Selective Etching Process Research Articles

Enhanced Two-Photon Absorption in a GaAs/AlAs Multilayer Cavity

A strong enhancement of two-photon absorption (TPA) has been demonstrated in a 30-period GaAs/AlAs multilayer with a GaAs half-wavelength (λ/2) cavity layer. In order to measure the time-resolved TPA signals, we successfully developed a selective etching process using an etch-stopper structure consisting of 5-nm-thick AlAs and 200-nm-thick Al0.3Ga0.7As double layers for removing the GaAs substrate. An analysis of the observed TPA results reveals that the average light intensity of the multilayer cavity is 41 times larger than that of a GaAs bulk sample. The obtained enhancement factor is in good agreement with the simulated value (45 times larger), which is determined from the simulated light intensity distribution by the conventional transfer matrix method.

Single cell detection using a glass-based optofluidic device fabricated by femtosecond laser pulses

We demonstrate the fabrication of integrated three-dimensional microchannel and optical waveguide structures inside fused silica for the interrogation and processing of single cells. The microchannels are fabricated by scanning femtosecond laser pulses (523 nm) and subsequent selective wet etching process. Optical waveguides are additionally integrated with the fabricated microchannels by scanning the laser pulse train inside the glass specimen. Single red blood cells (RBC) in diluted human blood inside of the manufactured microchannel were detected by two optical schemes. The first involved sensing the intensity change of waveguide-delivered He-Ne laser light (632.8 nm) induced by the refractive index difference of a cell flowing in the channel. The other approach was via detection of fluorescence emission from dyed RBC excited by Ar laser light (488 nm) delivered by the optical waveguide. The proposed device was tested to detect 23 fluorescent particles per second by increasing the flow rate up to 0.5 microl min(-1). The optical cell detection experiments support potential implementation of a new generation of glass-based optofluidic biochip devices in various single cell treatment processes including laser based cell processing and sensing.

InGaN-Based Light-Emitting Diodes with a Cone-Shaped Sidewall Structure Fabricated Through a Crystallographic Wet Etching Process

The InGaN-based light-emitting diodes (LEDs) were fabricated through a crystallographic etching process to increase their light extraction efficiency. After the laser scribing and the selective lateral wet etching processes at the LED chip edge region, the stable crystallographic etching planes were formed as the GaN {1012} planes and had an including angle with the top GaN (0001) plane measured as 40.3°. The AlN buffer layer acted as the sacrificial layer for the lateral wet process with a 27.5 μm/h etching rate. The continuous cone-shaped sidewall (CSS) structure of the treated LED has a larger light-scattering area and higher light extraction cones around the LED chips. The LED with the CSS structure around the chip edge region has a higher light output power compared to a conventional LED when measured in LED chip form.

Damage mechanism in low-dielectric (low-k) films during plasma processes

Plasma is extensively used for the etching/ashing of low-dielectric (low-k) films. However, since low-k films, such as SiOC films, are vulnerable to plasma irradiation, they are severely damaged during plasma processes, such as the extraction of methyl groups from low-k films. As a result, plasma irradiation increases the dielectric constant of low-k films and reduces the reliability of Cu/low-k interconnects. In previous work, the authors achieved highly selective and low-damage etching processes for low-k films by using their developed neutral beam process instead of the conventional plasma process. They have now investigated the damage mechanism in low-k films (porous SiOC films) during plasma processes by clarifying the effects of ions, radicals, and photons in plasma. First, they compared the damage in SiOC films etched by the conventional plasma process and the neutral beam process. Their results show that plasma processes change the structure of the SiOC film deeply within the film (over 100nm in depth) and increase the film’s dielectric constant, whereas the neutral beam process maintains the structure of the SiOC film. Additionally, they found that when a combination of the neutral beam process and a 172nm excimer lamp is used, photon irradiation enhances the extraction of methyl groups from the SiOC film by breaking Si–C bonds in the film. These results show that photon irradiation plays a very important role in the damage mechanism in low-k films during plasma processes.

Comparison Between Three Si1-xGex versus Si Selective Etching Processes

Three very different approaches to laterally etch SiGe layers selectively versus Si have been evaluated in terms of etch rate, selectivity and isotropy. The first one calls upon a CF4 plasma at low pressure and room temperature. The second one consists in the use of gaseous HCl at relatively high temperature and pressure in an epitaxy reactor. The third one is based on the use of appropriate chemistries in a wet bench. Germanium concentration impact on processes has been studied in the 20 - 40% range. To allow a strict comparison between so different processes, common test structures have been fabricated and etching targets have been jointly defined. Each technique entails its strengths and drawbacks, which will have to be carefully weighted when selecting one instead of another for a given sacrificial material configuration.

