Importance

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Abstract

An apparatus to generate an endpoint signal to control the polishing of thin films on a semiconductor wafer surface includes a through-hole in a polish pad, a light source, a fiber optic cable, a light sensor, and a computer. A pad assembly includes the polish pad, a pad backer, and a pad backing plate. The pad backer includes a pinhole and a canal that holds the fiber optic cable. The pad backer holds the polish pad so that the through-hole is coincident with the pinhole opening. A wafer chuck holds a semiconductor wafer so that the surface to be polished is against the polish pad. The light source provides light within a predetermined bandwidth. The fiber optic cable propagates the light through the through-hole opening to illuminate the surface as the pad assembly orbits and the chuck rotates. The light sensor receives reflected light from the surface through the fiber optic cable and generates reflected spectral data. The computer receives the reflected spectral data and calculates an endpoint signal. For metal film polishing, the endpoint signal is based upon the intensities of two individual wavelength bands. For dielectric film polishing, the endpoint signal is based upon fitting of the reflected spectrum to an optical reflectance model to determine remaining film thickness. The computer compares the endpoint signal to predetermined criteria and stops the polishing process when the endpoint signal meets the predetermined criteria.

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First Claim