ATOMISTIC MODELING OF HIGH-CONCENTRATION EFFECTS OF IMPURITY DIFFUSION IN SILICON

The vacancy mechanism of dopant diffusion in silicon is investigated o n a microscopic model level. The concentration dependence of the dopan t diffusion constant in the high-concentration regime is simulated usi ng the Monte-Carlo method and an atomistic model of clustering and pre cipitation. The simulation takes into account the microscopic forces b etween particles (dopant atoms and vacancies) in a quantitative manner . Since sufficiently accurate data for the binding strength and shape pf the interaction potentials are not available, we analyze a variety of model approaches for these interactions to come to general conclusi ons for the macroscopic consequences of microscopic models. First, pur e attractive forces between dopants and vacancies as usually assumed i n the literature [S. M. Hu, Phys. Status Solidi B 60, 595 (1973)] are discussed. In contradiction to previous results from the literature [S . T. Dunham and C. D. Wu, J. Appl. Phys. 78, 2362 (1995)] we find that with this approach it is not possible to fit the experimental results . Also, models with repulsive dopant-dopant potentials of Coulomb shap e together with attractive dopant-vacancy forces are found to give unr ealistic results. On the other hand, a good fit to the experimental da ta is obtained with the assumption of a nonbinding dopant-vacancy inte raction that only increases the mobility of the vacancy in the neighbo rhood of a dopant. The parameters of the atomistic potential are deriv ed from a fit of the simulations to the experimental values. The simul ation results for the different microscopic approaches are also used t o give an assessment of the validity of models for high-concentration diffusion that are based on percolation theory [D. Mathiot and J. C. P fister, J. Phys. (France) Lett. 43, L-453 (1982); D. Mathiot and J. C. Pfister, J. Appl, Phys. 66, 970 (1989)]. (C) 1998 American Institute of Physics.