Etching Of Substrate Research Articles

Sensing Enhancement of Electromagnetically Induced Transparency Effect in Terahertz Metamaterial by Substrate Etching

A broad range of terahertz (THz) metamaterials have been developed for refractive index sensing. However, most of these metamaterials barely make sufficient use of the excited electric field which is crucial to achieve high sensitivity. Here, we proposed a metamaterial sensor possessing electromagnetically induced transparency (EIT) resonance that is formed by the interference of dipole and quadrupole resonance. In particular, the strengthening of light-matter interaction is realized through substrate etching, leading to a remarkable improvement in sensitivity. Hence, three kinds of etching mode were presented to maximize the utilization of the electric field, and the corresponding highest sensitivity is enhanced by up to ~2.2-fold, from 0.260 to 0.826 THz/RIU. The proposed idea to etch substrate with a strong light-matter interaction can be extended to other metamaterial sensors and possesses potential applications in integrating metamaterial and microfluid for biosensing.

Influence of reduced application time on bonding durability of universal adhesives to demineralized enamel.

This study aimed to assess the effect of application time on the microshear bond strength (μSBS) of three universal adhesives in demineralized and sound enamel before and after aging. Bovine teeth (192) were prepared where buccal surfaces were ground and divided into two groups (sound enamel and demineralized enamel). The specimens in each group were divided into 12 subgroups by combining 3 adhesive agents (All-Bond Universal, Scotchbond Universal, and Tokuyama Universal Bond) × 4 adhesion strategy. Each adhesive was applied with either prolonged (PA) or reduced (RA) application time in etch-and-rinse or self-etch mode. Bonded composites were subjected to μSBS testing after 24-h or 2-year water storage. The results were evaluated using four-way ANOVA and Tukey's post-hoc test (α = 0.05). The μSBS of adhesives to sound enamel in both etching modes was mostly similar to demineralized enamel, regardless of application time and aging time. At 24-h, all adhesives with PA in self-etch mode showed higher μSBS when compared with RA, except Tokuyama Universal Bond, but after 2-year aging, no significant difference was found in μSBS between RA and PA. The μSBS of adhesives with PA in etch-and-rinse mode depended on used adhesive and enamel condition compared to RA, regardless of μSBS testing time. PA of adhesives did not reveal a significant difference in μSBS to enamel, regardless of substrate type and etching mode. After 2-year aging, the bond strength of universal adhesives presented no significant difference between PA and RA treatments.

Numerical Study of SF6/O2 Plasma Discharge for Etching Applications

SF6/O2 plasma discharge has extensive applications in semi-conductor industry for anisotropic etching of silicon. Herein, a self-consistent fluid model has been used to investigate the capacitive coupled SF6/O2 plasma discharge. A complete set of reactions in gas phase which include electron impact reactions, ion-ion reactions, neutral–neutral reactions and charge transfer reactions in tandem with the primary processes such as dissociation excitation, and ionization were incorporated in the model. The densities of dominant plasma species (both neutral and charged) were calculated. Furthermore, the impact of O2 concentration on the plasma characteristics was studied. The results showed a bell shape distribution for neutral species while uniform distribution for charged species at center of the discharge. Moreover, it was demonstrated that the dominant etching species in the discharge were F, O, S, SF5+, FO, F+, O+, O2+ and S+. With the increase of O2 concentration in the plasma, there is a decrease in the ratio of neutral species (i.e., F/ O) and overall etch rate, signifying that chemical etching is the prominent process for the discharge. In conclusion, the anisotropic etching of Si substrate can be efficiently achieved using the optimum input parameters for SF6/O2plasma discharge.

