Reactive Ion Etching Process Research Articles

Response analysis of MEMS based high-g acceleration threshold switch under mechanical shock

Failures of MEMS devices under shock are due to the overlap of the static and moving parts. The shock response of the microstructure under mechanical shock is investigated in this paper. This work presents modelling and simulation of the microstructures such as microcantilever, fixed–fixed flexure and serpentine structure and is further extended to optimize the response of high-g acceleration threshold switch under mechanical shock. The latching threshold for the high-g acceleration switch is estimated using the geometrical structure. The natural frequency of the serpentine spring-mass structure is selected to achieve the required displacement for latching. The dimensions of the switch are optimized in accordance with the natural frequency and to meet the requirement of latching for a given shock. The switch is fabricated on silicon on insulator wafer with a deep reactive ion etching process. The switch is tested on the static mechanical shock of 3500 g and shows a good agreement between analytical, numerical and experimental results.

High-Q THz Photonic Crystal Cavity on a Low-Loss Suspended Silicon Platform

In this article, we present an ultrahigh-Q cavity at terahertz (THz) frequencies. The designed cavity is built on a low-loss suspended silicon (Si) waveguide. The substrate removal under the waveguide and the use of optimized deep reactive ion etching processing are the main reasons for observing very low losses of this design α <; 0.09 dB/mm. This very low-loss behavior of this designed platform is also demonstrated by the measurement of a one-dimensional photonic wire crystal cavity with Q > 18000. Different cavity layouts are adjusted in order to maximize the transmittance while maintaining high Q. A design with reduced number of etched crystal holes achieve Q > 1500 and high transmittance T > 70%. These structures are presented at sub-mm waves (around 600 GHz) for the design of a gas sensor in this frequency region, but the principles can be scaled and redesigned for other frequencies in the THz band.

Femto-Second Carrier and Photon Dynamics in Site Controlled Hexagonal InGaN/GaN Isolated Quantum Dots: Natural Radial Potential Well and Its Dynamic Modulation

Quantum dot (QD) is slated to play a significant role in quantum technologies through its usage as a single-photon source. It also has promising applications as efficient light emitters through strain-relaxed structures. This work demonstrates the fabrication of high-quality site controlled InGaN/GaN QDs through a large contribution of chemical etching in an otherwise reactive ion etching process. Uniform sized QDs with a hexagonal base and radii of 15 and 6 nm are fabricated and characterized by photoluminescence and femtosecond transient absorption spectroscopy. The natural exposition of the inherent hexagonal base is a signature of the reduced defects in these dots. The QDs show the intuitive additional quantum confinement due to size reduction, and the photoluminescence peaks manifest a blue shift. The absorption spectra indicate that the QDs are heavily strain-relaxed at smaller radii, and their characteristics as a function of size and pump power are investigated. The degree of strain relaxation and change in energy-band diagram as a function of position along the radius are also determined. The changes are prominent near the periphery, which creates a natural potential well for both electrons and holes, restricting the carriers from reaching the sidewalls. Femtosecond carrier dynamics indicate a lower capture rate for the smaller size of the dots, indicating excessive electrical or optical pumping will not necessarily lead to increased luminescence. The radiative decay of carriers is faster for strain-relaxed QDs due to higher oscillator strength originating from increased electron–hole wave function overlap. Higher pump power is found to decrease the radiative rate due to the increased effective size of the QDs and thereby reducing carrier injection density. This is in stark contrast to the frequently observed increased decay rate due to Auger recombination. Dynamic modification of the size of the QDs by pump power may find potential use in optoelectronic applications.

