Etching Of Silicon Research Articles

Single-Nanoparticle-Based Nanomachining for Fabrication of a Uniform Nanochannel Sensor.

The structure of nanomaterials and nanodevices determines their functionality and applications. A single uniform nanochannel with a high aspect ratio is an attractive structure due to its unique rigid structures, easy preparation, and diverse pore structures and it holds significant promising importance in fields such as nanopore sensing and nanomanufacturing. Although the metal-nanoparticle-assistant silicon etching technique can produce uniform nanochannels, however, the fabrication of single through nanochannels remains a challenge thus far. A simple and versatile strategy is developed that allows for the retention of individual gold nanoparticle on a substrate, enabling single-nanoparticle nanomachining. This method involves three steps: the formation of a carbon protective layer on individual nanoparticles via electron-beam irradiation, selective removal of unprotected nanoparticles using a corrosive agent, and subsequent elimination of the carbon layer. This enables the fabrication of a single submillimeter-long uniform through nanochannel in the silicon wafer, which can be employed for nanopore sensing and shape-based nanoparticle distinguishing. The developed method can also facilitate single-nanoparticle studies and nanomachining for a broad application in materials science, electronics, micro/nano-optics, and catalysis.

Composition-adjustable silicon-germanium alloy films based on porous silicon matrices

Morphology and crystalline structure of silicon-germanium alloys formed by rapid thermal processing of germanium-filled porous silicon layers are evaluated. Two types of porous silicon are employed as matrices for electrochemical pore filling using GeO2 aqueous solutions and subsequently compared, the first one formed by electrochemical anodization and the second by silver-assisted chemical etching of monocrystalline silicon. The resulting alloys’ structure and composition are investigated using scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy and X-ray powder diffraction. It is shown that by varying the porosity of the initial matrix (by adjusting anodization current density for anodic porous silicon or changing silver deposition time for structures produced by metal-assisted etching) in the range from 55 to 75%, Si1-xGex alloys with germanium fractions of x = 0.31 to x = 0.83 can be formed, as indicated by Raman spectroscopy. It is concluded that composition-adjustable layers of silicon-germanium can be successfully formed on either type of porous silicon layer. While an increase in porosity generally leads to a decrease in silicon fractions in the alloy, the steepness of this effect varies heavily depending on the type of porous matrix used and should be considered independently for anodic porous silicon and silicon nanowires.

ReaxFF molecular dynamics simulation of single-crystalline silicon plasma polishing and subsurface damage removal

Recently, plasma etching has become one of the most promising polishing methods due to its low cost and environmental friendliness. In this study, the mechanism and parametric influence of plasma etching were investigated using ReaxFF-based molecular dynamics (RBMD) simulation, allowing the characterization of the process of F atom etching of monocrystalline silicon and the removal of subsurface defects from an atomic perspective. We simulated the process of F-atom etching and the mechanism of F-atom removal of the subsurface damage of single-crystalline silicon. The simulation results indicate that SiF4 generated by monocrystalline silicon under the action of F atoms gradually generated SiF5- groups and detached from the substrate as the reaction time increases. Simultaneously, under the action of F atoms, Si atoms gradually filled the subsurface defects, achieving damage removal. In addition, the incident angle can be increased in the plasma polishing process to reduce the thickness of the amorphous deformation layer and improve the surface quality.

Modern Scanning Electron Microscopy. 2. Test objects for Scanning Electron Microscopy

The review of the test objects intended for calibration of scanning electron microscopes and researches to secondary electronic emission of a relief surface of a solid state in scanning electron microscope is carried out. The test objects are divided on two parameters – kind of a relief and structure of a relief. By the form of relief the test objects are divided on single, pitch and periodic. On a structure of a relief of the test objects are divided into objects with a rectangular structure and objects with a trapezoid structure with the large and small corners of an inclination of lateral walls. The examples of such the test objects are given. Their characteristics and methods of certification of parameters are described. The advantages and lacks of the test objects are considered. Is shown, that the best characteristics have the tests objects representing pitch structures consisting of trapezoid trenches with the large corners of an inclination of lateral walls. The test objects are created in monosilicon with of a surface orientation by {100} by method liquid anisotropic etching of silicon. These test objects allow defining all characteristics scanning electron microscopes, influencing on measurement of the linear sizes of relief structures used in microelectronics and nanotechnology. With their help it is possible to carry out correlation measurements, which raise accuracy of calibration scanning electron microscopes up to ten times.

