Enhancing Si3N4 Selectivity over SiO2 in Low-RF Power NF3-O2 Reactive Ion Etching: The Effect of NO Surface Reaction.

Highly selective etching of silicon nitride (Si3N4) and silicon dioxide (SiO2) has received considerable attention from the semiconductor community owing to its precise patterning and cost efficiency. We investigated the etching selectivity of Si3N4 and SiO2 in an NF3/O2 radio-frequency glow discharge. The etch rate linearly depended on the source and bias powers, whereas the etch selectivity was affected by the power and ratio of the gas mixture. We found that the selectivity can be controlled by lowering the power with a suitable gas ratio, which affects the surface reaction during the etching process. X-ray photoelectron spectroscopy of the Si3N4 and QMS measurements support the effect of surface reaction on the selectivity change by surface oxidation and nitrogen reduction with the increasing flow of O2. We suggest that the creation of SiOxNy bonds on the surface by NO oxidation is the key mechanism to change the etch selectivity of Si3N4 over SiO2.

Artificial-Neural-Network-Driven Innovations in Time-Varying Process Diagnosis of Low-K Oxide Deposition.

To address the challenges in real-time process diagnosis within the semiconductor manufacturing industry, this paper presents a novel machine learning approach for analyzing the time-varying 10th harmonics during the deposition of low-k oxide (SiOF) on a 600 Å undoped silicate glass thin liner using a high-density plasma chemical vapor deposition system. The 10th harmonics, which are high-frequency components 10 times the fundamental frequency, are generated in the plasma sheath because of their nonlinear nature. An artificial neural network with a three-hidden-layer architecture was applied and optimized using k-fold cross-validation to analyze the harmonics generated in the plasma sheath during the deposition process. The model exhibited a binary cross-entropy loss of 0.1277 and achieved an accuracy of 0.9461. This approach enables the accurate prediction of process performance, resulting in significant cost reduction and enhancement of semiconductor manufacturing processes. This model has the potential to improve defect control and yield, thereby benefiting the semiconductor industry. Despite the limitations imposed by the limited dataset, the model demonstrated promising results, and further performance improvements are anticipated with the inclusion of additional data in future studies.

Diagnosing Time-Varying Harmonics in Low-k Oxide Thin Film (SiOF) Deposition by Using HDP CVD.

This study identified time-varying harmonic characteristics in a high-density plasma (HDP) chemical vapor deposition (CVD) chamber by depositing low-k oxide (SiOF). The characteristics of harmonics are caused by the nonlinear Lorentz force and the nonlinear nature of the sheath. In this study, a noninvasive directional coupler was used to collect harmonic power in the forward and reverse directions, which were low frequency (LF) and high bias radio frequency (RF). The intensity of the 2nd and 3rd harmonics responded to the LF power, pressure, and gas flow rate introduced for plasma generation. Meanwhile, the intensity of the 6th harmonic responded to the oxygen fraction in the transition step. The intensity of the 7th (forward) and 10th (in reverse) harmonic of the bias RF power depended on the underlying layers (silicon rich oxide (SRO) and undoped silicate glass (USG)) and the deposition of the SiOF layer. In particular, the 10th (reverse) harmonic of the bias RF power was identified using electrodynamics in a double capacitor model of the plasma sheath and the deposited dielectric material. The plasma-induced electronic charging effect on the deposited film resulted in the time-varying characteristic of the 10th harmonic (in reverse) of the bias RF power. The wafer-to-wafer consistency and stability of the time-varying characteristic were investigated. The findings of this study can be applied to in situ diagnosis of SiOF thin film deposition and optimization of the deposition process.

Boosting Electrochemical Activity of Porous Transparent Conductive Oxides Electrodes Prepared by Sequential Infiltration Synthesis.

