Polarization impact on partially coherent imaging

Abstract

Image formation and analyses in optical lithography illuminated with partially coherent polarized light are explored. The influence of polarization on the image formation of one-dimensional periodic patterns has been investigated and qualitatively understood by using the concept of the transmission cross-coefficient and coherency factor σ c. Three types of imaging are considered for line/space patterns: (1) 3-beam imaging (conventional imaging), (2) 2-beam imaging (Levenson type phase-shifting), and (3) the imaging with the 0 th and either the -1 st or the +1 st orders of diffracted waves (off-axis illumination). Results show that the aerial images are affected by polarization state in (2) and (3) at high numerical apertures. The illumination light polarized parallel to the lines and spaces gave much higher image qualities than the illumination polarized perpendicular to the lines and spaces. This suggests that it is possible to further improve the resolution of an optical system by controlling the polarization besides using phase-shifting masks or off-axis illumination. We studied the effects of polarized light on immersion lithography using alternating PSM, employing conventional and dipole illumination.