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1 October 2008 Coherence control of illumination optics in mask inspection systems
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One annoying problem that degrades high-fidelity pattern images in mask-defect inspection systems is the generation of ghost images in the imaging process. Ghost images arise from spatial coherence periodicity on the mask plane, which is due to periodic and discrete arrangements of fly-eye elements in mask inspection optics. By considering the contrast of ghost images under partial coherence illumination, we can derive the condition that represents the necessary number of fly-eye elements to substantially suppress ghost images in the image field. In addition, we confirm this theoretically derived condition of suppressing ghost images by numerical calculations. As a result, we prove that this suppresing condition is effective, and that the nonuniformity in distribution of image intensity can also be reduced in this way.
©(2008) Society of Photo-Optical Instrumentation Engineers (SPIE)
Akira Takada, Toru Tojo, and Masato Shibuya "Coherence control of illumination optics in mask inspection systems," Journal of Micro/Nanolithography, MEMS, and MOEMS 7(4), 043010 (1 October 2008).
Published: 1 October 2008

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