Patent ID: 7406394

Claim:
A computer program product, tangibly stored on machine readable medium, the product comprising instructions operable to cause a processor to: select two or more reference spectra, each reference spectrum representing a spectrum of light reflected from a film of interest on a first substrate when illuminated with white light; obtain two or more current spectra, each current spectrum being a spectrum of light reflected from a film of interest on a second substrate when illuminated with white light, the film of interest on the second substrate being subject to a polishing step, and the two or more current spectra being obtained from a single platen rotation of the polishing step; calculate differences between the current spectra and the reference spectra to generate a plurality of differences for the single platen rotation; select a smallest difference from the plurality of differences; and determine, for the second substrate, whether an endpoint of the polishing step has been achieved, the determining being based on the smallest difference.