17 April 2014 At-wavelength observation of phase defect using focused lensless microscope
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To evaluate defects on extreme ultraviolet (EUV) masks at the blank state of manufacturing, we developed a micro coherent EUV scatterometry microscope (micro-CSM). The illumination source is coherent EUV light with a 230-nm focus diameter on the defect using a Fresnel zoneplate. This system directly observes the reflection and scattering signals from a phase defect. The scattering distributions of 30-nm-wide defects were anisotropic due to interference with speckle from multilayer scattering. Thus, printability of the defects would depend on the defect position in the multilayer.
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Tetsuo Harada, Tetsuo Harada, Yusuke Tanaka, Yusuke Tanaka, Tsuyoshi Amano, Tsuyoshi Amano, Youichi Usui, Youichi Usui, Takeo Watanabe, Takeo Watanabe, Hiroo Kinoshita, Hiroo Kinoshita, "At-wavelength observation of phase defect using focused lensless microscope", Proc. SPIE 9048, Extreme Ultraviolet (EUV) Lithography V, 90483F (17 April 2014); doi: 10.1117/12.2050936; https://doi.org/10.1117/12.2050936

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