Multiplicity of nitrogen species in silicon: The impact on vacancy trapping

Nitrogen in silicon is known to affect dramatically the properties of voids. A plausible mechanism could be vacancy trapping by nitrogen interstitial species, mostly by the minor monomeric species (NI) with only a negligible contribution of the major dimeric Species (N-2). However, a more careful analysis of the published data shows that in Czochralski silicon no vacancy trapping occurs at the void formation stage (around 1100 degrees C). The implication is that the trapping reaction, V + N-1, although favoured thermodynamically, is of a negligible rate. Therefore, the nitrogen effect on voids in Czochralski Si is entirely due to nitrogen adsorption at the void surface. Quite a different mechanism operates in Float-Zoned crystals where voids are formed at lower T. Here vacancy trapping by N-2 seems to be responsible for void suppression.