Optimum Etching Conditions Research Articles

Fabrication of nanoporous manganese by laser cladding and selective electrochemical de-alloying

Fabrication of nanoporous Cu–Mn alloy coatings was investigated by a two-step process involving high power laser cladding of a homogeneous Cu40Mn60 alloy coatings followed by selectively electrochemical de-alloying. Auger mapping results indicate that nanoporous manganese was obtained by selective electrochemical etching of the less active Cu component owing to the passivation of the more active manganese in potassium nitrate solution. The surface morphology of the porous Mn was a ribbon-like structure, different from interconnected bicontinuous nanopores that are usually obtained by de-alloying. The influence of de-alloying time, electric potential and temperature on the formation of nanoprosity is systematically investigated. Nanopore sizes can be tailored to be less than 100nm. Under optimal etching conditions the nanopore size was below 25nm. The surface area of the nanoporous manganese layer was enhanced by up to 990 times compared with that of a polished sample.

Etching blazed grating into quartz substrate with selectivity 1:1 against photoresist by inductively coupled plasma technology

Inductively coupled plasma (ICP) etching technology is becoming widely used in the fabrication of micro-optical elements. Because of its advantages such as relatively high etching rate and anisotropic etching, ICP technology is receiving more attention. Selectivity 1:1 of the substrate against photoresist is very convenient, because we can easily get the same structures which were designed on the photoresist. Through extensive experiments we have achieved an optimized etching condition under which the transfer process generates fairly smooth etched structures with selectivity 1:1. The first order diffraction efficiency of the etched blazed gratings is 83.5% which is a little bit lower than the theoretical efficiency 88.9%. The diffraction of etched blazed gratings matches the theoretical results well.

A wafer-scale etching technique for high aspect ratio implantable MEMS structures

Microsystem technology is well suited to batch fabricate microelectrode arrays, such as the Utah electrode array (UEA), intended for recording and stimulating neural tissue. Fabrication of the UEA is primarily based on the use of dicing and wet etching to achieve high aspect ratio (15:1) penetrating electrodes. An important step in the array fabrication is the etching of electrodes to produce needle-shape electrodes with sharp tips. Traditional etching processes are performed on a single array, and the etching conditions are not optimized. As a result, the process leads to variable geometries of electrodes within an array. Furthermore, the process is not only time consuming but also labor-intensive. This report presents a wafer-scale etching method for the UEA. The method offers several advantages, such as substantial reduction in the processing time, higher throughput and lower cost. More importantly, the method increases the geometrical uniformity from electrode to electrode within an array (1.5 ± 0.5% non-uniformity), and from array to array within a wafer (2 ± 0.3% non-uniformity). Also, the etching rate of silicon columns, produced by dicing, are studied as a function of temperature, etching time and stirring rate in a nitric acid rich HF–HNO 3 solution. These parameters were found to be related to the etching rates over the ranges studied and more importantly affect the uniformity of the etched silicon columns. An optimum etching condition was established to achieve uniform shape electrode arrays on wafer-scale.

Characterization of dislocation etch pits in HVPE-grown GaN using different wet chemical etching methods

The hydride vapor phase epitaxy (HVPE) grown GaN samples were etched by H 3PO 4, mixed solution of H 2SO 4 and H 3PO 4 (HH) and molten eutectic of KOH–NaOH ( E), respectively. The etching characteristics and surface morphologies were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The density of etch pits obtained by E etching under optimum etching condition was around 3.0 × 10 8 cm −2, which was consistent with the results obtained by the cathodoluminescence (CL) investigation. Two types of etch pits with different sizes were all revealed on the GaN surface using different etching methods. The large etch pits were formed on screw or mixed dislocations, while small etch pits were formed on edge dislocations. The difference in the size of etch pits was interpreted by Cabrera's thermodynamic theory. Prolonging etching time, the morphology changes of etch pits were different by using H 3PO 4, HH and E. The etching rate by H 3PO 4 etching was the fastest and that by E etching was the slowest. According to these etching results, it could be concluded that E etching was a better method for evaluation of dislocations.

