He-vacancy interactions in Si and their influence on bubble formation and evolution

The mechanisms of He bubble and, after annealing, of void formation have been investigated for single and multiple He⁺ implants in Si. Several analytical techniques have been adopted: photoluminescence (PL), Rutherford backscattering of protons, transmission electron microscopy, and atomic force microscopy. When a second implant is performed a systematic enlargement of the bubble band reveals the importance of the interaction between He atoms and point defects generated during irradiation. Size effects of the implanted region protrusions indicated a He diffusion mechanism and an interaction with vacancies and divacancies for the bubble formation. PL spectra indicate the presence of complexes helium divacancies in the same temperature where self-interstitials annihilate at the sample surface. The interaction of helium atoms with divacancies allows the inversion in the vacancy-interstitial balance producing a supersaturation of vacancies in the silicon bulk. This vacancy supersaturation causes the observed annihilation of interstitial type defects after a suitable annealing.