The finest chips are drawn by light that glass cannot pass

Extreme-ultraviolet lithography patterns chips with 13.5-nanometre light. Air absorbs it. Glass absorbs it. The lenses are mirrors, and the machine is a vacuum.

A droplet of tin is hit by a laser and becomes a plasma that shines at 13.5 nanometres. The light never meets a lens. Multilayer mirrors of molybdenum and silicon reflect a fraction of it — Bragg reflectors, not bathroom glass — and they do it inside a vacuum, because a few centimetres of air would eat the beam. That light exposes a pattern on a wafer. It is how the tightest commercial layers of a modern processor are printed.

Older factories still print many layers with 193-nanometre light, in water, with tricks that place features smaller than the wavelength. EUV did not abolish that. It took over the layers where the tricks had run out. The mirrors absorb most of what hits them, which is why the tin plasma has to be so bright, and why the machine is the size of a room and the price of a small factory.