Precipitation of oxygen in silicon

At high temperatures (1200 °C) the precipitation of oxygen in bulk dislocation-free Czochralski silicon is inhibited by the absence of nucleation centers. A substantial supersaturation corresponding to a temperature drop of about 80 °C below the equilibrium saturation temperature is necessary for nucleation to occur. However, following a preliminary low-temperature treatment (700 °C) precipitation occurs at a substantially smaller undercooling. This suggests that precipitation in crystals without a prior low-temperature treatment occurs by homogeneous nucleation in the crystalline phase, in the absence of structural defects. Using classical nucleation theory the surface free energy of the precipitate is calculated to be about 100 erg/cm2 and the critical nucleus contains about 200 oxygen atoms.