Liquid Etching Research Articles

Tantalum oxide thin films as protective coatings for sensors

Reactively sputtered tantalum oxide thin films have been investigated as protective coatings for aggressive media exposed sensors. Tantalum oxide is shown to be chemically very robust. The etch rate in aqueous potassium hydroxide with pH 11 at 140 is lower than 0.008 Å . Etching in liquids with pH values in the range from pH 2 to 11 have generally given etch rates below 0.04 Å . On the other hand patterning is possible in hydrofluoric acid. Further, the passivation behaviour of amorphous tantalum oxide and polycrystalline is different in buffered hydrofluoric acid. By ex situ annealing in the residual thin-film stress can be altered from compressive to tensile and annealing at 450 for 30 minutes gives a stress-free film. The step coverage of the sputter deposited amorphous tantalum oxide is reasonable, but metallization lines are hard to cover. Sputtered tantalum oxide exhibits high dielectric strength and the pinhole density for 0.5 m thick films is below 3 .

Iatrogenic Mucosal Burn : A Case Report

A case of mucosal burn during the placement of fissure sealant on the first permanent molars of a 9-year-old Malay boy is presented. The erythematous lesion with accompanying burning sensation appeared a few minutes after the etching liquid, containing 37% by weight phosphoric acid, had accidentally come into contact with the buccal mucosa on the right side of the angle of the mouth. The mucosa showed complete healing after one week. The use of rubber dam for tooth isolation while doing fissure sealant is essential to avoid accidental contact of potentially caustic chemicals, such as the phosphoric acid etchant, with the oral mucosa as it can result in mucosal burns.

Symmetrical Field-Matching Waveguide for Low-loss Fiber-chip Butt Coupling

The problem of low-loss coupling of single-mode fibers to waveguides on an optoelectronic integrated chip based on III-V semiconductor materials is of critical importance for the practical application of integrated photonics in future communication systems. We report on a new fiber-matched InP waveguide fabricated with liquid phase epitaxy (LPE) and wet chemical etching (WET), which serves as an input waveguide to an integrated spot size transformer. First results as high as 85 % for the overlap efficiency to the fiber fundamental mode have been obtained, which are among the best results published in the literature [1-4] for taper concepts.

Using liquid chemical etching to manufacture technological structures of minimum size

We consider the effect of the electric field on the pulling of an etching liquid through holes in a thin insulating protective mask and the possibility of achieving high-resolution liquid etching for manufacturing LSI components of minimum size.

Structural properties of BN thin films obtained by plasma‐enhanced chemical vapour deposition

AbstractIn this work BN films have been deposited by the plasma‐enhanced chemical vapour deposition (PECVD) technique on p‐type (100) silicon substrates, using borazine and nitrogen as precursors. X‐ray photoelectron spectroscopy, infrared spectroscopy, x‐ray diffraction, nuclear reaction analysis and Rutherford backscattering spectroscopy were used to analyse the films. The results of quantitative XPS analysis indicate the formation of a thin surface layer (∼3 nm) of boron oxynitride, BNO0.3, over a bulk of nearly stoichiometric boron nitride, BN1.1. The presence of the hexagonal phase mixed with amorphous boron nitride was identified. Infrared and Rutherford backscattering spectroscopies combined with a liquid etching technique were used to determine the composition and structure across the film thickness. From these measurements we infer that the composition across the film is nearly constant but with a gradual transition from an amorphous structure close to the Si/BN1.1 interface to an hexagonal structure towards the outer layers. Thermal treatments of the boron nitride films up to a temperature of ∼1000°C in a nitrogen atmosphere resulted in a small decrease of both the B/N atomic concentration ratio and the refractive index of the film. The insulating characteristics of the boron nitride for application as an intermetal dielectric were also treated. The electrical conduction results can be interpreted in terms of a Schottky mechanism, which allows us to calculate the high‐frequency dielectric constant, εr = 3.2.

