Physics and technology development of multilayer EUV reflective optics

This thesis describes the development of molybdenum/silicon based multilayer reflective elements for the Extreme UV wavelength range, as motivated by their application in photolithography for semiconductor manufacturing. The thesis reflects the basic thin film physics, technological developments, and valorisation activities of the last two decades of research, a period in which the author was involved in more than 20 research projects, carried out at FOM with numerous academic and industrial partners. This thesis contains three major aspects: basic thin film growth and analysis studies, the development of deposition processes and associated instrumentation, and the demonstration of the knowledge by producing prototype industrial optics coatings for lithography. The thin film studies described contribute to answers to basic questions such as: what are the leading film growth processes for layers with nanoscale thicknesses, which mechanisms determine layer smoothening and interlayer formation, what determines the amorphous, crystalline or chemical state, how can one control atomic diffusion and arrive at temporally and thermally more stable multilayer structures? Also described are answers to the more applied aspects, like: how can multilayer induced stress be controlled, and what optical response can result from non-periodic or laterally structured multilayer systems? Dedicated process and instrumentation development has made many of these detailed studies possible. The various generations of deposition facilities that we designed, developed, and continuously improved during the last two decades have been based on e-beam evaporation, magnetron sputtering, as well as plasma and ion-beam surface treatments. Two new research facilities are being designed and built: the Atomic Growth and Analysis facility (AG/A) for fundamental thin film research and a large and versatile deposition system for multilayer development. The third aspect of the thesis work, its valorisation, concerns the production of proof-of-principle prototype multilayer depositions on industrial lithography optics. This includes the successful coating of optical components for ASML and Zeiss’ first two generations of EUV lithography machines. Demonstrations are described on achieving the lateral control of the deposition process over large area surfaces to meet all aspects of the optics design specifications. In short, in the thesis the author attempts to summarize his knowledge on stateof- the-art multilayer EUV deposition know-how and technology, in order to support the EUV activities and to form a basis for further, industrially-inspired thin film physics and development programmes.