Showing papers on "Etching (microfabrication) published in 2020"

Rational construction of hierarchical hollow CuS@CoS2 nanoboxes with heterogeneous interfaces for high-efficiency microwave absorption materials

Abstract: Hierarchical hollow structures have received considerable attention for light weight microwave absorption materials, however, constructing and regulating hollow structures with heterogeneous interfaces still remains a great challenge. In this work, hierarchical hollow CuS@CoS2 nanoboxes with double shells have been designed by a template-assisted process inspired by Pearson's hard and soft acid-base principle, in which the hollow nanoboxes are composed of CuS inner shell and CoS2 nanosheets outer shell. The formation of outer Co(OH)2 nanosheets is a key factor to achieve the double shells via a “coordinating etching and precipitating” route and the etching of cubic Cu2O precursor plays an important role to stabilize the hollow nanoboxes. As absorbers, the hierarchical hollow nanoboxes exhibit high-efficiency microwave absorption attenuation because of the synergistic effects of dipolar and interfacial polarizations, multiple scatterings, hollow/core-shell structures and matched impedance. Typically, the minimum reflection loss is up to −58.6 dB at 2.5 mm when the filler loading is 20 wt% and the absorption bandwidth exceeding −10 dB is 8.2 GHz at 2.2 mm with 30 wt% filler loading. Consequently, this strategy offers a unique thought for the construction of hollow nanoboxes with double shells and the as-fabricated nanoboxes can be used as a promising candidate for microwave absorption materials with light weight and high-efficiency.

Wafer-scale low-loss lithium niobate photonic integrated circuits

Abstract: Thin-film lithium niobate (LN) photonic integrated circuits (PICs) could enable ultrahigh performance in electro-optic and nonlinear optical devices. To date, realizations have been limited to chip-scale proof-of-concepts. Here we demonstrate monolithic LN PICs fabricated on 4- and 6-inch wafers with deep ultraviolet lithography and show smooth and uniform etching, achieving 0.27 dB/cm optical propagation loss on wafer-scale. Our results show that LN PICs are fundamentally scalable and can be highly cost-effective.

Mechanisms of Thermal Atomic Layer Etching

Abstract: ConspectusAtomic layer control of semiconductor processing is needed as critical dimensions are progressively reduced below the 10 nm scale. Atomic layer deposition (ALD) methods are meeting this challenge and produce conformal thin film growth on high aspect ratio features. Atomic layer etching (ALE) techniques are also required that can remove material with atomic layer precision. ALE processes are defined using sequential, self-limiting reactions based on surface modification and volatile release. Plasma ALE methods employ energetic ion or neutral species to release the modified material anisotropically using sputtering. In contrast, thermal ALE processes utilize gas species to release the modified material isotropically using thermal reactions. Thermal ALE can be viewed as the "reverse of ALD".There are a number of mechanisms for thermal ALE that have developed over the last five years. This Account will first examine the fluorination and ligand-exchange mechanism for thermal ALE. This mechanism is applicable for many metal oxide and metal nitride materials. Subsequently, the "conversion etch" mechanisms will be explored that are derived from the conversion of the surface of the substrate to a new material. The "conversion etch" mechanisms are needed when the initial material does not have a viable etching pathway via fluorination and ligand-exchange or when the material has a volatile fluoride. The thermal ALE mechanisms founded on either oxidation or halogenation of the initial substrate will then be examined with an emphasis on metal thermal ALE. Lastly, thermal ALE mechanisms will be considered that are based on self-limiting surface ligands or temperature modulation mechanisms. These various mechanisms offer a wide range of pathways to remove material isotropically with atomic layer control.Thermal ALE will be required to fabricate advanced semiconductor devices. This fabrication will increasingly occur beyond the limits of lithography and will extend into the third dimension. The situation is like Manhattan during the advent of skyscrapers. When there was no more room on the ground, building started to move to the third dimension. Three-dimensional devices require a sequential series of deposition and etching steps to build the skyscraper structures. Some etching needs to be vertical and anisotropic to make the elevator shafts. Other etching needs to be horizontal and isotropic to form the hallways. The mechanisms of thermal ALE will be critical for the definition of isotropic ALE processes.Reaching beyond the limits of lithography will also increase the need for maskless processing. The mechanisms of thermal ALE lead to strategies for selective etching of one material in the presence of many materials. In addition, area-selective deposition can benefit from the ability of thermal ALE to enhance deposition on the desired growth surfaces by removing deposition from other surrounding surfaces. Looking ahead, thermal ALE will continue to provide unique capabilities and will grow in importance as a nanofabrication processing technique.

