitoring system, and 
 change or polishing parameter or generate an alert based on the carrier head status parameter. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the polishing parameter comprises one or more of an amount of gimbaling of the carrier head, whether a chamber in the carrier head is properly pressurized, the presence of a gas bubble between the substrate and the carrier head, or whether the substrate is chucked to the carrier head. 
     
     
         3 . The apparatus of  claim 1 , wherein the acoustic sensor is attached to a bottom surface of the polishing pad. 
     
     
         4 . The apparatus of  claim 1 , wherein the polishing pad includes an acoustic window, and the acoustic sensor contacts a bottom surface of the acoustic window. 
     
     
         5 . The apparatus of  claim 1 , wherein the controller is further configured to determine a difference between at least two different portions of the acoustic signal. 
     
     
         6 . The apparatus of  claim 5 , wherein the controller is further configured to generate an alert based on the difference exceeding a threshold. 
     
     
         7 . The apparatus of  claim 6 , wherein the controller is further configured to determine a difference between the acoustic signal and a historical acoustic signal from a previous substrate, wherein the historical acoustic signal is stored on the controller. 
     
     
         8 . The apparatus of  claim 1 , wherein the controller is further configured to determine a difference in the acoustic signal from a first portion and a second portion of the surface of the ring assembly. 
     
     
         9 . A method of polishing, comprising:
 holding a substrate against a polishing surface of a polishing pad with a carrier head;   generating relative motion between the substrate and polishing pad such that an in-situ acoustic monitoring system passes beneath the carrier head;   monitoring the carrier head with an in-situ acoustic monitoring system oriented beneath the polishing pad to generate a signal comprising a sequence of segments;   identifying a first segment from the sequence of segments corresponding to the sensor being beneath a first portion of the carrier head;   identifying a second segment from the sequence of segments corresponding to the sensor being beneath a second portion of the carrier head;   determining a difference between the first segment and the second segment; and   changing a polishing parameter or generating an alert based on the determined difference.   
     
     
         10 . The method of  claim 9 , wherein the first and second portions of the carrier head are a first and second portion of a ring assembly of the carrier head. 
     
     
         11 . The method of  claim 9 , wherein the polishing parameter is a pressure of the carrier head. 
     
     
         12 . The method of  claim 9 , further comprising detecting the substrate leaving the polishing surface of the polishing pad based on the signal. 
     
     
         13 . The method of  claim 9 , further comprising detecting a presence of a bubble based on the signal. 
     
     
         14 . A computer program product, comprising a non-transitory computer-readable medium having instructions to cause one or more computers to:
 holding a substrate against a polishing surface of a polishing pad with a carrier head;   generating relative motion between the substrate and polishing pad such that the in-situ monitoring system passes beneath the carrier head;   monitoring the carrier head with an in-situ acoustic monitoring system oriented beneath the polishing pad to generate a signal comprising a sequence of segments;   identifying a first segment from the sequence of segments corresponding to the sensor being beneath a first portion of the carrier head;   identifying a second segment from the sequence of segments corresponding to the sensor being beneath a second portion of the carrier head;   determining a difference between the first segment and the second segment; and   changing a polishing parameter or generating an alert based on the determined difference.   
     
     
         15 . The computer program product of  claim 14 , wherein the first and second portions of the carrier head are a first and second portion of a retaining ring of the carrier head. 
     
     
         16 . The computer program product of  claim 14 , wherein the polishing parameter is a pressure of the carrier head. 
     
     
         17 . The computer program product of  claim 14 , further comprising detecting the substrate leaving the polishing surface of the polishing pad based on the signal. 
     
     
         18 . The computer program product of  claim 14 , further comprising detecting a presence of a bubble based on the signal