Dissociation energetics of SiF systems of relevance to etching reactions

The bond energies of the ²Π and ⁴Σ ^- states of SiF, the ¹Σ⁺ state of SiF⁺, the ³Σ^- state of SiF^-, the ¹A₁, ³B₁, and ¹B ₁ states of SiF₂, the ²A₁ state of SiF₂⁺, and the ground states of SiH₃-F, SiF₃-F, SiH₃-SiH₃, and SiH₃-SiF ₃ have been calculated using generalized valence bond and dissociation-consistent configuration interaction methods. Excellent bond energies are determined using only a relatively small number of configurations in the calculations. For example, the bond energy of the ²Π state of SiF is calculated to be 5.45 eV, in excellent agreement with the experimental value of 5.62 eV. For the inversion bend of SiF₃ we predict that the transition state is a T-shaped configuration rather than one of D_3h symmetry. Of note for the etching of solid silicon by reaction with F atoms is that unsaturated Si species react readily with F atoms to form strong bonds and that the bonding of a F atom to a lone pair of electrons on a Si atom is an activated process.