Wet Chemical Etching Process Research Articles

Room temperature emission in narrow (14 nm) [formula omitted] quantum wires with strong lateral confinement effects

We have fabricated deep etched Cd0.35Zn0.65SeZnSe quantum wires with lateral extensions down to 14 nm. The wires were defined by electron beam lithography and a low damage wet chemical etch process. Time-integrated and time-resolved photoluminescence spectroscopy was used to study excitonic properties in ultranarrow wide bandgap quantum wires. Lateral quantization causes a blue shift of the photoluminescence emission of up to 17 meV with respect to the 2D reference. A low temperature (T = 2 K) lifetime of about 110 ps was found, almost independent of the wire width. At room temperature, non-radiative sidewall recombination reduces the exciton lifetime from 330 ps for the 2D reference to about 21 ps in the case of a 28 nm wide wire.

Bulk micromachining of Si by Lithography and Reactive Ion Etching (LIRIE)

This paper reports on the development of a technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators and electronic circuits onto a single silicon chip. This technology is based on the highly anisotropic and selective dry etching of Si-monocrystals. Axes or stators (non-moving pans) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses. Both sides of the Si-membrane are covered with a 1.5 μm SiN xO y layer by a low stress (< 10 MP) PECVD-process. After that, all movable parts are created lithographically on the SiN xO y surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiN xO y sacrificial layer on the reverse side of the membrane by an RIE-process. This fixes the movable parts to the SiN xO y-layer. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiN xO y-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.

Photoluminescence efficiency study of wet chemically etched CdTe/Cd1−xMgxTe wires

Optically active semiconductor wires with lateral extensions between 60 nm and 5 μm based on CdTe/Cd1−xMgxTe quantum well structures have been fabricated by electron beam lithography and subsequent pattern transfer using a wet chemical etching process. Changes of the relative photoluminescence efficiency have been studied by photoluminescence spectroscopy as a function of the wire widths. For narrow wires nonradiative recombination at the wire sidewalls becomes the major recombination mechanism, strongly decreasing the photoluminescence efficiency. We discuss the influence of the exciton diffusion on the photoluminescence efficiency by investigating the wire width dependence of the photoluminescence intensity as a function of temperature and quantum well thickness. High photoluminescence efficiencies are obtained in the case of small diffusion lengths as for example at low temperatures and narrow quantum wells.

MEMS fabrication by Lithography and Reactive Ion Etching (LIRIE)

This paper reports on the development of a technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators, and electronic circuits onto a single silicon chip. Axes or stator (nonmoving parts) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses. Both sides of the Si-membrane are covered with a 1.5 μm SiN xO y layer by a low stress ( < 70 MP) PECVD-process. After that, all movable parts are created lithographically on the SiN xO y surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiN xO y sacrificial layer on the back side of the membrane by an RIE-process. This fixes the movable parts to the SiN xO y-layer. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiN xO y-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.

Fabrication of Superconducting Transistors using InAs/(AlGa)Sb Quantum Wells

We report on a fabrication process of superconducting weak links and superconducting transistors, which contain two-dimensional electrons in InAs/(AlGa)Sb quantum well. The superconducting transistors with lead alloy superconducting contacts were fabricated by using electron beam lithography, lift-off, and wet chemical etching processes. We have succeeded in fabricating a superconducting transistor with 0.4 µ m channel length and 0.17 µ m gate length between superconducting electrodes. Although the ideal performance of superconducting transistors has not been achieved yet, we present the results of superconducting weak links. The process of reducing contact resistance between lead alloy and InAs is also discussed, which is crucial to demonstrate the performance of the superconducting transistor.

X-Ray Photoelectron Spectroscopy and Optical Reflectivity Studies of Si Surfaces Prepared by Chemical Etching

Complementary X-ray photoelectron spectroscopy and optical reflectivity studies of crystalline Si(111) surfaces prepared by two different wet chemical etching processes were performed. These included aqueous HF solution etch or diluted CP-4 bath. Optical reflectivity spectra of Si surfaces, measured in the range 3.7-11 eV, were found strongly dependent on the applied etching process. Analysis of the core level X-ray photoelectron spectroscopy data has shown similarity of the surface structure, irrespectively of the etching procedure. Finally, comparison of optical reflectivity and valence 'band X-ray photoelectron spectra revealed a qualitative correlation between them indicating dominant influence of the bulk (here, the subsurface region containing polishing-induced defects) in the case studied. This paper is the first one which presents correlations between optical reflectivity and X-ray photoelectron spectroscopy data for Si and thus illustrates a bulk sensitivity of both techniques considered. PACS numbers: 78.40.Fy, 79.60.Bm

Emission Energy Shift in GaInAs/GaInAsP Strained Quantum-Box Structures Due to 0-Dimensional Quantum-Box Effect

