Ultrathin (10 nm) Ti films with an amorphous structure were deposited by low temperature (<500 &DEG;C) plasma enhanced chemical vapor deposition (PECVD) using TiCl4 and H-2 as reactants. Ammonia plasma was further employed to post-treat the PECVD-Ti barrier layer to improve barrier properties. An amorphous TiNx layer forms on the surface of the PECVD-Ti layer after ammonia plasma post-treatment. The resulting films have a multilayered amorphous Ti/TiNx structure. Furthermore, the effective resistivity of resulting Ti/TiNx film reduces to 122 μ&UOmega; cm. Improved barrier capability against Cu diffusion is found for the Ti/TiNx barrier layer because the Cu/TiNx /Ti/n(+)-p junction diodes retain low leakage current densities even after annealing at 500 &DEG;C for 1 h. Ti/TiNx barrier layers present lengthened grain structures to effectively impede Cu diffusion, thus acting as much more effective barriers than are conventional Ti and TiN films. (C) 2002 The Electrochemical Society.