(Invited) Ru-Based Binary or Ternary Thin Films By Atomic Layer Deposition for a Seedless Cu Interconnects

Ru has been suggested as a diffusion barrier that is compatible with the direct plating of Cu. However, previous studies showed that Ru itself is not a suitable diffusion barrier for Cu metallization due mainly to its poor microstructure with polycrystalline columnar grains. This study developed several Ru-based multi-component thin films, RuMn, RuSiN, and RuAlO using atomic layer deposition (ALD) process, which are compatible with the direct plating of Cu as well as show better diffusion barrier performance against Cu than Ru. Mn, SiN_x, AlO_x were incorporated into the Ru by combining the Ru and corresponding ALD cycles, and Ru-based binary alloy, RuMn, ternary thin films, RuSiN and RuAlO, were fabricated at 225 ^oC. As a typical example, the results on ALD-RuAlO were shortly described. The step coverage of ALD-RuAlO was perfect at contact holes with an aspect ratio of ~ 25 (top-opening diameter: ~ 85 nm). XRD and TEM results indicate that ALD-Ru film prepared without AlO_x ALD cycle forms a polycrystalline structure with columnar grains. But, with incorporating the AlO_x cycles, RuAlO films were formed with non-columnar grains and nano-crystalline microstructure consisting of Ru nano-crystals separated by amorphous AlO_x matrix. XRD analysis showed that the structure of Cu/ALD-RuAlO (8 nm)/Si was stable after annealing at 600 ^oC for 30 minute while Cu/Ru (15 nm)/Si structure was failed after annealing at 450 ^oC. It was also shown that the electroplating of Cu was directly achieved on a very thin (~8-nm-thick) RuAlO film at blanket and pattern wafer. In the case of binary ALD-RuMn film, it should be noted that after annealing ALD-RuMn film at 500 ^oC, the self-formation of Mn silicate barrier between Ru(Mn) film and SiO₂ was confirmed based on XRD and TEM analysis, which was due to the diffusion of Mn into underlying SiO₂, resulting in better diffusion barrier performance than Ru counterpart.

 Acknowledgements

This work was supported by the Technology Innovation Program (Industrial Strategic technology development program, 10035430, Development of reliable fine-pitch metallization technologies) funded by the Ministry of Knowledge Economy (MKE, Korea) and also partially supported by Tanaka Precious Metals, Japan.