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Deep reactive-ion etching (DRIE) is commonly used for high aspect ratio silicon micromachining. However, scalloping, which is the result of the alternating Bosch process of DRIE, can cause many problems in the subsequent process and degrade device performance. In this work, we propose a simple and effective method to smoothen the scalloping of DRIE trenches. The proposed method utilizes sidewall dry etching by reactive-ion etching (RIE) based sulfur hexafluoride (SF6) plasmas, following the DRIE process. To investigate the effect of the etch parameter on the scallop smoothing effect, the radio frequency (RF) power and gas flow are controlled. After the RIE treatment, the scallop smoothing effects were evaluated by measuring the average scallop depth under each condition. The scallop depth was reduced by 91% after implementing the scallop smoothing technique using RIE. Thus, our smoothening method based on SF6 plasmas would provide broad availabilities and applicability in silicon micromachining with the simple low-temperature process.

HighlightsHigh-density out-of-plane microneedle arrays were fabricated with a single photolithography and two deep reactive ion etching (DRIE) steps in anisotropic and isotropic modes, respectively.Microneedles in various heights were monolithically created by the identical DRIE processes and scanning electron microscopy images showed extremely sharp sub-micron (~145-nm-wide) tip.Diverse cross-sectional shapes of microneedles were implemented by altering photomask patterns.Out-of-plane microneedle structures are widely used in various applications such as transcutaneous drug delivery and neural signal recording for brain machine interface. This work presents a novel but simple method to fabricate high-density silicon (Si) microneedle arrays with various heights and diverse cross-sectional shapes depending on photomask pattern designs. The proposed fabrication method is composed of a single photolithography and two subsequent deep reactive ion etching (DRIE) steps. First, a photoresist layer was patterned on a Si substrate to define areas to be etched, which will eventually determine the final location and shape of each individual microneedle. Then, the 1st DRIE step created deep trenches with a highly anisotropic etching of the Si substrate. Subsequently, the photoresist was removed for more isotropic etching; the 2nd DRIE isolated and sharpened microneedles from the predefined trench structures. Depending on diverse photomask designs, the 2nd DRIE formed arrays of microneedles that have various height distributions, as well as diverse cross-sectional shapes across the substrate. With these simple steps, high-aspect ratio microneedles were created in the high density of up to 625 microneedles mm−2 on a Si wafer. Insertion tests showed a small force as low as ~ 172 µN/microneedle is required for microneedle arrays to penetrate the dura mater of a mouse brain. To demonstrate a feasibility of drug delivery application, we also implemented silk microneedle arrays using molding processes. The fabrication method of the present study is expected to be broadly applicable to create microneedle structures for drug delivery, neuroprosthetic devices, and so on.

This paper presents processes for glass micromachining, including sandblast, wet etching, reactive ion etching (RIE), and glass reflow techniques. The advantages as well as disadvantages of each method are presented and discussed in light of the experiments. Sandblast and wet etching techniques are simple processes but face difficulties in small and high-aspect-ratio structures. A sandblasted 2 cm × 2 cm Tempax glass wafer with an etching depth of approximately 150 µm is demonstrated. The Tempax glass structure with an etching depth and sides of approximately 20 μm was observed via the wet etching process. The most important aspect of this work was to develop RIE and glass reflow techniques. The current challenges of these methods are addressed here. Deep Tempax glass pillars having a smooth surface, vertical shapes, and a high aspect ratio of 10 with 1-μm-diameter glass pillars, a 2-μm pitch, and a 10-μm etched depth were achieved via the RIE technique. Through-silicon wafer interconnects, embedded inside the Tempax glass, are successfully demonstrated via the glass reflow technique. Glass reflow into large cavities (larger than 100 μm), a micro-trench (0.8-μm wide trench), and a micro-capillary (1-μm diameter) are investigated. An additional optimization of process flow was performed for glass penetration into micro-scale patterns.

The research field of metasurfaces has attracted considerable attention in recent years due to its high potential to achieve flat, ultrathin optical devices of high performance. Metasurfaces, consisting of artificial patterns of subwavelength dimensions, often require fabrication techniques with high aspect ratios (HARs). Bosch and Cryogenic methods are the best etching candidates of industrial relevance towards the fabrication of these nanostructures. In this paper, we present the fabrication of Silicon (Si) metalenses by the UV-Nanoimprint Lithography method and cryogenic Deep Reactive Ion Etching (DRIE) process and compare the results with the same structures manufactured by Bosch DRIE both in terms of technological achievements and lens efficiencies. The Cryo- and Bosch-etched lenses attain efficiencies of around 39% at wavelength λ = 1.50 µm and λ = 1.45 µm against a theoretical level of around 61% (for Si pillars on a Si substrate), respectively, and process modifications are suggested towards raising the efficiencies further. Our results indicate that some sidewall surface roughness of the Bosch DRIE is acceptable in metalense fabrication, as even significant sidewall surface roughness in a non-optimized Bosch process yields reasonable efficiency levels.

Deep reactive ion etching (DRIE) with the Bosch process is one of the key procedures used to manufacture micron-sized structures for MEMS and microfluidic applications in silicon and, hence, of increasing importance for miniaturisation in biomedical research. While guaranteeing high aspect ratio structures and providing high design flexibility, the etching procedure suffers from reactive ion etching lag and often relies on complex oxide masks to enable deep etching. The reactive ion etching lag, leading to reduced etch depths for features exceeding an aspect ratio of 1:1, typically causes a height difference of above 10% for structures with aspect ratios ranging from 2.5:1 to 10:1, and, therefore, can significantly influence subsequent device functionality. In this work, we introduce an optimised two-step Bosch process that reduces the etch lag to below 1.5%. Furthermore, we demonstrate an improved three-step Bosch process, allowing the fabrication of structures with 6 μm width at depths up to 180 μm while maintaining their stability.

