Endpoint control of multiple-wafer chemical mechanical polishing

Abstract

A computer-implemented method includes polishing substrates simultaneously in a polishing apparatus. Each substrate has a polishing rate independently controllable by an independently variable polishing parameter. Measurement data that varies with the thickness of each of the substrates is acquired from each of the substrates during polishing with an in-situ monitoring system. A projected time at which each substrate will reach a target thickness is determined based on the measurement data. The polishing parameter for at least one substrate is adjusted to adjust the polishing rate of the at least one substrate such that the substrates reach the target thickness closer to the same time than without the adjustment.

1 . A computer-implemented method, comprising:
 simultaneously polishing a plurality of substrates in a polishing apparatus, wherein each substrate has a polishing rate independently controllable by an independently variable polishing parameter;   acquiring measurement data from each of the plurality of substrates during polishing with an in-situ monitoring system, wherein the measurement data varies with a thickness of each of the plurality of substrates;   determining a projected time for each substrate of the plurality of substrates at which the substrate will reach a target thickness based on the measurement data; and   adjusting the polishing parameter for at least one substrate to adjust the polishing rate of the at least one substrate such that the plurality of substrates reach the target thickness closer to the same time than without such adjustment.   
   
   
       2 . The computer-implemented method of  claim 1 , wherein determining the projected time at which each substrate will reach a target thickness includes calculating a current polishing rate. 
   
   
       3 . The computer-implemented method of  claim 2 , wherein acquiring measurement data includes obtaining a sequence of thickness measurements. 
   
   
       4 . The computer-implemented method of  claim 3 , wherein calculating a current polishing rate includes fitting a linear function to the sequence of thickness measurements. 
   
   
       5 . The computer-implemented method of  claim 4 , wherein determining the projected time includes extrapolating when the linear function will reach the target thickness. 
   
   
       6 . The computer-implemented method of  claim 1 , wherein acquiring measurement data includes acquiring measurement data with an eddy current monitoring system. 
   
   
       7 . The computer-implemented method of  claim 6 , further comprising halting polishing upon detection of a polishing endpoint with a laser monitoring system. 
   
   
       8 . The computer-implemented method of  claim 1 , wherein acquiring measurement data includes acquiring measurement data with an optical monitoring system. 
   
   
       9 . The computer-implemented method of  claim 8 , wherein acquiring measurement data includes acquiring a sequence of current spectra of reflected light from the substrate. 
   
   
       10 . The computer-implemented method of  claim 9 , wherein acquiring measurement data further comprises comparing each current spectrum from the sequence of current spectra to a plurality of reference spectra from a reference spectra library and selecting a best-match reference spectra. 
   
   
       11 . The computer-implemented method of  claim 1 , wherein the polishing parameter is a pressure in a carrier head of the polishing apparatus. 
   
   
       12 . The computer-implemented method of  claim 1 , wherein the polishing parameter is a rotation rate of a carrier head of the polishing apparatus. 
   
   
       13 . The computer-implemented method of  claim 1 , wherein the polishing parameter is a rotation rate of a platen of the polishing apparatus. 
   
   
       14 . The computer-implemented method of  claim 1 , wherein adjusting the polishing parameter includes selecting a reference substrate from the plurality of substrates and adjusting the polishing parameter of a different substrate from the plurality of substrates. 
   
   
       15 . The computer-implemented method of  claim 14 , wherein adjusting the polishing parameter of the different substrate adjusts the polishing rate of the different substrate such that the different substrate reaches the target thickness at approximately the projected time for the reference substrate. 
   
   
       16 . The computer-implemented method of  claim 14 , wherein selecting a reference substrate includes selecting a predetermined substrate. 
   
   
       17 . The computer-implemented method of  claim 14 , wherein selecting a reference substrate includes selecting a substrate from the plurality of substrates having an earliest projected time of the plurality of substrates. 
   
   
       18 . The computer-implemented method of  claim 14 , wherein selecting a reference substrate includes selecting a substrate from the plurality of substrates having a latest projected time of the plurality of substrates. 
   
   
       19 . The computer-implemented method of  claim 1 , wherein adjusting the polishing parameter includes calculating an average time from the projected time for each substrate of the plurality of substrates. 
   
   
       20 . The computer-implemented method of  claim 19 , wherein adjusting the polishing parameter includes adjusting polishing parameters of the plurality of substrates such that the plurality of substrates reach the target thickness at approximately the average time. 
   
   
       21 . The computer-implemented method of  claim 1 , wherein the plurality of substrates are polished at the same platen. 
   
   
       22 . A computer program product, tangibly embodied in a computer readable media, comprising instructions for causing a processor to:
 cause a polishing apparatus to simultaneously polish a plurality of substrates with each substrate having a polishing rate independently controllable by an independently variable polishing parameter;   receive measurement data from each of the plurality of substrates during polishing with an in-situ monitoring system, wherein the measurement data varies with a thickness of each of the plurality of substrates;   determine a projected time for each substrate of the plurality of substrates at which the substrate will reach a target thickness based on the measurement data; and   adjust the polishing parameter for at least one substrate to adjust the polishing rate of the at least one substrate such that the plurality of substrates reach the target thickness closer to the same time than without such adjustment.   
   
   
       23 . A polishing apparatus, comprising:
 a plurality of carrier heads to hold a plurality of substrates against a polishing surface, each carrier head having an independently controllable pressure on a substrate held by the carrier head;   an in-situ monitoring system to generate measurement data from each of the plurality of substrates during polishing, wherein the measurement data varies with a thickness of a substrate being measured; and   a controller configured to
 cause the polishing apparatus to simultaneously polish the plurality of substrates, 
 receive the measurement data, 
 determine a projected time for each substrate of the plurality of substrates at which the substrate will reach a target thickness based on the measurement data, and 
 adjust the pressure applied by at least one of the carrier heads to adjust the polishing rate of at least one substrate such that the plurality of substrates reach the target thickness closer to the same time than without such adjustment.