Development of Polycrystalline Diamond Compatible with the Latest N-Polar GaN mm-Wave Technology

Integration of diamond on GaN can ease the challenges associated with thermal management of GaN-based power amplifiers which need to base on highly scaled transistors to push toward higher frequencies at high powers for 5G networks. The integration of diamond was achieved by growing polycrystalline (PC) diamond on nitrogen-polar GaN. A standard 5 nm Si3N4 layer which forms the gate dielectric was used as an interlayer between diamond and the GaN channel for etching protection. Since diamond growth conditions involve high temperature and H2 plasma, it can easily decompose the underlying dielectric as well as the GaN channel and degrade the channel conductivity and hence the device performance. Due to the incompatibility of conventional growth recipes with thin dielectrics (<5 nm), a novel two-stage-three-step growth recipe was designed for PC diamond integration on top of nitrogen-polar GaN high-electron-mobility transistors in a H2/CH4-plasma environment. Using only H2 and CH4 in the chamber guarantees a higher-phase-purity diamond than chambers with added argon or nitrogen for lower substrate etching. This recipe maintains the performance of the two-dimensional-electron gas and provides a less columnar diamond structure with a larger grain size. Our observations were supported by scanning transmission electron microscopy and Hall mobility measurements using the van der Pauw technique before and after diamond growth. A mobility of ∼1250 cm2/V s, a sheet carrier concentration of ∼1.30 × 1013 cm–2, and a sheet resistivity of ∼380 Ω/□ were maintained after the growth of diamond. The anisotropy ratio has been decreased from 3.75 to 1.12 with this growth recipe. Using long channel devices, we measured the difference in the channel temperature, which decreased by more than 100 °C in the range of 10–24 W/mm power after the integration of the diamond on top of the device.

Влияние асимметрии расположения металлических масок на согласование нижнего электрода с высокочастотным генератором смещения при реактивно-ионном травлении массивных подложек

The effect of the degree of asymmetry in the arrangement of metal masks on the matching of the lower electrode with a high-frequency displacement generator during selective reactive-ion etching of massive substrates in plasma-forming gas mixtures based on freon-14 is studied theoretically and experimentally. Theoretically, the absence of the influence of the asymmetry of the mask location on the specific reactive power is shown. It is shown that at the edge of the substrate, especially with a mask, there is a sharp increase in the RF current density, which proves mainly the surface (end) nature of its flow. The influence of the mask location on the behavior of the electric charge density, which correlates with the distribution of the RF current density in the near-surface layer of the substrate, is established. No redistribution of the charge density of the chemically active plasma particles at the edge of the mask was detected. In accordance with the theoretical results obtained, it is experimentally shown that metal masks with a side length ratio of 36/0 mm reduce the power reflection coefficient within 5%.

Features of the Semiconductor Surface structure containing silver particles on the porous Silicon Film Surface Formed by Metal-Assisted Etching

The porous silicon film surface region containing silver particles is studied by scanning electron microscopy and Raman spectroscopy. The porous silicon film is formed by metal-assisted etching of a single-crystal silicon substrate. It is found that the distribution of silver particles is controlled by the porous layer morphology. The formation of silver particles by chemical deposition results in certain smoothing of the por-Si film surface relief. In this case, the silicon crystallite structure does not change significantly.

Tribological properties of suspended hexagonal boron nitride under electric field

Hexagonal boron nitride (h-BN) has huge potential applications in micro-nano electromechanical system due to its good lubricity and insulation. In this paper, a microporous array is prepared on a SiO&lt;sub&gt;2&lt;/sub&gt;/Si substrate by the substrate etching process, and then the h-BN is transferred to the microporous substrate to form a suspension structure. The effect of electric field on tribological properties of suspended h-BN is studied by atomic force microscopy. The results show that the friction of the suspended h-BN is smaller than the friction on the h-BN supported by the substrate, because the greater in-plane stretch weakens the puckering effect. The electric field increases the friction of the suspended h-BN, and the influence of positive bias is greater than that of negative bias. The application of the electric field increases the electrostatic force on the tip, thereby increasing the additional load and the interface barrier in the friction process. The electric field causes the stick-slip behavior to change from single-slip to multi-slip. Compared with the h-BN supported by the substrate, h-BN in the suspended state is strongly affected by the electric field. The reduction of the interface distance and the absence of the substrate oxide layer lead the electrostatic force to increase. This paper proposes a method to adjust h-BN’s friction by electric field, which provides theoretical guidance for studying the friction characteristics of two-dimensional materials.

