Charge build-up and oxide wear-out during Fowler-Nordheim electron injection in irradiated MOS structures

The degradation phenomena and charge build-up during high-field Fowler-Nordheim stress in silicon dioxide layers of MOS structures, pre-degraded by ionizing radiation, has been studied from the point of view of dielectric strength wear-out and long-term reliability. External bias of both polarities was applied to the structures during irradiation to separate generated carriers, force the current flow, and to enhance or inhibit radiation-induced degradation. It has been found that breakdown and wear-out properties of the oxides remain unchanged after the irradiation regardless of irradiation conditions. On the other hand, while the rate of electron trap generation during the prolonged stress has not been found sensitive to irradiation, we have found that the initial voltage transients during constant-current stress may be strongly affected by the changes in the radiation-induced hole trap occupancy. The character of the initial transient may indicate both net positive or negative charge build-up, depending on the hole trap occupancy prior to the high-field degradation.