Water-Soluble Onium Salts - American Chemical Society

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Chapter 8

Water-Soluble Onium Salts: New Class of Acid Generators for Chemical Amplification Positive Resists Toshio Sakamizu, Hiroshi Shiraishi, and Takumi Ueno

Downloaded by FUDAN UNIV on March 17, 2017 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0614.ch008

Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185, Japan

Alkyl-substituted-sulfonium salts were synthesized and investigated with a view to applying them as the acid generator in chemical amplification positive resists. It was found that the solubility in water of alkyl-substituted onium salts is high, while that of triaryl-substituted onium salt is quite low. This dissolution promotion ability of alkyl-substituted onium salts increase with the decreasing molecular size of the alkyl group. The quantum yield for acid generation from dialkylarylsulfonium salt was one order of magnitude larger than those of trialkyl-substituted onium salts. A difference was observed in acid-generation efficiency between electron-beam exposure and deep-UV exposure. We will discuss with this difference in terms of acid generation mechanism. Water-soluble onium salts were determined to be effective acid generators for electron-team exposure: they can produce high resolution patterns (100-nm contact holes). Diaryliodonium salts and triarylsulfonium salts, which have been employed as photoinitiators for cationic polymerization (1), are widely used as photoacid generators for chemical amplification resist systems (2). These arylonium salts used in the resist systems exhibit a strong dissolution inhibition capability in an aqueous base developer because these onium salts are little soluble in the developer (3,4). Thus, the dissolution inhibition effect of the acid generator in positive resist lowers process latitude (5). Chemical amplification resists utilizing various non-ionic acid-generators have been reported(