Concentration-Dependent Wet Etching Behaviors of Ga-Doped ZnO Films Sputter-Deposited at Room Temperature Using Formic and Citric Acids

Transparent conducting Ga-doped zinc oxide (GZO) thin films (150 nm thick) were sputter-deposited on glass substrate at room temperature. As-deposited GZO films were wet-patterned with weak organic acid aqueous solutions containing formic or citric acid. Wet etching behaviors of the films were influenced by the type and concentration of organic acids used. The concentrations of formic and citric acids were varied from 0.02–0.1 and 0.0008–0.02 M, respectively. The concentration-dependent different etching behaviors, i.e., diffusion- vs reaction-limited etching modes, were observed for each etchant. Different rate-limiting behaviors were also verified by the calculated activation energy data for vertical etching of the films as a function of concentration of each etchant. With the optimal etching conditions for the GZO films on glass substrate, the wet patterning of the films deposited on poly(ethylene terephthalate) was also attempted.

Microstructure and chemical wet etching characteristics of AlN films deposited by ac reactive magnetron sputtering

The influence of the surface morphology of a molybdenum underlayer on the crystallinity and etchability of reactively sputtered c-axis oriented aluminum nitride thin films was investigated. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, high resolution x-ray diffraction, and defect selective chemical etching were used to characterize the microstructure of the Mo and AlN films. 1000nm thick films of AlN with a full width at half maximum (FWHM) of the x-ray rocking curve ranging from 1.1° to 1.9° were deposited on 300nm thick Mo underlayers with a FWHM of around 1.5°. The Ar pressure during the Mo deposition had a critical effect on the Mo film surface morphology, affecting the structure of the subsequently deposited AlN films and, hence, their wet etching characteristics. AlN films deposited on Mo sputtered at a relatively high pressure could not be etched completely, while AlN films deposited on low pressure Mo etched more easily. Postdeposition etching of the Mo surface in Ar rf discharge prior to deposition of the AlN film was found to influence the formation of AlN residuals that were difficult to etch. Optimal rf plasma etching conditions were found, which minimized the formation of these residuals.

Nanoporous Copper with Tunable Nanoporosity for SERS Applications

AbstractNanostructured materials with designable microstructure and controllable physical and chemical properties are highly desired for practical applications in nanotechnology. In this article, it is reported that nanoporous copper with a tunable nanopore size can be fabricated by controlling the dealloying process. The influence of acid concentration and etching potential on the formation of nanoprosity is systematically investigated. With optimal etching conditions, the nanopore sizes can be tailored from ∼15 to ∼120 nm by controlling the dealloying time. It is found that the tunable nanoporosity leads to significant improvements in surface‐enhanced Raman scattering (SERS) of nanoporous copper and peak values of SERS enhancements for both rhodamine 6G and crystal violet 10B molecules are observed at a pore size of ∼30–50 nm. This study underscores the effect of complex three‐dimensional nanostructures on physical and chemical properties and is helpful in developing inexpensive SERS substrates for sensitive instrumentations in molecular diagnostics.

III-nitride heterostructure field-effect transistors grown on semi-insulating GaN substrate without regrowth interface charge

Charge is observed at the regrowth interface for heterostructure field-effect transistors (HFETs) grown on semi-insulating (SI) bulk GaN substrates, even with Fe doping in the regrown buffer layer for reduction of the interface charge. Ultraviolet photoenhanced chemical (PEC) etching is used to treat the surface of SI bulk GaN substrates. Employing optimized etching conditions, a very smooth surface is achieved for the bulk GaN substrate after the etching. The charge at the regrowth interface is eliminated for HFETs grown on etched SI GaN substrates. Secondary ion mass spectrometry measurements show that the Si impurity concentration at the regrowth interface for HFETs grown on etched SI GaN substrates is much lower than that for HFETs grown on unetched SI GaN substrates, which suggests that the charge-containing layer on the SI substrate is removed by PEC etching and that the effects of the reduced charge layer near the regrowth interface can be eliminated by Fe doping for HFETs grown on etched SI substrates.

Inductively coupled plasma reactive ion etching of titanium nitride thin films in a Cl 2/Ar plasma

An inductively coupled plasma reactive ion etching of TiN thin films was carried out using a Cl 2/Ar gas chemistry. The etch characteristics such as the etch rate and etch profile were investigated by varying gas concentration and etch parameters including coil radio frequency (rf) power, dc-bias voltage and gas pressure. As the Cl 2 concentration increased, the etch rates of TiN thin films increased while the sidewall slopes of the etched films became slanted without the redeposition or etch residues. With increasing coil rf power and dc-bias voltage, the etch rates increased and etch slope became steep. Gas pressure has a little effect on etch rate and better etch profile was obtained at low gas pressure. Finally, highly anisotropic etching of TiN thin a film using a photoresist mask was achieved at the optimized etch condition.

