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In this paper a processing technique for sapphire is presented which combines laser-induced amorphization and subsequent selective wet etching of amorphized sapphire as well as anisotropic wet etching of single-crystalline sapphire (α-Al2O3). Using this technique, microstructures can be realized on the surface and in the bulk of sapphire substrates. By focusing ultra-short laser pulses inside sapphire, its structure can be transformed from crystalline into amorphous. The modified material can be selectively removed using etchants, such as hydrofluoric acid or potassium hydroxide (KOH), solely dissolving the amorphized part. In this work, however, an etchant consisting of a standard solution of sulphuric acid and phosphoric acid (96 vol% H2SO4: 85 vol% H3PO4, 3:1 vol%) at 180 °C is utilized. This method allows the realization of structures which are impossible to achieve when using conventional etchants which solely dissolve the amorphized sapphire. Ultrashort pulsed laser irradiation (230 fs) is used in this study as starting point for the subsequent anisotropic etching to form microstructures on the surface or in the bulk of sapphire that are terminated by characteristic crystal planes. In particular, the appearance of etching-induced patterns formed by stacks of rhombohedra is shown for structures below the surface, whereas triangular pits are achieved in surface processing.

We address experimentally the large-scale dynamics of Si(1 0 0) surfaces during the initial stages of anisotropic wet (KOH) chemical etching, which are characterized through atomic force microscopy. These systems are known to lead to the formation of characteristic pyramids, or hillocks, of typical sizes in the nanometric/micrometer scales, thus with the potential for a large number of applications that can benefit from the nanotexturing of Si surfaces. The present pattern formation process is very strongly disordered in space. We assess the space correlations in such a type of rough surface and elucidate the existence of a complex and rich morphological evolution, featuring at least three different regimes in just 10 min of etching. Such a complex time behavior cannot be consistently explained within a single formalism for dynamic scaling. The pyramidal structure reveals itself as the basic morphological motif of the surface throughout the dynamics. A detailed analysis of the surface slope distribution with etching time reveals that the texturing process induced by the KOH etching is rather gradual and progressive, which accounts for the dynamic complexity. The various stages of the morphological evolution can be accurately reproduced by computer-generated surfaces composed by uncorrelated pyramidal structures. To reach such an agreement, the key parameters are the average pyramid size, which increases with etching time, its distribution and the surface coverage by the pyramidal structures., This work was supported by Council of Scientific and Industrial Research (India) Scheme No. 03(1289)/13/EMR-II, and by MINECO/FEDER (Spain/UE) Grants Nos. FIS2012-38866-C05-01, MAT2014-54231-C4-1-P, BIO2016-79618-R, and FIS2015-66020-C2-1-P, as well as by Comunidad Autónoma de Madrid (Spain) Grant NANOAVANSENS S2013/MIT-3029.

In this paper, the structure of silicon crystal and the course of anisotropic etching have been presented in a simple way. Connections between etching anisotropy and surface morphology along with these between etching anisotropy and solution composition are shown. Correlation between solution composition and both morphology of the etched surface and shape of structures etched anisotropically using an oxide mask is analyzed. A simple scheme for designing cross-sections of etched structures and a simplified geometrical model of etching concave and convex structures are demonstrated. KOH and TMAH etching solutions, along with solutions containing additions of tensioactive compounds are compared. Special attention is paid to differences among these solutions.

Photolithography on three-dimensional structures is becoming a key process for realizing new micromechanical devices. Patterning on three-dimensional structures using the conventional mask aligner is a difficult task. In this paper, we present an approach for transferring patterns on cavities prepared by anisotropic etching. A new method of angled exposing is introduced for improving the uniformity of the incident-light-power density transmitted into the resist film deposited on the cavities. This method also reduces the number of reflections coming from the sidewalls of the cavities. Polarized light is used for realizing a pattern on the narrow cavities with a high aspect ratio.

