Plasma Etching Research Articles

Surface evolution mechanism for atomic-scale smoothing of Si via atmospheric pressure plasma etching

Atmospheric plasma etching-based machining methods generally suffer from surface roughness deterioration. To achieve an atomic-scale smooth surface of Si via purely plasma etching, clarifying the etching evolution and mechanism is essential. In this study, we study surface evolution and smoothening mechanisms from the perspective of plasma etching modes comprehensively. The morphology and roughness evolutions of isotropic, orientation-selective, and atom-selective etching are investigated, respectively. The semi-finishing effect is realized through the growing and merging of hemispherical pits during isotropic etching, with the surface roughness being reduced from 103 nm to 0.79 nm. Orientation-selective etching is a roughening process, transforming square-opening pits into pyramid structures. Under the atom-selective mode, an atomically smooth surface with Sa 0.17 nm can be obtained. The top-down smoothing process of atom-selective is much more efficient than isotropic etching. Atom-selective etching with a maximum removal rate of 22 μm/min enables the rapid thinning of Si substrate thickness from 715 μm to 90.4 μm within 45 min. Additionally, atom-selective etching is a universal polishing approach regardless of pre-processed methods and is a damage-less process. This paper provides a promising strategy for atomic and close-to-atomic scale manufacturing.

Low-temperature etching of silicon oxide and silicon nitride with hydrogen fluoride

Etching of high aspect ratio features into alternating SiO2 and SiN layers is an enabling technology for the manufacturing of 3D NAND flash memories. In this paper, we study a low-temperature or cryo plasma etch process, which utilizes HF gas together with other gas additives. Compared with a low-temperature process that uses separate fluorine and hydrogen gases, the etching rate of the SiO2/SiN stack doubles. Both materials etch faster with this so-called second generation cryo etch process. Pure HF plasma enhances the SiN etching rate, while SiO2 requires an additional fluorine source such as PF3 to etch meaningfully. The insertion of H2O plasma steps into the second generation cryo etch process boosts the SiN etching rate by a factor of 2.4, while SiO2 etches only 1.3 times faster. We observe a rate enhancing effect of H2O coadsorption in thermal etching experiments of SiN with HF. Ammonium fluorosilicate (AFS) plays a salient role in etching of SiN with HF with and without plasma. AFS appears weakened in the presence of H2O. Density functional theory calculations confirm the reduction of the bonding energy when NH4F in AFS is replaced by H2O.

Poly acrylic acid patterning by electron beam lithography

Poly acrylic acid (PAA) is a polymer and a derivative of acrylic acid that is a superabsorbent, being able to absorb and retain water, and swell many times beyond its original volume. This property classifies it into a group of polymers called hydrogels. Hydrogels are being investigated in emerging applications such as drug delivery, biosensors, tissue engineering, wound healing bandages, and more. The ability to lithographically pattern hydrogel materials to specific dimensions at the micro and nanoscales can be very useful in devices and sensors. Limited work has been done on characterizing PAA for lithographic purposes, and so, this work investigates the ability to pattern PAA by electron beam lithography (EBL). PAA is interesting in that its carrier solvent, developer, and remover are all water alone, which may make it attractive for processes or materials that cannot tolerate solvents, acids, and bases used with other common EBL resists. PAA behaves as a negative tone resist with a relatively low base dose of 75 μC/cm2 at 100 kV acceleration voltage. The resolution is limited to 1.8 μm due to a low contrast of 1.29. However, PAA may still have many uses at that resolution where the positioning and dimension control of a hydrogel could be useful. Furthermore, PAA can successfully be used for pattern transfer with either a metal liftoff process or a silicon plasma etch.

Digital Etching of Molybdenum Interconnects Using Plasma Oxidation

AbstractMolybdenum (Mo) has a high potential of becoming the material of choice for sub‐10 nm scale metal structures in future integrated circuits (ICs). Manufacturing at this scale requires exceptional precision and consistency, so many metal processing techniques must be reconsidered. In particular, present direct wet chemical etching methods produce anisotropic etching profiles with significant surface roughness, which can be detrimental to device performance. Here, it is shown that polycrystalline Mo nanowires can be etched uniformly using a cyclic two‐step “digital” method: the metal surface is first oxidized with isotropic oxygen plasma to form a layer of MoO3, which is then selectively removed using either wet chemical or dry isotropic plasma etching. These two steps are repeated in cycles until the intended metal recess is achieved. High uniformity of plasma oxidation defines the etching uniformity, and small metal recess per cycle (typically 1–2 nm) provides precise control over the etching depth. This method can replace wet etching where high etching precision is needed, enabling the reliable manufacturing of nanoscale metal interconnects.

