Analysis of imaging properties for hyper-NA ArF immersion lithography

As imaging properties of ArF Immersion optics are evaluated in a hyper-NA region, the polarization of illumination systems and vectorial mask diffraction play an important role. We investigate the effectiveness of polarized illumination for practical patterns including the border of dense line-and-space (L/S) patterns, semi-dense L/S patterns, isolated lines, and contact holes. The results show that polarized illumination is effective in projecting many patterns except semi-dense L/S patterns and relatively large contact holes. Secondly, we examine how bias settings of alternating phase-shift masks (AItPSMs) are affected by vectorial mask diffraction, which depends on the polarization of incident light and feature size on the mask. Although a reduction ratio of 8x facilitates bias settings compared with that of 4x, it is necessary to take into account the effect of vectorial mask diffraction even in the case of 8x. Since polarized illumination also simplifies bias settings, the illumination is useful for 4x projection optics. High-index fluids have recently attracted considerable attention because they are capable of extending the numerical aperture of projection optics beyond the refractive index of water (n=1.44). We study imaging properties of 1.50NA projection optics with an immersion fluid of n=1.64 and the preliminary requirements of fundamental optical characteristics of the fluid.