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17 December 2003 Vortex via validation
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The first vortex masks composed of rectangles with phases of 0°, 90°, 180° and 270° - as proposed at Photomask 2002 - have been fabricated and shown to print sub-100nm contacts. The walls of the phase trenches are very nearly vertical, with all four phase regions meeting at sharp corners which define the phase singularities. Arrays with pitches down to 210nm have been printed in negative DUV resist using KrF illumination with NA=0.73 and sigma=0.15. The developed contacts are somewhat elliptical, but their shapes can be corrected (if necessary) by OPC techniques. The depth of focus for +/-10% CD variation is >400nm for 85nm CD vias at 210nm pitch and >700nm for 100nm vias at 250nm pitch. The exposure latitude is ~15% at best focus. At constant exposure dose, the via CDs vary with pitch as predicted by simulations. Increasing exposure dose makes the openings smaller, more uniform and more circular. No significant surface development has appeared due to phase-edge printing. However, the spacewidth alternation phenomenon familiar from linear chromeless phase-edge lithography does cause small positional errors for vortex vias, and each of the four vortices in the repeating pattern behaves somewhat differently through focus, potentially limiting the common process window.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Marc David Levenson, Takeaki Ebihara, Yasutaka Morikawa, and Naoya Hayashi "Vortex via validation", Proc. SPIE 5256, 23rd Annual BACUS Symposium on Photomask Technology, (17 December 2003);

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