Fabrication of Spiral Micro Coil Lines for Electromagnetic Actuators

With the recent progress in downsizing and the sophistication of various industrial products, the need for more compact actuators is increasing. Actuators account for the larger percentage of volume and weight of a product compared with other parts and devices. We have proposed fabrication process of spiral micro coils that employs X-ray lithography. This process will be effective for fabricating coils of a high aspect ratio lines. Reducing the size of coil lines and increasing their aspect ratio are expected to reduce the size and increase the output of actuators. Using this process, we formed spiral coil lines that can be used in electromagnetic actuators. X-ray lithography was used to form a high aspect ratio helical structure on the surface of an acrylic resin pipe. As a measure to suppress void generation, which is one of the shortcomings of electroplating processes, the sputtering apparatus and plating equipment were improved, a pretreatment process was additionally provided, and the actual electroplating method was improved. As a result, a void-free metallic deposit could be formed on a thin coil line. At the final step of this research study, we etched the coil line to determine optimal etching conditions.

Etch characteristics of magnetic tunnel junction stack using a high density plasma in a HBr/Ar gas

AbstractEtch characteristics of magnetic tunnel junction (MTJ) stack masked with TiN thin films were investigated using an inductively coupled plasma reactive ion etching in HBr/Ar gas for the application of magnetic random access memory. The effect of HBr gas concentration on the etch profile of MTJ stacks was examined. As HBr gas concentration increased, the sidewall angles of etched patterns of MTJ stacks were slightly improved. The effect of etch parameters including coil rf power, dc‐bias voltage, and gas pressure on the etch profile of MTJ stack was explored. At low coil rf power, low dc‐bias voltage, and high gas pressure, the etching of MTJ stack displayed better etch profile. A high degree of anisotropic etching of MTJ stacks without redeposition was achieved using HBr/Ar gas at the optimized etch conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Etch characteristics of magnetic tunnel junction stack with nanometer-sized patterns for magnetic random access memory

Etch characteristics of magnetic tunnel junction (MTJ) stack masked with TiN films were investigated using an inductively coupled plasma reactive ion etcher in Cl 2/Ar and BCl 3/Ar gases for magnetic random access memory. The effect of etch gas on the etch profile of MTJ stacks was examined. As Cl 2 and BCl 3 concentrations increased, the etch slope of etched MTJ stack became slanted and the dimensional shrinkage was observed. A high degree of anisotropic etching of MTJ stacks was achieved using Cl 2/Ar gas at the optimized etch conditions.

Study on the Tracks in a Nuclear Track Detector (CR39) for Detection of Laser-Induced Charged Particles

Experiments on laser-induced charged particle generation are now well under way by using an ultrashot, intense Ti:sapphire laser developed at KAERI (Korea Atomic Energy Researc Institute). For the measurements of protons and light ions generated, TASTRAK (CR39) plastic of 0.75 mm in thickness, manufactured by Track Analysis Systems Ltd. at Bristol University, was used as a nuclear track detector. We investigated the dependence of track development on the energy of the laser-induced charged particles and the etching conditions. We use the measured bulk etching rate to present the optimal etching conditions for the experiments on laser-accelerated proton generation by using a 10-TW laser system.

다결정 실리콘 태양전지의 표면 텍스쳐링 및 반사방지막의 영향

The effects of texturing and anti-reflection coating on the reflection properties of multi-crystalline silicon solar cell have been investigated. The chemical solutions of alkaline and acidic etching solutions were used for texturing at the surface of multi-crystalline Si wafer. Experiments were performed with various temperature and time conditions in order to determine the optimized etching condition. Alkaline etching solution was found inadequate to the texturing of multi-crystalline Si due to its high reflectance of about 25%. The reflectance of Si wafer texturing with acidic etching solution showed a very low reflectance about 10%, which was attributed to the formation of homogeneous. Also, deposition of ITO anti-reflection coating reduced the reflectance of multi-crystalline si etched with acidic solution(<TEX>$HF+HNO_3$</TEX>) to 2.6%.

Inductively Coupled Plasma Reactive Ion Etching of GeSbTe Thin Films in a HBr/Ar Gas

ABSTRACT Inductively coupled plasma reactive ion etching of GeSbTe (GST) thin films with a photoresist mask was performed using a HBr/Ar gas mixture. The etch rate of GST films increased up to 20% HBr concentration and began to decrease with further increase of HBr concentration. The etch profiles were improved with increasing HBr gas concentration. In particular, clean and vertical etch profiles were achieved at 80∼ 100% HBr gas concentrations. As the coil rf power and dc-bias voltage increased, the etch rates increased. The gas pressure had little influence on the etch rate. The good etch profiles were obtained at high coil power, low dc-bias and high gas pressure. The x-ray photoelectron spectroscopy analysis reveals that Te showed highest reactivity with HBr gas chemistry. A high degree of anisotropic etching of GST films was achieved using HBr/Ar gas mixture at the optimized etch conditions.

