Etching Of Silicon Research Articles

Comprehensive stoichiometric studies on the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures.

The stoichiometry of the wet chemical etching of silicon in concentrated binary and ternary mixtures of HF, HNO3 and H2SiF6 was comprehensively investigated. A complete quantification of both dissolved and gaseous reaction products was carried out for a variety of different acid mixtures. It could be shown that the total nitric acid consumption is directly determined by the concentration of undissociated HNO3 in the mixture and can be attributed to the consumption in subsequent reactions with increasing concentration. Furthermore, a critical minimum concentration of undissociated HNO3 of q(HNO3, undiss) ≥ 0.35 mol kg-1 could be determined, which is required to start the reaction at 20 °C with agitation, irrespective of the composition of the mixture (binary/tertiary). The simultaneous determination of the nitrogen oxides in the gas phase supports the theory that NO is the only direct reduction product of HNO3 in the reaction with Si. Furthermore, the amount of formed hydrogen is determined by both the HF and the HNO3 concentration in the mixture. For binary mixtures, the H2 formation can be quantitatively described as a function of the concentration of HNO3, HF and H2O. The most important finding from comparative investigations between binary and ternary mixtures is that the overall reaction is largely determined by the formation of the reactive intermediate HNO2 as a result of complex reaction pathways. Both the formation and the accumulation of this intermediate are determined by the water content of the etching mixture. The consumption of HNO3 and also the formation of the reaction products NOx and H2 can therefore be functionally described on the basis of the H2O content in the etching mixture, regardless of a binary or ternary mixture.

Impact of silicon wafer surface treatment on the morphology of GaP layers produced by plasma enhanced atomic layer deposition

Investigations of atomic-layer deposition of GaP layers on Si substrates with different orientations and with different preliminary surface treatment have been carried out. The deposition of GaP was carried out by the method of plasma enhanced atomic-layer deposition using in situ treatment in argon plasma. It was shown that at the initial stage of the growth of GaP layers on precisely oriented (100) Si substrates and with misorientation, two-dimensional growth occurs both after chemical and plasma surface treatment. Upon growth on (111) substrates, after plasma treatment of the surface, a transition to three-dimensional growth is observed, at which the size of islands reaches 30-40 nm. The smallest root-mean-square roughness of the surface of the growing GaP layers (<0.1 nm) was achieved for (100) substrates with a misorientation of 4o. The GaP layers grown on (100) substrates had a roughness of ~0.1 nm, and on substrates with the (111) orientation --- 0.12 nm. It was found that the surface treatment of Si substrates with the (100) orientation in hydrogen plasma leads to a slight increase in the surface roughness of growing GaP layers (0.12-0.14 nm), which is associated with the effect of inhomogeneous etching of silicon in hydrogen plasma. When treating the (100) silicon surface in argon plasma, the surface roughness does not change significantly in comparison with the chemical surface treatment. On the surface of substrates with preliminary deposition of an epitaxial Si layer with a thickness of 4 nm, the morphology of GaP layers is the same as in the case of using hydrogen plasma. Keywords: PECVD, ALD, silicon, gallium phosphide

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Investigations of atomic-layer deposition of GaP layers on Si substrates with different orientations and with different preliminary surface treatment have been carried out. The deposition of GaP was carried out by the method of plasma enhanced atomic-layer deposition using in situ treatment in argon plasma. It was shown that at the initial stage of the growth of GaP layers on precisely oriented (100) Si substrates and with misorientation, two-dimensional growth occurs both after chemical and plasma surface treatment. Upon growth on (111) substrates, after plasma treatment of the surface, a transition to three-dimensional growth is observed, at which the size of islands reaches 30–40 nm. The smallest root-mean-square roughness of the surface of the growing GaP layers (<0.1 nm) was achieved for (100) substrates with a misorientation of 4 °. The GaP layers grown on (100) substrates had a roughness of ~ 0.1 nm, and on substrates with the (111) orientation - 0.12 nm. It was found that the surface treatment of Si substrates with the (100) orientation in hydrogen plasma leads to a slight increase in the surface roughness of growing GaP layers (0.12–0.14 nm), which is associated with the effect of inhomogeneous etching of silicon in hydrogen plasma. When treating the (100) silicon surface in argon plasma, the surface roughness does not change significantly in comparison with the chemical surface treatment. On the surface of substrates with preliminary deposition of an epitaxial Si layer with a thickness of 4 nm, the morphology of GaP layers is the same as in the case of using hydrogen plasma.

