Testing a new PECVD source
To obtain a better understanding of the interplay of soft organic and hard oxidic coatings in optical coating systems an innovative PECVD source has been integrated into a conventional turntable sputtering chamber for optical coating systems. It is characterized by a low amount of energy being supplied to the substrate during the coating process, what has advantages for the coating of plastic substrates. The objective of the activities at the Fraunhofer IST was to integrate and also to optimize the source with regard to the highest and most homogeneous coating rate possible, a low input of energy to the substrate and variable mechanical coating properties.
Homogeneous coatings with a high optical quality
In comprehensive testing of the source using hexamethyldisiloxane (HMDSO) as precursor and by running various simulation calculations, the coating rate, the energy input, the coating properties and the coating homogeneity of the source were optimized. The simulation calculations in particular proved very helpful here in remedying design weaknesses in the source (anodic hotspots). In addition, iterative improvement of the masks also made it possible to achieve considerable improvements in the homogeneity of the coatings. Furthermore, experiments confirmed that the mechanical properties of the coatings (elongation at break) can be varied by the source (see graphs on the opposite).
It is now possible with the aid of the modified deposition setup to integrate organically modified layers in the ceramic stack. This permits the creation of gradient coatings, for example, in which the mechanical properties of the coating are adapted to those of the substrate. In addition, outstanding barrier effects against the diffusion of water or oxygen can even be obtained by combinations of organic and inorganic layers.