  A two stream model of boron diffusion in silicon has been developed. The
model is intended for simulation of transient enhanced diffusion including
redistribution of ion-implanted boron during low temperature annealing. The
following mechanisms of boron diffusion were proposed, namely: the mechanism of
a long-range migration of nonequilibrium boron interstitials and the mechanism
due to the formation, migration, and dissolution of the "impurity atom -
silicon self-interstitial" pairs. Based on the model, simulation of the
redistribution of boron implanted into silicon substrates for annealing
temperatures of 800 and 900 Celsius degrees was carried out. The calculated
boron concentration profiles agree well with the experimental data. It was
shown that for a temperature of 800 Celsius degrees the transport of impurity
atoms occurred due to the long-range migration of nonequilibrium boron
interstitials generated during cluster transformation or dissolution. On the
other hand, it was found that at a temperature of 900 Celsius degrees the pair
diffusion mechanism played a main role in the significant transient enhanced
diffusion. A number of parameters describing the transport of nonequilibrium
boron interstitials and transient enhanced diffusion of substitutionally
dissolved boron atoms were determined. For example, it was found that at a
temperature of 900 Celsius degrees the time-average enhancement of boron
diffusion was approximately equal to 44 times. The results obtained are
important for the development of methods of transient enhanced diffusion
suppression keeping in mind the scaling of the dimensions of silicon integrated
microcircuits.
