A comparative study of sputtered TaC_x and WC_x films as diffusion barriers between Cu and Si

The barrier properties of sputter-deposited tantalum carbide (TaC_x) and tungsten carbide (WC_x) for Cu metallization were investigated and compared. The incorporation of the C atom is shown to be effective in decorating local defects of the barrier layer and improving the thermal stability of the Cu/barrier/Si contact system. Owing to a higher melting point and better chemical inertness, with respect to Si substrate, the TaC_x (600 Å) film shows a better thermal stability (up to 650°C) than that of WC_x (∼600°C) film based on material analyses, while the highest stable temperature as evaluated by the n⁺ p-diode leakage measurement is found to be approximately 550°C for the TaC_x and 500°C for the WC_x barrier layer. The failure of the TaC_x and WC_x barriers is found to be mainly due to Cu diffusion through the localized defects of the barrier layers into the Si substrate. The interfacial reaction between the WC_x layer and the Si substrate is found to play an additional role in the failure of the WC_x film.