Linewidth fluctuation in resist patterns is a serious problem in electron beam nanolithography. We have observed granular structures with a diameter of 20–30 nm in resist films, and have determined that these structures cause the linewidth fluctuations. The granules are made up of polymer aggregates. We discuss the origin of the aggregates from the result that their size depends on the polymer molecular weight. We also show that the linewidth fluctuation is reduced, though the developing rate is slow, when the pattern size is less than the aggregate size. The linewidth dependence of the fluctuation and of the developing rate can be explained by the influence of the resist polymer aggregate on the development behavior.
The effect of molecular weight on the roughness of the dissolution front (surface roughness) and line-edge roughness (LER) was investigated in a chain-scission-type of positive-tone electron-beam resist. Surface roughness and LER were measured by directly observing the surface of flood-exposed resists after development and the sidewall of patterns, respectively, with an atomic force microscope. It was clarified that the molecular weight dependencies of surface roughness and LER are quite different. Surface roughness was found to increase with molecular weight. This is because the size of aggregates protruding from the surface as a result of the development process becomes larger as the molecular weight increases. In contrast, LER was found to be larger in a low-molecular-weight resist than in a high-molecular-weight resist. Moreover, the dependence of LER on the latent-image profile is different for low- and high-molecular-weight resists. For low-molecular-weight resist, LER is independent of the steepness of the latent image; whereas, for high-molecular-weight resist, it increases rapidly as the steepness decreases. These results can be explained by the relationship between the size of aggregates and the width of the transition zone between low- and high-dose regions of the latent-image profile. This strongly suggests that low-molecular-weight resists are not necessarily advantageous in reducing LER.
Hyperpolarized [1‐13C]fumarate is a promising magnetic resonance imaging (MRI) biomarker for cellular necrosis, which plays an important role in various disease and cancerous pathological processes. To demonstrate the feasibility of MRI of [1‐13C]fumarate metabolism using parahydrogen‐induced polarization (PHIP), a low‐cost alternative to dissolution dynamic nuclear polarization (dDNP), a cost‐effective and high‐yield synthetic pathway of hydrogenation precursor [1‐13C]acetylenedicarboxylate (ADC) was developed. The trans‐selectivity of the hydrogenation reaction of ADC using a ruthenium‐based catalyst was elucidated employing density functional theory (DFT) simulations. A simple PHIP set‐up was used to generate hyperpolarized [1‐13C]fumarate at sufficient 13C polarization for ex vivo detection of hyperpolarized 13C malate metabolized from fumarate in murine liver tissue homogenates, and in vivo 13C MR spectroscopy and imaging in a murine model of acetaminophen‐induced hepatitis.
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