Fabrication of Si nanostructures with an atomic force microscope

A method for fabricating Si nanostructures with an air-operated atomic force microscope (AFM) is presented. An electrically conducting AFM tip is used to oxidize regions of size 10–30 nm of a H-passivated Si (100) surface at write speeds up to 1 mm/s. This oxide serves as an effective mask for pattern transfer into the substrate by selective liquid etching. The initial oxide growth rate depends exponentially on the applied voltage which produces an effective ‘‘tip sharpening’’ that allows small features to be produced by a relatively large diameter tip.

Fabrication of nanometer-scale conducting silicon wires with a scanning tunneling microscope

We report the fabrication of nanometer-scale conducting silicon wires by the STM-induced modification of a passivated silicon (100) surface followed by a selective liquid etch. The modified surface layer is a thin oxide a few monolayers thick which acts as a mask against subsequent liquid etching of the unmodified regions of the silicon surface. Silicon wires as narrow as 30 nm have been fabricated with this technique. More complicated patterns can be written by selectively pulsing the STM bias to a suitable writing voltage pixel-by-pixel during a low-bias (hence non-exposing) scan. The maximum pattern size is limited by the range of the piezoscanners, which for our system is in excess of 100 μm. Conducting silicon wires between contact pads were fabricated on a silicon layer on top of a buried insulating layer of SiO 2 formed by oxygen implantation and subsequent anneal (SIMOX). Backgating of these structures can drive them either into accumulation or inversion, thus allowing independent control of their conductance and carrier type. The techniques described here allow the simple, easy, and reliable fabrication of nanometer-scale devices using relatively inexpensive and widely available equipment.

Chemistry of silicon surfaces after wet chemical preparation: A thermodesorption spectroscopy study

Ultraclean wet chemical preparation in air and a fast new load-locking technique opens up a way to characterize real Si(111) surfaces after processing for microelectronic device fabrication with the proven surface-analytical tools available in an ultrahigh vacuum. For the first time thermodesorption spectroscopy can be utilized, without interference from typical artefacts like contamination introduced by the ex situ preparation, to investigate the chemical termination and molecular composition of silicon surfaces after initial wet chemical key processes in semiconductor technology (chemical and UV/ozone-enhanced cleaning, liquid and gaseous phase etching, rinsing with de-ionized water). By multiplexing a mass spectrometer and analyzing thermally desorbed molecules over a wide range of masses simultaneously, we can separate quantitatively between the major surface-terminating molecules that are inherently responsible for the different chemical surface properties (hydrophilic due to –OH groups after wet chemical or UV/ozone-enhanced oxidation; hydrophobic due to termination with hydrides after etching with hydrofluoric acid/ammonium fluoride, HF/NH4F) and minor species characteristic for details of the preparation process (physisorbed residues upon omission of a final rinsing step; contributions from residual carbon–hydride contamination). Furthermore, distinct desorption channels of hydrogen molecules from mono-, di-, and trihydride surface states allow a characterization of the pH-dependent etching by H2O:HF:NH4F [concentrated HF: selective removal of surface oxides; dilute HF: additional slow isotropic attack of bulk silicon; HF/NH4F: anisotropic attack by fast removal of higher hydride defect sites on Si(111)] and a determination of the resulting microroughness of the silicon surface. Slow regrowth of an ultrathin oxide on HF-treated surfaces during final rinsing with water can be monitored by a separation between H2O desorption at high temperature from surface silanol groups and low-temperature desorption of physisorbed water.

Fabrication of silicon nanostructures with a scanning tunneling microscope

A technique is presented for fabricating Si nanostructures with a scanning tunneling microscope operated in air. The process involves the direct chemical modification of a H-passivated Si(100) surface and a subsequent liquid etch. The chemically modified portions of the surface can withstand a deep (≳100 nm) liquid etch of the unmodified regions with no etch degradation of the modified surface. At a write speed of 1–10 μm/s, large-area (50 μm×50 μm) patterns with lateral feature sizes ∼25 nm are reliably fabricated.

