Two-step Etching Method Research Articles

Etch characteristics of maskless oxide/nitride/oxide/nitride (ONON) stacked structure using C4H2F6-based gas

Oxide/Nitride/Oxide/Nitride (ONON; SiO2/SiNx/SiO2/SiNx) stacked structure is widely used in the 3D vertical structure of semiconductor cells. Previously, to form a 3D cells, photoresist (PR) was patterned and repeatedly trimmed on the top of ONON after the etching of one ON layer. Due to the time-consuming process of etching layer-by-layer of ON layer, two-step etch processing using C4F8-based or C4F6-based gases composed of maskless ONON stack feature etching and followed one ON layer-by layer etching by PR trimming in the ONON stack feature are employed these days. However, the two-step etching method resulted in poor etch profiles of maskless ONON stack feature in addition to high global warming potential of C4F8 and C4F6. In this study, we investigated the etching of maskless ONON stack feature using C4H2F6-based gas having a low global warming potential and the effects of C4H2F6-based gas on the etch characteristics of maskless ONON stack feature such as etch rate, etch profile, change in critical dimensional (CD), and etch selectivity between SiO2 and SiNx have been investigated. C4H2F6-based gas showed the highest etch rates compared to C4F6 and C4F8-based gases in addition to the etch selectivity of ~ 1:1 between SiO2 and SiNx due to hydrogen included in the gas structure. In addition, the change in horizontal CD was lower in the order of C4H2F6, C4F6, and C4F8-based gases due to the more effective sidewall passivation in the order of C4F8, C4F6, and C4H2F6-based gases. The thicker carbon-based polymer layer on the sidewall also played an important role in maintaining the shape of the top edge shape of maskless ONON stack feature when etching a line feature in an environment without a mask.

Application of silicon nanowires in sensors of temperature, light and humidity

Resistive and capacitive types of sensors based on silicon nanowires (SiNWs) for measuring of physical quantities have been manufactured. Silicon nanowires were obtained through a two-step metal-assisted chemical etching (MACE) method. The surface morphology of the silicon nanowire array was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The impact of SiNWs synthesis parameters on sensor sensitivity has been investigated. In particular, the influence of deposition time of AgNPs and etching time of silicon, as well as the content of H2O2 in the etchant, preliminary texturing of the substrate, and additional post-processing in isotropic/anisotropic etchant after the MACE process, on the characteristics of physical quantity sensors has been determined. Static and dynamic parameters were calculated for the obtained sensors. To compare the obtained sensors, physical sensors without SiNWs were manufactured. The highest response value for temperature sensors was 132, which is two orders of magnitude better than for sensors without SiNWs. The presence of SiNWs on the surface of the sensor led to an increase in the response value by about two orders of magnitude for all types of sensors. The speed of humidity sensors improved by 3–4 times, and for temperature and light sensors by an order of magnitude. Further device applications include of multi-parameter sensors, human breath sensors, and solar radiation power sensors.

A FeCrAl-Al2O3 Composite Produced Via Laser Powder Bed Fusion of a Mixed Powder for Porous Catalyst Scaffolds

Abstract This study proposes a novel approach for synthesizing and etching bicontinuous FeCrAl-Al2O3 composites as a means for replacing FeCrAl foams as catalyst scaffolds in biodriven alcohol reactors for jet-fuel production. Conventional FeCrAl foams suffer from poor availability and consequent high costs. New additive manufacturing techniques provide an opportunity to produce tailored foams at reasonable times and at acceptable costs. This research aimed to generate a porous FeCrAl structure by etching a bicontinuous FeCrAl-Al2O3 composite produced by laser powder bed fusion of amalgamated FeCrAl and Al2O3 powders. The composite powder for laser powder bed fusion is created by ball-milling FeCrAl and Al2O3 powders. This research focuses on achieving a bi-continuous FeCrAl-Al2O3 structure, essential for the selective removal of the ceramic phase. The influence of laser processing parameters on the microstructure was examined across a range of laser powers (60–120 W) and scan speeds (100–400 mm/s), showing that higher powers and speeds produce finer metal struts. A bi-continuous microstructure was consistently obtained, marking a key achievement. The Al2O3 removal process involved a two-step etching method using hydrochloric and phosphoric acids, tested across various etching times. The alumina phase was reduced from 36 vol% to 17 vol% (corresponding to an increase in porosity from 24 vol% to 43 vol%), showing the potential for use as a porous catalyst scaffold. This research demonstrates the potential for using additive manufacturing to produce porous FeCrAl structures capable of replacing hard-to-source FeCrAl foams.

