Patent ID: 6878036

Claim:
A chemical mechanical polishing apparatus, comprising: a polishing pad with a polishing surface; a carrier to hold a substrate against the polishing surface; a motor coupled to at least one of the polishing pad and carrier head for generating relative motion therebetween; and a conductive layer thickness monitoring system including at least one inductor, a current source that generates a drive signal, the current source electrically coupled to the at least one inductor to induce an alternating current in the at least one inductor and generate an alternating magnetic field, sense circuitry including a capacitor electrically coupled to the at least one inductor to sense the alternating magnetic field and generate a sense signal, and phase comparison circuitry coupled to the current source and the sense circuitry to measure a phase difference between the sense signal and the drive signal and generate a signal indicative of a phase difference therefrom; and a computer to receive the phase difference signal and monitor the signal indicative of the phase difference for polishing endpoint criteria.