AlN films were deposited as capping (deposited on top of) and reaction barrier layers (placed between the Si substrate and La2O3 film) to improve the thermal stability of La2O3 films. The film structures were investigated by high-resolution transmission electron microscopy and angle-resolved X-ray photoelectron spectroscopy. The AlN-capped La2O3 film did not change its structure after thermal annealing, while that with the AlN barrier films showed a slight increase in the film thickness. The Al atoms diffuse onto the film surface during annealing in the La2O3/AlN/Si stack, which makes the bottom AlN barrier layer less effective than the capping layer. (c) 2007 The Electrochemical Society.