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The technique of the anisotropic wet chemical etching had turned into one of the widely used processes for manufacturing the functional materials in microelectromechanical systems. To better understand the issues of growth mechanisms for the characteristic surface morphologies during an anisotropic chemical etching, in this study the formation and evolution of surface structures were investigated by numerical simulation methods. A chemical etching model was established on the basis of chemical reaction and atomic diffusion. Affecting by the anisotropy of the crystalline structure and etching rate, various featured surface morphologies, including the rippling surface, cusp-like hillock, and nano-pyramid, were numerically developed in accordance with the etching conditions. These characteristic structures were also in well agreements with the corresponding experiments. From the theoretical point of view, the surface morphologies were critically influenced by the kinetic factors of the anisotropic etching rate and the atomic diffusion. With the enhancement of theoretical work in the formation mechanism for the anisotropic chemical etching, the practical technique would possess a more competitive advantage for the wide applications in the fields of the functional materials fabrication.
17Array structure of monocrystalline silicon surface processed by femtosecond laser machining assisted with anisotropic chemical etching
Array structure of monocrystalline silicon surface processed by femtosecond laser machining assisted with anisotropic chemical etching
Read more4Roughness kinetic and multiaffinity of anisotropic etched silicon
Roughness kinetic and multiaffinity of anisotropic etched silicon
79Writing FIB implantation and subsequent anisotropic wet chemical etching for fabrication of 3D structures in silicon
Writing FIB implantation and subsequent anisotropic wet chemical etching for fabrication of 3D structures in silicon
6A Simple Texturization Approach for Mono-Crystalline Silicon Solar Cell with Low TMAH Concentration Solution
Texturing for mono-crystalline silicon solar cell by chemical anisotropic etching is one of the most important techniques in photovoltaic industry. In recent years, tetramethylammonium hydroxide (TMAH) solution or a mixture of TMAH solution with IPA was reported to be used for random pyramids texturization on silicon surface due to its non-volatile, nontoxic, good anisotropic etching characteristics and uncontaminated metal ions. However, most of the studies were reported about the etching processes by using high TMAH concentration solutions. In this study, a simple and cost-effective approach for texturing mono-crystalline silicon wafers in low TMAH concentration solutions was proposed. Etching was performed on (100) silicon wafers using silicon-dissolved tetramethylammonium hydroxide (TMAH) solutions (0.5~1 %) without addition of surfactant. The surface phenomena, surface morphology and surface reflectance have been analyzed. A textured surface with smaller and smooth pyramids can be realized by using 1 % silicon-dissolved TMAH solutions.
Read more10Research progresses of SOI optical waveguide devices and integrated optical switch matrix
SOI (silicon-on-insulator) is a new material with a lot of important performances such as large index difference, low transmission loss. Fabrication processes for SOI based optoelectronic devices are compatible with conventional IC processes. Having the potential of OEIC monolithic integration, SOI based optoelectronic devices have shown many good characteristics and become more and more attractive recently. In this paper, the recent progresses of SOI waveguide devices in our research group are presented. By highly effective numerical simulation, the single mode conditions for SOI rib waveguides with rectangular and trapezoidal cross-section were accurately investigated. Using both chemical anisotropic wet etching and plasma dry etching techniques, SOI single mode rib waveguide, MMI coupler, VOA (variable optical attenuator), 2 × 2 thermal-optical switch were successfully designed and fabricated. Based on these, 4 × 4 and 8 × 8 SOI optical waveguide integrated switch matrixes are demonstrated for the first time.
Read more8Anisotropic etching of single crystalline SiC using molten KOH for SiC bulk micromachining
Microelectromechanical systems (MEMS) devices made of single crystalline silicon carbide (SiC) are attractive for applications in harsh environment, because SiC is chemically inert and semiconductor devices made of SiC can be operated at very high temperature. On the other hand, due to its chemical inertness, controllable etching of SiC has been difficult. Molten KOH etching has been widely used to detect crystalline defects in SiC as etch pit in crystal growth researchers. Some etch pits have hexagonal shape, indicating anisotropic etching nature. Therefore, molten KOH etching may have potential as a SiC MEMS fabrication process. In this study we have developed the anisotropic wet chemical etching of single crystalline hexagonal SiC using molten KOH for SiC bulk micromachining. 6H-SiC (0001)Si face and (000-1)C face substrates are used. Etching rates of (0001)Si and (000-1)C faces at 490 °C are evaluated to be 37 nm/min and 3.1 μm/min, respectively, indicating that the (0001)Si face is etched almost 100 times slower than the (000-1)C face is. Cross sectional analysis of etched structure of (000-1)C face revealed that inclined crystal plane was formed as a sidewall with some undercut. To assess in-plane etching anisotropy, ring shape mesa structures are formed on SiC (0001)Si face by RIE and then etched by molten KOH. Ring shape changed into hexagonal shape, clearly indicating etching rate along <11-20> direction is larger than <1-100> direction in (0001)Si face.
Read more12Fabrication of silicon field emission points for vacuum microelectronics by wet chemical etching
The fabrication of sharp silicon tips for field emission cathodes has been investigated using anisotropic and isotropic wet chemical etching techniques. Formulations of potassium hydroxide, water and alcohol are used as the anisotropic etchants. The effects of isopropyl, secondary butyl and tertiary butyl alcohols on tip formation are examined. An isotropic etchant using a mixture of hydrofluoric, nitro and acetic acids is also used to form similar cathode structures for comparison. The silicon needles formed are intended for use in vacuum microelectronic devices.