Investigation of Surface Nanoclusters and Paramagnetic Centers of ZnO/Por-Si Structures as the Basis of Sensory Properties

The detection of particles with uncompensated charge and the determination of the features of their interaction during the formation of nanocrystals on substrates with a developed surface are an interesting area of research. The porous surface formed via the electrochemical etching of silicon acquired fractal properties as a result of the deposition of zinc oxide layers. Microscopy methods using different resolutions revealed a hierarchical structure of the surface, where each of the three consecutive levels contains uniformly distributed formations. The deposition of 20 layers of ZnO maximizes the concentration of nanocrystals at the pore boundaries, while the deposition of 25 layers leads to the formation of a continuous layer. The increase in photoluminescence intensity with an increase in the number of deposited layers is due to the saturation of surface nanostructures with electrons through several mechanisms. Electron paramagnetic resonance (EPR) studies have shown that the main mechanism of radiation recombination is the capture of electrons on oxygen vacancies. The different nature of the EPR saturation of the signal of interconnected paramagnetic centers revealed the formation of zinc oxide particles at the boundaries of pores with different sizes. The results of these studies of surface-active structures effectively complement the knowledge about sensory materials.

High Aspect Ratio Nanoscale Pores through BCP-Based Metal Oxide Masks and Advanced Dry Etching.

The reliable and regular modification of the surface properties of substrates plays a crucial role in material research and the development of functional surfaces. A key aspect of this is the development of the surface pores and topographies. These can confer specific advantages such as high surface area as well as specific functions such as hydrophobic properties. Here, we introduce a combination of nanoscale self-assembled block-copolymer-based metal oxide masks with optimized deep reactive ion etching (DRIE) of silicon to permit the fabrication of porous topographies with aspect ratios of up to 50. Following the evaluation of our procedure and involved parameters using various techniques, such as AFM or SEM, the suitability of our features for applications relying on high light absorption as well as efficient thermal management is explored and discussed in further detail.

Fabrication and Characterization Study of Porous Silicon for NIR-VIS Photodetector Applications

In this paper, photoelectrochemical etching of the n-type silicon (n-Si) wafers is used to prepare porous silicon (PSi) with current density of 10 mA.cm[Formula: see text] for 10 min. Moreover, the structural and morphological properties of the n-PSi were analyzed by using XRD and AFM, FTIR and PL. XRD patterns of PSi show that the films are single-crystalline, with cubic structure. The major peak characteristics are allocated to plane (004). The atomic force microscope image and the distribution chart of the grains of the n-PSi displayed that the grain sizes were −8.98. FTIR is a powerful and easy-to-use technique to obtain the surface chemical state of PSi. The convenience results from the transparency of silicon for IR light and the high surface area. The basic features begin from the knowledge of the bondings to hydrogen, [Si–H], and to oxygen [Si–O]. The model calculations sometimes provide useful information in the assignment. By examining FTIR, the active bonds showed the formation of PSi. PL spectra were measured in the range of (600–900) nm, the emission peak for the fixed excitation wavelength at 500 nm, and spectral 1.78 eV and 1.24 eV. PSi is recognized as an attractive building block for photonic devices because of its novel properties including high ratio of surface to volume and high light absorption. We first report NIR and VIS (PDs) fabricated by PSi as a carrier collector and a photoexcitation layer.

Effects of C4F8 plasma polymerization film on etching profiles in the Bosch process

