Irradiation effect of HfO2 MOS structure under gamma-ray

The effect of gamma irradiation upon Al/HfO₂/SiO₂/Si MOS structure under different doses of ⁶⁰Co is studied in this article as a function of total dosage. MOS capacitors with a stacked gate dielectric of 2.8nm thick SiO₂ and 15nm thick HfO₂ having electrode areas of 1mm*1mm are prepared on the p-Si substrate using thermal oxidation and atomic layer deposition respectively. The MOS capacitors are under zero bias during irradiation under ⁶⁰Co gamma ray with total dose of 100Krad (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 of each structure are measured at room temperature before and after irradiation. As well as the C-V and I-V property, 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 before and after different doses of radiation. The oxide trapped charge calculated from the high frequency C-V measurement is in the order of 10¹² cm^-2 and increases linearly with the increase of applied total dose. The XRD spectrum exhibits several phases of SiO₂ and HfO₂ variation under each total dose. The XPS result shows that each different total dosage leads to the binding energy peak drifting to a different degree demonstrating the influence of irradiation on the valence state of the elements, which can be attributed to the gamma-ray induced interface states.