Abstract
The desorption of hydrogen and hydrogen chloride from Si surfaces is the rateβdetermining step of the low temperature CVD of silicon from both hydrogenated and chlorinated precursors. Thus, in order to model the deposition process, the rate of these reactions must be known to a high level of accuracy. In this work, the surface desorption kinetics of H~2~ and HCl from the Si(100)2βΓβ1 surface is investigated by modeling the surface through clusters of various dimensions (up to 60 Si atoms) and determining the reaction energies at the B3LYP, and coupled cluster methodology with inclusion of single, double and a perturbative estimation of triple excitations (CCSD(T)) levels. The investigated mechanisms are the pairwise intradimer and the 4Hβ2H reaction pathways. The desorption activation energy (57.4βkcalβmol^β1^) and adsorption barriers (15.9βkcalβmol^β1^) calculated for H~2~ for the 4H and 2H pathways are in good agreement with experimental data, confirming that these are the H~2~ main desorption and adsorption routes. The reaction mechanism of HCl is different to that of H~2~. The calculations in fact indicate that the less activated desorption pathway (65.0βkcalβmol^β1^) is the intradimer mechanism, followed by the 2H pathway (67.1βkcalβmol^β1^), which might thus compete with the intradimer pathway at low surface coverage. The HCl adsorption barrier on Si dimers is small (0.6βββ4.8βkcalβmol^β1^), confirming the high reactivity of HCl with Si surfaces.