Total dose response of Al₂O₃-based MOS structure under gamma-ray irradiation

The effect of gamma irradiation upon Al/Al₂O₃/Si MOS structure under different doses of ⁶⁰Co is studied in this article as a function of total dosage. Al₂O₃ MOS capacitors with a gate dielectric thickness of 4nm and electrode diameter of Φ 1mm are prepared on the p-Si substrate using atomic layer deposition. The MOS capacitors are under zero bias during irradiation under ⁶⁰Co gamma ray with total dose of 300Krad(Si)/500Krad (Si)/1Mrad (Si) and dose rate of 50rad (Si)/s. The high frequency Capacitor-Voltage (C-V) and Current-Voltage (I-V) characteristic are measured at room temperature before and after irradiation for each sample. In addition, Atomic Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (GIXRD), and X-ray Photoelectron Spectroscopy (XPS) are also applied to determine the surface morphology, physical and mechanical properties under different doses of radiation. The oxide trapped charge calculated from the high frequency C-V characteristics is in the order of 10¹¹ cm ^-2 and increases with the applied total dose. The XRD spectrum shows several phases of Al₂O₃ variation under each total dose. The XPS result shows that different total dosage leads to the drift of binding energy peak to a different degree, which indicates the influence of irradiation on the valence state of the elements attributed to the gamma-ray induced interface states.