Generation of thermal donors in silicon: Effect of self-interstitials

The generation of low-temperature thermal donors (TD) in silicon is sensiti ve to the sample cooling rate (from the anneal to room temperature) and the ambient (air or vacuum). This effect is most clearly pronounced in the cas e of annealing at 500 degreesC, is noticeable at 480 degreesC, and is pract ically undetectable at 450 degreesC. The results are interpreted satisfacto rily as being due to the TD generation becoming enhanced in the presence of silicon self-interstitial (Si-I) atoms. These atoms are emitted by thermal donors, to be subsequently absorbed by sinks, particularly the sample surf ace and grown-in microdefects (vacancy voids). When annealing in a vacuum, the surface acts as the main sink. If the anneal is done in air, this sink is passivated as a result of oxidation and/or contamination, with voids bec oming the main sinks; as a result, the concentration of Si-I atoms increase s substantially and the generation rate is enhanced. Rapid cooling brings a bout a partial passivation of the voids (as a result of their becoming deco rated by rapidly diffusing impurities) and an additional enhancement of the generation rate. The calculated rate curves obtained within this model are well fitted to the experiment. (C) 2000 MAIK "Nauka/ Interperiodica".