The performance of Ti0.3W0.7 and Nb thin films as diffusion barriers for Au was investigated by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). The films were sputter deposited in Ar:N2 (70:30 vol%) or pure Ar on amorphous SiO2. They were annealed in air at temperatures ranging from 250 °C up to 750 °C for several hours. In-depth profiles revealed an onset of oxidation of the barriers at 520 °C for Nb and about 600 °C for TiW. Barrier oxidation and extensive diffusion could be correlated. Distinct diffusion behavior as a function of temperature was established between TiW and Nb. A Nb multilayer structure was found to provide the best reliability as the barrier and as the adhesion layer.