ABINITIO STUDIES OF SILANE DECOMPOSITION ON SI(100)

The mechanism of silane decomposition on the Si(100)-(2 X 1) surface is investigated in the context of a many-electron theory that permits the accurate computation of molecule-solid surface interactions at an ab initio configuration-interaction level. The adsorbate and local surface region are treated as embedded in the remainder of the lattice electronic distribution, which is modeled as a three-layer, 19-Si-plus-21-H cluster. A possible energetic pathway is found for the reaction SiH4 --> SiH3 + H on the surface. It involves two separate steps: (1) scission of one Si-H bond; (2) formation of two bonds to SiH3 and H from two surface dangling bonds. The energy barrier, which is calculated to be 9 kcal/mol, occurs in the first step at a distance of 3.6 angstrom from the Si in SiH4 to a Si surface atom with a Si-H bond aligned with a surface dangling-bond direction. The overall dissociation process SiH4 --> SiH3 + H on the surface is found to be 2.8 eV exothermic. Quantum tunneling is found to play an important role in the process at room temperature. A symmetrical Eckart potential is used to estimate the quantum tunneling effect and the reaction probability is calculated to be small (on the order of 10(-5)) and relatively insensitive to the silane temperature.