Interfacial reactions and failure mechanism of Cu/Ta/SiO₂/Si multilayer structure in thermal annealing

The integrity of Cu/Ta/SiO₂/Si multilayer structure under nitrogen thermal annealing has been examined by sheet resistance measurement, X-ray diffraction, scanning electron microscopy, secondary ion mass spectroscopy, Rutherford backscattering spectrometry and cross-section transmission electron microscopy analysis. According to electrical measurement it was found that Ta diffusion barrier could preserve the integrity of the Cu/Ta/SiO₂/Si structure up to 650 °C in N₂ for 35 min. There are two causes by which the Cu/Ta/SiO₂/Si structure became degraded. One is the out diffusion Ta atoms towards the Cu film. The other factor is the formation of Cu, Ta and Cu-Ta oxide. Hence, Cu penetration is not the only reason to cause the failure; oxidation, phase transformation and interfacial reactions are also associated problems during thermal annealing.