Thickness dependence of the structural and dielectric properties of epitaxial ZrO2 films grown by limited reaction sputtering

Abstract

ZrO2 films with thicknesses of 5–51 nm prepared by the limited reaction sputtering technique with ozone assistance at 700 °C are investigated. The results indicate that tetragonal ZrO2 films are grown epitaxially on a Si (1 0 0) substrate. A fast relaxation occurs in the initial growth stage due to the lattice mismatch between ZrO2 and Si, and then oxygen vacancies lead to an expansion of the lattice constant in the two-dimensional epitaxial growth. The films below 26.3 nm exhibit a high permittivity of about 33, and the value is enhanced to 38 for the fully relaxed film. With an increase in the film thickness, frequency dispersions and interface state density become small, while the flatband shift and loop hysteresis are gradually increased, corresponding to the positive charges in the oxide. Moreover, the electrical conduction investigations suggest that for the as-deposited films below 20 nm the leakage behaviour is governed by the Schottky emission at low electric fields and by trap-assisted tunnelling at high electric fields.