Multi-step Etching Research Articles

Intrinsic Polarized Electric Field Induces a Storing Mechanism to Achieve Energy Storing Catalysis in V2 C MXene.

Efficient storage and separation of holes and electrons pose significant challenges for catalytic reactions, particularly in the context of single-phase catalysis. Herein, V2 C MXene, with its intrinsic polarized electric field, successfully overcomes this obstacle. To enhance hole storage, a multistep etching process is employed under reducing conditions to control the content of surface termination groups, thus exposing more defective active sites. The intrinsically polarized electric field confines holes to the surface of the layer and free electrons within the layer, leading to a lag in e- release compared to h+ . The quantities of stored holes and electrons are measured to be 18.13µmolg-1 and 106.37 µmol g-1 , respectively. Under dark, V2 C demonstrates excellent and stable dark-catalytic performance, degrading 57.91% of tetracycline (TC 40mg L-1 ) and removing 23% of total organic carbon (TOC) after 140 min. In simulated sunlight and near-infrared light, the corresponding degradation rates reach 72.24% and 79.54%, with corresponding TOC removal rates of 49% and 48%, respectively. The hole and electron induced localized surface plasmon resonance (LSPR) effects contribute to a long-lasting and enhanced broad-spectrum mineralization of V2 C MXene. This study provides valuable insights into the research and application of all-weather MXene energy storage catalytic materials.

Textured p-type crystalline silicon surfaces obtained by multi-step plasma process for SHJ solar cells

P-type monocrystalline silicon wafers were textured by means of a multi-step plasma etching technique with the aim of greatly reducing their reflectance and effectively exploiting the highest possible amount of solar radiation in heterojunction photovoltaic devices. Suitable surface morphologies, characterized by high light scattering, have to be obtained without damaging the c-Si electrical properties. For this reason, some aspects of the plasma etching process have been studied and improved. Modifications have been made to obtain both “cleaner” processes and energetically lower ion bombardment. By operating at high pressure (0.4 mbar), a process controlled by diffusion of reactive species towards the substrate was favoured. Another innovative aspect consisted in two “reconditioning” plasma processes of the Si surface before the actual silicon removal step with SF6 /O2 gas mixtures. A strong reduction in the average optical reflection down to 5% was obtained coupled with a minority carriers lifetime (τeff) of about 950 μs, value comparable to that of the untreated silicon. An interesting surface morphology, consisting in “U" shaped cavities, was obtained. Texture irregularities were easily removed by acid etching. The moderate depth of the cavities is very promising for an effective passivation with a-Si:H thin films.

Fabrication of a transparent array of penetrating 3D microelectrodes with two different heights for both neural stimulation and recording

Microelectrode array (MEA) is one of the representative platforms for recording and stimulating neurons to explore their populational electrophysiological activities. Due to the layered structures of the nervous system, various three-dimensional (3D) MEAs have been used to reach specific target depths of neuronal tissues. But it is still difficult to monolithically fabricate various heights of microelectrodes, particularly with optical transparency. Here, we present a 3D MEA with different heights fabricated by multi-step silicon deep reactive ion etching. The microelectrodes were embedded in reflowed glass for high transparency which enables both neural tissue observation and optical stimulation. The heights of microelectrodes were well controlled by our fabrication processes and electrical connections were made with through glass vias (TGVs) to the bottom side for individual addressing. To confine electric stimulation in a small area, we used microelectrodes neighboring a stimulation electrode as local returns. The feasibility of the fabricated MEA was demonstrated by stimulating the mouse retina and successfully recording spikes of ganglion cells located near the stimulation site. Consistent with our COMSOL simulation, the ex vivo experimental results showed the stimulation current confinement was effective. Our study provides a new tool for 3D nervous systems and its fabrication method.

A Novel Si Nanosheet Channel Release Process for the Fabrication of Gate-All-Around Transistors and Its Mechanism Investigation.