Laser-assisted liquid film etching

Laser-assisted liquid film etching (LALFE) is a new technique for maskless patterning of silicon substrates. This technique involves forming a thin liquid film of etchant on a silicon substrate and focusing a laser beam on the portion to be etched. Results are given for direct-writing, orientation dependent LALFE on (100) and (111)n-Si using films of polyvinyl alcohol (PVA) as a wetting agent for hydrofluoric acid on n-Si.

Observation of Polarization Reversal Process in the Commensurate-Ferroelectric Phase of K2ZnCl4

Nematic liquid crystal technique, etching technique and powder technique have been applied to the study of the polarization reversal process in the commensurate-ferroelectric phase of K 2 ZnCl 4 . A single domain crystal undergoes polarization reversal through the sidewise expansion of domains nucleated at the predetermined locations in the bulk or at the crystal edges. The phase of the primary order parameters differs by π between the switched and unswitched regions, and the whole crystal is finally switched to a single domain. The polarization reversal process in a multidomain crystal is very complicated. The crystal can hardly be changed into a single domain state by the application of a dc field.

The fabrication of suspended microstructures for devices

Free-standing microstructures such as resistors, superconductors and cantilever beams are made on Si substrates using the anisotropic etchant KOH+H2O. Resistant masks of Si3N4 or Nb are patterned by dry etching and then become partially suspended during the liquid etch process. Promising device structures include resistors suspended from each end for low mass sensors, and a long beam which is deflected electrostatically to control the size of, or to close, a gap.

Liquid Photoresist Techniques for Fine Pattern Flexible Printed Circuits

This paper presents a new roll‐to‐roll (R‐R) production system modified for fine line patterning of flexible printed circuits (FPCs) using the subtractive method. The R‐R system is especially suited to production of FPCs because the material used—copper‐clad laminate (CCU—can be handled as it is rolled. Consideration has been given to methods and materials in designing the machines. They are now operating successfully and are used in single‐sided flexible circuit manufacture. A liquid photosensitive etch resist and a collimated light source are recommended for the system and several factors necessary for achieving R‐R working conditions are discussed. Judging from the experimental results of these systems, using narrower width materials with chemical surface preparation is an effective technique for improving the yield rate. The selection of a liquid photoresist is not so common in the case of rigid printed circuit boards because of the difficulty of the coating process. On the other hand, in the case of flexible PCBs, it is successful not only in terms of resolution characteristics but also of productivity under several different types of coating conditions. It should be noted that use of the conventional subtractive method in the printed circuit field is still advantageous as some semiconductor technologies are applicable.

Fabrication of a gated gallium arsenide heterostructure resonant tunneling diode

Techniques used to fabricate a gated resonant tunneling diode (GRTD) are presented. Molecular-beam epitaxy (MBE), image reversal contact photolithography, liftoff metallization, anisotropic reactive ion etching, isotropic liquid etching, and a resulting self-aligned gate metal deposition technique were used to realize this effort. The physical sizes of the fabricated GRTDs were 2, 4, and 6 μm in diameter. The electrical size of the channel within the vertical resonant tunneling diode, however, was controlled by a simple, self-aligned rectifying electrode at the well region. Arrays of devices were fabricated to enhance detection while retaining small geometries. The results from these first devices indicate that an in situ transition from a two-dimensional resonant tunneling diode (RTD) to a zero-dimensional quantum dot is feasible using this design. Improvements in the design are realizable from straightforward modifications in the MBE material.

Retention of three fissure sealant resins. The effects of etching agent and curing method. Results over 3 years

Results are reported of a 3-year blind study comparing three different fissure sealants, using a system of contralateral control teeth. A total of 744 first permanent molars were sealed for 186 children, aged 6-7 years at the start of the study. Resin was applied by a dental therapist and all recall examinations were carried out by the same dentist. Resin was fully retained on 77% of teeth at the end of 3 years. After the same time an unfilled light-cured resin was significantly better retained than a filled light-cured resin. The two light-cured resins in the study were retained better on the right side of the mouth than on the left, but there was no comparable significant difference for retention of the control chemically-cured material. The use of enchant in gel form was as effective as liquid etching.

