Smarter, smaller, more powerful devices are only possible thanks to EUV lithography, an optical technology that uses extreme ultraviolet light to create highly advanced microchips. optiX fab in Jena, Germany plays a crucial role in this process, working with a high level of precision at an unimaginably tiny scale. Bühler has been at the side of the company’s founders for more than 20 years, supporting their success in this growing and important market.
Janet Anderson, February 2023
“We work in single digit picometer coating thickness accuracy,” says Dr. Torsten Feigl, CEO of optiX fab. “Imagine a millimeter divided in a thousand, that is a micrometer. Now divide a micrometer again by a thousand, that is a nanometer. Then if you divide a nanometer by a thousand, you get a picometer. In other words, it is equal to one trillionth of a meter. The human brain cannot imagine this world. It is as difficult as imagining light years.”
optiX fab is one of the few companies in optics that work at such a tiny scale. It does so in order to coat the most precise mirrors in the world, needed in the manufacture of advanced microchips.
As computer chips have gotten smaller and the amount of data that can be processed on them has grown, this means that writing on them must be carried out at the smallest resolution. The only way to do this is with EUV lithography, which uses extremely short-wave ultraviolet light to burn circuits on the chip. In order to focus the light beam, super-polished mirrors are used that have been coated with a highly reflective EUV layer system made of over 100 layers each only nanometers thick. This is where optiX fab’s expertise lies – working with atom level precision.
Based in Jena, the historic capital of the optics industry in Germany, optiX fab carries out its extraordinary work in an ordinary-looking old factory building. But looks can be deceptive. Thanks to the building’s history, it is the perfect place for Dr. Feigl and his team to work. Built in 1934 by Zeiss, the German manufacturer of optical systems and optoelectronics, it is one of the most stable industrial buildings in Germany. Each square meter can bear a load of 3.5 tons with no vibrations – nothing moves.
These are exactly the conditions optiX fab needs to house and operate its four NESSY coating machines, provided by Bühler. The NESSY is a magnetron sputtering system which optiX fab uses to coat the mirrors for EUV lithography. Each of the 12-ton machines fits neatly into the spaces between the pillars of the old building and can operate faultlessly for hours on end. “It is almost as if Zeiss knew back then what we would need to carry out EUV lithography today,” says Dr. Feigl with a smile.
optiX fab is a spin off from the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF). Dr. Feigl had been at the head of a working group at IOF that made extreme ultraviolet (EUV) coatings for the semiconductor industry and had already worked with NESSY, the first of which was delivered to IOF by Leybold Optics (now Bühler) in 2003.
The machine was developed by the two teams working together to meet the high requirements of the rapidly changing technology and market. As demand grew for chips that were faster, with more memory and more power at the same size, the industry began using light at shorter wavelengths to print smaller structures on the chips, shifting from 248 nanometers (nm) to 193nm.
“By the mid-1990s, it was not clear what technology the next generation of chip would require,” says Dr. Feigl. “That was when the industry decided to explore EUV – extreme ultraviolet.” There were several challenges with using this new wavelength. This meant a major shift in the hardware required – and NESSY was the result. In 2013, Dr. Feigl decided to take the technology and commercialize it.
EUV rays lie between X rays and UV rays. In this part of the spectrum, it is not possible to use lenses to focus the light to write on a chip. The reason is that at 13.5 nm the rays are absorbed by the materials around them. Instead of lenses, precisely shaped mirrors are therefore used to focus the light. And since even air absorbs the rays at this wavelength, the chips must be printed in a vacuum. Finally, at this wavelength the construction of the mirror requires great expertise to achieve sufficient reflectance. At a wavelength of 13.5 nm, each layer of coating on the mirror is only a fraction of a percent reflective. To make the mirror sufficiently reflective requires a complex multilayer coating.
“This is what we do at optiX fab,” says Dr. Feigl. “We take a highly polished substrate and build up layers of coatings.” The layers are built up of alternating materials, such as molybdenum and silicon. The alternating layers could be, for example, 2.7 nm and 4.2 nm thick respectively, built up in pairs to around 100 layers.
As the light passes through each layer, due to absorption it is reflected less and less the lower the layer – as little as 0.1% . The expertise is in building up the layers in such a way that together they create sufficient reflectance. The key to this is using the right materials, at the right thickness, in the right places – and this is where single-digit picometer accuracy is required. “We have to develop a coating recipe for each mirror. That’s a process that can take anything up to 2 years. When we get it right, we are able to achieve over 70% reflectance,” says Dr. Feigl.
The largest mirror that optiX fab has coated to date is a 662-millimetre diameter collector. Weighing 40 kilograms, it took a year to develop the coating recipe. There were 300 layers on the substrate. The angle of incidence varied from 6 degrees at the center to 36.5 degrees at the edge, requiring a variation in thickness of the layers from 6.883 nm to 8.459 nm – all at an accuracy of less than 10 picometers.
