Years out from an expected production run, I would be surprised to see any binding agreement. A letter of intent to buy is plenty for the chip manufacturer to be able to shop that around for funding if needed.
In the past, some semiconductor manufacturers themselves were happy to finance part of the cost of the run if you had a letter of intent, also. It used to frequently be a 50/50 split - half upfront, half after you have the money your customer(s) promised.