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5 July 2000 Impact of lens aberration on pattern symmetry of DRAM cells
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The impact of lens aberrations become more noticeable in the low k1 region, which is where a Krypton Fluoride (KrF) exposure tool exposes a pattern 0.18 micrometers . Lens aberrations affect pattern fidelity and line width uniformity across an exposure field. In particular, the isolation layer pattern of DRAM cells is very sensitive to lens aberrations. We focused on this pattern in our investigation of the impact of lens aberrations and found that asymmetric deformations were caused only by odd components expressed by Zernike polynomials. The magnitude of the impact changed by pattern condition, shape, image tonality, dimension, and term of Zernike polynomials. Using the Monte Carlo method, we simulated a permissible amount of lens aberrations that meet property requirements of a device. As a result, the odd components of lens aberrations were found to require less than 0.020 (lambda) in 0.18-micrometers generation and 0.015 (lambda) in 0.15-micrometers generation. Our rough estimate of the amount of lens aberrations on a KrF scanner was derived from the relationship between a practical printed image and simulated image.
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Katsuyoshi Kobayashi, Teruyoshi Yao, Yuichiro Yanagishita, and Isamu Hanyu "Impact of lens aberration on pattern symmetry of DRAM cells", Proc. SPIE 4000, Optical Microlithography XIII, (5 July 2000);

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