Influence of nitrogen doping on the barrier properties of sputtered tantalum carbide films for copper metallization

The effect of nitrogen doping on the barrier properties of sputter-deposited tantalum carbide (Ta-C) films was investigated for the first time. With increasing nitrogen concentration, it was found that the resistivity of the barrier layer increases, while the growth rate decreases. In addition, the use of an optimum N₂/Ar flow rate ratio of 2/24 during sputtering allows one to achieve tantalum carbon nitride (Ta-C-N) films with the highest thermal stability. According to I-V measurements on reverse-biased Cu/barrier/p⁺n diodes, the 600-Å-thick Ta-C-N barrier layer appeared to be effective in preventing Cu from reaching the Si substrate after 600°C annealing in N₂ for 30 min, which is about 100°C higher than that in the case without nitrogen incorporation. The failure of the thermally annealed Ta-C-N film was attributed to the Cu diffusion through the local defects or grain boundaries of the layer into the Si substrate, which results in a significant increase in the diode leakage current.