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

Abstract

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 VN = 1- x, where x is N/Zr ratio in ZrNx. Results showed that the VN 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 a0 from 4.582, through 4.578, 4.571, 4.564 to 4.548 Å with the increase of VN 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 VN from 0 to 0.24, which is due to vacancy-induced hardening. However, further increase of VN 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 VN 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, ZrZr (d-d) σ bonds and the valance electron density around Zr atoms had changed greatly due to the varied VN.