The results of dislocation unlocking experiments are reported. The stress required to unpin a dislocation from nitrogen impurities in nitrogen-doped float-zone silicon (NFZ-Si) and from oxygen impurities in Czochralski silicon (Cz-Si) is measured, as a function of the unlocking duration. It is found that unlocking stress drops with increasing unlocking time in all materials tested. Analysis of these results indicates that dislocation locking by nitrogen in NFZ-Si is by an atomic species, with a similar locking strength per atom to that previously deduced for oxygen atoms in Cz-Si. Other experiments measure dislocation unlocking stress at 550 °C in NFZ-Si annealed at 500–1050 °C. The results allow an effective diffusivity of nitrogen in silicon at 500–750 °C to be inferred, with an activation energy of 3.24 eV and a diffusivity prefactor of approximately 200 000 cm2 s−1. This effective diffusivity is consistent with previous measurements made at higher temperatures using secondary ion mass spectrometry. When the results are analyzed in terms of a monomer-dimer dissociative mechanism, a nitrogen monomer diffusivity with an activation energy in the range of 1.1–1.4 eV is inferred. The data also show that the saturation dislocation unlocking stress measured at 550 °C in NFZ-Si is dependent on the anneal temperature, peaking at 600–700 °C and falling toward zero at 1000 °C.

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Dislocation locking by nitrogen impurities has been investigated in float-zone silicon with nitrogen concentrations of 2.2 x 1015cm-3 and 3 x 1014cm-3. The stress required to unlock dislocations pinned by nitrogen impurities was measured as a function of annealing time (0 to 2500 hours) and temperature (550 to 830°C). For all conditions investigated the locking effect was found to increase linearly with annealing time before saturating. It is assumed that the rate of increase of unlocking stress with annealing time is a measure of transport of nitrogen to the dislocation core. This rate of increase was found to depend linearly on nitrogen concentration, which is consistent with transport by a dimeric species, whose activation energy for diffusion is approximately 1.4eV. The saturation unlocking stress has been found to be dependent on the nitrogen concentration. Additionally, the temperature dependence of the stress required to move dislocations immobilised by nitrogen impurities has been studied. By assuming a value for the binding energy of the nitrogen to the dislocation, the density of the locking species at the dislocation core has been calculated.

A measurement of nitrogen out‐diffusion from nitrogen‐doped float‐zone silicon made using a dislocation locking technique is presented. Specimens containing a well‐defined array of dislocation half‐loops are subjected to identical anneals at 750 °C, during which nitrogen diffuses both to the surface and to the dislocations. The specimens are then chemically etched so as to remove different thicknesses of material from the surface. The stress required to move the dislocations away from the nitrogen is then measured. The variation in this unlocking stress with thickness of material removed allows some measure of nitrogen diffusivity to be deduced. The result obtained is consistent with an extrapolation of SIMS out‐diffusion measurements previously performed at higher temperatures, but indicates a different activation energy for out‐diffusion to that associated with dislocation locking by nitrogen. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)