Though I haven't worked in a fab, I did work for a company that runs several fabs. The fabs run 24 hours a day - I assume that is true of any fab that makes chips. My understanding (but I could be wrong) is that these run 24 hours a day for two reasons. The obvious one is that the equipment in the factory is so bloody expensive that letting it sit idle for 8 or 16 hours a day may well be the difference between profitability and bankruptcy. At minimum the equipment is amazingly expensive.
The other reason and more germane here - I think that there are any number of process steps that are effectively continuous flow processes. Continuous flow production isn't happy about stopping.
Clean rooms are also hard to maintain in that state. What I remember reading years back is that the air in the clean room is fully exchanged every minute or two. "dust" in the air gets sucked out of the room fast. My guess is that losing the air flow to the room by itself will cause a delay in starting back up.
Dear lord I surely hope not!
The sorts of complex chips that we're talking about here have either 3 or 4 manufacturers remaining in the world. That is the fruit of decades of consolidation as each new technology node is so much more expensive than the last, that fewer and fewer companies had the necessary volume to make their manufacturing facility economic. So expensive that the volume needed to keep the factory running full time is only available at those few companies in the world. And I fully expect that number to shrink in the next few years as the newer nodes keep getting more expensive (the economics make it inevitable).
Those companies are Intel, Samsung, and Taiwan Semiconductor (TSMC). The 4th that I just don't know enough about is Global Foundries (AMD's former manufacturing facilities). Samsung and TSMC have the volume to be competitive and profitable due to their foundry work - they build other people's chip designs (such as Tesla's chip design). Samsung makes their own designs as well as other companies. TSMC is pure foundry.
Intel is the only remaining vertically integrated design and semiconductor manufacturing shop in the world (which is what Tesla would become as their own chip manufacturer). At the processor level Intel is doing hundreds of millions of units per year - Tesla is going to need a whole lot more demand / volume (I think 2 orders of magnitude, and possible a 3rd) to make their own chip manufacturing economic. Which also assumes that the chips Tesla needs are equally valuable as Intel's chips - some of Tesla's will be worth more, but many won't. That'll further drive the need for more volume. But hey if you've got the volume then there is a lot of value in vertical integration (co-optimize the design and manufacturing technology).
What Tesla can do (and any other design shop in the world) is pony up more money to their manufacturing partner - make sure they have a priority on wafer starts just by spending more for them.
My disclaimer: I used to work for Intel. These are my opinions, beliefs and understandings; don't put any of these on Intel.
