Abstract: An apparatus for detecting a polishing endpoint during chemical-mechanical planarization/polishing of a wafer senses an acoustic wave generated by rubbing contact between a polish pad and a hard surface underlying a softer material being removed. The apparatus includes a transducer for converting the acoustic wave energy in the range of 30 to 100 Hertz into an audio signal. The audio signal is processed by a low pass cutoff filter to remove high frequency noise. The filtered audio signal is supplied to a phase lock loop to detect a predetermined audio frequency and, in response, provide a logic signal to an integrator. The integrator integrates the logic signal over time to eliminate transient noise spikes, and supplies a detection signal only upon receiving the logic signal for a predetermined period. The detection signal starts a counter to provide a predetermined overpolishing time prior to termination of polishing operations.