Structural properties of epitaxial silicide layers on Si

The formation of epitaxially stabilized (pseudomorphic) Fe and Co silicides on Si(111) is reviewed. We show that, apart from the α-FeSi2 phase, which is also stable in bulk form at high temperatures, none of the pseudomorphic phases is ever likely to be the lowest energy phase, with the exception of FeSi with the CsCl structure. For FeSi, the positive contribution of the interface to the total energy of the bulk stable phase, ϵ-FeSi, is sufficiently large to reverse the stability, i.e. (CsCl)FeSi is truly stable for thicknesses below Hc ∼ 15 Å. From the structural point of view, Fe and Co silicides are found to be more similar than believed heretofore. In particular, we find that, at low substrate temperatures and under particular conditions, CoSi2 may crystallize with a CsCl structure with random metal vacancies instead of the well known bulk stable CaF2 structure.