Selectively Etching Vanadium Oxide to Modulate Surface Vacancies of Unary Metal–Based Electrocatalysts for High‐Performance Water Oxidation

Abstract: Electrocatalytic water splitting for hydrogen generation is hindered by the sluggish kinetics of water oxidation, and highly efficient electrocatalysts for the oxygen evolution reaction (OER) are u ...

A heterogeneously integrated silicon photonic/lithium niobate travelling wave electro-optic modulator.

Abstract: Silicon photonics is a platform that enables densely integrated photonic components and systems and integration with electronic circuits. Depletion mode modulators designed on this platform suffer from a fundamental frequency response limit due to the mobility of carriers in silicon. Lithium niobate-based modulators have demonstrated high performance, but the material is difficult to process and cannot be easily integrated with other photonic components and electronics. In this manuscript, we simultaneously take advantage of the benefits of silicon photonics and the Pockels effect in lithium niobate by heterogeneously integrating silicon photonic-integrated circuits with thin-film lithium niobate samples. We demonstrate the most CMOS-compatible thin-film lithium niobate modulator to date, which has electro-optic 3 dB bandwidths of 30.6 GHz and half-wave voltages of 6.7 V×cm. These modulators are fabricated entirely in CMOS facilities, with the exception of the bonding of a thin-film lithium niobate sample post fabrication, and require no etching of lithium niobate.

Exfoliation and Defect Control of Two-Dimensional Few-Layer MXene Ti3C2Tx for Electromagnetic Interference Shielding Coatings.

Abstract: Defect-controlled exfoliation of few-layer transition-metal carbide (f-Ti3C2Tx) MXene was demonstrated by optimizing chemical etching conditions, and electromagnetic interference (EMI) shielding coatings were explored. The structural features such as layer morphology, lateral size, layer thickness, defect density, and mechanical stability of the exfoliated f-Ti3C2Tx were strongly dependent on exfoliation conditions. By selecting appropriate exfoliation conditions, moderate etching time leads to the formation of quality f-Ti3C2Tx with lesser defects, whereas longer etching time can break the layer structure and increase defect density, structural misalignment, and oxidative products of f-Ti3C2Tx. The resultant fabricated free-standing flexible f-Ti3C2Tx films exhibited electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band of about 3669 ± 33 S/m and 31.97 dB, respectively, at a thickness of 6 μm. The large discrepancy in EMI SE performance between quality (31.97 dB) and defected (3.164 dB) f-Ti3C2Tx sheets is attributed to interconnections between f-Ti3C2Tx nanolaminates interrupted by defects and oxidative products, influencing EMI attenuation ability. Furthermore, the demonstrated solution-processable high-quality f-Ti3C2Tx inks are compatible and, when applied for EM barrier coating on various substrates, including paper, cellulose fabric, and PTFE membranes, exhibited significant EMI shielding performance. Moreover, controlling defects in f-Ti3C2Tx and assembly of heterogeneous disordered carbon-loaded TiO2-Ti3C2Tx ternary hybrid nanostructures from f-Ti3C2Tx by tuning etching conditions could play an enormous role in energy and environmental applications.

Top-Down Synthesis of Silicon/Carbon Composite Anode Materials for Lithium-Ion Batteries: Mechanical Milling and Etching

Abstract: Lithium-ion batteries (LIBs) providing high energy and power densities as well as long cycle life are in high demand for various applications. Benefitting from its high theoretical specific charge capacity of ≈4200 mAh g-1 and natural abundance, Si is nowadays considered as one of the most promising anode candidates for high-energy-density LIBs. However, its huge volume change during cycling prevents its widespread commercialization. Si/C-based electrodes, fabricated through top-down mechanical-milling technique and etching, could be particularly promising since they can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability. In this Review, the current progresses in the top-down synthesis of Si/C anode materials for LIBs from inexpensive Si sources via the combination of low-cost, simple, scalable, and efficient ball-milling and etching processes are summarized. Various Si precursors as well as etching routes are highlighted in this Review. This review would be a guide for fabricating high-performance Si-based anodes.

