Roll-to-roll deposition of silicon oxynitride layers on polymer films using a rotatable dual magnetron system

High performance permeation barrier coatings are usually multilayer stacks consisting of inorganic and organic layers. Besides the water vapor transmission rate, the optical properties of such layers have a high importance. This contribution focuses on the deposition of silicon oxynitride as an inorganic layer. This material attracts a widespread interest due to its varying refractive index depending on its oxygen and nitrogen content. The experiments were carried out in a roll-to-roll coating machine using a rotatable magnetron system. The layers were deposited by reactive pulse magnetron sputtering using targets of 1 m length. It was established that the ratio of oxygen to nitrogen in the layer was not only determined by the reactive gas mixture but also by the chosen set point of the closed loop control. Both the Secondary Ion Mass Spectrometry and the Glow Discharge Optical Emission Spectroscopy measurements revealed a vertically different composition of the SiOxNy layers. This could be supported by the simulation of the optical properties of the layers.