Nanoelectromechanical switch with low voltage drive

The triode structure vertical carbon nanotube based nanoelectromechanical switch shows excellent low voltage drive (∼4.5 V), owing to its vertical gate and the narrow gap between structural elements. The insulator deposition and the selective etching process steps simplify fabrication through self-alignment. The thickness of the insulator determines the width of the gap and the etching process, used to produce the vertical gate, removes the need for a complicated lithography step. The low drive voltage increases device stability and reliability and allows the device to be deployed in a wide range of applications.

Self-aligned nickel–platinum silicide oxidation

The oxidation of nickel silicide during selective wet etch is investigated for stable contact resistance. This paper describes chemical reactions of nickel–platinum alloy silicide during selective wet etch used to remove unsilicided Ni(Pt). These reactions depend on the nature of silicide phases and selective etch process parameters. For silicide formation conditions such as silicidation temperature, a silicon oxide layer is observed after selective wet etch, replacing nickel silicide layer formed during the first thermal treatment. The mechanism of oxide formation and growth related to the interaction between selective wet etch chemistries and Ni(Pt) silicidation is then discussed. Thanks to the monosilicide phase formation this detrimental phenomenon can be prevented.

Effects of a metal layer on selective etching of a Ge5Sb75Te20 phase-change film

Selective etching between an amorphous and a crystalline phase of a Ge5Sb75Te20 alloy film is carried out with an alkaline etching solution of NaOH. The etching selectivity is dependent not only on the concentration of the etching solution but also on the type of metal layer in the film structure. Specifically, Ag and Al metal films for a heat control function during writing in phase change recording show opposite behavior in the selective etching process. Surviving amorphous pits are obtained with the Al metal layer while etched amorphous pits are observed with the Ag metal layer. The etching selectivity of a sample with the survived amorphous pits with Al metal is better than that of the etched amorphous pits with an Ag metal layer.

Comparison between three Si1-xGex versus Si selective etching processes

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Fabrication of high-quality submicron Nb/Al-AlOx/Nb tunnel junctions

Nb/Al–AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and superconducting qubit applications of the Josephson devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality, submicron-sized Nb/Al–AlOx/Nb Josephson junctions. The technique follows the well-known selective Nb etching process and produces high-quality junctions with Vm = 100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm2, which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature dependence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions.

Selective Etching via Soft Lithography of Conductive Multilayered Gold Films with Analysis of Electrolyte Solutions

This experiment is designed to expose undergraduate students to the process of selective etching by using soft lithography and the resulting electrical properties of multilayered films fabricated via self-assembly of gold nanoparticles. Students fabricate a conductive film of gold on glass, apply a patterned resist using a polydimethylsiloxane stamp, and etch the unprotected gold. The resulting pattern is evaluated for changes in current, voltage flow, and resistance relative to the initial properties of the nonetched films. Students determine how changes in resistance applied to a conductive pattern affect the flow of current and voltage. Comparisons are made among different electrolyte solutions to demonstrate the electrical difference between strong, weak, and nonelectrolyte solutions, and how stronger electrolytes provide for better current flow.

Integration of enhancement/depletion- mode InGaP/InGaAs doped-channel pseudomorphic HFETs for direct-coupled FET logic application

InGaP/InGaAs-integrated enhancement/depletion-mode doped-channel pseudomorphic HFETs, fabricated on the same chip by a selective etching process, are demonstrated for the first time. For the depletion-mode device, the drain-to-source saturation voltage is only 0.3 V as VGS is fixed at 0 V. An extrinsic transconductance of 411 (278) mS mm−1 and a saturation current density of 221 (482) mA mm−1 are obtained for the enhancement (depletion) device. Furthermore, the noise margins NMH and NML values are up to 0.731 V (0.72 V) and 0.28 V (0.755 V) at a supply voltage of 1.5 V (2.0 V) in the direct-coupled FET logic application.

Metal nanostructures fabricated by selective metal nanoscale etch method

A new method for fabricating metal nanostructures, called ‘the selective metal nanoscale etch method (SMNEM)’, was developed. The SMNEM consists of a galvanic displacement and selective etching process. The process was found to be simple and produced a uniform surface with a self-controlled etch rate of 32.2 ± 2.1 nm per cycle at a temperature and immersion time of 75°C and 3 min, respectively. Since it is a wet chemical process, SMNEM provides high throughput and low temperature etching which is compatible with conventional semiconductor processes. Various metal nanostructures, such as nanostairs, nanogratings, and nanowires were produced using SMNEM.

