Everyone’s talking about a new technology in the semiconductor industry – EUV lithography. It uses extremely short-wave ultraviolet light to produce microchips in the tiniest format that can process enormous quantities of data in computers and smartphones. A team of Bühler customers has developed a system for EUV lithography and won the German Future Prize 2020.
The prestigious German Future Prize, the German Federal President’s Award for Technology and Innovation, has been awarded in 2020 to a team that has made a significant contribution to the development of a marketable solution for EUV lithography. The expert team consists of Dr. Peter Kürz from Carl Zeiss SMT, Dr. Michael Kösters from Trumpf Lasersystems, and Dr. Sergiy Yulin from the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) based in Jena, Germany. On November 25, the German Federal President Frank-Walter Steinmeier presented the renowned research prize to the three scientists. Together they developed a system for EUV lithography in which they also used coating systems from Bühler Leybold Optics. In an interview, Dr. Sergiy Yulin from Fraunhofer IOF talks about the collaboration with Bühler.
Dr. Yulin’s contribution to the project was the development and optimization of the coating stack of the mirrors integrated in the system. These consist of hundreds of individual molybdenum and silicon thin-film layers to achieve the highest possible degree of light reflection in the EUV range, thereby maximizing the productivity of the entire system.
Dr. Yulin, congratulations on you win. At the beginning of your work in 2002, no suitable coating system for your project existed on the market. Why wasn’t it possible to work with any of the technologies available at the time?
Our goal was to develop coating technologies for applications in EUV lithography. The requirements for these optics could no longer be met by the existing research facilities. This applies especially to requirements for substrate sizes and the possibility of producing coatings with very precise lateral gradients. We were convinced that we had to take the step from the evaporation technology that was widely preferred at that time for EUV coatings to sputtering technology and that at least four target materials would be required to control the interfaces with atomic precision.
What was the key to the breakthrough in plant technology?
That isn’t easy to answer. It was mainly the combination of different technical sub-aspects, the possibility of varying coating parameters across a very wide range along with other issues such as high process stability and reproducibility. Six cathodes gave us the ability to produce coatings with designs of greater complexity. Consequently, barrier coatings, oxidation protection layers, and smoothing layers were specifically developed and implemented to increase the performance and lifetime of the mirrors. This was an important basis, for example, to create systems with the highest possible degrees of reflection at 13.5 nanometers of up to 70 percent and extreme stability, such as at high temperatures of up to 600° C. We now use these approaches for practically all coatings for very short wavelengths, even beyond EUV.
What were the biggest hurdles you had to overcome?
One important challenge was the size of the substrates to be coated. The objective was not only to develop new coatings on a laboratory scale, but to scale them directly to dimensions that are relevant to the application. The implementation of gradients over large substrate surfaces requires precise knowledge and high stability of distribution in the system. It is therefore an elaborate process that requires a lot of test processes and extensive measurements. And, as I said, the number of cathodes plays a significant role for the possibilities of layer design and interface engineering. Of course, it took a great deal of work to convince the demanding high-end customers of the value of our technology.
In cooperation with Bühler Leybold Optics, the coating technology has been further developed in line with the continuous stream of new discoveries. How important was the collaboration with the system supplier for you?
The remote service option was a great help in discussing and solving problems during the first campaigns with the new technology. The exceptional demands relating to coating homogeneity and the implementation of precise coating thickness gradients was a very big challenge as well as being in an uncharted territory both in research at our company and in plant construction at Bühler Leybold Optics. Without a direct and open discussion in both directions, we would certainly not have come this far. I think Leybold Optics found us very challenging at times, but in the end this was the key to the breakthrough and both sides learned a great deal.
In addition to the basic development, commercial implementation is also a very important issue with EUV technology. What role did Fraunhofer IOF play in the practical implementation?
At the Fraunhofer Institute, we are closely involved with the industrial implementation of our research work. The interplay between research and application-oriented development as well as a solid value chain consisting of design, optics manufacturing, cleaning, characterization, coating, and logistics are a special strength at Fraunhofer IOF that also brings us international success in other fields, such as space optics. The boundaries between application-oriented research and production are sometimes not well-defined. Fraunhofer Institutes often act as an “enabler” for innovations in companies, because demonstrators can already be implemented due to their broad competence and comprehensive technology platforms, even when supply chains have not yet been established due to the small quantities and high risks entailed in the development phase. The importance of Fraunhofer, especially in this phase in the field of EUV lithography, is shown clearly, for example by projects with Intel, Cymer and ASML, that have even honored us with distinctions such as the “Cymer Supplier Award” – which was really wonderful. We then applied our discoveries to the industry in various ways, on the one hand through know-how transfer based on more than 15 patents, and also by intelligence – and more than 10 of our experts are now working in relevant companies. Finally, in 2015, the spinoff optiXFab was founded by my longstanding colleague Torsten Feigl, which has been successful in the market ever since. At the same time, we are continuing our research activities, for example moving towards even shorter wavelengths and other applications, such as microscopy in the so-called water window. There is still a lot to do.
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