DescriptionRotated EUV illumination through slit.png
English: The EUV reticle illumination angles are rotated at different slit positions due to the arc-shaped slit used in EUV lithography tools, necessary for feasible image field corrections.[1][2][3][4][5][6][7][8][9][10] The reason for this is a mirror is used to transform straight rectangular fields into ring (arc-shaped) fields.[11] This is due to the off-vertical position of the point source (left),[12][13] which is actually a pupil position reflecting an arc-shaped image, such as light from an arc-shaped facet,[14][15] or other arc-shaped source (diverging beamlet).[16] In general,
light reflecting from a curved optical surface (such as the condenser) produces arc shapes.[17] Consequently, the angle-dependent and wavelength-dependent mask multilayer reflectance manifests as an effective illumination nonuniformity (shown here as the color gradient) across the pupil (right).[18]
Origin of pupil illumination rotation.[5][13]Left: Collimation of light from two point sources into two directions, within the plane of incidence. Right: Outside the plane of incidence, the light from two different points projects into two directions within an arc shape (dashed curve), as long as the mirror is curved to focus the light, e.g., onto projection optics or the object plane. The arc presents a range of azimuthal illumination angles (for each point) in the plane of the illuminated object (the EUV mask).Demonstration of light reflected across the center of a concave surface into an arc-shaped field. The image-forming rays are rotated through the arc.
↑D. Hellweg et al., Proc. SPIE 7969, 79690H (2011).
↑A. V. Pret et al., Proc. SPIE 10583, 105830K (2018).
↑R. Capelli et al., Proc. SPIE 10957, 109570X (2019).
↑S-H. Jang and S-H. Lee, US Patent 9715170 (Samsung).
↑ abK. Hooker et al., Proc. SPIE 10446, 1044604 (2017).
↑R. Capelli et al., Proc. SPIE 9231, 923109 (2014).
↑H. N. Chapman and K. A. Nugent, Proc. SPIE 3767, 225 (1999).
↑N. Davydova et al., Proc. SPIE 8661, 866124 (2011).
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