High Numerical Aperture (NA) imaging with polarized illumination has been proposed as one of the solutions of the 65nm technology node and beyond. Aerial image simulations and experimental exposure results 1, 2 confirmed the advantage of the polarized illumination for high NA imaging. However, impact of imperfection of the polarization status upon imaging performance has not yet been fully investigated. We have studied the impact of error of the polarized illumination upon imaging performance including CD (critical dimension line width) variation and pattern displacements. We define parameter “Degree of Specific Polarization” (DSP) that shows how close the polarization status is to the ideal status. For a conventional illumination setting, Zernike polynomials are used to describe distribution of DSP across the illumination pupil and Zernike annular polynomials are used for a dipole (bow tie) illumination setting. Degradation of the imaging performance for each Zernike term is estimated using a vector-model aerial-image simulator, which is one of our in-house software, and allowable range of each Zernike term for DSP is investigated.