Can you do it, given the right tools, training, and patience? Yes.
Will they be any good? No.
Will they be cost-competitive? No.
Getting chips made on a shuttle run for an old node is very affordable. There's really no need for it.
(According to one MPW supplier, 10mm2 of 340nm, up to 10 dies, costs 6400 euros, and it's unlikely 340nm is achievable in a garage anyway)
I believe the way Sam Zeloof circumvents the enormous amount of capital needed for a chip fab by relying on modern technology to create 1970’s technology. He simply mounts a cheap digital projector onto a cheap microscope - they didn’t have that advantage in the 70s, and thus it cost millions to start a chip fab. My point is that it could conceivably be doable for an individual to create old computing technology with the advantages of living in the modern world. I certainly don’t have the drive to do it, but I wish someone did.
If you did it often and didn't count your own labor costs, then maybe the average cost would be less, but that's an incredibly specific situation.
> I believe the way Sam Zeloof circumvents the enormous amount of capital needed for a chip fab by relying on modern technology to create 1970’s technology
Yes, exactly.
Old lithographic technology is so crude that you can even use modern high resolution laserjets to print masks (10000 dpi is less than 3 microns).
Even so, 1970s-era CVD, PVD, and plasma etch is still quite complicated, and CMP is impossible (it hadn't even been invented yet). So the devices you can create are significantly integration-constrained.
This isn't hypothetical, I've done it -- in grad school we would send out (I believe) 30000 dpi print jobs on transparent polyester film, and then adhere those to glass blanks to create cheap masks for MEMS fabrication. We had an old Canon i-line lithographic aligner that accepted the glass blanks.
I think the print jobs cost us about $100 each.
Here's the first Google result for a vendor (I don't remember who we used). There's a price list on their page and it looks like they have capability up to 50,800 dpi.
https://hacker-fab.gitbook.io/hacker-fab-space/fab-toolkit/p...
This yes can be priceless in some circumstances.
Industrially (by which I mean how it was done circa 1970), silicon oxide and silicon nitride was etched using a buffered HF solution known as BOE (buffered oxide etchant). The buffer was typically ammonium fluoride; because of the presence of the buffer, the concentration of fluorine ions in solution stays constant even as some of the fluorine attacks the substrate to form e.g. hexafluorosilicic acid. Since the concentration of fluorine stays constant, so does the etch rate.
If you just pull some rust cleaner off the shelf at home depot, the etch rate will crash as the concentration of fluorine ions decreases. That's compounded by the fact that the HF concentration isn't very high in the first place.
As a result it would be very difficult to determine how long your wafer should remain in the etch bath. Underetching could easily cause "opens" in the circuits from unremoved insulator, and overetching and/or undercut can destroy the patterns you're trying to produce. Either way it can ruin the chip.
Ammonium fluoride definitely isn’t as easily accessible as rust cleaner, but you could buy it for a somewhat cheap price on Amazon.