The effect of the source/drain compressive stress on the mechanical stability of stacked Si nanosheets (NS) during the process of channel release has been investigated. The stress of the nanosheets in the stacking direction increased first and then decreased during the process of channel release by technology computer-aided design (TCAD) simulation. The finite element simulation showed that the stress caused serious deformation of the nanosheets, which was also confirmed by the experiment. This study proposed a novel channel release process that utilized multi-step etching to remove the sacrificial SiGe layers instead of conventional single-step etching. By gradually releasing the stress of the SiGe layer on the nanosheets, the stress difference in the stacking direction before and after the last step of etching was significantly reduced, thus achieving equally spaced stacked nanosheets. In addition, the plasma-free oxidation treatment was introduced in the multi-step etching process to realize an outstanding selectivity of 168:1 for Si0.7Ge0.3 versus Si. The proposed novel process could realize the channel release of nanosheets with a multi-width from 30 nm to 80 nm with little Si loss, unlocking the full potential of gate-all-around (GAA) technology for digital, analog, and radio-frequency (RF) circuit applications.

Luminescence efficiency improvement of small-size micro light-emitting diodes by a digital etching technology.

The decrease of light output efficiency with the reduction of LED (light-emitting diode) die size is one of the challenges of micro-LED displays. Here we propose a digital etching technology that employs multi-step etching and treatment to mitigate sidewall defects exposed after mesa dry etching. In this study, by two-step etching and N2 treatment, the electrical properties of the diodes show an increase of forward current and a decrease in reverse leakage due to suppressed sidewall defects. An increase of light output power by 92.6% is observed for 10 × 10-µm2 mesa size with digital etching, as compared with that with only one step etching and no treatment. We also demonstrated only 1.1% decrease in output power density for a 10 × 10-µm2 LED as compared with a 100 × 100-µm2 device without performing digital etching.

Thermal Performance Improvement of AlGaN/GaN HEMTs Using Nanocrystalline Diamond Capping Layers.

Nanocrystalline diamond capping layers have been demonstrated to improve thermal management for AlGaN/GaN HEMTs. To improve the RF devices, the application of the technology, the technological approaches and device characteristics of AlGaN/GaN HEMTs with gate length less than 0.5 μm using nanocrystalline diamond capping layers have been studied systematically. The approach of diamond-before-gate has been adopted to resolve the growth of nanocrystalline diamond capping layers and compatibility with the Schottky gate of GaN HEMTs, and the processes of diamond multi-step etching technique and AlGaN barrier protection are presented to improve the technological challenge of gate metal. The GaN HEMTs with nanocrystalline diamond passivated structure have been successfully prepared; the heat dissipation capability and electrical characteristics have been evaluated. The results show the that thermal resistance of GaN HEMTs with nanocrystalline diamond passivated structure is lower than conventional SiN-GaN HEMTs by 21.4%, and the mechanism of heat transfer for NDC-GaN HEMTs is revealed by simulation method in theory. Meanwhile, the GaN HEMTs with nanocrystalline diamond passivated structure has excellent output, small signal gain and cut-off frequency characteristics, especially the current–voltage, which has a 27.9% improvement than conventional SiN-GaN HEMTs. The nanocrystalline diamond capping layers for GaN HEMTs has significant performance advantages over the conventional SiN passivated structure.

Increasing the structural and compositional diversity of ion-track templated 1D nanostructures through multistep etching, plastic deformation, and deposition

Ion-track etching represents a highly versatile way of introducing artificial pores with diameters down into the nm-regime into polymers, which offers considerable synthetic flexibility in template-assisted nanofabrication schemes. While the mechanistic foundations of ion-track technology are well understood, its potential for creating structurally and compositionally complex nano-architectures is far from being fully tapped. In this study, we showcase different strategies to expand the synthetic repertoire of ion-track membrane templating by creating several new 1D nanostructures, namely metal nanotubes of elliptical cross-section, funnel-shaped nanotubes optionally overcoated with titania or nickel nanospike layers, and concentrical as well as stacked metal nanotube-nanowire heterostructures. These nano-architectures are obtained solely by applying different wet-chemical deposition methods (electroless plating, electrodeposition, and chemical bath deposition) to ion-track etched polycarbonate templates, whose pore geometry is modified through plastic deformation, consecutive etching steps under differing conditions, and etching steps intermitted by spatially confined deposition, providing new motifs for nanoscale replication.

