Coupled Plasma Reactive Ion Etching Research Articles

Production of vertical nanowire resonators by cryogenic-ICP–DRIE

Silicon resonant sensors with large surface area-to-volume ratios provide high weighing sensitivity. This fact implies the possibility for detection of slight mass changes [i.e. by attached nanoparticles (NPs)]. Vertical silicon nanowire (SiNW) resonators are therefore suitable for exposure assessment or airborne NPs. SiNW arrays are top-down fabricated by nanolithography and subsequent inductively coupled plasma reactive ion etching at cryogenic temperature. Nanolithography is performed by conventional UV-lithography and nanoimprint for even smaller structures. Wire diameters are further reduced by multiple thermal oxidations and oxide stripping at times. Parameter effects of cryogenic dry etching are studied for SiNW arrays.

Inductively coupled plasma etching of through-cell vias in III–V multijunction solar cells using SiCl4/Ar

In this work, inductively coupled plasma reactive ion etching processes with SiCl4/Ar gas chemistries were optimized to fabricate wafer-scale, high-density, small-area via-holes for InGaP/GaAs/InGaAs inverted metamorphic triple-junction solar cells. Anisotropic and smooth etching with good uniformity of both the etch profiles and etch depths across a full 4-in. wafer were obtained. By combining optical emission spectroscopy with an analytical size-effect model, calibrated end-point detection for small features is demonstrated.

Fabrication of GaN-based LEDs with 22° undercut sidewalls by inductively coupled plasma reactive ion etching

We use a simple and controllable method to fabricate GaN-based light-emitting diodes (LEDs) with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching (ICP-RIE). Our experiment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 mW under a 20-mA current injection, 6.75% higher than 32.6 mW, the output powers of the conventional LEDs under the same current injection.

Fabrication of sub‐wavelength structures on silicon dioxide

In this reported work, nanosphere lithography (NSL) and inductively coupled plasma reactive ion etching (ICP-RIE) are combined to successfully fabricate a sub-wavelength structure (SWS) on a glass substrate, achieving broadband antireflection and increasing the transmittance of incident light through the glass. The experimental results show that the SWS surfaces with 180 nm width and 50 nm height could be fabricated onto glass. The mean reflectance of a blank glass is 5.81% in the wavelength range of 400–950 nm, 3 min of ICP-RIE combined with NSL reduce the mean reflectance to 3.5% and increases the mean transmittance from 92.3 to 94.3%. An additional coat of a 200 A-thick gold layer on the 30 s etched surface sample reduces the transmittance in the visible light range (400–700 nm) to 36.6%, which is 2.25 times larger than that at the infrared range (700–950 nm). The proposed novel fabrication technology has the advantage of being low cost, and the fabricated nanodot array structure, which is gold coated, can be used on an insulated window.

Cavity‐first approach for microelectromechanical system–CMOS monolithic integration

Presented is a cavity-first approach for producing released microelectromechanical system (MEMS) structures from the front side of a silicon on insulator (SOI) wafer. This approach shows excellent process compatibilities to CMOS and is significantly valuable to MEMS–CMOS monolithic integration. In this approach, prior to metal layer deposition and other components fabrication, which are easily damaged by vapour-phase hydrofluoric (HF) acid, release holes with a diameter of a few micrometres were created in the active silicon layer, and the cavities were formed after removing the underneath SiO2 box layer by vapour-phase HF etching. An amorphous fluoropolymer thin film was then successfully introduced to refill those release holes without entering into the cavities, after which the wafer can be fabricated by standard process with negligible surface fluctuation. Finally, MEMS structures were released from the front side of the wafer by inductively coupled plasma reactive ion etching (ICP-RIE). This approach enables monolithic integration of MEMS with CMOS circuits on SOI wafers with easy-package capability, eliminates the requirements on device release by wet chemical etching or ICP-RIE from the backside of the wafer and reduces the risk of device damage by vapour-phase HF etching. This approach also excels others in simplicity and high yields with better thickness uniformity and less residual stress in a MEMS structure.

Surface Passivation of High Density InGaN/GaN Nanorods Fabricated by Reactive Ion Etching

High density GaN nanorods containing InGaN quantum disks (QD's) were fabricated by inductively coupled plasma reactive ion etching (RIE) with self-assembled nano masks. Optical properties of the QD were severely degraded because of the damage on etched sidewalls during the RIE. However, after surface treatment with (NH4)2S, the QD showed improved photoluminescence. This result suggests that surface damage of GaN nanostructure during the dry etching can be passivated by sulfur atoms.

