Reactive deposition epitaxy of CoSi2 films on clean and oxygen-adsorbed Si(001) surfaces

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 470degreesC 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 similar to20-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.