Chemical mechanical polishing of silicon wafers using developed uniformly dispersed colloidal silica in slurry

Abstract

It is a challenge to enhance the material removal rate (MRR) during the chemical mechanical polishing (CMP) of silicon wafers, with increasing the size of a wafer and reducing the feature size of integrated circuit. In this study, potassium ions were employed to improve the MRR of silicon wafers effectively in CMP, which was performed by developed slurry, consisting of monodisperse alkaline colloidal silica, organic/inorganic acids and inorganic salts. Experimental results show that the developed slurry has a good stability and dispersity for colloidal silica. The MRR of silicon wafers in CMP was increased by 53.42 % to 1778.71 Å/min, when the concentration of potassium ions was 125 mmol/L. In addition, the surface roughness Sa was also improved slightly to 0.887 nm. The CMP mechanism was investigated using X-ray photoelectron spectroscopy, friction coefficient meter and electrochemical analysis. It reveals that potassium ions could change the electrical characteristics of the formed soft layer on the silicon wafer surface, dissolving the soft layer and oxidizing the surface of silicon.