Patent ID: 7169016

Claim:
A method of identifying an endpoint of a chemical mechanical polishing (CMP) process performed on a polishing surface, the method comprising: polishing the polishing surface using a polishing pad assembly, the polishing pad assembly being arranged to contact the polishing surface; providing an optical signal through an optical signal path arrangement, the optical signal path arrangement including a fixed portion and a moving portion, wherein the moving portion is arranged to be at least partially contained by an annulus of the polishing pad assembly, the polishing surface being arranged to reflect the optical signal, and wherein the optical signal is provided by a light emitting diode (LED) through a first path of the optical signal path arrangement; receiving the reflected optical signal through the optical signal path arrangement when the fixed portion and the moving portion are aligned to allow the reflected optical signal to pass through the moving portion to the fixed portion, wherein the reflected optical signal is received by an annular fiberoptic ring of the fixed portion through a second path of the optical signal path; and processing the reflected optical signal to determine if the endpoint has been reached, wherein processing the reflected optical signal includes determining a depth associated with the polishing surface.