Enhanced ‘‘tail’’ diffusion of phosphorus and boron in silicon: Self-interstitial phenomena

It is well known that high surface concentration phosphorus diffusion leads to deeply penetrating ‘‘tails’’ in its concentration profile. At 700 °C the tail diffusivity exceeds that of low concentration phosphorus by a factor of 1000. Less spectacular, but very significant tailing also affects boron, making the conventional models contained in commonly available process simulation programs quite inaccurate for high concentrations of boron. We show that the observed tailing can be accounted for by a model whose central assumption is the local equality of dopant and oppositely directed defect fluxes.