Patent ID: 8190285

Claim:
A computer-implemented method, comprising: polishing a substrate having a plurality of zones, a polishing rate of each zone is independently controllable by an independently variable polishing parameter; storing a target index value; measuring a sequence of spectra from each zone during polishing with an in-situ monitoring system; for each measured spectrum in the sequence of spectra for each zone, determining a best matching reference spectrum from a library of reference spectra; for each best matching reference spectrum for each zone, determining an index value to generate a sequence of index values; for each zone, fitting a first linear function to the sequence of index values; for a reference zone from the plurality of zones, determining a projected time at which the reference zone will reach the target index value based on the first linear function of the reference zone; and for at least one adjustable zone, calculating an adjustment for the polishing parameter for the adjustable zone to adjust the polishing rate of the adjustable zone such that the adjustable zone has closer to the target index at the projected time than without such adjustment, the calculation including calculating the adjustment based on a feedback error calculated for a previous substrate; after adjustment of the polishing parameter, for each zone, continuing to measure the sequence of spectra, determine a best matching reference spectrum from a library of reference spectra, and determine an index value to generate a second sequence of index values obtained after the adjustment of the polishing parameter; for the at least one adjustable zone of each substrate, fitting a second linear function to the second sequence of index values; and calculating the feedback error for a subsequent substrate for the at least one adjustable zone based on an actual slope of the second linear function and a desired slope.