Reactively sputtered zirconium nitride coatings: structural, mechanical, optical and electrical characteristics

This paper presents the result of the substrate bias voltage effect on the properties of zirconium nitride films, such as structure, morphology, hardness, internal stresses, optical constants and electrical resistivity. The coatings are deposited on steel and silicon substrates by magnetron sputtering of a zirconium target in reactive Ar–N2 mixture. If a bias voltage is applied to the substrate holder, the film texture changes into a [1 1 1] one. For negative bias voltage values higher than −110 V, the lattice constant decreases and porosities are also observed on the films’ surface. These porosities result from a resputtering phenomenon, which occurs only at high values of negative bias voltage. Although the average crystal size is nearly unchanged by the use of a bias voltage, the films present a maximum of hardness (39.5 GPa) vs. this deposition parameter. The optical properties of ZrN films are correlated with the films structure and their hardness. Optical properties close to those of bulk zirconium nitride are obtained for films deposited with a bias voltage of −110 V. Finally, the electrical resistivity of reactively sputtered ZrN coatings has been measured using the four-point probe method.