No abstract

Aqueous precursors tailored for the deposition of thin film materials are desirable for sustainable, simple, low energy production of advanced materials. Yet the simple practice of using aqueous precursors is complicated by the multitude of interactions that occur between ions and water during dehydration. Here we use lithium polyoxoniobate salts to investigate the fundamental interactions in the transition from precursor cluster to oxide film. Small-angle X-ray scattering of solutions, total X-ray scattering of intermediate gels, and morphological and structural characterization of the lithium niobate thin films reveal the atomic level transitions between these states. The studies show that 1) Lithium-[H 2 Nb 6 O 19 ] 6has drastically different solution behaviour than lithium-[Nb 6 O 19 ] 8-, linked to the precursor salt structure 2) in both compositions, the intermediate gel preserves the polyoxoniobate clusters and show similar local order and 3) the morphology and phases of deposited films reflect the ions behaviour throughout the journey from cluster solution to metal oxide.

This work complements our recent discovery of new phases derived from zirconium perchlorate by addition of hydrogen peroxide. Here, we investigate analogous reactions with hafnium perchlorate, which is found to have modifications of the Clearfield–Vaughan tetramer (CVT). For hafnium perchlorate derivatives, we find distorted versions of CVT by X-ray diffraction and study the reaction solutions by SAXS, Raman spectroscopy, and ESI-MS. Furthermore, we investigate mixed Hf–Zr solution and solid phases and find the latter resemble the zirconium family at low Hf concentrations and the hafnium family at higher hafnium contents.

Inorganic resists are promising for nanomanufacturing because of their potential for high-resolution and low line-edge roughness patterning and exceptional sensitivity to extreme ultraviolet (EUV) radiation. Hafnium oxide peroxide hydroxide sulfate (HafSO x ) is a model EUV inorganic photoresist, wherein the EUV absorption coefficients for hafnium and O are much higher than for conventional polymer resists. Absorption of EUV radiation leads to electron emission that results in the HafSO x solubility change. We used desorption-based techniques to elucidate thermal- and radiation-induced processes that contribute to the HafSO x solubility switch. We found that low kinetic energy electrons render HafSO x insoluble and result in the desorption of molecular O2. Electron-stimulated desorption and postexposure Raman spectroscopy indicate similar kinetics for peroxide loss in HafSO x . Temperature-programmed desorption studies found that peroxide ligand desorption is best characterized as first order, with a broad distribution of thermal desorption energies. Finally, a pair distribution function analysis of X-ray scattering data of HafSO x solutions and powders provides an atomic-level model of local structure within the film that is consistent with other characterization data of solutions and deposited films.

Selective dissolution of hafnium-peroxo-sulfate films in aqueous tetramethylammonium hydroxide enables extreme UV lithographic patterning of sub-10 nm HfO2 structures. Hafnium speciation under these basic conditions (pH>10), however, is unknown, as studies of hafnium aqueous chemistry have been limited to acid. Here, we report synthesis, crystal growth, and structural characterization of the first polynuclear hydroxo hafnium cluster isolated from base, [TMA]6 [Hf6 (μ-O2 )6 (μ-OH)6 (OH)12 ]⋅38 H2 O. The solution behavior of the cluster, including supramolecular assembly via hydrogen bonding is detailed via small-angle X-ray scattering (SAXS) and electrospray ionization mass spectrometry (ESI-MS). The study opens a new chapter in the aqueous chemistry of hafnium, exemplifying the concept of amphoteric clusters and informing a critical process in single-digit-nm lithography.