Ti-diffusion barrier in Cu-based metallization

Reliability investigations, with or without a barrier layer, have been performed to study the penetration of copper into thermal oxide as a function of temperature and applied electric field. No copper diffusion was detected without a barrier into 100 nm thick oxide for temperature stress as high as 450°C for one hour and for bias temperature stress (BTS) as high as 300°C for 8 h at 1 MV/cm. This absence of diffusion was observed when thermal annealing was performed under vacuum. A 20 nm thick titanium layer was used as a diffusion barrier/adhesion promoter between the copper and the oxide. The devices using this barrier were not affected by a temperature stress of 600°C for 10 h and by BTS even at 450°C for 2 h at 1 MV/cm.