[polyfractal]

It exists! The technique is called Electron-beam lithography (https://en.wikipedia.org/wiki/Electron-beam_lithography), and it's exactly what you described. It's essentially an electron microscope that is used to etch patterns, instead of doing the whole projection lithography song and dance.

I believe it's used in academic research a fair amount, because it gives very good resolution (sub-10nm) and is very cheap (once you own the equipment). But as you said, it's also very slow :)

There's a contingent of hobbyists that run second-hand electron microscopes in their garage... I'd bet they could do electron-beam litho if they wanted to