Applied optics
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In optical lithography, light diffracted from photo mask structures has been customarily assumed to be constant with the angle of incidence of the light illuminating the photo mask. As numerical aperture increases to unity and beyond, to cope with the continuous demand for shrinking integrated circuits, device dimensions, and densities, this approximation is no longer valid. ⋯ We present a semianalytical model that is fast, accurate, and compatible with existing professional software in this domain. The accuracy of the model is studied using the finite-difference time-domain technique and is shown to be below 5% at the image plane, within angles of incidence between +/-20 degrees .