Mechanochemical Damage Self‐Repairable Photothermal Anti/De‐Icing Superhydrophobic Coating by Dynamic Bonding Phase‐Change Fillers with the Matrix

AbstractThe development of robust superhydrophobic coatings with the capacity for self‐healing against mechanochemical damage is pivotal for their practical deployment. This study develops a physically and chemically self‐healing superhydrophobic coating with exceptional durability for anti‐icing applications using a simple spray coating method. This is achieved by incorporating phase‐change fillers into a dynamic cross‐linked matrix via dynamic imine bonds. Specifically, oleylamine (ODA) is encapsulated within rigid diatomite nanopores and modified with dopamine (DOA), significantly enhancing the grafting efficiency of aminopropyl‐terminated polydimethylsiloxane (NH₂‐PDMS‐NH₂) (N‐DOA). The incorporation of 15% N‐DOA increases the water contact angle (WCA) of the acrylic resin/aminopropyl‐terminated polydimethylsiloxane (AR/NH₂‐PDMS‐NH₂) matrix to 159.7° and reduces the sliding angle (SA) to 2.9°, while also improving the mechanical durability of coating to withstand 600 abrasion cycles. The dynamic imine bonds between NH₂‐PDMS‐NH₂ and trimesic acid (BTC) facilitate the mobility of N‐DOA and NH₂‐PDMS‐NH₂, enabling rapid recovery of superhydrophobic properties and low ice adhesion strength after abrasions, scratches, oxygen plasma etching, and multiple de‐icing cycles due to the synergistic phase‐change effect of ODA. Thus, the self‐healing coating produced via this simple spray method presents a novel approach for superhydrophobic coatings in anti‐icing applications.

Fabrication and electroadhesion properties of parylene-coated carbon fiber arrays

Parylene-coated carbon fiber (CF) arrays with tunable inclination angles and heights were fabricated using oxygen plasma etching of composite wafers with embedded parallel CFs, followed by parylene coating via chemical vapor deposition. The effective elastic modulus of the CF arrays was found to decrease approximately in proportion to the square of the fiber length (5-60μm), with the parylene coating (∼2μm) further slightly reducing the modulus. Both experimental measurements and finite element simulations indicated that CF arrays with inclination angles below 75° exhibit ideal contact with glass wafers during electrostatic adhesion. However, the measured electrostatic adhesion between CF arrays and A4 paper was significantly lower than the predicted value for ideal contact, likely due to the porous nature of the paper. Electrostatic chuck prototypes based on the parylene-coated CF arrays demonstrated effective pick-and-place capabilities for A4 paper, plastic films, and glass wafers at voltages ranging from 500 to 900 V, without causing surface damage or leaving residue. These results highlight the potential of the parylene-coated CF arrays for applications in high-precision manufacturing and automated handling systems.

Towards atomic-scale smooth surface manufacturing of β-Ga2O3 via highly efficient atmospheric plasma etching

Abstract The highly efficient manufacturing of atomic-scale smooth β-Ga2O3 surface is fairly challenging because β-Ga2O3 is a typical difficult-to-machine material. In this study, a novel plasma dry etching method named plasma-based atom-selective etching (PASE) is proposed to achieve the highly efficient, atomic-scale, and damage-free polishing of β-Ga2O3. The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga2O3. The core of PASE polishing of β-Ga2O3 is the remarkable lateral etching effect, which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition. As revealed by density functional theory-based calculations, the intrinsic difference in the etching energy barrier of atoms at the step edge (2.36 eV) and in the terrace plane (4.37 eV) determines their difference in the etching rate, and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature. The polishing of β-Ga2O3 based on the lateral etching effect is further verified in the etching experiments. The Sa roughness of β-Ga2O3 (001) substrate is decreased from 14.8 to 0.057 nm within 120 s, and the corresponding material removal rate reaches up to 20.96 μm/min. The polished β-Ga2O3 displays significantly improved crystalline quality and photoluminescence intensity, and the polishing effect of PASE is independent of the crystal faces of β-Ga2O3. In addition, the competition between chemical etching and physical reconstruction, which is determined by temperature and greatly affects the surface state of β-Ga2O3, is deeply studied for the first time. These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga2O3 via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga2O3.

