Reactive Ion Etching Process Research Articles

Design and fabrication of a polydimethylsiloxane device for evaluating the effect of pillar geometry and configuration in the flow separation using deterministic lateral displacement.

The advancement of microfluidics and the manufacturing of microdevices has led to a strategic change in the biomedical industry. The flow through narrow channels and the pillars are placed strategically, leading to the phenomenon of particle separation through deterministic lateral displacement (DLD). In such a phenomenon, the shape, size, location and orientation of the obstacles play an important role. For the first time, particle separation is achieved with DLD modules having high row shift angles of 25°, 30° and 35°, reducing the number of pillars. The significance of circular and triangular micropillars executing deterministic lateral displacement, oriented at different angles, has been investigated, and it is found that the triangular pillars oriented at 75° resulted in better separation compared to the other configurations. In this report, the fabrication, location, orientation of the micropillars and the selection of appropriate process parameters are detailed. The structures are fabricated on silicon wafers using the standard photolithography process followed by the deep reactive ion etching process. These dies are further used to fabricate the polydimethylsiloxane-based microfluidic chips. These fabricated devices are characterised by their size, structure and quality using 3D microscopy and scanning electron microscopy. Further, blood plasma separation is carried out using the devices fabricated in this work, and the particles at the inlet and outlets are evaluated using microscopy and a novel image processing technique, replacing the use of a hemocytometer. The path traced by the particles at different flow conditions is numerically evaluated and validated with experiments. The novel device is capable of separating blood cells from plasma with a recovery factor varying from 44% to 100%. PDMS-PDMS bonding experiments using oxygen and argon plasma have been carried out to evaluate the maximum bond strength and flow velocity in the devices. It is observed that the oxygen plasma results in a bond strength of 0.404 N mm-1, thus a high throughput of 135.34 μL s-1 is achieved using the fabricated device.

Spectroscopic Reflectometry for Optimizing 3D Through-Silicon-Vias Process

The main challenges in 3D metrology involve measuring TSVs etched with very high aspect ratios, where the via depth to diameter ratio approaches 10:1–20:1. In this paper, we introduce an innovative approach to enhance our in-house spectroscopic reflectometer module by integrating aperture technology, resulting in a substantial amplification of interference signals. Our system offers the flexibility to conduct measurements on an average number of TSVs, individual TSVs, or specific periodic arrays of TSVs. Additionally, we demonstrate the utility of the spectroscopic reflectometer as a non-destructive, high-speed metrology solution for in-line monitoring of TSV etch uniformity. Through a series of experimental trials in a reactive ion etch (RIE) process, we show that leveraging feedback data from the reflectometer leads to marked improvements in etch depth uniformity.

Conductive Nanofiber Web Film with Polydimethylsiloxane Sidewalls Selectively Coated through a Plasma Process for High Performance Flexible Transparent Electrodes.

Transparent electrodes are commonly used in various applications, such as solar cells, touch screens, smart windows, wearable electronic devices, and rollable flexible displays. Currently, indium tin oxide (ITO) is widely used as a transparent electrode material. However, ITO is not suitable for next-generation transparent electrodes that require flexibility; therefore, alternative nanomaterials, such as carbon nanotubes, conductive polymers, and metal nanowires, are being studied. However, these nanomaterials have poor mechanical strength and limited substrate availability. In this study, we developed a high-performance transparent electrode web film fabrication process based on conductive nanofibers, in which metal nanofibers are semiembedded in polydimethylsiloxane (PDMS). The mechanical strength of the conductive nanofibers was improved through the PDMS coating on the entire surface of the film, and the semiembedded structure of the nanofibers was realized using the reactive ion etching (RIE) process. In this study, we confirmed through transparency/conductivity analysis and bending, cycle, and taping tests that the transparent electrode fabricated using our approach has excellent mechanical strength and conductivity. Finally, the transparent electrode fabricated using our method can be widely applied as a next-generation transparent electrode because the process is easy and simple and requires inexpensive equipment and materials.

