Patent ID: 8292693

Claim:
A method of controlling the chemical mechanical polishing of a substrate, comprising: polishing a 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 linear 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 linear function to the second sequence of values; determining a difference between the first linear function and the second linear function; adjusting at least one polishing parameter of the first set of polishing parameters based on the difference so as to reduce an expected difference between an expected first linear function for the first region and an expected second linear function for the second region during polishing of a second substrate on the first platen; and polishing the second substrate on the first platen using the adjusted polishing parameter.