Inductively coupled plasma–reactive etching (ICP-RIE) of InGaZnO (IGZO) thin films was studied with variations in gas mixtures of hydrochloride (HCl) and argon (Ar). The dry etching characteristics of the IGZO films were investigated according to radiofrequency bias power, gas mixing ratio, and chamber pressure. The IGZO film showed an excellent etch rate of 83.2 nm/min from an optimized etching condition such as a plasma power of 100 W, process pressure of 3 mTorr, and HCl ratio of 75% (HCl:Ar at 30 sccm:10 sccm). In addition, this ICP-RIE etching condition with a high HCl composition ratio at a moderate RIE power of 100 W showed a low etched pattern skew and low photoresist damage on the IGZO patterns. It also provided excellent surface morphology of the SiO2 film underneath after the entire dry etching of the IGZO layer. The IGZO thin film as an active layer was successfully patterned under the ICP-RIE dry etching under the HCl-Ar gas mixture, affording an excellent electrical characteristic in the resultant top-gate IGZO thin-film transistor.

Reactive ion etching (RIE) with fluorocarbon plasma is a facile method to tracelessly remove the subsurface damage layer of fused silica but has the drawback of unsatisfactory improvement in laser damage resistance due to the induction of secondary defects. This work proposes to incorporate O2 into the CHF3/Ar feedstock of RIE to suppress the formation of secondary defects during the etching process. Experimental results confirm that both the chemical structural defects, such as oxygen-deficient center (ODC) and non-bridging oxygen hole center (NBOHC) defects, and the impurity element defects, such as fluorine, are significantly reduced with this method. Laser-induced damage resistance is consequently greatly improved, with the 0% probability damage threshold increasing by 121% compared to the originally polished sample and by 41% compared to the sample treated with conventional RIE.

With aging, disability of the body can easily occur because the function of the body is degraded. Especially, swallowing disorder is regarded as a crucial issue because patients cannot obtain the nutrients from food by swallowing it. Hence, the rehabilitation of swallowing disorder is urgently required. However, the conventional device for swallowing rehabilitation has shown some limitations due to its external power source and internal circuit. Herein, a self-powered triboelectric nanogenerator for swallowing rehabilitation (TSR) is proposed. To increase the electrical output and pressure sensitivity of the TSR, the tilted reactive ion etching is conducted and the electrical output and pressure sensitivity are increased by 206% and 370%, respectively. The effect of the tilted reactive ion etching into the electrical output generated from the TSR is systematically analyzed. When the tongue is pressing, licking, and holding the TSR, each motion is successfully detected through the proposed TSR. Based on these results, the smart swallowing rehabilitation monitoring system (SSRMS) is implemented as the application and the SSRMS could successfully detect the pressing by the tongue. Considering these results, the SSRMS can be expected to be utilized as a promising smart swallowing rehabilitation monitoring system in near future.

During deep reactive ion etching (DRIE), microscale etch masks with small opening such as trenches or holes suffer from limited aspect ratio because diffusion of reactive ions and free radicals become progressively difficult as the number of DRIE cycle increases. For this reason, high aspect ratio structures of microscale trenches or holes are not readily available with standard DRIE recipes and microscale holes are more problematic than trenches due to omnidirectional confinement. In this letter, we propose an optimization for fabrication of high aspect ratio microscale hole arrays with an improved cross-sectional etch profile. Bias voltage and inductively coupled plasma power are considered as optimization parameters to promote the bottom etching of the high aspect ratio hole array. In addition, flow rates of octafluorocyclobutane (C4F8) and sulfur hexafluoride (SF6) for passivation and depassivation steps, respectively, are considered as optimization parameters to reduce the etch undercut. As a result of optimization, the aspect ratio of 20 is achieved for 1.3 μm-diameter hole array and etch area reduction at the bottom relative to the top is improved to 21%.

This study introduces a novel Vertical Sense Mass (VSM) design for MEMS gyroscope sensors, addressing the growing demand for miniaturization and enhanced performance in navigation and industrial applications. Leveraging Deep Reactive Ion Etching (DRIE) technology, the VSM design significantly reduces size while offering superior performance compared to traditional planar configurations. Comprehensive theoretical analysis and comparative evaluations demonstrate the VSM design’s advantages across critical metrics, including sensitivity, bandwidth, noise, and device footprint. This advancement represents a substantial leap in MEMS gyroscope technology, enabling high-performance sensing in compact form factors. Specifically, the VSM design achieves a 30 % reduction in sense mass area, resulting in a 36 % smaller sensor footprint. This size reduction is coupled with a significant improvement in the overall Performance Metric (PM), with the VSM design exhibiting a PM of 1090 mHz/dps2μm2 compared to 70.7 mHz/dps2μm2 for the planar design. These analytical findings are supported by existing literature, further validating the superior performance of the proposed VSM design. The detailed fabrication process flow of the structure is presented, and successful fabrication of thick-proof-mass structures using DRIE confirms the feasibility of this innovative approach. These results highlight the potential of the VSM design for future applications requiring compact, high-performance gyroscope sensors.