Showing papers on "Isotropic etching published in 2014"

Large area fabrication of vertical silicon nanowire arrays by silver-assisted single-step chemical etching and their formation kinetics.

Abstract: Vertically aligned silicon nanowire (SiNW) arrays have been fabricated over a large area using a silver-assisted single-step electroless wet chemical etching (EWCE) method, which involves the etching of silicon wafers in aqueous hydrofluoric acid (HF) and silver nitrate (AgNO3) solution. A comprehensive systematic investigation on the influence of different parameters, such as the etching time (up to 15 h), solution temperature (10–80 °C), AgNO3 (5–200 mM) and HF (2–22 M) concentrations, and properties of the multi-crystalline silicon (mc-Si) wafers, is presented to establish a relationship of these parameters with the SiNW morphology. A linear dependence of the NW length on the etch time is obtained even at higher temperature (10–50 °C). The activation energy for the formation of SiNWs on Si(100) has been found to be equal to ~0.51 eV . It has been shown for the first time that the surface area of the Si wafer exposed to the etching solution is an important parameter in determining the etching kinetics in the single-step process. Our results establish that single-step EWCE offers a wide range of parameters by means of which high quality vertical SiNWs can be produced in a very simple and controlled manner. A mechanism for explaining the influence of various parameters on the evolution of the NW structure is discussed. Furthermore, the SiNW arrays have extremely low reflectance (as low as <3% for Si(100) NWs and <12% for mc-Si NWs) compared to ~35% for the polished surface in the 350–1000 nm wavelength range. The remarkably low reflection surface of SiNW arrays has great potential for use as an effective light absorber material in novel photovoltaic architectures, and other optoelectronic and photonic devices.

Uniform Vertical Trench Etching on Silicon with High Aspect Ratio by Metal-Assisted Chemical Etching Using Nanoporous Catalysts

Abstract: Recently, metal-assisted chemical etching (MaCE) has been proposed as a promising wet-etching method for the fabrication of micro- and nanostructures on silicon with low cost. However, uniform vert...

Decoupling Diameter and Pitch in Silicon Nanowire Arrays Made by Metal‐Assisted Chemical Etching

Abstract: The fabrication of well-separated, narrow, and relatively smooth silicon nanowires with good periodicity is demonstrated, using non-close-packed arrays of nanospheres with precisely controlled diameters, pitch, and roughness. Controlled reactive ion etching in an inductively coupled plasma reduces the self-assembled nanospheres to approximately a tenth of their original diameter, while retaining their surface smoothness and periodic placement. A titanium adhesion layer between the silicon substrate and gold film allows much thinner catalyst layers to be continuous, facilitating the film liftoff and formation of the perforated pattern without influencing catalyzed etching of silicon. Using these methods, a periodic array of silicon nanowires with a large pitch and small diameter (e.g., a 490 nm pitch and 55 nm diameter) is created, a combination not typically found in the open literature. This approach extends the types and quality of silicon nanostructures that can be fabricated using the combined nanosphere lithography and metal-assisted chemical etching techniques.

Fabrication of porous silicon nanowires by MACE method in HF/H2O2/AgNO3 system at room temperature

Abstract: In this paper, the moderately and lightly doped porous silicon nanowires (PSiNWs) were fabricated by the ‘one-pot procedure’ metal-assisted chemical etching (MACE) method in the HF/H2O2/AgNO3 system at room temperature. The effects of H2O2 concentration on the nanostructure of silicon nanowires (SiNWs) were investigated. The experimental results indicate that porous structure can be introduced by the addition of H2O2 and the pore structure could be controlled by adjusting the concentration of H2O2. The H2O2 species replaces Ag+ as the oxidant and the Ag nanoparticles work as catalyst during the etching. And the concentration of H2O2 influences the nucleation and motility of Ag particles, which leads to formation of different porous structure within the nanowires. A mechanism based on the lateral etching which is catalyzed by Ag particles under the motivation by H2O2 reduction is proposed to explain the PSiNWs formation.

