Characterization of nanostructured Cr2Nx/Cu multilayers deposited by reactive DC magnetron sputtering

摘要

Nitride/metal nanostructured multilayers of Cr2Nx/Cu were deposited by reactive DC magnetron sputtering with various bilayer periods (2.5-30 nm) and substrate temperatures (25-400 degrees C). All films had a total thickness of about 470 nm and the overall chemical composition of the chromium nitride layers was close to Cr2N0.8. 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 degrees C had a well-defined multilayer structure and the chromium nitride layers were found to crystallize into N-deficient fcc CrN0.4 with traces of hexagonal Cr2N0.8. The layers were strongly textured with fee CrN0.4[002] and Cu[002] oriented along the growth direction - the fcc CrN0.4 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 degrees C the films were better described as non-textured nanocomposites with the chromium nitride crystallized entirely into the equilibrium hexagonal Cr2.N0.8 structure. Hardness values of the high-temperature films in the range of 4-8 GPa were measured. Multilayer films deposited at 25 degrees C were found to be thermally stable against post-deposition annealing at temperatures up to about 400 degrees C. Annealing at 500 degrees C caused severe structural changes - the fcc CrN0.4 phase transformed into hexagonal Cr2N0.8 accompanied by degradation of the periodic multilayer structure. The hardness decreased from the originally 8 GPa to about 5 GPa upon annealing. (c) 2006 Elsevier B.V. All rights reserved.