Engineering topics

Cordova, Isvar A.

Publications and source records attributed to Cordova, Isvar A..

5 records

DOE OSTI2021

Chemical and structural characterization of EUV photoresists as a function of depth by standing-wave x-ray photoelectron spectroscopy

The success in the miniaturization of the electronic device constituents depends mostly on the photolithographic techniques. Recently, to achieve patterning at the sub-10-nm node, extreme ultraviolet (EUV) lithography has been introduced into high volume production. Continued scaling of EUV via increased numerical aperture to achieve nodes at 3-nm and below requires the development of fundamentally new patterning materials and new characterization methods. Current EUV-resist film thicknesses are in the 20- to 40-nm range, and further thickness reduction is required for the next generation. Therefore, interfaces become exceedingly important, and the properties of the resist film would be dominated by top and bottom interfacial effects. X-ray photoelectron spectroscopy (XPS) combined with standing-wave excitation (SW-XPS), a fairly new method in the EUV lithography field, previously had been largely applied in multilayers and superlattices for characterizing the composition and electronic structure of buried layers and interfaces as a function of depth. We applied the SW-XPS method to organic/inorganic photoresists to provide depth-selective information on their structural and chemical conditions of as a function of temperature, EUV exposure, different underlayers, and other fundamental parameters. As a first attempt, we perform an SW-XPS feasibility study on self-assembled monolayer (SAM) films after exposure to an electron beam. By SW-XPS, we determined that the interface between the Al 2 O 3 underlayer and the SAMs is smooth, with a mean roughness of about 0.2 nm. Moreover, we determined that the SAM chains are, on average, tilted by 1/430 deg off the sample normal. The SW-XPS results also suggest that the SAM is not a perfectly aligned and uniform monolayer, with some areas having thickness higher than a single monolayer. We demonstrated that SW-XPS can provide useful information on ultrathin materials with high potential for being used as a characterization method of organic/inorganic photoresists.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Label-free characterization of organic nanocarriers reveals persistent single molecule cores for hydrocarbon sequestration

Self-assembled molecular nanostructures embody an enormous potential for new technologies, therapeutics, and understanding of molecular biofunctions. Their structure and function are dependent on local environments, necessitating in-situ/operando investigations for the biggest leaps in discovery and design. However, the most advanced of such investigations involve laborious labeling methods that can disrupt behavior or are not fast enough to capture stimuli-responsive phenomena. We utilize X-rays resonant with molecular bonds to demonstrate an in-situ nanoprobe that eliminates the need for labels and enables data collection times within seconds. Our analytical spectral model quantifies the structure, molecular composition, and dynamics of a copolymer micelle drug delivery platform using resonant soft X-rays. We additionally apply this technique to a hydrocarbon sequestrating polysoap micelle and discover that the critical organic-capturing domain does not coalesce upon aggregation but retains distinct single-molecule cores. This characteristic promotes its efficiency of hydrocarbon sequestration for applications like oil spill remediation and drug delivery. Such a technique enables operando, chemically sensitive investigations of any aqueous molecular nanostructure, label-free.

36 MATERIALS SCIENCE↗

DOE OSTI2020

LixNiO/Ni Heterostructure with Strong Basic Lattice Oxygen Enables Electrocatalytic Hydrogen Evolution with Pt-like Activity

The low-cost hydrogen production from water electrolysis is crucial for practical deployment of sustainable hydrogen economy, but is often constrained by the lack of active and robust electrocatalysts from Earth-abundant materials. We describe here an unconventional heterostructure composed of strongly coupled Ni-deficient LixNiO nanoclusters and polycrystalline Ni nanocrystals, and its exceptional activities toward hydrogen evolution reaction (HER) in aqueous electrolytes. The presence of unique lattice oxygen species with strong Brønsted basicity is a significant feature, which spontaneously split water molecules and effectively accelerate the sluggish Volmer H-OH dissociation step in neutral and alkaline HER. In combination with the unpreceded level of intimate LixNiO and Ni interfacial junctions that produces abundant “hotspots” for promoted hydride coupling, the catalyst exhibited kinetic activities almost identical as Pt/C and decent long term stability in universal pH.

Lu, Ke↗

DOE OSTI2019

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers

The performance of ion-conducting polymer membranes is complicated by an intricate interplay between chemistry and morphology that is challenging to understand. In this paper, we report on perfuoro ionene chain extended (PFICE) ionomers that contain either one or two bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers exhibit greater water uptake and conductivity compared to prototypical perfluorinated sulfonic acid ionomers. Advanced in situ synchrotron characterization reveals insights into the connections between molecular structure and morphology that dictate performance. Guided by first-principles calculations, X-ray absorption spectroscopy at the sulfur K-edge can discern distinct protogenic groups and be sensitive to hydration level and configurations that dictate proton dissociation. In situ resonant X-ray scattering at the sulfur K-edge reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated states. The enhanced conductivity of PFICE ionomers is attributed to a unique multi-acid side-chain chemistry and structure that facilitates proton dissociation at low water content in combination with a well-ordered phase-separated morphology with nanoscale transport pathways. Overall, these results provide insights for the design of new ionomers with tunable phase separation and improved transport properties as well as demonstrating the efficacy of X-rays with elemental sensitivity for unraveling structural features in chemically heterogeneous functional materials for electrochemical energy applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Reconstructing the three-dimensional latent image of extreme ultraviolet resists with resonant soft x-ray scattering

© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE). Extreme ultraviolet (EUV) lithography is one of the most promising printing techniques for high-volume semiconductor manufacturing at the 14-nm half-pitch device node and beyond. However, key challenges around EUV photoresist materials, such as the exposure-dose sensitivity or the line-width roughness, continue to impede its full adoption into industrial nanofab facilities. Metrology tools are required to address these challenges by helping to assess the impact of the EUV materials' properties and processing conditions along different steps of the nanofabrication process. We apply the resonant soft x-ray scattering (RSoXS) technique to gain insights into the structure of patterned EUV resists before the development step takes place. By using energies around the carbon K-edge to take advantage of small differences in chemistry, the electronic density contrast between the exposed and unexposed regions of the resists could be enhanced in order to image the patterns with subnanometer precision. Critical-dimension grazing-incidence small-angle x-ray scattering is then performed at energies where the contrast is maximized, enabling the reconstruction of the three-dimensional shape of the latent image. We demonstrate the potential of RSoXS to provide a high-resolution height-sensitive profile of patterned EUV resists, which will help in quantifying the evolution of critical features, such as the line-edge roughness, at a key step of the nanofabrication process.

Freychet, Guillaume↗