EUV lithography optics from ZEISS

In 1970, there was room for about 1,000 transistors on a microchip. Today there are 57 billion (semiconductor) components on an area only slightly larger than a fingertip. Mikrochips show structures 5,000 times finer than a human hair and are produced with light of the extremely short wavelength of 13.5 nanometers. For this purpose, EUV lithography optics from ZEISS SMT are used in production (no distribution in Germany). EUV technology is pushing the boundaries of what is technologically possible. For the next technological breakthrough. For future trends such as autonomous driving, artificial intelligence and 5G. For a digitalized life and work.  

EUV stands for "extreme ultraviolet" light. The light visible to humans has wavelengths between 400 and 800 nanometers. The range of ultraviolet light begins below 400 nanometers. The leading lithography process to date using "deep ultraviolet light" (DUV) operates at a wavelength of 193 nanometers. This makes structures with dimensions of 40 nanometers possible. EUV lithography uses light with an extremely short wavelength of 13.5 nanometers. Thus enables structures with dimensions of less than 20 nanometers.

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 are fired into a vacuum chamber every second. In there they are struck by two consecutive pulses from a high-power CO2 laser from TRUMPF. The so-called pre-pulse hits the tin droplets so that they virtually swell up. The trailing main pulse now hits the droplet at full power. This ignites the tin plasma, which emits the EUV radiation. To generate EUV light, the plasma has to be heated to a temperature of nearly 220,000 degrees Celsius. This is almost 40 times hotter than the average surface temperature of the sun.

Extremely thin layers of silicon and molybdenum – only a few atomic layers thick – are vapor-deposited onto the glass surface. For this, up to 100 layers lie on top of each other here. A single layer would only reflect a good one percent of the light – the loss would be far too great. To increase the efficiency of the mirrors, ZEISS SMT has developed a unique coating system together with the Fraunhofer Institute IOF that requires atomic-based precision. The layer thicknesses are only a few nanometers thin. The result is a reflectivity that makes up to 70 percent of the light usable. This happens through constructive interference: the EUV light is reflected by individual layers in each case. When these are precisely superimposed, the light is amplified because the individual radiation waves are perfectly superimposed.

The mirrorblock is part of the wafer stage and has precisely manufactured support structures for wafers and optical sensors. It enables precise alignment of the wafer to the mask and projection optics for the wafer exposure. Despite thermal loads and high dynamic stress in the wafer scanner, the mirrorblock keeps its shape almost perfectly.