Impregnation of Hydrogenated Graphite in Polyurethane Pad for Improved Performance in Chemical-Mechanical Polishing Processes

Abstract

This study aimed to fabricate a chemical-mechanical polishing (CMP) pad by impregnating a polyurethane matrix with graphite particles. Two kinds of pads—one employing 8 wt% hydrogenated graphite and another employing 8 wt% natural graphite—were fabricated and their performance was compared with that of a conventional polyurethane polishing pad. Hydrogenated graphite was obtained by heat-treating graphite particles under a layer of hydrogen ions at a temperature of about 600 °C for 30 min so as to disperse them uniformly in the polyurethane matrix. The surface characteristics and contact angle of the graphite-impregnated pads as well as the removal rate and non-uniformity of a dielectric oxide film polished with these pads were investigated and compared with the corresponding values for a conventional polyurethane pad. The results of this study confirmed that the hydrogenated-graphite-impregnated pad provided the smallest contact angle for slurry. Therefore, the fabricated pad has a higher ability to retain slurry than the conventional polishing pad. The site to be polished can be lubricated by wetting, thus enabling faster polishing of the wafer without damaging the local circuitry. The attenuated total reflectance–Fourier transform infrared and dynamics mechanical analysis results indicated that the chemical structure of the hydrogenated-graphite-impregnated pad was identical to that of the polyurethane pad. Oxide CMP tests revealed that the hydrogenated-graphite-impregnated pad provided the highest wafer removal rate and exhibited maximum uniformity; this pad also showed a higher wafer removal rate and more uniformity than a natural-graphite-impregnated pad. The pad also consumed less material because its hydrogenated graphite particles are distributed more uniformly than those in the natural-graphite polishing pad.