Особенности согласования нижнего электрода с высокочастотным генератором смещения при реактивно-ионном травлении массивных подложек

This paper presents theoretical and experimental results on reactive ion etching of massive substrates in freon-14 with RF bias at the lower electrode. A hypothesis is proposed according to which a large-sized substrate violates the matching of the lower electrode with the RF generator by adding an additional reactive component to the impedance of the lower electrode. A numerical simulation of reactive ion etching with substrates of various sizes in a CF4 environment is performed . The simulation results showed a significant increase in the reactive component of RF power at the lower electrode if the substrate area exceeds 50% of the area of the lower electrode, which is consistent with the proposed hypothesis. It has been experimentally shown that the etching of massive substrates violates the matching of the lower electrode with the RF generator. A special design of the substrate holder for massive substrates has been developed. It is shown that such a substrate holder significantly improves the matching of the RF generator with the lower electrode, especially when adding 0.3-0.9 l/h argon to the plasma-forming mixture.

Origin of carrier lifetime degradation in floating-zone silicon during a high-temperature process for insulated gate bipolar transistor

We report on the relationship between carrier lifetime degradation of floating-zone silicon (FZ Si) and the guard ring formation process for silicon integrated gate bipolar transistor (Si-IGBT). A clear carrier lifetime degradation was observed through the guard ring oxidation and annealing processes for Si-IGBT and showed interstitial oxygen (Oi) concentration dependence, which was obtained by Fourier transform infrared absorption spectroscopy. Based on the carrier lifetime measurements through the step etching of the FZ Si substrate, it has been suggested that the carrier lifetime degradation is not only caused by the Oi itself near the FZ Si surface region but also the other defects induced by the Oi injection. Diffused interstitial Si atoms kicked-out by the Oi into the FZ Si substrate, which has a longer diffusion length than Oi, can be considered to be the origin of the carrier lifetime degradation.

Surface preparation of porous Si-graphene nanocomposites for heteroepitaxy

We have investigated the fabrication process of an alternative approach for a direct integration of epitaxial structures onto a foreign substrate. Our approach is based on the synthesis of a nanocomposite made of graphenelike carbon and porous silicon. The nanocomposite was produced by anodization etching of a silicon substrate followed by a thermal carbonization step. The main study focused on the preparation of the nanocomposite surface for subsequent epitaxial deposition. While the nanocomposite must retain its carbon content for thermal stability at epitaxial temperatures, the surface must be stripped of its residual carbon to expose the silicon crystal and support layer nucleation. Our results show that the porous silicon substrate, carbonized at 750°C and subjected to an O2 plasma treatment of 20 W during 12 s, presented a carbon-free surface, while the bulk porous structure retained its carbon coating. Subsequent growth of a crystalline GaAs thin film demonstrated the substrate’s ability to support epitaxy.

Potential of micrometer-sized graphite as a catalyst for chemical etching of silicon

The chemical etching of silicon substrates, using graphite microparticles as a catalyst, was investigated. Graphite-coated silicon substrates were fabricated by drying a suspension of graphite particles onto substrates, which were then immersed in an etchant composed of HF and H2O2. The sections in the silicon surfaces covered with graphite particles sank down. The chemical etching proceeded only in the silicon beneath the graphite, similar to the conventional metal-assisted chemical etching that use noble metals as catalysts. The present graphite-assisted chemical etching provides a viable, low-cost micromachining process, which can replace conventional methods that employ expensive noble metal catalysts.

Plasma electrolytic oxidation of AZ31 and AZ91 magnesium alloys: Comparison of coatings formation mechanism

