Probing ion diffusion in chemically amplified resists through experiments and atomistic simulations

Abstract

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.