Structures and adsorption energetics for chemisorbed fluorine atoms on Si(100)-2×1

We report first-principles electronic-structure calculations related to the initial fluorination of the Si(100)-2×1 surface. Embedded finite silicon clusters are used to model an extended Si(100)-2×1 surface. Two theoretical approaches, including a geometry-mapping procedure and an evaluation of lateral interactions via a dicluster model, are presented. Adsorption of up to 2.0 monolayers of fluorine is considered. Heats of adsorption, activation barriers, preferred binding sites, equilibrium geometries, charge transfer, and vibrational frequencies are predicted for this coverage range. Lateral interactions between various adspecies are found to be critically important in determining their stability. Thermochemical predictions derived from these calculations are used to postulate a reaction mechanism associated with the initial etching steps and with the adsorption kinetics of ${\mathrm{XeF}}_2$ versus ${\mathrm{F}}_2$.