A wafer map lays out every die position on the wafer, colored by test bin, pass or fail, or a parametric value. Spatial signatures point to causes: an edge ring suggests film or etch nonuniformity near the edge, a center spot points to spin coating or gas flow, a line of failures follows a scratch, and a pattern repeating at fixed intervals tracks a reticle defect. Stacking maps from many wafers turns weak patterns into obvious ones.
Stack the wafer maps for lot 22 and you can see the scratch: a clean arc of bin 7 fails running from the notch.
Stack before you stare: one wafer map is noisy, but 25 stacked maps make a weak signature unmistakable.
Also heard as
- bin map
- die map
- wafer bin map
Related terms
Bin
Test category that each die or unit is sorted into at probe or final test, with bin 1 usually meaning good.
Bullseye
Wafer map pattern of concentric rings or a center spot, the signature of a radial process nonuniformity.
Yield
Fraction of units that come out good at a step or across a whole process, the headline number for any production line.
Defect density
Number of yield-killing defects per unit area of wafer or panel, the main input to yield models.
Excursion
Sudden departure of yield, defect counts or a key parameter from its normal band, big enough to trigger holds and an investigation.