Influence of Colloidal Abrasive Size on Material Removal Rate and Surface Finish in SiO2Chemical Mechanical Polishing

Abstract

This paper addresses the influence of nano-scale abrasive particle size in the polishing of thermally-grown silicon dioxide on 100 mm diameter, p-type, (100), single crystal silicon wafers. The abrasive particles are incorporated in a chemical slurry, which is used in chemical mechanical polishing (CMP). Polishing (material removal) rate was measured with six (6) slurries, each with a different mean abrasive particle diameter of 10, 20, 50, 80, 110 and 140 nm. The experimental results indicate that the material removal rate (MRR) is related to the particle size. Results confirm that there exists an optimum abrasive size (80 nm) with respect to material removal rate and surface finish, for a given set of experimental conditions. The variation of the MRR vs. particle size (on a log-log plot) varies as d^3.4. In addition, the surface polished with 10 nm and 20 nm abrasives was stained by the slurries. For a pad surface roughness of 5.2 μm (Ra), the slurry containing the 80 nm particles resulted in the highest material removal rate and best surface finish. The effects of polishing conditions and abrasive concentrations are also investigated in this paper. The nano-film polishing model that relates the particle size to the roughness of the pad can explain the polishing mechanism.