Nanostructured chromium nitride films with a valley of residual stress

Abstract

A series of chromium nitride films has been prepared by reactive DC magnetron sputtering onto multiple moving substrates. The films are characterized via an array of experimental techniques, including high-resolution synchrotron radiation X-ray scattering, transmission electron microscope (TEM), atomic force microscope (AFM) and double-crystal diffraction topography (DCDT). Chromium nitride films displays distinct phase structure, stress state and growth morphology, depending on nitrogen flows. The films deposited at very low nitrogen flows show significantly refined microstructures. The macrostructural refinement, accompanied by decreased surface roughness, takes place continuously with increasing nitrogen flow until a nanocrystalline film is obtained. The nanostructured film appears to occur only at the onset of transition from the hexagonal Cr 2N to a distorted cubic lattice CrN x . Correspondingly, a deep stress valley (i.e. a sudden reversal of tensile stress to compressive stress) is observed by DCDT. Deposition at higher nitrogen flows leads to the formation of nearly stoichiometric CrN films, with slightly elongated grain structures. The elongated grains also align up crystallographically in a unique direction related to the deposition geometry, indicating the development of tri-axial texture in the CrN films.