The incredible physics of ASML’s EUV scanner

Dr. Marcelo Ackermann, Full Professor – Chair of the XUV optics group at University of Twente, m.d.ackermann@utwente.nl

ASML’s EUV scanner has taken the world by storm – EUV is at the core of the newest chips, and the newest ‘High-NA’ scanners show unprecedented resolution down to 8nm! The short wavelength of the EUV light – 13.5nm – is the key to printing such small features. But working with this wavelength is also incredibly challenging: Not only is a completely new light source required – moving from ArF and KrF excimer lasers to Sn-based laser-produced-plasma, also all optical components had to be re-invented. The technology to make such a plasma – shooting at tiny Sn droplets with a 30 kW laser – is an incredible feat on its own. But focusing the light coming out of the plasma is equally challenging. Traditional lenses no longer work at 13.5 nm – as glass is not transparent at that wavelength. Mirrors with atomically perfect multilayer coatings had to be developed. Carl Zeiss SMT developed the mirrors in Southern Germany, and for the intricate multilayer coatings they collaborated with the XUV group form the University of Twente in the Netherlands. These coatings require atomically perfect layers and interfaces in order to reflect the EUV light in a world where every % of reflectivity, and hence scanner throughput counts. I will show how the XUV group at the University of Twente developed these multilayer coatings, and how today we still push to improve every optical element in the EUV scanner.