OPRX modifies the mask layout data to compensate for optical and
process proximity effects. Here is the basic idea of what OPRX does:
The figures on the left represent the specification for what the designer
wants to appear on the wafer. If that specification is used to specify
how the photomask is to be written, then, owing to the effects of
neighboring
features, edges will be moved from their desired locations, line ends
will be shortened and corners may have excessive rounding. These effects
can be compensated by modifying the specification of the photomask so
that the geometries which appear on the wafer are closer to the desired
ones. Given the specification on the left OPRX produces the modified
specification on the right. The actual amounts by which the edges
move and the sizes of the corner serifs and pullback are governed by
the sizes and positionings of the neighboring figures.
Now here is the proof that OPRX is effective in compensating dense
and isolated lines at the same time:
Notice how the central line in the uncorrected exposure broadens as it
emerges from the dense line array. That is the basic proximity effect. If
you examine the uncorrected image more closely you will see that
outermost lines in the of the array of 5 lines are wider than the
three middle lines. In the corrected exposure you can see that the
broadened lines have been narrowed so that all the lines and portions
of lines are the same width.
OPRX is also effective in correcting the complex geometries
in an SRAM cell:
To give you an idea of the changes OPRX makes to a mask layout here
is a not-trivial example:
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