A method for designing an illumination light source, includes acquiring a
control feature to control a dimension of a transferred pattern of a mask
pattern; designating a plurality of illumination elements illuminating
the mask pattern; designating first illumination lights to each of first
polarization states of a light emitted from each of the illumination
elements; calculating a first optical image of the control feature,
formed on a first imaging plane by each of the first illumination lights;
and determining an illumination shape and a polarization state
distribution of the light, based on an optical characteristic of the
first optical image.