Negative-/Positive-Bias-Instability Analysis of the Memory Characteristics Improved by Hydrogen Postannealing in MANOS Capacitors

We report the effect of hydrogen annealing on the gate-leakage-current and switching characteristics of metal-alumina-nitride-oxide-silicon (MANOS) capacitors by analyzing their negative-/positive-bias instability (NBI/PBI). One sample, namely, A, is annealed with rapid thermal annealing (RTA), and the other sample, namely, B, is first annealed with RTA and then further annealed in a furnace, using a N₂-H₂ (98% nitrogen and 2% hydrogen) gas mixture. In the NBI/PBI experiments, the flatband voltage shift ΔV_FB is observed to be smaller, i.e., the gate-leakage-current density is reduced for sample B at gate voltages less than ±3 V, a domain where trap-assisted tunneling is dominant. However, ΔV_FB increases rapidly for the same sample at gate voltages larger than ±6 V, a domain where the modified Fowler-Nordheim tunneling (MFNT) is dominant, which indicates faster program-and-erase characteristics. These results show that additional hydrogen annealing can improve both device reliability and switching characteristics of the MANOS-type memory by reducing interface traps between the silicon substrate and silicon oxide layers, as well as turn-on voltages for MFNT.