EUV Lithography: The Machine That Prints Microchips

01 The Basics of Semiconductor Fabrication

Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuits such as microprocessors, microcontrollers, and memories. It is a multiple-step photolithographic and physico-chemical process, with steps such as thermal oxidation, thin-film deposition, ion implantation, and etching, during which electronic circuits are gradually created on a wafer, typically made of pure single-crystal semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications. The wafer itself is a thin slice of purified silicon, up to 300 millimeters in diameter, polished to a mirror finish so smooth that surface irregularities are measured in nanometers.

The fundamental challenge of chipmaking is miniaturization. A modern processor contains billions of transistors, each of which must be patterned with features measured in nanometers. The process by which these patterns are transferred to the silicon wafer is called photolithography, and it is the single most critical and expensive step in the entire fabrication sequence. Every other process step, from deposition to etching, depends on the precision of the lithographic pattern. The wavelength of light used in lithography directly determines the minimum feature size that can be printed, which in turn determines how many transistors can fit on a chip and how fast and power-efficient that chip will be.

For decades, the semiconductor industry followed a rhythm defined by Moore's Law, the observation that the number of transistors per integrated circuit roughly doubles every two years. Sustaining this trajectory required continuous innovation in lithographic technology. Each generation of lithography used shorter wavelengths of light to print smaller features. The progression moved from visible light through ultraviolet wavelengths to deep ultraviolet, and eventually to the extreme ultraviolet regime that defines the current frontier. Each transition required overcoming enormous technical challenges, and the jump to EUV was the most difficult of all.

02 From Deep Ultraviolet to Extreme Ultraviolet

The lithography systems that dominated chip manufacturing from the late 1990s through the 2010s used deep ultraviolet light at a wavelength of 193 nanometers, produced by excimer lasers. To print features smaller than the wavelength of the light itself, engineers developed an ingenious technique called multiple patterning, which involves exposing the wafer multiple times with slightly shifted masks, effectively building up a pattern whose resolution exceeds what a single exposure could achieve. This approach allowed 193-nanometer lithography to produce features as small as 14 nanometers, but at the cost of dramatically increased process complexity, additional masks, and more exposures per layer.

By the mid-2010s, multiple patterning had reached its practical limits. The number of exposures per layer was growing, driving up costs and reducing yields. The industry needed a fundamentally shorter wavelength. The answer was extreme ultraviolet light at 13.5 nanometers, more than ten times shorter than the deep ultraviolet wavelength it replaced. This dramatic reduction in wavelength promised to restore the straightforward relationship between light wavelength and feature size, eliminating the need for complex multiple patterning schemes for the most critical layers.

The transition to EUV was not straightforward. Because EUV light is absorbed by virtually all materials, including air, the entire optical path must operate in a vacuum. Traditional refractive lenses cannot be used because the light would be absorbed before reaching the wafer. Instead, EUV systems use reflective optics, a series of precisely shaped mirrors coated with alternating layers of molybdenum and silicon to reflect the light through Bragg reflection. Each mirror reflects only a small percentage of the incoming light, so the system must generate an extremely bright source to compensate for losses through the optical chain.

03 Generating EUV Light: The Tin Droplet Laser

Producing EUV light is one of the most extraordinary engineering challenges in modern technology. Unlike deep ultraviolet sources, which are relatively straightforward laser systems, EUV light requires a fundamentally different approach. The method used in production systems involves firing a high-power carbon dioxide laser at microscopic droplets of molten tin falling through a vacuum chamber. The laser hits each droplet twice: first to flatten it into a pancake shape, and then to vaporize it into a plasma that emits light at the 13.5-nanometer wavelength.

This process happens fifty thousand times per second. Each tin droplet is about 30 micrometers in diameter, roughly the size of a human hair, and each must be hit with precise timing and positioning by the laser pulse. The resulting plasma reaches temperatures of several hundred thousand degrees Celsius, emitting EUV light that is collected by a curved mirror and directed through the optical system toward the wafer. The entire process consumes enormous amounts of energy, and the resulting EUV output is still only a fraction of the laser power input, making efficiency a constant concern.

