Measurements of Dislocation Locking by Near-Surface Ion-Implanted Nitrogen in Czochralski Silicon

Abstract

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 500–750°C . Using the assumption that the dislocation locking strength per nitrogen atom is the same as that of oxygen, a value of 200,000cm2normals−1 can be inferred for the effective diffusivity prefactor. If analyzed using the dissociative model, an activation energy of 1.1–1.4 eV is found for nitrogen monomer diffusion, with a diffusivity prefactor of 30cm2normals−1 .

Structural damage in thin SLIM-Cut c-Si foils fabricated for solar cell purposes: atomic assessment by electron spin resonance

“…In a first consideration, straightforward standard diffusion of N from the ambient into a freshly exposed, undamaged Si surface is of course excluded outright. No conventional diffusion process would enable N atoms to diffuse tens of μms deep [39,40] into the lift-off foil side (as observed; see figure 7) at the outlined processing temperatures [3] if no drastic enhancement factor is involved. To force substitution of N atoms so deep inside the c-Si lattice under these circumstances would need deep channel (crack) formation.…”