Patent ID: 7549909

Claim:
A method of measuring a change in the thickness of a layer disposed on a wafer while the layer is being polished by a polishing process, said method comprising the steps of: measuring a first thickness of a layer on a first wafer; directing light of a known wavelength towards the layer, said light emitted by a light source; thereafter polishing the layer with the polishing process while measuring the intensity of any of said light reflected from the layer with a light detector, wherein polishing continues until a predetermined wavelength of a first sinusoidal curve representing the intensity of the reflected light over the time of polishing is obtained; thereafter measuring a second thickness of the wafer; combining the first thickness and second thickness to calculate a first change in the thickness of the layer; and calibrating the first sinusoidal curve by correlating the first change in thickness of the layer to the predetermined wavelength of the first sinusoidal curve.