Performance of Dipole Illumination Combined with Pupil Filter

Abstract

The pupil filtering technique has been proposed as an effective method in the field of optics. In this work, pupil filtering is applied to an optical lithography system. We theoretically analyze partially coherent imaging, and not only the pupil filter but one combined with other optical elements, is suggested. Through these two methods, the following results are obtained: 1) twofold enhancement of depth of focus (DOF) and resolution limit improved to 0.26 µm (i-line, 0.60 NA) for lines and spaces, using the pupil filter combined with oblique illumination, i.e., dipole illumination; 2) twofold enhancement of DOF for hole, using the pupil filter assisted by a mask, i.e., shifterless halftone mask. In this paper, several calculations and experimental results of using an i-line stepper with pupil filtering are presented and the potential for pupil filtering in optical lithography is discussed.