<title>Influence of shape of the illumination aperture on the intrafield image displacement</title>

Abstract

Influence ofshape ofthe illumination aperture on the intrafield image displacementByeong-Chan Kim, Young-Jin Song, Hong-Seok Kim, and Jae Jeong KimAdvanced Process Technology Dept., ULSI Research LaboratoryLG Semicon Co., Ltd., Cheongju, 360-480, Rep. of KoreaABSTRACTThe intrafield image displacement with the various illumination apertthes (conventional, quadrupole,annular) was studied andits influence on the actual overlay accuracy was estimated quantitatively. It was found that deviation of the distortioncomponents of modified illumination apertures from conventional aperture (NA 0.57, c 0.6) brought about the overlaybetween conventional and modified illumination-exposed layers within lOnm in the ftill-field (22rnnf). Quadrupole andannular apertures with high oblique illumination ('out>06) showed relatively lower in absolute magnitude of distortioncomponents and narrower in fluctuation span across the field compared to conventional aperture. However, apertures with lowoblique illumination (a0t<O.5), also having small opening area, revealed the contrary results. In the telecentricity study,modified illumination apertures were seen to have the better characteristics than conventional apertures, whichimplies thatmore serious deviation ofoverlay could be happened ifthe two layer were exposed at the different defocus condition, let alonethe different illumination apertures. From these results, it seems obvious that there are some relationships between theintrafield image displacement of the projection lens and the geometrical shape of the illumination aperture. In the practicalreason, we have suggested the scheme with the magnification correction for the exposure step to minimize the overlay errors,