Two series of n-type Si samples α and β are implanted with Si ions at high dose (1 × 1016) and high energies, 0.3 and 1.0 MeV, respectively. Both sort of samples are then implanted with 5 × 1016 He cm−2 (at 10 or 50 keV) and eventually with B atoms. Some of the samples are annealed at temperatures ranging from 800 to 1000 °C to allow the thermal growth of He-cavities, located between sample surface and the projected range (Rp) of Si. After the triple ion implantation, which corresponds to defect engineering, samples were characterized by cross-section transmission electron microscopy (XTEM). Voids (or bubbles) are observed not only at the Rp(He) on all annealed samples, but also at the Rp(Si) on β samples implanted with He at 50 keV. The samples are also studied by positron annihilation spectroscopy (PAS) and the spectra confirm that as-implanted samples contain di-vacancies and that the annealed …