Exploring effects of plasma surface engineering on cellulose nanofilms via broadband THz spectroscopy

For the extended ultra-wideband THz band up to 10 THz and beyond, materials with different functional properties are required. In addition, the THz shielding devices require the desired thickness for different shielding effects, which can be tailored by the surface functionalities. Here, a plasma-assisted soft chemistry approach was used to tailor the cellulose nanofibrils (CNFs), and the effects of plasma surface treatment were investigated using non-destructive terahertz time-domain spectroscopy (THz-TDS). CNFs with three different thicknesses were investigated as a function of mild and strong plasma treatment. The ultra-broadband THz-TDS evaluation of CNF films overcomes the challenge by surpassing the conventional low-frequency THz-TDS measurements and reveals many characteristic THz features of CNF at 2.1, 3.1, 5.1, 7.0, 10.3 and 10.9 THz. THz-TDS analysis indicates thinning of CNF after plasma treatment due to the plasma etching effect. At the same time, the microcrystalline properties of the CNF samples remain intact even after significant surface modification under plasma carbonisation conditions. Apart from this, the studies proposed the required minimum thickness for THz shielding applications based on the optical parameters and THz properties derived from the plasma-treated CNF structures, which could be used to define the thickness of sustainable shielding materials for THz devices.

Diamond etching with near-zero micromasking

The outstanding material properties of single-crystal diamond have been the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. Etching and patterning diamond have proven challenging due to the hardness and chemical resistance of the material. In this work, the patterned etching process of single-crystal diamond has been investigated using the inductively coupled plasma etching technique. In order to avoid the micromasking phenomenon caused by the metal mask, this paper adopts the Ar/O2–Ar/Cl2/BCl3 two-step cycle etching process and investigates the effect of the Cl2/BCl3 gas ratio on the bottom morphology of single-crystal diamond grid grooves. A theoretical explanation is provided for the use of chlorine-based gases to eliminate micromasking and achieve a smooth etching surface. Finally, an Ar/O₂-Ar/Cl₂/BCl3 cyclic etching process for patterning single-crystal diamond with near-zero micromasking has been developed.

Hydrofluoroethane plasma etching of SiN, SiO2, and poly-Si films with CHF2CF3, CF3CH3, and CHF2CH3

Hydrofluoroethane plasma etching of SiN, SiO2, and poly-Si films with CHF2CF3, CF3CH3, and CHF2CH3

Controlling synthesis of defect state lignin-derived carbon and application for U(VI) removal from aqueous solution: Effects of oxygen-defect and grain-size

Lignin has deemed to be the main polluting component of paper industry wastewater. But developing a potential strategy for utilization of lignin is a challenges problem. Lignin derived materials present potential performance for heavy metal wastewater treatment due to their unique physicochemical properties, and were found to be promising candidate materials in U(VI) removal. However, it is still lacking of a comprehensive understanding that the influences of surface oxygen-defect and grain-size on U(VI) removal processes. Here, using lignin as the raw material, combining plasma treatment technology to prepare defect states Lignin Derived Carbon (LDC), and exploring the influences of surface oxygen-defect and grain-size on their removal U(VI) process. The results indicated that with the reducing of LDC particle size (from ∼4 to ∼ 1 μm), the removal performance of U(VI) was improved. And the U(VI) removal performance of LDC was further improved by introducing of oxygen defect via H2 plasma etch. The characterization analysis of defect states LDC before and after reaction with U(VI) shown that the U(VI) removal mechanism was dominated by defects site complexation. These finding provide deep insight into the recycling of industrial solid wastes lignin and improving of U(VI) removal performance via defect controlling technology.

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.

Recent Advances in Black Silicon Surface Modification for Enhanced Light Trapping in Photodetectors

The intricate nanostructured surface of black silicon (BSi) has advanced photodetector technology by enhancing light absorption. Herein, we delve into the latest advancements in BSi surface modification techniques, specifically focusing on their profound impact on light trapping and resultant photodetector performance improvement. Established methods such as metal-assisted chemical etching, electrochemical etching, reactive ion etching, plasma etching, and laser ablation are comprehensively analyzed, delving into their mechanisms and highlighting their respective advantages and limitations. We also explore the impact of BSi on the emerging applications in silicon (Si)-based photodetectors, showcasing their potential for pushing the boundaries of light-trapping efficiency. Throughout this review, we critically evaluate the trade-offs between fabrication complexity and performance enhancement, providing valuable insights for future development in this rapidly evolving field. This knowledge on the BSi surface modification and its applications in photodetectors can play a crucial role in future implementations to substantially boost light trapping and the performance of Si-based optical detection devices consequently.