This paper presents a method for etching tapered sidewalls in silicon using deep reactive ion etching. The method is based on consecutive switching between anisotropic etching using the Bosch proce ...

We previously proposed a novel fabrication process, which combined mechanical dicing and anisotropic wet etching, to reduce the cost of micro-electro-mechanical system devices, and fabricated various solid-type microneedle structures using this process for trans-dermal drug delivery systems. The current research involved us enhancing our previous processes by applying metal plating and using a minimum number of photolithography steps, and we fabricated a hollow-type micro-needle structure, in which a flow channel was formed at the center of the needle projection, for supplying medical solutions from the area behind the needle. We fabricated two different shaped needle structures, pyramidal and flattened needles. The height and pitch of both needle types were 120–250 µm and 230–280 µm, respectively. The developed process is useful for producing disposable microneedles for bio-medical applications.

Small self-assembled inverted hexagonal pyramids consisting of GaN:Mg and InGaN/GaN multi-quantum-well (MQW) structures were fabricated using photoelectrochemical wet etching. Lateral etching, bottom-up etching, and anisotropic etching are the sequential formation mechanism of such pyramids during the wet etching. The inverted hexagonal pyramids were measured to be 245 nm in width and 184 nm in height, and the angle between the top GaN:Mg surface and the pyramid sidewall was calculated to be about 56.3°. Due to the strain relief in the nano-disk MQW structure, we induced an emission peak of photoluminescence at the tip of the inverted hexagonal pyramids, which had a strong blue shift of 244 meV measured at 100 K.

Using the network etch rate function model, the anisotropic etch rate of p-type single crystal silicon was characterised in terms of microscopic properties including step velocity, step and terrace roughening. The anisotropic etch rate data needed have been obtained using a combination of 2 wagon wheel patterns on different substrate and 1 offset trench pattern. Using this procedure the influence of an applied potential has been investigated in terms of microscopic properties. Model parameter trends show a good correlation with chemical/electrochemical reaction mechanism and mono- and dihydride terminated steps reactivity difference. Results also indicate a minimum in (111) terrace roughening which results in a peak in anisotropic ratio at the non-OCP applied potential of -1250 mV vs OCP.

The Miller-indices determination of the arising surfaces at the Si(0 0 1) convex corner due to anisotropic etching is investigated. We propose a 2D zoning model in which the undercut planes arising at a masked convex corner are presumed to be in the same zone as the sidewalls forming the convex corner, which is characterized by the parallelism of the intersection lines of each pair of new surfaces and the sidewalls. Based on this model a method combining the experimental data, analytical geometry and stereographic projection is presented to systematically determine the Miller indices of the arising planes. The quantitative prediction of undercut planes is confirmed by the angle measurement using a surface profiler.

We developed a new fabrication process for pen-shaped microneedle structures by using non-photolithographic pattern transfer. The process is a combination of anisotropic wet etching and a dicing technology that uses a saw. The process has an advantage, in which the needle diameter is easily changed by altering the groove profile formed in the dicing-saw process. We fabricated pen-shaped needle structures in a dense array for medical applications. The needle height was larger than 200 µm, and the pitch distance was about 200 µm in the experiments. The width of the needle ranged from 10 to 30 µm. The radius at the needle tip was less than 100 nm.

We have performed an investigation to study the nature of surface roughness on {100} and {311} planes obtained by wet anisotropic etching of {100} silicon in 5% tetramethyl ammoniumhydroxide (TMAH) etchant. The surface roughness, which is in most cases a consequence of hillock formation at low concentrations of TMAH, was studied as a function of etch temperature, re-etch time, stirring conditions and the addition of small amounts of ammonium peroxodisulfate (AP). A short re-etching step performed in 25% TMAH or 5% TMAH+AP was found to decrease the total roughness obtained after the prolonged etching in 5% TMAH. We have found that smooth {311} planes without hillocks can be obtained by etching in 5% TMAH with the addition of only 0.25% of AP. Due to the decomposition of AP in the etching process as determined by increased surface roughness, a replenishing of the additive is proposed. Experimental results have shown an increased surface roughness and reduced etch rates of the {100} and {311} planes by increasing the agitation of the 5% TMAH etch solution.

