Oxygen-Induced Barrier Failure in Ti-Based Self-Formed and Ta/TaN Barriers for Cu Interconnects

摘要

To understand the electromigration degradation in Cu interconnects that utilize the TiO_x self-formed barrier (SFB) probably due to Cu oxidation at the Cu/barrier interface, Cu films deposited on TiO_x SFB and conventional Ta/TaN barriers were annealed in atmospheres of various oxygen concentrations. The Ta layer was preferentially oxidized to give Ta_2O_5, and contained a large amount of oxygen. The barrier layer, which consisted of Ta_2O_5 and Ta(O), could not suppress Cu diffusion. The TaN layer seemed to remain even after annealing at 400℃ in 10ppm O_2 and still suppressed Cu diffusion. This suggests that the TaN layer plays a key role to suppress barrier failure induced by oxygen originating from pores in dielectrics. On the other hand, the oxygen-induced barrier failure was observed in the TiO_x SFB after annealing at 500 ℃ in 5 ppm O_2 and more. Oxygen facilitated Cu_2O formation above the TiO_x SFB, and the Cu_2O formation caused discontinuity of the TiO_x SFB, leading to the barrier failure. The less oxidized Ti_2O_3 and TiO in the TiO_x SFB were not further oxidized to TiO_2 by oxygen in atmospheres, and thus they would not be oxygen absorbers suppressing the Cu_2O formation above the barrier. Thus, for suppressing the Cu_2O formation, it is essential to increase oxygen barrier ability of the TiO_x SFB (probably increasing Ti concentration of the TiO_x SFB).