Mechanism of electrical breakdown in SiO2 films

Abstract

The breakdown field associated with impact ionization and avalanche is estimated, using simple energy−momentum balance equations, for low−gap semiconductors and for high−gap insulators. Reasonable agreement is obtained in the former case, but estimated fields in the latter case turn out to be nearly an order of magnitude higher than those observed. This suggests that mechanisms other than avalanche are responsible for breakdown in insulators. A mechanism for SiO2 films, based on Fowler−Nordheim injection from a cathodic protuberance, filamentary Joule heating, and activation of mobile positive ions, which enhance the injecting field, is explored. The protuberance is taken to be spheroidal, with a dimension related to the thickness of the film and of order 100 Å. A mechanism for lateral spreading of the initial discharge and subsequent quenching by the substrate resistance gives the extent of the damaged area to be of the observed order in self−healing breakdowns. The breakdown field and its dependence on film thickness are in reasonable agreement with experiment.