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The effect of crystal orientation and microstructure on the mechanical properties of TaNx was investigated. TaNx films were grown on SiO2 substrates by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and at 350 °C. Unlike the Ti-N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta-N system could lead to layers which had nano-sized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the microstructure of TaNx layers were controlled by varing incident ion energy Ei (= 30eV~50eV) and nitrogen fractions (=0.1~0.15). TaNx layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films. The structure of the TaNx film transformed from B1-NaCl -TaNx to lamellar structured B1-NaCl -TaNx + hexagonal ε-TaNx or B1-NaCl -TaNx + hexagonal γ-TaNx with increasing the ion energy at the same nitrogen fraction . The hardness of the films also increased by the structural change. At the nitrogen fraction of 0.1~0.125, the structure of the TaNx films was changed from -TaNx + ε-TaNx to -TaNx + γ-TaNx with increasing the ion energy. However, at the nitrogen fraction of 0.15, the film structure did not change from -TaNx + ε-TaNx over the whole range of the applied ion energy. The hardness increased significantly from 21.1 GPa to 45.5 GPa with increasing the ion energy.