Effects of the size and the concentration of the abrasive in a colloidal silica (SiO2) slurry with added TMAH on removal selectivity of polysilicon and oxide films in polysilicon chemical mechanical polishing

Abstract

The effects of varying the size and the concentration of the abrasive in a colloidal Silica slurry and the concentration of tetra-methyl ammonium hydroxide (TMAH) were investigated in terms of the oxide film loss, the removal rate, the roughness of the film surface, and polysilicon-to-oxide film removal selectivity. These effects were investigated by performing chemical mechanical polishing (CMP) experiments using blanket wafers. It was found that with increasing TMAH concentration, the removal rate and the polysilicon-to-oxide selectivity were reduced after an initial increase, regardless of the abrasive size in the slurry. In addition, the removal selectivity at a lower abrasive concentration was slightly higher than it was at a higher abrasive concentration for the case of a smaller abrasive, but for the case of a larger abrasive, the removal selectivity was almost independent of the abrasive concentrations. The surface roughness, however, became worse at a lower TMAH concentration. The results qualitatively suggest a mechanism in which OH- ions bond to the Si surfaces of the abrasives in the slurry and then attach to the surface of the polysilicon film, as a result of hydrophobicity and interfacial tension, as indicated by contact angle measurements.