Ti2NTx MXene/rGO nanocomposites: Optical tunning, functional bonding and electrochemical analysis for supercapacitor electrode application

Ti2NTx MXene/rGO nanocomposites were prepared via a two-step chemical etching and reduction method. TEM confirmed the stacked multilayer structure with an average interplanar spacing of 0.2 nm and the formation of Ti2NTx/rGO QDs of size from 0.14 to 0.33 nm. The absorption of Ti2NTx MXene/rGO composites decreased from 5.59 to 4.53 eV with increasing rGO concentration due to quantum confinement and microstructural rearrangement of Ti2NTx MXene within the rGO network. Cyclic voltammetry showed a specific capacitance (Cp) of 47.6–247F/g at 5 mV/s in −0.2–0.8 V. Galvanostatic charge–discharge resulted in Cp of 329.14–1203.86F/g at 1 A/g in 1 M H2SO4. The highest capacitive retention of 84.3 % was observed after 5000 cycles for Ti2NTx MXene. Electrochemical impedance spectra revealed that the charge transfer rate was maximum in (Ti2NTx)0.50/rGO0.50 due to the lowest RCT of 7.23 Ω. From the corrosion test, the Icorr ranged from 3.73 to 5.79 µA, and the Vcorr ranged from −0.008 to 0.26 V in the Ti2NTx MXene/rGO composites. Ti2NTx MXene/rGO composite showed remarkable electrochemical properties in acid electrolytes, such as high Cp and corrosion resistance, making them intriguing materials for supercapacitor electrode application.

Enhancing anti-reflective properties of electronic glass through two-step chemical etching

With the rapid growth of the electronic display industry, aluminosilicate glass has emerged as a replacement for traditional soda lime silica glass as the cover plate of various display devices because of its excellent physical and chemical properties. High transmittance and low reflectivity are the inevitable requirements of its application. However, few studies have been reported about the antireflection of aluminosilicate glass. In this study, a two-step etching method was employed to treat both sides of the alkali-aluminosilicate glass to obtain surface antireflection. Analytical methods such as EPMA, AFM, and UV spectrophotometry were utilized to evaluate the effect of the etching process and resultant surface microstructure on the optical properties of the glass. Furthermore, comparative research was conducted to distinguish the etching reaction differences between alkali-aluminosilicate glass and other glass compositions like soda-lime glass and high-boron-silicon glass. The results demonstrated that the controlled two-step etching process created a micro-porous surface structure, with a gradient refractive index. Subsequent to the secondary etching, the glass exhibits an impressive average transmittance of 98.88% within the visible light spectrum (380–780 nm). Moreover, identical etchant across different composition glasses leads to discernible differences in transmittance.

Unlocking the plasma advantage in elevating the performance of silicon nanowires/ poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) hybrid solar cell

Silicon Nanowires (SiNWs) can be easily synthesized by following the two-step electroless metal-assisted chemical etching method. These SiNWs are well known for their low reflectivity due to their excellent light-harvesting characteristics. In this paper, we demonstrated the effect of plasma treatment time on the performance of SiNWs solar cells. The 1 min plasma-treated SiNWs/Poly 3,4-[ethylene dioxy thiophene:Polystyrene sulfonate] (PEDOT׃PSS) solar cell showed increased power conversion efficiency than the untreated SiNWs/PEDOT׃PSS solar cell. The photo Current density-Voltage (J-V) analysis showed that the open circuit voltage (VOC) of the plasma treated solar cell for 1 min is higher (270 mV) than that of the untreated solar cell (120 mV). The increase in the value of VOC comes from different factors׃ one is due to the formation of a good interface between the SiNWs and PEDOT׃PSS layer; other is the reduction of defect densities in SiNWs/PEDOT׃PSS heterojunction, consequently the reduction in the recombination processes. Hence from this research, we found that by controlling the plasma treatment on SiNWs, it can improve the SiNWs properties which can further improve the efficiency of the solar cell.

In Situ Raman Study of Surface Reconstruction of FeOOH/Ni3S2 Oxygen Evolution Reaction Electrocatalysts.