A Scalable, Hierarchical Rib Design for Larger-Area, Higher-Porosity Nanoporous Membranes for the Implantable Bio-Artificial Kidney

Silicon nanoporous membranes provide the fundamental underlying technology for the development of an implantable bio-artificial kidney. These membranes, which are comprised of micromachined slit-pores that are nominally 10 nm wide, allow for high-efficiency blood filtration as well as immunoprotection for encapsulated cells. Our approach takes advantage of well-established semiconductor fabrication technology to give us precise dimensional control over pore widths, thereby enabling a highly selective filtration function and a clear path towards further miniaturization. This work builds on our prior results on “ribbed nanoporous membranes” by adding a second-level hierarchy of significantly taller “mega-ribs” to further strengthen the membranes. Relying on a two-step Deep Reactive Ion Etch (DRIE) process, we etch $4~\mu \text{m}$ -deep as well as $40~\mu \text{m}$ -deep trenches into a silicon substrate, grow a thermal oxide liner, and deposit a layer of polysilicon into this “mold” to form membranes which, when released after a backside DRIE etch, feature a network of reinforcing ribs on the underside. We have fabricated and tested freestanding membrane spans that are up to 14 times wider than before, with approximately double the measured permeability per unit area. The new architecture can also improve cross-membrane mass-transfer rates and reduce chip-fabrication costs. [2020-0170]

Sub-20 nm multilayer nanopillar patterning for hybrid SET/CMOS integration

Abstract SETs (Single-Electron-Transistors) arouse growing interest for their very low energy consumption. For future industrialization, it is crucial to show a CMOS-compatible fabrication of SETs, and a key prerequisite is the patterning of sub-20 nm Si Nano-Pillars (NP) with an embedded thin SiO2 layer. In this work, we report the patterning of such multi-layer isolated NP with e-beam lithography combined with a Reactive Ion Etching (RIE) process. The Critical Dimension (CD) uniformity and the robustness of the Process of Reference are evaluated. Characterization methods, either by CD-SEM for the CD, or by TEM cross-section for the NP profile, are compared and discussed.

Effects of Post-Etch Microstructures on the Optical Transmittance of Silica Ridge Waveguides.

Silica waveguides are often etched by reactive ion etch (RIE) processes. These processes can leave residual topography that can increase optical loss. We investigated the relation between optical loss and various RIE etch. A wet etch step meant to remove microstructures was also considered and compared. Ridge waveguides were fabricated in plasma enhanced chemical vapor deposited films by three different RIE processes, each with a different gas composition, pressure setting, and applied power setting. Half of each set of waveguides were also subjected to a hydrofluoric acid (HF) solution. The waveguides were tested for optical transmission via the cutback method. The transmission vs waveguide length measurements were plotted to fit an exponential curve and the optical loss and measurement uncertainty for each waveguide set was calculated. Clear distinctions in optical loss were found between the different RIE processes. The HF treatment also has an effect, significantly reducing optical loss for two processes and increasing it for the third. Of the tested RIE processes, one can be suggested for silica waveguides. It results in the lowest optical loss and coincidently has the fastest etch rate.

Indium Tin Oxide optical access for magnetic tunnel junctions in hybrid spintronic–photonic circuits

The all-optical magnetization reversal of magnetic layers, by picosecond optical pulses, is of particular interest as it shows the potential for energy-efficient and fast magnetic tunnel junction (MTJ) elements. This approach requires memory elements that are optically and electronically accessible, for optical writing and electronic read-out. In this paper, we propose the integration of indium tin oxide (ITO) as a transparent conducting electrode for magnetic tunnel junctions in integrated spintronic–photonic circuits. To provide light with sufficient energy to the MTJ free layer and allow electrical read-out of the MTJ state, we successfully integrated indium tin oxide as a top transparent electrode. The study shows that ITO film deposition by physical vapor deposition with conditions such as high source power and low O2 flow achieves smooth and conductive thin films. Increase in grain size was associated with low resistivity. Deposition of 150 nm ITO at 300 W, O2 flow of 1 sccm and 8.10−3 mbar vacuum pressure results in 4.8 × 10−4 Ω.cm resistivity and up to 80% transmittance at 800 nm wavelength. The patterning of ITO using CH4/H2 chemistry in a reactive ion etch process was investigated showing almost vertical sidewalls for diameters down to 50 nm. The ITO based process flow was compared to a standard magnetic tunnel junctions fabrication process flow based on Ta hard mask. Electrical measurements validate that the proposed process based on ITO results in properties equivalent to the standard process. We also show electrical results of magnetic tunnel junctions having all-optical switching top electrode fabricated with ITO for optical access. The developed ITO process flow shows very promising initial results and provides a way to fabricate these new devices to integrate all-optical switching magnetic tunnel junctions with electronic and photonic elements.

