Comparison of Acid Generation in EUV Lithography Films of Poly(4-hydroxystyrene) (PHS) and Noria Adamantyl Ester (Noria-AD₅₀)

The mechanism for acid production in phenolic extreme ultraviolet (EUV) lithography films containing triphenylsulfonium triflate (Ph₃S⁺TfO^–) acid generator has been investigated by electron paramagnetic resonance (EPR) spectroscopy and by use of the acid indicator coumarin 6 (C6). Gamma radiolysis was substituted for the EUV radiation with the assumption that the chemistry generated by ionization of the matrix does not depend on the ionization source. Poly­(4-hydroxystyrene) (PHS) was first investigated as a well-studied standard, after which the water-wheel-like cyclic oligomer derivative containing pendant adamantyl ester groups, noria-AD₅₀, was investigated. EPR measurements confirm that the dominant free radical product is a phenoxyl derivative (PHS-O^• or noria-O^•) that exhibits quite slow stretched exponential recombination kinetics at room temperature. Also observed at 77 K was the presence of a significant hydrogen atom product of radiolysis. The <i>G</i> value or yield of acid production in thin lithography films was measured with the C6 indicator on a fused silica substrate. It was found that a significant amount of acid is generated via energy transfer from the irradiated fused-silica substrate to the Ph₃S⁺TfO^– in the films. By varying the film thickness on the substrates, the substrate effect on the acid yield was quantitatively determined. After subtraction of the contribution from the substrates, the acid yield <i>G</i> value in the PHS film with 10 wt % Ph₃S⁺TfO^– and 5 wt % C6 was determined to be 2.5 ± 0.3 protons per 100 eV of radiation. The acid yield of noria-AD₅₀ films was found to be 3.2 ± 0.3 protons per 100 eV