AAO Template-Assisted Fabrication of Ordered Ag Nanoparticles-Decorated Au Nanotubes Array for Surface-Enhanced Raman Scattering Detection

Highly sensitive and reproducible surface-enhanced Raman scattering (SERS) substrates are the main challenge for practical applications. In this work, an ordered and hierarchical Ag nanoparticles (Ag-NPs)-decorated Au nanotubes (Au-NTs) array was achieved based on a funnel-shaped pore anodic aluminum oxide (AAO) template-assisted strategy. First, funnel-pore-AAO templates were fabricated by further oxidation of conical-pore-AAO templates achieved by multistep anodization and etching. Then physical sputtering was used to assemble the Au-NTs and Ag-NPs using the as-prepared funnel-pore-AAO as sacrificial templates. SEM revealed abundant sub-10 nm neighboring gaps and sub-10 nm nanocavities at the bottom of the nanotubes because of the special shape of the AAO template, which resulted in abundant strong “hot spots” contributing to the sensitive SERS detection. The resultant hierarchical substrates manifested a SERS enhancement factor of 1.8 × 107 and reproducible response to 10−11 M rhodamine 6G and 10−8 M methyl parathion, showing potential in SERS-based rapid detection of trace pollutants in the environment.

Fabrication of Differently Shaped Polymeric Nanoneedle Arrays via Multistep Plasma Etching Using Silica Microparticles as Masks

We established a method to produce differently shaped polymeric nanoneedle arrays using silica microparticles by using multistep plasma etch processes. The etching conditions of each step were determined by exploring etching parameters such as power, bias power, gas composition and amount, pressure and time. The silica microparticles became unstable and irregular nanoneedle arrays were formed due to difference of etching rates between silica and polymer when silica microparticles were etched continuously in one step. Through the introduction of stabilization step in which selective etching is done on silica microparticle to reduce the diameter of silica microparticles and hence to move the center of mass of the silica microparticle inward, the instability of silica mask was removed and irregularity of nanostructures was minimized. As a result, multistep etching process to fabricate polymeric nanoneedle arrays was established. Depending on the conditions of each step, polymeric nanostructure arrays with various morphology were fabricated.

Flexible-templated imprinting for fluorine-free, omniphobic plastics with re-entrant structures

HypothesisCompared to vertical micro-pillars, re-entrant micro-structures exhibited superior omniphobicity for suspending liquids to Cassie-Baxter state. However, the existing re-entrant structures rely on complex multi-step deposition and etching procedures. The conventional, rigid-templated imprinting would instead damage the re-entrant structures. This leads to the question: is it possible to preserve the re-entrant curvatures by a flexible-templated imprinting? ExperimentsWe facilely imprinted the re-entrant structures on a plastic substrate using a flexible nylon-mesh template. The effect of imprinting time (15–35 min), temperature (110–120 °C) and pressure (15–50 Bar) was investigated. To further improve the liquid-repellency and abrasion resistance, the silica nanoparticles (30–650 nm) along with epoxy resin binder (10 mg/mL) were pre-coated. FindingsA one-step imprinting is sufficient to fabricate the re-entrant structures by utilizing flexible nylon-mesh template, without damaging the imprinted structures after the demolding process. The pre-coated silica nanoparticles and epoxy resin (1) improved liquid repellency by introducing hierarchical surface structures (e.g. contact angle hysteresis of olive oil reduced > 10°), and (2) acted as a protective layer against mechanical abrasion (omniphobicity maintained after 25 cycles, ~1.6 kPa sand paper abrasion). Additionally, the fluorine-free post-treatment was sufficient for the omniphobicity on the obtained plastic structures.