The Bosch process is a deep etching method for silicon that uses C4F8 plasma-deposited polymerized films as passivation films to protect the silicon sidewalls. This study measured the deposition rate of the passivation films and the etch rate with F-radical exposure and analyzed the chemical composition of the films. Additionally, we observed the deformation of the passivation films during the Bosch process and assessed its influence on the etch profiles. As the C4F8 flow rates increased, the deposition rates attained a local maximum, subsequently decreased to a local minimum and then increased again. The deposition rates were extremely low when the pressure exceeded 10 Pa. With the increasing C4F8 flow rates, inductively coupled plasma power, and pressure, the respective bond content varied up to 10%, and C—CFX and C—C bond contents were replaced with CF2 and CF contents, respectively. The results indicated that the chemical composition of the films did not affect the etch rates of the films, and upon exposure to F radicals, the chemical composition of all films transformed into an identical chemical composition with a higher CF2 bond content. Polymerized films with low CF2-bond content deformed with F-radical exposure, enabled the passage of F radicals, and did not serve as passivation films. In addition to high deposition rates and high F-radical resistance, the Bosch process requires passivation films with high CF2 bond content. The present findings will aid in tuning the parameters of the Bosch process and increase the productivity of silicon deep reactive-ion etching.

The Influence of Small F2, H2, and HF Additives on the Concentration of Active Particles in Tetrafluoromethane Plasma

A comparative study of the effect of small (up to 20%) substituting additives F2, H2, and HF on the kinetics and stationary concentrations of neutral particles in 50% CF4 + 50% Ar plasma under the typical conditions of reactive ion etching (RIE) of silicon and its compounds is carried out. It is shown that the vari-ation of the CF4/F2 and CF4/H2 ratios leads to opposite, interrelated, and nonadditive changes in the con-centrations of fluorine atoms and fluorocarbon radicals. This provides wide ranges of regulation of the etch-ing rate and polymerization capacity with the minimal disturbance of the parameters of the electronic and ionic components of the plasma. In contrast, the CF4/HF relation has the minimal effect on the rate of sur-face polymerization, but noticeably changes the concentration of fluorine atoms. Thus, there is a selective effect on the rate of the heterogeneous chemical reaction.

Interpolation and difference optimized machine learning model for accurate prediction of silicon etching depth with small sample dataset

A novel interpolation and difference optimized (IDO) machine learning model to predict the depth of silicon etching is proposed, which is particularly well-suited to addressing small sample problems. Our approach involves dividing both experimental and simulation data obtained from the Technology Computer-Aided Design (TCAD) software into training and testing sets. Both experimental data and TCAD simulation data are used as inputs to machine learning module 1 (ML1), while ML2 takes the actual experimental data as inputs and then learns the difference between the experimental data and the TCAD simulation data, outputting the difference. The outputs generated by ML1 and ML2 serve as input parameters to machine learning module 3 (ML3), and the weights of ML3 are updated through its own learning process to produce the final prediction results. We demonstrate that our IDO model, which contains three basic ML algorithms, achieves higher prediction accuracy compared to the basic ML algorithm alone. Moreover, through ablation studies, we establish that the three components of the IDO prediction model are inseparable. The IDO model exhibits improved generalization performance, making it particularly suitable for small sample datasets in the semiconductor processing domain.

Orientation-dependent etching of silicon by fluorine molecules: A quantum chemistry computational study

Anisotropic etching is a widely used process in semiconductor manufacturing, in particular, for micro- and nanoscale texturing of silicon surfaces for black silicon production. The typical process of plasma-assisted etching uses energetic ions to remove materials in the vertical direction, creating anisotropic etch profiles. Plasmaless anisotropic etching, considered here, is a less common process that does not use ions and plasma. The anisotropy is caused by the unequal etching rates of different crystal planes; the etching process, thus, proceeds in a preferred direction. In this paper, we have performed quantum chemistry modeling of gas-surface reactions involved in the etching of silicon surfaces by molecular fluorine. The results confirm that orientation-dependent etch rates are the reason for anisotropy. The modeling of F2 dissociative chemisorption on F-terminated silicon surfaces shows that Si–Si bond breaking is slow for the Si(111) surface, while it is fast for Si(100) and Si(110) surfaces. Both Si(100) and Si(110) surfaces incorporate a larger number of fluorine atoms resulting in Si–Si bonds having a larger amount of positive charge, which lowers the reaction barrier of F2 dissociative chemisorption, yielding a higher etch rate for Si(100) and Si(110) surfaces compared to Si(111) surfaces. Molecular dynamics modeling of the same reactions has shown that the chosen reactive bond order potential does not accurately reproduce the lower reaction barriers for F2 dissociative chemisorption on Si(100) and Si(100) surfaces. Thus, reparameterization is necessary to model the anisotropic etching process that occurs at lower temperatures.

