Measurement and modeling of diffusion characteristics in EUV resist

As a critical driver of the resolution, line edge roughness, sensitivity tradeoff, understanding acid diffusion in chemically amplified resist (CAR) is critical for its continued use in extreme ultraviolet lithography. Here we present an experiment that probes the nature of acid diffusion in a commercially available, conventional polymer CAR by measuring the developed linewidth of features as a function of post exposure bake time. In contrast to deep ultraviolet resists, the linewidth vs baketime relationship in the EUV resist studied is not linear. The observed trend in EUV was shown to be well described by the multivariate Poisson propagation model using a Gaussian diffusion kernel with a diffusivity of 25 nm2=s. Deviations from a purely Gaussian diffusion profile were modeled by the inclusion of base that reduces the effective acid concentration in unexposed regions of resist. We thus conclude that acid blur in EUV CAR can be well described as a Fickian diffusion process.