ORIGIN OF DISLOCATION LOOPS IN ALPHA-SILICON NITRIDE

Dislocation loops and stacking fault formation mechanism in alpha-Si3N 4 have been studied by annealing alpha-Si3N4 powders at 1500 degrees C and 1750 degrees C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been t entatively suggested to be two sources of vacancies in alpha-Si3N4. Fr om the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of alpha-Si3N4 lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of alpha-Si3N4 f abricated by different routes [chemical vapor deposition (CVD), silico n nitridation, silica carbothermal reduction, and imide decomposition] . A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of alpha-Si3N4 lattice aris en from the fact that the observed unit cell dimension of alpha-Si3N4 has a wide variation, and also to some related phenomena in processing of Si3N4.