Systematic considerations for the patterning of photonic crystal devices by electron beam lithography

Photonic crystal devices with feature sizes of a few hundred nanometers are often fabricated by electron beam lithography. The proximity effect, stitching error and resist profiles have significant influence on the pattern quality, and therefore determine the optical properties of the devices. In this paper, detailed analyses and simple solutions to these problems are presented. The proximity effect is corrected by the introduction of a compensating dose. The influence of the stitching error is alleviated by replacing the original access waveguides with taper-added waveguides, and the taper parameters are also discussed to get the optimal choice. It is demonstrated experimentally that patterns exposed with different doses have almost the same edge-profiles in the resist for the same development time, and that optimized etching conditions can improve the wall angle of the holes in the substrate remarkably.

Efficiency Improvement of GaN-Based LEDs with ITO Texturing Window Layers Using Natural Lithography

In conventional GaN light-emitting diodes (LEDs), a significant gap exists between the internal and external efficiencies owing to the narrow escape cone for light in high refractive index semiconductors. In this paper, p-side-up GaN/sapphire LEDs with surface-textured indium-tin-oxide (ITO) window layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm, while the polystyrene sphere on the textured ITO surface is maintained at about 250-300 nm in diameter. The LEDs fabricated using the surface-textured ITO provided an output power that exceeded that of the planar-surface LED by about 30% and 40% at 20 and 400 mA current injection, respectively. After calculating, the extraction quantum efficiency of ITO/GaN LEDs with and without textured surface is 22.6% and 17.4%, respectively. There is about 5.3% improvement in the extraction quantum efficiency

FORMATION OF Si NANOSTRUCTURES USING DRY ETCHING WITH SELF-ORGANIZED METAL OXIDE NANOPILLAR MASKS

ABSTRACT In this study, a novel method is being proposed for the formation of nanostructures, utilizing the electrochemical anodization of Al/metal layers and high density plasma etching. Self-assembled metal oxide pillars formed by anodizing Al/metal layers were employed as an etching mask for nanostructure formation. Once the shape and size of the metal oxide pillars have been determined, the shape and size of the Si dots are dependent on the etching conditions such as etching gas, coil power, and dc-bias. The etch characteristics of Si film and metal oxide pillars were investigated with regard to etch rate, selectivity and profile. Highly ordered Si nanodot arrays were fabricated on a wafer using optimized etching conditions.

INVESTIGATION ON ETCH CHARACTERISTICS OF GESBTE THIN FILMS FOR PHASE-CHANGE MEMORY

ABSTRACT Inductively coupled plasma reactive ion etching of GeSbTe (GST) thin films with a photoresist mask was carried out in a Cl2/Ar gas. The monotonous increase in etch rate with increasing Cl2 concentration indicates that the etching of GST films obeys the reactive ion etching mechanism. The etch rates increased with increasing coil rf power and dc-bias voltage. The etch profiles was improved with decreasing coil rf power and dc-bias voltage and gas pressure gave little influence on the etch profile. The x-ray photoelectron spectroscopy analysis reveals that the rate limiting step in GST etching study is the etching of Te. Anisotropic etching of GST films was achieved using a Cl2/Ar chemistry at the optimized etch conditions.

HIGH DENSITY PLASMA ETCHING OF IrRu THIN FILMS AS A NEW ELECTRODE FOR FeRAM

ABSTRACT The etch characteristics of IrRu thin films with TiN hard mask were studied using a high density inductively coupled plasma of Cl2/O2/Ar gas mixture. The etch rate and etch profile were investigated by varying the gas concentrations of O2 and Cl2. As the O2 concentration in a 30% Cl2/O2/Ar gas mix increased, the etch selectivity of IrRu to TiN increased, resulting in the vertical etch profile. As the Cl2 concentration increased, the etch profile became worse due to the low etch selectivity. It was revealed that the etch selectivity of IrRu to TiN was closely related to the etch profile. The residue-free IrRu etching with a high degree of anisotropy was achieved using the Cl2/O2/Ar mixture at the optimized etching conditions.