The machine needs to be stable over 12 hours to achieve this. With NESSY, Bühler made that happen. It is an engineering masterpiece.
Dr. Torsten Feigl, CEO of optiX fab
Today they achieve 1, 2, or 3 picometers accuracy. For a recent customer from Ireland, the team worked with wavelengths of 2.745 nm. This meant building up 2,000 layers that were between 0.1 nm and 0.6 nm thick each. One of the key parameters was to ensure that the first layer in the multilayer stack has exactly the same thickness as the last one. “The machine needs to be stable over 12 hours to achieve this. With NESSY, Bühler made that happen. It is an engineering masterpiece,” says Dr. Feigl.
For Klaus Herbig, head of the precision optics market segment at Bühler, it is still astonishing what the optiX fab team achieves – even though he has worked with them since the beginning. “Their technology input is at the physical edge,” he says. “We know how to build the machine that does the coating with unmatched levels of layer precision. They know how to combine the different materials and to keep them stable over time. It is not easy. They have to understand the process well to do it properly. The success relies on their skill.”
optiX fab technology input is at the physical edge. They know how to combine the different materials and to keep them stable over time. The success relies on their skill.
Klaus Herbig, Head of the precision optics market segment at Bühler
In the old Zeiss building, optiX fab has installed the four NESSYs in a row in the machine room. A load lock separates the machine room from the clean room. The process starts in the clean room, where the substrate to be coated is put in a “flow box”. In the clean room, there is next to no dust or vibration. In the flow box, the air is even cleaner than in the rest of the clean room. The substrate is installed in the coating holder, then transferred to the load lock using so-called “touchless tools”. In the load lock, the air pressure is pumped down and the substrate is then transferred to the coating chamber of NESSY, which works under ultra-high vacuum conditions.
The coating then runs automatically. The substrate spins below the target in a planetary movement. All the movements, speeds, and distances are programmed and controlled on the instrument panel, including the level of vacuum.
Twelve engineers and physicists are on hand to look after the four NESSYs. The different coating materials are stored in the machine room too. Some of these are supplied by Bühler. As the substrates and coating materials can be very expensive, tests are carried out before using the real substrate. The substrate shape is copied in aluminum, silicon samples placed within it at specific coordinates, it is then coated, and measurements taken to check the target values have been achieved. The test runs are carried out over and over again. It might take anything from 10 to 100 attempts to be sure before using the real substrate.
Once NESSY has done its job and the coating is completed, the mirrors are transferred back through the load lock to the clean room. Next, they are packed, sealed, and sent to the National Metrology Institute of Germany (Physikalisch-Technische Bundesanstalt) in Berlin, which measures the EUV reflectance. With this, optiX fab can prove that it is delivering exactly what its customers require. The mirrors are then returned to Jena and shipped to customers around the world – to the Netherlands, United States, Japan and Korea, but also increasingly to customers within Germany. Since its foundation, optiX fab has created more than 21,000 EUV and soft X-ray mirrors using this process – an average of almost 10 a day.
Today it is an established part of the industry, but it was a big step to take at the beginning. “When I placed my first order for a NESSY from Bühler, we had no long-term contracts. Now we have four NESSYs and demand is growing so much we will soon need another,” says Dr. Feigl. As optiX fab celebrates its 10th anniversary, the need for connectivity between people and things continues to grow. Furthermore, to many people’s surprise, Moore’s law shows no signs of stopping – the number of transistors per chip continues to grow, and the race goes on to produce the smallest and most efficient microchips in the world.
And exciting new applications of optiX fab’s technology are emerging. One example is in space. Two years ago, they supplied a coated mirror for the European Space Agency’s Solar Orbiter, and they are now in contact with NASA about the next solar mission.
It is still a growing market. With e-mobility and autonomous vehicles, the requirement for advanced chips will skyrocket. And with the growth of artificial intelligence, the market is far from saturated.
Dr. Torsten Feigl, CEO of optiX fab
With 12 employees, expanding to 15 this year, optiX fab is ready to meet the challenges. “When I started in the 1990s it was not clear if EUV technology would ever make it to production. Now we have products made with this technology that are used by people around the world every day. For example, since the iPhone 12, Apple has used chips created with EUV lithography. We delivered the hardware that made that possible,” says Dr. Feigl.
“It is still a growing market. With e-mobility and autonomous vehicles, the requirement for advanced chips will skyrocket. And with the growth of artificial intelligence, the market is far from saturated.” Herbig agrees. “To exploit many of these opportunities, we need computer chips with ever greater capacity. The need for EUV lithography is set to grow, and Bühler and optiX fab are driving in the same direction,” he says.
The optiX fab team has the expertise and the experience to achieve this, but Dr. Feigl says they could not do it without NESSY. “Our brain power and NESSY together create the outcome. We are like Michelin star chefs working with top-notch kitchen equipment – that is what NESSY is for us.”
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