Construction of heterojunctions is an effective strategy to enhanced electrocatalytic oxygen evolution reaction (OER), but the structural evolution of the active phases and synergistic mechanism still lack in-depth understanding. Here, an FeOOH/Ni3S2 heterostructure supported on nickel foam (NF) through a two-step hydrothermal-chemical etching method is reported. In situ Raman spectroscopy study of the surface reconstruction behaviors of FeOOH/Ni3S2/NF indicates that Ni3S2 can be rapidly converted to NiOOH, accompanied by the phase transition from α-FeOOH to β-FeOOH during the OER process. Importantly, a deep analysis of Ni─O bond reveals that the phase transition of FeOOH can regulate the lattice disorder of NiOOH for improved catalytic activity. Density functional theory (DFT) calculations further confirm that NiOOH/FeOOH heterostructure possess strengthened adsorption for O-containing intermediates, as well as lower energy barrier toward the OER. As a result, FeOOH/Ni3S2/NF exhibits promising OER activity and stability in alkaline conditions, requiring an overpotential of 268mV @ 100mAcm-2 and long-term stability over 200h at a current density of 200mAcm-2. This work provides a new perspective for understanding the synergistic mechanism of heterogeneous electrocatalysts during the OER process.

Modified two-step etching method for the synthesis of Ti3C2 MXene with enhanced electrochemical performance

This work presents a modified etching method for the synthesis of Ti3C2 MXene. The process involves two steps: washing Ti3AlC2 with a low concentration of HF and etching Ti3AlC2 with varying concentrations of FeCl3. FeCl3 can etch the Al layers of Ti3AlC2 by a metal displacement reaction at room temperature, resulting in Ti3C2 nanosheets with an accordion-like morphology. The obtained Ti3C2 MXene was tested as a working electrode for supercapacitors, achieving a maximum specific capacitance of 213.2F/g at 0.5 A/g in a 6 M KOH electrolyte solution, which is higher than that of a Ti3C2 electrode without modification. The method is simple, efficient and reduces the use of HF. This work shows the possibility of synthesizing various MXene-based frameworks using metallic cations with higher redox potentials.

Large scale fabrication of GaN nanorods template and characterization of MOCVD grown InGaN/GaN quantum wells on [formula omitted] plane of GaN nanorods

Gallium nitride (GaN) based low-dimensional optoelectronic devices offer distinct advantages over bulk counterparts owing to enhanced surface-to-volume ratio and better strain management. Among these devices, InGaN/GaN multi-quantum wells (MQWs) based on nanostructured GaN have garnered attention due to tunable bandgap along with reduced size for its possible integration into display technology. However, to mitigate the effects of polarization induced by polar planes of GaN, such as quantum confined stark effect, researchers are exploring the growth of MQWs on non-polar planes as a practical approach to improve emission characteristics and device performance. In this work, we present the fabrication of GaN nanorods (NRs) using a two-step etching method, followed by the growth of core-shell InGaN/GaN MQWs on the exposed non-polar {101‾0} sidewalls of GaN NRs. Our metrological studies confirmed the successful growth of InGaN/GaN MQWs on the non-polar sidewalls of strain-relaxed core GaN NRs. Furthermore, power-dependent luminescence study showed emission characteristics with absence of polarization-induced effects. Cathodoluminescence study validated the emission characteristics of InGaN/GaN MQWs grown on the exposed sidewalls of the GaN NRs.

Improving the adsorption performance of urea by using polyhydroxy groups to modify two-dimensional Ti3C2Tx

Wearable artificial kidney can provide continuous dynamic dialysis for uremia patients. For the sake of practical application, the critical step is to find an adsorbent that can effectively remove urea and have excellent biological compatibility. The layered Ti3C2Tx (DL-Ti3C2Tx) with high specific surface area and good dispersion was prepared by a two-step etching method. From the first principles calculation, urea can be adsorbed by different groups (−F, –O, –OH) on the surface of Ti3C2Tx, among which –OH has the greatest binding energy to urea. Therefore, DL-Ti3C2Tx was modified with different alkali solutions (KOH, NaOH, LiOH) to introduce –OH on the surface, which can increase the adsorption capacity of urea. The experimental results showed that DL-Ti3C2Tx (LiOH-Ti3C2Tx) after treated by LiOH had the highest urea adsorption efficiency, and the urea removal rate of LiOH-Ti3C2Tx was still higher than 92% when the urea concentration was 500 mg/L. In the Simulated dialysate, Ti3C2Tx treated with three kinds of alkali solutions still maintained a good adsorption efficiency for urea, and still had a certain adsorption capacity after recycling for four times. Biocompatibility experiments showed that Ti3C2Tx in different concentrations did not cause hemolysis of erythrocyte, and had no obvious damage to vascular endothelial cells. This study greatly improves the urea adsorption efficiency of MXene, which has a broad application prospect in the selection of adsorbent for wearable artificial kidney.

