In order to realize the effect of pattern-specific off-axis illumination under the conventional circular illumination, the
illumination method using a mask grating formed on the top side of a photo mask was evaluated and improved. Contrary
to an off-axis illumination, it could provide the locally different off-axis illumination depending on the pattern shape
defined on the bottom side of a mask. The structure of the mask grating was determined from the feature characteristics
of the mask pattern and its performance was evaluated with the simulated Bossung curves.