Density functional study of the initial stage of the anneal of a thin Co film on Si - art. no. 235303

Plane-wave pseudopotential calculations are performed to study the initial stages of an anneal of a thin Co film/Si couple. Preliminary calculations p rovide Co(x)Sil(1-x) structures and formation energies that are in reasonab le agreement with experiment. The early stages of the anneal are then inves tigated from two viewpoints: starting from (CoSi)-Si-2, and working backwar d in time; starting from bulk Si with low concentrations of Co, and working forward in time. The latter viewpoint indicates that the barrier to the gr owth of Co2Si is the formation of isolated Co interstitials. Once formed, t hey diffuse quickly and find it energetically favorable to form clusters. T hese clusters then bring about a reconstruction of the lattice. The former viewpoint suggests that an intermediate structure consisting of equal numbe rs of Co and Si atoms exists that can transform either into Co2Si by the ad dition of Co interstitials, or into CoSi by shearing. This provides an expl anation of the simultaneous growth of CoSi and Co2Si.