Sequential infiltration synthesis (SIS) is an emerging technique for producing inorganic-organic hybrid materials and templated inorganic nanomaterials. The application space for SIS is expanding rapidly in areas such as lithography, filtration, photovoltaics, antireflection, and triboelectricity, but not in the field of electrochemistry. This study performs SIS for the fabrication of porous, transparent, and electrically conductive films of indium zinc oxide (IZO) to evaluate their potential as an electrode for electrochemistry. The electrochemical activity of IZO-coated electrodes is evaluated when their surfaces are modified with ferrocenecarboxylic acid (FcCOOH), a model redox molecule. Results show a 25-fold enhancement in peak current densities mediated by an Fc/Fc+ redox couple for an IZO-coated electrode in comparison with bare electrodes; this is afforded by the porous morphology of the IZO film and the enhanced binding efficiency of FcCOOH on the IZO film. The results confirm the potential of SIS for the preparation of porous transparent conducting oxide electrodes, which will enable the application of SIS-derived materials in various electrochemical fields.

Understanding Physicochemical Mechanisms of Sequential Infiltration Synthesis toward Rational Process Design for Uniform Incorporation of Metal Oxides.

Sequential infiltration synthesis (SIS) is a novel technique for fabricating organic-inorganic hybrid materials and porous inorganic materials by leveraging the diffusion of gas-phase precursors into a polymer matrix and chemical reactions between the precursors to synthesize inorganic materials therein. This study aims to obtain a fundamental understanding of the physicochemical mechanisms behind SIS, from which the SIS processing conditions are rationally designed to obtain precise control over the distribution of metal oxides. Herein, in situ FTIR spectroscopy was correlated with various ex situ characterization techniques to study a model system involving the growth of aluminum oxides in poly(methyl methacrylate) using trimethyl aluminum (TMA) and water as the metal precursor and co-reactant, respectively. We identified the prominent chemical states of the sorbed TMA precursors: (1) freely diffusing precursors, (2) weakly bound precursors, and (3) precursors strongly bonded to pre-existing oxide clusters and studied how their relative contributions to oxide formation vary in relation to the changes in the rate-limiting step under different growth conditions. Finally, we demonstrate that uniform incorporation of metal oxide is realized by a rational design of processing conditions, by which the major chemical species contributing to oxide formation is modulated.

The Fabrication of Cesium Lead Bromide-Coated Cellulose Nanocomposites and Their Effect on the Detection of Nitrogen Gas.

In this work, we fabricate cesium lead bromide nanofibers (CsPbBr3 NFs) via the attachment of cesium lead bromide nanocrystals (CsPbBr3 NCs) on the surface of electrospun cellulose nanofibers (CNFs) and employ them in a sensor to effectively detect gaseous nitrogen. The CsPbBr3 NFs are produced initially by producing CsPbBr3 NCs through hot injection and dispersing on hexane, followed by dipping CNFs and ultrasonicate for 1 h. Morphological characterization through visual, SEM and TEM image, and crystalline structure analysis by XRD and FT-IR analysis of CsPbBr3 NFs and NCs show similar spectra except for PL due to unavoidable damage during the ultrasonication. Gaseous nitrogen is subsequently detected using the photoluminescence (PL) property of CsPbBr3 NFs, in which the PL intensity dramatically decreases under various flow rate. Therefore, we believe that the proposed CsPbBr3 NFs show significant promise for use in detection sensors in various industrial field and decrease the potential of fatal damage to workers due to suffocation.

Chromism-Integrated Sensors and Devices for Visual Indicators.

The bifunctionality of chromism-integrated sensors and devices has been highlighted because of their reversibility, fast response, and visual indication. For example, one of the representative chromism electrochromic materials exhibits optical modulation under ion insertion/extraction by applying a potential. This operation mechanism can be integrated with various sensors (pressure, strain, biomolecules, gas, etc.) and devices (energy conversion/storage systems) as visual indicators for user-friendly operation. In this review, recent advances in the field of chromism-integrated systems for visual indicators are categorized for various chromism-integrated sensors and devices. This review can provide insights for researchers working on chromism, sensors, or devices. The integrated chromic devices are evaluated in terms of coloration-bleach operation, cycling stability, and coloration efficiency. In addition, the existing challenges and prospects for chromism-integrated sensors and devices are summarized for further research.