Reproducibility in tunneling achieved through liquid etching of YBCO

We have developed a procedure for preparation of reproducible tunnel junctions of the S1IS2 type, where S1 is a chemically etched single crystal of YBa2Cu3Ox (YBCO), S2 is a film of Pb, and I is an insulting barrier of unknown nature which is formated at the surface of YBCO at 100°C in air. The structure in the dV/di (V) first appears at T=Tc= 89K and sharpens as T is decreased. There are two gap-like structures in dV/di at ∼4 and ∼19mV, and an additional structure at ∼45mV.

Optical waveguide phase modulator in GaInAsP using depletion edge translation

Under reverse bias a phase shift per unit length of up to 500°/mm is observed in a GaInAsP/InP inverted rib waveguide embedded in a double-heterostructure pin diode. The waveguides were fabricated by wet chemical etching and subsequent liquid phase epitaxy. Diodes were formed by selective Zn diffusion in the InP cladding layer. The planar structure is favourable for integration with other electronic or optoelectronic devices.

Toxic effects of two dental materials on human buccal epithelium in vitro and monkey buccal mucosa in vivo

Confluent cultures of human buccal epithelial cells were exposed to graded dilutions of Gluma Bond or 3M Etching Liquid for 5 min. The cytotoxic effects induced by this treatment were observed (epithelial cell damage, growth inhibition). In vivo, monkey buccal mucosa was exposed to Gluma Bond or 3M Etching Liquid for 5 min. Biopsies were taken after 24 h, and the buccal epithelium processed for light microscopic examination. The toxic reactions to Gluma Bond were far more pronounced compared with the toxic reactions to 3M Etching Liquid in both models. Data obtained suggest that the in vitro model may be useful in assessing mucosal toxicity and in studying mechanisms of toxic action.

The Toxic Effects of Two Dental Materials on Human Buccal Epithelium In Vitro and Monkey Buccal Epithelium In Vivo

The aim of the present study was to compare the toxicity in vitro with the toxicity in vivo of two commercial chemicals marketed for use in the oral cavity (GLUMA BondR and 3M Etching LiquidR). Confluent cultures of human buccal epithelial cells were exposed to graded concentrations of GLUMA Bond or 3M Etching Liquid for 5 minutes. The cytotoxic effects induced by this treatment were observed (cytomorphology, proliferation rate). In vivo, monkey buccal epithelium was exposed to GLUMA Bond or 3M Etching Liquid for 5 minutes. Biopsies were taken after 24 hours, and the buccal epithelium processed for light microscopical examination. In both models, the toxic reactions to GLUMA Bond were far more extensive than those caused by 3M Etching Liquid.

Kinetics of laser-induced liquid metal etching of a-Si films

It ist demonstrated that spatially modulated laser pulse-induced melting of semiconductor/metal films can be used to generate micropatterns in semiconductors. The kinetics of the phase transitions are traced by time-resolved electron microscopy down to specimen areas of 0.5 μm O. In the case of a-Si/Al films crystallization of a-Si, formation of Al-silicides and transport of material by liquid motion are observed. These processes proceeded with velocities of some 10 m/s. Es wird nachgewiesen, das Mikrostrukturen in Halbleitern durch ein ortlich moduliertes laserpuls-induziertes Schmelzen von Halbleiter/Metall-Schichten erzeugt werden konnen. Der Zeitverlauf der beteiligten Phasenumwandlungen wird mit zeitaufgeloster Elektronenmikroscopie bis hinab zu Objektbereichen von 0,5 μm O verfolgt. Bei a-Si/Al Schichten werden Kristallisation von a-Si, Entstehung von Al-siliziden und Materialtransport durch Flussigkeitsbewegung beobachtet. Diese Vorgange verlaufen mit Geschwindigkeiten von einigen 10 m/s.