Zirconium nitrides deposited by dual ion beam sputtering: physical properties and growth modelling

Zirconium nitrides reveal interesting optical and electrical properties which highly depend on the nitrogen stoichiometry. Indeed, the material exhibits a transition from the stable metallic ZrN (optical index for bulk at 633 nm: N=0.5−i3.2) to the metastable semi-transparent insulating Zr₃N₄ (N=3.2−i0.4). This work deals with the elaboration of homogeneous ZrN-like and Zr₃N₄-like coatings. These have been prepared using reactive Dual Ion Beam Sputtering (DIBS) using a Zr target and N₂ or N₂+Ar reactive gas. The influence of different elaboration parameters (ion energy, gas composition of the reactive beam and substrate temperature) on the nitrides composition and on their optical and electrical properties was particularly studied. A model was proposed to explain the influence of energy and temperature on the nitrogen composition. The nitrogen stoichiometry was shown to be controlled by a competitive mechanism between implantation of excess nitrogen amount in the subsurface and their elimination by exodiffusion. The first phenomenon is mainly controlled by the ion energy whereas the second one is enhanced by a high temperature and a high irradiation defects density. Therefore, the Zr₃N₄-like nitrides were obtained with low temperature and high energy (200 eV) conditions whereas high temperature and low energy led to ZrN-like materials.