Rapid thermal annealing and regrowth of thermal donors in silicon

Rapid thermal annealing (RTA) of 450° thermal donors in Si at temperatures between 600 and 1000 °C and their subsequent regrowth between 375 and 450 °C have been investigated by infrared absorption and resistivity measurements. Thermal donors for small oxygen clusters identified by their excited state absorption are present in as-grown Czochralski Si, whereas a large range of cluster sizes are observed after extended heating at 450 °C. The temperature required for RTA is lower when only small clusters are present. Removal of thermal donors by RTA restores 5–8 oxygen atoms to interstitial sites per electrically measured donor removed, which supports oxygen cluster models for thermal donors. Restoration of oxygen to interstitial sites upon removal of thermal donors also impacts models treating relationships between thermal donors and oxygen precipitation in Si. An activation energy of 2.5±0.2 eV is obtained for RTA removal of thermal donors, consistent with oxygen diffusion. Initial regrowth of thermal donors after RTA at 1000 °C occurs with an activation energy of 1.7±0.2 eV.