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21 March 2007 Molecular glass photoresists containing photoacid generator functionality: a route to a single-molecule photoresist
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A single molecule photoresist composed of tris(4-(tert-butoxycarbonyloxy)-3,5-dimethylphenyl) sulfonium hexafluoroantimonate (TAS-tBoc) was successfully synthesized and characterized. The synthesized triarylsulfonium was found to perform comparably to a commercial triphenylsulfonium triflate photoacid generator (PAG) when used purely as a PAG in blended molecular glass resist. TAS-tBoc formed excellent amorphous films when spin-coated out of solution. When exposed to 248 nm UV radiation, TAS-tBoc showed a sensitivity of 4 mJ/cm2 and a contrast ratio between 6 and 15, depending on development conditions. Its etch rate under standard silicon dioxide etch conditions was 0.87 as standardized to that of tBoc-PHOST in the same RIE plasma conditions. The outgassing level of the resist under EUV exposure was determined to be 1.08 x 1013 molecules/cm2, well below the maximum outgassing cutoff that is considered acceptable for EUV imaging. When imaged by e-beam, TAS-tBoc showed a relatively high dose-to-clear of 150 &mgr;C/cm2 as compared to conventional chemically amplified photoresists. Lines down to 50 nm wide with aspect ratios of 2.5:1 were imaged using e-beam. These lines exhibited an LER of only 3.96 nm, significantly better than the typical LER for polymeric chemically amplified resist, even when imaged using e-beam, and also one of the lowest values reported for molecular glass materials in general.
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Richard A. Lawson, Cheng-Tsung Lee, Robert Whetsell, Wang Yueh, Jeanette Roberts, Laren Tolbert, and Clifford L. Henderson "Molecular glass photoresists containing photoacid generator functionality: a route to a single-molecule photoresist", Proc. SPIE 6519, Advances in Resist Materials and Processing Technology XXIV, 65191N (21 March 2007);

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