Control Of Overpolishing Of Multiple Substrates On the Same Platen In Chemical Mechanical Polishing

Abstract

A polishing method includes simultaneously polishing a first substrate and a second substrate on the same polishing pad, storing a default overpolishing time, determining first and second polishing endpoint times of the first and substrates with the in-situ monitoring system, determining a difference between the first and second polishing endpoint times, and determining whether the difference exceeds a threshold. If the difference is less than the threshold, then an overpolishing stop time is calculated and polishing of the first substrate and the second substrates is halted simultaneously at the overpolishing stop time. If the difference is greater than the threshold, then first and second overpolishing stop times that equal the first and second endpoint times plus the default overpolishing time are calculated, and polishing of the first and second substrates is halted at the first and second overpolishing stop times, respectively.

What is claimed is: 
     
         1 . A polishing method, comprising:
 simultaneously polishing a first substrate and a second substrate on the same polishing pad;   storing a default overpolishing time;   monitoring the first substrate and the second substrate during polishing with an in-situ monitoring system;   determining a first polishing endpoint time of the first substrate with the in-situ monitoring system;   determining a second polishing endpoint time of the second substrate with the in-situ monitoring system;   determining a difference between the first polishing endpoint time and the second endpoint time;   determining whether the difference exceeds a threshold; and   determining which of
 if the difference is less than the threshold then calculating an overpolishing stop time and halting polishing of the first substrate and the second substrates simultaneously at the overpolishing stop time, and 
 if the difference is greater than the threshold then calculating a first overpolishing stop time that equals the first endpoint time plus the default overpolishing time and calculating a second overpolishing stop time that equals the second endpoint time plus the default overpolishing time, and halting polishing of the first substrate at the first overpolishing stop time and halting polishing of the second substrate at the second overpolishing stop time. 
   
     
     
         2 . The method of  claim 1 , wherein calculating the overpolishing stop time comprises calculating an average of the first polishing endpoint time and the second polishing endpoint time. 
     
     
         3 . The method of  claim 2 , wherein calculating the overpolishing stop time comprises adding the default overpolishing time to the average. 
     
     
         4 . The method of  claim 1 , wherein the default overpolishing time is between five and twenty seconds. 
     
     
         5 . The method of  claim 4 , wherein the default overpolishing time is between ten and fifteen seconds. 
     
     
         6 . The method of  claim 1 , wherein the threshold is between two and six seconds. 
     
     
         7 . The method of  claim 1 ,
 wherein determining the first polishing endpoint time comprises   storing a first target value for the first substrate,   generating a first sequence of values for the first substrate with the in-situ monitoring system,   fitting a first function to the first sequence of values, and   determining the first polishing endpoint time by calculating a projected time at which the first substrate will reach the target value based on the first function,   and wherein determining the second polishing endpoint time comprises   storing a second target value for the second substrate,   generating a second sequence of values for the second substrate with the in-situ monitoring system,   fitting a second function to the second sequence of values; and   determining the second polishing endpoint time by calculating a projected time at which the second substrate will reach the target value based on the second function.   
     
     
         8 . The method of  claim 7 , wherein the first function and the second function are linear functions. 
     
     
         9 . The method of  claim 7 , wherein the in-situ monitoring system comprises a spectrometric optical monitoring system. 
     
     
         10 . The method of  claim 9 ,
 wherein generating the first sequence of values comprises   measuring a first sequence of spectra from the first substrate during polishing with the optical monitoring system,   for each measured spectrum in the first sequence of spectra for the first substrate, determining a best matching reference spectrum from one or more libraries of reference spectra,   for each best matching reference spectrum for the first substrate, determining an index value to generate a sequence of first index values,   and wherein generating the second sequence of values comprises   measuring a second sequence of spectra from the second substrate during polishing with the optical monitoring system,   for each measured spectrum in the second sequence of spectra for the second substrate, determining a best matching reference spectrum from the one or more libraries of reference spectra, and   for each best matching reference spectrum for the second substrate, determining an index value to generate a sequence of second index values.   
     
     
         11 . The method of  claim 7 , wherein the in-situ monitoring system comprises an eddy current monitoring system. 
     
     
         12 . The method of  claim 11 , wherein the first sequence of values and the second sequence of values comprise eddy current signal values. 
     
     
         13 . The method of  claim 1 , wherein determining the first polishing endpoint time comprises detecting clearance of a first overlying layer from a first underlying layer on the first substrate. 
     
     
         14 . The method of  claim 13 , wherein detecting clearance of a first overlying layer comprises detecting a sudden change in a signal from the in-situ monitoring system. 
     
     
         15 . The method of  claim 1 , further comprising removing the first substrate and the second substrate from the polishing pad simultaneously. 
     
     
         16 . The method of  claim 15 , further comprising rinsing the polishing pad after removing the first substrate and the second substrate. 
     
     
         17 . The method of  claim 1 , wherein the default overpolishing time comprises a first default overpolishing time for the first substrate and a second default overpolishing time for the second substrate. 
     
     
         18 . A polishing method, comprising:
 simultaneously polishing a first substrate and a second substrate on the same polishing pad;   storing a default overpolishing time;   monitoring the first substrate and the second substrate during polishing with an in-situ monitoring system;   determining a first polishing endpoint time of the first substrate with the in-situ monitoring system;   determining a second polishing endpoint time of the second substrate with the in-situ monitoring system;   determining a difference between the first polishing endpoint time and the second endpoint time;   determining that the difference exceeds a threshold; and   calculating a first overpolishing stop time that equals the first endpoint time plus the default overpolishing time and calculating a second overpolishing stop time that equals the second endpoint time plus the default overpolishing time, and halting polishing of the first substrate at the first overpolishing stop time and halting polishing of the second substrate at the second overpolishing stop time.   
     
     
         19 . A polishing method, comprising:
 simultaneously polishing a first substrate and a second substrate on the same polishing pad;   storing a default overpolishing time;   monitoring the first substrate and the second substrate during polishing with an in-situ monitoring system;   determining a first polishing endpoint time of the first substrate with the in-situ monitoring system;   determining a second polishing endpoint time of the second substrate with the in-situ monitoring system;   determining a difference between the first polishing endpoint time and the second endpoint time;   determining that the difference is less than a threshold; and   calculating an overpolishing stop time and halting polishing of the first substrate and the second substrate simultaneously at the overpolishing stop time.