Patent ID: 7235154

Claim:
A system for measuring a change in thickness of a layer of material disposed on a wafer while said layer is polished, said system comprising: a polishing pad suitable for polishing the layer; a sensor assembly disposed in the polishing pad, said sensor assembly comprising: a light source capable of emitting a known wavelength of light; a light detector capable of detecting the intensity of light incident on the light detector; and an optical puck, wherein the light source and the light detector are contained within the optical puck and wherein the optical puck is transparent to a predetermined wavelength of light; a means for conveying power to the light source and to the light detector, said means for conveying power operably connected to the sensor assembly; and a processor operably connected to the light detector, wherein during polishing the intensity of light incident on the light detector varies sinusoidally with over the time of polishing, wherein the processor is programmed to measure a sinusoidal curve indicative of the intensity of detected light over time and wherein the processor is further programmed to measure the wavelength of the sinusoidal curve.