Abstract The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure, compositions (phase and elemental) and corrosion resistance. It was established that the coatings have a two- (outer and anodic) or three-layer structure (outer, inner and anodic) depending on the treatment time. Briefly, at short treatment time only an anodic layer and outer layer exists. Growth of the outer PEO layer takes place due to the micro discharges, which occur in vertical pores and voids with spherical cross-section. If the time is increasing, and electrolyte inside of the pores is heating-up, etching of the Mg substrate and oxide film becomes more dominant and horizontal pores in the interface between coating and metal are formed. In the pores new anodic layer will form and at this time the formation of the third inner layer starts. The growth of the inner layer happens via the anodic film as a result of micro discharge ignition in the horizontal pores, accompanied by formation of plasma in numerous micro-voids of this layer. The coatings formed on AZ91 alloy are denser, than those on AZ31, which is related to the difference in the rates of inner layer growth and dissolving of oxides which are located at the bottom of the horizontal pores. Because of the lower Al content, the AZ31 substrate itself and the also the oxide films are less stable and tend to dissolve at a higher rate compared to AZ91. Thus, it was demonstrated that a good corrosion resistance of the coatings was only obtained on AZ91 and if the average thickness of the coating is around 50 µm, correlating with the formation of a sufficiently dense inner layer. Knowing this mechanism, a new two-step treatment was suggested, combining the standard PEO treatment with a subsequent PEO process in an electrolyte supporting the inner film formation. The concept was successfully applied and a further improved corrosion resistance was obtained compared to the single stage PEO process. This improvement of corrosion resistance was related to the better sealing of porosity and formation of a denser inner layer.

Co3O4@Ni3S4 heterostructure composite constructed by low dimensional components as efficient battery electrode for hybrid supercapacitor

Redox activity and electrons/ions mobilities of electrode material are significant prerequisites for faradaic charge storage, the compositing of battery materials with different dimensionalities can satisfy the above two requirements simultaneously. Herein, a unique heterostructured Co3O4@Ni3S4 composite battery electrode with the coating of Ni3S4 nanosheets around/onto Co3O4 nanowires array was prepared via tandem hydrothermal reaction of Co salt, pyrolysis and followed sulfidation etching of Ni foam substrate. The different dimensionalities of Co3O4 core and Ni3S4 shell created porous network composite with high faradaic activity, sufficient exposure of surface sites, efficient electrons/ions migration and robust structural tenacity, therefore could offer high areal capacity (CA, 2.46C cm−2 at 1 mA cm−2), slow self-discharge rate and good cycleability (91% CA maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the Co3O4@Ni3S4 composite battery electrode exported high energy density (Ecell, 0.13 mW h cm−2 at 1.6 mW cm−2), slow self-discharge rate and good cycleability, showing the potential of heterostructured Co3O4@Ni3S4 composite electrode in faradaic energy storage.

Review of Growth Defects in Thin Films Prepared by PVD Techniques

The paper summarizes current knowledge of growth defects in physical vapor deposition (PVD) coatings. A detailed historical overview is followed by a description of the types and evolution of growth defects. Growth defects are microscopic imperfections in the coating microstructure. They are most commonly formed by overgrowing of the topographical imperfections (pits, asperities) on the substrate surface or the foreign particles of different origins (dust, debris, flakes). Such foreign particles are not only those that remain on the substrate surface after wet cleaning procedure, but also the ones that are generated during ion etching and deposition processes. Although the origin of seed particles from external pretreatment of substrate is similar to all PVD coatings, the influence of ion etching and deposition techniques is rather different. Therefore, special emphasis is given on the description of the processes that take place during ion etching of substrates and the deposition of coating. The effect of growth defects on the functional properties of PVD coatings is described in the last section. How defects affect the quality of optical coatings, thin layers for semiconductor devices, as well as wear, corrosion, and oxidation resistant coatings is explained. The effect of growth defects on the permeation and wettability of the coatings is also shortly described.

Simulation of Discharge Characteristics for the Plasma Etching of Large Area SiO2 Substrates

The electron density distribution and average electron temperature distribution in reactive ion etching (RIE) chamber are of great significance for the ionization and excitation reaction rate. The uniformity of radial distributions of the electron density and average electron temperature in the discharge chamber greatly affects the uniformity of the etching, especially the plasma etching of large area SiO2 substrates. We study the effects of discharge conditions (including power and pressure) on the electron density and average electron temperature of plasma-etched 400 mm SiO2 substrates in the reactive ion etching chamber; the simulation results show that the allowable major discharge conditions strongly affect the characteristics of plasma in the large area reactive ion etching chamber. Specifically, with increase in the power both the electron density and average electron temperature increase, being accompanied by deteriorating uniformity of their radial distributions. As the pressure increases, the electron density increases but average electron temperature decreases, being accompanied by deteriorating uniformity of their radial distributions. These methods and conclusions can provide reference for the improvement of cavity structure and large area RIE equipment designing and selection of the process parameters.