A Novel Simple Fabrication Method for Mechanically Robust Superhydrophobic 2024 Aluminum Alloy Surfaces

The mechanical durability of a superhydrophobic aluminum alloy surface is an important indicator of its practical use. Herein, we propose a strategy to prepare a superhydrophobic 2024 aluminum alloy surface with highly enhanced mechanical durability by using a two-step chemical etching method, using a NaOH solution as the etchant in step one and a Na2CO3 solution as the etchant in step two. Robust mechanical durability was studied by static contact angle tests before and after an abrasion test, potentiodynamic polarization measurements after an abrasion test and electrochemical impedance spectroscopy tests after an abrasion test. Furthermore, the mechanism for enhanced mechanical durability was investigated through scanning of electron microscopy images, energy-dispersive X-ray spectra, Fourier transform infrared spectra and X-ray photoelectron spectra. The testing results indicate that a hierarchical rough surface consisting of regular micro-scale dents and some nano-scale fibers in the micro-scale dents, obtained with the two-step chemical etching method, contributes to highly enhanced mechanical durability. Meanwhile, the as-prepared superhydrophobic 2024 aluminum alloy surface retained a silvery color instead of the black shown on the superhydrophobic 2024 aluminum alloy surface prepared by a conventional one-step chemical etching method using NaOH solution as the etchant.

Hydrogen etching of 4H–SiC(0001) facet and step formation

SiC has attracted much interest due to its vast applications in high power, high frequency and radiation-hardened electronics at high temperatures. Although the growth and processing technology for SiC wafers has matured, scratches created during surface preparation will unavoidably deteriorate both device performances and the quality of materials which are fabricated on it. Hydrogen etching has been proposed as an effective approach to obtain ideal SiC surfaces with large atomically flat steps. Here, we reported a systematical investigation on the effects of processing parameters to the hydrogen etching of 4H–SiC (0001). Accordingly, a new two-step etching method was developed with a specifically designed crucible to take advantage of the found correlation between those parameters and the terrace features. The method demonstrates high efficiency to realize atomically uniform SiC surface morphology with more than 70% coverage of the sample surface. It offers a possible route for large scale industrial SiC wafer planarization.

A two-step physical-chemical etching technique to improve laser damage resistance of fused silica

A two-step physical-chemical etching method, namely large incident angle ion beam etching followed by HF etching, is proposed to remove the damage precursors in fused silica surface to achieve good surface quality and significantly improve the laser damage resistance of fused silica. Ion beam etching with large incident angle is utilized to remove the metal impurities and most subsurface defects in fused silica surface, which can reduce the removal amount of subsequent HF etching of fused silica, thus suppressing the replication and expansion of the subsurface defects, deposition of reaction products and deterioration of surface shape during the HF etching process. After that, HF etching is used to remove the atomic-scale damaged layer and reduce the P–V value of the reflection surface shape induced by ion beam etching. Therefore, a better laser damage performance of fused silica can be obtained by the two-step etching method compared with single ion beam etching and single HF etching. The results show that the two-step physical-chemical etching can be developed to fabricate high-quality and high damage-resistant fused silica optical components with small etching amount and good surface quality for high-power laser application.

Fabrication of superhydrophobic surface on stainless steel by two-step chemical etching

A two-step chemical etching method for preparing superhydrophobic surfaces on stainless steel substrates is proposed. The stainless steel substrates were sequentially immersed in hydrochloric acid and ferric chloride solutions to create micro-nano structures, and then the surfaces were modified with low surface energy substances. Superhydrophobic surfaces with a contact angle of 159° and a sliding angle of 2° were prepared by varying the etching solution parameters. The fabricated superhydrophobic surfaces showed excellent stability and self-cleaning properties. This paper illustrates a low-cost and efficient chemical etching method that can be used for large-area surface fabrication.

