Temperature and field dependence of stress induced leakage currents in very thin (<5 nm) gate oxides

We have studied the electric field and temperature dependence of stress induced leakage currents that appear in 3.8 and 4.7 nm thick SiO2 oxides of metal oxide semiconductor structures after Fowler–Nordheim (FN) electron injections from the poly-Si gate and localized hot-hole injections from the p-Si substrate. Constant voltage or constant current stressing modes were used, which did not produce any difference in stress induced leakage currents (SILC) increase. A Schottky law apparently fits the field dependence of such currents in 4.7 nm samples, but the slope found in 3.8 nm thick oxides disagrees with the theoretical prediction. Moreover, the field dependence of the thermal activation energy found is much less than the Schottky prediction, which rules out the possibility of a thermoionic process to fully explain such currents in our samples. We show that a direct tunneling law, modified to account for a mechanism assisted by stress induced baricentric neutral defects, does correctly fit the oxide field dependence of these currents and is consistent with the observed thermal activation energy.