Oddur Ingólfsson

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 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 CF3+ representing the dominant product ion. Computed appearance energies align well with experimental trends and support a sequential fragmentation pathway involving loss of SO2, CF3, 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.

With extreme ultraviolet lithography (EUVL) being established alongside the conventional deep UVL in high-volume semiconductor manufacturing processes comes a transition from the use of non-ionizing radiation to the use of ionizing radiation in the lithographic process. Correspondingly, the chemistry in the solubility switching of the resist materials changes from photochemistry to electron-induced chemistry and may thus resemble the resist chemistry induced in electron beam lithography rather than the photochemistry governing deep ultraviolet lithography. This in turn calls for rethinking of the resist formulations, a better understanding of the respective electron induced chemistry, and eventually tailoring it to provide high performance EUVL formulations. In the current study, we take a step in this direction and revisit electron induced fragmentation of methyl acetate as the simplest model compound for the functional side group of polymethyl methacrylate (PMMA), a high-performance main chain scission resist material in electron beam lithography. Appearance energies for individual fragmentation reactions in dissociative ionization (DI) in the gas phase are determined, and quantum chemical calculations are conducted to elucidate the underlying reactions. The results are discussed in context to previous work on dissociative ionization and dissociative electron attachment (DEA) of methyl acetate, and quantum chemical calculations are used to explore the thermo-chemistry of decarboxylation as a path to main chain scission of PMMA through both DI and DEA when this resist material is exposed to EUV radiation.

Radiation‐induced processes in the aromatic cyano compound benzonitrile have attracted renewed interest since its detection in the interstellar medium in 2018, and recent studies have elucidated dissociative ionization pathways leading to species such as CN ^• and HCN, which can play important roles in interstellar chemistry. This work explores negative ion formation from benzonitrile upon electron attachment with mass spectrometry experiments and the most extensive theoretical study to date of the underlying negative ion states and their respective dissociative relaxation pathways. The measurements confirm the previously reported CN ⁻ formation at a collision energy of 3.0 eV as well as formation of the dehydrogenated parent anion and phenyl anion and CN ⁻ formation in the 7–10 eV energy range. Threshold energies for these dissociation channels are reported at the G4(MP2) level of theory for the first time. Furthermore, by using both scattering calculations and bound state techniques, CN ⁻ formation at around 3.0 eV may proceed from a ² B ₁ , π ₄ * shape resonance through nonadiabatic coupling with the σ*, CCN state. In the 7–10 eV range, complete active space plus second‐order perturbation (CASPT2) calculations suggest strong contributions from core excited π ₄ * and σ* resonances.

Propylene oxide, CH3CHOCH2, is the first chiral molecule detected in space and the third C3 oxide detected toward the Sagittarius B2 (Sgr B2 (N)) molecular cloud, the others being propanal, CH3CH2CHO, and acetone, (CH3)(2)CO. With homochirality being ubiquitous in the building blocks of living matter, the formation and decay paths of propylene oxide in space are of specific interest. Motivated by the significant role of photo- and secondary electrons in astrochemistry, we have studied electron ionization and fragmentation of propylene oxide. Ion appearance energies are determined and compared to threshold values for the respective processes calculated at the G4MP2 level of theory, and potential reaction pathways are computed at the DFT level of theory. Electron ionization is found to destabilize propylene oxide, leading to barrierless opening of the C1-C2 bond of the epoxy ring, hydrogen transfer, and fragmentation over the methyl vinyl ether or rupture of the C2-O bond of the epoxy ring and fragmentation of the allyl alcohol cation as an intermediate, rather than direct bond ruptures.

Motivated by the potential of focused-electron-beam-induced deposition (FEBID) in the fabrication of functional gold nanostructures for application in plasmonic and detector technology, we conducted a comprehensive study on [Au(CH₃)₂Cl]₂ as a potential precursor for such depositions. Fundamental electron-induced dissociation processes were studied under single collision conditions, and the composition and morphology of FEBID deposits fabricated in an ultrahigh-vacuum (UHV) chamber were explored on different surfaces and at varied beam currents. In the gas phase, dissociative ionization was found to lead to significant carbon loss from this precursor, and about 50% of the chlorine was on average removed per dissociative ionization incident. On the other hand, in dissociative electron attachment, no chlorine was removed from the parent molecule. Contrary to these observations, FEBID in the UHV setup was found to yield a quantitative loss and desorption of the chlorine from the deposits, an effect that we attribute to electron-induced secondary and tertiary reactions in the deposition process. We find this precursor to be stable at ambient conditions and to have sufficient vapor pressure to be suitable for use in HV instruments. More importantly, in the UHV setup, FEBID with [Au(CH₃)₂Cl]₂ yielded deposits with high gold content, ranging from 45 to 61 atom % depending on the beam current and on the cleanliness of the substrates surface.

Low energy electron-induced fragmentation of 2-(trifluoromethyl)acrylic acid a potential component of extreme ultraviolet lithography resist materials.