Showing papers on "Isotropic etching published in 1998"

Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration

Abstract: We have evaluated the orientation dependence in chemical anisotropic etching of single-crystal silicon. Etch rates for a number of crystallographic orientations have been measured for a wide range of etching conditions, including KOH concentrations of 30 to 50% and temperatures of 40 to 90 °C. Though the etchants all consist of the same components KOH and water, the orientation dependence varies considerably with change in etchant temperature and concentration. The resulting etch-rate database allows numerical prediction of etch profiles of silicon, necessary for the process design of microstructures. Changing the KOH concentration yields different etch profiles both analytically and experimentally.

Direct measurement of strain effects on magnetic and electrical properties of epitaxial SrRuO3 thin films

Abstract: By lifting an epitaxial thin film off its growth substrate, we directly and quantitatively demonstrate how elastic strain can alter the magnetic and electrical properties of single-domain epitaxial SrRuO3 thin films (1000 A thick) on vicinal (001) SrTiO3 substrates. Free-standing films were then obtained by selective chemical etching of the SrTiO3. X-ray diffraction analysis shows that the free-standing films are strain free, whereas the original as-grown films on SrTiO3 substrates are strained due to the lattice mismatch at the growth interface. Relaxation of the lattice strain resulted in a 10 K increase in the Curie temperature to 160 K, and a 20% increase in the saturation magnetic moment to 1.45 μB/Ru atom. Both values for the free-standing films are the same as that of the bulk single crystals. Our results provide direct evidence of the crucial role of the strain effect in determining the properties of the technologically important perovskite epitaxial thin films.

Self-cleaning etch process

Abstract: A process for etching a substrate 25 in an etching chamber 30, and simultaneously cleaning a thin, non-homogeneous, etch residue deposited on the surfaces of the walls 45 and components of the etching chamber 30. In the etching step, process gas comprising etchant gas is used to etch a substrate 25 in the etching chamber 30 thereby depositing etch residue inside the chamber 30. Cleaning gas is added to the process gas for a sufficient time and in a volumetric flow ratio that is sufficiently high, to react with and remove substantially all the etch residue deposited by the process gas. The present method advantageously cleans the etch residue in the chamber 30, during the etching process, and without use of separate cleaning, conditioning, and seasoning process steps.

Crystallographic wet chemical etching of gan

Abstract: We demonstrate well-controlled crystallographic etching of wurtzite GaN grown on c-plane sapphire using H3PO4, molten KOH, KOH dissolved in ethylene glycol, and NaOH dissolved in ethylene glycol between 90 and 180 °C, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {1010}, {101 1}, {101 2}, and {1013}. The vertical {1010} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope. The activation energy is 21 kcal/mol, indicative of reaction-rate limited etching.

Preparation of atomically flat surfaces on silicon carbide using hydrogen etching

Abstract: Hydrogen etching of 6H- and 4H-SiC(0001) surfaces is studied. The aspolished substrates contain a large number of scratches arising from the polishing process which are eliminated by hydrogen etching. Etching is carried out in a flow of hydrogen gas at atmospheric pressure and temperatures around 1600-1700 C attained on a tantalum strip heater. Post-etching atomic force microscopy (AFM) images show periodic arrays of atomically flat terraces that are a few thousand A wide. These terraces are separated by steps 15 A high in the directions. Often, the surface is seen to be faceted with steps on neighbouring facets forming 60 angles and offset in the c-direction by half a unit cell. Images of incompletely etched surfaces show early stages of etching where one can see remnants of surface damage in the form of arrays of hexagonal pits. On the larger scale, the surface has a hill-and-valley type morphology. The observed features are interpreted in a model based on the symmetry of the SiC unit cell and crystal miscut.