Characteristics of flexible ZnO nanorod UV photodetectors processed by using a direct silicon etching transfer method

A flexible UV photodetector based on ZnO NRs with good photoelectrical properties was fabricated by applying DSET to achieve superior UV-sensing properties.

ПРОГРАМНО-АПАРАТНИЙ АВТОМАТИЗОВАНИЙ КОМЛЕКС УПРАВЛІННЯ ФОРМУВАННЯМ ПОРУВАТОГО ШАРУ НА НАПІВПРОВІДНИКОВИХ ПЛАСТИНАХ

Purpose. Porous silicon is widely used in devices such as light emitters, sensors, and medical devices. The quality of operation of these devices depends on the diameter of the pore, the uniformity of its surface, and the thickness of the layer. To control the characteristics of the porous layer, the current density, etching time, and current shape are changed. As a rule, the growth is carried out using a constant current density. In this case, hydrogen bubbles are formed in the pores with a simultaneous decrease in the etching rate, which leads to the formation of small pores. This limits the pos-sibility of obtaining porous silicon with a high degree of reproducibility. Methodology The research was carried out on a semiconductor wafer. After cleaning, the silicon wafers were etched in an electrochemical cell at room temperature. For the study, two types of etching current were used: current in the form of rectangular pulses with a variable duty cycle and direct current. For the pulsed current, the density was 20 mA/cm2, the duty cycle of the pulses varied from 40 to 80% at a frequency of 7 Hz. For direct current, the etching current density was 20 mA/cm2. The etching time in both experiments was 30 minutes. Findings. The paper shows the influence of the shape of the silicon etching current on the formation of a porous layer. To control the etching process, a hardware-software automated complex for controlling the formation of a porous layer on semiconductor wafers was developed. Originality. When using a pulsed current, the structure of the porous layer becomes more uniform, as evidenced by an increase in the intensity of the photolumines-cence spectrum at a wavelength of 650 nm. Practical value. The results of the work can be used in the development of such devices as light emitters, sensors and medical devices. Сonclusions The method of etching single-crystal silicon has been improved in order to obtain a porous layer having a uniform structure by using the etching current in the form of pulses with a duty cycle of 80% and a frequency of 7 Hz.

Concept for Efficient Light Harvesting in Perovskite Materials via Solar Harvester with Multi-Functional Folded Electrode.

Conventional electrodes in typical photodetectors only conduct electrical signals and introduce high optical reflection, impacting the optical-to-electrical conversion efficiency. The created surface solar harvester with a multi-functional folded electrode (MFFE) realizes both a three-dimensional Schottky junction with a larger light detecting area as well as low optical reflection from 300 nm (ultra-violet light) to 1100 nm (near-infrared light) broadly without an additional anti-reflection layer. The MFFE needs silicon etching following the lithography process. The metal silver was deposited over structured silicon, completing the whole device simply. According to the experimental results, the width ratio of the bottom side to the top side in MFFE was 15.75, and it showed an optical reflection of 5–7% within the major solar spectrum of AM1.5G by the gradient refractive index effect and the multi-scattering phenomenon simultaneously. While the perovskite materials were deposited over the MFFE structure of the solar harvester, the three-dimensional electrode with lower optical reflection benefitted the perovskite solar cell with a larger detecting area and an additional anti-reflection function to absorb solar energy more efficiently. In this concept, because of the thin stacked film in the perovskite solar cell, the solar energy could be harvested by the prepared Schottky junction of the solar harvester again, except for the optical absorption of the perovskite materials. Moreover, the perovskite materials deposited over the MFFE structure could not absorb near-infrared (NIR) energies to become transparent. The NIR light could be harvested by the light detecting junction of the solar harvester to generate effective photocurrent output additionally for extending the detection capability of perovskite solar cell further. In this work, the concept of integration of a conventional perovskite solar cell with a silicon-based solar harvester having an MFFE structure was proposed and is expected to harvest broadband light energies under low optical reflection and enhance the solar energy conversion efficiency.

