The reliability of multistacked titanium/titanium nitride (Ti/TiN) films as a diffusion barrier has been investigated by electrical characteristic measurements and material analyses. Both the chlorine content and the resistivity of the multistacked Ti/TiN films are significantly decreased when compared with a single layer of chemical vapor deposited-TiN film with the same thickness. The endurance of the diffusion barrier to thermal stress is enhanced by increasing the number of stacked layers of Ti/TiN films. Secondary ion mass spectroscopy depth profiles of the multistacked Ti/TiN samples showed that Ti atom distribution is fairly uniform in filling the grain boundary of the TiN film. The result is consistent with the observation of X-ray transmission microscopy. Therefore, the leakage current resulting from junction spiking is further reduced by the grain boundary effects when employing multi-stacked Ti/TiN as the diffusion barrier layer instead of a single layer of TiN film.