Vertical sidewall of silicon nitride mask and smooth surface of etched-silicon simultaneously obtained using CHF3/O2 inductively coupled plasma

Abstract

Silicon nitride (SiNx) has been playing a vital role in the fabrication of micro- and nano-scale structures in numerous applications for several decades. Optimal etch recipes and a mechanistic understanding of the SiNx plasma-etching process are necessary for its adoption as a hard mask. We present a systematic investigation on SiNx films and underlying silicon (Si) plasma etching via an inductively coupled plasma (ICP) system using a CHF3/O2 mixture. Effects of ICP power, RF power, CHF3 flow rate on SiNx etching rate, CHF3/O2 gas ratio on SiNx sidewall profile, Si surface roughness, and SiNx/Si etching selectivity have been methodically investigated. We paid particular attention to studying the effect of O2 concentration on SiNx and Si etching mechanisms. It was found that SiNx sidewall profile, Si surface roughness, and SiNx/Si etching selectivity depend strongly on the O2 concentration. A nearly vertical SiNx sidewall of 89°, a low Si surface roughness of 0.2 nm, and a high SiNx/Si etching selectivity of 2 were simultaneously achieved by adjusting O2 concentration to 10% with CHF3+O2 total flow rate of 50 sccm. Finally, the composition of the residue on the surface of the processed sample was examined by X-ray photoelectron spectroscopy (XPS).