Quantum Chemical Investigation of Si Chemical Dry Etching by Flowing NF3 into N2 Downflow Plasma

摘要

A quantum chemical investigation of the chemical dry etching of N_2 downflow plasma and NF_3 flow into the downflow area was carried out by the B3LYP/6-31+G(d) method. The results provide a reasonable interpretation of how the chemical dry etching of Si takes place. Experimentally, it was reported that single-crystal silicon was etched in the N_2 downflow plasma with NF_3 flow and the etch rate depended on the etching conditions, and it had been deduced that the etchant was F atoms produced by the reaction of N~* + NF_3. It was found through our calculations that there were three reaction routes of NF_3 proceeding F production in the initial reaction step, with N(~2D~°) and N_2(A~3Σ_U~+) and by electron attachment, and it is thought that the most probable F production reaction in the downflow area is N(~2D~°) + NF_3→N = NF_2 + F and the next probable reaction is N_2(A~3Σ_U~+) + NF_3(~3E)→ N_2(~1Σ_g~+) + NF_2 + F.