ATOMISTIC ANALYSIS OF THE VACANCY MECHANISM OF IMPURITY DIFFUSION IN SILICON

The complete set of the four macroscopic transport coefficients descri bing the coupled diffusion of impurity atoms and vacancies in silicon is calculated from the atomistic mechanism by accurately taking into a ccount the effects of the microscopic forces between dopants and vacan cies. The aim of these simulations is to come to a decision concerning the validity of models like the pair diffusion model [e.g., M. Yoshid a, J. Appl. Phys. 48, 2169 (1977); R. B. Fair and J. C. C. Tsai, J. El ectrochem. Sec. 124, 1107 (1977); F. F. Morehead and R. F. Lever, Appl . Phys. Lett. 48, 151 (1986); B. J. Mulvaney and W. B. Richardson, App l. Phys. Lett. 51, 1439 (1987)] or the ''non-Fickian diffusion'' model [M. Kurata, Y. Morikawa, K. Nagami, and H. Kuroda, Jpn. J. Appl. Phys . 12, 472 (1973); Y. Morikawa, K. Yamamoto, and K. Nagami, Appl. Phys. Lett. 36, 997 (1980); V. V. Kozlovski, V. N. Lomasov, and L. S. Vlase nko, Radiat. Eff. 106, 37 (1988); O. V. Aleksandrov, V. V. Kozlovski, V. V. Popov, and B. E. Samorukov, Phys. Status Solidi 110, K61 (1988), K. Maser, Exp. Tech. Phys. (Berlin) 34, 213 (1986), K. Maser, Ann. Ph ys. (Leipzig) 45, 81 (1988), K. Maser, Exp. Tech. Phys. (Berlin) 39, 1 69 (1991)] that make contradicting predictions for very fundamental pr operties like the relative direction of the fluxes of dopants and vaca ncies driven by a vacancy gradient and for the relation alpha = Td(0)/ Dd(0) between two of the four transport coefficients. Simulation resul ts are shown for a variety of assumed interaction potentials that esta blish a functional dependence between ct and measurable quantities,;li ke the factor D-d/D-tracer of enhancement of dopant diffusivity over t racer diffusion, that holds for an arbitrary interaction. The comparis on with experimental values for D-d/D-tracer leads to confirmation of the pair diffusion model for boron and phosphorous. For arsenic and an timony, the large scatter of the experimental data prohibits an equall y definite conclusion, but at least a qualitative confirmation of pair diffusion theory (i.e., alpha>0 which means that dopant and vacancy f luxes have the same direction if caused by a vacancy gradient) is poss ible. (C) 1998 American Institute of Physics.