Interface stability and microstructure of an ultrathin α-Ta/graded Ta(N)/TaN multilayer diffusion barrier

An ultrathin α-Ta (5 nm)/graded Ta(N) (1.5 nm)/TaN (2.5 nm) multilayer film coated with Cu film was deposited on the Si substrate using reactive magnetron sputtering in N ₂/Ar ambient. The film stacks of Cu/α-Ta/graded Ta(N)/TaN/Si were then annealed in a vacuum chamber at 400-700 °C for 1 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and energy-dispersive spectrometer (EDS) line scans were employed to investigate the microstructure evolution and the diffusion behavior of the film stacks, respectively. The results show that the α-Ta/graded Ta(N)/TaN multilayer film as a diffusion barrier had sufficient interface stability, which could be attributed to a relative stable amorphous layer forming at the interface of Cu and α-Ta layer, to prevent Cu atom diffusion at elevated temperatures up to 700 °C. The relationship between the interface stability and the microstructure of the multilayer barrier were also investigated.