Molecular bixbyite-like In12-oxo clusters with tunable functionalization sites for lithography patterning applications

Ligand effect on In-Ti-oxo nanoclusters for nanolithography

Metal-oxo clusters have emerged as promising candidates for nanolithography technology. However, achieving precise control over their structures and compositions to enhance solution processability and film properties remains a significant challenge. This study introduces a novel ligand-regulation strategy for modularly assembling In-Ti-oxo clusters and represents the pioneering application of In-Ti-oxo clusters in nanolithography. Specifically, we explore the indium-based flexible trifurcate InL3 as a metalloligand (L = salicylate derivatives) to stabilize isomeric In4Ti12-cores with varying spherical shells: InOC-20V, InOC-21V, InOC-22V and InOC-23H. These isomers, in turn, induce markedly distinct solution processabilities. InOC-20V to InOC-22V feature vertically connected Ti6In2-SBUs, resulting in superior solubility compared to InOC-23H, which has parallel-connected Ti6In2-SBUs. In addition, the organic periphery is critical for film formation, and only InOC-20V, decorated with salicylate groups, produces high-quality films via spin-coating with 50 nm resolution patterns for lithography. To gain insight into the exposure mechanisms, a combination of DFT calculations, TGA-MS, XPS, and AFM-IR was used, indicating that the decarboxylation of the ligands significantly contributes to the solubility-switching behaviors necessary for lithography. These findings offer generalizable synthetic methods to expand the In-Ti-oxo cluster structural chemistry and highlight the efficacy of tailored structural modulation of cluster materials in enhancing solution processability and lithography performance, providing valuable insights for future material design and applications.

Enhanced Lithography Performance with Imino/Imido Benzenesulfonate Photoacid Generator-Bound Polymer Resists

The inherent acid diffusion during post-exposure baking poses significant challenges in balancing resolution, line-edge roughness, and sensitivity (RLS), thereby constraining the performance of chemically amplified photoresists (CARs) in advanced lithography. This study introduces a novel series of alkene-functionalized imino/imido benzenesulfonate photoacid generators (PAGs), characterized by their solubility, thermal stability, and polymerization attributes. These derivatives can copolymerize with acrylates and methacrylates to form PAG-bound copolymers, integrating non-ionic PAG units and acid-cleavable bulky alicyclic substituents, facilitating their use as "single-component" resists devoid of additives. Upon exposure to electron beams or ultraviolet radiation, the sulfonamide esters undergo N─O bond scission, producing photoacids that catalyze the deprotection of acidolytic groups. Compared to PAG-blended systems, these PAG-bound systems curtail acid diffusion by generating long-chain sulfonic acids, while preserving high sensitivity. The formulated single-component CARs demonstrate superior resolution and roughness, achieving a minimum linewidth of 42 nm at an electron beam dose of 73 µC cm- 2. This research provides a rational design for polymerizable imino/imido benzenesulfonate PAGs and single-component CARs, offering a viable solution to the RLS problem.

Synthesis and Characterizations of a Nonalkyl Tin Oxo Cluster and its Application as High EUV Absorption Coefficient and Etch Resistant Inorganic Resist for EUV Lithography

We introduce a novel nonalkyl tin oxo cluster, CNU-TOC-01(4C-C), synthesized through a reflux-based solution reaction using SnCl2, H2O, and pyrazole, which permits scalable production and molecular customization. Using field desorption-time-of-flight mass spectrometry (FD-TOF MS) and small-angle X-ray scattering (SAXS), CNU-TOC-01(4C-C) is characterized as a cyclic cluster with the molecular formula Sn4Cl3(C3N2H4)(C3N2H3)H4O8. The cluster size was measured to be 11.6 Å by SAXS and estimated to be 11.1 Å lengthwise in quantum chemical calculation. The synthesized material exhibits an extreme ultraviolet (EUV) linear absorption coefficient of 20.7 μm-1. Initial application in EUVL and electron beam lithography (EBL) achieved fine line and space patterns with the potential for ultrafine resolutions upon optimization. CNU-TOC-01(4C-C)'s high etch resistance underscores its exceptional suitability as an advanced resist material for future lithographic applications.

