This article presents an overview of the essential aspects in the fabrication of silicon and some silicon/germanium nanostructures by metal-assisted chemical etching. First, the basic process and mechanism of metal-assisted chemical etching is introduced. Then, the various influences of the noble metal, the etchant, temperature, illumination, and intrinsic properties of the silicon substrate (e.g., orientation, doping type, doping level) are presented. The anisotropic and the isotropic etching behaviors of silicon under various conditions are presented. Template-based metal-assisted chemical etching methods are introduced, including templates based on nanosphere lithography, anodic aluminum oxide masks, interference lithography, and block-copolymer masks. The metal-assisted chemical etching of other semiconductors is also introduced. A brief introduction to the application of Si nanostructures obtained by metal-assisted chemical etching is given, demonstrating the promising potential applications of metal-assisted chemical etching. Finally, some open questions in the understanding of metal-assisted chemical etching are compiled.

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Metal-Assisted Chemical Etching of Silicon: A Review

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

Silicon: the evolution of its use in biomaterials.

The recent advances in epitaxial SiC films' growth on Si are overviewed. The basic classical methods currently used for SiC films' growth are discussed and their advantages and disadvantages are explored. The basic idea and the theoretical background for a new method of the synthesis of epitaxial SiC films on Si are given. It will be shown that the new method is significantly different from the classical techniques of thin-film growth where the evaporation of the atoms onto the substrate surface is exploited. The new method is based on the substitution of some atoms in the silicon matrix by the carbon atoms to form the molecules of silicon carbide. It will be shown that the following process of SiC nucleation happens gradually without destroying the crystalline structure of the silicon matrix, and the orientation of a grown film is imposed by the original crystalline structure of the silicon matrix (not only by the substrate surface as in conventional methods of film growth). A comparison of the new method with other epitaxy techniques will be given.The new method of solid-phase epitaxy based on the substitution of atoms and on the creation of dilatation dipoles solves one of the major problems in heteroepitaxy. It provides the synthesis of low-defective unstrained epitaxial films with a large difference between the lattice parameters of the film and the substrate without using any additional buffer layers. This method has another unique feature distinguishing it from the classical techniques of SiC films' growth—it allows the growing of SiC films of hexagonal polytypes. A new kind of phase transformation in solids owing to the chemical transformation of one substance into another will be described theoretically and revealed experimentally. This type of phase transformation, and the mechanism of a broad class of heterogeneous chemical reactions between gas and solid phases, will be illustrated by an example of the growth of SiC epitaxial layers due to the chemical interaction of CO gas with the monocrystalline silicon matrix. The discovery of this mechanism yields a new kind of template: namely, substrates with buffer transition layers for wide-gap semiconductor growth on silicon. The properties of a variety of heteroepitaxial films of wide-gap semiconductors (SiC, AlN, GaN and AlGaN) grown on a SiC/Si substrate by solid-phase epitaxy will be reported. Grown films contain no cracks and have a quality sufficient to manufacture micro- and opto-electronic devices. Also, the new abilities in the synthesis of large (150 mm diameter) low-defective SiC films on Si substrates will be demonstrated.

https://iopscience.iop.org/article/10.1088/0022-3727/47/31/313001/pdf

Theory and practice of SiC growth on Si and its applications to wide-gap semiconductor films

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.

Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

The mechanism of stain formation in the chemical etching reaction of silicon has been investigated in HF–oxidizing agent–H2O solutions. The chemical formula of the stain formed during the silicon etching reaction is K2SiF6. The concentration of holes on silicon surface increases with the increase of redox potential and the concentration of oxidizing agent used in manufacturing the etching solution. The increase in the hole concentration accelerates not only the etch rate but also the formation rate of K2SiF6. The etched silicon surfaces are covered with a K2SiF6 layer when redox potential and concentration of oxidizing agent are great at low HF concentrations. This happens because the formation rate of K2SiF6 is much greater than its dissolution rate by HF. Sufficiently high HF concentration in the etching solution is apparently essential to increase the etch rate without the formation of K2SiF6.

