Development of tantalum carbon nitride (TaCN) diffusion barriers for copper metallization

The incorporation of nitrogen in the sputtered tantalum carbide (TaCx) film was investigated to improve its barrier property in Cu metallization. The film's resistivity increases with nitrogen concentration and the deposition rate decreases with increasing nitrogen to argon sputtering ratio. With an optimal N₂ to Ar sputtering ratio, the ternary alloy TaCN film was found to achieve a superior thermal stability than that of TaC or TaN barrier. From p⁺n junction leakage current measurement data, a 600 Å-thick TaCN film was effective in preventing Cu from diffusing into underlying Si after 600 °C annealing in N₂ for 30 min. This barrier temperature of TaCN is about 100 °C higher than that of TaCx film without nitrogen incorporation. Since the failure mechanism of TaCN barrier is dominant by the grain boundary diffusion, the improvement is attributed to the reduction of Cu diffusion through the barrier layer by the stuffing of nitrogen atoms in the grain boundaries of TaCx.