Highly efficient on-chip erbium–ytterbium co-doped lithium niobate waveguide amplifiers

The ability to amplify optical signals is of paramount importance in photonic integrated circuits (PICs). Recently, lithium niobate on insulator (LNOI) has attracted increasing interest as an emerging PIC platform. However, the shortage of efficient active devices on the LNOI platform limits the development of optical amplification. Here, we report an efficient waveguide amplifier based on erbium and ytterbium co-doped LNOI by using electron beam lithography and an inductively coupled plasma reactive ion etching process. We have demonstrated that signal amplification emerges at a low pump power of 0.1 mW, and the net internal gain in the communication band is 16.52 dB/cm under pumping of a 974 nm continuous laser. Benefiting from the efficient pumping facilitated by energy transfer between ytterbium and erbium ions, an internal conversion efficiency of 10% has been achieved, which is currently the most efficient waveguide amplifier under unidirectional pumping reported on the LNOI platform, to our knowledge. This work proposes an efficient active device for LNOI integrated optical systems that may become an important fundamental component of future lithium niobate photonic integration platforms.

Saturating quantum efficiency of SNSPDs with disorder manipulation of NbN films

Quantum efficiency is one of the most important performance metrics for superconducting nanowire single-photon detectors (SNSPDs). Specifically, near-infrared NbN-SNSPDs with high quantum efficiency are extremely desirable in quantum communications. However, due to the high energy gap of NbN, it is difficult to achieve a saturated quantum efficiency. In this paper, we systematically investigated the primary determinants of fabricating highly saturated NbN-SNSPD by changing the stoichiometric ratio during the growth of NbN thin films. Through electron beam lithography and reactive ion etching processes, NbN-SNSPDs with a saturated quantum efficiency were fabricated. It is worth noting that the saturated quantum efficiency is observed to be closely related to the stoichiometric ratio of NbN films. Artificially increasing the disorder in NbN films can enhance the probability of superconducting phase transition during photon detection. Our work provides a consistently simple and effective method for the fabrication of highly efficient quantum devices, which is crucial for achieving higher precision in future quantum communications.

Effective removal of metal-carbide contamination from diamond circuit boards by reactive ion etching

Recently, we have demonstrated the feasibility of using laser-patterned polycrystalline diamond sheets as a substrate for implantable circuit boards. The laser grooves in the diamond can be filled with biocompatible braze alloys such as Au-ABA and polished back to create long-lasting, hermetic circuit boards suitable for implantation in the human body. However, during the process of depositing molybdenum and niobium layers to aid adhesion of the Au-ABA braze, a residual film was found to form, which was resistant to both polishing and chemical etching, resulting in electrical shorting between features on the circuit board. Here, we report an optimised reactive ion etching process to remove the residual metal contamination and electrically isolate fine features on the diamond circuit boards. Samples were evaluated through energy dispersive spectroscopy elemental analysis and electrical testing of the diamond surface, confirming the complete removal of contaminants from the diamond surface.

On mechanisms to control SiO2 etching kinetics in low-power reactive-ion etching process using CF4 + C4F8 + Ar + He plasma

This work discusses effects of gas mixing ratios and bias power (at 13.56 MHz and 2 MHz) on both gas-phase characteristics and etching kinetics of SiO2 in the CF4 + C4F8 + Ar + He plasma. The subject was the low input power regime (∼0.05 W/cm3). The substitution of C4F8 for CF4 exhibits no principal influence on electrons- and ions-related plasma parameters, produces weakly increasing F atom density as well as causes a comparable increase in the etching rate. The latter is provided by the chemical etching pathway with the nearly constant reaction probability. The substitution of Ar for He sufficiently affects plasma parameters, reduces the F atom density, but accelerates the etching process due to increasing reaction probability. Probably, the latter traces decreasing surface passivation by fluorocarbon radicals. Bias parameters do not disturb bulk plasma, but do influence the etching kinetics through the ion bombardment energy. The growth of etching rate vs. bias power mainly appears due to increasing efficiency of chemical etching pathway. The 2 MHz bias frequency produces lower etching rates in spite of higher ion bombardment energies. This effect is probably due to higher desorption rate and lower sticking probability for F atoms. It was found that most effective parameters to control etching profile are Ar/He mixing ratio and bias frequency.

