Gamma-ray-irradiation effects on the leakage current and reliability of sputtered TiO2 gate oxide in metal–oxide–semiconductor capacitors

Abstract

The leakage current and reliability characteristics of γ-ray-irradiated sputtered titanium dioxide (TiO2) thin films have been systematically investigated. Analytical results revealed that the inferior polycrystallinity and the larger leakage current of the anatase structure of unirradiated TiO2 thin film could be effectively improved by raising the irradiation dose at low γ-ray doses [≦10 kGy(TiO2)]. However, any higher dose [>10 kGy(TiO2)] causes undesirable deterioration of the film crystallinity, yielding an increased leakage current. The optimal dose of γ-rays [10 kGy(TiO2) in this work] not only provides a proper energy transfer to the TiO2 film, but also reduces the oxygen deficiency and/or Si-diffusion contamination, resulting in a superior crystallinity, and thus causing the reduced leakage current. The excellent agreement between the E model (thermochemical-breakdown model) and the time-dependent-dielectric-breakdown data suggested strongly that the best long-term reliability of metal–oxide–semiconductor capacitors with the TiO2 gate oxide treated by 10 kGy(TiO2) of γ rays was due to the superior crystallinity and the smaller hole trap density at the TiO2/Si interface, resulting in an increased activation energy, thus reducing the occurrence of breakdown.