To me this is far more impressive than any of the other stuff posted here. It's actually doing it rather than talking about it or faking the first 99.9% of it.
Did he do his own etching? I'd say buying blank wafers would be a perfectly reasonable place to start, but if you're buying printed wafers, then you might as well buy the whole chip.
No, Sam Zeloof started from blank silicon wafers and did four layers of photolithography to produce PMOS gates. He used boric acid for the boron diffusion. He sputtered an aluminum layer on top for the metal and etched it with phosphoric acid.
So he "only" did metal deposition to make the interconnects? I haven't read the story, but I was thinking that there's no way you would handle some of the toxic chemicals used for doping.
They are not really that toxic. You do have to have a chemistry background and use a fume hood and a process sink with acid neutralization capability, like you find in many chem labs.
Good dopant choices would be phosphorus oxychloride and oxidized boron nitride wafers.
As I recollect, he started with silicon wafers with an epitaxy layer. He then did the usual oxidations, diffusions, and metallization, along with all the photolithographic steps. No small feat!
Silane, phosphene, and diborane gases are used to form epitaxial layers on silicon wafers. Those are truly dangerous gases. However, a simple wafer process using the reagents I mentioned can produce very credible ICs, if one buys the epi wafers.