A Si-based suspended tunnel structure with trapezoidal section by two-step etching

A two-step etching method is used to prepare a Si-based suspended tunnel structure with a trapezoidal section. In the first wet etching, surfactant Triton-X-100 is added to tetramethylammonium hydroxide (TMAH) enchant to inhibit crystal plane characteristics. Bulk Si Rib with trapezoidal cross section is formed, with inclination of side and height being modulated by changing etching time, to obtain good stability. After the SiO2 support layer is grown by thermal oxidation, pure 25% TMAH is used in the second wet etching to quickly lateral etch and undercut the bulk silicon under the support layer and form a suspended structure along <100> opening. Using additive-no additive two-step etching method, suspended structure with high stability and compressive strength, good insulation characteristics, high yield can be prepared. It lays a solid foundation for developing high sensitivity photo, thermal, chemical and gas sensors.

Fabrication of porous gallium nitride (GaN) utilizing two-step etching method and control of its optical properties

Fabrication of porous gallium nitride (GaN) utilizing two-step etching method and control of its optical properties

Coupled-ridge waveguide quantum cascade laser array lasing at λ ~ 5 µm

In this work, we demonstrated high-power quantum cascade laser (QCL) arrays lasing at λ ~ 5 µm by employing an optimized coupled-ridge waveguide (CRW) structure. Five-element QCL arrays were simulated and fabricated through a two-step etching method to extend the CRW structure to a mid-wave infrared regime. A lateral far-field with the main peak near a diffraction-limited intensity curve of about 10° was observed by properly designing a geometric shape of the ridges and interspaces. By introducing a buried 2nd-order distributed feedback (DFB) grating, substrate emission with a radiation power above 1 W at 25 °C is achieved. Single longitudinal mode operation is obtained by changing the temperature of the heatsink with a good linear wavelength tuning coefficient of –0.2 cm–1/K.

Kinked silicon nanowires prepared by two-step MACE process: Synthesis strategies and luminescent properties

We report the controlled fabrication of kinked silicon nanowires (SiNWs) using ethanol mixed facile two-step metal-assisted chemical etching (MACE) method. Accordingly, the kink angle, straight path, and the number of kinks in kinked SiNWs are controlled by varying the volume of ethanol and etching time in high concentrated plating and etching solutions. The silver nanoparticles (AgNPs) during the etching need to travel a critical length (≥1.5 μm) in a vertical direction before the kink formation. The presence of ethanol in etching solution affects the availability of H2O2 and HF at Si/Ag interface and has a major effect on the etching process. The room temperature photoluminescence (PL) emission of kinked SiNWs is tuned from the red region to the blue region by controlling the amount of ethanol in the etching solution. The temporal behaviour of the PL data of the kinked SiNWs has been provided to understand in depth the optical transition processes.

Electrochemical Etching of Tungsten for Fabrication of Sub-10-nm Tips with a Long Taper and a Large Shank

From the perspective of maximizing the practicability of tungsten nano-tips, a sharp tip, long taper, and large shank are usually expected. However, simultaneously satisfying the requirements for tip radius, taper length, and shank diameter is theoretically impossible with the conventional drop-off tip fabrication method, which is based on lamellae electrochemical etching. In this study, a two-step etching method is proposed to fabricate a sub-10-nm tungsten tip directly from a 1-mm rod. First, a floating electrolyte-based drop-off process is carried out to fabricate a tungsten needle with a long length taper of 10 mm. Then, an inversed lamellae drop-off process is conducted to realize fine etching of the needlepoint. As a result, an ultra-sharp tungsten nano-tip with a radius of 5.5 nm and taper length of 10 mm is successfully fabricated from a 1-mm tungsten rod.

Au Plasmonic Shofar Structures

We demonstrate a simple two-step etching method to fabricate Au plasmonic shofars (“shofar” is the Hebrew name for certain types of curved and tapered horns, such as from a ram). The structural, optical, and morphological properties were studied by using X-ray diffraction, UV-Vis spectrophotometry, and scanning electron microscopy (SEM). The etching mechanism and the light-guiding properties for this unique morphology are described. The leaky surface plasmon propagation (SPP) and guiding properties of shofars are investigated by using leakage radiation microscopy (LRM).