Barrier Properties of Amorphous Binary Ta-Ni Thin Films for Cu Interconnection

Highly thermally stable amorphous Ta _x Ni_1–x (x = 0.25 and 0.75) thin films were deposited on Si and Si/SiO₂ substrate by magnetron dc sputtering, and the performance of films (20-nm thick) as barriers for copper (Cu) interconnection was evaluated. The failure behaviors of the films were elucidated using a four-point probe, x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Auger emission spectrometry (AES). A highly (111) textured Cu film could be obtained when Cu was deposited on Si/Ta_0.25Ni_0.75 and Si/SiO₂/Ta_0.25Ni_0.75 substrates. The failure temperatures of Si/Ta_0.25Ni_0.75/Cu- and Si/Ta_0.75Ni_0.25/Cu-stacked films were 550°C and 600°C, respectively. Failure of the studied films initiated the penetration of Cu into the Si/Ta _x Ni_1–x interface and triggered the partial dissociation of the Ta _x Ni_1–x barrier layer, forming Cu₃Si precipitates, Ni-silicide and Ta-silicide. Increasing the Ta content enhanced the microstructural and thermal stability of the stacked films, markedly improving barrier properties. The experimental findings demonstrated that the barrier characteristic of Ta_0.75Ni_0.25 was substantially superior to that of Ta_0.25Ni_0.75.