Dynamics of Radical Cation of Poly(4-hydroxystyrene)-Based Chemically Amplified Resists for Extreme-Ultraviolet and Electron Beam Lithographies

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The elucidation of the reaction mechanism after the irradiation of ionizing radiation onto resist polymers is an important issue for extreme-ultraviolet and electron beam chemically amplified resist. The dynamics of radical cations of polymers is essential for elucidating the mechanism of acid formation (deprotonation) in resists. The transient absorption of poly(4-methoxystyrene) (PMOS) was observed in 1,2-dichloroethane and p-dioxane solutions by pulse radiolysis. In the near-infrared region, a characteristic charge resonance band, which represents the $\pi$–$\pi$ interaction between the two benzene rings of the intramolecular PMOS dimer radical cation [(Ph–OCH3)2+$\cdot$], was observed. In the presence of halogenated hydrocarbon molecules acting as electron scavengers, the yield of (Ph–OCH3)2+$\cdot$ was enhanced by the formation of an ion/charge transfer complex. Density functional theory (DFT) calculations were also performed to investigate the electronic state of (Ph–OCH3)2+$\cdot$.
2010-10-25