The tin debris from this process must be continuously managed, because any contamination of the sensitive optical surfaces would rapidly degrade system performance. Hydrogen gas flows through the chamber to react with tin debris, forming tin hydride gas that can be pumped away. The collector mirrors, despite being protected, gradually degrade over time and must be periodically replaced or cleaned, contributing to the operational costs of EUV systems. The complexity of the light source is a major reason why EUV systems cost roughly $200 million each, far more than their deep ultraviolet predecessors.

04 The Optics: Mirrors in a Vacuum

Once the EUV light is generated, it must be shaped and directed toward the wafer with extraordinary precision. Because EUV light is absorbed by all known transparent materials, conventional glass lenses are useless. Instead, the optical system uses a series of multilayer reflective mirrors, each coated with dozens of alternating layers of molybdenum and silicon, each layer just a few nanometers thick. These layers create a Bragg reflector that constructively reinforces the reflection of 13.5-nanometer light, allowing each mirror to reflect a meaningful percentage of the incoming radiation rather than absorbing it.

The mirrors themselves are among the most precisely manufactured objects ever created. Their surfaces must be polished to a smoothness measured in picometers, meaning that surface irregularities are smaller than the diameter of an individual atom. Any imperfection in the mirror surface would distort the reflected light and introduce errors in the pattern projected onto the wafer. A typical EUV system contains approximately a dozen of these mirrors in the projection optics alone, plus additional mirrors in the illumination system that shapes the light before it reaches the mask.

Each mirror in the optical path reflects only about 70 percent of the incoming EUV light, absorbing or scattering the rest. With multiple mirrors in the system, the total transmission can be quite low, which is why the light source must be so powerful. This cumulative loss is one of the fundamental challenges of EUV lithography and motivates ongoing research into more efficient mirror coatings and simpler optical designs. The numerical aperture of the optical system, which determines the resolution limit, is being increased in next-generation high-NA EUV systems from 0.33 to 0.55, enabling even smaller features without reducing the wavelength.

05 The Economics of EUV

An EUV lithography system costs approximately $200 million per unit, making it the most expensive piece of equipment in a semiconductor fab and one of the most expensive machines in the world. The cost reflects the extraordinary complexity of the system, from the tin droplet laser source to the atomic-scale mirror optics to the vacuum systems and precision wafer stage. Only one company, ASML, manufactures EUV lithography systems, creating a unique monopoly in one of the most critical links in the global technology supply chain.

The economic implications extend far beyond the cost of the machines themselves. Each EUV system processes a certain number of wafers per hour, and the throughput determines the cost per chip. EUV systems initially had relatively low throughput compared to mature DUV systems, meaning that chips produced using EUV were significantly more expensive per unit. As the technology has matured, throughput has improved, but EUV remains more expensive than the deep ultraviolet lithography it supplements. Chipmakers must carefully optimize which layers use EUV and which can still use less expensive DUV multiple patterning.

The capital investment required to build a modern semiconductor fab now exceeds $20 billion, and a significant fraction of that cost goes to lithography equipment. A single fab may contain dozens of lithography systems, each costing tens to hundreds of millions of dollars. This concentration of cost and technical complexity has driven consolidation in the semiconductor manufacturing industry, with only three companies, Intel, Samsung, and TSMC, capable of producing chips at the most advanced nodes. The barriers to entry are so high that no new company has joined this elite tier in over a decade, and geopolitical concerns about supply chain concentration have led to massive government investment programs aimed at expanding manufacturing capacity in multiple countries.

06 ASML and the Single-Supplier Problem

The fact that a single company, the Dutch firm ASML, is the only manufacturer of EUV lithography systems creates an extraordinary bottleneck in the global technology supply chain. No other company has successfully developed the combination of technologies required, from the tin droplet laser plasma source to the multilayer mirror optics to the precision wafer stage. ASML's EUV systems incorporate components from the German optics company Zeiss, the American laser company Cymer which ASML acquired, and numerous other specialized suppliers, but the final system integration is performed exclusively by ASML.

