For example i notice that the latest chips are 3 nm & below, & over the last decade i’ve seen it shrink little by little. What is it about this process that more money needs to be poured into each die shrink, & why couldn’t we just jump from 90nm to 3nm instead pf 65nm etc etc?
In: Engineering
every time a new smaller process size starts the number of defects is high. yield can drop from a mature process at >99% all the way to 10%. this is quickly worked back up to profitable levels but will fully take several months to a year where the die yield per wafer equals what was possible before.
this is because the new defects need to be characterised and rooted out iteratively. e.g. etch for 1 more second, increase plasma voltage by 5%, polish by 10 angstroms less, whatever it may be, depending on the defect.
a good shrink can get you breakeven at 70% yield compared to the previous process at 99% yield. anything above is better gross margins.
the real profits from the change come from Year 2 onwards to whenever it reaches end of life and the next jump begins. some companies do 4 year cycles, some faster some slower.
the time to develop the next jump is also longer than the time it takes to perfect it during manufacturing. design work on the next step can begin even before the current step has qualified and started low volume manufacturing.
There is a sweet spot to manage this whereby you want to keep improving technology at a steady rate but don’t want to hit the next jump before you have perfected the current step. in that sense you want to keep competing with other providers but do not want to bite off more than you can chew.
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