Thermally stimulated current in SiO2

Thermally stimulated current (TSC) techniques provide information about oxide-trap charge densities and energy distributions in MOS (metal-oxide-semiconductor) capacitors exposed to ionizing radiation or high-field stress that is difficult or impossible to obtain via standard capacitance–voltage or current–voltage techniques. The precision and reproducibility of measurements through repeated irradiation/TSC cycles on a single capacitor is demonstrated with a radiation-hardened oxide, and small sample-to-sample variations are observed. A small increase in E′_δ center density may occur in some non-radiation-hardened oxides during repeated irradiation/TSC measurement cycles. The importance of choosing an appropriate bias to obtain accurate measurements of trapped charge densities and energy distributions is emphasized. A 10 nm deposited oxide with no subsequent annealing above 400°C shows a different trapped-hole energy distribution than thermally grown oxides, but a similar distribution to thermal oxides is found for deposited oxides annealed at higher temperatures. Charge neutralization during switched-bias irradiation is found to occur both because of hole-electron annihilation and increased electron trapping in the near-interfacial SiO₂. Limitations in applying TSC to oxides thinner than 5 nm are discussed.