The properties of both oxygen indiffusion and oxidation resistance in aTa+RuO2layer 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. TheTa+RuO2/Sisystem sustained up to 800 °C without an increase in resistivity. TheTa+RuO2diffusion barrier showed a Ta amorphous microstructure and an embeddedRuOxnanocrystalline structure in the as-deposited state. TheTa+RuO2film showed the formation ofRuO2phase by reaction with the indiffused oxygen from atmosphere after annealing in an air ambient. TheTa+RuO2diffusion barrier showed that Ta is sufficiently bound to oxygen in the as-deposited state, butRuO2consists 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 byRuO2addition effectively prevented the indiffusion of oxygen up to 800 °C and its oxidation resistance was superior to various barriers reported by others.