Effect of alkaline agent in colloidal silica slurry for polycrystalline silicon chemical mechanical polishing

Abstract

Through chemical mechanical polishing (CMP) tests using polycrystalline silicon (polysilicon) and oxide blanket film wafers, the effects of alkaline agents added to colloidal silica slurries were investigated. With increasing concentration of the alkaline agent, a decreasing trend after an initial increase in the polysificon removal rate was found, along with a low oxide removal rate, enabling high selectivity. The surface roughness similarly became worse and then better with increasing concentration of the alkaline agent. The results suggest a mechanism in which hydroxide bonds to the Si surface of the abrasives in the slurry and OH- attaches to the polysilicon surface. The silanol group induces high polarization and thus weakens the Si-Si back bonds. These results can be qualitatively explained in terms of the chemical reaction between the polysilicon surface and the alkaline agent in the slurry, according to the hydrophobicity and hydrophylicity as indicated by contact angle measurements.