Measurements of dislocation locking by near-surface ion-implanted nitrogen in Czochralski silicon

A modified dislocation unlocking technique is used to measure dislocation locking due to nitrogen implanted into Czochralski silicon. The results show that near-surface dislocations can be locked by implanted nitrogen. The magnitude of the locking measured suggests that nitrogen transport proceeds by a dissociative mechanism, where transport occurs by the splitting of immobile dimers into fast monomers, rather than movement of nitrogen dimers. In other experiments, nitrogen-doped float-zone silicon is investigated using the standard dislocation unlocking technique. The results give an activation energy for effective nitrogen diffusion in silicon of 3.24±0.25eV at 500 to 750°C Using the assumption that the dislocation locking strength per nitrogen atom is the same as that of oxygen, a value of 200,000cm 2s-1 can be inferred for the effective diffusivity prefactor. If analysed using the dissociative model, an activation energy of 1.1 to 1.4eV is found for nitrogen monomer diffusion, with a diffusivity pre-factor of 30cm2s-1. © The Electrochemical Society