Etching Parameters Research Articles

Aspect ratio-dependent etching in silicon using XeF2: experimental investigation and comparative analysis with dry etching methods

Abstract Silicon machining plays a crucial role in shaping three-dimensional structures for Micro-Electro-Mechanical Systems (MEMS) applications. This study investigates Aspect Ratio Dependent Etching (ARDE) across various silicon etching processes, with a particular focus on Xenon Difluoride (XeF2) etching, in comparison to Reactive Ion Etching (RIE) and Deep Reactive Ion Etching (DRIE).By exploring different etching parameters, the study highlights the presence of ARDE in both plasma and non-plasma etching processes. Additionally, it is demonstrated that ARDE can be modeled by a saturating exponential function through experimental adjustment of parameters, enabling the prediction of etching profiles.

Inductively Coupled Plasma Reactive Ion Etching of (−201) β‐Ga2O3 Nano‐Fins

This study reports the effect of inductively coupled plasma reactive ion etching using a BCl3/Ar gas mixture on the sidewall taper angle (STA), etch rate, and surface morphology of (−201) β‐Ga2O3 substrates, as well as (−201)‐oriented β‐Ga2O3 films on sapphire, for nano‐fins of ≈200 nm width. Various etch parameters are systematically investigated for the β‐Ga2O3 films on sapphire, revealing that the STA is lower at high plasma density when chemical component increases, and the ion scattering decreases; achieving a STA of 1.5° ± 0.7°, accompanied by an etch rate of 114 nm min−1 and a reduction in surface roughness compared to before etching. Additionally, a strong positive correlation between the STA and the crystal orientation in the β‐Ga2O3 substrates is observed at lower plasma density, while a weak correlation is found between the STA and the crystal orientation at high plasma density. This study provides valuable insights for the fabrication of β‐Ga2O3 devices.

Impact of the Abrasive Solution Heating Process With Different Techniques on the Etching Parameters for the SSNTD (CN-85)

Abstract The presented work aims to compare and analyze the impact of the abrasive solution heating process using three different techniques on the etching parameters for the solid-state nuclear track detector (SSNTD) (CN-85). Water bath technique (WB) is using water as a conduction medium of heat transfer to heat the etching solution. The thermal oven technique (TO) is using air as a convection heat transfer medium to heat the etching solution. Finally, the micro-wave technique (MW) as electromagnetic radiation no need for a medium to heat the etching solution. That comparison will be achieved at different irradiation times to an Americium-241 source (241Am) of 5.486 MeV energy and 10 μCi activity as an alpha particle's emitter. Two irradiation times 10 s and 20 s are applied. Small pieces of CN-85 detectors (1 × 1) cm2 were used. CN-85 detector parameters of the etching process, with the three applying techniques (WB, TO, and MW), are estimated and compared. The obtained results from the three techniques are compared. The etching process time is developed to nearly 5 min for MW with heating by radiation mechanism compared to 25–35 min for etching techniques (WB and TO) with heating by conduction and convection mechanisms, respectively. The efficiency of MW technique with range of from 70% to 75% are five times greater than that for WB and TO techniques.

One-Step Dry-Etching Fabrication of Tunable Two-Hierarchical Nanostructures.

Two-hierarchical nanostructures, characterized by two distinct configurations along the height direction, exhibit immense potential for applications in various fields due to their significantly enhanced controllable degree compared to single-order structures. However, due to the limitations imposed by planar technology, the realization of two-hierarchical nanostructures encounters huge challenges. In this work, we developed a one-step etching method based on inductively coupled plasma reactive ion etching for two-hierarchical nanostructures. Thanks to the shrinking effect of the Cr mask and the generation of a passivation layer during etching, the target materials experienced two different states from vertical etching to shrink etching. Consequently, the achieved two-hierarchical nanostructure configuration features a cross-section of an upper triangle and a lower rectangle, showing higher controllable degrees compared to the one-order ones. Both the mask pattern and etching parameters play crucial roles, by which two-hierarchical structures with diversiform shapes can be constructed controllably. This method for two-hierarchical nanostructures offers advantages including excellent control over structural properties, high processing efficiency, uniformity across large areas, and universality in materials. This developed strategy not only presents a simple and rapid nanofabrication platform for realizing optoelectronic devices, but also provides innovative ideas for designing the next generation of high-performance devices.

