The so-called normal diffusivity,

D(cm2/s) = 0.13 exp[-2.53(eV)/kT]

of bond-centered interstitial oxygen atoms (Oi) in Si was determined at 350 to 1300C. Aggregation of Oi atoms in Czochralski Si to form SiO2 precipitates was rate-limited by the above relationship at above 650C. Below 500C, O2 dimers were formed predominantly but the formation of large On clusters, traditionally identified with thermal donor defects, could not be explained unless dimers diffused much more rapidly than Oi atoms and there was dissociation of clusters, allowing dimers to be released and then to be re-captured by larger clusters.

R.C.Newman: Defect and Diffusion Forum, 1997, 143-147, 993-8