In chemically amplified resists that utilize acid-catalytic reactions for pattern formation, proton dynamics is important from the viewpoints of the insoluble layer formation due to acid loss, the resolution decrease due to acid diffusion, and the image quality improvement due to base-quencher effects. For electron-beam lithography, the protons and anions of the acid are initially generated at different places. Protons migrate in the resist matrix toward counter anions, attracted by the opposite electric charges. However, the details of proton migration are still unclear. In this study, we investigated proton quenching in poly(4-hydroxystyrene) films using base quenchers with different proton affinities. When the proton affinity of the base quencher was increased, the equimolecular proton adduct of the acid-sensitive dye was quenched without postexposure bake. Although the proton affinity is a gas-phase value, the quenching effect correlated well with the proton affinity.
Protons generated in chemically amplified resists drive pattern formation reactions such as acid catalytic deprotection reactions. Proton dynamics is controlled by the addition of base quenchers so that ultrafine patterns are obtained. However, the details of interaction between protons and base quenchers are still unclear. In this study, we investigated the reactions of protons with base quenchers in a model system of chemically amplified resists with a typical backbone polymer, poly(4hydroxystyrene). We confirmed that an acid-base equilibrium was reached in the model system without elevating the temperature of the films. The proton affinities of resist ingredients give us a general estimation of protonation sites. When the proton affinities of resist ingredients are close to each other, we have to take into account acid-base equilibrium using pK a for the accurate prediction of protonation sites.
Poly(4-hydroxystyrene) (PHS) has been used in lithography as a backbone polymer and is also a promising material for extreme-ultraviolet or electron beam lithography. The dynamics of PHS radical cations generated upon exposure to electron beam were investigated. The transient absorption of PHS was observed in the near-infrared region in p-dioxane solutions by pulse radiolysis. Charge resonance (CR) bands that represent pi-pi interaction between the two chromophores of the intramolecular PHS dimer radical cation were observed, whereas p-cresol shows no distinct CR band. Although the radical cations of phenol derivatives are known to be easily deprotonated, it was found that the dimer radical cation formation leads to less deprotonation by its charge resonance stabilization.
The decomposition efficiency of acid generators upon exposure to ionizing radiation such as an electron beam is mainly determined by the reactivity of acid generators with thermalized electrons. The reactivity has been estimated using solvated electrons generated in solutions because there has been no method to directly observe the reaction with thermalized electrons generated in resist films. However, the reactivity estimated from the reaction with solvated electrons does not have sufficient accuracy to reproduce the difference between acid generators. In this study, we investigated the relationship between the acid yield and C 37 parameter of acid generators. The C 37 parameter was evaluated using tetrahydrofuran solution. The C 37 parameter has been believed to reflect the reaction of solutes with presolvated electrons generated in solutions. It was found that the C 37 parameter correlates with acid yields measured in resist films.
Ionizing radiation such as extreme ultraviolet (EUV) radiation and electron beams generates secondary electrons in resist materials. Acid generators are mainly decomposed by reaction with these electrons. The reaction of acid generators with solvated electrons has been well investigated. However, the reaction with electrons before solvation, in particular, during thermalization, has not been investigated because of measurement difficulties. Because the ejected electrons are not solvated in solid resist films, it is important to elucidate the reactions of acid generators with the electrons before solvation. The reactions before solvation are expected to give direct insight into the reactivity of acid generators with electrons in solid films. In this study, we investigated the reactivity of acid generators with electrons before solvation using picosecond pulse radiolysis. The dependence of reactivity on molecular structures was clarified in terms of C 37 parameters.
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