Dry etch performance of Novolak-based negative e-beam resist

Electron beam lithography (EBL) is pivotal for micro- and nanoscale fabrication, offering sub-micron precision. This study explores the utilization of the Novolac-based negative resist AR-N 7520 for EBL and its potential as an etch mask for reactive ion etching (RIE) of silicon. Recent comparisons of negative EBL resists have revealed promising results for AR-N 7520 in terms of resolution and adaptability with other lithography techniques. In this article, we conduct an exploration of patterning of AR-N 7520 (new) for EBL, addressing key parameters in achieving optimal patterning fidelity. Furthermore, we investigate its compatibility with RIE processes, aiming to provide insights into its effectiveness as an etch mask for creating sub-micron silicon structures. Experimental results show that optimal e-beam dose with 100 kV exposure is 300–350 μC/cm2. Selectivity of around 9:1 can be achieved by optimizing etching parameters for a continuous etch and higher than 14:1 for a cyclic etch process.

Microstructuring of fused silica by laser-induced microplasma using a pyrographite target for phase optical elements fabrication

In this paper, we purpose to use laser-induced microplasma occurred from a pyrographite target by laser ablation for microstruturing of fused silica plate to fabricate phase optical elements. Laser parameters for erosive plasma torch formation and subsequent etching of fused silica were determined based on preliminary experimental studies and estimated energy calculations. The influence of the overlap coefficients in the focal spot on the reproducibility of etching depths results and the deviation accuracy of etching depths with the found laser parameters was experimentally studied. The best results in terms of accuracy (no more than 0.1 μm) in deviations of etching depths are achieved with the overlap coefficient of 0.5. Moreover, the paper presents estimated calculations of the speed and efficiency of ablation, as well as the coefficient of energy conversion from laser radiation to the ablation energy of fused silica, which was ∼ 0.25. Based on achieved results an attempt was made to fabricate the 6-sector SPP for the wavelength of 355 nm.

Etch Characteristics of Cobalt Thin Films in High Density Plasma of Cl2/O2/Ar Gas Mixture

Inductively coupled plasma reaction ion etching (ICP-RIE) of cobalt thin films patterned with SiO2 hard masks was performed using Cl2/O2/Ar gas mixture. The etch characteristics of cobalt films in Cl2/Ar gas were examined to determine the roles of Cl2 and O2, respectively. The etch rates and etch profiles of cobalt films were investigated by varying the O2 concentration in Cl2/O2/Ar gas mixture.In the optimized Cl2/Ar gas mixture, systematic etching of cobalt films was performed by changing the etch parameters including ICP RF power, DC-bias voltage, and process pressure. As the DC-bias voltage and process pressure was increased, the etch rate increased and the etch profile improved. Through the etching parameters variation experiment, the etching properties were investigated by adding O2 to Cl2/Ar under optimized conditions. X-ray photoelectron spectroscopy and optical emission spectroscopy were used to investigate the etch mechanism in the Cl2/O2/Ar gas mixture. In addition, scanning probe microscope was used to observe roughness on the etched cobalt surface. Finally, the etching of cobalt films patterned with nanometer-scale in the optimized Cl2/O2/Ar gas mixture was successfully achieved with good etch profile.AcknowledgmentThis research was supported by the Ministry of Trade, Industry & Energy (MOTIE) (20019504) and Korea Semiconductor Research Consortium (KSRC) support program for the development of future semiconductor devices. This work was supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0008458, HRD Program for Industrial Innovation).