In this paper the mechanism of silicon convex corner (CC) undercutting at etch masks in pure aqueous KOH solutions is explained in a new way by the proposed `step flow model of 3D structuring'. The basic idea is to apply the general atomic explanation of the Si{111} anisotropic etching as a `peeling' process of {111} planes at 110 oriented steps with kink site atoms in order to understand the arising shape in Si{100} etching. By means of this proposed model, we are able to explain and to calculate the microscopic 3D shape of the characteristic CC undercutting in the case without compensation etch mask structures. The stepped morphology of the arising surfaces at a CC were shown by SEM and the quantitative predictions of the model were experimentally confirmed.

The objective of the present study is to investigate the influence of the etchmask properties on anisotropic etching of silicon in a KOH/O solution. The mechanical stress induced in the silicon substrate by an LPCVD- etchmask has been analysed by 3D finite element analysis. It is shown that the rise of the mechanical stress at the edges of etchmask openings is mainly affected by the thickness of the LPCVD- etchmask. The effect of the mechanical stress on the anisotropy ratio was experimentally determined. It has been found that the anisotropy ratio decreases with increasing LPCVD- etchmask thickness. Furthermore the use of /LPCVD- double-layer etchmasks resulted in rough side wall surfaces and a lower anisotropy ratio.

The anisotropic etching behaviour of monocrystalline quartz is studied both experimentally and with computer simulations. The etch rate minima were identified as the crystal planes m, r, r(2), s an ...

A design tool for fast and precise determination of the crystallographic orientation in (001) and (011) silicon wafers using anisotropic wet etching is introduced. The design takes advantage of the symmetric under-etching behaviour around, but not at (!), the -directions. The pattern needs to be etched only for a short time, and after a very quick optical inspection it can be used for aligning subsequent masks, using the same masking layer, more or less automatically. Two effects were investigated in a number of common anisotropic etchants: KOH, KOH with isopropyl alcohol (KOH/IPA), ethylenediamine based solutions (EDP), and tetramethyl ammonium hydroxide (TMAH). The precision of the method was found in most cases to be better than .

Etch hillocks are defects created during anisotropic etching of (100) silicon. From direct measurements of defect micrographs, we have determined the structure of etch hillocks to be pyramids bounded by (567) planes. The defects planes are different from those which are observed to emerge as anisotropic etch facets, such as (111), (211), (212), (133) and (411). We also describe the process by which defects are annihilated in high-concentration etchant. The relative stability of various defect edges is in agreement with calculations of the degree of backbonding of Si atoms along hillock edges. Our results suggest that the mechanisms responsible for hillock formation are distinct from those causing faceting during undercutting of convex corner masks.

Anisotropic etching of a (110) oriented silicon wafer has been used to realize a differential capacitive force sensor. This design is based on a simple concept allowing force to be measured in the plane of the sensor, giving a new and original product in the field of small force measurements. These sensors can be adjusted to measure force in the range 0.01 N to 10 N or, in a low rigidity version, to act as a high precision displacement sensor with an expected resolution of 20 nm. These sensors are planed to be used with a commercial capacitance measurement chip (nominal capacitance: 1 pF, resolution: 1 fF).

The etch rate in monocrystalline quartz depends on the crystalline orientation. Etch-rate diagrams for micromachining of monocrystalline quartz in, for instance, hydrofluoride-based etchants, are a necessity if one requires the best manufacturing conditions for an etched structure. In this paper we use the development of side-wall profiles in etched grooves, on a Z-cut quartz wafer, to produce two-dimensional etch diagrams. The etch conditions are eight combinations of temperature, from 22 degrees C to 80 degrees C, and etchant mixtures of HF and NH4F diluted in water.

