Improvement of the Diffusion Barrier Performance of Ru by Incorporating a WNx Thin Film for Direct-Plateable Cu Interconnects

A sputter-prepared Ru (7 nm)/WNx (8 nm) stacked layer was investigated as a diffusion barrier layer between Cu and Si for direct-plateable Cu interconnects, and its performance was compared with that of a Ru single layer with the same thickness (15 nm). X-ray diffractometry and sheet resistance measurements showed that the incorporation of WNx into the Ru single layer system significantly improved the barrier performance against Cu diffusion. The Ru/WNx bilayer barrier stack failed due to Cu diffusion attack after annealing at 750 degrees C for 30 min, while the Ru single layer failed after annealing at 450 degrees C by the formation of Cu silicide (eta(')-Cu3Si). A high resolution transmission electron microscopy analysis clearly suggested that this was due to the excellent diffusion barrier performance of WNx film with a nanocrystalline structure embedded in an amorphous matrix.