Page "Semiconductor device fabrication" Paragraph 23

The highly serialized nature of wafer processing has increased the demand for metrology in between the various processing steps.

Wafer test metrology equipment is used to verify that the wafers haven't been damaged by previous processing steps up until testing.

If the number of dies — the integrated circuits that will eventually become chips — etched on a wafer exceeds a failure threshold ( i. e. too many failed dies on one wafer ), the wafer is scrapped rather than investing in further processing.