Experimental and theoretical studies of coating thickness distributions obtained from high rate electron beam evaporation sources

Abstract

The study of the thickness distribution of thin films achieved by an electron beam evaporation source is the main purpose of this work. The different parameters which play a rule in the estimation of the coating deposition rate for substrates fixed throughout the deposition chamber are discussed. Three main parameters will be considered: the position of the substrate in relation to the evaporation source, the shape of this source and the space distribution of the evaporated atoms. While the influence of the first two parameters is well known, the effect of the spatial distribution of the vapor beam is considerably less so. Based an previous results showing that, at high evaporation rates, the distribution of vapour atom velocities does not follow a Maxwell form, it was possible to justify the experimental thickness distribution obtained on the entire half space over the vapour source. It is also shown in this paper that the incidence angle of the atoms deposited on the growing film plays an important rule on the film growth mode, leading to an important change in its specific gravity. This variation of specific gravity must be taken into account to correctly predict the deposition rate for any fixed point on the substrate located anywhere in the vacuum chamber. Finally, it was shown that these analytical models can be applied to the deposition of different materials such as copper or titanium and even, for a material like chromium that sublimates below the path of the electron beam. For this last case, a Monte Carlo simulation study of the atom emission from the vapour source was necessary to fit the experimental thickness distribution.