Optimization of deep silicon etching process for microstructures fabrication

The paper presents the study of cyclic process of deep anisotropic silicon etching, called Oxi-Etch, in which the steps of etching and oxidation alternate, allowing deep etching of silicon with an anisotropic profile. This process forms typical for cyclic etching process sidewall profile called scalloping. Opportunities for modification and optimization of the process for specific application were investigated. The effects of optimization of the bias voltage and the duration of the etching step on the parameters of the resulting structures, such as the etching depth, wall roughness, and the accuracy of transferring the lithographic size, are considered. Balance between etch rate and scalloping was established.

Physical Parameter Extraction and Modeling of Metallized Deeply-Etched Vertical Mirrors

In this work, vertical micromirrors that are fabricated using deep etching of silicon followed by metal sputtering are studied. Physical parameter extraction methodology, image processing, machine learning and discrete element analysis are used to extend the easy-to-take scanning electron microscope images into 3-D topographical information, that are usually obtained using atomic force microscope and transmission electron microscope. The experimental results show that vertical micromirrors surface quality has a granular nature showing degraded performance and a different optical response with respect to the bulk metal. A physical model is developed and validated by comparing the measured reflectivity of the fabricated micromirrors with a multi-layer reflectivity optical model based on the effective medium theory fed by the extracted physical parameters. In agreement with the experimental results, the model predicts a reflectivity of about 60 % for a sputtered aluminum thickness of 50 nm, compared to 97.5% reflectivity predicted by the bulk metal model. [2021-0154]

Single-step alkaline etching of deep silicon cavities for chip-scale atomic clock technology

This paper presents the results of experiments on the development of the technology of MEMS alkali vapor cells for a miniature quantum frequency standard. The classical design of a two-chamber silicon cell containing an optical chamber, shallow filtration channels and a technical container for a solid-state alkali source was implemented in a single-step process of wet anisotropic silicon etching. To prevent the destruction of the filtration channels during etching of the through silicon cavities, the shapes of the compensating structures at the convex corners of the silicon nitride mask were calculated and the composition of the silicon etchant was experimentally found. The experiments results were used in the manufacture of chip-scale atomic clock cells containing vapors of 87Rb or 133Cs isotopes in the neon atmosphere.

Realization of Three-Dimensionally MEMS Stacked Comb Structures for Microactuators Using Low-Temperature Multi-Wafer Bonding with Self-Alignment Techniques in CMOS-Compatible Processes.

A high-aspect-ratio three-dimensionally (3D) stacked comb structure for micromirror application is demonstrated by wafer bonding technology in CMOS-compatible processes in this work. A vertically stacked comb structure is designed to circumvent any misalignment issues that could arise from multiple wafer bonding. These out-of-plane comb drives are used for the bias actuation to achieve a larger tilt angle for micromirrors. The high-aspect-ratio mechanical structure is realized by the deep reactive ion etching of silicon, and the notching effect in silicon-on-insulator (SOI) wafers is minimized. The low-temperature bonding of two patterned wafers is achieved with fusion bonding, and a high bond strength up to 2.5 J/m2 is obtained, which sustains subsequent processing steps. Furthermore, the dependency of resonant frequency on device dimensions is studied systematically, which provides useful guidelines for future design and application. A finalized device fabricated here was also tested to have a resonant frequency of 17.57 kHz and a tilt angle of 70° under an AC bias voltage of 2 V.

Research progress of silicon nanostructures prepared by electrochemical etching based on galvanic cells

Metal-assisted etching of silicon in HF aqueous solution has attracted widespread attention due to its potential applications in electronics, photonics, renewable energy, and biotechnology. In this paper, the basic process and mechanism of metal assisted electrochemical etching of silicon in vapor or liquid atmosphere based on galvanic cells are reviewed. This paper focuses on the use of gas-phase oxidants O2 and H2O2 instead of liquid phase oxidants Fe(NO3)3 and H2O2 to catalyze the etching of silicon in the vapor atmosphere of HF aqueous solution. The mechanism of substrate enhanced metal-assisted chemical etching for the preparation of large-area silicon micro nanostructure arrays is summarized, and the impact of substrate type and surface area on reactive etching is discussed.