Improving the Lithography Sensitivity of Atomically Precise Tin-Oxo Nanoclusters via Heterometal Strategy

Tin-oxo clusters are increasingly recognized as promising materials for nanolithography technology due to their unique properties, yet their structural impacts on lithography performance remain underexplored. This work explores the structural impacts of heterometal strategies on the performance of tin-oxo clusters in nanolithography, focusing on various metal dopants and their coordination geometries. Specifically, SnOC-1(In), SnOC-1(Al), SnOC-1(Fe), and SnOC-2 were synthesized and characterized. These clusters demonstrate excellent solubility, dispersibility, and stability, facilitating the preparation of high-quality films via spin-coating for lithographic applications. Notably, this work innovatively employs Atomic Force Microscopy-based Infrared Spectroscopy (AFM-IR), neutron reflectivity (NR), and X-ray reflectivity (XRR) measurements to confirm film homogeneity. Upon electron beam lithography (EBL), all four materials achieve 50 nm line patterns, with SnOC-1(In) demonstrating the highest lithography sensitivity. This enhanced sensitivity is attributed to indium dopants, which possess superior EUV absorption capabilities and unsaturated coordination environments. Further studies on exposure mechanisms indicated that Sn-C bond cleavage generates butyl free radicals, promoting network formations that induce solubility-switching behaviors for lithography. These findings underscore the efficacy of tailored structural design and modulation of cluster materials through heterometal strategies in enhancing lithography performance, offering valuable insights for future material design and applications.

Additive-Assisted Forming High-Quality Thin Films of Sn-Oxo Cluster for Nanopatterning

Recently, metal-oxo clusters (MOCs) have attracted significant interest in fabricating nanoscale patterns in semiconductors via lithography. However, many MOCs are highly crystalline, making it difficult for them to form films and hindering subsequent nanopatterning processes. In this study, we developed a novel and simple method to enhance the film-forming ability of aromatic tetranuclear Sn-oxo clusters by adding additives. Theoretical calculations and Fourier-transform infrared (FTIR) analysis revealed the formation of intermolecular hydrogen bonds between the Sn-oxo clusters and additives, which induced a crystal-gel phase transition at -20 °C, thereby inhibiting the easy crystallization of the Sn-oxo clusters. High-quality and uniform thin films with surface roughness below 0.3 nm were prepared via spin coating. The obtained thin films exhibited good lithographic performance under deep ultraviolet (DUV), electron beam, and extreme-ultraviolet irradiation without a photo acid generator/photoinitiator, and 13- and 21 nm-wide line patterns were obtained on the films via electron-beam and extreme-ultraviolet lithographies. This study will pave the way for the further investigation of novel MOCs for advanced lithography and other thin-film applications.

Aggregate assembly of ferrocene functionalized indium-oxo clusters

In this study, we synthesized multi-nuclear indium oxide clusters (InOCs) using 1,1'-ferrocene dicarboxylic acid (H2FcDCA) as the chelating and surface protection ligand. The obtained clusters include the cubane-type heptanuclear InOCs ([In7]) and the sandwich-type thirteen-nuclear InOCs ([In13]). Notably, [In13] represents the highest nuclear number reported within the InOC family. In addition, the presence of labile coordination sites in these clusters allowed for structural modification and self-assembly. A series of [In7] clusters with adjustable band gaps have been obtained and the self-assembly of [In7] clusters resulted in the formation of an Fe-doped dimer, [Fe2In12], and an imidazole-bridged tetramer, [In28]. Similarly, in the case of [In13] clusters, the coordinated water molecules could be replaced by imidazole, methylimidazole, and even a bridged carboxylic acid, allowing the construction of one-dimensional extended structures. Additionally, part of the H2FcDCA could be substituted by pyrazole. This flexibility in replacing solvent molecules offered diverse possibilities for tailoring the properties and structures of the InOCs to suit specific applications.

A Single-Component Molecular Glass Resist Based on Tetraphenylsilane Derivatives for Electron Beam Lithography

A novel molecular glass (TPSiS) with photoacid generator (sulfonium salt group) binding to tetraphenylsilane derivatives was synthesized and characterized. The physical properties such as solubility, film-forming ability, and thermal stability of TPSiS were examined to assess the suitability for application as a candidate for photoresist materials. The sulfonium salt unit underwent photolysis to effectively generate photoacid on UV irradiation, which catalyzed the deprotection of the t-butyloxycarbonyl groups. It demonstrates that the TPSiS can be used as a 'single-component' molecular resist without any additives. The lithographic performance of the TPSiS resist was evaluated by electron beam lithography. The TPSiS resist can resolve 25 nm dense line/space patterns and 16 nm L/4S semidense line/space patterns at a dose of 45 and 85 μC/cm² for negative-tone development (NTD). The etching selectivity of the TPSiS resist to Si substrate is 8.6 under SF₆/O₂ plasma, indicating a potential application. Contrast analysis suggests that the significant solubility switch within a narrow exposure dose range (18-47 μC/cm²) by NTD is favorable for high-resolution patterns. This study supplies useful guidelines for the optimization and development of single-component molecular glass resists with high lithographic performance.

