Radiation-induced charge neutralization and interface-trap buildup in metal-oxide-semiconductor devices

Abstract

Effects of switched bias on the radiation response of metal-oxide-semiconductor (MOS) devices have been investigated. Transistors with 50-nm gate oxides were irradiated at +10-V bias to create a large trapped-hole density in the oxide. Irradiation was continued under varying negative and positive biases. Very little radiation-induced charge neutralization is observed at biases <−10 V for these devices. However, significant trapped-hole neutralization is observed at biases from −10 to 0 V, with a broad maximum in neutralization rate from −6 to −1 V. The peak charge neutralization rate is approximately equal to the rate of trapped-hole buildup under positive bias. This establishes an upper bound on the rate of radiation-induced charge neutralization, and demonstrates that, under peak neutralization conditions, the effective cross section for the capture of radiation-induced electrons by a filled hole trap is similar to the effective cross section for capture of a hole by an empty trap. Interface traps are found to build up at approximately the same rate when the oxide electric field at the Si/SiO2 interface is positive, regardless of the field direction in the bulk of the oxide. This suggests that near-interfacial hydrogen may play a key role in interface-trap buildup in MOS devices.