COBALT DISILICIDE GROWTH AND INTERFACE STRUCTURE ANALYSES

The thin-film growth process is often baffling as far as thermodynamics are concerned. The aim of this work was to gather results obtained from various means of growing cobalt silicide films. It is shown that the first phase formed depends on the film thickness. Indeed, cobalt films one or two monolayers thick lead to a CoSi2-like phase at room temperature; for thicker cobalt films a mixture of CoSi2-like and epitaxial CoSi grains are grown; from ten monolayers an intermediate and continuous epitaxial CoSi film is grown under a polycrystalline cobalt, CoSi and Co2Si film. The CoSi2-Si interface structure is studied in detail using high-resolution transmission electron microscopy. It is shown that three of six possible models deduced from the geometrical theory seem to apply. Nevertheless the main feature is the evolution of the structure all along the interface, the mismatch being accommodated either by misfit dislocations or by Somigliana dislocations which occur in steps and continuous distortion of the unit structure of the ideal interface.