Stress, texture, and microstructure in niobium thin films sputter deposited onto amorphous substrates

Abstract

Nbfilms with thicknesses 5, 20, 100, and 500 nm were deposited by magnetron sputtering onto Si wafers covered with amorphous layers of SiO 2 and Si 3 N 4 . The substrates were used in the as-received and sputter cleaned conditions. Various methods were applied for an extensive investigation of the physical properties of the Nbfilms: they were analyzed with respect to morphology (by focused ion beam imaging and by atomic force microscopy), chemical composition (by x-ray photoelectron spectroscopy sputter depth profiling and by x-ray reflectometry) and texture, (macro) stress and microstrain (by x-ray diffraction methods). An explanation for the strong dependence of the sharpness of the dominant {110} fiber texture in the Nbfilms on the type of substrate, the cleaning conditions, and the film thickness is presented. X-ray diffraction stress analysis revealed strong compressive stress parallel to the surface of the order of a few gigapascal within a layer close to the film surface. This was ascribed to the formation of oxides at the boundaries of the columnar grains after exposure of the films to air. By grazing incidence x-ray diffraction the existence of a stress gradient in the Nbfilms was confirmed. The growth stress and the microstrain, determined by line profile analysis, could be correlated with the sharpness of the texture of the Nbfilms.