Reliability of multistacked tantalum-based structure as the barrier film in ultralarge-scale integrated metallization

Diffusion barrier properties of Ta films with and without plasma treatments have been investigated in the study. The nitrogen-incorporated Ta films were prepared by NH₃ plasma treatment or reactive sputtering. Barrier properties were evaluated by sheet resistance, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and reverse-biased junction leakage current. An amorphous-like TaN_x layer was formed on Ta barrier film after plasma treatments. The thickness of the amorphous TaN_x layer is about 3 nm and NH₃ plasma-treated Ta films (TaN_x/Ta) possess lower resistivity and smaller grain sizes. The Cu/TaN_x/Ta(10 nm)/Si remained stable after annealing at 750 °C for 1 h. NH₃ plasma-treated Ta films (TaN_x/Ta) possess better thermal stability than Ta and TaN films. It is attributed to the formation of a new amorphous layer on the surface of Ta film after the plasma treatments. For thermal stability of Cu/Ta(-N)/n ⁺-p diodes, Cu/Ta/n⁺-p and Cu/TaN/n⁺-p junction diodes resulted in large reverse-bias junction leakage current after annealing at 500 and 525 °C, respectively. On the other hand, TaN _x/Ta diffusion barriers will improve the integrity of Cu/Ta(-N)/n⁺-p junction diodes to 650 °C.