Nitrogen interaction with vacancies in silicon

Nitrogen doping of float-zoned (FZ) crystals is known to suppress vacancy aggregation into voids (contrary to Czochralski-grown crystals). The frozen-in vacancy–nitrogen defects have been reported to behave in a complicated way during subsequent anneals. A model to account for these peculiarities is described; the most essential point is that the major vacancy trap, nitrogen single interstitial N1, is represented by two forms. The stable form N1A is fast equilibrated with nitrogen dimers but cannot trap vacancies. The metastable form N1B is not paired into dimers but can easily trap a vacancy to become a substitutional nitrogen, VN – a high-temperature form of vacancy–nitrogen defects. The grown-in form is concluded to be VN2 – produced by attaching N1B to VN at lower T.