Oxygen transport in Czochralski silicon investigated by dislocation locking experiments

Dislocation locking has been investigated in Czochralski silicon with different oxygen concentrations in the 350–850 °C temperature range. Specimens containing well-defined arrays of dislocation half-loops are subjected to isothermal anneals of controlled duration, during which oxygen diffuses to the dislocations. The stress required to bring about dislocation motion is then measured at 550 °C. The dislocation unlocking stress as a function of annealing time is found to obey distinct regimes. For all annealing temperatures investigated, the unlocking stress initially rises approximately linearly before taking a constant value. The unlocking stress data are analyzed to give values for the binding energy of oxygen to a dislocation and the effective diffusion coefficient of oxygen in silicon. At high temperatures (650–850 °C) the diffusion coefficient of oxygen is found to be in agreement with established values. At low temperatures (350–650 °C) oxygen transport is found to be strongly enhanced, with an activation energy of approximately 1.5 eV and a pre-factor which depends on oxygen concentration. For given annealing conditions, the dislocation unlocking stress has been found to depend on the temperature at which the unlocking process is carried out in the 450–700 °C temperature range. Furthermore, the dislocation locking technique has been used to study the effect of high concentrations of shallow dopants on oxygen diffusion in the 350–550 °C temperature range. Oxygen transport has been found to be unaffected by a high antimony concentration (∼3 × 1018 cm−3), but is found to be enhanced by a factor of approximately 44 in material with a high boron concentration (∼5 × 1018 cm−3).