The properties of both oxygen indiffusion and oxidation resistance in-a Ta+RuO2 layer for high density memory devices were investigated by using Rutherford backscattering spectroscopy, four point probe, x-ray diffraction, x-ray photoelectron spectroscopy, and planar transmission electron microscopy. The Ta+RuO2/Si system sustained up to 800 degrees C without an increase in resistivity. The Ta+RuO2 diffusion barrier showed a Ta amorphous microstructure and an embedded RuOx nanocrystalline structure in the as-deposited state. The Ta+RuO2 film showed the formation of RuO2 phase by reaction with the indiffused oxygen from atmosphere after annealing in an air ambient. The Ta+RuO2 diffusion barrier showed that Ta is sufficiently bound to oxygen in the as-deposited state, but RuO2 consists of Ru and Ru-O binding state. The Ta-O bonds showed little change compared to the as-deposited state with increasing annealing temperature, whereas Ru-O bonds significantly increased and transformed to conductive oxide, RuO2. Therefore, the Ta layer deposited by RuO2 addition effectively prevented the indiffusion of oxygen up to 800 degrees C and its oxidation resistance was superior to various barriers reported by others.