Characteristics of SiO2 Etching with a C4F8/Ar/CHF3/O-2 Gas Mixture in 60-MHz/2-MHz Dual-frequency Capacitively Coupled Plasmas

Nanoscale SiO2 contact holes were etched by using C4F8/CHF3/O-2/Ar gas mixtures in dual-frequency 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+O-2 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) /O-2 (5 sccm) while maintaining 20 mTorr, an anisotropic etch profile with an SiO2 etch rate of 3350 angstrom/min and an etch selectivity of higher than 6 over ACL could be obtained.