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With its first tool sales on the books, Eindhoven-based “start-up with experience” SALD is poised to introduce atomic layer deposition in a variety of new markets.
In the world of material deposition, nothing beats atomic layer deposition (ALD) when it comes to precision. The technique provides control over layer thickness and composition at the atomic level, while fully following the contours of a surface. However, this precision has its price: In its traditional form, ALD is not compatible with a continuous process. This restricts the production quantities that can be handled inexpensively and makes ALD unsuitable for a large number of commercial applications.
SALD has set out to change that. Founded in 2019, the company has developed devices for continuous ALD on a variety of substrates, enabling a number of industries that previously did not dream of using ALD to apply deposition technology. “We are working with companies and research institutes from all over the world to see how they can take advantage of ALD’ed functional nanolayers,” says Peter Visser, Business Developer at SALD.
SALD’s spatial ALD R&D tool. Photo credit: SALD / Oscar Vink
Three customers are already convinced and have bought an R&D tool from the Eindhoven-based company. When these and future customers have perfected their film recipes, SALD is confident that it will be able to deliver quickly with suitable production systems. “We can not only rely on the comprehensive know-how in system integration and plant construction in the Eindhoven Brainport region, SALD is a startup with experience,” says Visser.
Three billion
To see how this can be true, we have to look back to 2010 when the research institute TNO outsourced Solaytec to commercialize ALD devices for solar cell manufacturing. Or more precisely, to commercialize spatial ALD equipment for solar cell production.
ALD generally involves exposing a substrate to various gases, which react in a self-limiting manner with the surface, literally “coating” it atomic layer by atomic layer. In traditional (ie, temporal) ALD, the substrate remains stationary while a reactor is sequentially filled with the appropriate gases and emptied. With spatial ALD, on the other hand, the substrate is guided through alternating gas zones and forms a film during movement.
Solaytec’s spatial ALD equipment was designed to deposit a nano-layer of aluminum oxide on solar wafers, resulting in additional efficiency compared to other deposition methods. Several high-end solar cell manufacturers bought the company’s SALD tools, and they are still running today, but as the alumina layer became more prevalent in solar energy, so did the much cheaper Chinese batch ALD tools.
This forced Solaytec to investigate whether spatial ALD could broaden its horizons. When the answer was a resounding yes, the sister company SALD was founded. With decades of experience in the bag, of course, it doesn’t have to start from scratch. “When three billion wafers have run through your equipment in a part of the world where maintenance is not necessarily a high priority, you learn a thing or two,” assures Erik Kremers, CTO of SALD.
puzzle
This does not mean that Solaytec machines can be used for other applications. After all, they were developed for a very specific purpose: the deposition of aluminum oxide on solar wafers. Processing different sized, thick or thin or flexible substrates would not work, and the technology was never intended for the deposition of any material other than aluminum oxide.
And so SALD has developed a much more versatile version of spatial ALD over the past two years. “Everything boils down to the drop head, which we have made into a modular and scalable concept,” explains Kremers. A deposition head guides a gaseous precursor through parallel channels onto the moving substrate. Since the ALD process consists of two complementary half-reactions, two heads in sequence are required to complete the deposition of a single ALD layer in one pass. Inert gas ‘curtains’ built into each head prevent the reactants from mixing.
SALD target markets
SALD is currently monitoring a wide variety of markets. The most important perspectives are all in the area of cleantech:
– Solar 2.0. The introduction of ALD layers in thin-film CIGS or perovskite solar cells (tandem) of the next generation can significantly increase their performance.
– batteries. In lithium-ion batteries, an ALD-coated nano-layer, which protects the electrodes from the electrolyte, increases the stability and prevents the formation of harmful dendrites. The manufacture of the next generation of fast-charging high-performance solid-state batteries includes the coating of 3D nanostructures, for which spatial ALD is ideally suited.
– Packaging. ALD can be used to lay down airtight barrier layers that increase the shelf life of packaged goods and reduce the use of plastics or other packaging materials.
Through research partnerships, SALD is also investigating the potential of ALD in fuel cells and devices that capture CO2 from the ambient air.
Kremers: “In order to deposit more layers, as many heads are installed as are necessary to achieve the desired layer thickness. However, this type of configuration is only relevant for large-scale production. In our R&D tool, which prefers a small footprint, the substrate swings under three alternating heads in an ABA configuration. It is crucial that we use the same application heads in our R&D and production tools. The transformation of R&D into an industrial process will be smooth. ”SALD is currently assembling its R&D tools in-house, but plans to outsource the production of tools for industrial volumes to a systems integrator in the Brainport region.
Peter Visser (left) and Erik Kremers. Photo credit: Max Kniefel
The width of the separation head, typically a few centimeters, is determined by the separation properties of the gas flowing through it – with the SALD system, nano-layers made of many different materials can be deposited, even mixing of materials and layers is possible. However, the length of the head is flexible to accommodate a range of substrate widths that vary for different applications. “We switched to 3D printing to produce our rather complex application heads. So we can easily change the head length according to customer requirements. It is also a very reproducible method, ”reveals Visser.
“Solaytec’s heads are made of aluminum. We have switched to stainless steel, which is inert and therefore easier to clean chemically. Our new application head design greatly reduces contamination problems, but if one head needs cleaning it can simply be removed and replaced with another for off-line cleaning, ”adds Kremers.
The last piece of the puzzle to expand the scope of spatial ALD is substrate handling. Visser: “The Solaytec systems use gas cushions to transport the wafers. This method is not compatible with many substrates such as battery electrodes or plastic sheeting. That is why we develop suitable solutions to move our customers’ substrates past the separation heads. Our R&D tool has an oscillating stage while we expect high volume applications to include roll-to-roll production. We want to prove that next year. “
The SALD separator head in an ABA configuration. Photo credit: SALD / Oscar Vink
idea
There is more on the company’s roadmap, which currently employs 25 people. “Many ALD processes require elevated temperatures, if only to prevent the condensation of reaction partners such as water. That is why we are working on including plasma ALD in our offer. Plasmas are more reactive, which in itself makes sense, but can also be used to lower the process temperature, ”says Kremers.
SALD learns new things every day when sampling for customers. “Every day we have two people who take samples for customers. We get orders for all possible combinations of substrates and nanolayers. This gives us a wealth of experience that we use to help our customers get the most out of our tool, ”says Visser. In order to further promote application development, SALD works with the Plasma Materials Processing Group at the Technical University of Eindhoven and participates in a national spatial ALD research program.
So the big question is when customers will take the plunge and start integrating SALD’s spatial ALD technology into their manufacturing processes. It’s hard to predict, but Kremers has a clue which market will be first. “Next-generation thin-film solar cells have layers that can only realistically be deposited with ALD. The solar market is also already familiar with this technology. So I suspect that solar energy will get the ball rolling, but of course I wouldn’t be surprised if another green market develops even faster than that. “
This article was written in close collaboration with SALD.
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