Concurrent and Selective Determination of Dopamine and Serotonin with Flexible WS2 /Graphene/Polyimide Electrode Using Cold Plasma.

Makers of point-of-care devices and wearable diagnostics prefer flexible electrodes over conventional electrodes. In this study, a flexible electrode platform is introduced with a WS2 /graphene heterostructure on polyimide (WGP) for the concurrent and selective determination of dopamine and serotonin. The WGP is fabricated directly via plasma-enhanced chemical vapor deposition (PECVD) at 150 °C on a flexible polyimide substrate. Owing to the limitations of existing fabrication methods from physical transfer or hydrothermal methods, many studies are not conducted despite excellent graphene-based heterostructures. The PECVD synthesis method can provide an innovative WS2 /graphene heterostructure of uniform quality and sufficient size (4 in.). This unique heterostructure affords excellent electrical conductivity in graphene and numerous electrochemically active sites in WS2 . A large number of uniform qualities of WGP electrodes show reproducible and highly sensitive electrochemical results. The synergistic effect enabled well-separated voltammetric signals for dopamine and serotonin with a potential gap of 188 mV. Moreover, the practical application of the flexible sensor is successfully evaluated by using artificial cerebrospinal fluid.

Recyclable free-polymer transfer of nano-grain MoS2 film onto arbitrary substrates.

Clean transfer of transition metal dichalcogenides (TMDs) film is highly desirable, as intrinsic properties of TMDs may be degraded in a conventional wet transfer process using a polymer-based resist and toxic chemical solvent. Residues from the resists often remain on the transferred TMDs, thereby causing a significant variation in their electrical and optical characteristics. Therefore, an alternative to the conventional wet transfer method is needed-one in which no residue is left behind. Herein, we report that our molybdenum disulfide (MoS2) films synthesized by plasma-enhanced chemical vapor deposition can be easily transferred onto arbitrary substrates (such as SiO2/Si, polyimide, fluorine-doped tin oxide, and polyethersulfone) by using water alone, i.e. without residues or chemical solvents. The transferred MoS2 film retains its original morphology and physical properties, which are investigated by optical microscopy, atomic force microscopy, Raman, x-ray photoelectron spectroscopy, and surface tension analysis. Furthermore, we demonstrate multiple recycling of the resist-free transfer for the nano-grain MoS2 film. Using the proposed water-assisted and recyclable transfer, MoS2/p-doped Si wafer photodiode was fabricated, and the opto-electric properties of the photodiode were characterized to demonstrate the feasibility of the proposed method.

Development of Force Sensor System Based on Tri-Axial Fiber Bragg Grating with Flexure Structure.

Fiber Bragg grating (FBG) sensors have an advantage over optical sensors in that they are lightweight, easy to terminate, and have a high flexibility and a low cost. Additionally, FBG is highly sensitive to strain and temperature, which is why it has been used in FBG force sensor systems for cardiac catheterization. When manually inserting the catheter, the physician should sense the force at the catheter tip under the limitation of power (<0.5 N). The FBG force sensor can be optimal for a catheter as it can be small, low-cost, easy to manufacture, free of electromagnetic interference, and is materially biocompatible with humans. In this study, FBG fibers mounted on two different flexure structures were designed and simulated using ANSYS simulation software to verify their sensitivity and durability for use in a catheter tip. The selected flexure was combined with three FBGs and an interrogator to obtain the wavelength signals. To obtain a calibration curve, the FBG sensor obtained data on the change in wavelength with force at a high resolution of 0.01 N within the 0.1-0.5 N range. The calibration curve was used in the force sensor system by the LabVIEW program to measure the unknown force values in real time.

Flexible MoS2-Polyimide Electrode for Electrochemical Biosensors and Their Applications for the Highly Sensitive Quantification of Endocrine Hormones: PTH, T3, and T4.

