In situ Transmission Electron Microscope observations of mesotaxial silicide formation in the CoSi2/Si system

A new technique for synthesis of buried epitaxial metal silicide layers in Si (“mesotaxy”) by high-dose implantation of Co and Ni into Si surfaces has been developed. Subsequent to implantation at energies in the few hundred keV range and doses in the 1017Cm−2 regime, thermal annealing at temperatures up to 1000°C results in the formation of well-defined and relatively high quality Si/metal disilicide/Si structures.The exact implantation and processing conditions are crucial in determining the structure and quality of the buried silicide layer. In this work, we describe transmission electron microscope experiments which illuminate the silicide formation process both by static studies of as-implanted and annealed structures, and dynamical in-situ experiments where as-implanted structures are annealed inside the microscope to mimic the ex-situ annealing conditions. The structure geometry in these materials turns out to be close to ideal for such in-situ experimentation: typical implantation conditions for formation of a contiguous silicide layer result in tlqe metal layers being of the order a few hundred to a thousand Å and buried about 600-1000 Å below the Si surface. In-situ annealing in the plan-view geometry inhibits surface diffusion across the interfaces, which would be expected in the cross-sectional geometry (5). The typical penetration depths attainable in Si with 200 keV electrons, say ~ 1 micron, allow a significant thickness, hsubthin of Si substrate below the metal layer, thickness hm, to be retained during the in-situ experiment such that hm ≪hsubthin. This is important, as it ensures that the film stress condition (which arises because of the difference in bulk lattice parameters between the Si and metal silicide layers) is reasonably representative of the stress conditions relevant for the case of annealing on the unthinned substrate.