Metal assisted chemical etching of silicon in the gas phase: a nanofabrication platform for X-ray optics

Abstract: High aspect ratio nanostructuring requires high precision pattern transfer with highly directional etching. In this work, we demonstrate the fabrication of structures with ultra-high aspect ratios (up to 10 000 : 1) in the nanoscale regime (down to 10 nm) by platinum assisted chemical etching of silicon in the gas phase. The etching gas is created by a vapour of water diluted hydrofluoric acid and a continuous air flow, which works both as an oxidizer and as a gas carrier for reactive species. The high reactivity of platinum as a catalyst and the formation of platinum silicide to improve the stability of the catalyst pattern allow a controlled etching. The method has been successfully applied to produce straight nanowires with section size in the range of 10–100 nm and length of hundreds of micrometres, and X-ray optical elements with feature sizes down to 10 nm and etching depth in the range of tens of micrometres. This work opens the possibility of a low cost etching method for stiction-sensitive nanostructures and a large range of applications where silicon high aspect ratio nanostructures and high precision of pattern transfer are required.

Polydopamine sacrificial layer mediated SiOx/C@C yolk@shell structure for durable lithium storage

Abstract: SiOx has aroused great attention as a lithium-ion battery anode material owing to its lower cost and smaller volume expansion than Si. Nevertheless, its practical application is hindered by the still existing volume expansion and low electrical conductivity, resulting in rapid capacity decay. Herein, SiOx/C@N-doped carbon yolk@shell microspheres (denoted as YS-SiOx/C@C) have been constructed by a polydopamine-mediated selective etching strategy. In the constructed material, a SiOx/C composite core is encapsulated in a N-doped hollow carbon sphere with sufficient void space existing between the SiOx/C core and carbon shell. The yolk@shell structure could buffer the large volume fluctuation, resulting in significantly enhanced structural stability. Benefiting from the structural merits, the new composite delivers a stable high capacity of 804 mA h g−1 at 100 mA g−1 and long-term cyclability (1000 cycles at 500 mA g−1). Besides, the HF-free polydopamine-mediated selective etching strategy developed here paves a new way to construct yolk@shell structures for electrode materials.

Vertical Sandwich Gate-All-Around Field-Effect Transistors With Self-Aligned High-k Metal Gates and Small Effective-Gate-Length Variation

Abstract: A new type of vertical nanowire (NW)/ nanosheet (NS) field-effect transistors (FETs), termed vertical sandwich gate-all-around (GAA) FETs (VSAFETs), is presented in this work. Moreover, an integration flow that is compatible with processes used in the mainstream industry is proposed for the VSAFETs. Si/SiGe epitaxy, isotropic quasi-atomic-layer etching (qALE), and gate replacement were used to fabricate pVSAFETs for the first time. Vertical GAA FETs with self-aligned high-k metal gates and a small effective-gate-length variation were obtained. Isotropic qALE, including Si-selective etching of SiGe, was developed to control the diameter/thickness of the NW/NS channels. NWs with a diameter of 10 nm and NSs with a thickness of 20 nm were successfully fabricated, and good device characteristics were obtained. Finally, the device performance was investigated and is discussed in this work.

The preparation of V2CTx by facile hydrothermal-assisted etching processing and its performance in lithium-ion battery

Abstract: In this study, high-purity V2CTx MXene was successfully synthesized by etching V2AlC with fluoride and hydrochloric acid mixed solution using a hydrothermal-assisted method. This method is more concise and effective and has a low level of danger. The morphology and structure of the V2CTx MXene was characterized by X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical properties were investigated as an anode material for lithium ion batteries. The results show that the prepared V2CTx had a higher purity and showed excellent electrochemical properties as an anode of lithium-ion batteries. And V2CTx prepared with different etching system can he obtained with high yield and excellent purity by changing the reactive conditions of the system. However, electrochemical performance of V2CTx MXene obtained at different etching system is quite different. V2CTx synthesized in the mixed solution of ammonium fluoride and hydrochloric acid has the best performance, which originates from more accessible active sites for ion in the enlarged interlayer distance, and the smaller impedance of V2CTx.

