The electrical activity of implanted Al atoms was investigated. Precipitates of Al at the surface did not contribute to the conductivity. Upon annealing at 1250C, the Al precipitates disappeared. The low electrical activity of the Al atoms was related to the existence of Al precipitates, which corresponded to O precipitates, and to the out-diffusion of Al. By using a new annealing method in which a capping film covered the implanted surface, the out-diffusion of Al atoms from the implanted region into the capping film and simultaneous back-diffusion into the Si substrate was observed. Such a back-diffusion mechanism increased the Al atom concentration and the electrical activity.

M.Watanabe, O.Ishiwata, M.Nagano, H.Kirihata: Journal of the Electrochemical Society, 1991, 138[11], 3427-31