Wafer sort and bin maps: how a fab reads its own yield.
A bin map is a wafer drawn as a grid of pass and fail. The shape of the failures is often the fastest clue to their cause.
In brief
- At wafer sort, a prober tests every die before dicing.
- Failing dies are sorted into bins by the test they failed.
- Spatial patterns, or signatures, point to the process step at fault.
- Reading signatures fast is how yield learning speeds up.
First, the anatomy. A wafer carries many identical dies, separated by scribe lines and printed one reticle field at a time.
- 1Die. One copy of the chip. A wafer carries many.
- 2Scribe line. The lane between dies, cut away at dicing.
- 3Reticle field. What one lithography exposure prints, here six dies.
- 4Edge exclusion. A ring near the edge where dies are not usable.
- 5Partial die. Cut off by the edge, so never shipped.
- 6Notch. Tells every tool which way the wafer is turned.
- 7Test site. Structures used to check the process, not sold.
What sort does
A probe card lands on each die’s pads and the tester runs a test program. Each die gets a result: pass, or a fail bin that names the test it failed. Drawn on the wafer’s outline, the results become a bin map.
Four signatures worth knowing
Failures are rarely random. Where they fall on the wafer is evidence.
From signature to cause
- Name the signature. Edge, centre, line, cluster or repeating.
- Find the common history. Which tools, chambers and lots did the affected wafers share?
- Test the hypothesis. Split lots, inspection data, tool logs.
- Fix and confirm. The signature should disappear from the next maps.
This is the loss tree’s yield branch in practice. Our consultants run exactly this loop with your engineers.