Total dose irradiation effects on silicon and germanium MOS capacitors with alternative gate dielectrics
Alternative dielectrics are rapidly becoming necessary for the future of Metal-Oxide-Semiconductor (MOS) devices, as SiO2-based technology reaches scaling limits. In this thesis, the total ionizing dose irradiation effects on Si and Ge MOS capacitors with Hf-based gate dielectrics are investigated. The radiation response of the HfO2/Dy2O3 on Ge MOS devices exhibited no change in the capacitance-voltage characteristics. HfO2 has the tendency to trap large amounts of electrons relative to SiO2. However the high gate leakage current likely efficiently neutralized any radiation-induced charge build-up for these devices. We have also examined the radiation response and bias-temperature effects of Si MOS devices with HfSiON gate dielectrics. The results showed much improved radiation hardness relative to earlier Hf silicate devices (net oxide-trapped charge density ~ 16× less). The low-Si3N4 content film also displayed enhanced charge trapping relative to the high-Si3N4 content film. In addition, the HfSiON devices showed much reduced degradation from bias-temperature stress relative to SiO2 and HfO2 devices. However the improved bias-temperature stability likely results from difference in processing techniques, and comes at the cost of high density of process-induced interface traps. The material properties and processing techniques can significantly influence the reliability and radiation response of high-k MOS devices. The work in this thesis provides insights to the reliability and radiation degradation that are essential to the development of Hf-based MOS devices.