In chemically amplified resists (CARs), it is known that catalyst diffusion is accelerated by the deprotection reaction. However, the mechanisms that drive this enhancement are not yet known as it is difficult to probe local changes in polymer chemistry and density during the reaction, as well as their effects on catalyst diffusion, through experiments alone. We examine catalyst diffusion in a model terpolymer CAR, both in the presence and absence of reaction, using a combination of experiments and atomistic simulations. From experiments, we find that deprotection rates are faster than film densification, and that reaction enhances long-time catalyst diffusion lengths by a factor of four. From simulations, we find evidence that catalyst mobility is enhanced in recently reacted regions of the terpolymer. These results provide insight into the origins of accelerated catalyst diffusion during reaction, and will be utilized in the development of physics-informed models of CAR systems.
Catalyst diffusion is a critical component of the pattern formation process in chemically amplified resists (CARs). In this study, we used a concerted experimental and modeling effort to examine diffusion of an inert catalyst analogue (sodium triflate) in a hydroxystyrene-based ESCAP terpolymer resin. First, atomistic simulations at high temperatures reveal an order-of-magnitude enhancement of the Fickian diffusivity in the protected reactant versus the fully deprotected product, while time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements at temperatures near the glass transition show no appreciable differences. The data from simulations and experiments conform to a unified curve, enabling estimates of the Fickian diffusivity at relevant post-exposure bake (PEB) temperatures through extrapolation. Second, acid-catalyzed reaction kinetics were measured with Fourier-transform infrared spectroscopy and compared with reaction-diffusion models based on the estimated Fickian diffusivities. The initial kinetics in experiments is orders-of-magnitude faster than predictions, demonstrating that models of catalyst transport should capture effects beyond Fickian diffusion. Finally, the simulations examined ion-ion and polymer-ion interactions at the atomistic level, features that are difficult to probe by experimental investigations. These data show that ion pair clustering in the protected and deprotected materials is similar as temperature is reduced, and ion pair dynamics in both materials is dominated by interactions with hydroxystyrene repeat units. These trends explain the experimental observations that ion diffusion is similar in the protected and deprotected polymers.
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