Effect of oxygen concentration on diffusion length in Czochralski and magnetic Czochralski silicon

Abstract

This paper reports some new results on the influence of oxygen aggregation phenomena in the 450-850°C range on the diffusion length of minorities in both Czochralski (Cz) and magnetic Czochralski silicon. Thefeatures of the oxygen aggregation phenomena were studied by infrared spectroscopy at 20 K and the effect of these processes on the diffusion length was monitored by surface photovoltage measurements at 300 K. The results show that in Cz silicon the formation of thermal donors at 450°C is not associated with a detectable increase of the recombination activity, but that thermal donors are the precursors of other oxygen species, which grow during any further heat treatment. It was shown, moreover, that selfinterstitials injected from a surface oxide inhibit the oxygen segregation, in good agreement with predictions in the literature concerning the ‘volume exigency’ of oxygen segregation processes. Marked evidence of the influence of the cooling rate on the diffusion length was observed at 850°C, where the lifetime of heat treated Cz silicon was shown to be longer for a slow cooling process.

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