Illumination optical system, exposure apparatus, and exposure method

Abstract

An illumination optical system for, when installed in an exposure system, realizing a suitable 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 the light. The illumination optical system has a light source unit for supplying a linearly polarized light for illuminating surfaces to be illuminated therewith, and a polarized state changing device for changing the polarized state of the illuminating light from a predetermined polarized state to a nonpolarized state and vice versa. The polarized state changing device is arranged in the optical path between the light source unit and the surfaces to be illuminated. The polarized state changing device can be removed from the illumination optical path and has a depolarizer for selectively depolarizing the incident linearly polarized light.

1 . A lithographic apparatus comprising:
 an illumination system comprising a first optical element configured to condition a radiation beam so as to comprise substantially only linearly polarized radiation polarized in a first direction and/or linearly polarized radiation polarized in a second direction perpendicular to said first direction, one or more second optical elements subject to developing birefringence having an optical axis in said first direction and through which the linearly polarized radiation is transmitted, and a third optical element configured to, subsequent to the radiation being transmitted by the one or more second optical elements, transform at least a part of the linearly polarized radiation into unpolarized or circularly polarized radiation;   a support configured to support a patterning device, the patterning device configured to impart the radiation beam from the illumination system with a pattern in its cross-section to form a patterned radiation beam;   a substrate table configured to hold a substrate; and   a projection system configured to project the patterned radiation beam onto a target portion of the substrate.   
   
   
       2 . The apparatus according to  claim 1 , wherein the third optical element is a λ/4 plate configured to transform a part of the radiation beam into circularly polarized radiation. 
   
   
       3 . The apparatus according to  claim 1 , wherein the third optical element comprises a pair of adjacent wedges of material, a first of the wedges formed of an optically active material, and the second formed of an optically inactive material, configured to transform a portion of the radiation beam into unpolarized radiation. 
   
   
       4 . The apparatus according to  claim 1 , wherein the first optical element comprises a set of optically active plates or birefringent plates. 
   
   
       5 . The apparatus according to  claim 4 , wherein the optically active plates or birefringent plates are half-wavelength plates located in any of the condenser, adjustor or integrator. 
   
   
       6 . The apparatus according to  claim 4 , wherein the optically active plates or birefringent plates are half-wavelength plates located in or near a pupil plane. 
   
   
       7 . A device manufacturing method comprising:
 providing a substrate;   providing a conditioned radiation beam using an illumination system;   imparting a pattern to the radiation; and   projecting the patterned beam of radiation onto a target portion of the substrate;   wherein providing the conditioned radiation beam comprises conditioning a radiation beam so as to comprise substantially only linearly polarized radiation polarized in a first direction and/or linearly polarized radiation polarized in a second direction perpendicular to said first direction, transmitting the radiation through an optical element subject to developing birefringence having an optical axis in said first direction, and subsequent to the radiation being transmitted by the optical element subject to developing birefringence, transforming at least a part of the linearly polarized radiation into unpolarized or circularly polarized radiation.