Work out defect density to yield instantly with clear inputs, formula shown and shareable results.
Two yield mechanisms multiply: random defect yield e^(-A x D0) and cumulative process yield, which is per-layer yield raised to the number of critical layers. Twelve layers at 99.5% each already costs 5.8%, which is why layer count reduction is as valuable as defect reduction.
Combined yield
Y = e^(-A D0) x (layer yield)^layers
Because it compounds. At 99% per layer, 30 layers gives only 74% overall even with zero random defects.
Typically 0.05-0.3 defects per cm2 for a mature node, rising sharply during ramp-up of a new process.