Effects of plasma prenitridation and postdeposition annealing on the structural and dielectric characteristics of the Ta2O5/Si system

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 450degreesC 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 (N-h), as compared to the one on bare Si. In contrast, the interface state density (D-it) near the midgap is similar to10(13) cm(-2) eV(-1) for non-nitrided and NH3 nitrided samples, but it is similar to10(12) cm(-2) eV(-1) for the N2O nitrided sample. Postdeposition annealing at 650 or 800degreesC leads to an increment of Nh, except to a lesser extent for the N2O nitrided sample, and reduces all D-it to similar to10(12) 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 800degreesC. 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. (C) 2002 The Electrochemical Society.