In situ and real-time optical study of passive chemical etching of porous silicon and its impact on the fabrication of thin layers and multilayers

In this work, we report on the development and application of a simple reflectivity technique for real-time monitoring of the fabrication of porous-silicon multilayers. The technique allows for high-resolution quantification of the effective optical thickness of the layers during the fabrication process, enabling calibration of attack rates and detection of changes in porosity. Our experiments revealed that the porosity of the layers increases during the attack, indicating incomplete passivation of the pores. By studying thin porous-silicon layers in the absence of applied current, we developed a three-layer model to understand passive chemical etching. Furthermore, our study allowed discrimination between the two mechanisms responsible for the reduction of effective optical thickness with time, with changes in porosity being the dominant one. The technique has the potential to enable real-time control of multilayer fabrication, offering flexibility in controlling environmental conditions and silicon wafer conduction properties. Our results contribute to the understanding of multilayer fabrication and reflectivity-based process monitoring.

Ring Resonator of Hollow-Core Photonic Crystal Fiber Based on Spatial Coupling Scheme

In this paper, we proposed a hollow-core photonic crystal fiber (HCPCF) ring resonator based on a spatial coupling method, and the component is only 22×30×6mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . When using a 7-core photonic crystal fiber with a mode field diameter of 10um, a ring resonator with the measured finesse of 18 can be built, indicating that the coupling loss is as low as 0.41dB. Compact and low-loss closed resonator is accomplished using a highly integrated free space silicon optical bench manufactured by deep silicon etching and tiny optical lens package technology, which promotes the practicality of the HCPCF gyro. In addition, two important factors affecting the spatial optical coupling efficiency, the lens type and the fiber mode field size, are investigated in this paper. The obtained results are instructive for all spatial optical coupling systems.

Process optimization for shallow trench isolation etch using computational models

The critical dimensions of advanced semiconductor manufacturing processes have decreased to a few tens of nanometers while the aspect ratios have increased beyond 100. The performance of plasma etch patterning processes as well as the cost and time of the development cycle are critical to the success of ramping a new technology node toward profitable high-volume manufacturing. In this paper, a computational patterning software, ProETCH®, has been developed with rigorous physics and advanced algorithms for modeling the etch patterning process, with the featured capabilities in calibrating the reaction mechanisms and optimizing the etch process. A shallow trench isolation etch process using self-aligned double patterning was investigated. A reaction mechanism of silicon etch by Ar/Cl2 plasma was developed to address the surface reactions, and a plasma hypermodel was introduced to correlate process operating conditions to plasma parameters at the wafer surface. The parameters of the reaction mechanism and the plasma hypermodel were calibrated with experimental data obtained from cross-sectional scanning electron microscope (XSEM) images. The calibrated model is used to identify the different fundamental pathways that contribute to the observed profile metrics in XSEMs. The model was then used for process development and optimization by solving the forward and inverse problems. In the forward problem, the model is used to predict the etching profile at different process conditions. Predictions for both interpolation conditions (process parameters within the range used for developing the model) and extrapolation conditions (process parameters outside of the range used for developing the model) agree well with the experimental data with the root mean square error less than 4 nm (1 nm resolution used for the mesh). In the inverse problem, the developed model is used to search for process conditions (e.g., values of bias power and pressure), which could result in desirable profiles. The solutions to the inverse problem demonstrate a degeneracy in process space of the etching process for a given target profile.

Concentration of Fluorine Atoms and Kinetics of Reactive-Ion Etching of Silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 Mixtures

Concentration of Fluorine Atoms and Kinetics of Reactive-Ion Etching of Silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 Mixtures

Development of Through-Substrate via Process for Silicon-Based Monolithic Microwave Integrated Circuits SIS Mixer

We designed and fabricated superconducting monolithic microwave integrated circuits (MMICs) at 2 mm wavelengths. Balanced superconductor-insulator-superconductor (SIS) mixers and silicon membrane-based planar orthomode transducers are incorporated into the MMICs, which is used to develop compact heterodyne array receivers for radio astronomical observations. Because of substrate cavity modes, crosstalk between the outputs of balanced mixers was observed at intermediate frequencies, which deteriorated the noise rejection ratio. Three-dimensional electromagnetic simulation proved that the cavity modes can be effectively suppressed by introducing conducting through-substrate vias (TSVs). We have been developing a TSV fabrication process compatible with that for the superconducting MMICs containing silicon membranes by using non-Bosch deep silicon etching and using sputtered Nb films. The fabricated TSVs were characterized by scanning electron microscopy and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> measurement.

