A systematic study was made of the formation of He ion implantation-induced nanovoids in Si and how they influence the self-interstitial (Is) supersaturation, thus affecting the diffusion and electrical activation of implanted B in crystalline Si. Helium ions were implanted into (100)-oriented Si wafers, to doses ranging from 5 x 1015 to 8 x 1016He/cm2 and energies ranging from 25 to 110keV. Boron ions (12keV, 5 x 1014/cm2) were then implanted. All of the samples were annealed at 800C in N2 atmosphere. The role of nanovoids in already reducing B diffusion in the first stages of post-implantation annealing was demonstrated. The effect was attributed to the was trapping by the nanovoids that forces B to assume a box-like profile. Moreover, the nanovoid distribution was studied as a function of He-implanted dose and energy, demonstrating, by means of Cu gettering experiments, the beneficial effect of increasing dose or decreasing energy of He implantation on the B diffusion and electrical activation. In fact, if the nanovoid density was high in the proximity of implanted B, implantation-related damage could annihilate at the internal dangling bonds of nanovoids, thus consuming the nanovoid layer. The potential of He co-implantation as a method for controlling point-defect distributions in crystalline Si was presented and critically discussed.

He Induced Nanovoids for Point-Defect Engineering in B-Implanted Crystalline Si. E.Bruno, S.Mirabella, F.Priolo, E.Napolitani, C.Bongiorno, V.Raineri: Journal of Applied Physics, 2007, 101[2], 023515