Improved method for measuring photoacid generator kinetics in polymer thin films using normalized interdigitated electrode capacitance data

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Berger, Cody M.
Henderson, Clifford L.
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A data analysis method is presented that can be used to calculate kinetic rate constants for photoacid generation (Dill C values) in polymer and chemically amplified photoresist thin films using capacitance versus exposure dose data from resist coated interdigitated electrode (IDE) sensors. It is shown that the use of normalized IDE capacitance data can reduce or eliminate errors and variations in measured Dill C values obtained from our previous analysis method that are created by environmental factors such as humidity fluctuations and IDE factors such as variations in electrode geometry and size. Using this normalization method, the Dill C rate constants for 248 nm exposure of triphenylsulfonium triflate (TPS–Tf), triphenylsulfonium perfluoro-1-butanesulfonate (TPS–Nf), bis(4-tert-butylphenyl)iodonium triflate (TBI–Tf), and bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate (TBI–Nf) in poly(p-hydroxystyrene) (PHOST) were found to be 0.046, 0.040, 0.055, and 0.056 cmcm²/mJ, respectively. These results are shown to compare well with values obtained for these same systems using our original IDE data analysis method (0.045 cm²/mJ for TPS–Tf/PHOST, 0.039 cm²/mJ for TPS–Nf/PHOST, 0.056 cm²/mJ for TBI–Tf/PHOST, and 0.054 cm²/m/J for TBI–Nf/PHOST). The normalization method has a significant advantage in that it permits the determination of a Dill C parameter for a particular polymer-photoacid generator system using a single resist film coated IDE and a single exposure experiment.
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