Techniques for measuring aberrations in lenses used in photolithography with printed patterns.
In optical lithography, it is a serious problem that aberrations in projection lenses reduce the imaging quality. Therefore techniques to measure the aberrations are required that will predict the adverse effects of aberrations on lithographic imagery and reduce them. We present a measurement method that uses a fine grating and its imaging condition to quantify coma, astigmatism, and spherical aberration. With this method, these aberrations can be described with simple expressions from the measured results. Application of this method revealed the coma of Zernike polynomials for our krypton fluoride (KrF) excimer-laser scanner.
Nomura
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Microelectronics Engineering Laboratory, Toshiba Corporation, 8, Shinsugita-cho 235-8522 Japan.
Sato
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