Ta (3.3 nm)/ Ni – Al (3.3 nm) integrated films deposited on Si substrates by magnetron sputtering, annealed at various temperatures in a ultra-high vacuum, have been studied as diffusion barrier layers between Cu and Si for application in Cu interconnection. The images of transmission electron microscopy (TEM) prove that the cross-sectional interfaces of Cu / Ta / Ni – Al / Si sample annealed at 600°C are clear and sharp. No Cu –silicide peaks can be found from the X-ray diffraction (XRD) patterns of the 850°C annealed sample, but the sheet resistance of the sample increases abruptly. Moreover, large grooves are found from the image of atomic force microscopy (AFM) for the 850°C annealed sample, implying the failure of the diffusion barrier. The integrated Ta / Ni – Al barrier layer retains thermally stable nature up to at least 800°C, indicating that the Ta / Ni – Al integrated film is an excellent diffusion barrier between Cu and Si .

The diffusion barrier performance of an ultrathin amorphous Al–Ni (a‐Al–Ni) film as barrier layer in a sandwiched scheme Cu/barrier/Si and Cu/barrier/SiO2/Si is investigated. Microstructures, electrical properties, surface morphologies, and interfaces for the samples annealed at various temperatures are measured using X‐ray diffraction (XRD), sheet resistance measurements, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results present 4.5‐nm‐thick a‐Al–Ni can achieve good thermal stability up to 750 °C. Cu silicide cannot be observed in XRD data up to 800 °C. However, the abrupt increase in sheet resistance value and the appearing island‐like grains in AFM images for the sample annealed at 800 °C indicate the failure of the barrier structure. The failure mechanism of barrier layer is discussed and can be attributed to the dewetting of Cu film along grain boundary grooving. The amorphization of the barrier layer and clear interfaces with its adjacent layers are further authenticated by high resolution TEM. It is also found that the growth orientation and surface morphology of Cu film are related to the substrates (monocrystalline Si and amorphous SiO2) under the barrier layer.