Improving the Sensitivity of Sulfonium-Based Nonchemically Amplified Resists by Modulating the Bond Energy of the Photosensitive Group

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A series of nonchemically amplified resists based on dibenzothiophenium-functionalized polystyrene (PSSDx, x is the loading ratio of the sulfonium, x = 0.5, 0.7, 1.0) were designed and prepared. The lithographic performance of PSSDx resists was evaluated by electron beam lithography (EBL). The PSSD0.7 resist exhibited superior resolution (20 nm) compared with PSSD0.5 (25 nm) and PSSD1.0 (22 nm) resists under the same EBL processing conditions. By reducing the film thickness to 25 nm, the PSSD0.7 resist resolved the 18, 16, and 15 nm L/S patterns at doses of 1200–1500 μC cm–2 with LERs of 3.0–3.3 nm, demonstrating a superior comprehensive performance to the previously reported triphenylsulfonium-based PSTS0.7 model resist (18 nm L/S at 2400 μC cm–2). The PSSD0.7 resist was further investigated by extreme ultraviolet lithography (EUVL), achieving an impressive 14 nm pattern with a line edge roughness (LER) of 3.0 nm at an exposure dose of 148 mJ cm–2. The quartz crystal microbalance (QCM) analyzer confirms that the solubility behavior of PSSD0.7 and PSTS0.7 model resist films is not the main reason for the difference in sensitivity. The calculation and photochemical kinetics study suggest that the significantly reduced bond energy and the enhanced efficiency and rate of the photochemical reaction with the dibenzothiophenium group play a key role in the excellent lithographic performances of the PSSD0.7 resist.