Vertically aligned crystalline silicon nanowires with controlled diameters for energy conversion applications: Experimental and theoretical insights

Abstract: Vertically orientated single crystalline silicon nanowire (SiNW) arrays with controlled diameters are fabricated via a metal-assisted chemical etching method. The diameter of the fabricated nanowires is controlled by simply varying the etching time in HF/H2O2 electrolytes. The fabricated SiNWs have diameters ranging from 117 to 650 nm and lengths from 8 to 18 μm. The optical measurements showed a significant difference in the reflectance/absorption of the SiNWs with different diameters, where the reflectance increases with increasing the diameter of the SiNWs. The SiNWs showed significant photoluminescence (PL) emission spectra with peaks lying between 380 and 670 nm. The PL intensity increases as the diameter increases and shows red shift for peaks at ∼670 nm. The increase or decrease of reflectivity is coincident with PL intensity at wavelength ∼660 nm. The x-ray diffraction patterns confirm the high crystallinity of the fabricated SiNWs. In addition, the Raman spectra showed a shift in the first order transverse band toward lower frequencies compared to that usually seen for c-Si. Finite difference time domain simulations have been performed to confirm the effect of change of diameter on the optical properties of the nanowires. The simulation results showed good agreement with the experimental results for the SiNWs of different diameters.

Anti-reflection layers fabricated by a one-step copper-assisted chemical etching with inverted pyramidal structures intermediate between texturing and nanopore-type black silicon

Abstract: A new one-step copper-assisted chemical etching technique is reported to more economically prepare nanopore-type anti-reflective layers, which can effectively suppress reflection of Si wafer surfaces for solar cell applications. In contrast to the Au and Ag processes, phosphorous acid (rather than hydrogen peroxide) is utilized as a reducing agent to reduce Cu2+ to Cu0 nanoparticles. The Cu nanoparticles catalyse the oxidization of Si in the vicinity of the nanoparticles to SiO2, which is then etched by HF to form nanopores. The effects of the HF and H3PO3 concentrations, the HF : H2O volume ratio, and the etching time on the black silicon morphology with the corresponding Si surface reflectivity have been systematically investigated. The size and shape of the pores are controlled by [Cu2+] and the subsequent size of the NPs as controlled by [H3PO3], while the depth of the pores are limited by [HF] and the etch time. With [Cu2+] = 500 μM and [H3PO3] = 10 mM, the fabricated black silicon possesses the lowest relative effective reflectivity, 0.96%, and the shortest nanopore length (590 nm).

All-in-fiber optofluidic sensor fabricated by femtosecond laser assisted chemical etching

Abstract: An all-in-fiber prototype optofluidic device was fabricated by femtosecond laser irradiation and subsequent selective chemical wet etching. Horizontal and vertical microchannels can be flexibly created into an optical fiber to form a fluidic cavity with inlets/outlets. The fluidic cavity also functions as an optical Fabry–Perot cavity in which the filled liquid can be probed. The assembly-free microdevice exhibited a fringe visibility of 20 dB and was demonstrated for measurement of the refractive index of the filling liquids. The proposed all-in-fiber optofluidic micro device is attractive for chemical and biomedical sensing because it is flexible in design, simple to fabricate, mechanically robust, and miniaturized in size.

Alternative process for thin layer etching: Application to nitride spacer etching stopping on silicon germanium

Abstract: Silicon nitride spacer etching realization is considered today as one of the most challenging of the etch process for the new devices realization. For this step, the atomic etch precision to stop on silicon or silicon germanium with a perfect anisotropy (no foot formation) is required. The situation is that none of the current plasma technologies can meet all these requirements. To overcome these issues and meet the highly complex requirements imposed by device fabrication processes, we recently proposed an alternative etching process to the current plasma etch chemistries. This process is based on thin film modification by light ions implantation followed by a selective removal of the modified layer with respect to the non-modified material. In this Letter, we demonstrate the benefit of this alternative etch method in term of film damage control (silicon germanium recess obtained is less than 6 A), anisotropy (no foot formation), and its compatibility with other integration steps like epitaxial. The etch mechanisms of this approach are also addressed.