We demonstrate how the knowledge of physical sensor effects and integrated circuit (IC) technologies are brought together in microsensor research. We summarize recent microsensor prototypes manufactured by industrial IC processes combined with sensor-specific post-processing steps such as anisotropic etching. Selected examples include IC thermopiles and related gas flow, vacuum, electrical power, and infrared sensors. We also report acoustic microresonators for proximity sensors and diagnostic microstructures for measuring process-dependent material properties.

Large arrays of parallel metallic nanowires ranging from 20 - 120 nm in width are fabricated using a general and relatively simple technique. Holographic laser interference exposure of photoresist and anisotropic etching are used to pattern the surface of InP(001) substrates into V-shaped grooves of 200 nm period. Subsequently metal is evaporated at an angle onto the V-grooved substrates, naturally resulting in thousands of ultra-narrow metallic wires in parallel. Resistance measurements proof that as-prepared wires are electrically continuous.

As part of an integrated module in an optical instrument, optical attenuating elements are required. Such elements have been made by anisotropic etching of (110) silicon wafers. The thicknesses of these elements (Si-laminas) are 5 mu m (+or-1 mu m) or 20 mu m (+or-2 mu m). The measured attenuations-corresponding well with calculations-are 4.5 dB or 7.8 dB respectively.

We search for optimum growth conditions to realize flat BiTe layers on InP(111)B by hot wall epitaxy. The substrate provides a relatively small lattice mismatch, and so (0001)-oriented layers grow semicoherently. The temperature window for the growth is found to be narrow due to the nonzero lattice mismatch and rapid re-evaporation of BiTe. The crystalline qualities evaluated by means of x-ray diffraction reveal deteriorations when the substrate temperature deviates from the optimum not only to low temperatures but also to high temperatures. For high substrate temperatures, the Bi composition increases as Te is partially lost by sublimation. We show, in addition, that the exposure of the BiTe flux at even higher temperatures results in anisotropic etching of the substrates due, presumably, to the Bi substitution by the In atoms from the substrates. By growing BiTe layers on InP(001), we demonstrate that the bond anisotropy on the substrate surface gives rise to a reduction in the in-plane epitaxial alignment symmetry.

The use of atomistic methods, such as the continuous cellular automaton (CCA), is currently regarded as an accurate and efficient approach for the simulation of anisotropic etching in the development of micro-electro-mechanical systems (MEMS). However, whenever the targeted etching condition is modified (e.g. by changing the substrate material, etchant type, concentration and/or temperature) this approach requires performing a time-consuming recalibration of the full set of internal atomistic rates defined within the method. Based on the level set (LS) approach as an alternative and using the experimental data directly as input, we present a fully operational simulator that exhibits similar accuracy to the latest CCA models. The proposed simulator is tested by describing a wide range of silicon and quartz MEMS structures obtained in different etchants through complex processes, including double-sided etching as well as different mask patterns during different etching steps and/or simultaneous masking materials on different regions of the substrate. The results demonstrate that the LS method is able to simulate anisotropic etching for complex MEMS processes with similar computational times and accuracy as the atomistic models. © 2013 IOP Publishing Ltd., This work has been supported by the Spanish FPI-MICINN BES-2011-045940 grant and the Ramón y Cajal Fellowship Program by the Spanish Ministry of Science and Innovation. Also, we acknowledge support by the JAE-Doc grant from the Junta para la Ampliación de Estudios program co-funded by FSE and the Professor Partnership Program by NVIDIA Corporation.

Flat and smooth 45° micromirrors were successfully fabricated on a 4-in. silicon wafer by means of wet anisotropic etching at the industrially practical temperature of 80 °C using tetramethylammonium hydroxide (TMAH) solution with added NCW-1002, a nonionic surfactant with little environmental load. The effects of the TMAH concentration and the amount of NCW-1002 added were extensively investigated, and it was found that a high TMAH concentration (25 wt %) and a very low amount of NCW-1002, approximately 10 vol ppm, are the optimum conditions to fabricate optically smooth and geometrically flat micromirrors. The mechanism underlying the effects of the concentration of the surfactant is discussed in relation to the clouding point of the surfactant-added TMAH solution.

