Theoretical Investigation on Lithographic Properties of Zinc–Oxo and Cadmium–Oxo Clusters Ligated with Differently Substituted Benzoic Acids

Zinc–oxo clusters offer advantages over polymer
resists
for extreme ultraviolet lithography (EUVL) due to their smaller size
and higher EUV absorptivity. Although cadmium–oxo clusters
provide higher EUV absorption, their severe toxicity necessitates
safer alternatives. Elucidating the differences between zinc–oxo
and cadmium–oxo clusters is key to identifying the origin of
high performance in metal–oxo clusters (MOCs) and guiding the
design of safer materials. This study employs density functional theory
(DFT) to investigate the lithographic properties of ten distinct zinc–oxo
and cadmium–oxo clusters (M–L) ligated with benzoic
acid (BA), 4-methylbenzoic acid (MBA), 4-vinylbenzoic acid (VBA),
4-trifluoromethylbenzoic acid (TBA), and 4-cyanobenzoic acid (CBA).
Results demonstrate that the VBA and CBA enable zinc–oxo clusters
to surpass cadmium–oxo counterparts in lithographic properties.
Analysis of the state with the highest oscillator strength reveals
Zn–L, Cd–CBA, and Cd-VBA cluster transitions are dominated
by local excitation (LE), whereas Cd–BA, Cd–MBA, and
Cd–TBA clusters form hybrid LE/charge transfer (CT) states
with metal participation. Thermodynamic and kinetic calculations confirm
all clusters undergo photoreactions through three pathways (ionization,
electron attachment, and radical process), demonstrating a synergistic
Coulomb-induced and radical-mediated mechanism. This study establishes
quantitative structure–property relationships for the design
of high-performance and environmentally safer MOC photoresists.