Prediction of Femtosecond Laser Etching Parameters Based on a Backpropagation Neural Network with Grey Wolf Optimization Algorithm.

Investigating the optimal laser processing parameters for industrial purposes can be time-consuming. Moreover, an exact analytic model for this purpose has not yet been developed due to the complex mechanisms of laser processing. The main goal of this study was the development of a backpropagation neural network (BPNN) with a grey wolf optimization (GWO) algorithm for the quick and accurate prediction of multi-input laser etching parameters (energy, scanning velocity, and number of exposures) and multioutput surface characteristics (depth and width), as well as to assist engineers by reducing the time and energy require for the optimization process. The Keras application programming interface (API) Python library was used to develop a GWO-BPNN model for predictions of laser etching parameters. The experimental data were obtained by adopting a 30 W laser source. The GWO-BPNN model was trained and validated on experimental data including the laser processing parameters and the etching characterization results. The R2 score, mean absolute error (MAE), and mean squared error (MSE) were examined to evaluate the prediction precision of the model. The results showed that the GWO-BPNN model exhibited excellent accuracy in predicting all properties, with an R2 value higher than 0.90.

Pretreatments to bonding on enamel and dentin disorders: a systematic review.

This systematic review focuses on structural anomalies of enamel and dentin such as fluorosis (F), molar-incisor hypomineralization (MIH), amelogenesis imperfecta (AI), dentinogenesis imperfecta (DI), osteogenesis imperfecta (OI), and X-linked hypophosphatemia (XLH). These pathologies affect up to 31% of the population, posing challenges in the adhesion of direct restorations. The primary objective of this analysis is to examine the survival rate and/or bonding resistance of direct restorations on tissues affected by enamel and dentin disorders in humans. We aim to provide precise clinical recommendations for dentists to choose the appropriate bonding pretreatment for various enamel and dentin disorders. We systematically searched the medical literature to identify abstracts of interest indexed between 1993 and May 2024, from 4 databases (PubMed, PMC-PubMed, Web of Science and Cochrane Library). The results are reported following the PRISMA statement. The GRADE approach was used to assess the risk of bias. The two authors included 27 studies out of the 600 identified. The data extracted from these studies are highly heterogeneous, and the mentioned bonding protocols are all different. 15 articles pertain to F, 7 to MIH, 5 to AI, and none focus on HSPM, dentin disorders and XLH. We identified 12 pretreatments of enamel or dentin (7 for F, 2 for MIH, and 3 for AI), including 3 strong recommendations. Additional studies are necessary to confirm the effectiveness of certain pretreatments. In developmental enamel defects, the main recommendation we collected is to bond on enamel with an etch-and-rinse technique on F and MIH. Considerations with lower strength of evidence include a deproteinization step on enamel on F, MIH and AI and modifications of the etching parameters on F and AI. The research strategy was registered on the Prospero platform (CRD42023447502).

Study on Electrical and Mechanical Properties of Double-End Supported Elastic Substrate Prepared by Wet Etching Process.

Preparing elastic substrates as a carrier for dual-end supported nickel chromium thin film strain sensors is crucial. Wet etching is a vital microfabrication process widely used in producing microelectronic components for various applications. This article combines lithography and wet etching methods to microprocess the external dimensions and rectangular grooves of 304 stainless steel substrates. The single-factor variable method was used to explore the influence mechanism of FeCl3, HCl, HNO3, and temperature on the etching rate, etching factor, and etching surface roughness. The optimal etching parameter combination was summarized: an FeCl3 concentration of 350 g/L, HCl concentration of 150 mL/L, HNO3 concentration of 100 mL/L, and temperature of 40 °C. In addition, by comparing the surface morphology, microstructure, and chemical and mechanical properties of a 304 stainless steel substrate before and after etching treatment, it can be seen that the height difference of the substrate surface before and after etching is between 160 μm and -70 μm, which is basically consistent with the initial design of 0.2 mm. The results of an XPS analysis and Raman spectroscopy analysis both indicate that the surface C content increases after etching, and the corrosion resistance of the surface after etching decreases. The nano-hardness after etching increased by 26.4% compared to before, and the ζ value decreased by 7%. The combined XPS and Raman results indicate that the changes in surface mechanical properties of 304 stainless steel substrates after etching are mainly caused by the formation of micro-nanostructures, grain boundary density, and dislocations after wet etching. Compared with the initial rectangular substrate, the strain of the I-shaped substrate after wet etching increased by 3.5-4 times. The results of this study provide the preliminary process parameters for the wet etching of a 304 stainless steel substrate of a strain measuring force sensor and have certain guiding significance for the realization of simple steps and low cost of 304 stainless steel substrate micro-nano-processing.

