Positron annihilation spectroscopy in the Doppler broadening mode was used to study the effects of He and B implantation, and subsequent annealing, upon the vacancy profile of crystalline Si. The existence of two void layers, one consisting of large voids at the projected range (Rp) of He, and another containing so-called nanovoids which were slightly larger than divacancies, roughly halfway between the Rp of He and the surface, was demonstrated for samples implanted with He. The same nanovoid layer was shown to be absent from samples co-implanted with B; thus implying that interstitials created during B implantation became trapped in the nanovoids and filled them, thus indicating that the nanovoid layer caused the hindrance of B diffusion.

Vacancy Engineering by He Induced Nanovoids in Crystalline Si. S.Kilpeläinen, K.Kuitunen, F.Tuomisto, J.Slotte, E.Bruno, S.Mirabella, F.Priolo: Semiconductor Science and Technology, 2009, 24[1], 015005