Competitive metastable phase in low-temperature epitaxy of CoSi2/Si(111)

We analyzed the structural, elastic, and electric properties of CoSi2 films grown by stoichiometric codeposition onto Si(111) substrates. Films growing epitaxially at room temperature onto an ultrathin template, and films nucleating from the amorphous phase after a mild anneal, were considered. Both were found to crystallize predominantly with a CsCl-derived defect structure with random occupation of the metal sites. The kinetics of the phase transition to the stable bulk phase with the fluorite structure appears to be different for the two growth procedures. After annealing to 600 degrees C, grains with the CsCl defect structure were found to be present mainly in films grown on a template. This also explains the poorer electrical properties of these films. A microscopic model which explains the easy formation and the persistence of the CsCl-defected phase is derived on the basis of tight-binding molecular dynamics.