Electrochemical Investigation of the Effect of Hydrogen Peroxide Concentration on Platinum-Particle-Assisted Etching of p-Type Silicon in a Hydrofluoric Acid Solution

Metal-assisted etching (metal-assisted chemical etching) has attracted increasing attention as a low-cost and versatile microfabrication technique of semiconductors. In platinum (Pt)-particle-assisted etching of silicon (Si), a composite structure of straight macropores and a mesoporous layer can be produced, but the mechanism of the structure formation is still open to discussion. We employed an electrochemical approach to investigate the composite structure formation by the Pt-assisted etching. Polarization curves of Pt-deposited Si and bare Si were measured in hydrofluoric acid (HF) solutions containing different concentrations of hydrogen peroxide (H2O2). The open circuit potential during the Pt-assisted etching was more positive than that of the bare Si and it shifted in the positive direction with increasing the H2O2 concentration as a consequence of the enhancement of the H2O2 reduction reaction. For the structure observation, both the macropore depth and the mesoporous layer thickness increased with increasing the H2O2 concentration, while the ratio between them changed. We discussed the structure change on the basis of the polarization characteristics. The mesoporous layer formation can be explained by the hole consumption at the Si surface under the positive potential which is determined by mixed potential theory.

Microfabrication of Alkali Vapor MEMS Cells for chip-scale atomic clock

The technology of MEMS atomic cells containing rubidium or caesium vapors in an atmosphere of neon buffer gas has been developed. Two-chamber silicon cells containing an optical cavity, shallow filtration channels and a technical container for a solid-state alkali source have been implemented in a single-step process of anisotropic wet chemical etching. To prevent significant undercutting of the filtration channels during etching of the through silicon cavities, the shapes of the compensating elements at the convex corners of the silicon nitride mask have been calculated and the composition of the silicon etchant has been experimentally found. The sealing of the cells has been carried out by silicon-glass anodic bonding at a temperature of 250 °C. For this purpose the LK5 glass which has an increased ionic conductivity in comparison with the conventional glass Borofloat 33 was used. The best microfabricated cells allowed us to obtain estimates of the relative instability of the coherent population trapping resonance frequency at the level of 5 · 10-11 at 1 s.

Improvement of thermal‐type MEMS flow sensor chip via new process of silicon etching with sacrificial polycrystalline silicon layer

AbstractThis paper reports upon a new process for the flow sensor fabrication of a thermal microelectromechanical systems (MEMS) and its performance improvement. A unique feature of the proposed process is the silicon etching, which is a combination of normal crystal‐oriented silicon etching and isotropic etching of polycrystalline silicon (poly‐Si). The poly‐Si layer works as a sacrificial layer and promotes etching of the silicon substrate in the horizonal direction, thereby enabling location of the etching holes in the membrane of the flow sensor without the conventional etching rules. Some designs for the flow sensors, which have been infeasible with normal processes, were thus fabricated and evaluated. Hence, the new process improves the design flexibility of the membrane and enhances flow sensor performance, such as 38.3% reduction in power consumption.

Analysis of optical emission spectroscopy data during silicon etching in SF6/O2/Ar plasma

Silicon etching is an essential process in various applications, and a major challenge for etching process is anisotropic high aspect ratio etching characteristics. The etch profile is determined by the plasma parameters and process parameters. In this study, the plasma state with each process parameters were analyzed through the optical emission spectroscopy (OES) plasma diagnostic sensor by both chemical and physical approaches. Electron temperature and electron density were additionally acquired using the corona model with OES data that provides chemical species information, and the etch profile was evaluated through scanning electron microscope measurement data. The results include changes in profile with gas ratio, bias power, and pressure. We figure out that factors like ion energy and ion angular distribution as well as chemical reaction affect the anisotropic profile.

Effect of Phosphorus Doping on Photoinduced Thermal Processes in Silicon Nanowires

We report on the effect of phosphorus doping of silicon nanowires (SiNWs) on the photoinduced heating processes. SiNWs samples were prepared by metal-assisted chemical etching of low boron-doped crystalline silicon (c-Si) wafers followed with thermo-diffusional doping with phosphorous (P) up to 1020 cm-3. We establish that the P-doping (n-type) results in effective heat conduction along SiNWs toward the c-Si substrate during laser heating. Partial phase transition in P-doped SiNWs under intense photoheating was detected by means of Raman spectroscopy and photoluminescence. The observed doping effects were explained by a contribution of charge carriers (electrons) to the heat distribution along SiNWs and partial screening of the crystal lattice potential. The obtained results can be useful for the development of new photonic and optoelectronic devices based on SiNWs.