Solid-State Au Nanocone Arrays Substrate for Reliable SERS Profiling of Serum for Disease Diagnosis.

Surface-enhanced Raman scattering (SERS) is a widely used rapid and noninvasive method for detecting biological substances in serum samples and is commonly employed in disease screening and diagnosis. Solid-state nanoarray SERS substrates used in serum detection may cause spectral instability due to imperfections in the detection method. For the purpose of identifying optimal detection conditions, various dilution levels of the serum were tested in this study. The study found that a complete and stable serum SERS spectrum can be obtained when the serum is diluted by a factor of 50. The study reports the successful preparation of an Au nanocone array (Au NCA) plasmonic substrate with a uniform, controllable microstructure and high activity, achieved through a combination of PS colloidal sphere template-assisted reactive ion etching (RIE) process and magnetron sputtering deposition technology. Based on this substrate, a standard detection scheme was developed to obtain highly stable and repeatable serum SERS spectra. The study verified the reliability of the optimized serum detection scheme by comparing the SERS spectra of serum samples from healthy individuals and gastric cancer patients, and confirmed the potential benefits of the scheme for disease screening and diagnosis.

Evolution of physical and mechanical properties of fused silica after subsurface damage layer removal by RIE treatment

The subsurface damage of polished fused silica can be removed by various post-treatments to improve the strength of fused silica in high energy laser systems, but the evolution of physical and mechanical properties of fused silica after the removal of subsurface damage remains unclear. In this study, the physical and mechanical properties of fused silica are studied after various depths of subsurface damage removal by reactive ion etching process. The results show that as the etching depth increases, the concentration of metal ions contamination in the subsurface of fused silica decreases significantly, the water contact angle of fused silica decreased, while homogeneity of adsorbed water molecules on fused silica surface increases, especially at higher humidity conditions. Furthermore, the nanohardness and reduced modulus of fused silica increases with the etching depth. These results will be helpful for optimizing the manufacturing and lifetime of fused silica in high energy laser systems.

Real-time 3D plane-wave imaging using annular capacitive micromachined ultrasonic transducer array

Imaging methods and 2D sparse arrays have been extensively researched to realize real-time 3D volumetric imaging with higher frame rates. In this study, we developed a 3D plane-wave imaging method using an annular capacitive micromachined ultrasonic transducer (CMUT) array as a breakthrough technique for realizing 3D imaging with a limited number of elements. We adopted the double oxidation and wafer bonding processes for creating the cavity of a CMUT with a 2 µm silicon membrane. To ensure surface uniformity before the bonding process, we implemented an additional reactive ion etching process after the second oxidation. The characterization results showed that the resonant frequency of the proposed device was 6.2 MHz with 65 V collapse voltage. The demonstration of real-time 3D volumetric imaging was conducted in oil using a Vantage 64 ultrasound research system. A plane-wave imaging scheme was used to detect wire phantoms immersed in the oil, with 289 plane waves transmitted over a range of 20° from the center of the annular array. The reconstructed data were used to create three orthogonal cross sections of the target region. The − 6 dB lateral and axial resolutions were 0.56 mm and 0.35 mm for the wires positioned at 18 mm from the proposed device, which were narrow enough to detect a wire phantom of 380 µm diameter. The normalized frame rate was calculated and compared with that in a previous study. We verified that plane-wave imaging has advantages in real-time imaging when compared with the classic phased array and synthetic phased array. Thus, the annular CMUT array is a promising mechanism for real-time 3D imaging with higher frame rate than that possible with previous methods.

Balancing of Flow at Microfluidic Apertures

Computational fluid dynamics simulations are used to obtain a radially symmetrical flow profile at an aperture of a microfluidic channel by manually arranging flow‐directing obstacles around the aperture. For the first time, the flow profile is improved by calculating the coefficient of variation (CoV), which is applied to the flow velocity magnitude along coaxially arranged circles below the aperture in the microfluidic channel. A minimum CoV of 0.03 is obtained at the circle with the same diameter as the aperture. Channels with the optimized design are fabricated by lamination of two layers of dry film resist and patterned with UV‐lithography. The aperture is formed by using an inductively coupled plasma reactive ion etching process. Video recording of the flow behavior confirmed the simulation results experimentally. The proposed channel design and the optimization method can favorably be used for a balanced hydrodynamic trapping of particles or cells at apertures.