Alternative Treatments for Zirconium Oxide to Compare Commonly Used Surface Treatments to Determine Which Has the Least Effect on the Phase Transformation.

Traditional mechanical processing of zirconium leads to an unfavorable transformation, from a metastable tetragonal phase to a monoclinic phase (t→m), which weakens the structure of the material and subsequently leads to damage to the prosthetic restoration. The aim of this research is to compare commonly used surface treatments to determine which has the least effect on t→m. Thirty cylindrical samples made of sintered zirconium were divided into six groups based on the following treatments: polishing, grinding, sandblasting, chemical etching, laser structuring or dry plasma etching. After surface treatment, the samples were subjected to the following tests: X-Ray Diffraction, microscopic examination, surface wettability and surface roughness measurements. Chemical etching, laser structuring and plasma etching significantly reduce the content of the monoclinic phase. All surface treatments significantly reduced the final amount of the monoclinic phase. However, chemical etching did not provide sufficient surface roughness. Both laser and plasma processing offer the advantage of creating structural patterns on the surface of elements. However, as plasma etching requires a mask to obtain the appropriate pattern on the surface, it seems that laser processing offers more and varied structuring possibilities. Laser structuring is easier to control and more economical than the other methods.

Passivating and low damaging plasma etching of GaN using Cl2 and SiCl4 for recessed gate MOSc-HEMT devices

Passivating and low damaging plasma etching of GaN using Cl2 and SiCl4 for recessed gate MOSc-HEMT devices

Marangoni flow-guided molecular accumulation for sensitive and rapid SERS detection of phthalates

Public attention has been emerging for the prevention and assessment of healthcare risks from phthalate esters (PAEs) in daily life. For the effective detection of small environmentally hazardous materials, we suggest two major points: i) the formation of high-density hotspots and ii) the delivery of molecules to the activated plasmonic regions. In this study, we developed a method for laser-induced Marangoni flow in cotton fabric (CF) nanopillars (NPs) deposited with Au (Au/CFNPs) for the detection of PAEs by surface-enhanced Raman spectroscopy (SERS). We optimized the performance of the Au/CFNP platforms by adjusting both the maskless plasma etching time and the Au deposition thickness. Narrow (∼8 nm) and populated hotspots were achieved at an Ar plasma treatment time of 30 s and a Au thickness of 150 nm. The molecular behaviors were observed via real-time monitoring of SERS signals. Under continuous laser illumination, Marangoni radial convection flow became predominant over the outward capillary force, resulting in molecular accumulation in the detection areas. For small probe dyes and PAEs, the maximum intensities were achieved within 80 s after the injection of analytes and their signal fluctuations were estimated to have a relative standard deviation of < 10 %, which indicated sensitive and reproducible sensing. The prediction of PAEs extracted from the actual samples was investigated on the basis of a model used to quantitatively fit reference samples and the results were compared with those obtained by high-performance liquid chromatography. The results demonstrated that the combination of densified hotspots on three-dimensional porous substrates and laser-induced Marangoni flow is highly desirable for on-site early screening assays for low-quantity harmful materials present in surrounding environments.

Research on wafer-level SiC microgroove array process via integrated molding-etching process

Silicon carbide (SiC) microgroove arrays (MGAs) play a pivotal role as optical components in modern optical engineering. This paper introduces an innovative approach for the fabrication of MGAs on hard materials. This method integrates hot embossing (HE) and inductively coupled plasma (ICP), utilizing polydimethylsiloxane (PDMS) as the intermediary mold due to its excellent demolding performance and shape replication qualities. The process involves transferring the MGAs from the Ni-P master mold to the PDMS mold, followed by replication onto the photoresist surface by hot embossing. Subsequently, the MGAs on the photoresist mask is etched into the hard substrate material using ICP etching. For efficient customization of MGAs, a reliable geometrical model based on angular dependence theory is developed to assist in selecting process parameters and designing masks. The correlation between etching selectivity and characteristic dimension is elucidated. Experimental results demonstrate that the sidewall angle decreases with higher selectivity and increases with a greater sidewall angle on the patterned mask. Plasma etching reveals unaffected areas in convex corners and the forming errors in concave corners, highlighting a high angular dependence of the etch rate. Moreover, minimizing microdefects can be achieved by optimizing process parameters and reducing etch time.

