  As feature sizes shrink, it will be necessary to use AAPSM
(Alternating-Aperture Phase Shift Masking) to image critical features,
especially on the polysilicon layer. This imposes additional constraints on the
layouts beyond traditional design rules. Of particular note is the requirement
that all critical features be flanked by opposite-phase shifters, while the
shifters obey minimum width and spacing requirements. A layout is called
phase-assignable if it satisfies this requirement. If a layout is not
phase-assignable, the phase conflicts have to removed to enable the use of
AAPSM for the layout. Previous work has sought to detect a suitable set of
phase Conflicts to be removed, as well as correct them. The contribution of
this paper are the following: (1) a new approach to detect a minimal set of
phase conflicts (also referred to as AAPSM conflicts), which when corrected
will produce a phase-assignable layout; (2) a novel layout modification scheme
for correcting these AAPSM conflicts. The proposed approach for conflict
detection shows significant improvements in the quality of results and runtime
for real industrial circuits, when compared to previous methods. To the best of
our knowledge, this is the first time layout modification results are presented
for bright-field AAPSM. Our experiments show that the percentage area increase
for making a layout phase-assignable ranges from 0.7-11.8%.
