Novel aspects of oxygen diffusion in silicon

Normal diffusion of interstitial oxygen atoms (O_i ) accounts for the rate of oxygen aggregation in silicon for T > 500C. There is evidence for the dissociation of SiO₂ precipitates (Ostwald ripening) and the formation of self-interstitials (I-atoms) to accommodate the local increase in volume. For T < 500 C, measurements of the loss of oxygen atoms from solution indicate that O₂ dimer formation is the rate-limiting process, but dissociation of dimers must be taken into account when modelling this process. Large clusters of up to 10–20 O_i atoms, usually assigned to thermal donor (TD) defects cannot form unless dimer diffusion is much greater (by a factor of 10⁴ to 10⁷ ) than diffusion of O_i atoms and unless there is dissociation of clusters with the emission of dimers. Hydrogen impurities enhance O_i diffusion by a catalytic process and speed up donor formation. Infrared absorption measurements reveal H-O_i complexes and there is also partial passivation of TD defects to produce shallow thermal donors (STDs).