Newswise — WASHINGTON, D.C., October 23, 2018 -- An international team of researchers has developed a new class of molecular layer deposition (MLD) chemistry that paves the way for a new photoactivated molecular layer deposition (pMLD) technique. They report that their new method will expand the tool kit for forming covalently bound organic multilayers at surfaces. These emerging deposition techniques have enabled engineers to produce organic thin films with improved conformality.
Stanford University professor Stacey Bent investigates how MLD and pMLD could be used to improve semiconductor processing and nanotechnologies. Richard Closser, a student in Bent’s lab, will present the team’s findings at the upcoming AVS International Symposium and Exhibition, taking place in Long Beach, California, Oct. 21-26, 2018. His talk, “Photoactivated Molecular Layer Deposition of Fluoropolymer Thin Films,” is featured in the Thin Films Division session.
Like atomic layer deposition (ALD), MLD takes advantage of the sequential, self-limiting surface reactions that allow researchers to deposit thin films with angstrom-level thickness control onto high aspect-ratio features, but applied specifically to polymer film deposition. Conventional MLD techniques preclude researchers from using solvents and many catalysts because of its vapor phase nature. As a result, most MLD polymers do not include carbon-carbon bonding moieties, which prevents common polymers from forming.
In pMLD, UV light activates monomers to create metastable radicals that the researchers then react with alkenes. At the AVS symposium, Bent will explain how the team deposited an alternating hydrocarbon-fluorocarbon polymer via pMLD using bifunctional diiodofluoroalkanes and dienes. They then used ellipsometry to verify that the deposition occurred at a constant growth rate and displayed saturation behavior. Furthermore, X-ray photoelectron spectroscopy confirmed that new carbon-carbon bonds formed.
“We wanted to see if we could direct energy input from UV light to induce formation of covalent, nonpolar C-C linkages. The result was the pMLD process that we report,” Bent said. Ultimately, their fluoropolymer exhibited high-temperature stability up to 400 degrees Celsius and chemical resistivity to a battery of acids, bases and solvents. The team is now testing the pMLD film for ALD inhibition; they have shown that other organic films can block up to 100 cycles of ALD and hope to expand the types of organic layers that inhibit ALD. This is significant because “area-selective ALD allows patterned films to be formed by a bottom-up, additive process without the need for repeated lithography and etch steps,” Bent explained.
Going forward, the team plans to continue to explore new MLD and pMLD chemistries. “The development of pMLD enables a variety of new organic synthesis methods previously unavailable to MLD, including the potential for some click chemistry and new ALD-MLD hybrid materials,” said Bent. “We will also expand on our previous studies to understand the growth mechanisms and properties of these promising films.”
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Presentation “Photoactivated Molecular Layer Deposition of Fluoropolymer Thin Films,” by Richard Closser, Mie Lillethorup, David Bergsman, Jingwei Shi and Stacey Bent, is at 5 p.m. PT, Oct. 23, 2018, in Room 102A in the Long Beach Convention Center, Long Beach, California.
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MORE ABOUT THE AVS 65TH INTERNATIONAL SYMPOSIUM & EXHIBITION
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Meeting Link: AVS 65th International Symposium and Exhibition
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