Characterization of sputtered tantalum carbide barrier layer for copper metallization

In this study, tantalum carbide (TaC_X) 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/TaC_x/n-Si and Cu/TaC_x/p⁺n systems as a function of annealing temperature are reported and analyzed. The deposited TaC_X, having an amorphous structure and a low resistance of around 385 μΩ 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 angstroms TaC_X in Cu/TaC_X/Si structure can effectively prevent Cu penetration up to 600 °C for 30 min, while more sensitive diode leakage measurement of Cu/TaC_X/p⁺n indicates that the failure temperature is around 500 °C. The failure of the TaC_X layer was found to be mainly due to the diffusion of Cu along the localized defects of the TaC_X barrier layer into underlying silicon. This has caused the formation of copper silicides and high junction leakage currents.