The decrease in microelectronic device dimensions and the continuous effort to increase the speed and performance of devices have led to the need to replace the current metallization of Al(Cu) with Cu. This metal must be isolated from the neighboring dielectrics by a thin diffusion barrier layer. The currently employed diffusion barrier materials are Ta and TaN produced by advanced physical vapor deposition methods. The need for conformality and for the use of extremely thin layers serves as a driving force to look for chemical vapor deposition as the future deposition method. TiSiN films produced by using a cyclic process of thermal decomposition of tetrakis-dimethylamino-titanium followed by H-2/N-2 plasma and a flash of SiH4 are attractive candidates as diffusion barriers for Cu metallization in future devices. In this research, we have extensively studied the barrier integrity using secondary ion mass spectroscopy (SIMS) depth profiling and SECCO etch-pitting test. The sample configuration used was Cu/barrier/Si. Cu diffusion was detected by SIMS after annealing at 500 degreesC. Etch pits were first found after annealing at 600 degreesC. It was found that the plasma treatment is the main factor improving the barriers ability to prevent Cu diffusion to the substrate, most probably due to the higher density of the treated film, while the addition of SiH4 only slightly improves the barriers integrity due to the formation of Si3N4. A correlation between the TiSiN microstructure and its barrier integrity is proposed.