Production challenges of making EUV mask blanks

Mask Blanks for EUV Lithography require a lot of new properties and features compared to standard Chrome-on-Glass blanks. Starting from completely new low thermal expansion substrate materials with significantly improved surface quality over multilayer coatings for EUV reflection, buffer layers, up to new absorber layers with improved dry etching and inspection properties. In addition highly sophisticated metrology is needed for further improvements and process control. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to routinely produce EUVL mask blanks meeting already many of the ITRS roadmap requirements. Our improvements on low defect EUV multilayer coatings as well as on our metrology methods will be elucidated and some aspects of this will be explained in detail. In addition a new design of EUVL absorber material with experimental results will be reported, including optical performance at inspection wavelength.