Making at home transistors, or even small-scale integrated circuits is not exceedingly difficult.

However, making at home a useful microcontroller or FPGA would require not only an electron-beam lithography machine, but also a ion-implantation machine, a diffusion furnace, a plasma-etch machine, a sputtering machine and a lot of other chemical equipment and measurement instruments.

All the equipment would have to be enclosed in a sealed room, with completely automated operation.

A miniature mask-less single-wafer processing fab could be made at a cost several orders of magnitude less than a real semiconductor fab, but the cost would still be of many millions of $.

With such a miniature fab, one might need a few weeks to produce a batch of IC's worth maybe $1000, so the cost of the equipment will never be recovered, which is why nobody does such a thing for commercial purposes.

In order to have distributed semiconductor fabs serving small communities around them, instead of having only a couple of fabs for the entire planet, one would need a revolution in the fabrication of the semiconductor manufacturing equipment itself, like SpaceX has done for rockets.

Only if the semiconductor manufacturing equipment would be the result of a completely automated mass production, which would reduce its cost by 2 or 3 orders of magnitude, affordable small-scale but state-of-the-art fabs would be possible.

But such an evolution is contrary to everything that the big companies have done during the last 30 years, during which all smaller competitors have been eliminated, the production has become concentrated in quasi-monopolies and for the non-consumer products the companies now offer every year more and more expensive models, which are increasingly affordable only for other big companies and not for individuals or small businesses.