= Solution
\b[Use multilayer reflective optics and a reflective patterned mask.] Near the usual <extreme ultraviolet> <wavelength> of 13.5 nm, ordinary lenses and thick transmissive masks absorb too strongly. Multilayer mirrors focus and project the image, while an absorber pattern on a multilayer-coated mask defines the exposed regions.
The optical path operates in <vacuum> to avoid absorption by air. The key distinction is reflective mask projection, rather than a transparent chromium-on-glass mask or a scanned <electron> probe.
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