Effect of Wettability on the Agglomeration of Silicon Nanowire Arrays Fabricated by Metal-Assisted Chemical Etching

Abstract: The effect of wettability on the undesirable bundling of silicon nanowire (SiNW) arrays fabricated by metal-assisted chemical etching (MACE) method is investigated. This paper reports a simple and low-cost approach to achieve dense SiNW arrays with excellent lateral separation. A hydrophilic pretreatment on the initial wafer substrate prior to the etching procedure, followed by a hydrophobic post-treatment of the fabricated SiNWs, allows the fabrication of large and dense arrays of SiNWs with no agglomeration. These results are discussed within the framework of the detailed balance of forces acting on the nanowires.

Bulk micromachining of Si by metal-assisted chemical etching.

Abstract: Bulk micromachining of Si is demonstrated by the well-known metal-assisted chemical etching (MaCE). Si microstructures, having lateral dimension from 5 μm up to millimeters, are successfully sculpted deeply into Si substrate, as deep as >100 μm. The key ingredient of this success is found to be the optimizations of catalyst metal type and its morphology. Combining the respective advantages of Ag and Au in the MaCE as a Ag/Au bilayer configuration leads to quite stable etch reaction upon a prolonged etch duration up to >5 h. Further, the permeable nature of the optimized Ag/Au bilayer metal catalyst enables the etching of pattern features having very large lateral dimension. Problems such as the generation of micro/nanostructures and chemical attacks on the top of pattern surface are successfully overcome by process optimizations such as post-partum sonication treatment and etchant formulation control. The method can also be successful to vertical micromachining of Si substrate having other crystal orientations than Si(100), such as Si(110) and Si(111). The simple, easy, and low-cost nature of present approach may be a great help in bulk micromachining of Si for various applications such as microelectromechanical system (MEMS), micro total analysis system (μTAS), and so forth.

Developing Barbed Microtip-Based Electrode Arrays for Biopotential Measurement

Abstract: This study involved fabricating barbed microtip-based electrode arrays by using silicon wet etching. KOH anisotropic wet etching was employed to form a standard pyramidal microtip array and HF/HNO3 isotropic etching was used to fabricate barbs on these microtips. To improve the electrical conductance between the tip array on the front side of the wafer and the electrical contact on the back side, a through-silicon via was created during the wet etching process. The experimental results show that the forces required to detach the barbed microtip arrays from human skin, a polydimethylsiloxane (PDMS) polymer, and a polyvinylchloride (PVC) film were larger compared with those required to detach microtip arrays that lacked barbs. The impedances of the skin-electrode interface were measured and the performance levels of the proposed dry electrode were characterized. Electrode prototypes that employed the proposed tip arrays were implemented. Electroencephalogram (EEG) and electrocardiography (ECG) recordings using these electrode prototypes were also demonstrated.

Deep Etching of Single- and Polycrystalline Silicon with High Speed, High Aspect Ratio, High Uniformity, and 3D Complexity by Electric Bias-Attenuated Metal-Assisted Chemical Etching (EMaCE)

Abstract: In this work, a novel wet silicon (Si) etching method, electric bias-attenuated metal-assisted chemical etching (EMaCE), is demonstrated to be readily available for three-dimensional (3D) electronic integration, microelectromechinal systems, and a broad range of 3D electronic components with low cost. On the basis of the traditional metal-assisted chemical etching process, an electric bias was applied to the Si substrate in EMaCE. The 3D geometry of the etching profile was effectively controlled by the bias in a real-time manner. The reported method successfully fabricated an array of over 10 000 vertical holes with diameters of 28 μm on 1 cm2 silicon chips at a rate of up to 11 μm/min. The sidewall roughness was kept below 50 nm, and a high aspect ratio of over 10:1 was achieved. The 3D geometry could be attenuated by the variable applied bias in real time. Vertical deep etching was realized on (100)-, (111)-Si, and polycrystalline Si substrates. Complex features with lateral dimensions of 0.8–500 μm wer...

