Laser-fluence effects on NbNx thin films fabricated by pulsed laser deposition

Niobium nitride films were deposited on Nb substrate using pulsed laser deposition (PLD) with a Q-switched Nd:YAG laser at different laser fluences. The film crystal structure and surface morphology were studied. The microstructure, texture and surface morphologies of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscope (AFM). Highly textured NbNx films were produced by PLD on niobium substrates at different laser fluences for constant background nitrogen pressure and substrate deposition temperature. When the fabrication parameters are fixed except the laser fluence, surface roughness, deposition rate, nitrogen content, and grain size increase together with increasing laser fluence. The nitrogen content in NbNx films increases with the laser fluence up to 15 J cm−2 and decreases thereafter. The films exhibit highly textured structure with a preferential orientation of (1 1 0) parallel to the substrate. The NbNx layers are formed in mixed phase (cubic and hexagonal) with the ratio of hexagonal phase to cubic phase dependent on the laser fluence. These observations can be used to establish guidelines for optimizing the laser fluence to achieve the desired morphology and phase of the grown NbNx thin film.