What Is EUV Lithography? How 13.5 nm Light Prints Chips
EUV lithography prints the circuit patterns of a chip using very short-wavelength "light" (extreme ultraviolet) at 13.5 nm. The shorter the wavelength, the finer the pattern it can print, so it is used for the finest layers of leading-edge chips. This light is absorbed even by air. So the inside of the machine is a vacuum, and mirrors carry the light instead of lenses.
What you'll learn
- What exposure does (the roles of the resist and the mask)
- Why shorter-wavelength light can print finer patterns
- How the industry moved from 193 nm light to 13.5 nm EUV
- Why EUV needs mirrors and a vacuum, and how tin is used to make the light
- The hurdles to volume production, High-NA EUV, and why only ASML makes the machines
Prerequisites: it helps to know that chips are made by adding films, printing patterns and etching, over and over. "How Are Chips Made?" explains this in detail.
In the news: "EUV"
"Rapidus has installed an EUV lithography machine at its fab in Hokkaido, Japan." "Without machines from ASML in the Netherlands, leading-edge chips cannot be made." You may have seen headlines like these. In December 2024, Rapidus announced that it had moved an EUV machine for volume production into its fab in Chitose, Hokkaido. The company said it was the first EUV machine in Japan to be used for mass production.
EUV lithography is essential for making chips of the most advanced generations, with names such as "2nm." Even so, it is only one of the many steps in making a chip. This article explains, step by step, what EUV lithography does and why it needs such special machines.
What exposure is: copying a pattern with light
A chip's circuits are built by adding films to a round slice of silicon, called a wafer, and etching them, again and again. Exposure decides where to etch and where to leave material. The whole series of steps that copies a pattern with light is called lithography.
First, a thin coat of a chemical that changes when light hits it is spread on the wafer. This chemical is called photoresist, or resist for short. In most cases, only the parts hit by light will later dissolve in a developer liquid. Other types work the other way, and the parts not hit by light dissolve.
Next, light is shone through a master plate that carries the circuit pattern. This plate is called a mask. The machine usually shrinks the mask pattern to one quarter of its size and prints it onto the wafer. Each shot covers only part of the wafer, so the machine steps across it bit by bit to cover the whole surface.
After exposure, a liquid dissolves part of the resist, leaving the pattern in the resist. Etching away the parts the resist does not protect gives the film the shape of the circuit. You can follow this flow in the figures of "How Are Chips Made?"
Shorter wavelengths print finer patterns
Light behaves like a wave. The distance from one wave crest to the next is called the wavelength. Visible light has wavelengths of about 400–700 nm. A nanometer (nm) is one millionth of a millimeter.
When light passes through a narrow gap, it spreads out and bends around on the other side. This is called diffraction. The finer the mask pattern, the more the light spreads after passing through, and the blurrier the image. If the pattern gets too fine, neighboring lines can no longer be told apart.
The shorter the wavelength, the less the light spreads. So printing finer patterns needs shorter-wavelength light. In fact, exposure light has moved from mercury lamps (436 nm and 365 nm) to lasers (248 nm and 193 nm).
Wavelength is not the only thing that sets how fine a pattern can be. It also matters how wide an angle the lenses or mirrors can collect light from. The number that describes this width is called the numerical aperture (NA), and a larger NA prints finer patterns. Clever mask shapes and lighting can also push closer to the limit.
How fine a pattern can be printed is also called the resolution. Resolution is proportional to the wavelength and inversely proportional to NA. As a formula, resolution = k1 × wavelength ÷ NA, known as the Rayleigh equation. k1 is a factor set by the lighting, the mask and the resist. A smaller k1 means harder conditions, and in theory it cannot go below 0.25 in a single exposure. You can try different numbers in the lithography resolution calculator.
From 193 nm light to EUV
From the 2000s, the workhorse was a laser that gives off ultraviolet light at 193 nm. It uses argon and fluorine gases, so it is called an ArF laser after their chemical symbols. Machines that use this light still print many of the layers in a chip today.
To print even finer patterns with 193 nm light, engineers began filling the gap between the lens and the wafer with water. In water, the wavelength of light becomes shorter than in air. This effect lets NA go above 1. The method is called immersion lithography. ASML says its immersion machine has an NA of 1.35 and can print features as fine as 38 nm.
