Lesson 5 — The Secret of Lithography
How Do Chips Actually Work?
Learning Material
1 pagesLesson 5 — The Secret of Lithography
Understanding the Complex: How Do Chips Actually Work?
In the basement of a research facility in Veldhoven, Netherlands, engineers spent the better part of two decades trying to do something that most of their colleagues thought was impossible: focus light at a wavelength of 13.5 nanometers with sufficient precision to print circuits on silicon.
To put that wavelength in context: visible light ranges from about 380 to 700 nanometers. The extreme ultraviolet (EUV) light they were working with is far beyond what the human eye can perceive, and so energetic that it is absorbed by almost everything — air, glass, metal, mirrors. The only materials that reflect it at all do so poorly, with around 70 percent absorption even off the best-engineered reflective surfaces.
Building a machine to focus this light, bounce it off mirrors, project it through a mask, and land it precisely on a silicon wafer — all while maintaining tolerances measured in fractions of a nanometer — took more than $9 billion in development, contributions from research labs across multiple continents, and over 5,000 suppliers. The result is the ASML EUV lithography machine: a device so complex that it fills a room, weighs 180 tons, and costs approximately €150 million per unit.
Only one company makes them. This fact is at the center of everything.
Understanding lithography: printing at the nanoscale
Chip manufacturing is, at its heart, a printing process. The circuit patterns — transistors, wires, logic gates — are defined in advance as a design, then reproduced at nanometer scale on the silicon wafer, layer by layer. The tool that does this printing is a lithography machine (from the Greek lithos, stone, and graphia, writing — a technology that predates electronics by two centuries).
The basic principle borrows from photography. A light-sensitive chemical called a photoresist is applied to the silicon wafer. Light is then shone through a mask — a template of the circuit pattern — and projected onto the wafer. Where light hits the resist, a chemical reaction occurs; where it doesn't, the resist remains unchanged. The exposed or unexposed resist is then washed away (depending on whether it's a positive or negative tone resist), leaving a pattern on the surface. Chemical processes then etch or deposit materials through this pattern, building up the circuit layer by layer.
The challenge is resolution: how small a feature can you print? The fundamental limit is the wavelength of light. You cannot reliably print features smaller than roughly half the wavelength of your light source. This is why the history of lithography is, in large part, a history of chasing shorter and shorter wavelengths.
From mercury lamps to ArF lasers
Early chip makers used mercury vapor lamps, which emit light at several ultraviolet wavelengths. As chips shrank below 1 micrometer, they switched to argon fluoride (ArF) excimer lasers, which emit at 193 nanometers. This wavelength became the workhorse of the industry for nearly three decades — an extraordinary longevity achieved not by changing the light source but by engineering increasingly elaborate tricks to push the resolution beyond the theoretical limit.
One such trick is immersion lithography: filling the gap between the lens and the wafer with ultra-pure water, which has a higher refractive index than air and effectively shortens the wavelength. Another is multi-patterning: exposing the same layer of resist multiple times, with slightly different masks, to create features finer than a single exposure could achieve. Some advanced chips require over 100 exposures of a single layer.
These tricks extended the life of 193nm lithography well past what anyone thought possible. But they added complexity, time, and cost to every wafer. A single 5nm-process chip might require up to 1,000 process steps, many of them lithography exposures.
EUV: the breakthrough that changed the economics
Extreme ultraviolet lithography operates at 13.5 nanometers — a wavelength 14 times shorter than ArF. In principle, this allows features 14 times finer with a single exposure, eliminating the need for multi-patterning at smaller nodes.
The physics of EUV are deeply uncooperative. Because EUV is so energetic, it ionizes air molecules — so the entire optical path must be in a vacuum. It cannot be focused with glass lenses, because glass absorbs it; instead, precision-polished mirrors are used, coated with layers of molybdenum and silicon that reflect EUV light with about 70 percent efficiency. After bouncing through six to eight mirrors, only a small fraction of the original light reaches the wafer.
The light source itself is extraordinary. A powerful laser fires at tiny tin droplets — smaller than the period at the end of this sentence — at a rate of 50,000 times per second. The laser vaporizes each droplet into a plasma, which emits EUV light. This plasma is hotter than the surface of the sun.
The machine collects the EUV light, focuses it through the reflective optical system, and projects it through a reflective mask (ordinary transmissive masks would absorb the EUV) onto the resist-coated wafer. The entire system must maintain optical alignment to tolerances of less than one nanometer — roughly the diameter of ten hydrogen atoms — while operating at high speed and maintaining that precision in an industrial environment.
ASML, the Veldhoven company that developed this system, spent approximately $9 billion over 25 years bringing it to market. The first EUV-produced chips entered volume production at TSMC in 2019, used in Apple's A14 processor — the first consumer chip made at the 5nm node.
Why ASML is a monopoly — and what that means
ASML is not merely the leading supplier of EUV lithography machines. It is the only supplier. No other company has managed to develop the technology. IBM, Intel, and Motorola all participated in early research programs and eventually withdrew. Nikon and Canon — ASML's competitors in conventional lithography — never developed a working EUV system.
This monopoly is not incidental. It reflects decades of accumulated expertise, intellectual property, and supply chain relationships that cannot be replicated quickly. The precision required to manufacture EUV machines — their mirrors alone are polished to tolerances where, if scaled to the size of Germany, the tallest peak would be one centimeter — represents the work of thousands of engineers over decades.
The geopolitical implications became visible in 2019, when the United States government asked the Dutch government to revoke ASML's export license for EUV machines to China. The Dutch complied. China has not received a single EUV machine. Its domestic equivalent programs have shown some progress, but as of 2026, no Chinese company has produced working EUV equipment at the manufacturing scale ASML achieves.
Next lesson: Taiwan's Invisible Power — why a single foundry on a geographically small island has come to produce most of the world's most advanced chips, and what that means for everyone.
Reading time: approx. 10–11 minutes