TaN(x) thin films as copper barriers sputter-deposited at various NH(3)-to-Ar flow ratios

Abstract

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 NH(3) and Ar. The composition of the film changed from Ta(2)N to TaN, as evidenced from deposition rates and N-to-Ta ratios, when we increased the NH(3)-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 NH(3)-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 mu A-increased from 450 to 550 degrees C upon increasing the NH(3)-to-Ar flow ratio from 0.075 to 0.3. It appears that the NH(3)-to-Ar flow ratio influences the properties of TaN(x) films predominantly through modification of the crystal structure. (C) 2008 Published by Elsevier B.V.