Behaviour of oxygen in CZ-silicon during 430–630°C heat treatment

The generation of thermal donors (TDs) depends on initial oxygen concentration, annealing temperature and its duration. An annealing process at 450°C for several hours generates upto ≈1016 cm−3 TDs. We found that maximum concentration of TDs formed at 480°C was ≈1.0×1015 cm−3 which reduces to a minimum of ≈2.6×1014 cm−3 at 510°C suggesting thereby that the TDs got annihilated in this temperature range. The number of TDs now increases with a corresponding increase in annealing time giving birth to new donors (NDs). Activation energy for oxygen diffusion was found to be 0.6±0.1 eV and of silicon self interstitials ≈0.4 eV. Therefore, it is quite logical to conclude that oxygen diffusion at low temperatures depends on the transport of the self interstitials which are chiefly due to the formation of molecule-like oxygen clusters. This confirms the formation and diffusion of molecule-like oxygen clusters in silicon at low temperatures.