The stresses required to un-pin a dislocation from nitrogen impurities in nitrogen-doped float-zone silicon, and from oxygen impurities in Czochralski silicon, were measured as a function of the unlocking duration. It was found that the unlocking stress decreased with increasing unlocking time. The results indicated that dislocation-locking by nitrogen in nitrogen-doped float-zone silicon involved an atomic species, with a similar locking strength per atom to that previously deduced for oxygen atoms in Czochralski silicon. Other experiments measured the dislocation unlocking stress at 550C in nitrogen-doped float-zone silicon, annealed at 500 to 1050C. The results permitted the effective diffusivity of nitrogen in silicon at 500 to 750C to be deduced, yielding:

D (cm2/s) = 2 x 105exp[-3.24(eV)/kT]

This effective diffusivity was consistent with previous measurements made at higher temperatures using secondary ion mass spectrometry. When the results were analyzed in terms of a monomer-dimer dissociative mechanism, a nitrogen monomer diffusivity with an activation energy of 1.1 to 1.4eV was deduced. The data also showed that the saturation dislocation unlocking stress measured at 550C in nitrogen-doped float-zone silicon depended upon the annealing temperature, and peaked at 600 to 700C. It fell towards zero at 1000C.

Nitrogen Diffusion and Interaction with Dislocations in Single-Crystal Silicon. C.R.Alpass, J.D.Murphy, R.J.Falster, P.R.Wilshaw: Journal of Applied Physics, 2009, 105[1], 013519