Quantum Chemical Investigation for Chemical Dry Etching of SiO₂ by Flowing NF₃ into H₂ Downflow Plasma

A quantum chemical investigation of the chemical dry etching of SiO 2 using H 2 downflow plasma with flowing NF 3 was carried out using the B3LYP/6-31+G(d,p) method. The results provide a reasonable interpretation of how the chemical dry etching of SiO 2 takes place in a down flow area. Experimentally, it was found that the etch rates of thermal silicon oxide film range from 1 to 10 nm/min depending on the etching conditions, and white powder was produced on the etched surface. It was deduced that the etchants were HF and NH 3 produced by the reaction of H+ NF 3 , and that the white powder on the etched surface was produced by the decomposition of (NH 4 ) 2 SiF 6 formed on the etched surface. The calculated results support the HF and NH 3 production mechanism and clarify the molecular structures of (NH 4 ) 2 SiF 6 and the white powder. Another important point in the chemical dry etching of SiO 2 was the realization of a high etching selectivity to Si. As the F atom was deduced to be the main etchant of Si, its generation mechanism in H 2 down flow plasma with the addition of NF 3 was also studied and a method of suppressing F atom production was proposed in this research.