Read more14Novel Mold Fabrication for Nano-Imprint Lithography to Fabricate Single-Electron Tunneling Devices
A novel method of fabricating a nano-imprinting mold for a single-electron device is newly proposed, which makes use of the peculiarity of anisotropic wet chemical etching. A row of resist patterns for quantum dots is placed to keep an offset angle θ against a <110> crystalline axis on a (100) Si surface. By an anisotropic wet chemical etching, the Si substrate is diagonally etched along the <110> and <110> directions, and an inverted pyramidal hole with a (111) plane surface is formed. The gap between them becomes narrower than that of the original pattern. Using this method, the nano-imprinting mold for a quantum dot array with narrow gaps beyond the resolution limit of conventional lithography is obtained.
Read more16Integrated folding 4/spl times/4 optical matrix switch with total internal reflection mirrors on SOI by anisotropic chemical etching
A folding rearrangeable nonblocking 4×4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20×1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a fast response of 7.5 μs. The power consumption of each 2×2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of /spl plusmn/0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.
Read more5Fabrication of Sio2-based microcantilevers by anisotropic chemical etching of (100) single crystal Si
The undercutting process of thermal SiO2 microcantilevers with different orientations on (100) Si wafer was studied. The silicon substrate was removed by anisotropic chemical etching with a 25 wt. % aqueous solution of TMAH or a 30 wt. % aqueous KOH solution at 80 ?C. It was found that [110] oriented cantilevers were undercutting frontally along the length and [100] oriented cantilevers experience undercutting along the width of the cantilever, which is a less time consuming process. The studies showed that the [100] orientation of SiO2 microbridges enables theirs fabrication on a (100) oriented Si substrate.
Read more38Evolutionary continuous cellular automaton for the simulation of wet etching of quartz
Anisotropic wet chemical etching of quartz is a bulk micromachining process for the fabrication of micro-electro-mechanical systems (MEMS), such as resonators and temperature sensors. Despite the success of the continuous cellular automaton for the simulation of wet etching of silicon, the simulation of the same process for quartz has received little attention—especially from an atomistic perspective—resulting in a lack of accurate modeling tools. This paper analyzes the crystallographic structure of the main surface orientations of quartz and proposes a novel classification of the surface atoms as well as an evolutionary algorithm to determine suitable values for the corresponding atomistic removal rates. Not only does the presented evolutionary continuous cellular automaton reproduce the correct macroscopic etch rate distribution for quartz hemispheres, but it is also capable of performing fast and accurate 3D simulations of MEMS structures. This is shown by several comparisons between simulated and experimental results and, in particular, by a detailed, quantitative comparison for an extensive collection of trench profiles.
Read moreInvestigation of the technological features of anisotropic chemical etching upon the production of sensors of physical quantities
The procedures for forming elements of sensors of physical quantities by anisotropic etching are examined. How etching conditions influence the roughness of silicon wafers is investigated and ways to decrease the roughness are determined. It is shown that, to etch silicon wafers, the liquid etching procedure is predominantly used. The morphology and roughness of silicon-wafer surfaces are investigated with the help of scanning electron microscopy and atomic-force microscopy.
Read moreWet chemical etching of Al 0.65 Ga 0.35 N in aqueous KOH solutions
We have investigated wet chemical etching of Al0.65Ga0.35N in 20% (by weight) aqueous KOH solutions at 85, 95 and 102 °C. The etch rates were 0.48, 0.64 and 0.96 μm/min, respectively. Scanning electron microscope, atomic force microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy were employed to characterize the surface morphology and stoichiometry before and after wet chemical etching. Experimental results show that aqueous KOH solutions can effectively etch Al 0.65 Ga 0.35 N. SEM results show that the root-mean-square (rms) roughness increased from 16.189 to 50.496 nm. Degradation in surface smoothness is attributed to selective anisotropic wet chemical etching. The AES measurements show that after the untreated sample was wet chemical treated in a 20% KOH solution at 85 °C for 15 seconds, the oxide formed in the surface was removed and a lower content of oxide layer near the surface was formed and the N content is higher. XPS measurements show that the banding energies of Ga 3d shifted to low energy direction after the untreated sample was successively wet chemical treated. It indicated that the atom Ga tended to form Ga-N rather than Ga-O bonding on the surface after KOH solution treatment. The damage and oxide layer induced by dry etching processes was effectively removed by wet chemical treatment and the damage surface was refreshed.
Read more10The influence of the AlN film texture on the wet chemical etching
The influence of the AlN film texture on the wet chemical etching
28Proximity ferroelectricity in wurtzite heterostructures.
Proximity ferroelectricity is an interface-associated phenomenon in electric-field-driven polarization reversal in a non-ferroelectric polar material induced by one or more adjacent ferroelectric materials. Here we report proximity ferroelectricity in wurtzite ferroelectric heterostructures. In the present case, the non-ferroelectric layers are AlN and ZnO, whereas the ferroelectric layers are Al1-xBxN, Al1-xScxN and Zn1-xMgxO. The layered structures include nitride-nitride, oxide-oxide and nitride-oxide stacks that feature two-layer (asymmetric) and three-layer (symmetric) configurations1-3. Ferroelectric switching in both layers is validated by multimodal characterization methods, including polarization hysteresis, anisotropic chemical etching, second harmonic generation, piezo response force microscopy, electromechanical testing and atomic resolution polarization orientation imaging in real space by scanning transmission electron microscopy. We present a physical switching model in which antipolar nuclei originate in the ferroelectric layer and propagate towards the internal non-ferroelectric interface. The domain wall leading edge produces elastic and electric fields that extend beyond the interface at close proximity, reducing the switching barrier in the non-ferroelectric layer, and allowing complete domain propagation without breakdown. Density functional theory calculations of polymorph energies, reversal barriers and domain wall energies support this model. Proximity ferroelectricity enables polarization reversal in wurtzites without the chemical or structural disorder that accompanies elemental substitution, opening new questions and opportunities regarding interface-based ferroelectricity.
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