The codeposition of Co and Si by molecular beam epitaxy on Si substrates in a highly Si rich flux ratio results in the growth of epitaxial CoSi2 columns surrounded by high quality single crystal Si. The formation of such columnar layers is indicative of selectivity in the growth of CoSi2 and Si. The nature of this selectivity was explored by examining the effects of depositing Si, CoSi2 and Co respectively, on ‘template’ layers containing CoSi2 columns grown on (111) oriented Si substrates at 800°C.

Increased selectivity was observed with increasing growth temperature in the range of 650 - 800°C. The overgrown Si and CoSi2 appear to grow preferentially on exposed Si and CoSi2 areas respectively, of the template layer. The selectivity could be reduced by either a decrease in the growth temperature or an increase in the Co:Si flux ratio. Surface diffusion of the growth species coupled with a high rate of bulk diffusion of Co in Si appears to promote the selective growth behavior, resulting in changes in the sub-surface dimensions of the CoSi2 columns in the template layer as well. The deposition of Co alone results in the growth of large islands of CoSi2, seeded on the exposed surfaces of CoSi2 columns in the template layer. These islands are probably a consequence of the formation, migration and coalescence of CoxSiy clusters on the substrate surface.