An amorphous TaxMnyOz layer with 1.0 nm thickness was studied as an alternative Cu diffusion barrier for advanced interconnect. The thermal and electrical stabilities of the 1.0-nm-thick TaxMnyOz barrier were evaluated by transmission electron microscopy (TEM) and current density-electric field (J-E) and capacitance-voltage (C-V) measurements after annealing at 400 °C for 10 h. X-ray photoelectron spectroscopy revealed the chemical characteristics of the TaxMnyOz layer, and a tape peeling test showed that the TaxMnyOz barrier between the Cu and SiO2 layers provided better adhesion compared to the sample without the barrier. TEM observation and line profiling measurements in energy-dispersive X-ray spectroscopy after thermal annealing revealed that Cu diffusion was prevented by the TaxMnyOz barrier. Also, the J-E and C-V measurements of the fabricated metal-oxide-semiconductor sample showed that the TaxMnyOz barrier significantly improved the electrical stability of the Cu interconnect. Our results indicate that the 1.0-nm-thick TaxMnyOz barrier efficiently prevented Cu diffusion into the SiO2 layer and enhanced the thermal and electrical stability of the Cu interconnect. The improved performance of the TaxMnyOz barrier can be attributed to the microstructural stability achieved by forming ternary Ta-Mn-O film with controlled Ta/Mn atomic ratio. The chemical composition can affect the atomic configuration and density of the Ta-Mn-O film, which are closely related to the diffusion behavior. Therefore, the 1.0-nm-thick amorphous TaxMnyOz barrier is a promising Cu diffusion barrier for advanced interconnect technology.