Design and fabrication of ultrathin and highly thermal-stable α-Ta/graded Ta(N)/TaN multilayer as diffusion barrier for Cu interconnects

A one-step strategy of magnetron sputtering deposition with dynamic regulation of sputtering atmosphere was developed to prepare alpha-Ta/graded Ta(N)/TaN multilayer films on the Si substrate. The evolution of Ta clusters shows a significant effect on the crystal structure of the Ta film. The experimental results validate that the formation of alpha-Ta was attributed to the nucleation of larger Ta clusters. After being annealed at 600 degrees C, the alpha-Ta/graded Ta(N)/TaN multilayer film can still effectively block the diffusion of Cu. The mechanisms of the forming of the alpha-Ta and the thermal stability of the film stacks are characterized in detail.