Sub-resolution assistance feature (SRAF) has become one of popular resolution enhancement technique because it is
the most easily applicable technique that can be adopted for sub-65 nm node technology. The SRAF can be realized, for
example, by locating lines having width below resolution limit around isolated feature. With the SRAF, intensity profile
of the isolated feature will be modified to dense-like one and, as a result, focus response of the isolated feature can be
improved up to dense feature level. Previous works on SRAF have focused mainly on the critical dimension (CD) margin
window. However, CD margin window is not sufficient to evaluate optimum SRAF configuration because process
margin degradation due to irregular pattern profile such as line edge roughness (LER) would become more prominent as
technology node goes beyond sub-65nm node. Therefore, appropriate methodology to optimize SRAF configuration both
for CD margin window and pattern profile is indispensable for those applications.
In this paper, we focus on the impact of SRAF configuration to pattern profile as well as CD margin window. The
SRAF configuration was adjusted by varying assistance feature to main feature distance and pitch of the assistance
features at mask level. Pattern profile was investigated by measuring LER with varying assistance feature parameters
quantitatively. From the results, we prove the impact of SRAF configuration both on pattern profile and CD margin
window. We also show that the experimental data can easily be predicted by calibrating aerial image simulation results to
measured LER. As a conclusion, we suggest methodology to set up optimum SRAF configuration with regard to both
CD margin window and pattern profile.