Improving aluminum nitride plasma etch process for MEMS applications

We present a new plasma etch process optimized for etching piezoelectric aluminum nitride (AlN) film deposited on thin molybdenum (Mo) metal electrode. Such film stack finds application in the integration of AlN-based RF microelectromechanical systems devices. The process is based on Cl2/BCl3/Ar gas chemistry with added buffer gas in inductively coupled plasma reactive ion etching system. The new gas mixture overcomes a generic problem of etched surface roughness without significant drop in AlN etch rate. Using design of experiment, the process window is optimized for improving selectivity to Mo and reducing microtrenching while maintaining smooth etched surface. Finally, an etching rate of 280 nm min−1 with reliable etch stop on Mo electrode and smooth bottom surface is reported. The integration suitability of the developed etch process is tested by etching 2.0 to 5.0 µm size square shaped via holes in 1.0 µm thick (0 0 2) oriented piezoelectric AlN on 0.2 µm thick Mo electrode while integrating contour mode resonators.

Fabrication of transferrable, fully suspended silicon photonic crystal nanomembranes exhibiting vivid structural color and high-Q guided resonance

The authors report the fabrication and optical characterization of fully suspended, transferrable, and deflectable silicon photonic crystal nanomembranes. Starting with a silicon-on-insulator wafer, the authors used electron beam lithography and inductively coupled plasma reactive ion etching (ICP-RIE) to introduce various photonic crystal patterns in silicon. A membrane containing the photonic crystal patterns was then defined by photolithography combined with ICP-RIE and released from the handle wafer by wet chemical etching. Finally, a free-standing photonic crystal membrane was obtained by a wet transfer and alignment process over a perforated foreign substrate. In the fabricated structures, the authors observed vivid structural colors in dark-field optical images of square lattice photonic crystals and measured a guided resonance mode with a quality factor as high as 5600 in a novel slot-graphite photonic crystal.

Inductively coupled plasma–reactive ion etching of c- and a-plane AlGaN over the entire Al composition range: Effect of BCl3 pretreatment in Cl2/Ar plasma chemistry

Inductively coupled plasma (ICP)–reactive ion etching (RIE) patterning is a standard processing step for UV and optical photonic devices based on III-nitride materials. There is little research on ICP-RIE of high Al-content AlGaN alloys and for nonpolar nitride orientations. The authors present a comprehensive study of the ICP-RIE of c- and a-plane AlGaN in Cl2/Ar plasma over the entire Al composition range. The authors find that the etch rate decreases in general with increasing Al content, with different behavior for c- and a-plane AlGaN. They also study the effect of BCl3 deoxidizing plasma pretreatment. An ICP deoxidizing BCl3 plasma with the addition of argon is more efficient in removal of surface oxides from AlxGa1−xN than RIE alone. These experiments show that AlxGa1−xN etching is affected by the higher binding energy of AlN and the higher affinity of oxygen to aluminum compared to gallium, with oxides on a-plane AlGaN more difficult to etch as compared to oxides on c-plane AlGaN, specifically for high Al composition materials. The authors achieve reasonably high etch rate (∼350 nm/min) for high Al-content materials with a smooth surface morphology at a low DC bias of ∼−45 VDC.

Discovery during Hydrogen Annealing: Formation of Nanoscale Fluorocarbon Tubular Structures

A novel fabrication method for nanoscale tubular structures is presented in this paper. The tubular structures can be obtained by heating single-crystal silicon trenches or pillars formed by the inductively coupled plasma reactive-ion etching (ICP-RIE) Bosch process in hydrogen ambient. The importance of initial vacuum in the reaction chamber for tube formation and the tube formation mechanism were discussed. The components and sidewall size of the tubular structure were also studied to verify that the tube is made of the fluorocarbon (CF) passivation layer deposited by the Bosch process. The CF tubular structure would be a promising structure for BioMEMS.

Formation of low resistance ohmic contacts in GaN-based high electron mobility transistors with BCl3 surface plasma treatment

A BCl3 surface plasma treatment technique to reduce the resistance and to increase the uniformity of ohmic contacts in AlGaN/GaN high electron mobility transistors with a GaN cap layer has been established. This BCl3 plasma treatment was performed by an inductively coupled plasma reactive ion etching system under conditions that prevented any recess etching. The average contact resistances without plasma treatment, with SiCl4, and with BCl3 plasma treatment were 0.34, 0.41, and 0.17 Ω mm, respectively. Also, the standard deviation of the ohmic contact resistance with BCl3 plasma treatment was decreased. This decrease in the standard deviation of contact resistance can be explained by analyzing the surface condition of GaN with x-ray photoelectron spectroscopy and positron annihilation spectroscopy. We found that the proposed BCl3 plasma treatment technique can not only remove surface oxide but also introduce surface donor states that contribute to lower the ohmic contact resistance.

