Effect of the varied nitrogen vacancy concentration on mechanical and electrical properties of ZrNx thin films

ZrNx films were deposited with reactive magnetron sputtering in different [Ar]/([Ar] + [N2]) atmospheres and analyzed using X-ray photoelectron spectroscopy, glancing incidence X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, nanoindentation techniques, and four-point probe meter. N vacancy concentration is defined as V-N = 1- x, where xis N/Zr ratio in ZrNx. Results showed that the V-N ranged from 0.02, through 0.08, 0.13, 0.24 to 0.30. The glancing incidence X-ray diffraction results showed a decrease in lattice parameter a(0) from 4.582, through 4.578, 4.571, 4.564 to 4.548 angstrom with the increase of V-N from 0 to 0.30. Berkovich nanoindentation results showed that the hardness of ZrNx films increased from 18 +/- 1.3 GPa to 24 +/- 1.2 GPa with the increase of V-N from 0 to 0.24, which is due to vacancy-induced hardening. However, further increase of V-N to 0.30, a drop-in hardness was observed, which was attributed to vacancy-induced softening. Both hardening and softening proved the existing of a turning point at V-N around 0.24. In addition, the fracture toughness and sheet resistance of ZrNx films also presented the same tendency. The experimental results agreed with first principle predictions that the metal-N (d-p) bonds, Zr-Zr (d-d) sigma bonds and the valance electron density around Zr atoms had changed greatly due to the varied V-N.