Quantum chemical investigation for chemical dry etching of SiO by flowing NF into H downflow plasma

A quantum chemical investigation of the chemical dry etching of SiO using H downflow plasma with flowing NF 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 takes place in a down flow area. Experimentally, it was found that the etch rates of thermal silicon oxide film range from 1 to 10nm/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 produced by the reaction of H + NF , and that the white powder on the etched surface was produced by the decomposition of (NH ) SiF formed on the etched surface. The calculated results support the HF and NH production mechanism and clarify the molecular structures of (NH ) SiF and the white powder. Another important point in the chemical dry etching of SiO 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 down flow plasma with the addition of NF was also studied and a method of suppressing F atom production was proposed in this research. © 2012 The Japan Society of Applied Physics.