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Tetramethylammonium hydroxide (TMAH) aqueous solutions has been used as a developer for chemically amplified resists (CARs), dissolving polymer with polar groups generated by exposure. Although the dissolution kinetics of CARs has been widely studied, it is necessary to understand molecular-level information such as interaction between polymer chains, to consider the dissolution of thin and minute resist films that are used nowadays. In this study, we used dynamic light scattering (DLS) to study the state of PHS chains in TMAH aqueous solution. The effect of the concentration of each ionic species on dispersion of PHS chains was investigated using solutions whose base concentrations were changed by two methods: dilution with pure water and neutralization with acid. PHS chains were well dispersed as the base concentration and ionic strength of the solution increased, while they aggregated as these two factors decreased. We also studied the dissolution behavior of PHS films under nearly identical conditions using quartz crystal microbalance (QCM). The dissolution of the films was also affected by the two factors described above. In addition to this, with the decrease in the above two factors, we observed formation of large swollen layer as we have reported in the past. We assumed these effects on dissolution of films were mainly due to the acid-base equilibrium at the solid-liquid interface.
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