Cost per good die
Beginner
What one working chip costs to make, counting the ones that came out broken.
Novice
The cost of one wafer divided by the number of working chips it gives: .
Expert
The silicon part of unit cost. Add testing and packaging, then spread the one-time costs (NRE) over the number of chips sold to get unit cost. Because both dies per wafer and yield fall as area grows, cost rises faster than area.