Illumination optical system, exposure apparatus, and exposure method

Abstract

An illumination optical system and method illuminates an irradiated surface based on linearly polarized light supplied from a light source. The illumination optical system includes a depolarizer which is selectively positioned between a first position in an optical path of the illumination optical system and a second position outside of the optical path, and has a crystal member whose thickness in a direction along an optical axis of the illumination optical system varies in a direction crossing the optical axis.

1 . An illumination optical system that illuminates an irradiated surface based on linearly polarized light supplied from a light source, the illumination optical system comprising:
 a depolarizer, which is selectively positioned between a first position in an optical path of the illumination optical system and a second position outside of the optical path, and has a crystal member whose thickness in a direction along an optical axis of the illumination optical system varies in a direction crossing the optical axis.   
   
   
       2 . The illumination optical system according to  claim 1 , further comprising:
 a controller that controls the depolarizer (1) so as to position the depolarizer at the second position at a time of a first illumination mode in which the irradiated surface is illuminated by the linearly polarized light, and (2) so as to position the depolarizer at the first position at a time of a second illumination mode in which the irradiated surface is illuminated by non-linearly polarized light.   
   
   
       3 . The illumination optical system according to  claim 1 , further comprising:
 a phase member that is arranged in the optical path of the illumination optical system and rotates a polarization direction of the linearly polarized light about the optical axis.   
   
   
       4 . The illumination optical system according to  claim 3 ,
 wherein the phase member includes a ½ wavelength plate, which is rotatable about the optical axis.   
   
   
       5 . The illumination optical system according to  claim 3 , further comprising:
 a second phase member, which is arranged in the optical path of the illumination optical system closer to the light source than the phase member, and that changes an elliptical degree of the polarized light.   
   
   
       6 . The illumination optical system according to  claim 5 ,
 wherein the second phase member includes a ¼ wavelength plate, which is rotatable about the optical axis.   
   
   
       7 . The illumination optical system according to  claim 1 ,
 wherein the thickness of the crystal member of the depolarizer in the direction along the optical axis continuously changes in the direction crossing the optical axis.   
   
   
       8 . The illumination optical system according to  claim 7 ,
 wherein the crystal member has a wedge shape.   
   
   
       9 . A method of illuminating an irradiated surface based on linearly polarized light supplied from a light source, comprising:
 arranging, in an illumination optical path, a depolarizer that has a crystal member whose thickness in a direction along the illumination optical path varies in a direction crossing the illumination optical path; and   changing a polarization direction of the linearly polarized light entering the depolarizer and a direction of a crystal axis of the crystal member in order to switch between a first illumination mode, in which the irradiated surface is illuminated with the linearly polarized light, and a second illumination mode, in which the irradiated surface is illuminated with unpolarized light.   
   
   
       10 . The illumination method according to  claim 9 ,
 wherein the direction of the crystal axis of the crystal member is a direction within a plane crossing the illumination optical path.   
   
   
       11 . The illumination method according to  claim 10 ,
 wherein when the polarization direction of the linearly polarized light entering the depolarizer and the direction of the crystal axis of the crystal member are changed, the crystal member is rotated, using the direction along the illumination optical path as an axis.   
   
   
       12 . The illumination method according to  claim 10 , further comprising:
 changing the polarization direction of the linearly polarized light entering the depolarizer.   
   
   
       13 . The illumination method according to  claim 12 , further comprising:
 rotating the polarization direction of the linearly polarized light supplied from the light source, using the direction along the illumination optical path as an axis in order to switch between a first illumination mode, in which the irradiated surface is illuminated with linearly polarized light, and a second illumination mode, in which the irradiated surface is illuminated with unpolarized light.