Diffusion barrier effect of Ta/Ti bilayer in organic dielectric/Cu interconnects

This study describes a Ta/Ti bilayer to improve the adhesion between Cu and a dielectric material and to enhance the barrier effect for Cu interconnects in electronic circuits. The addition of Ti improves the adhesion between Ta and Polybenzoxazoles (PBO) from the industry standard of 0B (worst level) to 5B (best level), as evaluated via a peeling test. The results of a comparative study demonstrate that a Ta/Ti bilayer (40 nm/10 nm) enables a higher annealing temperature vs. pure films of either Ta or Ti (50 nm respectively) by preventing diffusive mixing of Cu/Si. Using an accelerated high-temperature testing system, the results show stable annealing at 550 °C for the bilayer as compared to 500 °C for Ta and 350 °C for Ti. Under accelerated low-temperature and long-term conditions, both material systems (Cu/Ta/Ti/PBO/Si and Cu/Ta/Ti/Si) remained stable and reliable. The results suggest the improved diffusion barrier property of the Ta/Ti bilayer is due to the strong Ta/Ti interface and the greater oxygen attraction by the Ti layer. The Ta/Ti bilayer is a promising candidate for use as a diffusion barrier and an adhesion promoter, especially in applications in which the insulation layer exhibits poor adhesive properties.