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A G R E AT E R M E A S U R E O F C O N F I D E N C E process control. Our definition of adaptive
testing is not simply changing control limits
after measurements are complete6. Instead,
it involves changing force/measure levels or
changing the number of sites test based on
a well-documented decision process. Three
primary components of a test strategy can be
changed on the fly: (1) type and number of
tests; (2) number of die tested, (3) number of
wafers tested. Some or all of these test strat-
egy components can be adaptively changed
for operational benefit at the die (or site),
wafer, and lot levels.
Several characteristics of the parametric
Adaptive Test Adds
test cell in the fab make it particularly ap-
propriate for adaptive test techniques. Para-
metric test uses a sampling strategy rather
Value to Parametric
than measuring every die on every wafer, as
in functional test. This allows adding or sub-
tracting die as needed. Also, fabs typically
Electrical Wafer Probe measure three classes of electrical param-
eters on wafers, so tests can also be added or
subtracted as needed: