The damage created in SiO2 layers by low-energy Ar ions (130 keV) and the reconstruction of the structure after various annealing steps have been characterized as a function of the implantation dose. Quantitative determinations of the damage produced have been performed from infrared spectroscopy. We show that two dose thresholds for damage are encountered: At 1014 cm−2 damage saturates and for doses above 1017 cm−2 sputtering effects dominate. Annealing at high temperatures (1100 °C) restores the structure of the initial nonimplanted oxide only for doses below the second threshold, although some disorder remains. Electroluminescence measurements show that annealing is able to eliminate electrically active defects. For implantation doses greater than 1017 cm−2, annealing is unable to restore the structure completely as sputtering effects create a depleted oxygen layer at the surface and substoichiometric defects appear. The presence of microcavities created by the Ar atoms at such high doses may affect th...