Modeling of the long-range interstitial migration of ion implanted boron

A model for interstitial migration of ion implanted boron during rapid thermal annealing of the silicon layers amorphized by implantation of germanium has been developed. It is supposed that boron interstitials are generated continuously during the whole annealing due to dissolution or rearrangement of the clusters of dopant atoms which are formed in the ion implanted layer with impurity concentration above the solubility limit at the initial stage of the treatment. The local elastic stresses arising due to a small atomic radius of boron also contribute to the generation of boron interstitials. A simulation of boron redistribution during thermal annealing for 60 s at a temperature of 850 °C has been carried out. The calculated profile agrees well with the experimental data thus confirming adequacy of the model proposed. A number of the parameters of interstitial boron diffusion have been derived. In particular, the average migration length of nonequilibrium boron interstitials is equal to 12 nm. It was also obtained that approximately 1.8-2% of the boron atoms became interstitial, participated in the fast interstitial migration, and then became immobile again occupying substitutional lattice sites or forming complexes with the crystal lattice defects.