NEGATIVE STRESS-INDUCED CURRENT IN OXIDIZED NITRIDE LAYERS OF DIFFERENT NITRIDE THICKNESSES (LESS-THAN-5 NM)

Two nitride films of thicknesses 4.1 and 3.0 nm have been oxidized for a fixed duration of time and at a fixed temperature and the stress-in duced degradation characteristics are evaluated. It is observed that f or a constant current stress of - 10 mA cm(-2), the gate voltage is sh ifted to the positive direction for the oxidized thick nitride, but fo r the oxidized thin nitride film, just like nitride films, it is shift ed to the negative direction. In addition, the TDDB life time is longe r for the oxidized thin nitride compared to the oxidized thick nitride . Hence, from the experimental results, it can be said that owing to e lectron injection from the gate, the current increases in oxidized thi ck and thin nitride layers are different. In oxidized thick nitride el ectron-hole pairs are generated at the interface of the oxide and nitr ide as well as in the bulk nitride films, and then the holes drift bac k to the gate. As a result of hole trapping, the current increases abr uptly. In contrast, in oxidized thin nitride a very small number of el ectron-holes are generated at the interface, while most of the electro ns tunnel through the thin nitride films. As a result, compared to the oxidized thick nitride, in oxidized thin nitride after stress the var iation of current is very small. Therefore, it is observed that the ox idization of a thin nitride layer improves the stress-induced current and the TDDB characteristics.