page_title: Extreme ultraviolet lithography
section_title: Thick mask shadowing effects
hierarchical_section_title: Extreme ultraviolet lithography / EUV-specific optical issues / Reflective optics / Thick mask shadowing effects
caption_attribution_description: English: A feature on an EUV mask can easily be considered optically thick, when the width is comparable to the thickness (e.g., 70 nm). In such a case, the shadow distance can be a substantial portion of the linewidth or critical dimension (CD).
context_page_description: Extreme ultraviolet lithography is a lithography technology using a range of extreme ultraviolet wavelengths, roughly spanning a 2% FWHM bandwidth about 13.5 nm.
  While EUV technology is available for mass production, 53 machines worldwide capable of producing wafers using the technique were delivered since Q1 2018, while 201 immersion lithography systems were delivered during the same period. Issues that make EUV adoption difficult are tool costs, tool uptime and stochastic phenomena. The latest NXE:3400 tools have been equipped with lower pupil fill capability for better imaging, but this leads to lower productivity due to limited use of the exposure field.
context_section_description: The oblique incidence in a reflective optical system leads to shadowing effects in the presence of a mask absorber. For example, one side (behind the shadow) would appear brighter than the other (within the shadow).
caption: Shadowing effect on an EUV mask. When the feature size on the mask is comparable to the thickness, the shadowing effect is more significant to the formed image, since the shadow clearance distance is not negligible compared to the feature size.
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