Ion beam assisted deposition under off-normal ion incidence: an experimental and analytical study of re-sputtering effects

Ion beam assisted deposition (IBAD) is a coating technique which combines the condensation of a material and ion bombardment. Ion bombardment strongly affects not only the features of the growing film such as composition or microstructure but it also leads via re-sputtering processes to a loss of condensating material. This mostly undesirable effect reduces the film growth velocity and may become critical when the ion impact angle deviates from the substrate surface normal. Because material modification processes including deposition and ion bombardment are more and more transferred into industrial application, the knowledge of angular-dependent re-sputtering yields is of utmost importance for applicability of the process to component parts or workpieces. In the present study cylindrical samples were coated with several monoelemental films by means of ion bombardment during electron beam evaporation and also the decoupled process of bombardment after deposition. Thickness losses for the ‘dynamic’ and ‘static’ process are determined with Rutherford Backscattering Spectroscopy. An analytical equation is applied which describes the thickness reduction over all angles of ion incidence including an expression for the angular dependence of the re-sputtering yield with only three adjustable parameters. A correlation is found between these parameters and the film’s atomic number and surface binding energy. Furthermore, the results are discussed in terms of whether a ‘dynamic’ re-sputtering yield exists or the ‘static’ process gives an appropriate description of ion beam-induced re-sputtering during deposition.