Gamma-irradiation effect on electrical properties of SiO2 gate dielectric of MOS structure

The total dose effect of ⁶⁰Co gamma-irradiation on MOS (metal-oxide-semiconductor) structure of Al/SiO₂/p-Si with different insulation layer thickness has been investigated in this article. MOS capacitors with oxide layer thickness of 5nm/19nm/29nm and electrode area of 1mm² were prepared using thermal oxidation method. Each structure was stressed with no bias during ⁶⁰Co gamma-source irradiation with the total dose of 100k/500k/1Mrad. The low and high frequency C-V characteristic of each structure was measured at room temperature before and after gamma-irradiation. Besides of the electric properties, Atomic Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) with Ar⁺ etching were also measured before and after different total dose gamma-irradiation. AFM results showed that the surface of the oxide was relatively smooth with the roughness under 5%. Low and high frequency C-V results indicated that the interfacial states between Si and SiO₂ and oxide traps varied with insulation layer thickness and different total dose. On the other hand, the XRD property change under gamma irradiation differs with oxide layer thickness. And the Si 2p peak and O 1s peak result derived from the XPS drifted with different total dose and oxide layer thickness. These results offered necessary theory assistance for the nuclear hardening of the microelectronic devices with ultrathin insulation layer, which can advance the safety of weapons in the high-tech warfare.