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 TaNx 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 TaNx 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 TaNx films during the sputtering process. When incorporated in Cu/TaNx/n+np+ diodes, the thermal stability of the TaNx 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 TaNx films predominantly through modification of the crystal structure.