Electrical conduction in silicon nitrides deposited by plasma enhanced chemical vapour deposition

Current conduction in Si-rich and stoichiometric silicon nitride as well as in oxynitride is studied in detail. Representative samples from each of the three categories exhibit Ohmic, Poole-Frenkel and Fowler-Nordheim tunnelling currents to differing extents. All the samples show an Ohmic region at low electric fields. The oxynitride sample has the largest Ohmic region, and the Si-rich sample the smallest. Under intermediate and high fields, the oxynitride sample shows only Fowler-Nordheim tunnelling but the Si-rich sample is dominated by Poole-Frenkel emission. The stoichiometric sample shows a Poole-Frenkel region at intermediate fields and a Fowler-Nordheim region at high fields. These results indicate that the oxynitride sample has the lowest density of traps, and the Si-rich sample has the highest. Our observations are explained in terms of the flexibility of bonding configurations of N and O atoms, and the formation of Si-Si bonds in Si-rich silicon nitride.