Etching Of Si Research Articles

Wafer-Scale Fabrication of Silicon Nanocones via Controlling Catalyst Evolution in All-Wet Metal-Assisted Chemical Etching.

All-wet metal-assisted chemical etching (MACE) is a simple and low-cost method to fabricate one-dimensional Si nanostructures. However, it remains a challenge to fabricate Si nanocones (SiNCs) with this method. Here, we achieved wafer-scale fabrication of SiNC arrays through an all-wet MACE process. The key to fabricate SiNCs is to control the catalyst evolution from deposition to etching stages. Different from conventional MACE processes, large-size Ag particles by solution deposition are obtained through increasing AgNO3 concentration or extending the reaction time in the seed solution. Then, the large-size Ag particles are simultaneously etched during the Si etching process in an etching solution with a high H2O2 concentration due to the accelerated cathode process and inhibited anode process in Ag/Si microscopic galvanic cells. The successive decrease of Ag particle sizes causes the proportionate increase of diameters of the etched Si nanostructures, forming SiNC arrays. The SiNC arrays exhibit a stronger light-trapping ability and better photoelectrochemical performance compared with Si nanowire arrays. SiNCs were fabricated by using n-type 1–10 Ω cm Si(100) wafers in this work. Though the specific experimental conditions for preparing SiNCs may differ when using different Si wafers, the summarized diagram will still provide valuable guidance for morphology control of Si nanostructures in MACE processes.

Исследования комплексного дефектообразования в кремнии, легированном никелем

The behavior of nickel and hydrogen impurities in silicon has been studied by deep-level transient spectroscopy (DLTS) and Raman spectroscopy. It is shown that the vibrations of Ni and H atoms in Si are in the range of 925-985 cm-1. The DLTS spectra in n - and p -type silicon doped with Ni atoms exhibit two deep levels with energies Ev +0.17 eV and Ec -0.42 eV. It was found that during chemical etching in Si doped with Ni, various hydrogen-bonded defect complexes are formed, the energies of which are Ec -0.18 eV, Ec -0.54 eV, Ev +0.26 eV, and Ev +0.55 eV.

Optimization of triangular-profiled Si-grating fabrication technology for EUV and SXR applications

Anisotropic wet etching of vicinal monocrystalline Si (111)4o wafers was used to obtain blazed gratings that are highly efficient in the soft X-ray (SXR) and extreme ultraviolet (EUV) applications. An improved experimental technology for the fabrication of triangular-grooved Si gratings, both medium-frequency (250 and 500 mm-1) and high-frequency (2500 mm-1) ones, is presented. The stages of forming a Cr-mask for grooves etching, removing Si nubs in order to smooth the profile, and polishing the surface to reduce nanoroughness have been optimized. This paper describes the way of simultaneously (in one process) obtaining a smoothed triangular profile of the Si grating and a polished surface of facets by wet etching. Keywords: diffraction grating, Si wet etching, triangular groove profile, AFM, SEM.

Blazed Diffraction Gratings on Si --- First Results

Using direct laser lithography and wet etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 grooves/mm with a blaze angle of 4o were fabricated. The manufacturing process of a reflective Si-grating with the triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for grooves etching; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the RMS roughness was less than 0.3 nm. Using PCGrateTM software and taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating. Keywords: diffraction grating, wet etching technology of Si, sawtooth groove profile, AFM, SEM, diffraction efficiency modelling.

Оптимизация технологии изготовления дифракционных Si-решеток треугольного профиля для мягкого рентгеновского и экстремального ультрафиолетового излучения

Anisotropic wet etching of vicinal single-crystallyne Si (111)4° wafers was used to obtain blazed gratings with high efficiency for soft X-ray (SXR) and extreme ultraviolet (EUV) applications. An improved experimental technology for the fabrication of triangular Si gratings, both medium frequency (250 and 500 mm-1) and high-frequency 2500 mm-1, is presented. The stages of a Cr mask formation for grooves etching, removing Si protrusions in order to smooth the profile, and polishing the surface to reduce nanoroughness are optimized. This work describes the method for simultaneous (in one process) obtaining a smoothed triangular profile of the Si grating and a polished surface of grooves by wet etching.

