Ultraviolet annealing of tantalum oxide films grown by photo-induced chemical vapour deposition

Abstract

We report the effect of ultraviolet annealing at 400 °C of tantalum pentoxide films photo-deposited at 350 °C from tantalum ethoxide and nitrous oxide mixtures using 172 nm radiation. A significant reduction in the leakage current density of the films has been found. This is attributed to the formation of SiO2 on the surface of the Ta2O5 and the reduction of suboxides, oxygen vacancies and defects in the films. We find excellent agreement between the two techniques of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy for detection of the unexpected formation of a thin SiO2 layer on the surface of the Ta2O5, which implies that Si atoms outdiffuse from the Si substrate through Ta2O5 films into the overlaying Ta2O5 film. Effective dielectric constant value of 20 and very low leakage current densities in capacitors incorporating the oxide around 7.7 × 10-9 A cm-2 at a voltage of 3 V, compare very favourably with films grown by alternative higher temperature techniques. This low-temperature, atmospheric-pressure UV annealing process offers a simple, but very effective, method for the fabrication of high-quality Ta2O5 films with low leakage currents for practical use in high-density dynamic random access memories.