Solution-based organometallic nanoclusters are unique nanoscale precursors due to the ability to precisely control their size, shape, structure, and assembly. The interaction of extreme ultraviolet (EUV) or X-ray photons with these organometallic nanoclusters can result in processes that can lead to a change in solubility. This makes these materials prime candidates for next-generation photoresists for EUV nanolithography. In this study, we investigate the interaction of X-ray radiation with a charge neutral, sodium templated, butyl-tin Keggin (beta-NaSn13) nanocluster. This nanocluster is used as a model EUV photoresist to better understand the radiation induced solubility transition. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to characterize the beta-NaSn13 thin films, where Sn 3d, O ls, and C is core levels were measured under a range of ambient conditions, including ultrahigh vacuum and 1 mbar of oxygen, water, methanol, or nitrogen. A photon dose array was obtained for each ambient condition to determine their effect on the photon induced chemistries which result in the solubility transition. The resulting contrast curves indicate that an oxygen ambient significantly reduces the required photon dose for the solubility transition relative to UHV, while all other ambients increase the required photon dose for the solubility transition relative to UHV. We performed in situ XPS after postexposure annealing beta-NaSn13 thin films in multiple ambients to study the chemistry that occurs after a postexposure bake (PEB). The beta-NaSn13 thin films retained a significant amount of aliphatic carbon following the PEB in all the ambients we studied. On the basis of our studies, we propose that the solubility transition for beta-NaSn13 thin films occurs through radical hydrogen abstraction and radical-radical coupling reactions. These studies further improve the understanding of photon induced chemistries in a beta-NaSn13 model resist and provide mechanistic insights for EUV lithography processing with organometallic nanomaterials.

Three organotin carboxylate species stabilized by the same ligands, but varying in size and structure, were studied to elucidate the effects of the structure on reactivity in the context of direct-write electron beam patterning. The chemical reactions that occur between the organotin reagents and the electron beam, the patterned film products, and the ligand decomposition and desorption byproducts were compared across all species. We found that both the metal-oxo content and the ligand coordination mode of each organotin reagent affected the reaction efficiency during electron beam patterning. In each case, an insoluble metal-oxo product formed after irradiation, but the composition, structure, and surface morphology of the products were nearly indistinguishable from the initial films. Examining the byproducts of the irradiation chemistry using electron-stimulated desorption confirmed that many of the organic ligands remained in the film during the reaction, likely crosslinking the clusters together to form a metal oxo polymer product. Finally, we discuss the implications of the chemical transformations that occur during patterning for the use of these organotin reagents as both photoresists for lithography and direct-write functional nanomaterials.

The electronic structure of multimetal, amorphous oxides can be varied across a wide range of elemental compositions. Bulk properties such as conductivity, work function, and absorption can thus be tailored to suit a range of applications spanning from carrier-selective contacts to catalysis. Missing, however, is an understanding of how the surface reactivity is impacted in mixed metal-oxide amorphous films. Here we investigate the propensity of Al(1-x)M(x)Oy (M = Fe, Mn) amorphous oxide films to dissociate water into hydroxyl groups in a humid environment and find comparable hydroxylation at the low relative humidity (similar to 0.3% RH) probed by ambient pressure X-ray photoelectron spectroscopy. In contrast, films with both Al and Fe show an increased formation of methoxy groups upon methanol exposure compared to pure Al- and Fe-oxide end members, indicating that the coordination environment of the amorphous oxide network impacts the acidity and redox character of surface metal and oxygen sites. These results provide guidance for the rational design of amorphous oxide layers with tailored chemical reactivity or passivity for a given application.

