Structure of the metallic films deposited on small spheres trapped in the rf magnetron plasma

Abstract

Metallic coatings were deposited onto glass spheres having diameters from several to one hundred micrometers by the magnetron sputtering. Two different experimental schemes were exploited. One of them had the traditional configuration where a magnetron sputter was placed at one hundred millimeters from particles. In this scheme, continuous mechanical agitation in a fluidized bed was used to achieve uniformity of coatings. In the second scheme the treated particles (substrates) levitated in a magnetron rf plasma over a sputtered rf electrode (target) at the distance d of few mm from it and at gas pressure p values of 30-100 mTorr. These parameters are essentially different from those in the traditional sputtering. Agitation due to the features of a particle confinement in dusty plasma was used here to obtain uniform coatings. Thickness and morphology of the obtained coatings were studied. As it is known, film growth rate and structure are determined by the substrate temperature, the densities of ion and neutral atom fluxes to the substrate surface, the radiation flux density, and the heat energy produced due to the surface condensation of atoms and recombination of electrons and ions. These parameters particularly depend on the product of p and d. In the case of magnetron rf dusty plasma, it is possible to achieve the pd value several times lower than the lowest value proper to the first traditional case. Completely different dependencies of the film growth rate and structure on the pd value in these sputtering processes were observed and qualitatively explained.