Structural Nonuniformity and Internal Stress in Chromium Films Deposited by Magnetron Sputtering

Using high-resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction methods, the microstructures and lattice parameters of different parts of Cr films deposited by magnetron sputtering under different deposition conditions have been studied. It was revealed that the microstructure and lattice parameter of the films deposited onto nonheated substrates vary in the film thickness direction. Lattice parameter a has a maximal value in the film-substrate interface region and gradually decreases towards the conventional value in the middle and upper film parts. In accordance with this, the internal tensile stress decreases, while the grain size increases in the direction from the substrate to the film surface. Elevation of the substrate temperature results in smoothing of nonuniformity of the film microstructure and stress distribution along the thickness. At a certain combination of a substrate temperature and bias voltage, unstressed large-grained films with uniform microstructure have been deposited. The model proposed for explanation of the obtained results is based on the supposition of dynamic elevation of condensation surface temperature during film growth that promotes the formation of the film with structure and stress nonuniformly distributed in the thickness direction.