Surface chemical reactions studied via ab initio-derived molecular dynamics simulations : fluorine etching of Si(100)

Previous isothermal dynamics simulations of the interaction of F with Si(100) failed to predict any reaction beyond saturation of the surface dangling bonds. We show that this lack of reactivity was due to the overly repulsive nature of the empirical potential employed. We used the method of simulated annealing to fit a new analytic interaction potential to data from ab initio configuration interaction calculations. This potential was then utilized in isothermal molecular dynamics simulations to explore the mechanism by which fluorine begins to etch silicon. Calculated adsorption and reaction probabilities, as a function of both fluorine coverage and structure, reveal that the buildup of the fluorosilyl layer occurs via several competing reactions and that it does not follow a well defined reaction sequence. This competition creates disorder in the adsorbed fluorosilyl layer, which is shown to be an important precursor to continued reaction. Idealized ordered surface structures are shown to be unstable relative to highly disordered structures for coverages of more than 1.25 ML of fluorine.