"The mirrors guiding this light, made of sandwiched layers of silicon and molybdenum, are ground so precisely that, if scaled to the size of Germany, they would have no bumps bigger than a millimetre" <https://www.economist.com/business/2020/02/29/how-asml-becam...>

Also, I've heard some say that if China were to try and develop its own ASML like lithography machine, it would take at least 10 years. I wonder if anyone could throw any light on that claim?

Back in 2016, the ITRS body for semiconductor roadmaps with a now-failed prediction since there are several process nodes in development, in part with the help of tech from ASML:

https://www.hpcwire.com/2016/07/28/transistors-wont-shrink-b...