To generate an accurate yield model accurate defect data is
essential. The critical area method may require defects to be
classified in a different way to the current practice in your fab.
The defect data required for a critical
area based yield model is all of
the defects present in the process that could cause a fault (if
they landed in the wrong place). Therefore, it is important when
collecting defect data to consider all defects irrespective of
where they land on the chip. So even if the defect falls in an area
with no layout it should still be "counted" as a defect. This is
because we are trying to build up picture of the defect statistics
independently of the layout. The critical area measurements take
care of the layout interaction with defects. Of course only real
defects should be counted and not nuisance or cosmetic defects.
Defect Classification
Defect should be classified according to their fault mechanism.
That is shorting faults, breaks, pinhole, dielectric faults etc.,
so that they can be matched to the critical area measurements. All
faults that cause the same kind of fault in a layer can be grouped
together or if they can be put into sub-groups (e.g., black dome
shorts, pancake shorts) counted in a sub-group. This way the yield
loss associated with the sub-group can be identified (as shown
here).
A defect shorting conductor lines causing a
fault.
If you would like more information on how fabs have tackled the
preparation of defect data for critical area based yield modeling
please contact us.