Flexibile biosensors have a lot of applications in measuring the concentration of target bioanalytes. In combination with its flexibility, electrochemical sensors containing 2D materials have particular advantages such as enlarged area compatibility, transparency, and high scalability. A flexible biosensor was fabricated by direct synthesis of molybdenum disulfide (MoS2) on a polyimide (PI) substrate, which can be used as the working electrode in electrochemistry platforms. The direct formation of 2D-MoS2 on the PI was achieved using plasma-enhanced chemical vapor deposition (PE-CVD). Since the MoS2 provides higher electrical conductivity, the MoS2-Au-PI flexible sensor is able to provide highly sensitive detection of target proteins with a relatively fast response via cyclic voltammetry. To evaluate the high performance of the fabricated sensor, we selected the endocrine-related hormones parathyroid hormone (PTH), triiodothyronine (T3), and thyroxine (T4) as analytes because they are one of the most important markers for the determination of endocrinopathy, however, they are very difficult to quantify. The newly developed biosensor achieved highly sensitive detection of the hormones and could determine their location with high accuracy. In addition, we performed electrochemical measurements of hormones obtained from 30 clinical patients' sera with confirmed agreement and compared with the measurements performed with standard immunoassay equipment (E 170, Roche Diagnostics, Germany).

Wafer-Scale and Low-Temperature Growth of 1T-WS2 Film for Efficient and Stable Hydrogen Evolution Reaction.

The metallic 1T phase of WS2 (1T-WS2 ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS2 (2H-WS2 ) is inherently stable, methods for synthesizing 1T-WS2 are limited and complicated. Herein, a uniform wafer-scale 1T-WS2 film is prepared using a plasma-enhanced chemical vapor deposition (PE-CVD) system. The growth temperature is maintained at 150 °C enabling the direct synthesis of 1T-WS2 films on both rigid dielectric and flexible polymer substrates. Both the crystallinity and number of layers of the as-grown 1T-WS2 are verified by various spectroscopic and microscopic analyses. A distorted 1T structure with a 2a0 × a0 superlattice is observed using scanning transmission electron microscopy. An electrochemical analysis of the 1T-WS2 film demonstrates its similar catalytic activity and high durability as compared to those of previously reported untreated and planar 1T-WS2 films synthesized with CVD and hydrothermal methods. The 1T-WS2 does not transform to stable 2H-WS2 , even after a 700 h exposure to harsh catalytic conditions and 1000 cycles of HERs. This synthetic strategy can provide a facile method to synthesize uniform 1T-phase 2D materials for electrocatalysis applications.

Effect of Copper Foil Crystal Orientation on Graphene Quality Synthesized by Chemical Vapor Deposition.

Line defects such as wrinkles are believed to change the electrical properties of graphene. However, they are often observed in graphene grown via chemical vapor deposition; hence, it is important to study the impact of the substrate condition on graphene quality. In this work, graphene was synthesized on various copper domains with different crystal orientations and surface morphologies. During the synthesis process, three typical crystal orientations were obtained Cu(001), Cu(101), and Cu(111) showing different surface morphologies with various densities of wrinkles. Graphene wrinkles along with copper wrinkles were studied using atomic force microscopy and Kelvin probe force microscopy. The quality of graphene on different crystal orientations and morphologies was evaluated as well. It was found that different crystallographic orientations lead to different degrees of wrinkle and roughness. In addition, these wrinkle defects exhibited characteristic surface potential variations and the density of substrate wrinkles was closely associated with the uniformity of graphene and led to a disordered structure and low crystallinity.

Sol-Gel Assisted Isotropic Morphological Progression in Nanostructured MoO3 and Allied Investigations on Photocatalytic Dye-Degradation.