Growth mechanism of graphene/h-BN intra-layer interface

Graphene has received many attentions from the scientist due to its outstanding properties since it was mechanically exfoliated. The rise of graphene has stimulated immense research on analogous two-dimensional (2D) materials, such as the hexagonal boron nitride (h-BN), monolayer transition metal dichalcogenides, black phosphorene, silicene, borophene and germanene. However, as a semimetal, gapless graphene has been limited in the application like semiconducting electronics. Previous theoretical calculations predict that a small bandgap will arise when the graphene is placed onto an h-BN substrate. Then graphene/h-BN (G/h-BN) lateral heterostructures have been fabricated by many research groups on metal substrates. Comparing vertical vdW layer assembling, the atomic G/h-BN system combining both the high carrier mobility and tunable bandgap can build in-plane integrated circuit directly. However, to reduce the interface scattering, a sharp atomic interface between graphene and h-BN is required. To date, some experiments have built high quality G/h-BN heterostructures with sharp atomic interfaces, while many others did not. The underlying growth mechanism is crucial to control the size and shapes of the G/h-BN heterostructures of high quality. In this review, we first review the growth mechanism of graphene, mainly focusing on the nucleating process, which plays a vital role to reduce the grain boundary in the overall growth. The nucleation behavior of graphene is influenced by the growth temperature, substrate, carbon source partial pressure and hydrogen partial pressure. We review the structure and energy evaluation of clusters in the graphene nucleation stage on the Ir(111) and Ni(111) surface. Moreover, the nucleation barrier and size can also be obtained by combing the first-principles calculations and classical nucleation theory. Secondly, we present an overview on experimental fabrication of G/h-BN heterojunctions. Up to now, lateral G/h-BN heterojunctions has been produced on some metal substrates such as Cu foil, Ru(0001), Rh(111), Ni(111), Ir(111) and Pt(111). There are several methods to construct G/h-BN heterojunctions in experiments which can be classified into two kinds: Batch chemical vapor deposition and two/multi-step growth. In the earlier period, the large area randomly hybridized h-BN and graphene are fabricated by this method through supplying C precursors and NH3-BH3 at the same time. Another routine is two/multi-step growth technique in which G/h-BN is deposited on a metal surface beforehand as seeds of the second step of growth. And afterwards, by alternating the type of source supply, in plane heterojunctions with the predeposited grains will be formed. The growth sequence is proved to be a crucial factor that determines the quality of heterostructures. For multistep growth, lithographically technology and etching process are introduced to get spatially controlled heterostructures. Then, we introduce recent studies on the growth mechanism of G/h-BN lateral heterostructure both by atomistic first-principles calculations and experimental observations. The heteroepitaxial growth of graphene along the predeposited h-BN domains is systematically investigated by classical nucleation theory. At the initial stage, C atoms tend to attach linearly along the B/N-edges rather than perpendicular to the edges which resemble the graphene growth on the metal surface. When the carbon concentration is low, the nucleation barriers of graphene at B/N-edges are lower compared to the case of a Cu terrace. Nevertheless, under high carbon concentration, the nucleation barriers and nucleation rates in the two cases become comparable. Therefore, the chemical potential of the carbon source should be controlled within a suitable range to produce high quality G/h-BN lateral heterostructures with sharply and continuously atomic interface. Finally, we give a prospect on this rising field.

Curvature-Modulated Si Spherical Cap-Like Structure Fabricated by Multistep Ring Edge Etching.

To create approximately spherical structures with curved sidewalls, this paper presents a method for building a series of decreasing slopes along the sidewall of a circular truncated cone. The multistep ring-edge etching technology of first reducing the concentric mask and then cutting the top off to create a mesa shape can be used to form the slopes. This wet-etching method avoids the constraints of crystallographic properties with surfactant-added Tetramethylammonium hydroxide (TMAH), enabling the manufacture of successive given inclination angles, the precise modulation of the spherical curvature by reduction design of concentric masks, and the setting of etching time. The newly approximated spherical Si microstructure patterns can be used for microlenses, quartz crystal resonators, micropulleys, and other applications. The present research is an approach to fabricate advanced microelectromechanical systems (MEMS) curved-surface structures, extending the range of 3D structures fabricated by silicon wet etching.

