EUV lithography

In order to generate the EUV light, ASML and TRUMPF designed a unique light source. In a plasma source developed by ASML, 50,000 droplets of tin per second are fired into a vacuum chamber, where they are struck by two consecutive pulses from a high-power CO2 laser from TRUMPF.

To generate EUV light, the plasma has to be heated to a temperature of nearly 220,000 degrees Celsius. – almost 40 times hotter than the average surface temperature of the sun. With 30 kilowatts of power, the TRUMPF laser required for this process is the most powerful industrial laser in the world.

Since ultraviolet light is absorbed by all materials – including air, ZEISS SMT created an optical system  for the EUV lithography machine that operates in the vacuum chamber and is made up of mirrors. Because the mirrors have to be held in position as precisely as possible during the exposure process, an entirely new mechatronics concept was required for maximum tilt stability. The results speak for themselves: If one of these EUV mirrors were to redirect a laser beam and aim it at the Moon, it would be able to hit a ping pong ball on the Moon’s surface.

The mirrors are also the product of significant innovations. Since even the smallest irregularities cause aberrations, the world’s “most precise” mirror had to be developed for EUV lithography. If this mirror were to be enlarged to the size of Germany, the height of the Zugspitze mountain would be just 0.1 millimeters. In addition to such high precision, EUV mirrors require maximum quality and reflectivity.

The Fraunhofer Institute IOF served as an important research partner for the development of EUV mirrors through special multi-layer coatings, so-called Bragg mirrors. Here, a layer stack consisting of more than 100 layers, each one just a few nanometers thick, is applied with atomic precision. The particular challenge is achieving the highest reflexivity possible over the entire mirror surface as well as the longevity of the coating during exposure to EUV light.