Relationship of etch reaction and reactive species flux in C4F8/Ar/O2 plasma for SiO2 selective etching over Si and Si3N4

The relationship between reactive species flux and their modified surfaces was studied in a SiO2 highly selective etching over Si and Si3N4. Sample specimens with large patterns and φ 0.35 μm contact holes were etched using C4F8/Ar/O2 plasma in a dual-frequency (27/0.8 MHz) parallel-plate etching system. The amount of CFx reactive species was controlled by adjusting the C4F8 flow rate ratio while keeping the ion flux (3×1016 cm−2 s−1) and the Vpp of bias radio frequency (1450 V) constant. The highly selective etch process is attained in a certain condition of the radical flux. Quantitative analysis using x-ray photoelectron spectroscopy revealed that the etch rate strongly depended on the fluorocarbon (CF) film thickness formed during the etch reaction on SiO2, Si3N4, and Si. In the large-area-etching of Si and Si3N4, the CF film (< 2 nm) formed under conditions with low selectivity for SiO2 was thinner than the film (5–6 nm) formed in high-selectivity etch conditions. The CF film thickness on SiO2 were l...