What is the most advanced and performant processor which may be reasonably manufactured in a home garage?
Take a look at this fella: http://sam.zeloof.xyz/first-ic/
The page has a short video goes over some of the tools and materials that went in to making a small amplifier chip.
I don't have any experience with making integrated circuits but just from the looks of it, scaling it up to make an entire processor seems a little far fetched.
If you're in it for the fun of having a small project you can pretty easily make your own PCB and solder microchips onto it in almost any home garage.
It's like the Saturn V - the documentation/blueprints/etc was massive, secret, spread all over, making it basically impossible to recreate the rocket just by "following instructions", replacement stuff would have to be recreated from scratch.
The US has tightly controlled the export of advanced processes, which is why even TSMC isn't allowed to manufacture in China with processes below 22nm.
I believe (Chinese based company) SIMC has a new 8nm process they developed themselves, but people have doubts about the yield.
See https://warontherocks.com/2020/06/the-chip-wars-of-the-21st-... for some details about this.
What's more we are constantly building new plants and processes. This isn't like the Saturn V where the plans were mothballed.
Sure, if you killed all semi-conductor engineers, and everyone at Intel and TSMC and Samsung I'm sure there would be problems. But realistically chip manufacture is one of the things I'd feel more confident about being able to recover.
If not, there's still knowledge of older, but decent processes like 130nm/90nm, which should be doable pretty fast...
...probably equivalent in performance to a minicomputer from the 70s.
I.e.:
- space
- power and cooling capacity
- freshwater and wastewater capacity
- legality of storing / disposing of toxic materials
- proximity to a residential dwelling
- equipment cost
- amount of noise produced
It's simply amazing how bleeding edge modern fabrication is.