Supersonic molecular beam scattering as a probe of thin film deposition processes

The reactions of silane, SiH₄, disilane, Si₂H₆, and phosphine, PH₃, on single crystalline Si(100) and Si(111) surfaces, and methylsilane, SiH₃CH₃, on a β‐SiC surface have been examined employing supersonic molecular beam scattering. The emphasis here is not on any one experimental result, but rather on the specific experimental approaches adopted and a selected set of results that serve to demonstrate the similarities and differences between these systems and the more extensively studied reactions occurring on transition metal surfaces. All reactions have been examined at substrate temperatures characteristic of steady‐state thin film growth. Translational activation is observed to be an efficient means to promote the reactivity of the group IV species: SiH₄, Si₂H₆, and SiH₃CH₃. In all cases, the reactivity increases exponentially with scaled incident kinetic energy, where the scaling analysis specifically takes into account the microcorrugation of the gas‐surface potential in terms of how incident kinetic energy and angle of incidence couple to determine the probability of dissociative chemisorption. The reaction probability of SiH₄ is described quantitatively over a wide range of reaction conditions by a recently published model that adapts Rice–Ramsperger–Kassel–Marcus theory to translationally activated dissociative chemisorption. In contrast, PH₃, due to its coordinative unsaturation, is found to react almost exclusively via a trapping‐mediated precursor dissociation channel. By employing a novel analysis scheme, the dependence of PH₃ dissociative chemisorption on the fractional coverage of both P(a) and H(a) has been deduced under conditions where the desorption of H₂ and P₂ are finite. The experimental techniques described here, and the associated conclusions made in this work, should be of tremendous value in future studies directed at examinations of the gas‐surface chemistry involved in epitaxial thin film growth.