Sub resolution assist feature study in 28nm node poly lithographic process

The semiconductor industry is being driven by “Moore´s law” towards smaller and smaller feature sizes and pitches. The 28nm technology node is facing many challenges especially at the POLY layer lithography process, which is the most critical and tight pitch design. The double patterning technology (DPT) is proved to be an effective technology to enhance resolution; however, DPT hasn´t been implemented on the 28nm tech node yet due to the concern of cost and process complexity. Therefore, others resolution enhancement technology (RET), such as Sub Resolution Assist Feature (SRAF) plays more critical role than before. In this paper, we studied how the SRAF setting affects the Depth of Focus (DOF) from view of both result of simulation and Si wafer verification. The DOF trend of multiple pitches from Si wafer verification is well matched with the trend simulation result. Furthermore, we found an interesting phenomenon that side-lobe occurring in some particular pitch pattern, the further study and experiment showed that the side-lobe could be suppressed by implementing SRAF.