We report, for the first time, the emission energy shift in GaInAs/GaInAsP quantum-box (QB) structures due to an obvious 0-dimensional quantum-box size effect. Ga1-x Inx As QBs with x=0.33 (tensile), 0.53 (unstrained), and 0.70 (compressive) were embedded in a GaInAsP (band-gap wavelength of 1.1 µm) optical absorption layer. These QB samples were fabricated by 2-step organometallic vapor-phase-epitaxy (OMVPE) growth, cross line lithography with electron-beam-exposure (EBX) direct writing, and the wet chemical etching process. The pitch of the QB array was 100 nm. The size of the boxes was controlled by changing the EB line dose, and measured by scanning electron microscope (SEM) to be 152–402 nm2. Photoluminescence spectra at liquid helium temperature were measured. The emission peak of unstrained (US)-QB samples shifted from that of the reference quantum-film (QF) sample due to an obvious 0-dimensional quantum-size effect. This QB effect was investigated for US-, tensile (T)- and compressive-strained (CS)-QB structures systematically. Energy shift obtained for the CS-QB sample (ΔE=45–63 meV) is much larger than those for US-QB (9–19 meV) and TS-QB (19–23 meV) samples with the same box size (S=252 nm2) by factors of 3–4 and 2–3 times, respectively. This is because of the reduction of the lateral hole effective mass in the compressive-strained case. From these results, we found that compressive-strained structure is expected to be more advantageous for low-threshold QB lasers.

Lasing action of Ga 0.67 In 0.33 As/GaInAsP/InPtensile-strained quantum-box laser

The lasing action of a Ga0.67In0.33As/GaInAsP/InP quantum-box (QB) laser with single-layer tensile-strained (TS)-QB active region is demonstrated for the first time. The fabricated QB is 30nm in diameter and 12nm thick with a period of 70nm. The sample was fabricated by using two-step MOVPE growth, electron-beam-exposure (EBX) direct writing, and wet-chemical etching processes. The threshold current density was 7.6KA/cm2 at 77K with pulse current injection.

Effects of Thin Film Stress in Sub Micron Multilevel Devices

ABSTRACTSubmicron high density devices require multilevel interconnections. In multilevel interconnections, issues relating to planarity, stress voiding of metals and stress cracking of the dielectric(s) play an dominant role.As the levels of interconnect go up so does the stress level. A high stress level in the intermediate dielectric can cause cracks which ultimately lead to device failure. In this paper we present a novel method to detect stress cracking using focussed ion beam. This method is correlated with wet chemical etch process and RIE.The phenomenum of cracking of dielectric(s) is studied and different technology aspects are considered. Using the focussed ion beam a robust dielectric is developed.

Wet chemical etching of silicate glasses in hydrofluoric acid based solutions

The etching of silicate glasses in aqueous hydrofluoric acid solutions is applied in many technological fields. In this review most of the aspects of the wet chemical etching process of silicate glasses are discussed. The mechanism of the dissolution reaction is governed by the adsorption of the two reactive species: HF and HF 2 - and the catalytic action of H+ ions, resulting in the breakage of the siloxane bonds in the silicate network. The etch rate is determined by the composition of the etchant as well as by the glass, although the mechanism of dissolution is not influenced. In the second part of this review, diverse applications of etching glass objects in technology are described. Etching of SiO2 and doped SiO2 thin films, studied extensively for integrated circuit technology, is discussed separately.

Real‐Time Monitoring and Analysis of Chemical Wet Etching of III‐V Compound Semiconductors

We report the use of optical interferometry for in situ real‐time monitoring and analysis of chemical wet etching processes in and structures with or without masked regions. Interference between reflections from the etching surface and buried heterointerfaces in the wafer allows determination of the etch depth and any degradation of surface quality, identification of heterointerfaces, and detection of changes in etch rate and end point in real‐time. We have used a sensor consisting of a 0.95‐μm light‐emitting diode and four detectors enclosed in a 12.5‐mm‐diameter transparent Teflon tube which is kept in front of the substrate being etched. The etching process can be stopped as soon as the desired etched depth is achieved. The technique can be useful particularly in regrowth requiring etching of base epitaxial structures, fabrication of lasers, and many other devices, and development of an etching process.

Wet etching of gold films compatible with high T c superconducting thin films

We report a wet etch process for selective patterning or removing gold (Au) layers on top of high Tc YBa2Cu3O7 (YBCO) thin-film structures. As an etchant for Au, an aqueous solution of potassium iodide (KI) and iodide (I) was chosen. This etchant does not degrade YBCO or any commonly used substrate materials (SrTiO3, MgO, zirconia, and NdGaO3). This KI and I solution gives convenient etch rates of 200–300 Å/min and easily stops on the YBCO due to its high selectivity. Using this wet chemical etching process, we have fabricated structures with better than 1 μm resolution. We have found this etchant to be very useful for secondary electron microscopy analysis of high Tc device structures.

