POSTIRRADIATION FORMATION OF SI-SIO2 INTERFACE STATES IN A HYDROGEN ATMOSPHERE AT ROOM-TEMPERATURE

Si MOSFETs were irradiated with x-rays and then exposed to various partial pressures of H-2 at either room temperature or 125-degrees-C. The number of interface traps and the net positive oxide trapped charged were measured during the hydrogen exposure using spectroscopic charge pumping techniques. During the hydrogen exposure the gate electrode was held at a positive bias to maintain a field of 0.65 MV/cm across the gate oxide. It was found that during the room temperature hydrogen exposure the number of interface traps increased by a factor of about two. The change in the oxide trapped charge during hydrogen exposure indicated that the decrease in the number of positively charged oxide traps was approximately the same as the increase in the number of interface traps. The time evolution and bias dependence of these changes are explained by a model that we previously proposed. In this model positively charged radiation induced defects in the oxide crack the H-2 to form H+. Under positive gate bias the H+ then drifts to the Si-SiO2 interface where it forms an interface state, while at the same time removing positive charge from the oxide.