Effectiveness of Ta addition on the performance of Ru diffusion barrier in Cu metallization

Ru-Ta and Ru thin films (∼15 nm in thickness) as diffusion barrier for Cu metallization on SiO₂ Si and Si substrates are studied. Experimental results show that the Ru-Ta film exhibits amorphous structure until annealing at 700°C, whereas the Ru film crystallizes in as-deposited and annealed states. Sheet resistances of CuRu and CuRu-Ta stacking layers increase after annealing at 500 and 700°C, respectively, regardless of whether the substrate is SiO₂ Si or Si. Increase in resistance is concurrent with the formation of Ru₂Si₃ and Cu₃Si when Cu/barrier stacks are deposited on Si substrate. Increase in resistance for Cu/barrier stacks deposited on SiO₂ Si substrate is related to the diffusion of Cu through the crystallized barrier to the underlayers. Furthermore, current-voltage measurement also reveals that the CuRu-Ta metallization has a lower leakage current than the CuRu system. The failure mechanism and the effectiveness of Ta addition on barrier performance are discussed.