Characteristics of SiO₂ Etching with a C₄ F₈ /Ar/CHF₃ /O₂ Gas Mixture in 60-MHz/2-MHz Dual-frequency Capacitively Coupled Plasmas

Nanoscale SiO₂ contact holes were etched by using C₄F₈/CHF₃/O₂/Ar gas mixtures in dualfrequency capacitively coupled plasmas (DF-CCPs) where a 60-MHz source power was applied to the top electrode while a 2-MHz bias power was applied to the bottom electrode. The initial increase in the CHF₃ gas flow rate at a fixed CHF₃+O₂ flow rate increased the SiO₂ etch rate as well as SiO₂ etch selectivity over that of the amorphous carbon layer (ACL). When the high-frequency (HF) power was increased both SiO₂ etch rate and the etch selectivity over ACL were increased. For a 300 W/500 W power ratio of 60-MHz HF power/ 2-MHz low-freqeuncy (LF) and a gas mixture of Ar (140 sccm) /C₄F₈ (30 sccm) /CHF₃ (25 sccm) /O₂ (5 sccm) while maintaining 20 mTorr, an anisotropic etch profile with an SiO₂ etch rate of 3350 Å/min and an etch selectivity of higher than 6 over ACL could be obtained.