We report tunable-morphology oriented facile yet scalable route to synthesize 1D (nanorod) and 2D (nanobelt) MoO3 nanostructures at gram scale using conventional as well as sonochemistry assisted sol-gel technique. The structural, morphological and optical properties of the samples can be befittingly altered by varying the synthesis protocol. The resultant orthorhombic MoO3 nanomorphs demonstrated efficient and expeditious photocatalytic degradation of the pollutant dye, Methylene Blue (MB). We have observed that appreciable photocatalytic MB dye-degradation can be accomplished within 30 minutes with high rate constants of 0.0786 min-1 and 0.233 min-1 for rod and belt-like MoO3-nanostructures, respectively. The pilot results indicate that the resultant MoO3 nanomorphs can be potentially used as solar light driven industrial photocatalyst material with their intrinsic photostability.

Highly uniform wafer-scale synthesis of α-MoO3 by plasma enhanced chemical vapor deposition.

Molybdenum oxide (MoO3) has gained immense attention because of its high electron mobility, wide band gap, and excellent optical and catalytic properties. However, the synthesis of uniform and large-area MoO3 is challenging. Here, we report the synthesis of wafer-scale α-MoO3 by plasma oxidation of Mo deposited on Si/SiO2. Mo was oxidized by O2 plasma in a plasma enhanced chemical vapor deposition (PECVD) system at 150 °C. It was found that the synthesized α-MoO3 had a highly uniform crystalline structure. For the as-synthesized α-MoO3 sensor, we observed a current change when the relative humidity was increased from 11% to 95%. The sensor was exposed to different humidity levels with fast recovery time of about 8 s. Hence this feasibility study shows that MoO3 synthesized at low temperature can be utilized for gas sensing applications by adopting flexible device technology.

Electron Release via Internal Polarization Fields for Optimal S-H Bonding States.

Transition metal dichalcogenides (TMDs) have received considerable attention as promising electrocatalysts for the hydrogen evolution reaction (HER), yet their potential is often constrained by the inertness of the basal planes arising from their poor hydrogen adsorption ability. Here, the relationship between the electronic structure of the WS2 basal plane and HER activity is systemically analyzed to establish a clear insight. The valance state of the sulfur atoms on the basal plane has been tuned to enhance hydrogen adsorption through sequential engineering processes, including direct phase transition and heterostructure that induces work function-difference-induced unidirectional electron transfer. Additionally, an innovative synthetic approach, harnessing the built-in internal polarization field at the W-graphene heterointerface, triggers the in-situ formation of sulfur vacancies in the bottom WSx (x < 2) layers. The resultant modulation of the valance state of the sulfur atom stabilizes the W-S bond, while destabilizing the S-H bond. The electronic structural changes are further amplified by the release and transfer of surplus electrons via sulfur vacancies, filling the valance state of W and S atoms. Consequently, this work provides a comprehensive understanding of the interplay between the electronic structure of the WS2 basal plane and the HER activity, focusing on optimizing S-H bonding state.

Key Factors in Enhancing Pseudocapacitive Properties of PANI-InOx Hybrid Thin Films Prepared by Sequential Infiltration Synthesis.

Sequential infiltration synthesis (SIS) is an emerging vapor-phase synthetic route for the preparation of organic-inorganic composites. Previously, we investigated the potential of polyaniline (PANI)-InOx composite thin films prepared using SIS for application in electrochemical energy storage. In this study, we investigated the effects of the number of InOx SIS cycles on the chemical and electrochemical properties of PANI-InOx thin films via combined characterization using X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and cyclic voltammetry. The area-specific capacitance values of PANI-InOx samples prepared with 10, 20, 50, and 100 SIS cycles were 1.1, 0.8, 1.4, and 0.96 mF/cm², respectively. Our result shows that the formation of an enlarged PANI-InOx mixed region directly exposed to the electrolyte is key to enhancing the pseudocapacitive properties of the composite films.

Uniformity of HfO2 Thin Films Prepared on Trench Structures via Plasma-Enhanced Atomic Layer Deposition.

