The transient enhanced diffusion of acceptor impurities severely affects the realization of ultra-high doping regions in miniaturized Si-based devices. Fluorine co-doping was found to suppress this transient diffusion, but the mechanism underlying this effect was not understood. It was proposed that F-impurity or F–native-defect interactions may be responsible. This mechanism was clarified here by combining first-principles theoretical studies of F in Si and purposely designed experiments on Si structures containing B and F. The central interaction mechanism was the preferential binding of F to Si-vacancy dangling bonds and the consequent formation of vacancy-F complexes. The latter effectively act as traps for the excess self-interstitials that would normally cause B transient enhanced diffusion. Instead, F-B interactions were marginal and do not play any significant role. The results were also consistent with other observations, such as native-defect trapping and bubble formation.

Fluorine in Si - Native-Defect Complexes and the Suppression of Impurity Diffusion. G.M.Lopez, V.Fiorentini, G.Impellizzeri, S.Mirabella, E.Napolitani: Physical Review B, 2005, 72[4], 045219 (7pp)