The diffusion barrier properties of as-deposited amorphous TaNx (x approximate to 0.5) and crystalline TaN between Cu and SiO2 have been investigated in Cu/Ta-N/Ta/SiO2 structures. The thermal reactions of Cu/TaNx/Ta/SiO2 and Cu/TaN/Ta/SiO2 after annealing in vacuum at 500 to 900degreesC were investigated by using sheet resistance measurements, glancing incident angle X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, and Rutherford backscattering spectrometry. No significant reaction and change of sheet resistance were detected for both systems after annealing up to 800degreesC. As compared to TaN, TaNx exhibited better electrical properties and capability for preventing Cu diffusing through it. However, the sheet resistance of both systems increased abruptly after annealing at 900degreesC, especially the TaNx system. The severe increase in sheet resistance corresponds to the deterioration of Cu surfaces. Broken holes were seen in the TaNx layer, which were the initial sites for the structural failure. The cause of failure in Cu/Ta-N/Ta/SiO2 stacks is discussed on the basis of the characteristics of Ta-N films upon heat-treatment. (C) 2004 The Electrochemical Society.