| 摘要 |
A reduction projection objective for projection lithography has a plurality of optical elements configured to image an effective object field arranged in an object surface of the projection objective into an effective image field arranged in an image surface of the projection objective at a reducing magnification ratio |beta|<1. The optical elements form a dry objective adapted with regard to aberrations to a gaseous medium with refractive index n'<1.01 filling an image space of finite thickness between an exit surface of the projection objective and the image surface. The optical elements include a largest lens having a maximum lens diameter D<SUB>max </SUB>and are configured to provide an image-side numerical aperture NA<1 in an effective image field having a maximum image field height Y'. With COMP=D<SUB>max</SUB>/(Y'.(NA/n')<SUP>2</SUP>) the condition COMP<15.8 holds. Preferred embodiments have relatively small overall numbers of lenses which allows to fabricate the projection objectives relatively small in size with relatively low material consumption, yielding high performance, light weight, compact reduction projection objectives for dry lithography.
|
