Effect of a titanium interlayer on the performance of the titanium nitride diffusion barrier

We have studied the effect of a Ti interlayer on the behavior of a TiN diffusion barrier for Al and Cu metallizations. Thermal stability of Al/Ti/TiN/〈Si〉 and Al/TiN/〈Si〉 samples annealed at 400-600°C for 30 min was investigated using Auger electron spectroscopy (AES), glancing angle X-ray diffraction and scanning electron microscopy (SEM). Sheet resistance was measured for electrical characterization. After annealing at 400°C and 500°C, the Al/TiN/〈Si〉 samples exhibited the same sheet resistance as the as-deposited one, while the sheet resistances of the Al/Ti/TiN/〈Si〉 samples increased upon annealing. After annealing at 600°C, pyramidal pits developed on the surface of the Al/TiN/〈Si〉 sample, but not on the Al/Ti/TiN/〈Si〉 sample. Sheet resistance measurements for the 600°C-annealed Al/TiN/〈Si〉 sample resulted in a more scattered distribution and a higher average value than for the Al/Ti/TiN/〈Si〉 sample. The results clearly indicate that the performance of the TiN barrier layer is significantly improved by including a thin Ti film between the TiN and the Al. The Ti interlayer also improves the TiN barrier performance for the Cu metallization system.