Influence of Electrolyte Concentration on Metal Removal Rate and Surface Finish Quality in Electrochemical Machining Masking

Electrochemical machining (ECM) is a specialized and precise manufacturing technique involving selective metal removal to achieve the desired shape or form. This article’s primary focus is examining the technical facets associated with the procedure. The elements mentioned encompass the system’s design and optimization, the electrolyte solution’s careful selection, and the precise control of the etching parameters. When considering the overall framework, it is essential to consider important factors such as the concentration of electrolytes, the operational voltage, and the value of the current flowing through the system. The main objective of this study is to evaluate the influence of different concentrations of sodium chloride electrolyte on the metal removal rate (MRR). This will be achieved by utilizing a direct current power supply. The present investigation used aluminum, steel, and stainless steel materials as the substrate for experimentation. These materials were selected to have identical dimensions for the anode and cathode. The main objective of this study is to evaluate the influence of varying concentrations (0.5, 1, 1.5, and 2 mole/liter) of sodium chloride electrolyte on the material removal rate and surface roughness. The findings have been disclosed, revealing the utmost removal rate for aluminum, steel, and stainless-steel materials across all levels of electrolyte concentration. The experimental information is currently presented, related to the rates of metal removal at various electrolyte concentrations of 2 moles per liter. The rates of mass loss observed in aluminum are comparatively higher when compared to those surveyed in steel and stainless steel. The roughness of a machined surface is inversely proportional to the concentration of the electrolyte.

Oxygen-Terminated Polycrystalline Boron-Doped Diamond Superhydrophobic Surface with Excellent Mechanical and Thermal Stabilities.

Superhydrophobic surfaces are of great interest because of their remarkable properties. Due to its maximal hardness and chemical inertness, diamond film has great potential in fabricating robust superhydrophobic surfaces. In the present study, an oxygen-terminated polycrystalline boron-doped diamond (O-PBDD) superhydrophobic surface with micro/nano-hierarchical porous structures is developed. The preparation method is very simple, requiring only sputtering and dewetting procedures. The former involves sputtering gold and copper particles onto the hydrogen-terminated polycrystalline boron-doped diamond (H-PBDD) to form gold/copper films, whereas the latter involves placing the samples in an atmospheric tube furnace to form hierarchical pores. By controlling the etching parameters, the wettability of the O-PBDD surface can be adjusted from hydrophilic to superhydrophobic, which is significantly different to the normal hydrophilicity feature of O-termination diamonds. The water contact angle of the obtained O-PBDD surface can reach 165 ± 5°, which is higher than the superhydrophobic diamond surfaces that are reported in the literature. In addition, the O-PBDD surface exhibits excellent durability; it can maintain satisfactory superhydrophobicity even after high-pressure, high-temperature, and sandpaper friction tests. This work provides a new research direction for fabricating robust superhydrophobic materials with diamond film.

The Synthesis and Assembly Mechanism of Micro/Nano-Sized Polystyrene Spheres and Their Application in Subwavelength Structures.

