Patent ID: 8874250

Claim:
A method of controlling a chemical mechanical polishing operation, comprising: polishing a substrate, wherein polishing the substrate comprises rotating a platen; storing a library having a plurality of reference spectra, each reference spectrum of the plurality of reference spectra having a stored associated value, and wherein each stored associated value is a number of rotations of the platen at which the reference spectrum with the stored associated value is expected to be observed from the substrate undergoing polishing; measuring a sequence of spectra from the substrate in-situ during polishing to obtain measured spectra; for each measured spectrum of the sequence of spectra, finding a best matching reference spectrum from the plurality of reference spectra to generate a sequence of best matching reference spectra; determining the stored associated value for each best matching spectrum from the sequence of best matching reference spectra to generate a sequence of values; fitting a function to the sequence of values; and at least one of adjusting a polishing rate or halting polishing based on the function.