TaNx thin films as copper barriers sputter-deposited at various NH3-to-Ar flow ratios

To optimize the performance of copper diffusion barriers, we deposited TaN_x thin films through radio frequency (RF) sputtering at various flow ratios of the reactive gases NH₃ and Ar. The composition of the film changed from Ta₂N to TaN, as evidenced from deposition rates and N-to-Ta ratios, when we increased the NH₃-to-Ar flow ratio from 0.075 to 0.3. Furthermore, the structure of the TaN_x thin film transformed from body-centered cubic (BCC) to face-centered cubic (FCC) to nanocrystalline upon increasing the NH₃-to-Ar flow rate, as revealed by the three steps in the rate of formation of the TaN_x films during the sputtering process. When incorporated in Cu/TaN_x/n⁺np⁺ diodes, the thermal stability of the TaN_x thin film—measured in terms of the leakage current remaining below 3 μA—increased from 450 to 550 °C upon increasing the NH₃-to-Ar flow ratio from 0.075 to 0.3. It appears that the NH₃-to-Ar flow ratio influences the properties of TaN_x films predominantly through modification of the crystal structure.