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching.

Abstract: The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MACE.

Tracking the Effects of Ligands on Oxidative Etching of Gold Nanorods in Graphene Liquid Cell Electron Microscopy.

Abstract: Surface ligands impact the properties and chemistry of nanocrystals, but observing ligand binding locations and their effect on nanocrystal shape transformations is challenging. Using graphene liquid cell electron microscopy and the controllable, oxidative etching of gold nanocrystals, the effect of different ligands on nanocrystal etching can be tracked with nanometer spatial resolution. The chemical environment of liquids irradiated with high-energy electrons is complex and potentially harsh, yet it is possible to observe clear evidence for differential binding properties of specific ligands to the nanorods' surface. Exchanging CTAB ligands for PEG-alkanethiol ligands causes the nanorods to etch at a different, constant rate while still maintaining their aspect ratio. Adding cysteine ligands that bind preferentially to nanorod tips induces etching predominantly on the sides of the rods. This etching at the sides leads to Rayleigh instabilities and eventually breaks apart the nanorod into two separate nanoparticles. The shape transformation is controlled by the interplay between atom removal and diffusion of surface atoms and ligands. These in situ observations are confirmed with ex situ colloidal etching reactions of gold nanorods in solution. The ability to monitor the effect of ligands on nanocrystal shape transformations will enable future in situ studies of nanocrystals surfaces and ligand binding positions.

Composition for etching and manufacturing method of semiconductor device using the same

Abstract: The composition for etching is a high-selectivity composition that can selectively remove a nitride film while minimizing the etch rate of an oxide film, and which does not have problems such as particle generation, which adversely affect the device characteristics.

Towards the Fabrication of High-Aspect-Ratio Silicon Gratings by Deep Reactive Ion Etching

Abstract: The key optical components of X-ray grating interferometry are gratings, whose profile requirements play the most critical role in acquiring high quality images. The difficulty of etching grating lines with high aspect ratios when the pitch is in the range of a few micrometers has greatly limited imaging applications based on X-ray grating interferometry. A high etching rate with low aspect ratio dependence is crucial for higher X-ray energy applications and good profile control by deep reactive ion etching of grating patterns. To achieve this goal, a modified Coburn–Winters model was applied in order to study the influence of key etching parameters, such as chamber pressure and etching power. The recipe for deep reactive ion etching was carefully fine-tuned based on the experimental results. Silicon gratings with an area of 70 × 70 mm2, pitch size of 1.2 and 2 μm were fabricated using the optimized process with aspect ratio α of ~67 and 77, respectively.

Redeposition-Free Deep Etching in Small KY(WO4)2 Samples

Abstract: KY(WO4)2 is a promising material for on-chip laser sources. Deep etching of small KY(WO4)2 samples in combination with various thin film deposition techniques is desirable for the manufacturing of such devices. There are, however, several difficulties that need to be overcome before deep etching of KY(WO4)2 can be realized in small samples in a reproducible manner. In this paper, we address the problems of (i) edge bead formation when using thick resist on small samples, (ii) sample damage during lithography mask touchdown, (iii) resist reticulation during prolonged argon-based inductively coupled plasma reactive ion etching (ICP-RIE), and (iv) redeposited material on the feature sidewalls. We demonstrate the etching of 6.5 µm deep features and the removal of redeposited material using a wet etch procedure. This process will enable the realization of waveguides both in ion-irradiated KY(WO4)2 as well as thin KY(WO4)2 membranes transferred onto glass substrate by bonding and subsequent polishing.

Scalable gas-phase purification of boron nitride nanotubes by selective chlorine etching.

Abstract: Current processes to manufacture nanotubes at commercial scales are unfortunately imperfect and commonly generate undesirable by-products. After manufacturing, purification is necessary and is a ra...

Enzyme–Nanozyme Cascade Reaction-Mediated Etching of Gold Nanorods for the Detection of Escherichia coli

Abstract: Species-specific enzyme detection refers to an important modality in the field of monitoring foodborne pathogens. Particularly, β-galactosidase (β-gal) has been extensively employed for ascertainin...