Effects of Bubbles on Manufacturing Gold Dendrites and Silicon Nanowires Through the Fluoride-Assisted Galvanic Replacement Reaction

Abstract The fluoride-assisted galvanic replacement reaction is a conventional method for fabricating metallic dendrites on silicon wafers. However, whether bubbles affect manufacturing metallic dendrites is unclear. This study investigated the effects of bubbles on manufacturing Au dendrites and silicon nanowires through metal-assisted chemical etching. The results of manufacture under three conditions (standard, shaking, and vacuum conditions) were compared. Synchronous growth of Au dendrites and silicon nanowires were observed on the silicon wafers. The Au dendrite deposition rate was higher than the silicon etching rate. Compared with the standard condition, the vacuum condition increased the synthesis rates of Au dendrites and silicon nanowires by 1.1 and 0.2 μm/min, respectively. Therefore, the elimination of bubbles by vacuum can considerably accelerate manufacturing Au dendrites and silicon nanowires.

On Relationships between Plasma Chemistry and Surface Reaction Kinetics Providing the Etching of Silicon in CF4, CHF3, and C4F8 Gases Mixed with Oxygen.

In this work, we discuss the effects of component ratios on plasma characteristics, chemistry of active species, and silicon etching kinetics in CF4 + O2, CHF3 + O2, and C4F8 + O2 gas mixtures. It was shown that the addition of O2 changes electrons- and ions-related plasma parameters rapidly suppresses densities of CFx radicals and influences F atoms kinetics through their formation rate and/or loss frequency. The dominant Si etching mechanism in all three cases is the chemical interaction with F atoms featured by the nonconstant reaction probability. The latter reflects both the remaining amount of fluorocarbon polymer and oxidation of silicon surface.

On the low temperature limits for cryogenic etching: A quasi in situ XPS study

The cryogenic plasma etching of silicon for nano- and microelectromechanical devices is known to show an optimal operating temperature around –100 °C. The physicochemical mechanisms occurring beyond this limit, however, are not often discussed. Thus, to explore the adsorption of residual gases on the uppermost surface of a Si/SiO2 wafer at –100 ≤T≤ –147 °C, we performed a comprehensive, quasi in situ X-ray photoelectron spectroscopy (XPS) study. Precisely, the cooling down of the sample was performed in a typical plasma-etching reactor at a residual pressure of 10−4 Pa, being afterwards transferred to the XPS chamber at a constant temperature, under high vacuum. We report that water build-up on the surface becomes a major issue for T< –120 °C, as detected in the O 1 s spectra and modelled by QUASES-Generate. The thickness of the H2O layer increases exponentially as the surface temperature decreases, following an anti-Arrhenius behavior. At –147 °C, the overlayer thickness is estimated to ∼125 Å, thus, the silicon is barely probed by XPS. Adsorbed fluorine can also be detected at low temperatures, although less markedly. Finally, the effect of the temperature-dependent Fermi level change on the Si 2p peak binding energy is discussed.

Concentration of Fluorine Atoms and Kinetics of Reactive-Ion Etching of Silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 Mixtures

A comparative study of the electrophysical parameters of the plasma, the fluorine atom concentra-tions, and the kinetics of reactive-ion etching of silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 mixtures of a variable (0–75% O2) initial composition is carried out. It is shown that the dominant etching mecha-nism is always the ion-stimulated chemical reaction Si + xF → SiFx, whose rate has a maximum in the region of 20–50% O2. Based on the results of plasma diagnostics, it is found that the similar behavior of the concen-tration of fluorine atoms is typical only for mixtures of CF4 + O2 and CHF3 + O2, while in the C4F8 + O2 mix-ture, there is a nonmonotonic change in the probability of the interaction. It is assumed that the latter effect is caused by the competition between the processes of reducing the thickness of the fluorocarbon polymer film and the oxidation of the silicon surface by oxygen atoms.