Superhydrophilic catenoidal aluminum micropost evaporator wicks

We introduce the superhydrophilic catenoidal aluminum (Al) wicks fabricated by a multi-step wet etching process followed by wet chemical oxidation. The unique three-dimensional sidewall morphology of the developed wick provides the re-pinning of the liquid meniscus during the receding, which substantially increases the thin evaporative film area and the resulting heat transfer performance. The nanostructured aluminum oxide layer (AlO(OH)) was incorporated to enhance both the corrosion resistance as well as the wettability of the wick with water. The experiment shows that the heat transfer coefficient of the developed wick rapidly increases as the heat flux increases up to ~60 W/cm2. The maximum heat transfer coefficient of the catenoidal wick is measured to be ~117% higher than that of the previously-reported cylindrical ones. The numerical simulation clarifies that the increase in the heat transfer coefficient was due to the ~75% increase in the thin evaporative film area. The polarization scanning test shows that the corrosion resistance of the superhydrophilic catenoidal wicks was increased by ~82% compared to the unstructured ones, which clarifies the incorporated aluminum oxide layer acts as an effective corrosion barrier. This work introduces the Al evaporator wicks with substantially improved heat transfer as well as anti-corrosion performances, which will help develop ultra-light, high-performance heat spreaders.

Wafer-scale 3D shaping of high aspect ratio structures by multistep plasma etching and corner lithography

The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density. In this work, a wafer-scale out-of-plane 3D silicon (Si) shaping technology is reported, which combines a multistep plasma etching process with corner lithography. The multistep plasma etching procedure results in high aspect ratio structures with stacked semicircles etched deep into the sidewall and thereby introduces corners with a proper geometry for the subsequent corner lithography. Due to the geometrical contrast between the gaps and sidewall, residues are left only inside the gaps and form an inversion mask inside the semicircles. Using this mask, octahedra and donuts can be etched in a repeated manner into Si over the full wafer area, which demonstrates the potential of this technology for constructing high-density 3D structures with good dimensional control in the bulk of Si wafers.

Study on reducing side etching of Copper microelectrode by multi-step etching process

A method for reducing the amount of copper (Cu) electrode side etching at the micro-nano scale by multi-step etching process was proposed. Taking the positive photoresist (PR) BP212 as a masking layer, the Cu electrode was patterned by two etching solutions, which can effectively reduce the side etching. The x-ray diffraction (XRD) test showed that the intermediate product formed on the surface of Cu during the corrosion of FeCl3 solution was cuprous chloride (CuCl). The removal of CuCl by KCl solution instead of FeCl3 solution greatly reduced the residence time of Cu in FeCl3 solution; The effect of different concentrations of FeCl3 solution on reducing the amount of side etching was studied. The result shows that the FeCl3 solution with mass concentration of 0.03 g ml−1 was used for multi-step etching, and the amount of side etching is reduced from 25 μm to 5 μm.

Electromagnetic design of a 220 GHz BWO with experimental study of micro-fabricated folded waveguide structure

ABSTRACTBackward-wave oscillator (BWO) is the most promising source for the generation of a few watts of power at millimetre wave and sub-millimetre wave frequencies. This paper presents the electrical design of a folded waveguide BWO at 220 GHz. The dispersion of the structure was theoretically calculated and further validated by numerical simulation using CST MWS. A minimum output power of 5 W at 220 GHz, was obtained using the particle-in-cell simulation of CST MWS, at the beam voltage of 10 kV and a current of 50 mA. Also, a power of around 1 W is obtained over a band of 4.5 GHz by voltage tuning. The ultra-thick ∼750 µm height Au-structure is fabricated using multi-step photolithography and etching processes while keeping the surface roughness well below the skin depth. The slow wave structure was tested and it was found that the return-loss is in good agreement with the simulation results within ∼5 dB, throughout the 185–260 GHz band.