The following study involved the utilization of dispersion polymerization to synthesize micron/nano-sized polystyrene (PS) spheres, which were then deposited onto a silicon substrate using the floating assembly method to form a long-range monolayer. Subsequently, dry etching techniques were utilized to create subwavelength structures. The adjustment of the stabilizer polyvinylpyrrolidone (PVP), together with changes in the monomer concentration, yielded PS spheres ranging from 500 nm to 5.6 μm in diameter. These PS spheres were suspended in a mixture of alcohol and deionized water before being arranged using the floating assembly method. The resulting tightly packed particle arrangement is attributed to van der Waals forces, Coulomb electrostatic forces between the PS spheres, and surface tension effects. The interplay of these forces was analyzed to comprehend the resulting structure. Dry etching, utilizing the PS spheres as masks, enabled the exploration of the effects of etching parameters on the resultant structures. Unlike traditional dry etching methods controlling RF power and etching gases, in the present study, we focused on adjusting the oxygen flow rate to achieve cylindrical, conical, and parabolic etched structures.

Fabrication of three-dimensional microstructures on GaN surfaces through the integration of femtosecond laser ablation and ICP etching

Gallium nitride (GaN) surface microstructures are crucial for enhancing the performance and reliability of high-power devices. However, the direct fabrication of patterned three-dimensional (3D) microstructures on GaN surfaces remains a significant challenge. This paper introduces an innovative approach, employing a maskless femtosecond laser combined with inductively coupled plasma (ICP) etching, to efficiently fabricate petal-shaped 3D microstructures on GaN surfaces. By fine-tuning the ICP etching and femtosecond laser parameters, we have obtained the regularities of the dimensional variations of these 3D microstructures. Additionally, our investigation reveals that the design of microstructural concavity and convexity characteristics can be flexibly manipulated by controlling the ICP etching rate, which is influenced by the oxide content in the laser-modified zone. This study presents a novel method for straightforward fabrication of microstructures on gallium nitride surfaces.

Tuning the Optical Anisotropy in Gradient Porous Germanium on Si Substrate

AbstractPorous semiconductors have garnered significant attention owing to their distinctive physical and chemical properties. In this study, optical anisotropy is presented in porous germanium (PGe) on a Si (001) substrate. Both n‐ and p‐type PGe, achieved through bipolar electrochemical etching, exhibit optical anisotropy along the Ge <001> direction, as determined by spectroscopic ellipsometry. Birefringence and depolarization factors are controllable by adjusting the etching parameters and doping concentration of the epitaxial Ge layer. The gradient porosity and pore distribution in PGe can be well captured by the optical models. The findings of optical anisotropy in PGe‐on‐Si hold promise for applications in optical elements or sensors for gas or biomolecules.

Fabrication of Bulk Tungsten Microstructure Arrays for Hydrophobic Metallic Surfaces Using Inductively Coupled Plasma Deep Etching.

Hydrophobic surfaces have attracted great attention due to their ability to repel water, and metallic surfaces are particularly significant as they have several benefits, for example they self-clean and do not corrode in marine environments, but also have several applications in the aircraft, building and automobile industries. Tungsten is an ideal material for metallic surfaces due to its remarkable mechanical properties. However, conventional micromachining methods of micro- or nanostructures, including mechanical fabrication and laser and wet etching are incapable of balancing functionality, consistency and cost. Inspired by the etching process of silicon, deep etching of bulk tungsten has been developed to achieve versatile microstructures with the advantages of high efficiency, large scale and low cost. In this article, fabrication methods of tungsten-based hydrophobic surfaces using an ICP deep etching process were proposed. Micro- or hierarchical structure arrays with controllable sidewall profiles were fabricated by optimizing etching parameters, which then exhibited hydrophobicity with contact angles of up to 131.8°.

Optimization of waveguide fabrication processes in lithium-niobate-on-insulator platform.