Discovering high-performance broadband and broad angle antireflection surfaces by machine learning

Eliminating light reflection from the top glass sheet in optoelectronic applications is often desirable across a broad range of wavelengths and large variety of angles. In this paper, we report on a combined simulation and experimental study of single-layer films, nanowire arrays, and nanocone arrays to meet these antireflection (AR) needs. We demonstrate the application of Bayesian learning to the multiobjective optimization of these structures for broadband and broad angle AR and show the superior performance of Bayesian learning to genetic algorithms for optimization. Our simulations indicate that nanocone structures have the best AR performance of these three structures, and we additionally provide physical insight into the AR performance of different structures. Simulations suggest nanocone arrays are able to achieve a solar integrated normal and 65° incidence angle reflection of 0.15% and 1.25%, respectively. A simple and scalable maskless reactive ion etching process is used to create nanocone structures, and etched samples demonstrate a solar integrated normal and 65° reflection of 0.4% and 4.9%, respectively, at the front interface.

Electrofluidic displays based on inkjet printing and phase change filling

The patterned fluoropolymer film hydrophobicity and colored oil layer uniformity were critical for electrofluidic displays. Typically, reactive ion etching (RIE) is commonly used to pattern fluoropolymer films due to the chemically inert nature of fluorinated materials. However, the RIE process permanently changed the surface properties of the fluoropolymer film. These affect the function of the electrofluidic displays. The development of inkjet printing technology provides an innovative manufacturing pathway for functional materials, such as fluoropolymers. In this work, for the first time, an amorphous fluoropolymer (AF 1600) was patterned by a piezoelectric inkjet printer as a hydrophobic layer for an electrofluidic display. The pattered fluoropolymer films can be inkjet printed by varying the concentration of the fluoropolymer solution and adjusting printing parameters. Phase change filing was explored in combination with inkjet printing of colored oil, enabling the manufacture of electrofluidic cells in the air for the first time. The fluoropolymer and colored oil properties were systematically investigated to fulfill the inkjet printing requirements. The cost of manufacturing can be significantly reduced for large scale production by employing inkjet printing in combination with phase change filling. Furthermore, electrical and optical characterization of the printed electrofluidic cell shows better visual performance, dielectric stability, and fast electrical response and than the traditionally produced devices.

Patterning nickel for extreme ultraviolet lithography mask application. II. Hybrid reactive ion etch and atomic layer etch processing

A two-step plasma-thermal atomic layer etching (ALE) process that is capable of etching Ni with high selectivity with respect to the SiO2 hard mask and high anisotropy is evaluated in this work with a reactive ion etching (RIE) process to highlight the contrast between these two processes and the advantages of combining these two processes to tailor the sidewall profile with greater processing efficiency. The RIE chemistry leveraged the enhanced volatility of chlorinated nickel in the presence of hydrogen atoms. The hybrid RIE and ALE process achieved the desired sidewall profile, with no measurable residual halogen.

