The diffusion barrier properties of Ta, both as deposited without ion bombardment and deposited concurrent with ion energy, were investigated in the Cu/Ta/Si contact system using Auger electron spectroscopy, x-ray diffraction, optical microcopy, transmission electron microscopy : and sheet resistance measurements. It was found that the ion bombardment during deposition of Ta films influenced the microstructural characteristics, such as the packing density of grain boundaries, the grain size, and the preferred orientation of Ta grains. The Ta film deposited concurrent with 150 eV ion energy (0.13 mA/cm(2)) showed the increased packing density of grain boundaries, low resistivity, and preferred orientation. The densification of grain boundaries of the Ta barrier layer, followed by an increase of silicide formation temperature, significantly enhanced the barrier property of Ta in the Cu/Ta/Si system.