NbN/SiN x [X][D] δ′-NbN/SiN x [D] Multilayer [B] Nano-indentation [C] Physical vapour deposition
We deposit cubic δ-NbN/SiN x and hexagonal δ′-NbN/SiN x nano-multilayer films using reactive magnetron sputtering in discharge of a mixture of Ar and N 2 gas, and explore the effects of SiN x layer thickness on the microstructure and mechanical properties for both cubic δ-NbN/SiN x and hexagonal δ′-NbN/SiN x multilayer films by virtue of X-ray diffraction, electron diffraction, high-resolution transmission electron microscope, and nanoindentation measurements. We find that the structure for NbN layers is a critical factor in determining the hardness of NbN/SiN x multilayer films. For cubic δ-NbN/SiN x nano-multilayer films, as SiN x layer thickness is smaller than or equal to 0.4 nm, the cubic δ-NbN layers force SiN x layers to crystallize, accompanied with a remarkable increase in hardness with maximum hardness of 32 GPa. With an increase in thickness, SiN x layers become amorphous, and correspondingly the hardness decreases. For hexagonal δ′-NbN/SiN x nano-multilayer films, both the stress and hardness decrease with increasing the SiN x layer thickness and the nano-multilayer films do not show any enhancement in hardness, compared to δ′-NbN single layer film.