Simulation of thermal stress in ion beam sputtered Ta2O5/SiO2 multilayer coatings on different substrates by finite element analysis

Abstract

The delamination and failure of thin-film system induced by thermal stress have long been of interest in processes of coatings deposition. In spite of ion beam sputtering depositing (IBSD) exhibiting low processing temperature, the thermal stress still has significant influence when a tremendous difference exists between physical and thermal properties of the bonded materials. Therefore, the investigation for a conventional optical multilayer stack consisting of tantalum pentoxide and silicon dioxide deposited on four substrates with different materials (calcium fluoride, zinc selenide, silicon, and fused silica) in this paper is presented. In order to calculate the thermal stress distribution along thickness remote from the edge, a two-dimensional finite element model of the system is established. Based on this model, the peeling stress and the shear stress at the interfaces between the substrates and coatings are discussed to judge whether the interface delamination is possible, as well as the interfacial peeling moments and interfacial shear forces. Meanwhile, the corresponding samples were coated by the method of IBSD, and the experimental results show excellent agreement with the predictions. Based on the above analyses, we discussed the delamination phenomenon of the experiment, and also proposed some possible approaches to reduce the possibility of the interface delamination.