Preferred orientation, phase transition and hardness for sputtered zirconium nitride films grown at different substrate biases

We deposit zirconium nitride films on silicon (100) substrates using direct current reactive magnetron sputtering, and investigate the effects of the substrate bias voltage on the preferred orientation, phase transition and hardness for the obtained films via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and nanoindentation measurement. It is our finding that the preferred orientation for the films changes significantly with increasing the substrate bias voltage, which can be attributed to an increase in the biaxial compressive stress. With a further increase the substrate bias voltage, leading to a high biaxial stress, a phase transition from substoichiometric to overstoichiometric zirconium nitride with a Th3P4 structure (Zr3N4) occurs. The thermodynamic calculation proves that the driving force for the evolution of preferred orientation and phase transition results from a decrease in the strain energy. The Zr3N4 phase shows a high hardness.