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

概要

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To understand the electromigration degradation in Cu interconnects that utilize the TiOx self-formed barrier (SFB) probably due to Cu oxidation at the Cu/barrier interface, Cu films deposited on TiOx SFB and conventional Ta/TaN barriers were annealed in atmospheres of various oxygen concentrations. The Ta layer was preferentially oxidized to give Ta2O5, and contained a large amount of oxygen. The barrier layer, which consisted of Ta2O5 and Ta(O), could not suppress Cu diffusion. The TaN layer seemed to remain even after annealing at 400 °C in 10 ppm O2, 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 TiOx SFB after annealing at 500 °C in 5 ppm O2 and more. Oxygen facilitated Cu2O formation above the TiOx SFB, and the Cu2O formation caused discontinuity of the TiOx SFB, leading to the barrier failure. The less oxidized Ti2O3 and TiO in the TiOx SFB were not further oxidized to TiO2 by oxygen in atmospheres, and thus they would not be oxygen absorbers suppressing the Cu2O formation above the barrier. Thus, for suppressing the Cu2O formation, it is essential to increase oxygen barrier ability of the TiOx SFB (probably increasing Ti concentration of the TiOx SFB).
2012-04-25