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 10(12) and 10(13) 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 degrees 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 degrees 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 x 10(18) cm(-3) for clustering at 400-500 degrees C.