Substrate thickness measuring during polishing

A computer program product, encoded on a computer-readable device, operable to cause a data processing apparatus to perform operations, comprising:nobtaining a first spectrum of reflected light from a first zone on a substrate and a second spectrum from a second zone on the substrate during a polishing sequence;comparing the first spectrum and the second spectrum to a spectra library to determine a first index for the first spectrum and a second index for the second spectrum;obtaining a third spectrum of reflected light from the first zone and a fourth spectrum from the second zone at a different time during the polishing sequence;comparing the third spectrum and the fourth spectrum to the library to determine a third index for the first zone and a fourth index for the second zone;determining a polishing rate at the first zone from the first index and the third index and a polishing rate at the second zone from the second index and the fourth index; andbased on the first polishing rate, the second polishing rate, a first target relative thickness for the first zone and a second target relative thickness for the second zone, determining an adjusted polishing rate for the second zone to cause the second zone to be polished to the second target relative thickness at substantially the same time as the first zone is polished to the first target relative thickness.

A computer program product, encoded on a computer-readable device, operable to cause a data processing apparatus to perform operations, comprising:ndirecting a multi-wavelength light beam onto a substrate undergoing polishing and measuring a spectrum of light reflected from the substrate;causing the light beam to move in a path across the substrate surface;extracting a sequence of spectral measurements from a signal describing the spectrum of the light and determining a radial position on the substrate for each of the spectral measurements;sorting the spectral measurements into a plurality of radial ranges according to the radial positions, including a first range and a second range;comparing the one or more spectral measurements from the first range and one or more spectral measurements from the second range to a spectral library to determine a first index for the first range and a second index for the second range;extracting a sequence of spectral measurements from the a signal describing the spectrum of the light captured at a later point in time and determining a radial position on the substrate for each of the spectral measurements;sorting the spectral measurements captured at the later point in time into the plurality of radial ranges according to the radial positions;comparing, for the spectral measurements from the later point in time, the one or more spectral measurements from the first range and one or more spectral measurements from the second range to the library to determine a third index for the first range and a fourth index for the second range;determining a polishing rate at the first range from the first index and the third index and a polishing rate at the second range from the second index and the fourth index; anddetermining a polishing endpoint for the substrate from the polishing rates of the first range or second range.