In order to develop a fabrication process to prepare thermally stable TiN thin films, the TiN films were prepared by the sputter-deposition technique with various process parameters. The barrier property of the TiN films which prevented the Cu diffusion into Si or SiO2 were found to be influenced by the radio-frequency power, Ar/N-2 gas ratio, and substrate temperature of the sputtering system. By adjusting these process parameters, the 25-nm-thick TiN films with excellent thermal stability that prevented the Cu diffusion at 850 degreesC for 30 min were successfully prepared. Microstructural analysis by X-ray diffraction and transmission electron microscopy indicated that the microstructure of the TiN films was sensitive to the thermal stability and that the TiN films with strong fiber structure and large grain size had higher resistance to the Cu diffusion into Si.