Plasma etching method

Abstract: A plasma etching method that can improve an etching selection ratio of a film to be etched to a film different from the film to be etched compared with the related art is provided. The present invention provides a plasma etching method for selectively etching a film to be etched against a film different from the film to be etched, in which plasma etching of the film to be etched is performed using a gas that can cause to generate a deposited film containing similar components as components of the different film.

Methods for barrier layer removal

Abstract: Implementations described herein generally relate to semiconductor manufacturing and more particularly to methods for etching a low-k dielectric barrier layer disposed on a substrate using a non-carbon based approach. In one implementation, a method for etching a barrier low-k layer is provided. The method comprises (a) exposing a surface of the low-k barrier layer to a treatment gas mixture to modify at least a portion of the low-k barrier layer and (b) chemically etching the modified portion of the low-k barrier layer by exposing the modified portion to a chemical etching gas mixture, wherein the chemical etching gas mixture includes at least an ammonium gas and a nitrogen trifluoride gas or at least a hydrogen gas and a nitrogen trifluoride gas.

Wet etching processes for recycling crystalline silicon solar cells from end-of-life photovoltaic modules

Abstract: The ideal approach for disposing of end-of-life photovoltaic (PV) modules is recycling. Since it is expected that more than 50 000 t of PV modules will be worn out in 2015, the recycling approach has received significant attention in the last few years. In order to recover Si wafers from degraded solar cells, metal electrodes, anti-reflection coatings, emitter layers, and p–n junctions have to be removed from the cells. In this study, we employed two different chemical etching processes to recover Si wafers from degraded Si solar cells. Each etching process consisted of two steps: (1) first etching carried out using a nitric acid (HNO3) and hydrofluoric acid (HF) mixture and potassium hydroxide (KOH), (2) second etching carried out using phosphoric acid (H3PO4) and a HNO3 and HF mixture. The first etching process resulted in deep grooves, 36 μm on average, on the front of recycled wafers that rendered the process unsuitable for wafers to be used in solar cell production. Such grooves occurred due to different etching rates of Ag electrodes and silicon nitride (SiNx). On the other hands, the second etching process did not result in such grooves and produced a recovered Si wafer with a uniform and smooth surface. The recycled wafers obtained by the second etching process showed properties almost identical to those of commercial virgin wafers: thickness, 173 μm; minimum and maximum resistivity, 1.6 and 10 Ω cm, respectively; and average carrier lifetime, 1.785 μs. In addition, P and Al atoms were not detected in the recycled wafers by secondary ion mass spectroscopy.

Three-dimensional glass monolithic micro-flexure fabricated by femtosecond laser exposure and chemical etching

Abstract: Flexures are components of micro-mechanisms efficiently replacing classical multi-part joints found at the macroscale. So far, flexures have been limited to two-dimensional planar designs due to the lack of a suitable three-dimensional micromanufacturing process. Here we demonstrate and characterize a high-strength transparent monolithic three-dimensional flexural component fabricated out of fused silica using non-ablative femtosecond laser processing combined with chemical etching. As an illustration of the potential use of this flexure, we propose a design of a Hoecken linkage entirely made with three-dimensional cross-spring pivot hinges.

Near-infrared optical absorption enhanced in black silicon via Ag nanoparticle-induced localized surface plasmon

Abstract: Due to the localized surface plasmon (LSP) effect induced by Ag nanoparticles inside black silicon, the optical absorption of black silicon is enhanced dramatically in near-infrared range (1,100 to 2,500 nm). The black silicon with Ag nanoparticles shows much higher absorption than black silicon fabricated by chemical etching or reactive ion etching over ultraviolet to near-infrared (UV-VIS-NIR, 250 to 2,500 nm). The maximum absorption even increased up to 93.6% in the NIR range (820 to 2,500 nm). The high absorption in NIR range makes LSP-enhanced black silicon a potential material used for NIR-sensitive optoelectronic device.