Two‐Step Reactive Ion Etching Process for Diamond‐Based Nanophotonics Structure Formation

Diamond surface modification is one of the most important technological challenges in the creation of diamond quantum photonics devices. It is necessary to fabricate different 3D structures on the crystal surface with both vertical and V‐shaped etching grooves for waveguides, grating couplers, and mesastructures. Herein, the applicability of SF6‐based plasma for diamond processing is studied. SF6 plasma etches diamond five times faster than commonly used Ar/O2 3:1 at the same pressure and bias, but it cannot provide vertical diamond structures due to the ion scattering. Herein, the two‐step plasma processing method is developed with Molybdenum protective masks that provide steep diamond 3D structures with sidewall roughness less than 40 nm and is, therefore, suitable for nanophotonics and other diamond applications. Mo can be chemically patterned by low‐power SF6 plasma and then used as a hardmask for anisotropic etching of diamond in Ar/O2 plasma with a selectivity of 27. Unlike common methods of diamond processing, the proposed two‐step method does not require chlorine.

PLASMA PARAMETERS AND SiO2 ETCHING KINETICS IN C4F8 + Ar + O2 GAS MIXTURE

The effect of Ar/O2 mixing ratio on plasma parameters, steady-state densities of active species and SiO2 etching kinetics in the three-component C4F8+Ar+O2 gas mixture was studied under typical conditions of reactive ion etching process (inductive 13.56 MHz RF discharge, total gas pressure of 6 mTorr, input power of 700 W and bias power of 200 W). The investigation combined etching rate measurements, plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling in order to determine steady-state densities and fluxes of plasma active species. It was found that the full substitution of Ar for O2 at constant fraction of fluorocarbon gas (in fact, the transition from 50% C4F8 + 50% Ar to 50% C4F8 + 50% O2 gas system): 1) results in weakly non-monotonic (with a maximum) SiO2 etching rate with close values for both O2-free and Ar-free plasmas; 2) causes the monotonic decrease in both F atom flux and ion energy flux; and 3) suppresses the formation of the fluorocarbon polymer film on the etched surface through its oxidative destruction pathway. The model-based analysis of SiO2 etching kinetics allowed one to conclude that an increase in effective probability for SiO2 + F reaction contradicts with the behavior ion energy flux as well as demonstrate the agreement with the change in gas-phase parameters characterizing the fluorocarbon film thickness. Therefore, an increase in O2 content in a feed gas influences the effective reaction probability by decreasing fluorocarbon film thickness and providing better access of F atoms to the etched surface.

Concerning the Effect of Type of Fluorocarbon Gas on the Output Characteristics of the Reactive-Ion Etching Process

The comparative research of the parameters, steady-state composition, and the effects of heterogeneous interaction in the plasma of fluorocarbon gases CxHyFz with various z/x relations in conditions of an induction RF (13.56 MHz) discharge is carried out. The binary systems CxHyFz + Ar based on CF4 (z/x = 4), CHF3 (z/x = 3), and C4F8 (z/x = 2) are used as the subjects of research. Through the methods of diagnostics and simulation of plasma we found (a) the reasons of the differences in the physical parameters (temperature and density of electrons, energy of ion bombardment) of the plasma in the studied systems; (b) the special characteristics of the kinetics of the plasma-chemical processes determining the steady state concentrations of fluorine atoms and polymer-forming radicals; and (c) the special characteristics of the kinetics of the heterogeneous process forming the output parameters (rate, selectivity, anisotropy) of the reactive ion etching of Si and SiO2.

Catalytic etching of {100}-oriented diamond coating with Ni and Cu nanoparticles under hydrogen

Nanopores formed in insulating solid state membrane is of great importance in many fields such as detection of DNA/RNA molecules in their internal environment, probing and manipulating biopolymers. Here, we present an effective and convenient method to form nanopores in diamond etched by self-assembled Ni or Cu nanoparticles in hydrogen atmosphere. With our method, homogeneous nanopores with lateral size in the range of [Formula: see text]–[Formula: see text] were created without using Reactive Ion Etching (RIE) process. In this work, the etching pits of Ni and Cu etched diamond were investigated, respectively. A novel step-like pattern of etching pits was observed on diamond etched by Ni. In order to study the etching process and figure out the etching mechanism of diamond, Scanning Electron Microscopy (SEM) was used to observe the etching morphology. Atomic Force Microscopy (AFM) and Laser Scanning Confocal Microscope (LSCM) were used to visualize the image of diamond etching pits and investigate the step-like pattern. A fixed step height was observed in each pit. Based on these observations and findings, a hypothesis is proposed, which can help to provide a new controllable etching method.

