Electrical characterization of oxide and Si/SiO/sub 2/ interface of irradiated NMOS transistors at low radiation doses

Abstract

N-channel MOSFET's of different dimensions were first irradiated with /sup 60/Co Gamma rays source at several total doses (low doses) and then their gate oxides, SiO/sub 2/ and interfaces, Si/SiO/sub 2/ 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 diminution of net positive charge (Turn around effect) due to generation of negative charge or/and transformation of positive oxide traps to interface traps. While the interface traps exhibit a linear increase with radiation doses.