In this work we demonstrate that He co-implantation can be a powerful tool to control B diffusion in crystalline silicon (c-Si). In particular, the He induced damage leads to the formation of a distribution of nano voids near the surface that locally suppress the amount of self-interstitial s (Is) generated by further B implantation. Thus, B diffusion is reduced and the B implanted profile assumes a box-like shape. In particular, we analyze the microscopic mechanisms leading to the implanted B-nanovoids interaction, demonstrating that the Is ...