Polarity determination for GaN films grown on (0001) sapphire and high-pressure-grown GaN single crystals

Abstract: In order to resolve any doubt in lattice polarity calibrations, a given undoped GaN layer deposited on (0001) sapphire by metalorganic chemical vapor deposition and a given high-pressure-grown GaN single crystal have been studied by three different techniques: Hemispherically scanned x-ray photoelectron diffraction, convergent beam electron diffraction, and chemical etching. We conclude that Ga-polar surfaces are resistant to a 200 °C molten NaOH+KOH etching whereas N-polar surfaces are chemically active. All the observed flat GaN films grown on (0001) sapphire have Ga polarity. On the contrary, the native flat faces of undoped GaN bulk crystals have N polarity.

Photovoltaic element and method for manufacture thereof

Abstract: A photovoltaic element which directly converts an optical energy such as solar light into an electric energy. After many uneven sections are formed on the surface of an n-type crystalline silicon substrate (1), the surface of the substrate (1) is isotropically etched. Then the bottoms (b) of the recessed sections are rounded and a p-type amorphous silicon layer (3) is formed on the surface of the substrate (1) through an intrinsic amorphous silicon layer (2). The shape of the surface of the substrate (1) after isotropic etching is such that the bottoms of the recessed sections are slightly rounded and therefore the amorphous silicon layer can be deposited in a uniform thickness.

Track size and track structure in polymer irradiated by heavy ions

Abstract: The structure of latent tracks in polyethylene terephthalate (PET) was studied using chemical etching combined with a conductometric technique. Polymer samples were irradiated with Ar, Kr, Xe, Au, and U ions with energies in the range of 1 to 11.6 MeV/u. The etching kinetics of the tracks was investigated in the radii range 0–100 nm. The highly damaged track core manifests itself on the etching curves as a zone where the etch rate changes dramatically and reaches its minimum at a radius of a few nm. It was found that the track core radius is approximately proportional to (dE/dx)0.55. The track core is surrounded by a halo. In the track halo the etching proceeds at a rate that slowly increases approaching a constant value. Cross linking of macromolecules causes reduction of the etch rate in the halo which extends up to distances exceeding 100 nm in the case of the heaviest ions. Measurable change of the etch rate at such large radii could not be predicted from the shape of the calculated spatial distributions of energy dissipated in tracks. Obviously, formation of the extended track halo is influenced by the diffusion of active intermediates from the track core to the polymer bulk.

Deep ultraviolet enhanced wet chemical etching of gallium nitride

Abstract: We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally doped n-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid (H3PO4) and potassium hydroxide (KOH) solutions of pH values ranging from −1 to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in dilute H3PO4 and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN.

Characterization of AlGaInN diode lasers with mirrors from chemically assisted ion beam etching

Abstract: Current-injection InGaAlN heterostructure laser diodes grown by metalorganic chemical vapor deposition on sapphire substrates are demonstrated with mirrors fabricated by chemically assisted ion beam etching. Due to the independent control of physical and chemical etching, smooth vertical sidewalls with a root-mean-squared roughness of 4–6 nm have been achieved. The diodes lased under pulsed current-injection conditions at wavelengths in the range from 419 to 423 nm. The lowest threshold current density was 25 kA/cm2. Lasing was observed in both gain-guided and ridge-waveguide test diodes, with cavity lengths from 300 to 1000 μm; and output powers of 10–20 mW were achieved. Laser performance is illustrated with light output-current and current–voltage characteristics and with a high-resolution optical spectrum.

Effects of surface treatment on the surface chemistry of NiTi alloy for biomedical applications

Abstract: Alloys of NiTi have gained popularity in biomedical applications; however, Ni is known to cause toxic and allergic reactions in the body, and concerns have been expressed regarding the material's biocompatibility. In this study, coupons of equiatomic NiTi were prepared by four methods, namely, mechanically polishing to a mirror finish, electropolishing, chemical etching and argon plasma etching, to produce various levels of roughness, and then examined by atomic force microscopy (AFM), XPS and AES. The resulting surface chemistry depended upon the method of preparation and was found not to be a function of surface roughness. The mechanically polished samples, although having the smoothest surface, showed the highest level of Ni in the near-surface region. The other preparation methods produced surfaces that were predominantly TiO2, with the electropolished surfaces showing the next smoothest surface and the least Ni in the near-surface region. The correlation between method of preparation, surface roughness and surface chemistry may be important in the preparation of NiTi for biomedical applications. © 1998 John Wiley & Sons, Ltd.

