Moore's Law is also the result of a struggle along the resolution theory formulated by the German physicist Ernst Abbe in 1873.

Accordingly, the resolution of an optical instrument, such as a microscope, increases the smaller the wavelength of the light used.

The structures in the semiconductor material of computer chips are transferred to the silicon by means of light using so-called photolithography.

The more you manage to increase the resolution of the process, the finer structures can be realized - and the more transistors can be accommodated on a chip.

In the 1970s, the light from a mercury vapor lamp with a wavelength of 434 nanometers reached from the blue-violet, i.e. still visible, part of the spectrum.

Other light sources followed, and the last stage of development came in the early 2000s with the argon fluoride laser.

Its ultraviolet light has a wavelength of 193 nanometers.

However, as early as the late eighties, research began on a development that takes the integration density of microchips to a new level today: lithography with extreme ultraviolet radiation (EUV).

Extreme ultraviolet mirror

Dutch lithography machine maker ASML got into this research around the turn of the millennium, but it would take two decades to get the technology from the labs to the manufacturing floor.

That is directly related to the shortness of that wavelength.

At EUV it measures 13.5 nanometers.

This radiation is absorbed by oxygen atoms, which is why there must be a vacuum in the lithography machine.

“Before EUV, it all just worked in the air,” says Marco Pieters from ASML.

The comparatively longer-wave light could also be passed through glass lenses.

For EUV rays, however, glass is opaque.

Instead of lenses, curved mirrors therefore first direct the light onto a mask with the structures required in the respective manufacturing step and then onto the wafer.

These mirrors are among the most precise ever built.

The German physicist Peter Kurz developed it at the Zeiss company in Oberkochen.

"If you were to inflate one of these mirrors on the surface of Germany, the largest deviations from the target shape would be just 0.1 millimeters," says Kurz.

To generate the actual EUV rays, the machine shoots tin droplets with a laser.

This creates a plasma at 220,000 degrees Celsius that emits the rays.

Flying tin patties

For an industrial application, the radiation source must deliver at least 250 watts of power. Only then can the machine expose over 100 wafers per hour and thus work economically. For the lasers, ASML turned to the Swabian machine tool manufacturer Trumpf. In 2010 Michael Kösters took over the work on the EUV machine there. “Back then there were ten of us,” he recalls, “today about 250 people are working on the development.” In the meantime, even he had doubts whether they would ever achieve the required performance, admits Kösters. It wasn't because of the lasers themselves. With an output of 30 kilowatts, they are the most powerful pulsed industrial lasers in the world. The aim was to efficiently convert this power into extreme ultraviolet radiation.

A first crucial step was to hit each tin droplet twice. The first laser pulse expands the droplet into a kind of pancake. This means that it has the optimum diameter when the second pulse strikes and causes the plasma to glow extremely ultraviolet. Precision is required here. A nozzle fires 50,000 droplets per second one after the other into a chamber. They fly through a light barrier at around 360 kilometers per hour and trigger the laser. But even this system was not efficient enough at first. The droplets reflect part of the laser light back to its amplifiers. "If that hits the sensitive components, the beam starts to flicker," explains Kösters. He had to stabilize the laser. The solution was a system of adjustable crystals.They direct the actual laser pulse in the direction of the droplets. As soon as it is reflected, they change their lattice structure and bend the returning light in a different direction.

The finished machine is the size of a bus and weighs 180 tons. It takes three cargo planes to get them to ASML's customers. The company has built around 100 of these machines so far. Only four large semiconductor manufacturers are currently able to integrate them into their manufacturing processes. But all these superlatives are not forever. That's Moore's Law. ASML is working on higher resolutions. "We ask Zeiss: 'Can't we make the mirrors even smoother?'" Says Marco Pieters, thinking of even more performance. “That's tricky, but we're discussing it with Trumpf, for example.” Michael Kösters is already working on the matter and is thinking about how he could make his laser a bit more stable.