Effect of coating-induced polarization aberrations on the focusing properties in high numerical aperture optical system

Abstract

The incident angles of the optical systems with high numerical apertures, such as lithography or microscope, are larger than those of normal ones. For these systems, polarized illumination is widely adopted. The coatings on their surfaces will make s and p polarization components of oblique incident light experience diverse amplitudes and phase modulations, and induce extra polarization aberrations. We apply the vectorial diffraction theory to assess the effects of coating-induced polarization aberrations on the focusing properties of these systems. By applying the generalized Debye integral, the relationship between the parameters of coating and electric field vector near the focal spot is established. Considering x linearly polarized light as the incident light field, we evaluate the potential influence of the coatings on the intensity and the full width at half maxium of focal spots. In the further discussion, we compare the results of different coatings when the various optimization goals are set, and certify that the phase difference caused by coating has more effect on focusing property. Based on this, the additional constraint conditions of coating design are proposed to suppress such disturbance, i.e. to properly increase relative weight of phase constraint conditions. With this proposed constraint conditions, we design and optimize an anti-reflection coating with low polarization aberrations. By applying this designing, the central intensity of focal spot can be enhanced by 12.5%, and the light energy utilization will be improved effectively.