Well I reckon for 100M you could fabricate a chip at nearly any process size you want but probably not at a speed at which you could sell them for a profit. For

Well I reckon for 100M you could fabricate a chip at nearly any process size you want but probably not at a speed at which you could sell them for a profit. For example many universities have the capabilities to fabricate their own chips for research and development. It also depends on what type of thing you're trying to fabricate. For example in a phone: cpu, ram, power, radio and sensors might want their own unique fabrication. It gets even more crazy when you want to go into things like automotive or industrial power. I'll over generalize things and say that you can probably make a fab that goes down to 90nm without too much issue. It was the 65nm node when the lithography started to need something different and new chemistries were required for the fabrication process due to leakage becoming and issue that could no longer be ignored. At least for me it was the jump to 65nm when I remember things getting hard and staying hard. The cell deigns had to change, the layout took twice as long, the models for simulations were always off and tapeing out to different fabs has vastly different results. It seemed like very node after that the documents that arrived from the fab about the new process were at least twice as thick as the last.