Patent ID: 8088298

Claim:
A computer implemented method comprising: selecting two or more reference spectra, each reference spectrum of the two or more reference spectra being a spectrum of white light reflected from a film of interest that is on a first substrate and that has a thickness greater than a target thickness, the reference spectra being selected for particular spectra based endpoint determination logic so that the target thickness is achieved when endpoint is called by applying the particular spectra based endpoint logic; obtaining two or more current spectra, each current spectrum of the two or more current spectra being a spectrum of white light reflected from a film of interest that is on a second substrate and that has a current thickness that is greater than the target thickness, the film of interest on the second substrate being subject to a polishing step; and determining, for the second substrate, whether an endpoint of the polishing step has been achieved, the determining being based on the reference spectra and the current spectra.