He implantation in Si for B diffusion control

A definitive method to prevent undesired phenomena related to B implantation in crystalline Si is still lacking. In fact, B undergoes enhanced diffusion, clustering and electrical deactivation as a consequence of interaction with implantation related damage. In this work we investigated the effect of He and B co-implantation in Si on point-defect population. We implanted Si wafers with B 12 keV, 5 × 1014 ions/cm2 and/or He 25–80 keV, 0.5–3 × 1016 ions/cm2. By means of B diffusion and Cu gettering experiments, we studied the effectiveness of He induced nanovoids on controlling self-interstitials generated by implantation. We demonstrated that nanovoids strongly affect B diffusion, producing a B box-like shape, and that their efficiency increases with increasing He fluence. Moreover, this beneficial effect is still present increasing the annealing temperature from 700 to 1000 °C, leading to a reduction of B clustering, while maintaining a strong confinement of the implanted B profile.