0.32 μm pitch random line pattern formation by dense dummy pattern and double exposure in KrF wavelength

0.32 mu m pitch on-grid random line pattern formation by double exposure in KrF wavelength is proposed based on optical image calculations. For first exposure, mask patterns are generated by combination of designed patterns and dense dummy patterns, all of which are laid out at on-grid positions with a pitch of 0.32 mu m. An attenuated phase shift mask and an annular illumination are applied. The imaging performance is significantly enhanced because all patterns in this mask are categorized "dense" with almost the same pitch of 0.32 mu m. The mask pattern for second exposure are simply generated from the dummy patterns by tone inversion. The image size required for erasing dummy pattern is much larger than that for the first exposure. Consequently, large latitude, to erase the dummy patterns and not to affect the designed patterns, can be obtained by conventional exposure method with low coherent illumination. Even in this method, OPC is required to obtain desirable CD. However, OPC in this method can be performed by simple rules based method, because on-grid restriction to layout much reduces the variation of pattern configuration. As a result, 0.32 mu m pitch on-grid random line patterns are formed accurately with DOF larger than 0.6 mu m in KrF wavelength.