PRECIPITATION KINETICS IN SILICON DURING ION-BEAM SYNTHESIS OF BURIEDSILICIDE LAYERS

Under appropriate conditions, high dose implantation of metal ions suc h as Co+, Ni+, Fe+ or Cr+ into heated Si substrates and subsequent ann ealing results in the formation of buried epitaxial silicide layers. I n the present paper, the kinetics of the underlying transient processe s is discussed. The formation of silicide precipitates during implanta tion is described by a diatomic diffusional nucleation model. From thi s, guidelines for a favourable choice of the implantation parameters a re 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 implan ted peak are driven by solute gradients associated with the peaked dis tribution of the precipitate sizes. It is shown that the possibility t o narrow the spatial silicide distribution by an annealing procedure i s limited. This principal limitation explains the experimental finding s that the formation of a continuous buried layer requires the implant ation of a minimum peak concentration of metal ions.