Structural studies of amorphous and crystallized tungsten nitride thin films by EFED, XRD and TEM

Energy-filtered electron diffraction (EFED), X-ray diffraction (XRD), and transmission electron microscopy (TEM) have been used to investigate the structural properties of amorphous and crystallized W_1-xN_x (0.12≤x≤0.35) thin films prepared by reactive magnetron sputtering in an Ar-N₂ atmosphere. XRD θ-2θ scans combined with plan-view and cross-sectional TEM showed that the as-deposited W_1-xN_x films were amorphous in structure. Annealing of the as-deposited films at 600 °C or above resulted in crystallization of the amorphous phases, forming a two-phase structure consisting of W₂N and bcc W or a single-phase structure of W₂N, which was related to the initial nitrogen concentration in the films. The crystalline films (150 nm in thickness) near stoichiometry of W₂N had a columnar microstructure with an average column width of 15-20 nm near the film surface. For films with a lower N concentration, the column grains were larger. EFED data collected from a range of crystalline films were Fourier transformed to a reduced density function (RDF), which was compared to the theoretical calculations based on the fraction of the crystalline phases determined from the experiment. The transformed fraction was shown to agree with the calculations.