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New resists are needed to advance EUV lithography. Tailored design of efficient photoresist is impossible without fundamental understanding of EUV induced chemistry. Resists incorporating high cross-section elements efficiently utilize EUV photons via radiation absorption by core-level electrons, resulting in emission of primary electrons. However, this is only an initial step in the process. Auger emission, molecular fragmentation, and subsequent electron-resist interactions are also critical. Understanding all these steps is crucial to harness all the deposited energy for improved patterning results.
In this work, we present recent results of multimodal experimental approaches to study photoresist materials. To build our grasp of EUV photochemistry from the ground up we aim for understanding the whole variety of processes happening after absorption of an EUV photon by a single building block of resist material – a resist molecule. Model photoresist constituent molecules functionalized with halogen atoms, are isolated in the gas phase and exposed to tunable EUV radiation from the Advanced Light Source, Berkeley Lab and the direct processes are investigated by photoelectron spectroscopy and photoionization mass spectrometry. We quantify the performance of several candidate molecules in terms of photoemission cross-sections and electron yield per primary photoionization event. We demonstrate that some prototype resist molecules can emit several (photo- and Auger) electrons after single EUV photon absorption. Following the electron emission, the atomic relaxation leads to the molecule fragmentation, which also depends on the halogen functionalization. Secondary electron-driven reactions are studied by tunable electron impact ionization and dissociative electron attachment mass spectrometry. We demonstrate that even very low kinetic energy electrons may lead to the molecule dissociation.
While gas-phase studies do provide insight into the primary EUV photon or electron induced events in the individual resist molecules, we seek to understand these processes in the condensed phase as this is where industrially relevant processes will occur. We discuss techniques allowing for generation of resist nanoparticles of different morphology, representing either condensed resist or a substrate coated by a resist film. The same techniques, as applied to investigate resist’s building blocks, are used to study the condensed resist material, connecting our understanding of the fundamental phenomena from each isolated molecule to the solid state system.
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