27 March 2014 Positive tone cross-linked resists based on photoacid inhibition of cross linking
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A resist imaging design that utilizes photoacid inhibition of cationic polymerization and cross-linking during a postexposure bake step has been studied. The key to the design approach is the use of two different polymerization catalysts/initiators: (1) a photoacid produced from a photoacid generator (PAG) upon exposure of the resist that can result in polymerization and cross-linking of the resist matrix and (2) a thermal cross-linking catalyst (TCC) designed to thermally catalyze epoxide-phenol cross-linking. The TCC can be chosen from a variety of compounds such as triphenylphosphine (TPP) or imidazole. When only one of these catalysts (e.g TPP or photoacid) is present in an epoxide and phenol containing resist matrix, it will individually catalyze cross-linking. When they are present together, they effectively quench one another and little to no cross-linking occurs. This approach can be used to switch the tone of a resist from negative (photoacid catalyzed) to positive (TCC catalyzed and photoacid inhibited). The effect of the ratio of TCC:PAG was examined and the optimal ratio for positive tone behavior was determined. Resist contrast can be modified by optimization of epoxide:phenol ratio in the formulation. Dual tone behavior with positive tone at low dose and negative tone at higher doses can be observed in certain formulation conditions. Initial EUV patterning shows poor results, but the source of the poor imaging is not yet understood.
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Richard A. Lawson, Richard A. Lawson, Jun Sung Chun, Jun Sung Chun, Mark Neisser, Mark Neisser, Laren M. Tolbert, Laren M. Tolbert, Clifford L. Henderson, Clifford L. Henderson, "Positive tone cross-linked resists based on photoacid inhibition of cross linking", Proc. SPIE 9051, Advances in Patterning Materials and Processes XXXI, 90510E (27 March 2014); doi: 10.1117/12.2046619; https://doi.org/10.1117/12.2046619

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