Sidewall surface chemistry in directional etching processes

Abstract: A prerequisite of successful microstructure fabrication in electronic materials using plasma-based etching methods is the ability to maximize the ratio of ion-enhanced etching reactions relative to spontaneous etching reactions. To produce vertical etching profiles, the rate of the etching reaction in line-of-sight of the plasma has to be large, whereas the lateral etching rate should vanish. We present a review of the approaches that have been used for silicon, aluminum, SiO2 and polymeric materials to suppress etching reactions at microstructure sidewalls. These approaches include the judicious choice of the primary etching gas, adding certain gases to the main etching gas, lowering the substrate temperature, mask material redeposition, or alternate etch and deposition cycles. Our knowledge of the sidewall chemistry resulting from these approaches, e.g. the production of sidewall passivation layers, and experimental methods that have been employed to study these, are reviewed. The impact of sidewall chemistry on the etching profiles of the final microstructure is also discussed.

Dry etching method, chemical vapor deposition method, and apparatus for processing semiconductor substrate

Abstract: In performing plasma etching or plasma CVD, a gas containing an interhalogen compound gas or a XeF2 gas is used as a process gas Such a process gas generates, in the state of non-plasma and with activation energy lower than a specified level, a volatile material from a deposition species generated in the above etching so as to contribute to the suppression of film formation For example, the XeF2 gas, a BrF3 gas, a BrCl gas are used in the cases of etching a silicon dioxide film, a silicide film, and a polysilicon film, respectively On the surface of a substrate is formed a non-volatile protective film so as to improve the profiles of an opening At the wall surface of a reaction chamber which is barely influenced by the plasma, the deposition species is turned into a volatile material (eg, SiF4) so as to suppress the deposition of reaction products thereon If the interhalogen compound gas, XeF2 gas, or the like is added to a main gas for performing CVD, the same effects can be achieved

Chemical etching of molybdenum trioxide : a new tailor-made synthesis of moo3 catalysts

Abstract: Crystalline catalysts of orthorhombic MoO3 have been prepared via a vapor phase deposition method, and their crystallographic structure has been affirmed by XRD and FTIR investigations. A chemical etching method has been developed for restructuring these thermally processed catalysts. Using a 0.1 M NaOH etchant, {001} and {100} plane areas of the catalysts can be significantly increased while surface steps, ledges, and terraces are created. Moreover, alternate crystal plane combinations of either {100} and {010} or the {001} and {010} are observed on crystal edges and rectangular etch pits in the basal planes {010}. Both materials chemistry of MoO3 and etching mechanisms have been studied on the basis of the surface morphological evolution of etching patterns of the catalysts. Technological merits and the processing parameters of this new method have also been identified. Following the findings of the current work, it is believed that the chemically carved surface structures may be crucial for certain MoO...

Chemical etching of ion tracks in LiF crystals

Abstract: In LiF, the formation of defects upon electronic excitations was studied using various heavy ions with energies up to 11.4 MeV/u. The induced damage was revealed by the technique of selective chemical etching. Track etching was successful only in those cases where the linear energy transfer of the ions had surpassed a critical threshold of about 1 keV/A. Annealing tests after ion irradiation show that track etching is possible up to a temperature of 450 °C, i.e., the thermal stability of the etchable damage in ion tracks is much higher than simple defects such as color centers. It is concluded that the etchability of tracks in LiF is strongly related to the creation of defect aggregates.

