Small MEEF is important as well as a large process window to control dense line CD variation. The MEEF and the process window are both strong functions of mask bias. In this study, MEEF and process windows were analyzed mainly with 100nm node dense lines with varied mask bias using 9% attPSM and conventional binary mask. Illumination influences were also analyzed. Flare is one of the big concerns of the lithographic performance, but its influences are not well understood. Long range flare was also studied in terms of CD control. Flare definitely reduces the process window, but has no influence on MEEF. A systematic analysis was done in order to explain the results.