Fabrication of superoleophobic hierarchical surfaces for low-surface-tension liquids

Abstract: This study demonstrates the fabrication of hierarchical surfaces with super-repellency even for low-surface-tension liquids, including octane (surface tension of 21.7 mN m−1). Dual-pore surfaces were prepared by a combination of practical wet processes on an aluminium substrate: chemical etching, anodizing, and organic monolayer coating. The size of the larger pores formed by the chemical etching of aluminium is controlled by the concentration of HCl in the CuCl2/HCl etching solution. The etched aluminium is then anodized to introduce nanopores, followed by a pore-widening treatment that controls the nanopore size and porosity. The repellency for low-surface-tension liquids is enhanced by increasing the size of the larger pores as well as the porosity of the walls of the larger pores in this dual-pore morphology. Under optimized morphology with a fluoroalkyl-phosphate monolayer coating, an advancing contact angle close to 160°, a contact angle hysteresis of less than 5° and a sliding angle of 10° is achieved even for octane.

Novel Approach to Surface Processing for Improving the Efficiency of CdZnTe Detectors

Abstract: We emphasize an improvement of the surface processing procedures for cadmium zinc telluride (CZT) detectors, which is one of the principal problems limiting the technology. A rough surface enhances the leakage current into the medium, creating additional trapping centers and thereby degrading the detector’s performance. Mechanical polishing followed by chemical treatment yields smoother surfaces as required, but chemical treatment, especially with bromine-based solutions, induces unwanted surface features, increases the surface conductivity, and generates chemical species that alter the material’s surface and interfacial properties. It is essential to avoid such adverse consequences of surface etching in the manufacturing of highly efficient radiation detectors. We approached the problem of processing the crystals’ surfaces by using two different solutions (a low-concentration bromine-based etchant mixture in conjunction with a surface-passivation reagent and a non-bromine-based etchant). The chemomechanical treatment yielded smooth nonconductive surfaces with fewer detrimental features, therefore allowing us to fabricate better devices. We determined the surface roughness using atomic force microscopy and optical profilometry (OP). We analyzed the surface structure, orientations of the crystals, and formation of chemical species by x-ray photoelectron spectroscopy techniques and delineated their effects on the devices’ electrical properties and performance. Our experimental data revealed that our new chemical etching process produced nonconductive surfaces with fewer surface defects and so improved the detectors’ charge transport and efficiency. We detail the results of our new etchants and compare them with those for conventional Br-methanol etchants.

Laser ablating structures for antenna modules for dual interface smartcards

Abstract: Laser etching antenna structures (AS) for RFID antenna modules (AM). Combining laser etching and chemical etching. Limiting the thickness of the contact pads (CP) to less than the skin depth (18 m) of the conductive material (copper) used for the contact pads (CP). Multiple antenna structures (AS1, AS2) in an antenna module (AM). Incorporating LEDs into the antenna module (AM) or smartcard (SC).

Wet chemical thinning of molybdenum disulfide down to its monolayer

Abstract: We report on the preparation of mono- and bi-layer molybdenum disulfide (MoS2) from a bulk crystal by facile wet chemical etching. We show that concentrated nitric acid (HNO3) effectively etches thin MoS2 crystals from their edges via formation of MoO3. Interestingly, etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets. The flakes obtained by chemical etching exhibit electronic quality comparable to that of mechanically exfoliated counterparts. Our findings indicate that the self-limiting chemical etching is a promising top-down route to preparing atomically thin crystals from bulk layer compounds.

Vapor phase metal-assisted chemical etching of silicon

Abstract: This work introduces and explores vapor phase metal-assisted chemical etching (VP-MaCE) of silicon as a method to bypass some of the challenges found in traditional liquid phase metal-assisted chemical etching (LP-MaCE). Average etch rates for Ag, Au, and Pd/Au catalysts are established at 31, 70, and 96 nm/min respectively, and the relationship between etch rate and substrate temperature is examined experimentally. Just as with LP-MaCE, 3D catalyst motion is maintained and three-dimensional structures are fabricated with nanoparticle- and lithography-patterned catalysts. VP-MaCE produces less microporous silicon compared with LP-MaCE and the diffusion/reduction distance of Ag+ ions is significantly reduced. This process sacrifices etch rate for increased etch uniformity and lower stiction for applications in micro-electromechanical systems (MEMS) processing.