Is enhanced interstitial oxygen diffusion necessary to explain the kinetics of precipitation in silicon at temperatures below 650 degrees C?

Oxygen precipitation in silicon has been studied in the temperature range 500 to 600 degrees C using infrared absorption measurements of the 19.5 mu band. The data have been fitted to theoretical models described by Ham (1958) for the diffusion limited growth of randomly distributed particles. Values of c s , the equilibrium concentration of oxygen, were obtained directly, and assuming the normal diffusion coefficient for interstitial oxygen the authors determined the number density of the precipitates and their spherical radii. These results are linked to previous data obtained at higher and lower temperatures, yielding a self-consistent model. The value of c s decreases to a value of 8*10 15 cm -3 at 650 degrees C, but then increases again to 2*10 17 cm -3 at 450 degrees C. This behavior, not previously reported, is attributed to the importance of the surface energy for very small agglomerates. The results imply that if the thermal donors and cosite precipitates which are observed at low temperatures arise from oxygen aggregation, they could not form unless an oxygen complex, such as a di-oxygen species, has a much larger diffusion coefficient than an isolated interstitial oxygen atom.