Reactivity of Silicon Surfaces in the Presence of Adsorbed Hydrogen and Chlorine

Abstract

AbstractThe desorption of hydrogen and hydrogen chloride from Si surfaces is the rate‐determining 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 H2 and HCl from the Si(100)2 × 1 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 4H‐2H reaction pathways. The desorption activation energy (57.4 kcal mol−1) and adsorption barriers (15.9 kcal mol−1) calculated for H2 for the 4H and 2H pathways are in good agreement with experimental data, confirming that these are the H2 main desorption and adsorption routes. The reaction mechanism of HCl is different to that of H2. The calculations in fact indicate that the less activated desorption pathway (65.0 kcal mol−1) is the intradimer mechanism, followed by the 2H pathway (67.1 kcal mol−1), which might thus compete with the intradimer pathway at low surface coverage. The HCl adsorption barrier on Si dimers is small (0.6 − 4.8 kcal mol−1), confirming the high reactivity of HCl with Si surfaces.