Direct Measurements and Analysis of Catalyst Diffusion and Reaction Fronts in Chemically Amplified Resists

Abstract The propagation of both catalyst diffusion and reaction fronts in a polymeric chemically amplified resist (CAR) is evaluated by time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling, and is compared with the propagation of catalyst diffusion fronts in inert resist analogues. We report that catalysts display accelerated and highly non-Fickian dynamics in the reactive CAR, even when located well behind the propagation front, while simple Fickian diffusion is observed for the same conditions in inert resist analogues. The complex catalyst dynamics of reactive systems is attributed to two key factors: (1) Transient free volume following deprotection events, which is a long-hypothesized acceleration mechanism acting on the diffusion front; and (2) a newly identified plasticization process induced by inert, nonvolatile byproducts of catalyst photoactivation. We propose a physics-informed model of enhanced catalyst diffusion due to the independent contributions of these two processes, and demonstrate that this model coupled to a first-order reaction provides a reasonable prediction of both the diffusion and reaction fronts. Our study presents a critical evaluation of mechanisms that control the spatial extent of reaction in CARs, and suggests that quantitative models of the patterning process should account for the impact of nonvolatile catalyst activation byproducts.