Analysis of the dynamics of reactions of SiCl ₂ at Si(100) surfaces

The dynamics of reactions of SiCl ₂ at Si(100) surfaces was investigated through the molecular orbital method at the B3LYP/6-31G(d,p) level of theory, with the surface being modeled using clusters of silicon atoms. The intradimer adsorption of a SiCl ₂ molecule proceeded with no energy barrier, and in the structure of the product of the adsorption reaction the Si atom of the SiCl ₂ adsorbate formed a triangular structure with the two Si atoms of the surface dimer, in agreement with theoretical predictions published recently in the literature for a small cluster. However, the dynamics reported in this work indicates that SiCl ₂ undergoes molecular adsorption at the silicon surface, in contrast with the dissociative adsorption suggested by some available kinetic models. Intradimer adsorption of a second SiCl ₂ molecule, and interdimer adsorptions of a first, a second, and a third SiCl ₂ molecule were also seen to proceed without significant energy barriers, suggesting that the formation of the first additional layer of silicon atoms on the surface would be fast if the adsorption of SiCl ₂ were the only type of reaction proceeding in the system. The diffusion of the SiCl ₂ adsorbate over the surface and its desorption from the surface were found to have comparable activation energies, so that these reactions are expected to compete at high temperatures.