The failure mechanisms of the tantalum-based nitride diffusion barrier using between copper metal and the SiGe/Si layers grown with UHV/CVD have been studied. The TaN and Cu films were deposited with RF sputtering technique. The structure of these films was analyzed by X-ray diffraction. The stoichiometry of TaN was characterized by XPS (X-ray photoelectron spectroscopy). The morphology of the films was examined with SEM and the microstructure of the interface between several layers was observed with TEM. With comparing the XRD patterns of the samples which were annealed in the different temperatures, the failure temperature of the TaN barrier layer can be identified and the failure mechanism of this barrier layer cab be elucidated with TEM observation. The results revealed that the deposited TaN film with low sputtering power had better performance for preventing the Cu atoms diffusing into the SiGe layer. The high composition of Ge in the SiGe alloy degraded the blocking ability of the TaN barrier layer due to the released the existed strain between the SiGe and Si. When the failure temperature was reached, The Cu3Si phase was formed first in the interface of the TaN/SiGe and inside the TaN film. If the annealed temperature went higher, the TaSi2 phase also was formed. Compared with SiGe/Si and Si substrate, the TaN diffusion barrier layer has a higher failure temperature in Si than those in SiGe layer.