PRECIPITATION KINETICS IN SILICON DURING ION-BEAM SYNTHESIS OF BURIED SILICIDE LAYERS

Under appropriate conditions, high dose implantation of metal ions such as Co+, Ni+, Fe+ or Cr+ into heated Si substrates and subsequent annealing results in the formation of buried epitaxial silicide layers. In the present paper, the kinetics of the underlying transient processes is discussed. The formation of silicide precipitates during implantation is described by a diatomic diffusional nucleation model. From this, guidelines for a favourable choice of the implantation parameters are deduced. The local precipitate coarsening and the narrowing of the spatial silicide distribution is described by an inhomogeneous Ostwald ripening process in which solute fluxes from both sides of the implanted peak are driven by solute gradients associated with the peaked distribution of the precipitate sizes. It is shown that the possibility to narrow the spatial silicide distribution by an annealing procedure is limited. This principal limitation explains the experimental findings that the formation of a continuous buried layer requires the implantation of a minimum peak concentration of metal ions.