Formation mechanism of stains during Si etching reaction in HF–oxidizing agent–H2O solutions

The dependency of void shape on Si surface orientation was investigated in the growth of silicon carbide (SiC) films on Si substrates. The orientation of the SiC films followed that of the Si substrate. In the silicon side of the SiC/Si interface, reverse-triangle-shaped voids were observed for the growth of SiC(100) on Si(100), whereas trapezoid-shaped voids were observed for the growth of SiC(111) on Si(111). The origin of the voids seemed to be the oxygen-relative defects inherently existing in bulk Si wafers. The shape of the voids was determined by that of the etch pit initially formed during the hydrogen etching process, which depends on the orientation of the silicon substrate. The mechanism of the void formation in the growth of SiC films on Si substrates was proposed based on the experimental results.

Formation mechanism of interfacial voids in the growth of SiC films on Si substrates

We have used a rapid thermal chemical vapor deposition technique to grow epitaxial SiC thin films on Si wafers by pyrolyzing tetramethylsilane (TMS). The films were observed to grow along the (111) direction of 3C–SiC at temperatures above 1000 °C. The quality of the films was significantly influenced by the TMS flow rate in the gas mixture, the growth temperature, and the gas pressure in the reactor. Single-crystal SiC films were grown at TMS flow rates below 1.0 sccm with a H2 carrier gas flow rate of 100 sccm. The gas pressure in the reactor has a great influence on the crystallinity, morphology, and thickness of the SiC film grown. Gas phase analyses indicated that TMS dissociates into hydrogen, silicon atoms, and hydrocarbons such as CH4, C2H2, and C2H4 at the growth temperature. The chemical composition of the grown films was analyzed. The growth mechanism of the SiC film on the Si substrate without the carbonization process is discussed based on the experimental results.

Growth mechanism of 3c-sic(111) films on si using tetramethylsilane by rapid thermal chemical vapor deposition

The effects of growth parameters have been examined for the epitaxial growth of a void-free SiC film on a Si substrate. Experiments were performed under various growth conditions by pyrolyzing tetramethylsilane (TMS) in a rapid thermal chemical vapor deposition reactor. Void-free single crystalline SiC films were grown when the Si substrate was heated after the flow of TMS. The increase of TMS flow rate produced void-free SiC films but the crystallinity of the films varied from single crystalline to polycrystalline. The growth of void-free single crystalline SiC films was observed at substrate temperatures below 1000°C. The outdiffusion of Si atoms from the Si substrate surface and the void formation in the silicon side of the SiC/Si interface were investigated using various experimental techniques. The mechanism of the void formation is briefly discussed in this work.

Effects of Experimental Parameters on Void Formation in the Growth of 3C‐SiC Thin Film on Si Substrate

It has long been argued whether the luminescent mechanism of anodized porous silicon is mainly due to the chemical compounds such as siloxene derivatives, or the quantum size effect. We performed a comprehensive study using atomic force microscope, infrared transmission, Raman scattering, and photoluminescence measurements in terms of various annealing temperatures. Low ‐ temperature photoluminescence spectra have also been observed. This leads us to conclude that not only the siloxene derivatives but also the quantum size effect gives the luminescence in porous silicon. The previous pseudopotential calculations are used for the explanation of our experimental results.

Young Hun Seo

Papers

Formation mechanism of stains during Si etching reaction in HF–oxidizing agent–H2O solutions

Formation mechanism of interfacial voids in the growth of SiC films on Si substrates

Growth mechanism of 3c-sic(111) films on si using tetramethylsilane by rapid thermal chemical vapor deposition

Effects of Experimental Parameters on Void Formation in the Growth of 3C‐SiC Thin Film on Si Substrate

Light‐emission phenomena from porous silicon: Siloxene compounds and quantum size effect