Foley & Lardner
Projection exposure apparatus
 A projection exposure apparatus performs focus adjustment to correct variations in the focal position of a projection optical system which are caused by absorption of exposure light by a refraction system in the projection optical system. The projection optical system arranged in this projection exposure apparatus includes a refraction system having a positive refracting power, and a reflecting mirror positioned to be coaxial with the refraction system. The projection exposure apparatus includes a photodetection device for detecting light, of light emitted from an illumination optical system and transmitted through a first substrate, which is transmitted through the reflecting mirror, and an adjustment device for adjusting the in-focus state between the first substrate, a second substrate, and the projection optical system in accordance with an output from the photodetection device. 
Nikon Corporation
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