CoSi2/Si(111) interface: Determination of the interfacial metal coordination number.

Abstract

The morphology and the surface and interface structure of flat ${\mathrm{CoSi}}_{2}$ films (thickness \ensuremath{\sim}2 Si-Co-Si triple layers) epitaxially grown on Si(111) have been investigated using medium-energy ion scattering with ultrahigh energy resolution. The data show that the silicide is attached to the substrate through Co-Si bonds rather than through Si-Si bonds. At the interface, the silicide is terminated by a full Si-Co-Si triple layer. The interface metal atoms are thus eightfold coordinated. The silicide-substrate distance is expanded by 0.16\ifmmode\pm\else\textpm\fi{}0.08 \AA{}. The first Si substrate layer is relaxed outward by 0.08\ifmmode\pm\else\textpm\fi{}0.08 \AA{}. The length of the Co-Si interface bond is thus dilated by 0.08 \AA{}. At the silicide surface, the first Co-Si interplanar distance is found to be relaxed inward by 0.14\ifmmode\pm\else\textpm\fi{}0.04 \AA{}. Our measurements suggest that the silicide lattice strain is almost fully relaxed. We propose that such relaxation occurs through a high density of microcracks in the film. The average spacing between cracks is then smaller than roughly 50 \AA{}.