Atomic Layer Deposition of RuAlO Thin Films as a Diffusion Barrier for Seedless Cu Interconnects

Ruthenium (Ru)-based ternary thin films (RuAlO) were prepared by thermal atomic layer deposition (ALD) with repeated super-cycles consisting of Ru and Al 2 O 3 ALD sub-cycles at 225°C. The step coverage of ALD-RuAlO was excellent, around 93% at contact holes with an aspect ratio of ∼29 (top-opening diameter: ∼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 Al 2 O 3 . 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°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.