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Table 1: Summary of dX, dY error statistics for R1,
R2, R3.
Die placement error measurement
With the accuracy of the measurements Figure 5: Die placement error (mm) a) dX, and b) dY heat maps.
and the correspondence between the processing. T he disr uptive EMC Data analysis, yield prediction and
exposure and measurement coordinate curing effect renders the ty pical
systems established, it is possible to g lob a l a l ig n m e nt s olut io n u s e d throughput
evaluate the placement errors of die on by lithography tools useless, as it The process specifies overlay errors less
FOPLP panels. Dummy die embedded assumes linear corrections for scaling, than +/-15µm. As long as the measured
in molding compound to form a FOPLP rotation, orthogonality. Only site- errors are within the correction capability
substrate were supplied courtesy of by-site corrections can accommodate of the stepper, it is possible to yield 100%
ESWIN. Measurements of two points these types of errors. To apply site-by- by correcting each die, so called “die-
for every die, top and bottom, allowed site corrections, each exposure needs by-die” exposure individually, but this
the system to calculate translation to be matched to the local errors to imposes an unacceptable penalty on
(X,Y) and rotation (ϴ) offsets for each. provide good overlay. stepper throughput. Increasing the size
The software algorithm generates of the exposure to cover multiple die will

Figure 6: a) dX (mm), b) dY (mm), and c) rotation (rad) data histograms.

“heat maps” that visualize the dummy
measurements before cor rections
are applied (Figure 5). Histograms
of the X and Y placement errors and
rotational errors (Figure 6) show the
distributions of these measurements.
The multimodal distributions of
the dX and dY histograms ref lect
the nonlinear die placement errors
obser ved in the heat maps. T his
nonlinear error can be attributed to
the epoxy molding compound (EMC)
curing process, which is typical for
most FOPLP reconstit uted panel Figure 7: Predicted a) dX and b) dY overlay data histogram (mm) for 3 X 3 field, 100% yield.

18 Chip Scale Review January • February • 2020 [ChipScaleReview.com]
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