Dry etching of silicon carbide in ICP with high anisotropy and etching rate

A detailed study of the influence of technological parameters of the plasma chemical etching process in inductively coupled plasma on the etching rate of single-crystal silicon carbide is presented. The physicochemical substantiation of experimentally revealed patterns is given. The optimal gas mixture was determined in terms of the etching rate of SiC. It was experimentally established that the dependence of the etching rate of silicon carbide on the percentage of oxygen in the total gas mixture is non-linear. Thus, with an increase in the percentage of O2 up to 23%, the etching rate of SiC gradually increases to 560 nm/min, a further increase in the percentage of O2 leads to a sharp decrease in the etching rate of SiC up to 160 nm/min at an oxygen content of 31%. The effect of the distance between the sample and the plasma generation zone on the etching rate of SiC was studied. It was shown that the greatest increase in speed is caused by an increase in the bias voltage, so at Ubias = - 50 V the etching rate is 300 nm/min, and at Ubias = - 150 V the value of the etching rate is 840 nm/min. The optimal parameters of the plasma-chemical etching process were selected for high-speed directional etching of single-crystal silicon carbide substrates.

SERS Barcode Libraries: A Microfluidic Approach

Microfluidic technologies have emerged as advanced tools for surface‐enhanced Raman spectroscopy (SERS). They have proved to be particularly appealing for in situ and real‐time detection of analytes at extremely low concentrations and down to the 10 × 10−15 m level. However, the ability to prepare reconfigurable and reusable devices endowing multiple detection capabilities is an unresolved challenge. Herein, a microfluidic‐based method that allows an extraordinary spatial control over the localization of multiple active SERS substrates in a single microfluidic channel is presented. It is shown that this technology provides for exquisite control over analyte transport to specific detection points, while avoiding cross‐contamination; a feature that enables the simultaneous detection of multiple analytes within the same microfluidic channel. Additionally, it is demonstrated that the SERS substrates can be rationally designed in a straightforward manner and that they allow for the detection of single molecules (at concentrations as low as 10−14 m). Finally, it is shown that rapid etching and reconstruction of SERS substrates provides for reconfigurable and reusable operation.

Interplay between solution chemistry and mechanical activation in friction-induced material removal of silicon surface in aqueous solution

Shear-induced chemical etching reactions of single-crystalline Si(100), Si(110), and Si(111) surfaces were studied in acidic, neutral, and basic aqueous solutions. Measuring the applied load dependence of substrate etching yield and analyzing the data with the mechanically-assisted thermal activation model, the critical activation volume and activation barrier were determined for mechanochemical etching of three crystallographic surfaces. The pH dependence of Si(110) etching is quite distinct from those of Si(100) and Si(111). The results suggested that the mechanochemical activation effect is larger for Si(100) and Si(111) than Si(110) which is chemically more reactive than the other two surfaces. The findings of this study may provide deeper insights for mechanistic understanding of the scanning probe microscopy based nanomanufacturing and chemical mechanical polishing processes.

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method.

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.

Freestanding ultra-thin silica

Silica (SiOx) thin films are promising for a wide range of applications, including catalysis, separation technology, biomedicine, or transparent super-hydrophilic films. Here, we present a study demonstrating a unique way of producing ultra-thin, freestanding silica films via silicon etching. This method utilizes silicon wafers with thermally oxidized surfaces and two common inorganic elements (sulfur and tellurium), which leads to high-rate chemical etching of the Si substrate, leaving behind freestanding silica layers. Thermodynamic calculations of the tellurium–silicon–sulfur (Te–Si–S) ternary phase diagram suggest that the removal of the Si substrate from the silica layers is due to chemical reactions that result in liquid/vapor formation of Si–S and Si–Te phases. Importantly, the chemical and physical properties of the silica film post-etch are comparable to those of the starting material. The process described here provides a route to produce large area, flexible glass substrates with widely tunable thicknesses from tens to thousands of nanometers.