All the research that was founded by tax dollars in the 70s before all the research was privatised (like nor more scientific publications how it was done etc).
my question was more: what is the short laundry list of the exact developments/research that allowed Zeloof's garage-size/at-home chip-making?
Further, capital costs will rapidly start rising as well as the required knowhow as the feature size shrinks, so I think he's already quite close to the limit a one person hobby project can achieve.
All this being said, this is an extremely impressive achievement. There's a long way from reading how stuff is supposed to work, to actually doing it your garage. My hat's off to Mr. Zeloof.