Fabrication and chemical composition of rf magnetron sputtered Tl-Ca-Ba-Cu-O high T c superconducting thin films

High-temperature superconducing Tl-Ca-Ba-Cu-O (TlCaBaCuO) thin films were fabricated by rf magnetron sputtering on strontium titanate (SrTiO3) substrates. Thin films of 0.5–0.7-μm thickness were deposited by pure argon sputtering from a single composite powder target of Tl2Ca2Ba2Cu3Ox at an rf power of 250 W and a pressure of 5 mTorr. As-deposited thin films were sintered and annealed in a thallium-rich ambient to obtain superconductivity with a zero resistance temperature (Tc0) at 107 K. X-ray diffraction results showed highly c-axis oriented films with Tl2Ca2Ba2Cu3Ox (2223) and Tl2Ca1Ba2Cu2Ox (2122) phases present. Auger electron spectroscopy survey and depth profiles were performed to determine the compositional uniformity and impurity contents of the thin films. X ray photoelectron spectroscopy high-resolution spectra were obtained at the surface, in the bulk, and near the interface with the substrate. Our XPS results support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca2+ for Tl3+ and (2) charge transfer from Tl3+ to the CuO layers resulting in a valence of Tl between +3 and +1 states and the creation of holes in the CuO layers. In addition, a wet chemical etching process was developed for patterning the as-deposited TlCaBaCuO thin films. A 125-μm-wide line was formed using standard photolithography and wet chemical etching which, after heat treatments, showed superconductivity with a Tc0 of 80 K.

Thermochemical dry etching of single crystal ferrite by laser irradiation in CCl4 gas atmosphere

Single crystal ferrite has been etched by focused Ar+ laser irradiation in a CCl4 gas atmosphere. The etched groove showed cracks due to thermal stresses when samples were etched by a laser vaporization process in a vacuum, while in a CCl4 atmosphere, such cracks were not observed. An etching rate of 68 μ/s obtained for a thermochemical process by laser irradiation was four orders of magnitude higher than that for a wet chemical etching process. A high aspect (depth-to-width) ratio of up to 10 was obtained for etched grooves. Under specific conditions, bending of the groove and orientation dependence in etching rate were observed.

GaInAsP/InP single-quantum-well (SQW) laser with wire-like active region towards quantum wire laser

Lasing operation of a GaInAsP/InP single-quantum-well laser with very narrow (0.12 μm) wire-likeactive region was obtained for the first time under CW condition at 77 K. It was fabricated by a two-step organometallic vapour phase epitaxy (OMVPE) and wet chemical etching process. The threshold current density of the laser was 810 A/cm2. This lasing operation with such a narrow active region indicates that the technique employed here would be suitable for realising a higher-dimensional quantum-well laser, such as quantum wire and box lasers.

Formation of a p n junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using metalorganic chemical vapor deposition. A wet chemical etching process was used to expose the intersecting (111)Ga and (1̄1̄1)Ga planes with 6 μm periodicity. Charge collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

Reticulated Single‐Crystal Luminescent Screen

A new wet chemical etching process has been developed for the fabrication of a YAG luminescent screen with truncated square mesas. A large fraction of the cathodoluminescence can be directed through the untextured front surface of the crystal. An improvement in phosphor efficiency by a factor of three has been achieved. The improvement is linearly dependent on the height of the mesa.

Monolithic integration of curved waveguides and channeled-substrate DH lasers by wet chemical etching

Integration of AlGaAs/GaAs curved waveguides and other two-dimensional waveguides with DH lasers and detectors is demonstrated. Devices are fabricated from LPE AlGaAs/GaAs layers by wet chemical etching processes. Differential transfer efficiencies of \eta_{t}= 5 percent are routinely achieved in a structure consisting of an integrated laser, a 90° curved waveguide with 150μm radius, and a detector, for the case where one laser mirror is etched and one cleaved. This value is \eta_{t}= 4 percent if both mirrors are etched. A comparison of waveguide attenuation between straight and curved rib waveguides is given, along with the transfer characteristics of curved waveguides. The loss coefficient of curved rib waveguides with 150-μm radius is about two times that of a straight waveguide of the same length. The fabrication and properties of channeled-substrate crescent (CSC) lasers and detectors with transverse single-mode confinement, monolithically integrated by means of passive CSC interconnecting waveguides, is also described.

UV laser photopolymerization of volatile surface-adsorbed methyl methacrylate

The localized UV laser photopolymerization of surface-adsorbed methyl methacrylate has been used to deposit poly(methyl methacrylate) films for direct patterning of wet and dry chemical etching processes. Using this negative resist process, submicrometer linewidths both in the polymer deposition and in pattern transfer into Si and SiO2 have been demonstrated. The chemical kinetics of simple and catalyzed photopolymerization have been studied by dynamic lensing experiments and modeled as a dynamic equilibrium between competing surface photoreactions.