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Extreme ultraviolet (EUV) is short-wavelength ultraviolet radiation. Its exact wavelength boundaries depend on the convention or instrument being discussed: NASA’s astronomy chart places EUV at 10–90 nm, while NASA’s Extreme Ultraviolet Explorer observed from 7–76 nm. Semiconductor lithography uses a specific EUV wavelength—about 13.5 nm—not the entire EUV band.
What wavelength is extreme ultraviolet light?
There is no single boundary accepted across every field between ultraviolet, extreme ultraviolet (also called XUV in some scientific contexts), and X-rays. The range depends on the spectral convention or the instrument in question.
- Astronomy spectrum convention: NASA HEASARC’s chart places EUV at 100–900 angstroms, or 10–90 nm, corresponding to photon energies of roughly 14–124 eV. NASA HEASARC’s 2021 chart is an astronomy-oriented convention.
- One spacecraft’s observing range: NASA gives the Extreme Ultraviolet Explorer (EUVE) an observing range of 7–76 nm. That is the mission’s instrument range, not a universal definition of EUV. NASA’s EUVE mission overview describes the spacecraft.
These ranges serve different purposes, so their differing endpoints are not a contradiction. When precision matters, state which convention or instrument defines the range.
How EUV differs from ultraviolet and X-rays
EUV sits within the short-wavelength ultraviolet region, but spectral labels at its boundaries are conventional rather than universal. Shorter wavelength means higher photon energy; the NASA HEASARC chart’s 10–90 nm EUV band corresponds to roughly 14–124 eV. A source or instrument may use a different range, as EUVE’s 7–76 nm operating range illustrates.
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For semiconductor manufacturing, the useful comparison is with deep-ultraviolet (DUV) lithography: NIST contrasts DUV at approximately 193 nm with EUV around 13–13.5 nm. The 13.5 nm figure describes a lithography application, not the endpoints of the EUV spectrum.
Why EUV is difficult to handle optically
EUV is strongly absorbed by materials, including materials that transmit visible light. NIST notes that radiation near 13 nm is well within the vacuum ultraviolet, where it is strongly absorbed by all materials. This makes ordinary transparent lenses impractical and makes transmitting EUV through air or conventional optical materials difficult.
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In the vacuum ultraviolet and EUV, a material’s refractive index is complex: its real component describes phase propagation, while its imaginary component is associated with attenuation. NIST expresses the drop in intensity through an absorbing medium as I = I₀ exp(−αt), where α is related to the extinction coefficient and wavelength, and t is the distance traveled through the material. Because lenses are not practical at EUV wavelengths, systems instead use mirrors, often synthetic multilayer mirrors. NIST’s EUV lithography project page discusses the optical challenges.
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Why EUV is used to make chips
EUV lithography uses short-wavelength light to create patterns in photoresist on silicon wafers. NIST identifies 13.5 nm as a semiconductor manufacturing wavelength that supports smaller features and greater device area density.
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- A silicon wafer is coated with photoresist.
- The wafer is exposed to EUV through a patterned photomask.
- The exposure changes the resist’s solubility.
- Development removes selected portions of the resist, leaving a pattern for later fabrication steps.
The short wavelength helps pattern small features, but the strong absorption of EUV requires specialized, mirror-based optical systems rather than ordinary lenses.
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Astronomy and solar observation
Space instruments use EUV to observe celestial sources. NASA reports that EUVE’s all-sky survey cataloged 801 sources, including the first detections of objects beyond our galaxy in this light. NIST also lists solar physics and astronomy among EUV-related research applications.
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Specialized detector calibration
NIST’s silicon EUV photodiode transfer standard is used to support detector measurements across a 5–254 nm calibration range. This is a specialized radiometric instrument range, not a general consumer detector specification. NIST’s Si EUV Photodiode Transfer Standard page describes the standard.
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