The pupil-filtering lens system for optical lithography experimentally
evaluated in this study is based on an i-line stepper lens with a num
erical aperture (NA) of 0.5, and its pupil function can be set arbitra
rily to change the image characteristics. With the previously proposed
super-FLEX filter, the depth of focus was three times that of the sys
tem without the filter, and the resolution for window patterns was 20%
higher. Image characteristics of the filter, such as the edge-enhanci
ng eff ect and the proximity eff ect, are discussed and were experimen
tally evaluated. The optical and mechanical tolerances required for th
is system are shown to be within ranges that are attainable in practic
al stepper systems.