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Proceedings Paper

Polarization effect of illumination light
Author(s): Yasuyuki Unno
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Paper Abstract

Vector diffraction theory was applied for the calculation of aerial images to explore the polarization effect of illumination light in optical lithography. The Hopkins theory was used for the calculation of partially coherent imaging with a new pupil function defined for each electric field component. Three types of imaging were considered for line/space patterns: (1) the imaging with the 0th, the -1st and the +1st orders of diffracted waves (ordinary imaging), (2) the imaging with the -1st and the +1st orders of diffracted waves (Levenson type phase-shifting), and (3) the imaging with the 0th and either the -1st or the +1st orders of diffracted waves (off-axis illumination). As a result, it was found that the aerial images were remarkably affected by the polarization state in (2) and (3) at high numerical apertures, i.e., 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. Their differences were too large to be neglected even when the decrease of the effective numerical aperture in the photoresist was taken into consideration. This fact 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. The polarization dependence of the image quality was mainly attributed to the behavior of the field component parallel to the optical axis, and its characteristics were qualitatively understood using the transmission cross-coefficient defined for the component.

Paper Details

Date Published: 8 August 1993
PDF: 13 pages
Proc. SPIE 1927, Optical/Laser Microlithography, (8 August 1993); doi: 10.1117/12.150485
Show Author Affiliations
Yasuyuki Unno, Canon Research Ctr. (United States)

Published in SPIE Proceedings Vol. 1927:
Optical/Laser Microlithography
John D. Cuthbert, Editor(s)

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