An Approach to Extracting SRAF Rules from Inverse Lithography Technology Results

Inserting sub-resolution assist feature (SRAF) has great effect on improving the process window. Rule-based SRAF (RBSRAF) provides full chip application but its performance and development time mainly depends on experience. Inverse lithography technology (ILT) provides SRAF that significantly enhance the process window, but it takes too long for full chip application. In order to achieve SRAF performance close to ILT process, meanwhile keep the high processing speed of RBSRAF, we propose an approach to extract SRAF rules from ILT results, trying to insert ILT-like RBSRAF. The type of geometry parameters extracted from the ILT results refer to the variability of SRAF rules, namely the editable configurations in Calibre nmSRAF tool. The extracted rule has achieved significant process window enhancement in 55nm contact layer in a much shorter processing time, as compared to that of experience-based RBSRAF.