On the correlation between radiation-induced oxide- and border-trap effects in the gate-oxide nMOSFET’s

Abstract

In this study, combined voltage- and frequency-charge pumping techniques were used to investigate the generation and evolution of border-traps in degraded NMOS transistors by using 1.25 MeV 60Co γ-rays. In addition, gate length effects on border-trap charge density were discussed. First result, both border- and oxide-trap reveal two behaviors as function of total dose at low dose rate. Primarily, there is an increase of both trapped charges, followed later by a decrease of their net charge. Second result, border-trap presents a strong dependence on designed transistor channel length. Transistors with longer gate lengths exhibit less important border-trap during irradiation than transistors with smaller gate lengths. This is due to differences in the near-interfacial stress. However, the same effects were observed for oxide-traps. These results show a great correlation between radiation-induced border- and oxide-trap behaviors at low dose rate. Therefore, this similarity strengthens the idea that both border- and oxide-trap could have the same defect ( E ′).