https://www.technologyreview.com/2021/10/27/1037118/moores-law-computer-chips/
To give a sense of scale, if you took the mirror in your bathroom and blew it up to the size of Germany, it would have bumps about five meters high. Blown up to the same size, the smoothest EUV mirror Zeiss’s engineers had yet made—for space telescopes—would have bumps only two centimeters high. These mirrors for ASML would have to be orders of magnitude smoother: if they were the size of Germany, their biggest imperfections could be less than a millimeter high. “These are really the most precise mirrors in the world,” says Peter Kürz, who is responsible for the development of the next generation of EUV optics at Zeiss.
A big part of Zeiss’s work would be inspecting the mirrors to look for imperfections and then using an ion beam to knock individual molecules off, gradually smoothing the surface over months and months of work.
While Zeiss was developing the mirrors, Benschop and other ASML suppliers were working on their other big challenge: how to create a light source that would produce a steady flow of EUV.
It would haunt them for years.