Patterns finer than that have been made by splitting one pattern into several exposures and overlaying them. This method is called multiple patterning. But it adds more exposure and etch steps. That costs time and money, and the layers are more likely to be misaligned.
The answer that reached practical use is EUV lithography, which uses light with a wavelength of 13.5 nm. EUV stands for extreme ultraviolet. Its wavelength is about one fourteenth of 193 nm, so it can print fine patterns in a single exposure. In 2019, TSMC announced that it was shipping products in volume from a generation (N7+) made with EUV.
Why mirrors and a vacuum are needed
EUV light has a troublesome property. Almost every material absorbs it, including glass and air. ASML also explains that EUV is absorbed even by air. So the whole light path, from the source to the wafer, is kept in a vacuum.
The light cannot pass through glass, so ordinary lenses don't work either. Instead, only mirrors that bounce the light are used to collect it and shrink the pattern. The mask is the same. Instead of a stencil that lets light through, it is a "mirror mask" that reflects light in the shape of the pattern.
But an ordinary mirror reflects almost no EUV. So the mirrors are made of dozens of very thin, alternating layers of molybdenum (a metal) and silicon. Each boundary between layers reflects a little light, and these reflections line up their wave crests and add up. Such a mirror is called a multilayer mirror.
Even so, one mirror reflects about 70% at most, and absorbs the rest. For example, after 10 mirrors, you multiply 0.7 by itself 10 times, and only about 3% of the light is left (a simple example calculation). This is one reason EUV machines need a very bright light source.
The mirror surfaces must also be extremely smooth. The mirrors are made by ZEISS in Germany. ZEISS explains that if a mirror were scaled up to the size of Germany, its largest bump would be only about 0.1 mm.
Making the light: firing a laser at tin droplets
Light at 13.5 nm cannot be made with a light bulb or an ordinary laser. An EUV machine makes its light from tiny droplets of the metal tin. Molten tin droplets fly through a vacuum chamber at a rate of about 50,000 a second (according to ASML).
A powerful carbon dioxide (CO2) laser hits each droplet in flight. First, a weak flash flattens the droplet. Then a strong pulse heats it all at once. The tin becomes a very hot gas whose atoms have lost electrons. This state is called plasma.
Tin plasma gives off strong light right around 13.5 nm. This wavelength also matches the light that molybdenum-silicon multilayer mirrors reflect well. So the odd-looking number 13.5 nm was chosen because the light source and the mirrors work well together.
A large mirror around the plasma, the collector mirror, gathers the light and sends it deeper into the machine. From there, several mirrors light up the mask. The pattern reflected from the mask is then shrunk and printed onto the wafer.
Hurdles to volume production: brightness and random defects
To be used in a factory, printing fine patterns is not enough. How many wafers a machine can process per hour has a big effect on the price of a chip. The industry calls this processing rate throughput.
If the light is weak, it takes longer to expose the resist fully, and throughput drops. The mirrors also lose light, so making the source brighter was a challenge for a long time. The machine that began shipping in 2024 (NXE:3800E) handles up to 220 wafers per hour (ASML's 2024 annual report).
Another hurdle is the number of light particles. Light also behaves like a stream of tiny packets of energy. Each packet is called a photon. One EUV photon carries about 14 times the energy of a 193 nm photon. So for the same energy, there are only about one fourteenth as many photons.
With few photons, random unevenness stands out: some spots get more, some get fewer. The fewer photons arrive, the larger the relative swing from the average. As a result, line edges can come out jagged, and small holes can occasionally fail to open. More light reduces the unevenness, but each wafer takes longer and throughput drops. Reducing these defects that happen by chance is a major challenge for EUV.
Keeping dust off the mask also gets harder. If a tiny particle lands on a mask, every chip printed with that mask gets the same defect. So a thin film is stretched a little above the mask to keep dust from landing directly on it. This film is called a pellicle.
With EUV, the pellicle also absorbs light. With a mirror mask, light passes through the film twice, going in and coming back, so the loss doubles. A 2021 report said ASML had developed a pellicle that lets through about 90% of the light and was aiming for volume production. The film must be extremely thin and still survive the heat of the intense light.
High-NA EUV: a larger numerical aperture for even finer patterns
Making the wavelength even shorter would mean redesigning both the light source and the mirrors, which is not easy. So the next step was to increase NA. Larger mirrors collect light from a wider angle. This is called High-NA EUV.
