Deposition of complex optical interference filters on polymer substrates by magnetron sputtering and PECVD processes

Abstract

Polymer substrates for optical coatings show some significant advantages such as low cost, low weight and mechanical flexibility. However, the deposition of complex optical interference filters on plastics is much more challenging than the deposition on glass. Important issues are the temperature and plasma stability of the substrates, their surface quality (roughness), the adhesion of the coated layers, the different thermal expansion of polymers and the oxide layer systems and the strain in the layers caused by mechanical deformation of the coated substrates. In this work we present the results of experiments to deposit interference filters with thicknesses > 3 μm and layer counts > 30, which can be used, for example, as triple notch filters for channel separation in 3D projection systems. In detail, we compared a filter deposited by magnetron sputtering with filters in which some of the sputtered layers have been replaced by layers made with plasma enhanced chemical vapor deposition (PECVD). The purely sputtered optical system showed good optical performance, good layer adhesion and a relatively low crack onset strain of 0.7 %. Optical layer systems made from sputtered oxide layers and PECVD made plasma polymers showed significant increase of the crack onset strain of 1.4 %