Extended Hückel calculations were used to estimate the change in electron density on Si-O back-bonds, and the total electronic energy during reaction at the oxide film surface. It was demonstrated that the desorption of SiF4 occurred via a series of steps. Firstly, HF2- ions dissociated into HF monomers plus F- ions near to the surface. Secondly, F- ions attacked the -SiF3 surfaces and H ions attacked the O atoms of the back-bond. Thirdly, the O-Si-F bond-angle decreased and the Si-O bond strength was weakened. Finally, the H atoms passivated the O atoms after tetrahedral SiF4 molecules were generated and the Si-O back-bonds were broken. The activation energy for the desorption of SiF4 was estimated to be 0.8eV.

T.Oku, K.Sato, M.Otsubo: Japanese Journal of Applied Physics - 1, 1997, 36[3B], 1374-9