Self-Aligned Thin-Film Patterning by Area-Selective Etching of Polymers

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http://hdl.handle.net/10138/334604

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Zhang, C.; Leskelä, M.; Ritala, M. Self-Aligned Thin-Film Patterning by Area-Selective Etching of Polymers. Coatings 2021, 11, 1124.

Title: Self-Aligned Thin-Film Patterning by Area-Selective Etching of Polymers
Author: Zhang, Chao; Leskelä, Markku; Ritala, Mikko
Publisher: Multidisciplinary Digital Publishing Institute
Date: 2021-09-16
URI: http://hdl.handle.net/10138/334604
Abstract: Patterning of thin films with lithography techniques for making semiconductor devices has been facing increasing difficulties with feature sizes shrinking to the sub-10 nm range, and alternatives have been actively sought from area-selective thin film deposition processes. Here, an entirely new method is introduced to self-aligned thin-film patterning: area-selective gas-phase etching of polymers. The etching reactions are selective to the materials underneath the polymers. Either O<sub>2</sub> or H<sub>2</sub> can be used as an etchant gas. After diffusing through the polymer film to the catalytic surfaces, the etchant gas molecules are dissociated into their respective atoms, which then readily react with the polymer, etching it away. On noncatalytic surfaces, the polymer film remains. For example, polyimide and poly(methyl methacrylate) (PMMA) were selectively oxidatively removed at 300 °C from Pt and Ru, while on SiO<sub>2</sub> they stayed. CeO<sub>2</sub> also showed a clear catalytic effect for the oxidative removal of PMMA. In H<sub>2</sub>, the most active surfaces catalysing the hydrogenolysis of PMMA were Cu and Ti. The area-selective etching of polyimide from Pt was followed by area-selective atomic layer deposition of iridium using the patterned polymer as a growth-inhibiting layer on SiO<sub>2</sub>, eventually resulting in dual side-by-side self-aligned formation of metal-on-metal and insulator (polymer)-on-insulator. This demonstrates that when innovatively combined with area-selective thin film deposition and, for example, lift-off patterning processes, self-aligned etching processes will open entirely new possibilities for the fabrication of the most advanced and challenging semiconductor devices.


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