Abstract 3297: Deep reactive ion etched microneedle array for in-vivo melanoma cancer monitoring via cancer exosome isolation

Abstract This study reports a deep-reactive-ion-etched microneedle device (ExoNeedle chip) coated with a hybrid hydrogel that can directly capture cancer-associated extracellular vesicles (EVs) in interstitial fluid (ISF) in a minimally invasive manner, as opposed to conventional liquid biopsy methods involving sample extraction and EV isolation in-vitro or tissue biopsies for melanoma. Tumor derived EVs give insight into a tumor’s mutational burden and provide both prognostic and diagnostic value as a liquid biopsy tool. Melanoma is an aggressive cancer with a lack of promising markers for early detection, onset of metastasis, and monitoring of recurrence. The ExoNeedle chip is intended to pierce through the epidermis and parts of the dermis to isolate melanoma secreted EVs from the ISF to alleviate these unmet needs. The microneedle arrays were created through the Deep Reactive Ion Etching (DRIE) process and a subsequent wet etching step to sharpen the needles. A 4 inch silicon wafer spin coated with 3 microns of positive photoresist was lithographically patterned and etched by DRIE using the standard Bosch processes to expose arrays of cylindrical pillars. Next, the cylindrical features were sharpened using an isotropic wet etch consisting of a mixture of hydrofluoric and nitric acid. The microneedle arrays were made and cleaved into individual patches. Meanwhile, hybrid hydrogel solution was made from Polyvinyl alcohol (PVA) and alginate by dissolving each of them separately in water under heat, followed by mixing the solutions. After centrifuging and filtering the hydrogel, it was conjugated with Annexin V (Av) protein to give it affinity for cancerous exosomes. Lastly, this hydrogel complex was added onto the microneedle patches and gelated with the help of a humidifier that deposited Ca2+ ion vapor over the hydrogel. The microneedles were first optimized and validated using melanoma cell line secreted EVs. Melanoma EVs were successfully isolated and quantified to evaluate the efficacy of the microneedle patches yielding above an 80% capture efficiency from purified serum samples. The microneedle patches were DiO stained, fluorescently imaged, visualized in a scanning electron microscope, and protein concentration was determined respectfully. Additionally, the functional hydrogel coatings on the microneedles are dissolved in ethylenediaminetetraacetic acid (EDTA), subsequently unbinding EVs from Av due to EDTA-based Ca2+ chelation. The dissolved solution is then used for enumeration and quantification of EVs by nanoparticle tracking analysis. We are further validating these patches in skin mimicking models and patient derived xenograft models of melanoma. The technology developed in this study for the isolation of melanoma EVs can broadly pave the way for minimally invasive point of care cancer diagnostics and tracking for melanoma patients. Citation Format: Scott M. Smith, Abha Kumari, Thiago Reis, Yoon-Tae Kang, Sunitha Nagrath. Deep reactive ion etched microneedle array for in-vivo melanoma cancer monitoring via cancer exosome isolation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3297.

Inert-gas ion scattering at grazing incidence on smooth and rough Si and SiO2 surfaces

Molecular dynamics simulations for the scattering of neon, argon, and xenon ions on silicon and silicon dioxide surfaces were performed at grazing incidence to examine how the angular distribution of reflected ions deviates from that of the ideal specular reflection, depending on the ion mass, incident angle, and surface material and its roughness. This study is motivated to understand how energetic ions interact with the sidewalls of high-aspect-ratio (HAR) channels when reactive ion etching (RIE) is used to form such HAR channels in semiconductor manufacturing. It is found that the higher the ion mass is, the less grazing the ion incident angle is, or the rougher the surface is, the larger the angular distribution of reflected ions becomes around the corresponding specular reflection angles. Quantitative information on such reflected ions can be used to predict the profile evolution of HAR channels in RIE processes.

