| 摘要 |
An illumination optical system for, when installed in an exposure system, realizing an adequate illumination condition by varying the polarized state of the illumination light according to the pattern characteristics of the mask while suppressing the loss of the intensity of light. The illumination optical system has a light source unit (1) for supplying a linearly polarized light for illuminating surfaces (M, W) to be illuminated therewith and polarized state changing means (10, 20) for changing the polarized state of the illuminating light from a specific polarized state to a nonpolarized state and vice versa. The polarized state changing means are arranged in the optical path between the light source unit and the surfaces to be illuminated. The polarized state changing means can be removed from the illumination optical path and has a depolarizer (20) for depolarizing the incident linearly polarized light as necessary.
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