Growth shape of crystallites in thin film deposition

Abstract

A general theory is presented for the growth of island-like crystallites in deposition of thin films. In contrast with current theories the crystallite is not assumed to have a constant growth shape and the change of its shape during growth is analyzed. A general kinetic equation is derived and by solving it formulae are obtained for the time dependence of the crystallite volume, mean height and a suitably defined shape factor. The analysis shows that when the crystallite can be approximated by a spherical cap it has an effective wetting angle which, typically, is a weak power function of time. The general theory is applied to a particular case of crystallite growth in thin film deposition from vapours in order to reveal the dependence of the crystallite growth shape on the deposition rate, substrate temperature and time. It is found that the growth shape changes rather slowly with time and that the crystallites become higher with increasing temperature in incomplete condensation and with decreasing temperature in complete condensation.