The effect of DRIE notching on field emission enhanced breakdown in SOI based MEMS electrodes

Microscale (<5 μm) gas breakdown is usually dominated by field emission, which is influenced largely by electrode surface morphology. At present, there is a large number of studies on the breakdown and discharge of different metal electrode geometry and electrode spacing as well as micro-electro-mechanical system (MEMS) device structures, but few studies on the breakdown of MEMS electrodes affected by notching, which will greatly change the electrode surface morphology but is difficult to completely avoid in deep reactive ion etching process based on silicon on insulator (SOI) wafer. In response to this situation, this paper conducted breakdown tests and field emission tests on MEMS samples with and without notching. It was found that samples with notching could withstand more breakdowns of about 6–13 times before the formation of internal resistance, increased by 200%–300% compared with samples without notching, and have a lower breakdown voltage of about 210 V, 16% lower than that of samples without notching. In addition, it was also found that for the samples with notching, the field enhancement factor gradually decreases with the increase of the number of breakdown events. When the field enhancement factor decreases to about 100, the subsequent breakdown is highly likely to cause the sample to form electrical connection, thus completely damaging the sample. Above conclusions have certain reference value for designing the actuation voltage of MEMS devices based on SOI wafers.

Large-Area and Rapid Fabrication of a Microlens Array on a Flexible Substrate for an Integral Imaging 3D Display.

A curved integral imaging three-dimensional (3D) display attracts a lot of interest due to its enhanced 3D sense of immersion and wider viewing angle. In this paper, a microlens array (MLA) based on a flexible poly(ethylene terephthalate) (PET) substrate was achieved by a straightforward, rapid, and low-cost technique. The reactive ion etching (RIE) process treated PET/CYTOP covered with a flexible mask to generate a hydrophilic-hydrophobic patterned surface. The well-designed arrays of confined adhesive droplets with a controlled geometry on a hydrophilic-hydrophobic patterned surface were formed using the blade-coating method. A flexible MLA with a diameter of 820 μm, a size of 5.3 cm × 5.1 cm, and a radius of curvature of 25 cm was fabricated and combined with a curved two-dimensional (2D) monitor to realize a lateral viewing range of 6.4 cm at a viewing distance of 25 cm, which is 4 times larger than with flat integral imaging 3D display system. The flexible MLA has the advantages of a controllable lens profile and large pitch, and it can be manufactured on a large scale. In addition, it provides a large viewing angle for the reconstructed 3D image.

Terahertz Barcodes Enabled by All‐Silicon Metasurfaces for Process Control and Monitoring Applications

AbstractProcess control and monitoring (PCM) is crucial for the quality control and yield improvement of semiconductor products. Terahertz inspection of semiconductor devices has been of interest since the progress of terahertz spectroscopic techniques. However, due to the diffraction limit, high‐resolution measurement of geometric sizes and multiple parameter monitoring are challenging for terahertz PCM techniques. In this article, XX present terahertz all‐dielectric metasurfaces as the interface on a silicon substrate for monitoring material properties and fabrication errors in the silicon deep reactive ion etching (DRIE) process. It is shown that four different metasurfaces can encode multiple information simultaneously, including the carrier density of silicon substrates, etching depth and linewidth error, forming a terahertz barcode for PCM. By correlating the measured reflection spectra of the barcode with those in the simulation database, the three parameters are retrieved with a mean square error (MSE) of ≈0.5. The results indicate that this proposed technique using emerging artificial photonic materials as PCM structures paves a pathway toward high‐efficiency semiconductor quality control and other sensing applications.

