EUV lithography – how does it work?

The ASLM system exposes more than 170 wafers an hour with an extreme ultraviolet (EUV) beam. Here, exposing means structuring photoactive paint on wafers with an optical mask in around a hundred exposure passes with such precision that structures seven nanometers (nm) wide can be created. In doing so, EUV lithography makes it possible to realize ten billion transistors on a surface the size of a fingernail. The key is the leap from the 193 nm previously customary in chip exposure to a wavelength of 13.5 nm.

The technological core

The heart of the process is the laser optic system whose main components were developed by ASML with ZEISS, TRUMPF and the Fraunhofer IOF. In a vacuum, a pulsed 30 kW laser system from Trumpf fires 100,000 laser pulses per second at tiny droplets of tin. Each droplet is hit twice. The first pulse cuts the droplet into razor thin slices. The second pulse heats these to 220,000°Celsius, 40 times hotter than the surface of the sun. The tin vaporizes into plasma which emits EUV radiation. A collector mirror collects this radiation and directs it onto the wafer via several highly precise mirrors — according to Zeiss, “the most precise mirrors in the world.” The sensor and actuator technology of these projection optics works with such precision that a laser beam redirected with them would hit a golf ball on the moon. In order to achieve maximum reflectivity, the mirrors are made up of around 100 layers of silicon and molybdenum, each a few nm thin. According to Zeiss, if you were to scale the surface to the size of Germany, the largest deviation from its ideal form would be only 0.1 mm. By comparison: For the highly precise mirror optics used in space telescopes, it would be 2 cm. Another central condition for this nano precision is that the mirror material developed in cooperation with Jena-based Fraunhofer IOF researchers hardly expands at all under the heat.

The effect

Chips created using EUV lithography have a 40% higher surface efficiency and a 50% smaller energy demand than the previous generation of chips structured with 193-nm beams.

More information

You can find a very interesting documentary at Youtube