Post-irradiation behavior of the interface state density and the trapped positive charge

The postirradiation behavior of the energy distribution of interface states, D_it, and of the trapped positive charge, N_ot, of MOS devices is studied. The shift of interface state density from the broad peak at 0.7 eV to below midgap is found to be reversible. The direction of the shift is determined by the surface potential. The postirradiation introduction of hydrogen into the gate oxide increases the interface state density across the bandgap and decreases N_ot by a similar amount. Following the introduction of hydrogen, the reversibility of N_ot is increased by an order of magnitude. These effects show the connection between the experimental conditions and the type of postirradiation behavior that is observed. Models for the hydrogen-induced D _it buildup and for the reversibility of D_it and N_ot are discussed