Diffusion of substitutional impurities in silicon at short oxidation times: An insight into point defect kinetics

Abstract

Oxidation-enhanced diffusion of phosphorus, arsenic, and boron and oxidation-reduced diffusion of antimony in silicon have been studied as a function of oxidation time. Data for the early phase of oxidation in dry oxygen from 5 to 60 min have been obtained. Oxidation-enhanced diffusivities show a steady decrease with decreasing oxidation rate for phosphorus, arsenic, and boron, with enhancements at long oxidation times in agreement with previously reported results. Antimony shows a reduction in diffusivity during oxidation. A model allowing calculation of diffusivity enhancement or reduction for all elements and oxidation times has been developed. The present data support the theory of a dual vacancy-interstitialcy diffusion mechanism for all the elements studied. The fraction of interstitialcy diffusion fI has been calculated, yielding fI=0.38 for phosphorus at 1000 °C, fI=0.30 for boron at 1000 °C, fI=0.35 for arsenic at 1090 °C, and fI=0.015 for antimony at 1100 °C. It has also been shown that the oxidation-induced supersaturation of self-interstitials is accompanied by an undersaturation of vacancies during oxidation. This undersaturation can be explained by a rate-limited bimolecular annihilation mechanism. This theory yields, for the first time, values for the vacancy-interstitial recombination-limited intrinsic vacancy lifetime in silicon under near-equilibrium conditions at high temperature; it also indicates the presence of an energy barrier to this recombination of the order of 1.4 eV.