Ionizing Radiation Effects in MOS Capacitors with Very Thin Gate Oxides

Abstract

The positive oxide charge buildup and interface trap generation by γ-ray irradiation in MOS structures have been investigated as a function of gate oxide quality, gate oxide thickness, and applied oxide field. The radiation-induced shift in the flat-band voltage V FB is shown to have a maximum at a field of about 2 MV/cm, and a minimum at the flat-band bias. The dependence of the shift in V FB on the oxide field becomes weaker with decreasing gate oxide thickness. A large number of interface traps are generated under a positive oxide field, whereas the number of interface traps generated under a negative oxide field is negligible. Si–OH bond breaking at the Si–SiO 2 interface, enhanced by hole capturing, is proposed as the dominant mechanism for interface trap generation. The formation of very thin gate oxides (∼10 nm) by dry O 2 oxidation is also shown to be a highly-promising process for fabricating radiation-hardened MOS devices.