Impact of assistance feature to pattern profile for isolated feature in sub-65 nm node

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.