arXiv subjects

Fabian Holzmeier

Publications and source records attributed to Fabian Holzmeier.

6 recordsLinked to original sources

arXiv2026

More is not always better: Dissociative photoionization limits the EUV absorbing photoacid generator pentafluorophenyl triflate in photolithography

Pentafluorophenyl triflate has been explored as a highly absorbing neutral photoacid generator (PAG) candidate for next generation chemically amplified resists used in extreme ultraviolet (EUV) lithography. Although increased fluorination enhances EUV absorption, this study demonstrates that such an approach does not necessarily improve photoacid generation efficiency. Using photoelectron-photoion coincidence (PEPICO) spectroscopy at the 92 eV photon energy of the EUV scanners in combination with quantum chemical calculations, the dissociative photoionization of pentafluorophenyl triflate was systematically investigated. The photoionization mass spectrum reveals extensive fragmentation, with the parent ion contributing only 3.1 % of the total signal and CF$_3^+$ representing the dominant product ion. Computed appearance energies align well with experimental trends and support a sequential fragmentation pathway involving loss of SO$_2$, CF$_3$, and CO. Crucially, none of the major dissociation channels yield precursors capable of forming triflic acid, the strong photoacid required for efficient deprotection reactions in chemically amplified resists. Combined with previous dissociative electron attachment studies indicating similarly unfavorable fragmentation, the results demonstrate that despite its high EUV absorption cross section, pentafluorophenyl triflate is unsuitable as a PAG for EUV lithography. The findings highlight the importance of understanding fundamental photoionization and electron interaction mechanisms to guide the rational design of next generation high performance EUV photoresists.

physics.chem-ph↗

arXiv2026

Two-colour coherent control of nuclear and electron dynamics in photoionization of molecular hydrogen with FEL pulses

The extension of coherent $ω$-$2ω$ control schemes, recently implemented in free-electron lasers (FELs), to molecular systems offers new opportunities to control chemical dynamics on the electronic timescale, potentially allowing for the steering of reactions along previously inaccessible pathways. We have implemented such a scheme at the seeded FERMI FEL to retrieve the relative phases between one-photon (frequency $2ω$) and two-photon (frequency $ω$) ionization paths in the hydrogen molecule as a function of photoelectron energy and emission angle. The narrow bandwidth of the XUV pulses enables selective excitation of vibrational levels of neutral intermediate H$_2$ states in the two-photon ionization path. Here we focus on $ω$--$2ω$ ionization of H$_2(X\,^{1}Σ_g^{+},\,v=0)$ into the H$_2^{+}(X\,^{2}Σ_g^{+},\,v_f)$ ground state involving the H$_2(B\,^{1}Σ_u^{+},\,v'=6)$ intermediate state. The relative phases of the $ω$ and $2ω$ interfering photoionization amplitudes exhibit a strong dependence on photoelectron energy, i.e.\ on the final vibrational state $v_f$ in the H$_2^{+}$ cation. With the help of accurate theoretical calculations, the observed phase jumps are assigned to the coupled electronic and nuclear dynamics at play in the two-photon process, significantly influenced by H$_2(^{1}Σ_g^{+}$ and $^{1}Π_g)$ autoionizing states and the mapping of the H$_2(B\,^{1}Σ_u^{+},\,v'=6)$ intermediate-state nuclear wavefunction into the final vibrational states of H$_2^{+}(X\,^{2}Σ_g^{+})$. The present work establishes the fundamental concepts required to access coupled electron--nuclear dynamics in molecules using $ω$--$2ω$ coherent control schemes currently available at free-electron laser facilities.

physics.chem-ph↗

arXiv2025

Fundamental Understanding of Exposure and Process Chemistry for Enhanced Lithography and Stability of Metal Oxide Resists

Metal oxide resists (MORs) have shown great promise for high resolution patterning in extreme ultraviolet (EUV) lithography, with potential for integration into high volume manufacturing. However, MORs have recently been shown to exhibit sensitivity to process conditions and environment, leading to critical dimension (CD) variation. While this variation can be reduced with proper process control, there is little knowledge on how these aspects affect the image formation mechanism. To bridge these knowledge gaps, we deploy a coordinated, fundamentals-focused approach to yield deep insights into MOR exposure and process chemistry. Our results on a model MOR, an n-butyl Sn-Oxo system, reveal how parameters such as exposure dose, post-exposure bake temperature, and atmospheric species influence the image formation mechanism. Our results, and the coordinated approach using correlative spectroscopies, provide a strong foundation for understanding the image formation mechanism in MOR materials with potential to link mechanistic aspects to CD variation.

cond-mat.mtrl-sci↗

arXiv2024

Dissociative photoionization of EUV lithography photoresist models

The dissociative photoionization of \textit{tert}-butyl methyl methacrylate, a monomer unit found in many ESCAP resists, was investigated in a gas phase photoelectron photoion coincidence experiment employing extreme ultraviolet (EUV) synchrotron radiation at 13.5 nm. It was found that the interaction of EUV photons with the molecules leads almost exclusively to dissociation. However, the ionization can also directly deprotect the ester function, thus inducing the solubility switch wanted in a resist film. These results serve as a building block to reconstruct the full picture of the mechanism in widely used chemically amplified resist thin films, provide a knob to tailor more performant resist materials, and will aid interpreting advanced ultrafast time-resolved experiments.

cond-mat.mtrl-sci↗

arXiv2024

Photoemission Spectroscopy on photoresist materials: A protocol for analysis of radiation sensitive materials

Device architectures and dimensions are now at an unimaginable level not thought possible even 10 years ago. The continued downscaling, following the so-called Moore's law, has motivated the development and use of extreme ultraviolet (EUV) lithography scanners with specialized photoresists. Since the quality and precision of the transferred circuit pattern is determined by the EUV induced chemical changes in the photoresist, having a deep understanding of these chemical changes is of pivotal importance. For this purpose, several spectroscopic and material characterization techniques have already been employed so far. Among them, photoemission can be essential as it not only allows direct probing of chemical bonds in a quantitative way but also provides useful information regarding the generation and distribution of primary and secondary electrons. However, since high energy photons are being employed for characterization of a photosensitive material, modification of the sample during the measurement is possible and this must be considered when investigating the chemical changes in the photoresist before and after exposure to EUV light.

physics.chem-ph↗

arXiv2021

Influence of Shape Resonances on the Angular Dependence of Molecular Photoionization Delays

Characterizing time delays in molecular photoionization as a function of the ejected electron emission direction relative to the orientation of the molecule and the light polarization axis pro-vides unprecedented insights into the attosecond dynamics induced by extreme ultraviolet or X-ray one-photon absorption, including the role of electronic correlation and continuum resonant states. Here, we report completely resolved experimental and computational angular depend-ence of single-photon ionization delays in NO molecules across a shape resonance, relying on synchrotron radiation and time independent ab initio calculations. The angle-dependent time delay variations of few hundreds of attoseconds, resulting from the interference of the resonant and non-resonant contributions to the dynamics of the ejected electron, are well described using a multichannel Fano model where the resonance time delay is angle-independent. Comparing these results with the same resonance computed in e-NO+ scattering highlights the connection of photoionization delays with Wigner scattering time delays.

physics.atom-ph↗