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Line end shortening and corner rounding for novel off-axis illumination source shapes

Previous study has shown that off-axis illumination (OAI) which employs duplicate conventional source shape such as double dipole, double annular or double quadrupole can reduce the effect of line width fluctuation and process window degradation at the forbidden pitch. In this paper, influence of the new OAI source shape on line end shortening and corner rounding effect is studied. Despite the advantage of reduced line width fluctuation, the proximity effect at line ends and corners for new source shapes need to be examined because both lateral and longitudinal pattern fidelity is important in actual implementation. Simulation study will be used for the study of line end shortening and corner rounding effect using new source shapes and the results will be compared with those resulted from annular illumination. Line end structures such as end to end, staggered, and T-shaped patterns are used for line end shortening study. For corner rounding, L-shaped and U-shaped structure are used. The pattern density and line end separation of feature will be varied to determine the important factors that cause image distortion. Results has shown that new source shapes have similar line end shortening and corner rounding characteristic with the conventional one. Besides, the variation of new source shapes for different pattern density and line end separation is relatively smaller compared with conventional OAI source shapes.