Patent ID: 7494929
Filing Date: 2009-02-24
Classification: B24B

Abstract:
1. A computer implemented method for calibrating, comprising: commencing a polishing step in which a film on a substrate is polished by a chemical mechanical polisher that includes a polishing pad and an in-situ monitoring system, polishing being effected by causing the film to be in contact with the polishing pad while there is relative motion between the film and the polishing pad; during the polishing step, causing the in-situ monitoring system to monitor the film being polished through a first portion of the polishing pad; during the polishing step, generating a first electronic signal from a detector in the in-situ monitoring system with a gain for the in-situ monitoring system set to a first value, the detector sensitive to a characteristic of the film being polished; and during the polishing step, evaluating whether the first electronic signal satisfies one or more constraints and, when the first electronic signal is evaluated not to satisfy the one or more constraints, adjusting the gain for the in-situ monitoring system to a second value different from the first value so that the first electronic signal would satisfy the one or more constraints; wherein the gain was set to the first value before the first electronic signal was generated; when the first electronic signal was generated, the first portion has a current thickness that is different from a thickness that the first portion had when the gain was set; a change in thickness of the first portion of the polishing pad changes a property exhibited by the first electronic signal; and the adjusting compensates for a change in thickness of the first portion that occurred from when the gain was set to the first value and when the first electronic signal was generated.