Special Issue "Micro- and Nano-Fabrication by Metal Assisted Chemical Etching"

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (1 March 2020).

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A printed edition of this Special Issue is available here.

Special Issue Editor

Dr. Lucia Romano
E-Mail Website
Guest Editor
1. Institute for Biomedical Engineering, University and ETH Zürich, 8092 Zürich, Switzerland
2. Paul Scherrer Institute, Forschungsstrasse 111, CH-5232 Villigen, Switzerland
Interests: X-ray optics; gratings; silicon etching; metal-assisted chemical etching; silicon nanowires
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Special Issue Information

Dear Colleagues,

Metal assisted chemical etching (MacEtch) has recently emerged as a new etching technique capable of fabricating high aspect ratio nano- and micro-structures in a few semiconductors substrates—Si, Ge, poly-Si, GaAs, and SiC—and using different catalysts—Ag, Au, Pt, Pd, Cu, Ni, and Rh. Several shapes have been demonstrated with a high anisotropy and feature size in the nanoscale—nanoporous films, nanowires, 3D objects, and trenches, which are useful components of photonic devices, microfluidic devices, bio-medical devices, batteries, Vias, MEMS, X-ray optics, and so on. With no limitations of large-areas and low-cost processing, MacEtch can open up new opportunities for several applications where high precision nano- and micro-fabrication is required. This can make semiconductor manufacturing more accessible to researchers in various fields, and accelerates innovation in electronics, bio-medical engineering, energy, and photonics. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments in MacEtch, and its use for various applications.

Dr. Lucia Romano
Guest Editor

Manuscript Submission Information

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Keywords

  • silicon microfabrication
  • nanowires
  • semiconductor processing
  • 3D microstructures
  • wet etching
  • anisotropic etching
  • X-ray optics
  • high aspect ratio
  • deep trench

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Published Papers (8 papers)

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Editorial

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Editorial
Editorial for the Special Issue on Micro- and Nano-Fabrication by Metal Assisted Chemical Etching
Micromachines 2020, 11(11), 988; https://doi.org/10.3390/mi11110988 - 31 Oct 2020
Viewed by 702
Abstract
Discovered by Li and Bohn in 2000 [...] Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)

