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

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 SiO 2 on the surface of the Ta 2 O 5 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 SiO 2 layer on the surface of the Ta 2 O 5 , which implies that Si atoms outdiffuse from the Si substrate through Ta 2 O 5 films into the overlaying Ta 2 O 5 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 Ta 2 O 5 films with low leakage currents for practical use in high-density dynamic random access memories.