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12 May 2005 Hot spot free diffractive DUV-homogenizer for high NA-illumination
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In the optimization process of DUV-illumination systems for inspection tools and lithographic devices, more and more an exact control of angular distribution and homogeneity of the illumination will be required. On the one hand, diffractive homogenizers enable homogeneous illumination of areas with almost arbitrary shape with a high numerical aperture. On the other hand, diffractive optical elements produce a zero order or so called “hot spot”. If the optical axis is within the illuminated area, this hot spot will decrease the homogeneity of illumination. The zero order is caused by profile aberrations and its intensity can be decreased by increasing the fabrication accuracy. But the higher the numerical aperture, the larger the ratio between zero order brightness and brightness of the surrounding homogenized area. I.e., in cases of high NA the zero order of a homogenizer cannot be reduced to the brightness of the surrounding area. We present a novel approach of beam homogenization using a combination of two serially arranged diffractive optical elements that produces an intensity distribution without hot spot. Such compact two-element homogenizers have been realized for wavelengths down to 193nm. A homogenizer for 193nm producing a homogeneously illuminated rectangle with 0.3 NA will be presented.
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Matthias Cumme, Mirko Riethmuller, Dirk Mademann, Manfred Schrenk, and Peter Weissbrodt "Hot spot free diffractive DUV-homogenizer for high NA-illumination", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005);

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