Enhanced Diffusion and Out-Diffusion in Ion-Implanted Silicon

Backscattering and channeling-effect measurements were used to determine the lattice disorder and distribution, lattice location, and diffusion of species (Rb, Cs, Zn, Cd, Hg, Se, I, and Sb) implanted in Si. During anneal sequences we observed (1) enhanced diffusion towards the surface (Sb, Se, and Cd), (2) retardation or precipitation at the surface (Sb, Se, and Cd), and (3) a connection between out-diffusion and reordering of the amorphous layer (Zn, Cd, Hg, and I). The data also suggest that release of atoms from trapping (precipitation) sites in the implanted layer can be the rate-limiting process in some cases. These results indicate that out-diffusion studies such as gas release, may not represent bulk diffusion properties in crystals.