Anti/de-icing superhydrophobic coating with durability and self-healing by infiltrating photothermal self-stratifying organic layers into plasma-sprayed porous Al2O3–13%TiO2 underlayer

Superhydrophobic coatings simultaneously exhibiting high substrate binding, mechanical durability and self-healing properties are of great significance for anti/de-icing applications. In this study, we fabricated a high substrate binding and mechanical durability anti/de-icing superhydrophobic coatings (SL-AP/SPS-SiO2) with self-healing performance by spray-coating a photothermal self-healing organic layers (AP/SPS-SiO2) plasma-sprayed porous Al2O3–13%TiO2 underlayer (SL), the resulting soft-hard interlocking structure significantly increased the adhesion strength of the coating to 16.7 ± 0.36 MPa while reducing the ice adhesion strength to 46.5 ± 3.0 kPa. In the as-obtained organic layers, self-stratifying acrylic resin (AR)/20%polymethylsiloxane (PDMS) (AP), not only enhanced the bonding strength with the underlayer but also imparted photothermal self-healing capability to the coating through the action of the photothermal agent (SPS-SiO2). And sodium alginate (SA) guided the self-oxidative polymerization of dopamine (DA) and its deposition on hydrophilic SiO2 to form a π-π stacked fiber structure photothermal agent (SPS), after hydrophobic SiO2 modification increased the coating's roughness and photothermal performance. Remarkably, the coating achieved a contact angle of up to 158.4 ± 0.89° and a rolling angle of 3.5 ± 0.89°, maintaining its superhydrophobic properties even after exposure to acid-base immersion and mechanical abrasion. Furthermore, the coating exhibited self-healing capabilities in superhydrophobicity against O2 plasma etching, with a contact angle recovery rate of up to 98.9% after undergoing 10 cycles of O2 plasma etching and light exposure. Enhancing mechanical and chemical stability with self-healing capabilities is beneficial for extending the lifespan of superhydrophobic coatings used in anti-/de-icing applications.

Optimal condition-based maintenance policy considering nested conditional value-at-risk and operational availability: A case study on semiconductor manufacturing equipment

To address concerns regarding economic risks and reliability issues in existing maintenance practices, this study introduces a novel condition-based maintenance model that considers failure risks in terms of both cost and availability. Utilizing a Markov decision process, this model determines inspection intervals and maintenance policies aimed at minimizing the nested conditional Value-at-Risk of cumulative costs while satisfying operational availability constraints. By applying this model to the plasma etching process, we demonstrate its effectiveness compared with existing maintenance models. Additionally, we found that higher risk levels do not necessarily lead to stricter maintenance policies, whereas achieving better operational availability incurs additional costs. These findings highlight the importance of balancing cost and availability risks when determining an optimal maintenance policy.

Atomic scale etching of diamond: insights from molecular dynamics simulations

Abstract Diamond is a promising material for multiple applications in quantum information processing and sensing as well as applications in microelectronics. However, diamond devices can be limited by surface defects that compromise charge stability and spin coherence, among others. Improved strategies in plasma etching of diamond could play an important role in minimizing or eliminating these defects. In this work, we explore plasma-assisted atomic scale etching of diamond using argon ions (Ar+), hydrogen ions (H+) and hydrogen atoms (H). We employ classical molecular dynamics (MD) simulations and test several interatomic potentials based on the Reactive Empirical Bond Order (REBO) form with comparisons to a variety of published experimental results. We performed MD simulations of low-energy hydrogen ( ⩽ 50 eV) and argon ( ⩽ 200 eV) ion bombardment of diamond surfaces. Ar+ bombardment can be used to locally smooth initially rough diamond surfaces via the formation of an amorphous C layer, the thickness of which increases with argon ion energy. Subsequent exposure with hydrogen ions (or fast neutrals) will selectively etch this amorphous C layer, leaving the underlying diamond layer mostly intact if the H energy is maintained below about 10 eV. The simulations suggest that combining Ar+ smoothing with selective, near threshold energy H removal of amorphous C can be an effective strategy for diamond surface engineering, leading to more reliable and sensitive diamond color center devices.