Characterization of nanostructured Cr 2N x/Cu multilayers deposited by reactive DC magnetron sputtering

Abstract

Nitride/metal nanostructured multilayers of Cr 2N x /Cu were deposited by reactive DC magnetron sputtering with various bilayer periods (2.5–30 nm) and substrate temperatures (25–400 °C). All films had a total thickness of about 470 nm and the overall chemical composition of the chromium nitride layers was close to Cr 2N 0.8. The deposited films were characterized by Rutherford Backscattering (RBS), low-angle X-ray reflectivity (XRR), high-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness and elastic modulus were measured by nanoindentation. The films deposited at 25 °C had a well-defined multilayer structure and the chromium nitride layers were found to crystallize into N-deficient fcc CrN 0.4 with traces of hexagonal Cr 2N 0.8. The layers were strongly textured with fcc CrN 0.4[002] and Cu[002] oriented along the growth direction — the fcc CrN 0.4 and Cu grains growing with a cube-on-cube relationship. The measured hardness values were about 8 GPa, and showed no dependence on the bilayer period. Higher deposition temperatures caused the multilayer structure to degrade, and at 400 °C the films were better described as non-textured nanocomposites with the chromium nitride crystallized entirely into the equilibrium hexagonal Cr 2N 0.8 structure. Hardness values of the high-temperature films in the range of 4–8 GPa were measured. Multilayer films deposited at 25 °C were found to be thermally stable against post-deposition annealing at temperatures up to about 400 °C. Annealing at 500 °C caused severe structural changes — the fcc CrN 0.4 phase transformed into hexagonal Cr 2N 0.8 accompanied by degradation of the periodic multilayer structure. The hardness decreased from the originally 8 GPa to about 5 GPa upon annealing.