UV-optical and microstructural properties of MgF2-coatings deposited by IBS and PVD Processes

In high quality otpical coating systems for the DUV-spectral range, MgF2 is one of the preferred deposition materials. MgF2-coatings exhibit relatively low optical losses as well as high stability and laser induced damage thresholds. In the present joint research effort of several European laboratories, the potentiality of MgF2 is evaluated in respect to the production of improved optical coatings for applications in laser technology and semiconductor lithography. For this purpose, single layers of MgF2 were deposited on superpolished fused silica and CaF2-substrates by ion beam sputtering, boat and e-beam evaporation in different laboratories. Besides photometric inspecti ons, the samples were characterized by an optical scatter measurement facility at 193 nm and 633 nm. The structural properties were assessed using AFM, XRD, and adapted TEM-techniques invovling conventional thinning methods for the layers. For the measurement of mechanical stress in the coatings, special sil icon sub strates were coated and analyzed.