HF/H2O vapor etching of SiO2 sacrificial layer for large-area surface-micromachined membranes

Abstract: An HF/H 2 O vapor etching technique has been applied as a sacrificial oxide etching process step in surface-micromachining technology. This technique does not suffer from the notorious problem known as stiction, i.e., permanent attachment of movable structures to the underlying substrate during drying after a conventional wet etch process is used. Vapor condensation has been controlled by adjusting the temperature difference between the substrate and the HF/H 2 O liquid source of vapor. Optical modulator devices have been fabricated to demonstrate the large possibilities of the vapor etching technique. Movable polysilicon membranes with a surface area of 10 mm 2 and a thickness of 0.73 μm over a 1.65 μm air gap have been routinely obtained with a 100% yield.

Radiation defects in lithium fluoride induced by heavy ions

Abstract: Single crystals of lithium fluoride were irradiated with various species of heavy ions in the energy regime between 1 and 30 MeV/u. The induced radiation damage was studied with techniques such as optical absorption spectroscopy, small-angle X-ray scattering, chemical etching and profilometry, complemented by annealing experiments. Clear evidence is given for a complex track structure and defect morphology. Single defects such as F-centers are produced in a large halo of several tens of nanometers around the ion trajectory. The defect creation in this zone is similar to that under conventional radiation. For heavy ions above a critical energy loss of 10 keV/nm, new effects occur within a very small core region of 2–4 nm in diameter. The damage in this zone is responsible for chemical etching and for a characteristic anisotropic X-ray scattering. It is assumed that in this core, complex defect aggregates (e.g., cluster of color centers, molecular anions and vacancies) are created. Their formation is only slightly influenced by the irradiation temperature and takes place even at 15 K where diffusion processes of primary defects are frozen. Furthermore, irradiation with heavy ions leads to pronounced swelling effects which can be related to an intermediate zone of around 10 nm around the ion path.

Silicon field emitter cathodes: Fabrication, performance, and applications

Abstract: This article gives an overview of fabrication and performance of a class of vacuum microelectronic devices, namely, silicon tip-on-post field emitter arrays (FEAs). Experimental data illustrating the device performance are presented in the context of requirements for field emission flat panel display and microwave power amplifier applications. Critical geometrical parameters of the device are discussed, and a fabrication process flow designed to optimize these parameters is described. Equipment and methods for testing electrical performance of the FEAs and results thus generated are presented. Specifically, emission current versus gate voltage characteristics for arrays with tips formed using anisotropic (crystallographic–orientation–dependent) or isotropic etching techniques, uniformity of these characteristics across a 4 in. diameter substrate, stability of emission current in ultrahigh vacuum conditions, and changes in emission current upon exposure to active gases at varying pressure are discussed.

Microfabricated silicon gas chromatographic microchannels: fabrication and performance

Abstract: Using both wet and plasma etching, we have fabricated micro-channels in silicon substrates suitable for use as gas chromatography (GC) columns. Micro-channel dimensions range from 10 to 80 {micro}m wide, 200 to 400 {micro}m deep, and 10 cm to 100 cm long. Micro-channels 100 cm long take up as little as 1 cm{sup 2} on the substrate when fabricated with a high aspect ratio silicon etch (HARSE) process. Channels are sealed by anodically bonding Pyrex lids to the Si substrates. We have studied micro-channel flow characteristics to establish model parameters for system optimization. We have also coated these micro-channels with stationary phases and demonstrated GC separations. We believe separation performance can be improved by increasing stationary phase coating uniformity through micro-channel surface treatment prior to stationary phase deposition. To this end, we have developed microfabrication techniques to etch through silicon wafers using the HARSE process. Etching completely through the Si substrate facilitates the treatment and characterization of the micro- channel sidewalls, which domminate the GC physico-chemical interaction. With this approach, we separately treat the Pyrex lid surfaces that form the top and bottom surfaces of the GC flow channel.