Microfabrication of X-ray Optics by Metal Assisted Chemical Etching: A Review.

Abstract: High-aspect-ratio silicon micro- and nanostructures are technologically relevant in several applications, such as microelectronics, microelectromechanical systems, sensors, thermoelectric materials, battery anodes, solar cells, photonic devices, and X-ray optics. Microfabrication is usually achieved by dry-etch with reactive ions and KOH based wet-etch, metal assisted chemical etching (MacEtch) is emerging as a new etching technique that allows huge aspect ratio for feature size in the nanoscale. To date, a specialized review of MacEtch that considers both the fundamentals and X-ray optics applications is missing in the literature. This review aims to provide a comprehensive summary including: (i) fundamental mechanism; (ii) basics and roles to perform uniform etching in direction perpendicular to the Si substrate; (iii) several examples of X-ray optics fabricated by MacEtch such as line gratings, circular gratings array, Fresnel zone plates, and other X-ray lenses; (iv) materials and methods for a full fabrication of absorbing gratings and the application in X-ray grating based interferometry; and (v) future perspectives of X-ray optics fabrication. The review provides researchers and engineers with an extensive and updated understanding of the principles and applications of MacEtch as a new technology for X-ray optics fabrication.

Effects of Ion Energy and Density on the Plasma Etching-Induced Surface Area, Edge Electrical Field, and Multivacancies in MoSe2 Nanosheets for Enhancement of the Hydrogen Evolution Reaction.

Abstract: Plasma functionalization can increase the efficiency of MoSe2 in the hydrogen evolution reaction (HER) by providing multiple species but the interactions between the plasma and catalyst are not well understood. In this work, the effects of the ion energy and plasma density on the catalytic properties of MoSe2 nanosheets are studied. The through-holes resulting from plasma etching and multi-vacancies induced by plasma-induced damage enhance the HER efficiency as exemplified by a small overpotential of 148 mV at 10 mA cm-2 and Tafel slope of 51.6 mV dec-1 after the plasma treatment using a power of 20 W. The interactions between the plasma and catalyst during etching and vacancies generation are evaluated by plasma simulation. Finite element and first-principles density functional theory calculations are also conducted and the results are consistent with the experimental results, indicating that the improved HER catalytic activity stems from the enhanced electric field and more active sites on the catalyst, and reduced bandgap and adsorption energy arising from the etched through-holes and vacancies, respectively. The results convey new fundamental knowledge about the plasma effects and means to enhance the efficiency of catalysts in water splitting as well insights into the design of high-performance HER catalysts.

Elucidating the Effect of Etching Time Key-Parameter toward Optically and Electrically-Active Silicon Nanowires.

Abstract: In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9–15% in comparison with Si wafer. I–V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung’s model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs’ length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.

Porous Nitride Semiconductors Reviewed

Abstract: Porous nitride semiconductors are a fast-developing area of study, which open up a wide range of new properties and applications, including strain free optical reflectors, chemical sensors and as a pathway to device lift-off. This article reviews the current progress in porous nitrides formed through electrochemical and photoelectrochemical methods. Using a simple electrochemical cell, pores are formed by injecting holes into the surface layer in order to oxidise the material into a soluble form and releasing nitrogen gas. The process is controlled principally by the electric field that drives the injection of holes and hence the applied potential and doping density are the key parameters for controlling pore morphology, along with how and whether illumination is used. We describe the mechanisms responsible for this process in detail and outline the trends for changing pore size and pore shape. For example, larger applied potential creates a larger electric field and hence larger pores. These methods have been used to produce a wide variety of different structures. We present a layered porous structure created by the modulation of the applied potential. Alternatively, layered structures can be produced by growing alternate doped and non-intentionally doped layers. Electrochemical etching can then create pores only in the doped layers, as they are conductive. This process can be performed by etching laterally through access trenches that expose the doped material or through the etching of dislocations to create nanopipes that allow subsurface porosity to form. This process requires no prior processing steps. We combine this method with patterning of surface protective layers to influence where the resulting pores grow. Based on these various fabrication processes, significant progress has been made towards applications of porous GaN across optoelectronics, sensing and for improving material quality.