Effect of Ta₂N crystallinity on diffusion barrier properties

Ta₂N thin films deposited at different substrate temperatures onto silicon (001) substrates can produce amorphous and crystalline phase with different preferred orientations. Upon annealing at 500°C for 30min, these films exhibit crystalline phases with the strong preferred orientation from (101) for the film deposited at 500°C to (002) for the film deposited at higher temperatures. Subsequently, the viability of employing them as the diffusion barriers between copper and silicon is investigated by annealing in a vacuum chamber at 500, 600, 700, and 800°C for 30 min following sputtering, where the thicknesses of Cu and Ta₂N are fixed at 150nm and 100nm, respectively. The results show that the chemical reactions of Ta₂N with Cu and Si and the structural stability at high temperatures are dependent on the crystalliniry of Ta₂N and the Ta₂N phase with the highest (002) preferred orientation exhibits the highest structural stability. This suggests that the (002) orientation in the poly-Ta₂N can prevent copper diffusion more effectively.