The conversion of isolated oxygen atoms to a fast diffusing species in Czochralski silicon at low temperatures

New measurements of oxygen out-diffusion in Czochralski silicon confirm previous reports that it occurs over an anomalously long range at low temperatures (T<700 °C). The surface concentration is shown to decrease with increasing anneal time at ∼430 °C while the depth to which the concentration is depleted remains almost constant. The rate of decrease of the surface concentration is correlated with the rate of loss of isolated oxygen atoms in the bulk. All these observations are explained if isolated oxygen atoms are converted slowly during the anneal to an oxygen-containing fast diffusing species (Ofds) which diffuses over long distances before being trapped. High concentrations (0.6–1.7×1017 cm−3) of substitutional carbon in the crystal increase the trapping rate of Ofds but this rate tends to decrease with increasing anneal time, tending to the value for carbon-free material. Estimates of the rate of formation of Ofds are close to the expected rate of dimerization in a dilute solution at the lowest temperatures (T<450 °C), but tend to be below the expected rate at higher temperatures. There is no clear indication of Ofds dissociation over the whole temperature range (T⩽700 °C). These observations suggest that the formation of Ofds is more complicated than one would expect if it were the O2 dimer. Alternatives such as the oxygen vacancy complex should be considered.