Spectra based endpointing for chemical mechanical polishing

A computer program product encoded in a non-transitory machine-readable medium, the product comprising instructions operable to cause a processor to:

• store a reference spectrum, the reference spectrum representing a spectrum resulting from reflection of white light from a reference substrate;
• receive a plurality of measured spectra from an optical sensor for each sweep of a plurality of sweeps of the optical sensor across a substrate undergoing polishing, each measured spectrum of the plurality of measured spectra for each sweep being a spectrum resulting from reflection of white light from the substrate undergoing polishing;
• for each sweep of the plurality of sweeps, determine a difference between each measured spectrum of the plurality of measured spectra obtained in the sweep and the reference spectrum to generate a plurality of differences for each sweep;
• for each sweep of the plurality of sweeps, select a difference from the plurality of differences for the sweep based on a comparison of magnitudes of the plurality of differences, thus generating a sequence of selected differences;
• determine a polishing endpoint based on the sequence of selected differences;
• and
• cause polishing of the substrate to halt at the polishing endpoint.

A computer program product encoded a non-transitory machine-readable medium, the product comprising instructions operable to cause a processor to:

• store a plurality of reference spectra, each reference spectrum of the plurality of reference spectra representing a spectrum resulting from reflection of white light from a reference substrate;
• receive a measured spectrum from an optical sensor for each sweep of a plurality of sweeps of the optical sensor across a substrate undergoing polishing, the measured spectrum being a spectrum resulting from reflection of white light from the substrate undergoing polishing;
• for each sweep of the plurality of sweeps, determine a difference between the measured spectrum and each reference spectrum of the plurality of reference spectra to generate a plurality of differences for each sweep;
• for each sweep of the plurality of sweeps, select a difference from the plurality of differences for the sweep based on a comparison of magnitudes of the plurality of differences, thus generating a sequence of selected differences;
• determine a polishing endpoint based on the sequence of selected differences;
• and
• cause polishing of the substrate to halt at the polishing endpoint.