The locking of dislocations by O was investigated experimentally in Czochralski Si (Cz-Si) with different concentrations of shallow dopants. Specimens containing well-defined arrays of dislocation half-loops were subjected to isothermal annealing at 350 to 550C, and the stress required to bring about dislocation motion at 550C was then measured. This dislocation unlocking stress was found to increase with annealing time due to O diffusion to the dislocation core. The dislocation unlocking stress was measured in n-type Cz-Si with a high Sb doping level (~3.4 x 1018/cm3) and p-type Cz-Si with a low B doping level (~1.3 x 1015/cm3). An analysis of the data taking the different O concentrations into account showed that the rate of increase in dislocation unlocking stress was unaffected by the high level of Sb doping. This indicated that a high Sb doping level has no significant effect on O transport for the conditions used in this experiment. However, in p-type Cz-Si with a high B doping level (~5.4 x 1018/cm3), the dislocation unlocking stress was found to rose at a much faster rate than in Cz-Si with a low B doping level or high Sb doping level. This enhancement in dislocation locking was by a factor of approximately 60 at 400C. By performing a numerical simulation to solve the diffusion equation for O transport to a dislocation, the effective diffusivity of O was deduced, from the dislocation unlocking data, to be given by:

D (cm2/s) = 2.7 x 10-6 exp[-1.4(eV)/kT]

in the highly B-doped Cz-Si. In the temperature range studied, the effective diffusion coefficient in the highly B-doped Cz-Si was found to be approximately 44 times higher than expected in low B doped Cz-Si with an identical oxygen concentration.

Enhanced Oxygen Diffusion in Highly Doped p-Type Czochralski Silicon. J.D.Murphy, P.R.Wilshaw, B.C.Pygall, S.Senkader, R.J.Falster: Journal of Applied Physics, 2006, 100[10], 103531 (6pp)

Table 77

Diffusivity of O in Si