This concentration has not gone unnoticed by policymakers. The United States and the Netherlands have negotiated export restrictions that limit the sale of advanced lithography systems to certain countries, effectively using control over EUV technology as a lever in international relations. The restrictions have significant implications for countries seeking to develop domestic semiconductor manufacturing capabilities, as access to EUV is a prerequisite for producing chips at the most advanced nodes. The intersection of technology, economics, and geopolitics in the EUV supply chain is one of the defining features of the contemporary technology landscape.

The monopoly also creates risks for the industry as a whole. If ASML's production were disrupted, whether by natural disaster, supply chain disruption, or political conflict, the entire global semiconductor industry would be affected. The long lead times for EUV systems, often measured in years, mean that capacity cannot be quickly expanded in response to demand surges. Chipmakers must plan their capital investments years in advance, locking in orders for systems that may cost $200 million each and take years to deliver and install.

07 High-NA EUV and the Future

The next generation of EUV lithography systems, known as High-NA EUV, increases the numerical aperture of the optical system from 0.33 to 0.55, enabling even smaller feature sizes without changing the wavelength of the light. This improvement comes at the cost of a smaller field size, meaning the pattern projected onto the wafer covers a smaller area, which requires changes to how patterns are stitched together across the wafer. High-NA systems are expected to enable the 2-nanometer node and beyond, continuing the march of Moore's Law into ever more miniature territory.

Beyond High-NA, the industry is already researching potential successors. One candidate is non-EUV approaches such as directed self-assembly, which uses block copolymers that spontaneously form nanoscale patterns. Another is nanoimprint lithography, which physically stamps patterns onto the wafer rather than using light. Each approach faces significant technical challenges, and none has yet demonstrated the combination of resolution, throughput, and yield needed for high-volume manufacturing. EUV and its High-NA successor are likely to remain the dominant lithographic technologies for the remainder of this decade.

The ultimate limit of optical lithography is set by the wavelength of the light used. Even with High-NA systems at 13.5 nanometers, the practical resolution limit is expected to reach around 1 to 2 nanometers within the coming years. Going beyond this would require either a shorter wavelength, such as the 6.x-nanometer light explored in research labs, or a fundamentally different patterning approach. The industry is investing heavily in both paths, recognizing that the future of computing depends on the ability to continue printing ever-smaller transistors on silicon wafers.

08 Why EUV Matters for AI and Computing

The connection between EUV lithography and artificial intelligence may not be immediately obvious, but it is profound. The current revolution in generative AI and large language models is enabled by advances in computing hardware, specifically the graphics processing units and specialized AI accelerators that run these models. These chips contain tens of billions of transistors packed into areas smaller than a fingernail, and manufacturing them at the most advanced process nodes requires EUV lithography. Without EUV, the chips that power modern AI would be impossible to produce at the scale and performance levels that the technology demands.

The economic stakes are enormous. The global semiconductor industry generates hundreds of billions of dollars in annual revenue and underpins trillions more in downstream technology and services. Every smartphone, computer, data center, and AI system depends on chips that were patterned by lithographic systems. The ability to manufacture these chips at ever-smaller nodes, at acceptable cost and yield, is what enables continued improvement in computing performance and energy efficiency. EUV is not just a technical curiosity; it is a strategic capability that determines which countries and companies can participate in the most advanced tiers of the technology economy.

As AI models continue to scale and demand ever more computing power, the pressure on semiconductor manufacturing intensifies. The training of frontier AI models already requires massive clusters of specialized processors, and the inference costs of deploying these models at scale are driving demand for more efficient hardware. EUV lithography, by enabling denser and more efficient chip designs, is one of the key technologies that makes this trajectory sustainable. The machines that print microchips at 13.5-nanometer resolution are, in a very real sense, the machines that print the future of computing.