EVALUATION OF PUPIL-FILTERING IN HIGH-NUMERICAL APERTURE I-LINE LENS

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.