Soft X-Ray Absorption and Fragmentation of Tin-oxo Cage Photoresists

Albert Manfred Brouwer*, Jarich Haitjema, Sonia Castellanos, Olivier Lugier, Ivan Bespalov, Rebecka Lindblad, Martin Timm, Christine Bülow, Vicente Zamudio-Bayer, J. Tobias Lau, Bernd von Issendorff, Ronnie Hoekstra, Katharina Witte, Benjamin Watts, Thomas Schlathölter*

*Corresponding author for this work

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Abstract

ABSTRACT “Tin-oxo cage” organometallic compounds are considered as photoresists for extreme ultraviolet (EUV) photolithography. To gain insight into their electronic structure and reactivity to ionizing radiation, we trapped bare gas-phase n-butyltin oxo cage dications [(BuSn)12O14(OH)6]2+ in an ion trap and investigated their fragmentation upon soft X-ray photoabsorption by means of mass spectrometry. In complementary experiments, the tin-oxo cages with hydroxide and trifluoroacetate counter-anions were cast in thin films and studied using X-ray transmission spectroscopy. Quantum-chemical calculations were used to interpret the observed spectra. At the carbon K-edge, a distinct pre-edge absorption band can be attributed to transitions in which electrons are promoted from C1s orbitals to the lowest unoccupied molecular orbitals, which are delocalized orbitals with strong antibonding (Sn−C σ*) character. At higher energies, the most prominent resonant transitions involve C‒C and C‒H σ* valence states and Rydberg (3s and 3p) states. In the solid state, the onset of continuum ionization is shifted by ~5 eV to lower energy with respect to the gas phase, due to the electrostatic effect of the counterions. The O K-edge also shows a pre-edge absorption, but it is devoid of any specific features, because there are many transitions from the different O1s orbitals to a large number of vacant orbitals. In the gas phase, formation of the parent [(BuSn)12O14(OH)6]3+ radical ion is not observed at the C K-edge nor at the O K-edge, because the loss of a butyl group from this species is very efficient. We do observe a number of triply charged photofragment ions, some of which have lost up to 5 butyl groups. Structures of these species are proposed based on quantum-chemical calculations, and pathways of formation are discussed. Our results provide insight into the electronic structure of alkyltin-oxo cages, which is a prerequisite for understanding their response to EUV photons and their performance as EUV photoresists.
Original languageEnglish
Pages (from-to)5986-5998
Number of pages39
JournalPCCP : Physical Chemistry Chemical Physics
Volume26
Issue number7
Early online date24-Jan-2024
DOIs
Publication statusPublished - Feb-2024

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