Material and dielectric properties of Ta2O5 layers grown on bare Si, as well as N2O and NH3 plasma nitrided Si substrates, before and after postdeposition annealing in oxygen, were investigated. X-ray photoelectron spectroscopy reveals that NH3 and N2O plasma nitridation on Si at 450°C formed a nitrogen-rich and an oxygen-rich SiOxNy layer, respectively. Capacitance-voltage (C-V) measurements show that Ta2O5 layers deposited on the prenitrided Si exhibit a higher relative dielectric constant and contain a lower density of charge trapping sites (Nh), as compared to the one on bare Si. In contrast, the interface state density (Dit) near the midgap is ∼1013 cm-2 eV-1 for non-nitrided and NH3 nitrided samples, but it is ∼1012 cm-2 eV-1 for the N2O nitrided sample. Postdeposition annealing at 650 or 800°C leads to an increment of Nh, except to a lesser extent for the N2O nitrided sample, and reduces all Dit to ∼1012 cm-2 eV-1. Concurrently, crystallization of the Ta2O5 layer and depletion of nitrogen in the SiOxNy interlayer formed by NH3 plasma nitridation are observed after annealing at 800°C. As for current-voltage (I-V) characteristics, all as-deposited samples exhibit large leakage currents, regardless of the prenitridation process. Postdeposition annealing will significantly lower the leakage currents, and the annealed Ta2O5 deposited on N2O nitrided Si exhibits better I-V character than the others at high electric field. Effects of various prenitridation and postannealing processes on the structural and electrical characteristics of Ta2O5/Si systems are discussed.
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