>99.8% yield on each step of a 500 step process is good for 38% overall recovery.
What does that mean? Is 'yield' not the end usable product from the batch?
What does that mean? Is 'yield' not the end usable product from the batch?
It's a familiar concept from organic chemistry.
Edit: If yield per step averages 99.8%, and there are 500 steps, overall yield is 36.8%.
At the same time, when wafers get scrapped, they do justify why they were scrapped. There are metrology processes and tests performed as you go to ensure you don't run ruined wafers through additional manufacturing steps.
The gist of that part is meant to show how important and impressive the entire process is. In "normal" manufacturing, 99.8% good parts is a pretty darn good process. Many of the easy wins are already implemented. Most normal things are manufactured in far fewer steps, so even if you're only making 95% good parts, it doesn't absolutely kill your total recovery (start to finish).