The location and annealing of paramagnetic oxygen vacancies (E1' centres) in silicon implanted with high doses of oxygen

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Abstract
Electron paramagnetic resonance measurements have been made on samples of (100) n-type silicon which have been implanted with 200 keV oxygen ions in the implantation temperature range of 500-620 degrees C and with doses ranging from 0.5 to 2.2*1018 O cm-2. Amongst the various defects observed in the as-implanted samples are E1' centres whose population per unit area of implanted surface exhibits a maximum at a dose of 1.4*1018 cm-2, which is the dose above which a continuous buried oxide layer is formed. These E1' centres, in a sample implanted with 1.8*1018 O cm-2, begin to anneal at about 350 degrees C-a process which is irreversible. Subsequent electron or gamma -irradiation at room temperature increases the E1' centre concentration but only in those samples containing a buried oxide layer. This increase saturates at a dose of about 7 Mrad. The results can be explained by assuming that for the as implanted samples all E1' centres are in the oxide precipitates and that those 'reactivated' by electron or gamma irradiation are all in the buried layer. The latter also begin to anneal irreversibly at about 350 degrees C but can be annealed reversibly at lower temperatures. The anneal mechanisms are examined in the light of these results.