Oxide charge accumulation in metal oxide semiconductor devices during irradiation

An analysis of a simple physical model for radiation induced oxide charge accumulation in the SiO2 layer of metal oxide semiconductor (MOS) structure has been developed. The model assumes that both electron and hole traps exist in the oxide layer. These traps can capture electrons as well as holes during irradiation. Using this model, final oxide charge distributions in the oxide layer of MOS capacitors exposed to a total dose radiation can be predicted. The resulting charge distribution is calculated to yield the midgap voltage shifts as functions of total dose, bias voltage, and oxide thickness. The results are shown to agree well with the experimental data. Furthermore, the model successfully analyzes the radiation-induced negative oxide charge distribution in an ion-implanted, radiation-hard MOS capacitor. These negative oxide charge distributions not only partially compensate the effects of trapped positive oxide charges but also reduced the density of positive oxide charges trapped near the Si/SiO2 interface. We found the reduction of the positive oxide charge density near the Si/SiO2 interface is due to internal electric field modification in the oxide layer.