Inductively coupled plasma etching of poly-SiC in SF6 chemistries

Abstract

A study was made to find a low-cost and robust etching solution for silicon carbide (SiC) using a commercially available inductively coupled plasma etching tool. Sulfur hexafluoride (SF6) was selected because of its high degree of F dissociation and nonhazardous nature. A parametric study of the etching characteristics of poly-SiC in inductively coupled plasma (ICP) SF6 chemistries was performed. Etch chemistry was found to greatly affect etch rate, selectivity, and the postetch surface condition. Etch rates as high as 5884Å∕min were achieved with high SiC∕Cr selectivity (36) using a SF6∕CF4∕He gas mixture, but the etched surface was relatively rough (134 Å rms). He addition was found to increase the SiC etch rate, and this effect is believed to be caused by increased ionization of SF6 in the plasma and the resulting increases in the SF3+ and fluorine (F) radical concentrations. The formation of pillar-like structures and sidewall deposition was observed on the etched SiC surfaces under some conditions. These unwanted etch byproducts exhibited a high concentration of chromium (Cr) and fluorine. However, an argon (Ar) plasma preclean of the substrate, high ICP, and/or bias powers, and CF4 addition reduced the pillar formation significantly.