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30 July 2002 Spherical aberration measurement and in-situ correction
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The continuing demand to decrease device feature dimensions has put pressure on trying to minimize the levels of aberrations in today's lithographic lenses. Though the lenses that are currently used in the most advanced lithography tools have less aberrations than any preceding generations, the impacts of these aberrations are greater because of the smaller geometries being printed. In addition, most of the resolution enhancement techniques (RET), such as phase-shifting masks (PSM) and off-axis illumination (OAI), that have been reported to extend the resolution limit and increase the depth-of-focus (DOF) of optical lithography provide less immunity to aberrations than conventional approaches. Recently, concern has been surfaced from the implications of spherical aberration on printable features. Best focus position shift and isofocal tilt are one of the well known phenomena resulted from spherical aberration. By varying the reticle height, we observed a decrease in the effect of spherical aberration. In this paper, we explore various techniques that provide us a way of measuring spherical aberration. And we also develop a way to correct the spherical aberration without modifying projection optics.
© (2002) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alden Acheta, Jongwook Kye, and Harry J. Levinson "Spherical aberration measurement and in-situ correction", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002);

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