| Abstract: | A model is presented with which the effect of lens distortion on the optical transfer function is calculated for a step-and-scan lithographic system. The spatially varying lateral image shift and the relative loss in modulation depth are derived from the exposure pattern that is built up during the image scanning. Other important phenomena such as lens aberrations, the effect of finite image aperture, and polarization are deliberately left out of the model; from the simplified model, analytic expressions can be obtained that relate the distortion coefficients of the projection system to the local shift and the relative loss in modulation depth of the exposed pattern that is built up during scanning. As a scanning aperture, we have taken either part of an annulus or a rectangular section in the image field. |