Earlier EUV machines have an NA of 0.33. High-NA machines raise NA to 0.55. According to ASML, the finest printable feature goes from 13 nm to 8 nm.
It is not all upside, though. A larger NA makes the range of depth that stays in focus shallower. Also, each exposure covers only half the area of earlier machines. The reason is that the pattern is shrunk by different amounts in the two directions: to one quarter one way and one eighth the other. This limits the angle of light hitting the mask. Large chips need workarounds, such as printing in two parts and stitching them together.
Why only ASML can make them
As of 2026, ASML of the Netherlands is the only company selling EUV lithography machines as a product. In its 2025 annual report, ASML describes itself as "currently the world's only manufacturer" of EUV lithography systems. Rapidus, which bought the machine, says the same. Nikon and Canon, which also make lithography machines, do not sell EUV machines.
One reason is the huge amount of time and money development took. EUV was researched for many years, and it only began to be used in volume factories around 2019. In 2012, ASML set up a program in which Intel, TSMC and Samsung invested in the company and covered part of the development costs.
Another reason is close ties with the companies that make special parts. In 2013, ASML bought Cymer, a US maker of light sources. Optical parts such as the mirrors come from ZEISS in Germany. The powerful CO2 lasers for the light source come from TRUMPF, also in Germany. An EUV machine only works by combining the technologies of companies like these.
A foundry, a company that makes chips to order, cannot compete at the most advanced generations without EUV machines. "What Is a Semiconductor Foundry?" explains how the industry divides the work.
Common myths
Myth: EUV draws lines 2 nm wide
In fact, "2nm" is the name of a technology generation. It does not mean any part of the chip measures 2 nm. According to ASML, the finest feature an EUV machine can print in one exposure is 13 nm, and 8 nm even with High-NA. Both numbers are written in nm, so people tend to link them. "What Does 2nm or 3nm Mean?" explains this in detail.
Myth: Every layer of a leading-edge chip is printed with EUV
In fact, EUV is used only for some of the finest layers. Many other layers are still printed with ArF and other light. EUV machines are expensive to buy and to run, so chipmakers use them only where needed. Even in the EUV generation TSMC launched in 2019, EUV was used for only a few critical layers.
Myth: EUV lithography draws circuits with laser light
In fact, the laser only "lights the fire" that makes the tin plasma. The pattern is printed by the 13.5 nm light that comes from the plasma. Also, the machine does not move a spot of light to draw lines one by one. It shrinks the mask pattern and prints it by sweeping a band of light across it. The myth often comes from phrases like "burning circuits with a laser."
By the numbers
| Number | What it means |
|---|---|
| 13.5 nm | Wavelength of the light used in EUV lithography |
| 193 nm | Wavelength of ArF laser light (about 14 times EUV) |
| 38 nm | Finest feature an ArF immersion machine (NA 1.35) can print (ASML) |
| 13 nm → 8 nm | Finest feature an EUV machine can print, from NA 0.33 to High-NA at NA 0.55 (ASML) |
| About 1/14 | Number of photons for the same energy (EUV compared with 193 nm light) |
| About 70% | Rough upper limit of light one multilayer mirror can reflect |
| About 50,000 | Tin droplets the light source fires per second (ASML and TRUMPF) |
| 220 | Maximum wafers per hour for the NXE:3800E (ASML, 2024 annual report) |
| 0.1 mm | Largest bump if a mirror were scaled up to the size of Germany (ZEISS) |
Lined up, the numbers show how hard EUV lithography is. Light that even air absorbs is carried only by extremely smooth mirrors, and it is made from tens of thousands of tin droplets every second. On top of that, the machine keeps printing 13 nm patterns on more than 200 wafers an hour.
Learn more
- Compare in a table: "EUV vs DUV Lithography" (wavelength, optics, masks, cost), "SADP vs SAQP vs LELE" (multiple patterning methods), "Reticle vs Photomask"
- Tricks that push toward the limit: "OPC vs Phase-Shift Mask vs Off-Axis Illumination" compares techniques that make k1 smaller.
- Try the numbers: the lithography resolution calculator shows how changing wavelength and NA changes the finest printable feature and the depth of focus.
- Related articles: "How Are Chips Made?" (the whole process), "What Does 2nm or 3nm Mean?" (how to read generation names), "What Is a Semiconductor Foundry?" (how the industry divides the work)