Improving spatial resolution of scanning SQUID microscopy with an on-chip design

Scanning superconducting quantum interference device (sSQUID) microscopy is currently one of the most effective methods for direct and sensitive magnetic flux imaging on the mesoscopic scale. A SQUID-on-chip (SOC) design allows integration of field coils for susceptometry in a gradiometer setup which is very desirable for measuring magnetic responses of quantum matter. However, the spatial resolution of such a design has largely been limited to micrometers due to the difficulty in approaching the sample. Here, we used electron beam lithography technology in the fabrication of the 3D nano-bridge-based SQUID devices to prepare pick-up coils with diameters down to 150 nm. Furthermore, we integrated the deep silicon etching process in order to minimize the distance between the pick-up coil and the wafer edge. Combined with a tuning-fork-based scanning head, the sharpness of the etched chip edge enables a precision of 5 nm in height control. By scanning measurements on niobium chessboard samples using these improved SQUID devices, we demonstrate sub-micron spatial resolutions in both magnetometry and susceptometry, significantly better than our previous generations of nano-SQUIDs. Such improvement in spatial resolution of SOC is a valuable progress for magnetic imaging of quantum materials and devices in various modes.

Pd/Alumina Catalysts for Beneficial Transformation of Harmful Freon R-22

Chlorodifluoromethane (R-22), the most abundant freon in the atmosphere, was subjected to successful hydrodechlorination in the presence of palladium supported on γ-alumina, at a relatively low reaction temperature (180 °C). The combination of catalytic actions of alumina (performing freon dismutation) and Pd nanoparticles (catalyzing C–Cl bond splitting in the presence of hydrogen) results in the transformation of freon into valuable, chlorine-free products: methane and fluoroform, the mixture of which is used in plasma etching of silicon and silicon nitride. Very highly metal dispersed Pt/Al2O3 catalysts, with metal particles of ~1.3 nm in size, are not as effective as Pd/Al2O3, resulting in only partial dechlorination. A long-term dechlorination screening (3–4 days) showed good catalytic stability of Pd/alumina catalysts.

Dry etching of monocrystalline silicon using a laser-induced reactive micro plasma

Dry etching is a prevalent technique for pattern transfer and material removal in microelectronics, optics and photonics due to its high precision material removal with low surface and subsurface damage. These processes, including reactive ion etching (RIE) and plasma etching (PE), are performed at vacuum conditions and provide high selectivity and vertical side wall etched patterns but create high costs and efforts in maintenance due to the required machinery.In contrast to electrically generated plasmas, laser-induced micro plasmas are controllable sources of reactive species in gases at atmospheric pressure that can be used for dry etching of materials.In the present study, we have demonstrated the laser-induced plasma etching of monocrystalline silicon. A Ti:Sapphire laser has been used for igniting an optically pumped plasma in a CF4/O2 gas mixture near atmospheric pressure. The influence of process parameters, like substrate temperature, O2 concentration, plasma-surface distance, etching duration, pulse energy and crystal orientation on etching rate and surface morphology has been investigated.Typical etching rates of 2–12 µm x min−1 can be achieved by varying mentioned parameters with a decreasing etching rate during the process. Different morphologies can be observed due to the parameters set, smooth as well as rough surfaces or even inverted pyramids.The presented etching method provides an approach for precise machining of silicon surfaces with good surface qualities near atmospheric pressure and sufficiently high material removal rates for ultraprecise surface machining.

Comparison between Bosch and STiGer Processes for Deep Silicon Etching.

The cryogenic process is well known to etch high aspect ratio features in silicon with smooth sidewalls. A time-multiplexed cryogenic process, called STiGer, was developed in 2006 and patented. Like the Bosch process, it consists in repeating cycles composed of an isotropic etching step followed by a passivation step. If the etching step is similar for both processes, the passivation step is a SiF4/O2 plasma that efficiently deposits a SiOxFy layer on the sidewalls only if the substrate is cooled at cryogenic temperature. In this paper, it is shown that the STiGer process can achieve profiles and performances equivalent to the Bosch process. However, since sidewall passivation is achieved with polymer free plasma chemistry, less frequent chamber cleaning is necessary, which contributes to increase the throughput.