Ruthenium (Ru)-based ternary thin films (RuAlO) were prepared by thermal atomic layer deposition (ALD) with repeated super-cycles consisting of Ru and Al2O3 ALD sub-cycles at 225 degrees C. The step coverage of ALD-RuAlO was excellent, around 93% at contact holes with an aspect ratio of similar to 29 (top-opening diameter: similar to 74 nm). Transmission electron microscopy analysis showed that RuAlO films formed with non-columnar grains and a nano-crystalline microstructure consisting of Ru nano-crystals separated by amorphous Al2O3. The sheet resistance and X-ray diffraction showed that the structure of Cu (100 nm)/RuAlO (15 nm)/Si was stable after annealing at 650 degrees C for 30 min. Fifty nanometer-thick Cu was electrodeposited directly on RuAlO film, suggesting that it could be a viable candidate as a Cu direct plateable diffusion barrier. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3556980] All rights reserved.