Study of electron-beam and extreme-ultraviolet resist utilizing polarity change and radical crosslinking

Resists used for the fabrication of next-generation of semiconductor circuits must exhibit resolution better than 10 nm and sensitivity comparable to or better than that of chemically amplified resists (no more than 1 mJ/cm² for the bulk sensitivity). As described previously [T. Kozawa, J. J. Santillan, and T. Itani, Jpn. J. Appl. Phys., Part 1 53, 106501 (2014)] acid diffusion in chemically amplified resists limits resolution to about 10 nm. To avoid acid diffusion without jeopardizing sensitivity, the authors propose a negative-type polymer resist for extreme ultraviolet (EUV) and electron beam (EB) lithography that utilizes the polarity change and radical crosslinking triggered by EUV/EB exposure. Polymers having triarylsulfonium cations and 2,2,2-trisubstituted acetophenone as side chains were designed to realize a dual insolubilization property. 2,2,2-trisubstituted acetophenone was incorporated for efficient radical generation on the polymer structure to induce crosslinking. An onium salt was incorporated for the efficient use of thermalized electrons to induce a polarity change and radical generation on the side chain. The authors demonstrated experimentally that these polymer resists require a dose between 1 and 2 mJ/cm² with EUV exposure.