A new MOS radiation-induced charge: negative fixed interface charge

The irradiation behavior [up to ~1.3 Mrad (SiO₂)] of MOS capacitors (50-nm-thick dry-grown SiO₂, Al, or poly-Si gate) with or without postoxidation annealing (POA) in Ar at 1000°C has been studied by conventional capacitance-voltage (C-V ) analysis and thermally stimulated current techniques. The most important finding is that all of the samples processed for radiation hardness, i.e., without POA, exhibited a charge compensation effect. The radiation-induced positive oxide charge is partially compensated by a negative fixed interface charge that either lies outside the energy range accessible by C-V and similar techniques or extends spatially away from the interface into the oxide without acquiring the characteristics of a bulk oxide charge