Inductively coupled plasma etching of poly-SiC in $SF6$ chemistries

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.