The effects of nitridation and reoxidation on the off-state leakage currents of n-channel metal-oxide-semiconductor-field-effect transistors have been investigated. It is found that nitridation greatly increases the gate leakage in the low-field range but ensuing reoxidation can effectively reduce it. Nitridation-induced oxide traps could be responsible for this leakage, along with traps introduced during the source/drain implant. A trap-assisted tunneling model has been proposed to explain this off-state gate leakage.

Using rapid thermal processing (RTP), SiO2 films with a thickness of 35 nm were annealed in NH3 and subsequently reoxidized. The properties of charge trapping and interface state generation of these films were investigated by an avalanche hot-electron injection technique. Experimental results indicate that by reoxidation, both the density of NH3 annealing induced traps and their capture cross section can be reduced; the hardness of the interface against hot-electron bombardment is improved while the low oxide fixed charge and interface state density as well as the high breakdown field are also preserved. A correlation between the interface state generation and the history of thermal nitridation is observed. Results also show that rapid thermal NH3 annealing induced traps must be water related and have a much smaller capture cross section than that of the conventionally nitrided oxide. It is proposed that hydrogen dissolved from NH3 during nitridation introduces defects in the form of unsaturated Si--O bonds which may be responsible for the high density of electron traps while the interface-incorporated nitrogen will help to increase the resistance to the hot-electron injection induced damage. An oxygen deficiency model can be used to explain the origin of these traps as well as the generation of interface states and the mechanism of reoxidation.