Thin films of TiN interposed between Cu and SiO2 layers have been examined as a diffusion barrier as well as an adhesion-promoting layer for Cu metallization. Reliability of TiN barrier layer has been investigated by studying the penetration of copper into thermal oxide as a function of temperature. We have used X-ray diffraction, Auger electron spectroscopy and capacitance-voltage(C-V) measurements in order to investigate the Cu/TiN/SiO2/Si metallization system. The characteristics of metal/oxide/silicon capacitors employing this barrier layer were not significantly affected by a temperature stress of up to 600 degrees C for 1 h.