Reactive Deposition Epitaxy of CoSi2 Films on Clean and Oxygen-Adsorbed Si(001) Surfaces

Abstract

We have studied the surfactant effects of adsorbed oxygen layers of 1-2 monolayer thicknesses on the film evolution of CoSi2(001) in reactive deposition epitaxy at 470°C on Si(001). The O atoms segregating to the growth front play essential roles in suppressing the Si outward diffusion from the substrate and Co lateral migration, which promote two-dimensional layer growth of CoSi2(001) films and make the surfaces smooth. A kinetic mechanism is suggested in which Co atoms easily diffuse without interaction through the O layers toward the substrate and react with Si atoms. Nevertheless, {111}-twinned CoSi2 is formed at the very initial growth stage on O-adsorbed Si, similarly to that on clean Si. We have also investigated the morphology and crystallinity of ∼20-nm-thick CoSi2(001) films. The O atoms remaining on the surface effectively restrain film surface roughening even at this thickness; however, they cannot lower the interface roughness owing to the formation of {111} facets and {111}-twinned boundaries. The twin boundaries formed in the initial stage grow into the substrate during the epitaxy.