Tailoring the Post-Etching of Room-Temperature-Fabricated H and Ti Co-Doped ZnO Films for Efficient Harvested Light Trapping

Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide films for efficient light-scattering in silicon thin-film solar cells. Based on experimental findings from our previous studies, two types of experimental techniques, a combination of HCl/NaOH and NaOH/HCl etching modes as well as a multi-step etching process, were considered to improve the light-trapping ability of room-temperature-deposited H and Ti co-doped ZnO (HTZO) films. The effects of the employed experimental procedures on the optical, electrical, and morphological properties of the HTZO films were systematically investigated. After optimization, higher haze values of 96.2%, 90.6%, and 74% at 550 nm, 800 nm, and 1100 nm, as well as a higher average haze value of 90.1% in the range of 400–1100 nm were achieved, which are better than those of the reference conventional HCl-etched Al-doped ZnO (AZO), high-light-trapping AZO, and SnO2:F films. These findings reveal a method to develop high-performance ZnO films for the front electrodes in high-efficiency Si thin-film solar cells.

Strengthening of very large crystalline and polycrystalline Nd:YAG rods for high-power laser applications

A multistep thermochemical etching procedure was applied to very large Nd3+:YAG rods to increase their fracture strength. The strengthening procedure combined selection of high-quality material, fine centerless grinding, thermochemical etching, and (after completion of the lapping, polishing and AR coating) an additional hot thermochemical etching, with rod ends protected with poly-tetra-fluoro-ethylene (Teflon) caps. The final cleaning step, not previously reported, is essential in removing fracture causing contaminations on the rod surface. A unique thermal load-to-fracture technique was applied on test rods to measure their fracture strength. The rods were thermally loaded up to fracture by means of optical pumping in a specially designed laser pump chamber. The results thus obtained were analyzed by Weibull distribution statistics appropriate to these tests. The strengthened laser rods of this study sustained a maximum pump power density of $$ I_{{\ell_{\hbox{max} } }} $$ = 500 W cm−1. This value is higher by a factor of four over untreated rods and also higher than any previously published data for such large rods. High-power diode-pumped laser heads were operated with the strengthened crystalline and polycrystalline Nd:YAG rods, yielded output power of ~ 3 kW, when pumped with 7 kW. Such performance was routinely achieved without any instance of rod fracture. Reliability of the strengthening procedure was further demonstrated by the failure-free operation of an azimuthally polarized high-power master-oscillator power-amplifier system (composed of oscillator, preamplifier, and six power amplifiers), emitting an output power in excess of 10 kW.

Preparation of Textured Surfaces on Aluminum-Alloy Substrates.

The ways of producing porous-like textured surfaces with chemical etching on aluminum-alloy substrates were studied. The most appropriate etchants, their combination, temperature, and etching time period were explored. The influence of a specifically textured surface on adhesive joints’ strength or superhydrophobic properties was evaluated. The samples were examined with scanning electron microscopy, profilometry, atomic force microscopy, goniometry, and tensile testing. It was found that, with the multistep etching process, the substrate can be effectively modified and textured to the same morphology, regardless of the initial surface roughness. By selecting proper etchants and their sequence one can prepare new types of highly adhesive or even superhydrophobic surfaces.

A multi-step etch method for fabricating slightly tapered through-silicon vias based on modified Bosch process

In this paper, a multi-step etching method based on Bosch process was investigated to fabricate a slightly tapered via. The diameter of vias was scaled from 40 to 100 µm. Isotropic etching step was added into Bosch process to control the angle of the tapered vias. The slope angle could be adjusted by changing the time settings of isotropic etching step. The influence of the platen temperature was also studied. The passivation and etching steps are extremely sensitive to temperature. Silicon grass could be formed at low temperature. The two different processes of isotropic SF6 etching and Cl2/HBr etching were also compared. The wrinkles and cracks were observed on the surface after treatment with isotropic SF6 etching. The Cl2/HBr etching method is much better for removing the scallops.