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.