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 ind uced leakage currents that appear in 3.8 and 4.7 nm thick SiO2 oxides of me tal oxide semiconductor structures after Fowler-Nordheim (FN) electron inje ctions from the poly-Si gate and localized hot-hole injections from the p-S i 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 dis agrees with the theoretical prediction. Moreover, the field dependence of t he thermal activation energy found is much less than the Schottky predictio n, which rules out the possibility of a thermoionic process to fully explai n such currents in our samples. We show that a direct tunneling law, modifi ed to account for a mechanism assisted by stress induced baricentric neutra l defects, does correctly fit the oxide field dependence of these currents and is consistent with the observed thermal activation energy. (C) 2001 Els evier Science B.V. All rights reserved.