NOVEL ASPECTS OF OXYGEN DIFFUSION IN SILICON

Normal diffusion of interstitial oxygen atoms (O-i) accounts for the r ate of oxygen aggregation in silicon for T > 500 degrees C. There is e vidence for the dissociation of SiO2 precipitates (Ostwald ripening) a nd the formation of self-interstitials (I-atoms) to accommodate the lo cal increase in volume. For T < 500 degrees C, measurements of the los s of oxygen atoms from solution indicate that O-2 dimer formation is t he rate-limiting process, but dissociation of dimers must be taken int o account when modelling this process. Large clusters of up to 10-20 O -i atoms, usually assigned to thermal donor (TD) defects cannot form u nless dimer diffusion is much greater (by a factor of 10(4) to 10(7)) than diffusion of Oi atoms and unless there is dissociation of cluster s with the emission of dimers. Hydrogen impurities enhance O-i diffusi on by a catalytic process and speed up donor formation. Infrared absor ption measurements reveal H-O-i complexes and there is also partial pa ssivation of TD defects to produce shallow thermal donors (STDs).