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Highly thermally stable amorphous Ta x Ni 1-x (x = 0.25 and 0.75) thin films were deposited on Si and Si/SiO 2 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 0.25 Ni 0.75 and Si/SiO 2 /Ta 0.25 Ni 0.75 substrates. The failure temperatures of Si/Ta 0.25 Ni 0.75 /Cu-and Si/Ta 0.75 Ni 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 Cu 3 Si 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 0.75 Ni 0.25 was substantially superior to that of Ta 0.25 Ni 0.75 .