Fabrication of High-Verticality Grating Nanostructures Using Twice-Deposited Etching Mask Layers

To study the influence of twice-deposited mask layers on the verticality of side wall and the aspect ratios of silicon-based nanostructures, the performance of focused ion beam (FIB) and CF4-based inductive coupled plasma reactive ion etching (ICP-RIE) processes was realized. The first etching mask of chromium (Cr) was deposited by radiofrequency (RF) magnetron sputtering as the conductive and etching barrier layers. Next, the Cr layer was directly patterned by a dual-beam FIB system to form nanograting patterns. Thereafter, a secondary mask layer of oxide (SiO2) with a thickness of 50 nm was deposited by sputtering. In order to study the influence of various deep etching parameters on verticality and aspect ratios, we examined argon flow rates, coil powers, platen powers, and chamber pressures. The SiO2 barrier layer on the side wall could be retained to maintain a high verticality contour and reduce the line-width shrinking ratio to surmount over etching during the use of fluorine-based gas. The residual Cr and SiO2 layers were dissolved and removed using a wet etching process consisting of a Cr-etching solution (CR-7). Measurements show that the verticality and aspect ratios of the grating nanostructures were 92.1° and 5.63, respectively.

The development of an atom chip with through silicon vias for an ultra-high-vacuum cell

This paper describes the development, fabrication and examination of an atom chip through silicon vias (TSV), which is anodically bonded with a Pyrex glass cell to form an ultra-high-vacuum system for the application of Bose–Einstein condensation (BEC) experiments. The silicon via is etched by the inductively coupled plasma reactive ion etch and filled by copper plating technology. The metal wires on both sides of the atom chips are patterned by the lithography process. Three different sizes of TSV are made and tested by continuously applying a maximum current of 17 A under the vacuum (70 Torr) and in air. In addition, after the thermal cycling of an anodic bonding process (requested at 350 °C) and a high electric field of 1000 V m−1, the TSV on atom chips can still hold the ultra-high vacuum (UHV). The conductive and vacuum yields of the TSV improved from 50% to 100% and from 75% to 81.25%, respectively after the modification of the fabrication process. Finally, the UHV test of TSV on atom chips at room temperature can be reached at 8 × 10−10 Torr, thus satisfying the requirements of atomic physics experiments under the UHV environment.

SU-8 etching in inductively coupled oxygen plasma

Structuring or removal of the epoxy based, photo sensitive polymer SU-8 by inductively coupled plasma reactive ion etching (ICP-RIE) was investigated as a function of plasma chemistry, bias power, temperature, and pressure. In a pure oxygen plasma, surface accumulation of antimony from the photo-initiator introduced severe roughness and reduced etch rate significantly. Addition of SF6 to the plasma chemistry reduced the antimony surface concentration with lower roughness and higher etch rate as an outcome. Furthermore the etch anisotropy could be tuned by controlling the bias power. Etch rates up to 800nmmin−1 could be achieved with low roughness and high anisotropy.

Cross-plane thermoelectric transport in p-type La0.67Sr0.33MnO3/LaMnO3 oxide metal/semiconductor superlattices

The cross-plane thermoelectric transport properties of La0.67Sr0.33MnO3 (LSMO)/LaMnO3 (LMO) oxide metal/semiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMO/LMO superlattice heterostructures on (100)-strontium titanate substrates. X-ray diffraction and high-resolution reciprocal space mapping indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively, this coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMO/LMO superlattices reveal a lowering of the effective barrier height to 223 meV as well as an increase in cross-plane conductivity by an order of magnitude compared to high resistivity superlattices. These results suggest that controlling the oxygen deficiency in the constituent materials enables modification of the effective barrier height and increases the cross-plane conductivity in oxide superlattices. The cross-plane LSMO/LMO superlattices showed a giant Seebeck coefficient of 2560 μV/K at 300 K that increases to 16 640 μV/K at 360 K. The giant increase in the Seebeck coefficient with temperature may include a collective contribution from the interplay of charge, spin current, and phonon drag. The low resistance oxide superlattices exhibited a room temperature cross-plane thermal conductivity of 0.92 W/m K, this indicating that the suppression of thermal conductivities due to the interfaces is preserved in both low and high resistivity superlattices. The high Seebeck coefficient, the order of magnitude improvement in cross-plane conductivity, and the low thermal conductivity in LSMO/LMO superlattices resulted in a two order of magnitude increase in cross-plane power factor and thermoelectric figure of merit (ZT), compared to the properties of superlattices with higher resistivity that were reported previously. The temperature dependence of the cross-plane power factor in low resistance superlattices suggests a direction for further investigations of the potential LSMO/LMO oxide superlattices for thermoelectric devices.

