Extreme ultraviolet (EUV) lithography (92 eV) has recently entered logic and memory high-volume manufacturing to ensure the continuation of Moore’s Law into advanced technology nodes (sub 5 nm). In parallel to advancements in the lithographic system, the development of suitable photoresists plays an equally important role in pushing the boundaries of EUV lithography. Fundamental work on well-established chemically amplified resists (CAR) for EUV as well as the upcoming resists based on metal-organic materials have indicated that the lithographic mechanism is largely governed by electron mediated chemistry. In a simplified model, the electrons emitted upon ionization of the material generate further secondary electrons, which interact with the resist components and induce a solubility switch driven by electron and radiation chemistry. To develop a better performing resist, it is of utmost importance to understand the photoelectron kinetic energy spectrum, secondary electrons and their generation efficiency, and the electron mean free path in the photoemission process. In this work, we use photoemission spectroscopy with a table-top, coherent, 92 eV photon source to shed light on the chemistry driven by photon exposure. The valence band photoelectron spectrum (PES) of an environmentally stable chemically amplified photoresist (ESCAP), as well as a model material for an open-source metal oxide (OSMO) resist were measured using our tabletop EUV photoemission setup. We report the evolution of the PES as a function of exposure dose; capturing chemical changes.
Science stands on three legs: hypothesis, experiment, and simulation. This holds true for researching extreme ultraviolet (EUV) exposure of photoresist. Hypothesis: For resist exposure as patterns get smaller and closer together, approaching molecular units in width and resist-height, the molecular dynamics will limit the working resolution of the resist due to the formation of printing defects. Without taking proper consideration of these dynamics, the single-patterning lithography roadmap may end prematurely. Experimentally we are developing methods for sub-picosecond tracking of photoionization-induced processes. Using ultrashort pulses of light to excite and probe new materials with techniques that show the interactive dynamics of electronic and nuclear motion at the very limits of light-speed. This certainly holds true for exposing photoresists with EUV where ultrafast photoreactions induce chemical change via multiple pathways such as high-energy ionization fragmentation, recombination, and multispecies combination that ideally end in low-energy electron transfer reactions, analogous to lower energy photoreaction (but with a charge). In the nonideal case, these reaction processes lead to incompatible byproducts of the radiolysis that lead to types of stochastic defects. To do ultrafast studies we must build a foundation of knowledge using atomistic simulation to interpret transient molecular dynamic processes. Before we can do this, we need to learn how to simulate various spectral modalities to provide a starting point. In this work, we examine X-ray Photoelectron Spectroscopy of a model resist and use atomistic simulation to interpret the reactant-product composition of the spectral samples.
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