Ru/WNx Bilayers as Diffusion Barriers for Cu Interconnects

Abstract

Bilayers of Ru (7 nm)/WNx (8 nm) prepared by sputtering were investigated as diffusion barriers between Cu and Si, and their performances were compared as a function of N2 flow rate during the deposition of WNx. The Ru/WNx bilayer diffusion barriers were stable upon annealing at up to at least 650 °C for 30 min while a Ru single layer (15 nm in thickness) failed after annealing at 450 °C owing to the formation of Cu silicide. Grazing-angle X-ray diffractometry results showed that the crystallinity of the WNx film was degraded but that its nanocrystalline state preserved upon annealing at higher temperatures with increasing N2 flow rate during the deposition. These resulted in the better performance against Cu attack of bilayer diffusion barriers with the WNx film prepared with a higher N2 flow rate.