High efficiency chemical mechanical polishing for silicon wafers using a developed slurry

Abstract

Improving the material removal rate (MRR) of silicon wafers is a challenge in chemical mechanical polishing (CMP), to meet the demands of the development of integrated circuits. In this study, four environmentally friendly additives, including sorbitol, gluconic acid, citric acid, and ammonium citrate, were incorporated into polishing slurries to promote the MRR of silicon wafers. The polishing results reveal that the highest MRR was obtained by ammonium citrate as an additive. When the concentration of ammonium citrate was 0.05 mol/L, the MRR increased by 71.6% to 1979.88 Å/min, and the surface roughness Sa was decreased from 1.131 nm to 0.563 nm. Meanwhile, the polishing slurry containing colloidal silica as abrasives maintained good dispersibility. Polishing mechanism was interpreted using electrochemical analysis, X-ray photoelectron spectroscopy, and coefficient of friction tests. It is indicated that NH4+ions, generated by hydrolysis of ammonium citrate, could modify the electrical characteristics of the silicate layer and catalyze the chemical reactions between Si atoms and H2O on the surface of silicon wafers. This work emphasizes the interfacial action between the polishing slurry and silicon wafers and provides a new idea for high efficiency CMP of silicon wafers in the manufacture of integrated circuits and photovoltaic industry.