page_title: Extreme ultraviolet lithography
section_title: H-V asymmetry
hierarchical_section_title: Extreme ultraviolet lithography / EUV-specific optical issues / Reflective optics / H-V asymmetry
caption_attribution_description: English: Nontelecentricity from EUV quadrupole illumination with angle differences results in tendency for pattern shift.
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: Most fundamentally, the behavior of light rays within the plane of reflection (affecting horizontal lines) is different from the behavior of light rays out of the plane of reflection (affecting vertical lines). Most conspicuously, identically sized horizontal and vertical lines on the EUV mask are printed at different sizes on the wafer.
caption: EUV non-telecentricity. Left: Due to large multilayer reflection angle differences, one side of the illumination pupil results in more reflected light. Right: Consequently, illumination from one side will be dominant. This results in an optical path difference between diffraction orders with respect to defocus, leading to a tendency for the pattern to shift.
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