In short: EUV lithography uses 13.5nm extreme-ultraviolet light to print the smallest features on a chip. Because no material is transparent at that wavelength, the entire optical system is reflective, works in vacuum, and relies on a laser-produced tin plasma as its light source. This single technology is what makes 7nm, 5nm and 3nm logic nodes manufacturable at scale.
EUV lithography (extreme-ultraviolet lithography) is the photolithography technique that patterns circuits using light with a wavelength of 13.5 nanometers — roughly 14 times shorter than the 193nm deep-ultraviolet (DUV) light used in the previous generation of scanners. In semiconductor manufacturing, the wavelength of light sets a hard limit on how small a feature you can resolve. Shrinking from 193nm to 13.5nm gives designers the resolution headroom needed to keep shrinking transistors.
What makes EUV radically different is not just the shorter wavelength but everything that wavelength forces you to change. At 13.5nm, light is absorbed by essentially all matter — glass, air, even thin films. You cannot build a lens, you cannot expose in open air, and you cannot use a conventional lamp. EUV therefore replaces refractive lenses with mirrors, replaces the atmosphere with vacuum, and replaces the light bulb with a superheated tin plasma.
Resolution in lithography is governed by the Rayleigh criterion: the smallest printable half-pitch is proportional to the wavelength divided by the numerical aperture of the optics. With DUV at 193nm, engineers pushed resolution for years using tricks like immersion (water between lens and wafer) and multiple patterning (printing one layer in several passes). Those tricks grew expensive and error-prone. Moving the wavelength itself down to 13.5nm restores a large margin of resolution in a single exposure.
The catch is that 13.5nm photons are absorbed by any lens material you might use. So EUV optics are built entirely from mirrors, not lenses. But even mirrors do not naturally reflect EUV — a plain metal surface absorbs it. The mirrors are coated with 40 to 50 alternating nanometer-thin layers of molybdenum and silicon. This Bragg reflector stack works by constructive interference: each interface reflects a sliver of light, and the layer spacing is tuned so those reflections add up at exactly 13.5nm. Even so, each mirror reflects only about 70% of the light, and a scanner uses roughly ten of them in series, so only a small fraction of the generated light ever reaches the wafer. That loss is a central reason EUV sources must be so powerful.
Unlike older scanners that shine light through a transparent mask, EUV uses a reflective mask (reticle). The reticle is itself a molybdenum-silicon mirror with an absorber pattern on top that defines the circuit. Light bounces off the clear regions and is swallowed by the absorber regions, carrying the image into the projection optics, which demagnify it (typically 4×) onto the wafer's photoresist.
The exposure is a scanning, step-and-repeat process. The reticle and wafer move in synchrony so a narrow slit of EUV light sweeps the pattern across each field, the wafer steps to the next field, and the sequence repeats. The animation below shows that expose-and-step rhythm.
The light source is an engineering marvel in its own right. A droplet generator ejects molten-tin spheres about 25µm across into a vacuum chamber. A pre-pulse laser flattens each droplet into a pancake; a second, much higher-energy CO₂ laser pulse then hits it and heats the tin to a plasma around 40 times hotter than the sun's surface. That plasma radiates the 13.5nm light, which a large curved collector mirror gathers and funnels into the scanner. This happens tens of thousands of times a second.
Because each EUV photon carries much more energy than a DUV photon, far fewer photons deliver the same exposure dose. With so few photons per feature, random variation — called stochastic noise — can cause missing or bridged lines. Managing stochastics with better resists, higher source power, and smart mask design is one of the hardest ongoing problems in EUV.
The payoff of EUV is simplicity at the smallest dimensions. The critical layers of a 7nm, 5nm or 3nm chip have features finer than DUV can print in one pass. Without EUV, foundries must split each such layer into three, four, or even more separate DUV exposures — multiple patterning — each with its own mask, alignment step, and defect risk. EUV collapses many of those passes back into a single exposure.
In short, EUV did not just shrink one dimension — it kept the economics of Moore's Law alive by making the hardest layers manufacturable again. That is why every leading-edge logic fab today depends on it.
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Explore CourseTron Courses →At 13.5nm, light is absorbed by virtually every transparent material, including the glasses used for refractive lenses. There is nothing to make a lens out of, so EUV systems use multilayer molybdenum-silicon mirrors and operate in vacuum, since air absorbs EUV too.
From a laser-produced plasma. A high-power CO₂ laser vaporizes molten-tin droplets tens of thousands of times per second, and the resulting superheated plasma emits extreme-ultraviolet light at 13.5nm, which a collector mirror gathers.
No. EUV is used for the most critical, finest layers of advanced nodes. The many less-demanding layers of a chip are still patterned with cheaper, well-proven DUV scanners. A modern fab runs both.
High-NA EUV is the next evolution of EUV optics, raising the numerical aperture from about 0.33 to roughly 0.55. The higher NA improves resolution so manufacturers can print even smaller features for nodes beyond 3nm.
Related: Photolithography process · Glossary · all courses.