Dislocation locking by nitrogen impurities in FZ-silicon

The locking of dislocations by nitrogen impurities in nitrogen-doped FZ-grown (NFZ) silicon crystals was investigated as a function of time in the temperature range 550–830°C. It was found that nitrogen impurities induce a strong locking effect on stationary dislocations after a sufficiently long anneal. The locking is similar in magnitude to that observed for oxygen atoms in Czochralski-grown crystals (Cz), although the nitrogen concentration in the NFZ samples (2.2×1015cm−3) is two orders of magnitude lower than the usual oxygen concentration in Cz silicon. The unlocking stress initially increases with annealing time and then saturates to a value of approximately 50MPa for all the temperatures investigated. Information concerning nitrogen diffusion is deduced and by making certain physically realistic assumptions, data is inferred regarding the binding energy of nitrogen and the dislocation pinning force per nitrogen atom at the dislocation core.