Organotin photoresists have shown promise for next-generation lithography because of their high extreme ultraviolet (EUV) absorption cross sections, their radiation sensitive chemistries, and their ability to enable high resolution patterning. To better understand both temperature and radiation-induced reaction mechanisms, we have studied a model EUV photoresist, which consists of a charge-neutral butyl-tin cluster. Temperature-programmed desorption (TPD) showed very little outgassing of the butyl-tin resist in ultrahigh vacuum and excellent thermal stability of the butyl groups. TPD results indicated that decomposition of the butyl-tin resist was first order with a fairly constant decomposition energy between 2.4 and 3.0 eV, which was determined by butyl group desorption. Electron-stimulated desorption (ESD) showed that butyl groups were the primary decomposition product for electron kinetic energies expected during EUV exposures. X-ray photoelectron spectroscopy was performed before and after low-energy electron exposure to evaluate the compositional and chemical changes in the butyl tin resists after interaction with radiation. The effect of molecular oxygen during ESD experiments was evaluated, and it was found to enhance butyl group desorption during exposure and resulted in a significant increase in the ESD cross section by over 20%. These results provide mechanistic information that can be applied to organotin EUV photoresists, where a significant increase in photoresist sensitivity may be obtained by varying the ambient conditions during EUV exposures.

We have investigated the thermal and radiation chemistry of an organotin-based model photoresist to elucidate patterning mechanisms related to extreme ultraviolet (EUV) lithography. Butyltin oxide hydroxide (BuSnOOH) was dissolved in organic solvents and spin-coated to form uniform thin films. The thermal stability and radiation sensitivity of the thin films were characterized by temperature programmed desorption (TPD), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). From the TPD studies, we determined that decomposition of BuSnOOH occurs at similar to 653 K through cleavage of the butyl-tin bond. Low kinetic energy electron (E-kin, = 80 eV) and X-ray (1486.6 eV) exposure also resulted in cleavage of the butyl-tin bond with the resulting desorption of butyl ligands from the film. From the ESD data, we estimated that the butyl ligand desorption cross section was similar to 4.3 x 10(-14) cm(2) for electrons with 80 eV kinetic energy. From the XPS results, we found a significant reduction in C is intensity for extended X-ray exposures, which corresponds to butyl ligand loss. There were also changes in the O 1s spectra indicating loss of hydroxyl groups and tin oxide network formation during radiation exposure. These results indicate the preferential dissociation and desorption of butyl ligands that can occur through either thermal or radiation induced processes, and that butyl ligand loss leads to the solubility contrast.

Advances in extreme ultraviolet (EUV) photolithography require the development of next-generation resists that allow high-volume nanomanufacturing with a single nanometer patterning resolution. Organotin-based photoresists have demonstrated nanopatterning with high resolution, high sensitivity, and low-line edge roughness. However, very little is known regarding the detailed reaction mechanisms that lead to radiation-induced solubility transitions. In this study, we investigate the interaction of soft X-ray radiation with organotin clusters to better understand radiation-induced chemistries associated with EUV lithography. Butyltin Keggin clusters (β-NaSn13) were used as a model organotin photoresist, and characterization was performed using ambient-pressure X-ray photoelectron spectroscopy. The changes in relative atomic concentrations and associated chemical states in β-NaSn13 resists were evaluated after exposure to radiation for a range of ambient conditions and photon energies. A significant reduction in the C 1s signal versus exposure time was observed, which corresponds to the radiation-induced homolytic cleavage of the butyltin bond in the β-NaSn13 clusters. To improve the resist sensitivity, we evaluated the effect of oxygen partial pressure during radiation exposures. We found that both photon energy and oxygen partial pressure had a strong influence on the butyl group desorption rate. These studies advance the understanding of radiation-induced processes in β-NaSn13 photoresists and provide mechanistic insights for EUV photolithography.

