Making a chip is like baking a cake with a 100 layers, one layer at a time, with 100 different ovens in a custom kitchen built just for that recipe. Each one of those ovens needs a 99.9% yield, to yield 90% overall. Not to mention all the cake books (i.e. the Process Design Kits) you give to your customers.
Shut down and disband that kitchen, and you need to start all over again, even if you bought the same equipment.
It’s also like an auto assembly line that needs 2 years to re-tool even if 80% if the equipment is the same.
The fab is a giant, finally ticking machine with thousands of process steps all requiring 99.999% yield.
