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23 June 2000 Design and study of aqueous processable positive-tone photoresists
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Interest in developing materials with reduced environmental impact has led us to design resist formulations that can be cast from and developed with aqueous media. A water soluble chemically amplified positive tone photoresist based on thermal decarboxylation of a half ester of malonic acid has been designed. Two solubility switches are required for this application. Sequential volatilization of ammonia followed by decarboxylation of a malonic acid gives the first solubility switch and an acid catalyzed thermolysis of an acid labile protecting group gives the second. The thermal stability of the acid labile protecting group is critical in this design. Tert-butyl esters decompose during the decarboxylation process resulting in poor imaging contrast. Polymers bearing isobornyl esters are more thermally stable, and show excellent reaction selectivity between the decarboxylation and the thermolysis of the ester. Preliminary imaging of this system provided 1 micrometer resolution with 248 nm exposure and standard TMAH developer. The dry etch stability of the photoresist films is comparable to a conventional photoresist APEX-ER.
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Shintaro Yamada, Jordan Owens, Timo Rager, Morton Nielsen, Jeff D. Byers, and C. Grant Willson "Design and study of aqueous processable positive-tone photoresists", Proc. SPIE 3999, Advances in Resist Technology and Processing XVII, (23 June 2000);

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