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.