Kinetic model of thermal donor evolution

Kinetic aspects of thermal donor (TD) formation in Czochralski silicon are shown to be consistent with the evolution of small oxygen clusters, as described within the classical theory of nucleation. predictions for TD generation and interstitial oxygen loss are presented. Favorable agreement with experimental data requires that the rate constants describing cluster evolution be increased over those expected for a diffusion-limited flux based on a normal diffusion coefficient for oxygen in silicon. This may signal an anomalously high diffusion rate for temperatures less than 500 degrees C, as has been suggested by others. However, it may instead signal an enhanced concentration of free oxygen near clusters smaller than the critical size for nucleation. This is expected when the interfacial attachment rates become comparable with the rates at which oxygen atoms arrive in the vicinity of the sub-critical clusters. The link between thermal donor generation and oxygen precipitation processes demonstrated here provides a consistent framework for better understanding and controlling oxygen precipitation in silicon Further, the kinetic TD generation and oxygen loss data provide a new window into the dynamical processes for small clusters, which underlie all nucleation phenomena.