Origin of dislocation loops in α-silicon nitride

Abstract

Dislocation loops and stacking fault formation mechanism in α–Si₃N₄ have been studied by annealing α–Si₃N₄ powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si₃N₄. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si₃N₄ lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si₃N₄ fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si₃N₄ lattice arisen from the fact that the observed unit cell dimension of α–Si₃N₄ has a wide variation, and also to some related phenomena in processing of Si₃N₄.