The oxidation and reduction of metal oxides and their interaction with the environment play a critical role in material stability and the ability to catalyze reactions. The local change in valence and formation of surface adsorbates affect the oxide electronic structure and chemical reactivity, yet are challenging to probe experimentally. In this paper a detailed study of the oxidation and reduction of Cr in the perovskite oxide family of La (1– x ) Sr x CrO 3 using ambient pressure X‐ray photoelectron spectroscopy is presented. The incorporation of Sr increases the propensity to oxidize at the surface, leading to the presence of Cr 4+ and Cr 6+ principally confined to the top unit cell when in equilibrium with O 2 gas. These acidic sites are readily reduced to Cr 3+ in equilibrium with H 2 O vapor, and the resultant amount of hydroxyls formed from the dissociation of H 2 O is directly proportional to the density of surface sites formerly oxidized. The quantification of the redox stability of La (1– x ) Sr x CrO 3 and the relationship between the extent of oxidation, reduction, and hydroxylation with Sr yield important insight into the surface functionality during electrochemical applications.

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 O-2. 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.

Metal oxide nanomaterials have shown promise for use as EUV resists. Recently, significant efforts have focused on tinoxo clusters that have high absorption coefficient Sn centers and radiation sensitive organic ligands. In our studies, we have investigated a β-Keggin butyl-Sn cluster (β-NaSn13), which is charge-neutral and allows studying radiation induced chemistries without interference from counterions. We have used ambient pressure X-ray photoelectron spectroscopy (APXPS) to investigate the contrast properties of the β-NaSn13 in ultrahigh vacuum (UHV) and in the presence of ambient oxygen. These contrast studies indicate that ambient oxygen reduces the dose requirements for the solubility transition of the β-NaSn13 photoresists. APXPS spectra collected before and after the solubility transition shows that ambient oxygen causes a greater loss of butyl ligands from the samples and the formation of more tin oxide for larger doses, suggesting the presence of reactive oxygen species. APXPS was also used to study processes during the post exposure bake, where we compared the differences in film chemistries in ambient oxygen or in UHV. There were only very small differences in the APXPS spectra before exposure and after exposure and the post exposure bake. However, ambient oxygen resulted in some changes for unexposed regions during the post exposure bake; there was a greater ratio of tin oxide to other oxygen species (alkoxy ligands, hydroxyls) for samples annealed in oxygen. These results have significance for EUV and e-beam lithography processing parameters, as well as implications for cluster design and ligand chemistries.

Titanium dioxide/graphene composites have recently been demonstrated to improve the photocatalytic activity of TiO2 in visible light. To better understand the interactions of TiO2 with graphene we have investigated the growth of TiO2 nanoclusters on single-layer graphene/Ru(0001) using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Deposition of Ti in the O2 background at 300 K resulted in the formation of nanoclusters nucleating on intrinsic defects in the graphene (Gr) layer. The saturation nanocluster density decreased as the substrate temperature was increased from 300 to 650 K, while deposition at 700 K resulted in the significant etching of the Gr layer. We have also prepared nanoclusters with Ti2O3 stoichiometry using lower O2 pressures at 650 K. Thermal stability of the TiO2 nanoclusters prepared at 300 K was evaluated with AES and STM. No change in oxidation state for the TiO2 nanoclusters or etching of the Gr layer was observed up to ∼900 K. Annealing studies revealed that cluster ripening proceeds via a Smoluchowski mechanism below 800 K. Above 800 K, the changes in cluster shapes indicate an onset of diffusion within the clusters. At even higher temperatures, the nanoclusters undergo reduction to TiOx (x ≈ 1-1.5) which is accompanied by oxidation and etching of the Gr. Our studies demonstrate that highly thermally stable TiOx nanoclusters of controlled composition and morphology can be prepared on Gr supports.

Dodecameric (Sn12 ) and hexameric topologies dominate monoalkyltin-oxo cluster chemistry. Their condensation, triggered by radiation exposure, recently produced unprecedented patterning performance in EUV lithography. A new cluster topology was crystallized from industrial n-BuSnOOH, and additional characterization techniques indicate other clusters are present. Single-crystal X-ray analysis reveals a β-Keggin cluster, which is known but less common than other Keggin isomers in polyoxometalate and polyoxocation chemistry. The structure is formulated [NaO4 (BuSn)12 (OH)3 (O)9 (OCH3 )12 (Sn(H2 O)2 )] (β-NaSn13 ). SAXS, NMR, and ESI MS differentiate β-NaSn13 , Sn12 , and other clusters present in crude "n-BuSnOOH" and highlight the role of Na as a template for alkyltin Keggin clusters. Unlike other alkyltin clusters that are cationic, β-NaSn13 is neutral. Consequently, it stands as a unique model system, absent of counterions, to study the transformation of clusters to films and nanopatterns.

