In this study, tantalum carbide (TaCX) films deposited by a sputtering. process with a TaC target as diffusion barriers for Cu metallization were investigated for the first time. The thermal stability of Cu/TaCX/n-Si and Cu/TaCX/p(+)n systems as a function of annealing temperature are reported and analyzed. The deposited TaCX, having an amorphous structure and a low resistance of around 385 mu Omega cm, were characterized by sheet resistance measurement, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), secondary ion mass spectroscopy, and diode leakage current measurement. From XRD and SEM analysis, it was found that 600 Angstrom TaCX in Cu/TaCX/Si structure can effectively prevent Cu penetration up to 600 degrees C for 30 min, while more sensitive diode leakage measurement of Cu/TaCX/p(+)n indicates that the failure temperature is around 500 degrees C. The failure of the TaCX layer was found to be mainly due to the diffusion of Cu along the localized defects of the TaCX barrier layer into underlying silicon. This has caused the formation of copper silicides and high junction leakage currents.