Analytical Method for Image Characteristics of Annular Illumination with a Spatial Filter in Optical Projection Lithography

Annular illumination with a spatial filter, or SSBL (single-sideband optical lithography), has performance equivalent to phase shifting in optical column technology. This paper presents an analytical method for examining image deformation characteristics in optical projection systems including SSBL. We express image intensity as the sum of a symmetric and an antisymmetric component. Image deformation can be clearly observed by using the antisymmetric component. From the point of view of proximate interaction, we show that the real part of mutual intensity is useful in interpreting image deformations. Optical image deformations are unavoidable in the range of 0.2-0.3 µm at the KrF-line wavelength. We present a simplified correction method for mask data which reduces computational time.