Vacancy-type defects created by single-shot and chain ion implantation of silicon

Vacancy-type defects created by single-energy implantation of Czochralski-grown single-crystal silicon by 4 MeV silicon ions at doses of 1012 and 1013 cm−2 have been compared with those created by an energy chain of implants of 0.4, 0.9, 1.5, 2.2 and 4 MeV ions, each at one-fifth of the single-energy dose. Measurements were taken for as-implanted samples and after annealing to temperatures up to 600 °C. In contrast to the expectation that a more uniform depth distribution of interstitials and vacancies would lead to a more efficient recombination and consequently fewer surviving vacancies, vacancy-related damage survived in the chain-implanted samples to higher temperatures, before almost complete annealing at 600 °C. It is therefore concluded that it is the absolute initial monovacancy concentration, rather than any initial separation of vacancy- and interstitial-rich regions, that determines the probability of survival as divacancies, and that there exists a threshold divacancy concentration of 1–2 × 1018 cm−3 for clustering at 400–500 °C.