Electrical characterization of oxide and Si/SiO2 interface of irradiated NMOS transistors at low radiation doses

N-channel MOSFET´s of different dimensions were first irradiated with ⁶⁰Co gamma rays source at several low radiation total doses. Then their SiO₂ gate oxides and Si/SiO₂ interfaces were characterized by using the standard charge pumping (CP) and the extended standard CP to low frequencies techniques. Both techniques reveal two radiation-induced oxide charge traps formation mechanisms, caused by low radiation total doses. Initially, there is a build-up of positive charge in the oxide layer, followed later by a diminution of net positive charge (turn around effect) due to generation of negative charge or/and transformation of positive oxide traps to interface traps. The interface traps exhibit a linear increase with radiation doses