Lithium niobate (LN) is used in diverse applications such as spectroscopy, remote sensing, and quantum communications. The emergence of lithium-niobate-on-insulator (LNOI) technology and its commercial accessibility represent significant milestones. This technology aids in harnessing the full potential of LN's properties, such as achieving tight mode confinement and strong overlap with applied electric fields, which has enabled LNOI-based electro-optic modulators to have ultra-broad bandwidths with low-voltage operation and low power consumption. Consequently, LNOI devices are emerging as competitive contenders in the integrated photonics landscape. However, the nanofabrication, particularly LN etching, presents a notable challenge. LN is hard, dense, and chemically inert. It has anisotropic etch behavior and a propensity to produce material redeposition during the reactive-ion plasma etch process. These factors make fabricating low-loss LNOI waveguides (WGs) challenging. Recognizing the pivotal role of addressing these fabrication challenges for obtaining low-loss WGs, our research focuses on a systematic study of various process steps in fabricating LNOI WGs and other photonic structures. In particular, our study involves (i) careful selection of hard mask materials, (ii) optimization of inductively coupled plasma etch parameters, and finally, (iii) determining the optimal post-etch cleaning approach to remove redeposited material on the sidewalls of the etched photonic structures. Using the recipe established, we realized optical WGs with total (propagation and coupling) loss value of -10.5 dB, comparable to established values found in the literature. Our findings broaden our understanding of optimizing fabrication processes for low-loss lithium-niobate waveguides and can serve as an accessible resource in advancing LNOI technology.

Influence of CoSi Oxidation and Passivation During Silicide Selective Etching on Junction Leakage: Applications to Schottky Diodes Devices

For new analogic microelectronic circuits development based on non-linear devices such as Schottky diodes formed in Si active regions, new Co-silicide integrations are required to reduce junction leakages. To gather targeted device requirements, precise Co silicide/Si interface optimization and a limited silicide formation at the active edges is needed. The selective etching during the “Salicide” process plays a real role in the oxidation and/or passivation of the silicide layer. Here, we propose a systematic study including a very large spectrum of experiments around the main parameters of CoSi selective etching. The main conclusions are (1) diode leakages are directly linked to SiO2 layer thickness formed during the SC1 dispense or by air exposure over the CoSi layer, (2) significant effect of dispense flow on SiO2 formation is measured through X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry characterizations; (3) optimized diode leakages together with contact resistances are then demonstrated for low SC1 delivery flow and long dispense time; and (4) major changes in final CoSi2 layer morphology and silicide/silicon interface are observed by transmission electron microscopy-energy-dispersive X-ray analyses for different selective etching processes, which are potentially explained by enrichment in Co atoms at CoSi/Si during SiO2 overlayer growth.

Influence of Growth Process on Suppression of Surface Morphological Defects in 4H-SiC Homoepitaxial Layers.

To address surface morphological defects that have a destructive effect on the epitaxial wafer from the aspect of 4H-SiC epitaxial growth, this study thoroughly examined many key factors that affect the density of defects in 4H-SiC epitaxial wafer, including the ratio of carbon to silicon, growth time, application of a buffer layer, hydrogen etching and other process parameters. Through systematic experimental verification and data analysis, it was verified that when the carbon-silicon ratio was accurately controlled at 0.72, the density of defects in the epitaxial wafer was the lowest, and its surface flatness showed the best state. In addition, it was found that the growth of the buffer layer under specific conditions could effectively reduce defects, especially surface morphology defects. This provides a new idea and method for improving the surface quality of epitaxial wafers. At the same time, we also studied the influence of hydrogen etching on the quality of epitaxial wafers. The experimental results show that proper hydrogen etching can optimize surface quality, but excessive etching may lead to the exposure of substrate defects. Therefore, it is necessary to carefully control the conditions of hydrogen etching in practical applications to avoid adverse effects. These findings have important guiding significance for optimizing the quality of epitaxial wafers.

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

Boron nitride-silicon dioxide (BN–SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN–SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN–SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δ m) of the two BN–SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δ m values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN–SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.