Patent ID: 8679979

Claim:
A method of controlling the chemical mechanical polishing of a substrate, comprising: polishing the substrate on a first platen using a first set of polishing parameters; obtaining a first sequence of measured spectra with an in-situ optical monitoring system, each measured spectrum from the first sequence of measured spectra being a spectrum of light reflected from a first region of the substrate; generating a first sequence of values from the first sequence of measured spectra; fitting a first function to the first sequence of values; obtaining a second sequence of measured spectra with the in-situ optical monitoring system, each measured spectrum from the second sequence of measured spectra being a spectrum of light reflected from a second region of the substrate; generating a second sequence of values from the second sequence of measured spectra; fitting a second function to the second sequence of values; determining an adjustment for at least one polishing parameter of a second set of polishing parameters based on a difference between the first function and the second function so as to reduce an expected difference between an expected first function for the first region and an expected second function for the second region in polishing of the substrate on a second platen; and polishing the substrate on the second platen using the adjustment for the at least one polishing parameter.