Sub-Resolution-Assist-Feature (SRAF) placement is an essential approach of Resolution Enhancement Technology (RET) [1], especially for technology node below 45nm. A lot of studies show SRAF can help to improve semi-dense and isolated patterns resolution and process window. However SRAF effect to dense pattern is rarely focused. The border line of the dense pattern is an isolated line on the outer direction. SRAF plays an important role not only to the border line, but also to the interior line beside the border line. In this paper, the SRAF effect to the dense pattern was analyzed. SRAF placement optimization experiments were carried out to a dense line pattern. From the experiments result, SRAF space affects the resolution of dense line pattern much more than SRAF width. The best SRAF space value has been recommended through experiment and optical intensity analysis.
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