State of the art non EUV photo lithography uses light with a 193 nm wavelength. 20nm is significantly below that which would imply usage of highly advanced lithography techniques like multiple patterning. A chip manufactured with a 20nm resolution would involve dozens of masks which were created through electron-beam lithography. Just the mask set alone would cost millions of dollars.

The only hobbyist that I am aware of used a pretty nifty mask less technique but the resolution doesn't come close at all. I think you just mixed up your units.

That's really not possible. 20um probably. Micro not nano.

Can't edit this, what I saw was definitely um and not nm.

I recall this but don't remember seeing anything smaller being posted. Sub 100nm for a hobbiest would be pretty awesome. https://youtu.be/YAPt_DcWAvw