Inductively coupled plasma reactive ion etching of magnetic tunnel junction stacks using H2O/CH4 mixture

Magnetic tunnel junction (MTJ) stacks patterned with hard masks of 90×90nm2 were etched and the etch characteristics were investigated using inductively coupled plasma ion etching (ICPRIE) in a H2O-based gas mix. As the H2O concentration in H2O/Ar mixtures increased, the etch profile of MTJ stacks improved and the redeposition decreased. Field emission transmission electron microscopy revealed that etching of the MTJ stacks in H2O plasma was stopped on a MgO barrier layer on which heavy redeposition occurred; however, the addition of CH4 gas to H2O solved this issue. Specifically, as the CH4 concentration in the H2O/CH4 gas mixture increased, the etch profile became more vertical and the redeposition was reduced considerably. Overall, the etching of MTJ stacks with a high degree of anisotropy without any redeposition was accomplished using a H2O/CH4 gas mixture in an ICPRIE system.

Etch characteristics of CoFeB magnetic thin films using high density plasma of a H2O/CH4/Ar gas mixture

Etch characteristics of CoFeB magnetic thin films patterned with TiN hard masks were investigated using inductively coupled plasma reactive ion etching in H2O/Ar and H2O/CH4 gas mixes. As the H2O concentration in the H2O/Ar gas increased, the etch rates of CoFeB and TiN films decreased simultaneously, while the etch selectivity increased and etch profiles improved slightly without any redeposition. The addition of CH4 to the H2O gas resulted in an increase in etch selectivity and a higher degree of anisotropy in the etch profile. X-ray photoelectron spectroscopy was performed to understand the etch mechanism in H2O/CH4 plasma. A good pattern transfer of CoFeB films masked with TiN films was successfully achieved using the H2O/CH4 gas mix.

Investigation on etch characteristics of FePt thin films using a H2O/Ar plasma

• Development of a H 2 O/Ar gas to etch FePt magnetic films. • Films etched by inductively coupled plasma reactive ion etching. • Etch mechanism of FePt films in H 2 O/Ar plasma. • Etching of FePt films with high degree of anisotropy without redeposition or etch residue. The etch characteristics of FePt thin films patterned with a TiN hard mask were investigated using inductively coupled plasma reactive ion etching (ICPRIE) in a H 2 O/Ar plasma. As the H 2 O concentration increased, the etch rates of the FePt films and TiN hard mask decreased gradually, but the etch profile improved with a high degree of anisotropy without redepositions or etch residues. The improvement of etch profiles was attributed to the formation of a protective layer containing hydrogen species on the sidewall of the patterns and the formation of metal oxides during etching. The optical emission spectroscopy of H 2 O/Ar plasma revealed an increase of [H]/[Ar] and [O]/[Ar] ratios with increasing H 2 O concentration. As the ICP rf power and dc-bias voltage increased, and the gas pressure decreased, the etch rates of the FePt films increased and more vertical etch slopes were obtained. X-ray photoelectron spectroscopy of etched FePt films confirmed the existence of Fe oxide compounds formed by the etching. Overall, the results indicated that the etching of FePt films in a H 2 O/Ar plasma follows a chemically-affected sputtering etching mechanism.

Chamber conditioning process development for improved inductively coupled plasma reactive ion etching of GaAs/AlGaAs materials

Dry-etch tool preparation, which is critical to ensuring reproducible etch conditions, is particularly important in multiple-user, multiple-process-tool settings. A reproducible dry-etch process has been developed, utilizing inductively coupled plasma reactive ion etching (ICP-RIE) of GaAs and AlGaAs materials, for the fabrication of ridge structures in slab-coupled optical waveguide semiconductor diode lasers and amplifiers. A commercial ICP-RIE system was used, configured with aluminum-oxide-coated chamber components and a SiCl4/Cl/Ar etch gas mixture. Passivation of etch chamber component surfaces by preconditioning or “seasoning” contributed to a chemically stable etch environment as monitored by tracking the GaAs etch rate. The etched areas and sidewall profiles obtained using this process were smooth, and run-to-run etch depth control was ±2% of the desired target depth of ∼1.25 μm. Energy dispersive analysis x-ray of the etch chamber surfaces before and after chamber conditioning is reported.

Fabrication of boron doped diamond chip electrodes for single drop analysis

As a prototype for a “highly sensitive electrochemical detection system for single drop analysis using boron-doped diamond (BDD) electrodes”, a three-electrode system for the measurement of samples consisting of a single drop was fabricated. An Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) system, employing the Bosch process in order to realize high-aspect-ratio near vertical structures, was used to etch the BDD. A single drop (10 μL) was analyzed using the resulting fabricated ‘BDD chip electrode’ which exhibited the typical superior electrochemical properties of BDD electrodes.