Research

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Article
Curved Structure of Si by Improving Etching Direction Controllability in Magnetically Guided Metal-Assisted Chemical Etching
Micromachines 2020, 11(8), 744; https://doi.org/10.3390/mi11080744 - 30 Jul 2020
Cited by 2 | Viewed by 1355
Abstract
Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching [...] Read more.
Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching direction using an external magnetic field. However, the controllability of the etching direction diminishes with an increase in the etching dimension, owing to the corrosion of Fe due to the etching solution; this impedes the wider application of this approach for the fabrication of complex micro Si structures. In this study, we modified a tri-layer metal catalyst (Au/Fe/Au), wherein the Fe layer was encapsulated to improve direction controllability; this improved controllability was achieved by protecting Fe against the corrosion caused by the etching solution. We demonstrated curved Si microgroove arrays via magnetically guided MACE with Fe encapsulated in the tri-layer catalyst. Furthermore, the curvature in the curved Si microarrays could be modulated via an external magnetic field, indicating that direction controllability could be maintained even for the magnetically guided MACE of bulk Si. The proposed fabrication method developed for producing curved Si microgroove arrays can be applied to electronic devices and micro-electromechanical systems. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Article
Black GaAs: Gold-Assisted Chemical Etching for Light Trapping and Photon Recycling
Micromachines 2020, 11(6), 573; https://doi.org/10.3390/mi11060573 - 05 Jun 2020
Cited by 4 | Viewed by 972
Abstract
Thanks to its excellent semiconductor properties, like high charge carrier mobility and absorption coefficient in the near infrared spectral region, GaAs is the material of choice for thin film photovoltaic devices. Because of its high reflectivity, surface microstructuring is a viable approach to [...] Read more.
Thanks to its excellent semiconductor properties, like high charge carrier mobility and absorption coefficient in the near infrared spectral region, GaAs is the material of choice for thin film photovoltaic devices. Because of its high reflectivity, surface microstructuring is a viable approach to further enhance photon absorption of GaAs and improve photovoltaic performance. To this end, metal-assisted chemical etching represents a simple, low-cost, and easy to scale-up microstructuring method, particularly when compared to dry etching methods. In this work, we show that the etched GaAs (black GaAs) has exceptional light trapping properties inducing a 120 times lower surface reflectance than that of polished GaAs and that the structured surface favors photon recycling. As a proof of principle, we investigate photon reabsorption in hybrid GaAs:poly (3-hexylthiophene) heterointerfaces. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Article
Silicon Conical Structures by Metal Assisted Chemical Etching
Micromachines 2020, 11(4), 402; https://doi.org/10.3390/mi11040402 - 11 Apr 2020
Cited by 7 | Viewed by 1366
Abstract
A simple and inexpensive method to obtain Si conical structures is proposed. The method consists of a sequence of steps that include photolithography and metal assisted chemical etching (MACE) to create porous regions that are dissolved in a post-etching process. The proposed process [...] Read more.
A simple and inexpensive method to obtain Si conical structures is proposed. The method consists of a sequence of steps that include photolithography and metal assisted chemical etching (MACE) to create porous regions that are dissolved in a post-etching process. The proposed process takes advantage of the lateral etching obtained when using catalyst particles smaller than 40 nm for MACE. The final shape of the base of the structures is mainly given by the shape of the lithography mask used for the process. Conical structures ranging from units to hundreds of microns can be produced by this method. The advantage of the method is its simplicity, allowing the production of the structures in a basic chemical lab. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Article
Fabrication of Ultra-High Aspect Ratio (>420:1) Al2O3 Nanotube Arraysby Sidewall TransferMetal Assistant Chemical Etching
Micromachines 2020, 11(4), 378; https://doi.org/10.3390/mi11040378 - 03 Apr 2020
Cited by 3 | Viewed by 1084
Abstract
We report a robust, sidewall transfer metal assistant chemical etching scheme for fabricating Al2O3 nanotube arrays with an ultra-high aspect ratio. Electron beam lithography followed by low-temperature Au metal assisted chemical etching (MacEtch) is used to pattern high resolution, high [...] Read more.
We report a robust, sidewall transfer metal assistant chemical etching scheme for fabricating Al2O3 nanotube arrays with an ultra-high aspect ratio. Electron beam lithography followed by low-temperature Au metal assisted chemical etching (MacEtch) is used to pattern high resolution, high aspect ratio, and vertical silicon nanostructures, used as a template. This template is subsequently transferred by an atomic layer deposition of the Al2O3 layer, followed by an annealing process, anisotropic dry etching of the Al2O3 layer, and a sacrificial silicon template. The process and characterization of the Al2O3 nanotube arrays are discussed in detail. Vertical Al2O3 nanotube arrays with line widths as small as 50 nm, heights of up to 21 μm, and aspect ratios up to 420:1 are fabricated on top of a silicon substrate. More importantly, such a sidewall transfer MacEtch approach is compatible with well-established silicon planar processes, and has the benefits of having a fully controllable linewidth and height, high reproducibility, and flexible design, making it attractive for a broad range of practical applications. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Article
Metal-Assisted Chemical Etching and Electroless Deposition for Fabrication of Hard X-ray Pd/Si Zone Plates
Micromachines 2020, 11(3), 301; https://doi.org/10.3390/mi11030301 - 13 Mar 2020
Cited by 5 | Viewed by 1521
Abstract
Zone plates are diffractive optics commonly used in X-ray microscopes. Here, we present a wet-chemical approach for fabricating high aspect ratio Pd/Si zone plate optics aimed at the hard X-ray regime. A Si zone plate mold is fabricated via metal-assisted chemical etching (MACE) [...] Read more.
Zone plates are diffractive optics commonly used in X-ray microscopes. Here, we present a wet-chemical approach for fabricating high aspect ratio Pd/Si zone plate optics aimed at the hard X-ray regime. A Si zone plate mold is fabricated via metal-assisted chemical etching (MACE) and further metalized with Pd via electroless deposition (ELD). MACE results in vertical Si zones with high aspect ratios. The observed MACE rate with our zone plate design is 700 nm/min. The ELD metallization yields a Pd density of 10.7 g/cm 3 , a value slightly lower than the theoretical density of 12 g/cm 3 . Fabricated zone plates have a grid design, 1:1 line-to-space-ratio, 30 nm outermost zone width, and an aspect ratio of 30:1. At 9 keV X-ray energy, the zone plate device shows a first order diffraction efficiency of 1.9%, measured at the MAX IV NanoMAX beamline. With this work, the possibility is opened to fabricate X-ray zone plates with low-cost etching and metallization methods. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Article
Investigation of the Pd Nanoparticles-Assisted Chemical Etching of Silicon for Ethanol Solution Electrooxidation
Micromachines 2019, 10(12), 872; https://doi.org/10.3390/mi10120872 - 12 Dec 2019
Cited by 2 | Viewed by 1142
Abstract
The formation of porous silicon by Pd nanoparticles-assisted chemical etching of single-crystal Si with resistivity ρ = 0.01 Ω·cm at 25 °C, 50 °C and 75 °C in HF/H2O2/H2O solution was studied. Porous layers of silicon were [...] Read more.
The formation of porous silicon by Pd nanoparticles-assisted chemical etching of single-crystal Si with resistivity ρ = 0.01 Ω·cm at 25 °C, 50 °C and 75 °C in HF/H2O2/H2O solution was studied. Porous layers of silicon were studied by optical and scanning electron microscopy, and gravimetric analysis. It is shown that por-Si, formed by Pd nanoparticles-assisted chemical etching, has the property of ethanol electrooxidation. The chromatographic analysis of ethanol electrooxidation products on por-Si/Pd shows that the main products are CO2, CH4, H2, CO, O2, acetaldehyde (CHO)+, methanol and water vapor. The mass activity of the por-Si/Pd system was investigated by measuring the short-circuit current in ethanol solutions. The influence of the thickness of porous silicon and wafer on the mass activity and the charge measured during ethanol electrooxidation was established. Additionally, the mechanism of charge transport during ethanol electrooxidation was established. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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Review

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Review
Microfabrication of X-ray Optics by Metal Assisted Chemical Etching: A Review
Micromachines 2020, 11(6), 589; https://doi.org/10.3390/mi11060589 - 12 Jun 2020
Cited by 12 | Viewed by 1634
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 [...] Read more.
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 <100> 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. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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