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

A quantum chemical investigation of the chemical dry etching of N2 downflow plasma and NF3 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 N2 downflow plasma with NF3 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*+ NF3. It was found through our calculations that there were three reaction routes of NF3 proceeding F production in the initial reaction step, with N(2Do) and N2(A3Σu+) and by electron attachment, and it is thought that the most probable F production reaction in the downflow area is N(2Do) + NF3→N=NF2+ F and the next probable reaction is N2(A3Σu+) + NF3(3E)→N2(1Σg+) + NF2+F.