Inorganic resists are of interest for nanomanufacturing due to the potential for high resolution, low line width roughness, and high sensitivity. The combination of high absorption coefficient elements and radiation sensitive ligands can improve inorganic resist sensitivity while still allowing high contrast for extreme ultraviolet (EUV) lithography. A prototypical resist is Hf(OH)4-2x-2y(O2)x(SO4)y·qH2O (HafSOx), which has both high absorption coefficient elements (Hf) and radiation sensitive ligands (peroxides). Herein, we evaluate the use of electron stimulated desorption (ESD) to characterize HafSOx. These results indicate that the peroxo species are extremely radiation sensitive, even for low kinetic energy electrons that approximate the range of electron energies expected during EUV exposures. The primary desorption products from HafSOx are O2 and H2O, where the time evolution suggest much faster desorption kinetics for O2. These data provide insight into the radiation-induced changes responsible for the solubility transition upon exposure and dissolution during development, and the role of low kinetic energy electrons in these processes. The following describes our experimental methodology for the ESD studies, and the specific kinetic model used to extract total desorption cross sections from the ESD data.

The authors present a facile, low-cost methodology to fabricate high-performance In-Ga-Zn-O (IGZO) bottom contact, bottom gate thin-film transistors (TFTs) by soft lithography. The IGZO channel and indium tin oxide (ITO) source and drain were patterned using microcontact printing of an octadecylphosphonic acid self-assembled monolayer (SAM). A polymer stamp was used for the pattern transfer of the SAMs, which were then used as a chemical protection layer during wet etching. Excellent pattern transfer was obtained with good resolution and sharp step profiles. X-ray photoelectron spectroscopy indicated that the microcontact printed SAMs can be effectively removed from the ITO source/drain surfaces, allowing a high-quality interface to the IGZO channel for good device performance. Scanning electron microscopy cross-sections of the devices indicate a smooth and defect-free transition regions between the source/drain and semiconductor regions. The fabricated TFTs have negligible gate-leakage currents, high average electron mobilities of 10.2 cm2/Vs, and excellent on-off ratios of 2.1 × 108. These results may provide new methodologies for low-cost and large-area integration of IGZO-TFTs for a range of applications including flexible and transparent displays.

In this paper we present a novel fabrication technique that utilizes polycaprolactone (PCL) as a bonding medium due to its low melting temperature property. PCL is biodegradable polyester with a melting point of 60 degrees C, and a glass transition temperature of -60 degrees C [1-10]. It is used as a rapid bonding medium in the fabrication process that readily produces complete microfluidic chips. The microchannels are produced via laser ablation micromachining and thermal embossing, followed by bonding with PCL. The PCL is uniformly coated on a piece of polymer sheet to produce a thin film on its surface. A complete microfluidic channel is formed by enclosing the open channel with the PCL-coated polymer piece. This fabrication technique lends itself readily to various polymers, such as (poly) methylmethacrylate (PMMA), polycarbonate (PC), polyetherimide (PEI) and poly(ethylene terephthalate) (PETE), facilitating device production for a variety of application, even permitting hybrid polymer chips. The bonding was performed rapidly at 60 degrees C. This approach provides a more direct method to generate hard polymer microfluidic chips than classical techniques and is therefore highly amendable to rapid prototyping. This work also explores the use of PCL as an alternative approach to making simple, cost-effective universal adhesive for bonding interconnects. Bonding is performed at 60 degrees C, by placing the adhesive layer in between an interconnect port and a microchip. This method allows for connections to be made easily and quickly.