Effect of radio frequency power on nano-metal induced self-masking subwavelength structures mechanism

Randomly subwavelength structures (SWSs) were fabricated by reactive ion etching (RIE) process on the fused silica substrate, on the basis of an advanced metal nanodot induced one-step self-masking technology. Metal fluoride nanodots induce the deposition of fluorocarbon polymer stably. It acts as micromasks during the RIE process. With an increase in radio frequency (RF) power, the average sample height increases, the aspect ratio of the structure becomes greater and more uniform, and the average optical transmittance increases. Moreover, the maximum transmittance for single-sided SWSs can reach 95.5%. The theoretical simulation is in good agreement with the experiment results. The calculated results indicate that the profile of prepared structures may be close to a cylinder profile.

Graphene-nanowalls/silicon hybrid heterojunction photodetectors

We study and fabricate graphene nanowalls/silicon hybrid heterojunction photoconductive detector to provide process technology of the device and theoretical foundation for the purpose of preparation of high-performance photodetectors. The graphene nanowalls (GNWs) film is patterned by double-layered photoresist-based photolithography and reactive ion etching (RIE) process to achieve high quality GNWs channel and fabricate three different GNWs/Si heterojunction photoconductive detectors with n-doped, intrinsic and p-doped silicon substrates (n-Si, i-Si, p-Si), respectively. The GNWs film not only acts as a photoconductive channel for carrier transport, but also constructs a Schottky heterojunction with the silicon to participate in the separation and transport of photogenerated carriers. Since the injection of holes needs to pass through the Schottky junction region, the height of the Schottky barrier determines the injection ability of photogenerated carriers, which directly affects the photoconductive gain of the GNWs and silicon. In addition, under low bias VDS, the GNWs/n-Si photoresponse current is maximum and the GNWs/p-Si photoresponse current is minimum. The photoresponse is attributed to the barrier heights of the GNWs/n-Si, GNWs/i-Si, and GNWs/p-Si with values of 0.73 eV, 0.69 eV, and 0.63 eV, respectively. The higher the barrier, the more the number of photogenerated carriers injected into the GNWs will be, and the photoresponse current is large as well.

High-Efficiency Flexible Perovskite Solar Cells Enabled by an Ultrafast Room-Temperature Reactive Ion Etching Process.

Perovskite solar cells (PSCs), which have surprisingly emerged in recent years, are now aiming at commercialization. Rapid, low-temperature, and continuous fabrication processes that can produce high-efficiency PSCs with a reduced fabrication cost and shortened energy payback time are important challenges on the way to commercialization. Herein, we report a reactive ion etching (RIE) method, which is an ultrafast room-temperature technique, to fabricate mesoporous TiO2 (mp-TiO2) as an electron transport layer for high-efficiency PSCs. Replacing the conventional high-temperature annealing process by RIE reduces the total processing time for fabricating 20 PSCs by 40%. Additionally, the RIE-processed mp-TiO2 exhibits enhanced electron extraction, whereupon the optimized RIE-mp-TiO2-based PSC exhibits a power conversion efficiency (PCE) of 19.60% without J-V hysteresis, when the devices were optimized with a TiCl4 surface treatment process. Finally, a flexible PSC employing RIE-mp-TiO2 is demonstrated with 17.29% PCE. Considering that the RIE process has been actively used in the semiconductor industry, including for the fabrication of silicon photovoltaic modules, the process developed in this work could be easily applied toward faster, simpler, and cheaper manufacturing of PSC modules.

