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

Quantitative reaction-diffusion models are critical to the design of high-resolution lithographic processes based on acid-catalyzed deprotection of glassy polymer resins. We present a concerted experimental and computational effort to examine diffusion of an inert catalyst analogue (a cation-anion pair) in the protected and deprotected states of a model terpolymer resin. Multi-microsecond molecular dynamics simulations provide insight into ion-ion association, polymer-ion interactions, and transport mechanisms at temperatures well-above the glass transition and reveal that ion diffusivity is slightly reduced with deprotection. Time-of-flight secondary ion mass spectrometry demonstrates that ion diffusivities are independent of extent-of-deprotection at temperatures below the glass transition. Models of reaction-diffusion based on these values capture long-time deprotection kinetics, but deviations persist at short times that are attributed to transient states generated by reaction. This study highlights the potential of atomistic modeling coupled with targeted experiments for interrogating the physical and chemical processes of patterning in next-generation lithographic materials.