Project number: HTSM2014 13913
Title: Enhanced multilayer mirror stability through heterogeneous materials (Heterocaps)
Executive organisational unit: XUV Optics, MESA+ Institute for Nanotechnology, University of Twente  
Project leader:  Dr. J.M. Sturm (j.m.sturm@utwente.nl)
Duration: 2013-2020
Researcher:  O. Soroka, C. Stilhano Vilas Boas
Industrial partner:  Carl Zeiss SMT


Multilayer mirrors form the basic optical element for EUV lithography, as well as for synchrotron and free electron laser beam lines. To maximise the optical throughput of these systems, the reflectivity must be preserved for as long as possible. However, the ionizing radiation may create a plasma near the surface of the mirror, which reacts with the mirror surface, degrading it. Chemical reactions, ion implantation, and diffusion all combine to damage the mirror’s surface, and create sub-surface damage, which may, eventually, evolve into surface blisters. To slow or prevent these processes, we are investigating heterogeneous top layers. We exploit material combinations that will react with their environment, and, upon stabilisation, prevent further degradation or diffusion. In this way, we expect to greatly extend the lifetime of EUV optics when used under harsh conditions.