Advanced dopant and self-diffusion studies in silicon

Abstract

The growth of isotopically enriched epitaxial Si and SiGe layers enables the preparation of material heterostructures, highly appropriate for simultaneous self- and dopant-diffusion studies. The advance in solid state diffusion is demonstrated by dopant diffusion in isotopically controlled Si multilayer structures. Experiments on B, As and P diffusion are presented indicating that dopant diffusion strongly affects self-diffusion. The demand to describe both the self- and dopant-profiles sets strong constraints as to the underlying mechanisms of atomic transport and the properties of the point defects involved. The relative contributions to dopant diffusion and the type and charge state of the native point defects involved are determined. The energy level scheme deduced for the native defects shows a reverse level ordering for the donor levels of the self-interstitials, that is, the doubly positively charged self-interstitial mediates the extrinsic diffusion of B and the self-diffusion via self-interstitials under p-type doping. Self-consistent modeling of P and Si profiles requires that a mobile positively charged phosphorus defect exists. This defect and the supersaturation of self-interstitials are responsible for the tail observed after P diffusion.