Overpressurized bubbles versus voids formed in helium implanted annealed silicon

The formation of helium induced cavities in silicon is studied as a function of implant energy (10 and 40 keV) and dose (131015, 131016, and 531016 cm22). Specimens are analyzed after annealing (800 °C, 10 min) by transmission electron microscopy (TEM) and elastic recoil detection (ERD). Cavity nucleation and growth phenomena are discussed in terms of three different regimes depending on the implanted He content. For the low (131015 cm22) and high (531016 cm22) doses our results are consistent with the information in the literature. However, at the medium dose (131016 cm22), contrary to the gas release calculations which predict the formation of empty cavities, ERD analysis shows that a measurable fraction of the implanted He is still present in the annealed samples. In this case TEM analyses reveal that the cavities are surrounded by a strong strain field contrast and dislocation loops are generated. The results obtained are discussed on the basis of an alternative nucleation and growth behavior that allows the formation of bubbles in an overpressurized state irrespective of the competition with the gas release process