Coordination-Delayed-Hydrolysis Method for the Synthesis and Structural Modulation of Titanium-Oxo Clusters

ConspectusAtomically precise titanium-oxo clusters (TOCs) are the structure and reactivity model compounds of technically important TiO₂ materials, which could help build structure-property relationships and achieve property modulation at the molecular level. However, the traditional formation of TOCs has relied on the poorly controllable hydrolysis of titanium alkoxide in the solvent for a long time, limiting the development of TOC structural chemistry to a great extent. In addition, easily hydrolyzable alkoxy groups would be still coordinated on the surface of the TOCs generated by this method, making the clusters sensitive and unstable to the moisture. To achieve controllable preparation of TOCs, we believe it is crucial to attenuate the hydrolysis of titanium ions in the formation process of a cluster. To this end, we have recently applied an effective coordination-delayed-hydrolysis (CDH) strategy for TOC synthesis, which provides powerful tools for tuning their structures.In this Account, at the beginning, a brief introduction to the coordination-delayed-hydrolysis strategy is supplied, and its predominant features for constructing novel TOCs are highlighted. In subsequent sections, we discuss how the applied chelating organic/inorganic ligands (named hydrolysis delayed ligands) influence the hydrolysis process of Ti⁴⁺ ions to form a large family of TOCs with various nuclearities and core structures. Various hydrolysis delayed ligands have been explored, ranging from common O-donor ligands (carboxylate, phenol, or sulfate) to rarely used N-donor ligands (pyrazole) or bifunctional O/N-donor ones (quinoline, oxime, or alkanolamine). Breakthroughs in the symmetry, configuration, and cluster nuclei of TOCs have been accordingly achieved. Then, we show that this CDH method can be used to tune the surface structure of TOCs by modifying functional organic ligands. As a result, the physicochemical properties of TOCs, especially optical band gaps, can be optimized, and their stability under ambient conditions is significantly improved. In addition, we illustrate that the reversible bonds between hydrolysis delayed ligands and Ti ions further allows us to introduce active heterometal ions or clusters upon or inside the Ti-O cores to prepare heterometallic TOCs with unprecedented structures and properties. In particular, noble metal (Ag ions or clusters) has been incorporated into Ti-O clusters for the first time. As a summary, the coordination-delayed-hydrolysis strategy has realized the controllable hydrolysis of Ti⁴⁺ ions to some extent, breaking through the limitations of traditional synthesis methods and producing fruitful results in the field of titanium-oxo clusters. It is believed that this CDH method would also be effective for synthesizing oxo clusters of other easily hydrolyzed metal ions (Al³⁺, Sn⁴⁺, In³⁺, etc.) to afford significant contribution for the cluster community.

Mononuclear, hexanuclear and polymeric indium(III) pyrazolido complexes; structural characterization, dynamic solution studies and luminescent properties

A new family of six mononuclear indium(III) complexes of formula mer-[In^IIICl₃(pz*H)₃]-pz*H = pyrazole (pzH), or substituted pyrazoles: 4-Cl-pzH, 4-Br-pzH, 4-I-pzH, 4-Ph-pzH and 3,5-Me₂-pzH-were synthesized by addition reactions of InCl₃ and pz*H and crystallographically characterized. The fluxional behaviour of the complexes, probed by variable temperature ¹H NMR spectroscopy in the 328 K to 173 K range, was attributed to (at least) four simultaneous processes: pyrazole N-H proton dissociation/association, cis/trans-pyrazole exchange, and N¹/N² tautomerization of the cis- and of the trans-pyrazoles. Three novel trianionic hexanuclear complexes of general formula (pipH)₃[In₆Cl₆(μ₃-OH_0.5)₂(μ-OH)₆(μ-pz*)₆]-pz* = pz, 4-Cl-pz and 4-Ph-pz-showing μ-hydroxo and μ-oxo bridges were synthesized from the corresponding mer-[In^IIICl₃(pz*H)₃] and characterized by single crystal X-ray diffraction and ¹H NMR. Under different solvent conditions, multicolour emitting polymeric complexes of general formula [In(μ-pz*)₃]_n-pz* = pz, 4-Cl-pz, 4-I-pz and 4-Ph-pz-were obtained also from mer-[In^IIICl₃(pz*H)₃] after addition of a base. Luminescence and lifetime calculations were performed for all polymers formed.