Patent ID: 7086929

Claim:
A chemical mechanical polishing apparatus, comprising: a platen to support a polishing pad, the platen being rotatable about an axis and including a plurality of optical apertures positioned at different angular positions about the axis; a carrier head to hold a substrate against the polishing pad; a first optical system located in the platen and including a first light source to generate a first light beam that is directed through a first one of the plurality of optical apertures, the first optical system including a first sensor to measure light from the first light beam that is reflected from the substrate to generate a first intensity signal; a second optical system located in the platen and including a second light source to generate a second light beam that is directed through a second one of the plurality of optical apertures, the second optical system including a second sensor to measure light from the second light beam that is reflected from the substrate to generate a second intensity signal, the first and second light beams having different effective wavelengths; and a processor to receive the intensity signal from each of the plurality of optical systems and determine a polishing endpoint.