Thermally Stimulated Current Measurements on Irradiated MOS Capacitors

Thermally stimulated current and high frequency C-V measurements have been used to study the properties of hole traps near the Si-SiO2 interface in irradiated silicon MOS capacitors. Pre-irradiation bias-temperature (BT) instabilities, both for negative and positive bias, were observed in non-ion-contaminated samples. The activation energy for BT instabilities for both polarities is 1.0 eV independent of radiation hardness. Distributions of activation energies for trapped holes produced by Co60 irradiation are centered at 0.85 and 1.3 eV. The 0.85 eV distribution occurs only if Na+ was previously present at the Si-SiO2 interface. The 1.3 eV distribution consists of multiple overlapping distributions. Mechanisms that could lead to these distributions of activation energies are discussed.