Lithography

Lithography is the most important step in manufacturing computer chips. A chip consists of billions of tiny switches arranged in ultra-thin layers on a silicon wafer. These patterns are not drawn or milled, but transferred using light. A template is projected onto the wafer in strongly reduced form, similar to how a slide projector casts an image onto a wall — only in reverse, going from large to small. The wafer is coated with a light-sensitive layer that changes chemically wherever light hits it. In subsequent steps, the exposed pattern is then etched into the material.

Why entire nations are fighting over these machines

How small the structures on a chip can be depends almost entirely on lithography. Smaller structures mean more switches on the same surface area. More switches mean more computing power at the same power consumption. Decades of progress in computing thus rest substantially on ever-better exposure machines.

The most advanced of these machines are built by only a single company worldwide: the Dutch corporation ASML. Depending on the configuration, a single machine costs between 150 and over 350 million euros and is delivered in several airplane loads. There is no second supplier that can keep up technically. This dependency turns the technology into a political issue.

The USA and the Netherlands have restricted the export of the best machines to China. The idea behind this: whoever lacks modern exposure machines cannot manufacture the most advanced chips — not even for artificial intelligence or military technology. Hardly any other industrial product currently carries as much foreign-policy weight.

From light to circuit trace

The process is always the same. A thin film of light-sensitive resist is applied to the silicon wafer. A mask — essentially a stencil bearing the desired pattern — is held above it. Light passes through the mask, is reduced in size by lenses and mirrors, and hits the resist. Afterward, the exposed resist is washed away and the exposed silicon is etched or coated with metal.

This cycle repeats eighty times or more for a modern chip, layer by layer. The layers must align on top of each other with precision down to a few nanometers. A nanometer is one millionth of a millimeter; a human hair is roughly 70,000 nanometers thick.

The limit is set by the wavelength of the light: the shorter the wave, the finer the possible pattern. For a long time, ultraviolet laser light with a wavelength of 193 nanometers was used. For the finest chips today, EUV is used — extreme ultraviolet light with a wavelength of just 13.5 nanometers. This light is generated by vaporizing tiny droplets of tin tens of thousands of times per second using a laser. Because it is absorbed by air and even by glass, the entire optical system must operate in a vacuum and consist of highly precise mirrors.

Lithography in the news and in your phone

You never see lithography directly. But every processor in a smartphone, every graphics card, and every AI accelerator in a data center was made this way. When a manufacturer advertises a “3-nanometer chip,” that is a marketing name for a manufacturing generation — it no longer describes an actually measured feature size, but rather a technology tier.

In business news, the term usually appears in connection with companies like ASML, TSMC, Samsung, or Intel. Debates about export controls, the European Chips Act, or new factories in Germany and the USA also revolve at their core around this technology. Anyone who understands what lithography does will understand such news much better.

A common misconception is that lithography is the only step in chip manufacturing. In fact, etching, coating, cleaning, and inspection are also needed. However, lithography is the step that defines the boundary of what is technically possible — and by far the most expensive one.