Selective etching of independent contacts in a double quantum-well structure: Quantum-gate transistor

Double GaAs quantum wells (QWs) embedded between modulation-doped AlGaAs barriers with different aluminium (Al) contents were grown by molecular beam epitaxy. Independent electric contacts to each well were realized by applying different etching techniques without substrate removal. In particular, the lower quantum well was electrically pinched off by a local undercut of the lower AlGaAs barrier exploiting an Al selective etching process. In contrast, the upper quantum well was locally depleted by top etched trenches. Transistor operation of quantum wires defined in such bilayers is demonstrated at room temperature with one GaAs layer used as conducting channel controlled by the other nearby GaAs layer as efficient quantum gate.

Low temperature plasma etching for Si3N4 waveguide applications

Highly selective and anisotropic low temperature electron cyclotron resonance plasma etching process for silicon nitride optical rib waveguide devices compatible with integrated circuit technology is presented. Etching at low temperatures (−30°C) with SF6∕O2 chemistry in combination with a silicon dioxide hard mask achieved good anisotropy with the vertical sidewalls.

A Study on Selective Etching for Elevated PtSi Salicide Process and Work Function Modulation of PtSi Alloying with Hf

The selective etching process for elevated self-aligned silicide (salicide) utilizing PtSi has been investigated. We have developed novel selective etching process utilizing a diluted aqua regia followed by a diluted HF light etching. It was found that the residual Pt-rich silicide layers on the sidewall have been successfully removed. We have also investigated a work function modulation of PtSi alloying with Hf. The barrier height for electron of PtSi has been reduced approximately 0.1 eV for PtxHf1-xSi formed by the silicidation of Pt(17 nm)/Hf(4 nm)/Si(100) stacked layer structures.

Fabrication of nanoline arrays of noble metals by electroless plating and selective etching process

The fabrication of one-dimensional metallic nanostructures has attracted much attention because they can be utilized to components of nanoelectronic devices. In this paper, we report the fabrication of nanoline array composed of Cu, Au, Cu/Ag by the electroless plating and etching technique. In all case, the metallic layers uniformly coated the template surface with sub-100 nm thickness. Bilayer structure of Cu and Ag layer was also formed by the sequential plating of Ag and Cu. Top layer and the template were selectively removed by dry etching process with Ar, H 2 and O 2. Nanoline array of Cu, Au, and Ag/Cu were finally formed on a Si wafer. The width of the metallic line is close to the thickness of the original coating layer. Our process provides the rapid and cost-efficient nanofabrication of metal nanoline.

Growth and characterization of free-standing single crystalline tin and tin oxide nanobelts

Free-standing single crystalline tin nanobelts have been synthesized from tin foil by a novel selective etching process in NaOH solutions under hydrothermal conditions at low temperatures. The process requires neither catalysts nor templates to yield single crystalline tin nanobelts which are oriented and aligned on tin substrate. The crystal structure and morphology of these nanobelts were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, showing that oriented, single crystalline tin nanobelts were formed and grew along [101] crystal direction. These single crystalline tin nanobelts were easily converted into single crystalline tin oxide nanobelts by a shape-preserving oxidation process.

Air-suspended two-dimensional polymer photonic crystal slab waveguides fabricated by nanoimprint lithography

Air-suspended membrane-type photonic crystals were fabricated in polystyrene. The two-dimensional photonic crystal slab nanostructures were replicated by a thermal nanoimprint process, and then air-suspended membrane structures were generated by a selective sacrificial layer etch process. The optical transmission showed clear band gap characteristics at 1550nm wavelength, which is in good agreement with the theoretical calculations.

Post-treatment of screen-printed carbon nanotube emitter by selective plasma etching

Screen-printed carbon nanotube (CNT) emitter arrays were prepared by using slurry of mixture of multiwall CNTs, organic vehicles, and inorganic binder, i.e., silicon dioxide sol. The composition of the slurry was optimized by varying the CNT content in the mixture. It was found that only the cathode with appropriate CNT contents had low turn-on field and high emission current density. A post-treatment process was introduced to further improve the field emission properties which selectively etches away the silicon dioxide binder by inductively coupled plasma etching. The results show that the selective etching process could effectively remove the inorganic binder layer from screen-printing CNT emitters and improve field emission performances.