Etching an oxidized organo-silane film

Abstract: A process for etching an oxidized organo-silane film exhibiting a low dielectric constant and having a most preferred atomic composition of 52% hydrogen, 8% carbon, 19% silicon, and 21% oxygen. The process of etching deep holes in the organo-silane film while stopping on a nitride or other non-oxide layer is preferably performed in an inductively coupled high-density plasma reactor with a main etching gas mixture of a fluorocarbon, such as C 4 F 8 , and argon while the pedestal electrode supporting the wafer is RF biased. For very deep and narrow holes, oxygen or nitrogen may be added to volatize carbon. In an integrated process in which an oxygen plasma is used either for the film etching or for post-etch treatments such as ashing or nitride removal, the oxygen plasma should be excited only when no RF bias is applied to the pedestal electrode, and thereafter the sample should be annealed in an inert environment to recover the low dielectric constant.

Anisotropic, fluorine-based plasma etching method for silicon

Abstract: A method for anisotropic plasma etching of laterally defined patterns in a silicon substrate is described. Protective layers made of at least one silicon compound with a second reaction partner that is entirely compatible with the chemistry of the etching process are deposited before and/or during plasma etching onto the sidewalls of the laterally defined patterns.

Bulk micromachining characterization of 0.2 μm HEMT MMIC technology for GaAs MEMS design

Abstract: Front-side bulk micromachining based on 0.2 μm GaAs HEMT MMIC technology is presented. Several chemical solutions have been used to perform the etching procedure characterization in respect to the obtained vertical profiles. It has been verified that citric acid solution is the most appropriate selective etchant to build suspended GaAs/AlGaAs mesa-shaped structures, while both H 3 PO 4 and NH 4 OH based anisotropic systems seem to be the most suitable for the free-standing triangular prism-shaped structures. Moreover, all these three solutions could be applied to suspend only metal and intermetallic materials. Etch rates as well as cross-section profiles were obtained. Furthermore, the compatibility of the etching procedure with the integrated electronics and the pad metallization has been successfully tested. The features and applications linked to the obtained structures are also discussed.

Epidermal abrasion device with isotropically etched tips, and method of fabricating such a device

Abstract: A probe includes an elongated body with a top surface, a bottom surface, a first side wall between the top surface and the bottom surface, and a second side wall between the top surface and the bottom surface. An end is defined by the bottom surface converging into a tip, an isotropically etched portion of the first side wall converging into the tip, and an isotropically etched portion of the second side wall converging into the tip. The elongated body is less than approximately 700 μm wide and less than approximately 200 μm thick. The elongated body may incorporate a fluid channel. The elongated body may be formed of silicon that is not doped with Boron. In such a configuration, integrated circuitry or a micromachined device, such as a heater or pump may also be formed on the device. A number of novel processing techniques are associate with the fabrication of the device. The device may be formed by relying solely on isotropic etching. Alternately, a combination of isotropic and anisotropic etching may be used. Unlike prior art micromachined devices, the disclosed device may be processed at relatively low temperatures below 1100° C. and without using the carcinogen ethylenediamin pyrocatechol.

Anisotropic etching properties of silicon in KOH and TMAH solutions

Abstract: We investigated anisotropic etching properties of single-crystal silicon as a function of crystallographic orientations in order to fabricate a variety of 3D microstructures on silicon substrates. We measured etching rates for a number of crystallographic orientations using hemispherical specimens. From the dimensional change of the specimen surface, we evaluated the etching rates for a number of crystallographic orientations. We carried out a series of experiments in KOH and TMAH solutions changing their concentration and temperature and compared anisotropic etching properties between KOH and TMAH solutions. The orientation dependencies of their etching rates differed, especially for near [111] orientations. This means that these two etchants have different etching mechanisms. Effects of etchant circulation on the etching rates were not negligible in TMAH in contrast to KOH.