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

► An ultrathin α-Ta/graded Ta(N)/TaN multilayer film was prepared. ► The reliability of Ta/TaN film is sensitive to variation of Ta phase structure. ► An amorphous interlayer can improve the properties of the diffusion barrier. ► The α-Ta/graded Ta(N)/TaN multilayer could block Cu diffusion at 700 °C.