Characterization of small phase defects using a micro-coherent extreme ultraviolet scatterometry microscope

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To evaluate defects on extreme ultraviolet (EUV) masks in the blank state of manufacture, we developed a micro-coherent EUV scatterometry microscopy (micro-CSM) system. Its 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 intensities, which are strongly related to the printability of a defect. After observing pit-type program phase defects with a 60 nm width and 1 nm depth, we estimated the reflection and scattering intensities of each defect using step-and-repeat measurement around the defect. The reflection and scattering intensities from the program defects of the same design fluctuated. This indicates that the actual volumes of all defects differ even for the same design. Additionally, the scattering distributions of 30-nm-wide defects were anisotropic owing to interference with speckle from multilayer scattering. Thus, micro-CSM demonstrates that the scattering distribution depends on the defect position in the multilayer.

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