  A model of interstitial impurity migration is proposed which explains the
redistribution of ion-implanted boron in low-temperature annealing of
nonamorphized silicon layers. It is supposed that nonequilibrium boron
interstitials are generated either in the course of ion implantation or at the
initial stage of thermal treatment and that they migrate inward and to the
surface of a semiconductor in the basic stage of annealing. It is shown that
the form of the "tail" in the boron profile with the logarithmic concentration
axis changes from a straight line if the average lifetime of impurity
interstitials is substantially shorter than the annealing duration to that
bending upwards for increasing lifetime. The calculated impurity concentration
profiles are in excellent agreement with the experimental data describing the
redistribution of implanted boron for low-temperature annealing at 750 Celsius
degrees for 1 h and at 800 Celsius degrees for 35 min. Simultaneously, the
experimental phenomenon of incomplete electrical activation of boron atoms in
the "tail" region is naturally explained.
