Packing density/surface morphology relationship in thin sputtered chromium films

Abstract

Abstract Modifying and engineering the properties of materials can be achieved by coating them with thin films possessing specific characteristics. The final properties of the coating are determined by the deposition conditions and by the associated film's growth mode. To gain a better understanding and eventually control over the growth and properties of very thin films (thickness less than 50 nm), various chromium films were deposited by magnetron sputtering and their electrical and optical properties were measured. This paper presents the relationships between the stress, the material's surface morphology and the properties of such chromium thin films. We observed an increase in electrical conductivity and photopic reflection of the films with the increase of the deposition power. Our analyses further revealed that the surface morphology is directly responsible for the enhancement of these properties, as surfaces presenting the least air fraction ratio (smooth surface with large grains and a Gaussian roughness distribution) were the most conductive and most reflective. We also demonstrated that calculating the residual film stress is an incomplete way of assessing the structure of the film, as films having similar residual stress exhibited different properties. In conclusion, the surface morphology and its roughness distribution represent a convenient way to estimate the packing density of sputtered thin films.