Effects of Plasma Prenitridation and Postdeposition Annealing on the Structural and Dielectric Characteristics of the Ta2 O 5 / Si System

Abstract

Material and dielectric properties of Ta 2 O 5 layers grown on bare Si, as well as N 2 O and NH 3 plasma nitrided Si substrates, before and after postdeposition annealing in oxygen, were investigated. X-ray photoelectron spectroscopy reveals that NH 3 and N 2 O plasma nitridation on Si at 450°C formed a nitrogen-rich and an oxygen-rich SiO x N y layer, respectively. Capacitance-voltage ( C ­ V ) measurements show that Ta 2 O 5 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 ∼ 10 13   cm − 2   eV − 1 for non-nitrided and NH 3 nitrided samples, but it is ∼ 10 12   cm − 2   eV − 1 for the N 2 O nitrided sample. Postdeposition annealing at 650 or 800°C leads to an increment of N h , except to a lesser extent for the N 2 O nitrided sample, and reduces all D it to ∼ 10 12   cm − 2   eV − 1 . Concurrently, crystallization of the Ta 2 O 5 layer and depletion of nitrogen in the SiO x N y interlayer formed by NH 3 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 Ta 2 O 5 deposited on N 2 O 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 Ta 2 O 5 / Si systems are discussed. © 2002 The Electrochemical Society. All rights reserved.