In this study, we assessed the physical and chemical properties of HfO2 thin films deposited by plasma-enhanced atomic layer deposition (PEALD). We confirmed the self-limiting nature of the surface reactions involved in the HfO2 thin film's growth by tracing the changes in the growth rate and refractive index with respect to the different dose times of the Hf precursor and O2 plasma. The PEALD conditions were optimized with consideration of the lowest surface roughness of the films, which was measured by atomic force microscopy (AFM). High-resolution X-ray photoelectron spectroscopy (XPS) was utilized to characterize the chemical compositions, and the local chemical environments of the HfO2 thin films were characterized based on their surface roughness and chemical compositions. The surface roughness and chemical bonding states were significantly influenced by the flow rate and plasma power of the O2 plasma. We also examined the uniformity of the films on an 8″ Si wafer and analyzed the step coverage on a trench structure of 1:13 aspect ratio. In addition, the crystallinity and crystalline phases of the thin films prepared under different annealing conditions and underlying layers were analyzed.

The first progress of plasma-based transition metal dichalcogenide synthesis: a stable 1T phase and promising applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted attention as polymorphs depending on their phases (1T and 2H) when applying typical synthesis methods. The 2H phase is generally synthesised through chemical vapour deposition (CVD) on a wafer-scale at high temperatures, and many synthesis methods have been reported owing to their thermodynamic stability and semiconductor properties. By contrast, although the 1T phase is meta-stable with an octahedral coordination, thereby limiting the use of synthesis methods, the recent structural advantage in terms of the hydrogen evolution reaction (HER) has been emphasised. Despite this demand, no large-area thin-film synthesis method for 1T-TMDs has been developed. Among several strategies of synthesizing metallic-phase (1T) TMDs, chemical exfoliation (alkali metal intercalation) is a major strategy and others have been used for electron-beam irradiation, laser irradiation, defects, plasma hot electron transfer, and mechanical strain. Therefore, we suggest an innovative synthesis method using plasma-enhanced CVD (PECVD) for both the 1T and 2H phases of TMDs (MoS2 and WS2). Because ions and radicals are accelerated to the substrate within the sheath region, a high-temperature source is not needed for vapour ionisation, and thus the process temperature can be significantly lowered (150 °C). Moreover, a 4-inch wafer-scale of a thin film is an advantage and can be synthesised on arbitrary substrates (SiO2/Si wafer, glassy carbon electrode, Teflon, and polyimide). Furthermore, the PECVD method was applied to TMD-graphene heterostructure films with a graphene-transferred substrate, and for the first time, sequential metal seed layer depositions of W (1 nm) and Mo (1 nm) were sulfurized to MoS2-WS2 vertical heterostructures with Ar + H2S plasma. We considered the prospects and challenges of the new PECVD method in the development of practical applications in next-generation integrated electronics, HER catalysts, and flexible biosensors.

Bioaerosol monitoring by integrating DC impedance microfluidic cytometer with wet-cyclone air sampler.

The recent outbreak of COVID-19 has highlighted the seriousness of airborne diseases and the need for a proper pathogen detection system. Compared to the ample amount of research on biological detection, work on integrated devices for air monitoring is rare. In this work, we integrated a wet-cyclone air sampler and a DC impedance microfluidic cytometer to build a cyclone-cytometer integrated air monitor (CCAM). The wet-cyclone air sampler sucks the air and concentrates the bioaerosols into 10 mL of aqueous solvent. After 5 min of air sampling, the bioaerosol-containing solution was conveyed to the microfluidic cytometer for detection. The device was tested with aerosolized microbeads, dust, and Escherichia coli (E. coli). CCAM is shown to differentiate particles from 0.96 to 2.95 µm with high accuracy. The wet cyclone air-sampler showed a 28.04% sampling efficiency, and the DC impedance cytometer showed 87.68% detection efficiency, giving a total of 24.59% overall CCAM efficiency. After validation of the device performance, CCAM was used to detect bacterial aerosols and their viability without any separate pretreatment step. Differentiation of dust, live E. coli, and dead E. coli was successfully performed by the addition of BacLight bacterial viability reagent in the sampling solvent. The usage could be further extended to detection of specific species with proper antibody fluorescent label. A promising strategy for aerosol detection is proposed through the constructive integration of a DC impedance microfluidic cytometer and a wet-cyclone air sampler.