Atomic layer etching of nanowires using conventional reactive ion etching tool

Innovative material and processing concepts are needed to further enhance the performance of complementary metal-oxide-semiconductor (CMOS) transistors-based circuits as the scaling limits are being reached. To supplement that, we report on the development of an atomic layer etching (ALE) process to fabricate small and smooth nanowires using a conventional dry etching tool. Firstly, a negative tone resist (hydrogen silsesquioxane) is spin-coated on Silicon Germanium-on-insulator (SiGeOI) samples and electron beam lithography is performed to create nanopatterns. These patterns act as an etch mask and are transferred into the SiGeOI layer using an inductively-coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, an SF6 and Ar+ based ALE process is employed to smoothen the nanowires and reduce their widths. SF6 modifies the surface of the samples, while in the next step Ar+ removes the modified surface. To investigate the effect of this process on the nanowire width, several ALE cycles are performed. The etched features are inspected using scanning electron microscopy. With the increasing number of ALE cycles, a reduction in the width is observed. An etch per cycle of 1.1 Å is obtained.

Adaptive Weight Tuning of EWMA Controller via Model-Free Deep Reinforcement Learning

Exponentially weighted moving average (EWMA) controllers have been extensively studied for run-to-run (RtR) control in semiconductor manufacturing processes. However, the EWMA controller with a fixed weight struggles to achieve excellent performance under unknown stochastic disturbances. To improve the performance of EMWA via online parameter tuning, an intelligent strategy using deep reinforcement learning (DRL) technique is developed in this work. To begin with, the weight adjusting problem is established as a Markov decision process. Meanwhile, simple state space, action space and reward function are designed. Then, the classical deep deterministic policy gradient (DDPG) algorithm is utilized to adjust the weight online. Moreover, a quantile regression-based DDPG (QR-DDPG) algorithm is further verified the effectiveness of the proposed method. Finally, the developed scheme is implemented on a deep reactive ion etching process. Comparisons are conducted to show the superiority of the presented approach in terms of disturbance rejection and target tracking.

Laser trimming for lithography-free fabrications of MoS2 devices

Single-layer MoS2 produced by mechanical exfoliation is usually connected to thicker and multilayer regions. We show a facile laser trimming method to insulate single-layer MoS2 regions from thicker ones. We demonstrate, through electrical characterization, that the laser trimming method can be used to pattern single-layer MoS2 channels with regular geometry and electrically disconnected from the thicker areas. Scanning photocurrent microscope further confirms that in the as-deposited flake (connected to a multilayer area) most of the photocurrent is being generated in the thicker flake region. After laser trimming, scanning photocurrent microscopy shows how only the single-layer MoS2 region contributes to the photocurrent generation. The presented method is a direct-write and lithography-free (no need of resist or wet chemicals) alternative to reactive ion etching process to pattern the flakes that can be easily adopted by many research groups fabricating devices with MoS2 and similar two-dimensional materials.

Process-induced magnetic tunnel junction damage and its recovery for the development of spin–orbit torque magnetic random access memory

The generation of torques in heterostructures of heavy metals and ferromagnets (HM / FM) in spin–orbit torque magnetic random access memory (SOT-MRAM) makes them interesting for the development of magnetic memory technology. Currently, the emerging SOT-MRAM technology faces major challenges in etching based on current manufacturing tools. In that respect, we experimentally investigate the two different etching recipes (namely, CF-Etch, & NH-Etch) of the reactive ion etching (RIE) process on the performance of a Ta/CoFeB/MgO/Ta (hard mask) magnetic film stacks to develop the SOT-MRAM technology. The experimental results demonstrate that CF-Etch etches Ta very fast, and MgO etches very slowly. In contrast, NH-Etch etches those two materials at a comparable rate. Both etches are terminated before MgO is removed. Based on the experimental results, we found that the CF-Etch reduces the interfacial anisotropy of CoFeB/MgO films. Moreover, the CF-Etch also destroys the magnetic moment of CoFeB film, which further deteriorates after the annealing process. In contrast, the magnetic properties of the stack are only slightly affected when the NH-Etch recipe is used. We also discuss the advantages and disadvantages of these two recipes based on the experimental study. Finally, we developed the SOT-MRAM devices based on these two etching recipes of the RIE process to improve the etching yield of this technology. The current SOT-MRAM fabrication process enables a uniform etch stop on the thin tunnel barrier layer and the Ta heavy metal layer (HM). A wafer-level statistical study of SOT switching characteristics, including tunnel magnetoresistance (TMR), SOT switching thresholds, and parallel/antiparallel state resistances (RP/RAP), has been performed.