Effects of mid-frequency power on SiO2 etching profile for fluorocarbon gas mixture in 100 MHz, 13.56 MHz, and 2 MHz triple-frequency capacitively coupled plasma

This study investigates the etching profile of SiO2 using a C4F6/C4F8/Ar/O2 gas mixture in 100 MHz, 13.56 MHz, and 2 MHz triple-frequency capacitively coupled plasma. As 13.56 MHz power increased, electron density rose, altering gas dissociation and the CF2/F radical ratio. It also improved plasma uniformity, which influenced the formation of fluorocarbon passivation layers, thereby affecting the etch rate, selectivity, and etch profile. Increasing 13.56 MHz power from 0 to 1000 W led to an increase in SiO2 etch depth and a decrease in mask height. Etch selectivity was maximized under optimal 13.56 MHz and 2 MHz power conditions, highlighting the crucial role of ion energy control in determining etch characteristics. Etch profile analysis revealed mask necking, tapering and lateral etching effects, demonstrating that the mask neck critical dimension significantly impacts SiO2 profile geometry.