Improvement of Process Reproducibility and Particle Reduction for YF3 Coating by Collision Assisted Sintering Process in Reactive Ion Etching

In reactive ion etching process, generation of particles and deterioration in process reproducibility due to high aspect ratio processing have become problems. In this study, YF3 coating was investigated using collision assisted sintering process (CASP) technique to reduce particles and improve process reproducibility. It was clarified that the CASP had possibility of a high-density coating with fewer cracks and voids than atmospheric plasma spraying (APS) coating. The amount of etching and surface roughness reduced to 92% and 31%, respectively, as compared to APS coating. The surface polishing for the APS-YF3 coating also reduced the amount of etching by 4%, and the CASP-YF3/APS-Y2O3 structural coating reduces desorption rate of particles by 25%. These results suggested that the possibility of suppressing particle generation and improving process reproducibility due to a high-density coating.

Effects of current density on fracture behaviors for micron-sized crystalline silicon electrodes

The large volume change during lithiation/delithiation leads the silicon electrodes in lithium-ion batteries to severely degrade the mechanical performance and the silicon electrodes in lithium-ion batteries to further deteriorate electrochemical properties, which limits the commercial applications of silicon electrodes. After several year’s studies, the whole process of fracture for crystalline silicon anodes has been almost understood. However, the relationship between fracture behaviors and the lithiation depth has not been sufficiently studied. In this work, the &lt;i&gt;in-situ&lt;/i&gt; observations of morphological changes (e.g., volume expansion, crack initiation, propagation, and debonding of lithiated silicon) during lithiation at the different current densities are reported for silicon micropillars fabricated by standard photolithography and a deep reactive ion etching process. Also, this work focuses on the relative depth of lithiation of silicon electrodes at the moment of crack initiation, which is one of the crucial parameters representing the utilization of active materials with no crack. The results show that the silicon micropillars are broken faster (i.e., crack initiation and pulverization in a shorter lithiation time) and more seriously at a large current density, exhibiting more prominent symmetry of morphology. However, the relative depths of lithiation at the different current densities have just a slight difference (i.e., 18%–22%), when cracks are initiated. Here in this work, a silicon micropillar fracture is confirmed by the optical observation, while the relative depth of lithiation is calculated according to the capacity data recorded by the charge/discharge battery test system. The small fluctuation of the relative depth of lithiation with the large wave of current density can be ascribed to the dominant role of local stress concentration caused by anisotropic volume change in fracture behavior, which is validated by the results obtained by the finite element model (i.e., the depth of lithiation predicted by numerical simulations is ～ 22.6%). Therefore, the relationship between fracture behavior and the lithiation kinetics is established, providing an effective strategy for estimating the utilization of active materials under crack-free operation. With the help of the theoretical mechanics model considering both volume change and concurrent movement of reaction front, the stress state in the lithiated silicon at the moment of crack initiation is given, showing the tensile hoop stress near the reaction front. Consequently, these results suggest that the fracture behaviors depend on the current density, but the position of crack initiation (i.e., the depth of lithiation with no crack) is unrelated to current density (at least in a relatively broad range) for large micron-sized crystalline silicon electrodes, thereby shedding light on the fracture mechanisms and the design of alloy anodes (e.g., size and structure) in lithium-ion batteries.

A patterned look into a mysterious phase

Solid-State Physics A thin superconducting film can become insulating by, for example, exposure to a sufficiently large magnetic field. In between the superconducting and insulating regimes, an intermediate metallic state has been observed whose nature remains unresolved. To study the superconductor–metal insulator transition, C. Yang et al. patterned a film of the high-temperature superconductor yttrium barium copper oxide (YBCO) into a network of triangular superconducting islands connected by bridges (see the Perspective by Phillips). The reactive ion-etching process used for patterning reduced the quality of the film in a controlled manner. By increasing the etching time, the film's transport properties could be tuned from superconducting, through metallic, to insulating. The metallic phase exhibited a bosonic character. Science , this issue p. [1505][1]; see also p. [1450][2] [1]: /lookup/doi/10.1126/science.aax5798 [2]: /lookup/doi/10.1126/science.aaz9902