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 VFB 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 VFB 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–SiO2 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 O2 oxidation is also shown to be a highly-promising process for fabricating radiation-hardened MOS devices.