In this paper, we present an innovative sub-wavelength patterning method for fabricating high-compact nanowires, which adopts nanometer steps as sacrificial structures in spacer technology. The nanometer steps, with adjustable stair widths and heights, are produced by alternating processes of photoresist ashing and anisotropic etching. Nanometer sidewalls are then formed with the function of the steps as sacrificial structures in spacer technology. Subsequently, the nanometer sidewalls are transferred to the substrates to generate high-compact nanowires. A diversity of parallel nanowires of different shapes produced by this method have widths of 85–155 nm and spacings ranging from 150 nm to 440 nm. Also, the uniformity of the nanowires can be controlled in this method.

Low-dimensional Si structures, including Si nanobelts and Si micropyramids, were formed on the surface of n-type silicon by microindentation and anisotropic etching in 30 wt% KOH solution at a temperature of 50 °C. The indentation was performed to create local plastic deformation and residual stresses. The residual stresses caused the formation of the Si nanobelts around the sites of indents on the surface of Si (1 1 1) and the Si micropyramids at the sites of indents on the surface of Si (1 0 0). The formation of the Si micropyramids was due to the local ‘mask’ created by the indentation and the residual stress around the indents. The residual hydrostatic stress at the tensile state increased the local etching rate, which resulted in a surface depression around the indents. The combination of indentation and wet etching process provides a maskless process to potentially produce low-dimensional Si structures in KOH solution at low temperatures.

Detailed characteristics of three classical rectangular convex corner compensation structures on (100) silicon substrates have been investigated, and their common design steps are summarized. By combining the basic method of a silicon wet anisotropic etching process, a general method of generating compensation structures for a rectangular convex corner is put forward. This calls for the following two steps: define the topological field and fit some borderlines together into practical compensation patterns. The rules, which must be obeyed during this process, are summarized. By introducing this method, some novel compensation patterns for rectangular convex corner structures are created on both (100) and (110) substrates, and finally simulation results are given to prove this new method's validity and applicability.

A new approach for the simulation of wet anisotropic etching, using a geometric method is described. The influence of the whole exposed surface on the etched shape of the device is taken into account by consideration of the free surface energy at the etch front. This enables the unequivocal simulation of the etch fronts even in sophisticated cases. A criterion for the stability of a given structure exposed to etch solutions can also be derived.

One-step growth of lateral p-n junctions on GaAs patterned substrates is investigated to demonstrate the possibility of obtaining a current confinement structure by utilizing the amphotericity of Si. Rectangular patterns of the (001) plane encircled by four {110} sidewalls were etched on the substrates by means of anisotropic etching of an NH4OH+H2O2+H2O solution with high H2O content. Si-doped GaAs layers are grown on thus-prepared patterned substrates by molecular beam epitaxy. A cathodoluminescence study shows the layers grown on the {110} sidewalls are p-type, whereas they are n-type on the (001) surface. The potential of the lateral p-n junctions for forming a current confinement structure for surface light emitting devices is discussed.

The radical generation mechanisms and the effect of radical composition in a SiCl4 discharge on the directionality of aluminum etching are discussed using the results of optical emission spectra and plasma density measurements. It was found that the chlorine radical concentration is almost proportional to gas pressure and plasma density, while the silicon radical density is almost proportional to the square of the plasma density, but is weakly dependent on the gas pressure. At lower pressure or a higher power density, where the ratio of silicon radical concentration to chlorine radical concentration increases, lateral side etching is inhibited by the silicon deposition, and anisotropic etching can be achieved. From these experiments, it is concluded that a control of gas dissociation is needed for a more precise control of the anisotropic etching.