Wetting behavior of silicon nanowires array fabricated by Metal-assisted chemical etching

A silicon (Si) substrate exhibits a hydrophobic surface (contact angle, CA ∼ 90.2⁰), and upon anodization, the porous Si (PSi) also possesses a hydrophobic surface (CA ∼ 142.4⁰). Silicon nanowires (SiNWs) array, also known as black silicon, exhibits lotus effect, i.e., water droplet role-over the surface without penetrating inside the surface. An array of SiNWs, fabricated by metal-assisted chemical etching (MACE) of Si, act as a superhydrophobic surface (i.e., CA > 150⁰) without using any functionalization material. The MACE fabricates etched-Si, using PSi substrate that also possesses a superhydrophobic surface. Trapped air, present among the conical tips of the densely formed SiNWs array, reduces the solid–liquid contact area and improves the de-wetting behavior. The trapped air increases on increasing the length of SiNWs, which further enhances the de-wetting behavior. The wetting behavior changes to hydrophobic/hydrophilic when kept for a longer duration due to the aging effect. Oxidation causes aging and changes the conical/dendrite structure of the SiNWs/etched-Si surface. The Fourier transform infrared spectroscopy confirms the hydrogen passivation on the surfaces of SiNWs because of HF etching and highly oxidized surfaces due to the effect of aging.

Fundamental study on the selective etching of SiGe and Si in ClF3 gas for nanosheet gate-all-around transistor manufacturing: A first principle study

We conduct an atomic-level investigation on how a Ge atom impacts on the SiGe etching rate. The plasmaless dry-etching process in ClF3 gas is considered in this study. We perform the density functional theory to model the elementary reactions of an etchant molecule fluorinating Si/Ge atom. Based on the modeling results, the activation energy (Ea) of a single-F-transfer breaking Ge-Ge bond is 0.4 eV lower than the Si-Si bond, with the Ea of Si-Ge cases fall between. The overall smaller Ea suggests that the relatively active fluorination reaction enabled by a Ge atom facilitates the selective etching. In addition, a unique double-F-transfer from ClF3 is identified, which simultaneously fluorinates two adjacent Ge atoms. The reaction enhances selective etching with the drastically lowered Ea and the more negative total energy change. We modeled different locations of a Ge atom with respect to the fluorinated Si atom. The results show that the effect of the Ge atom on lowering the Si fluorination Ea has a long-range nature. The calculation predicts a reduced Ea even when the Ge atom is on the second-nearest-neighbor site to the fluorinated Si atom. The finding implies that the Ge-induced Ea reduction can continuously assist the selective etching with a Ge-percentage as low as 6 at. %. Details of the surface chemical reactions and byproduct formation are discussed in the report.

Comparative study of CF4 + O2 and C6F12O + O2 plasmas for reactive‐ion etching applications

AbstractThis work represents a comparative study of gas‐phase parameters and reactive‐ion etching kinetics for Si and Si and SiO2 in CF4 + O2 and C6F12O + O2 plasmas. An interest to the C6F12O gas is because it combines the low global warming potential (low environmental impact) and weakly studied dry etching performance. It was shown that the investigated gas systems showed similar effects of processing conditions on electron‐ and ion‐related plasma parameters as well as on the densities of F and O atoms. Etching experiments showed identical behaviors of Si and SiO2 etching rates as well as very similar SiO2/Si etching selectivities. The notable feature of the C6F12O + O2 plasma is only the systematically lower absolute etching rates that correlate with lower in F atom densities.

Optimization of Metal-Assisted Chemical Etching for Deep Silicon Nanostructures.

High-aspect ratio silicon (Si) nanostructures are important for many applications. Metal-assisted chemical etching (MACE) is a wet-chemical method used for the fabrication of nanostructured Si. Two main challenges exist with etching Si structures in the nanometer range with MACE: keeping mechanical stability at high aspect ratios and maintaining a vertical etching profile. In this work, we investigated the etching behavior of two zone plate catalyst designs in a systematic manner at four different MACE conditions as a function of mechanical stability and etching verticality. The zone plate catalyst designs served as models for Si nanostructures over a wide range of feature sizes ranging from 850 nm to 30 nm at 1:1 line-to-space ratio. The first design was a grid-like, interconnected catalyst (brick wall) and the second design was a hybrid catalyst that was partly isolated, partly interconnected (fishbone). Results showed that the brick wall design was mechanically stable up to an aspect ratio of 30:1 with vertical Si structures at most investigated conditions. The fishbone design showed higher mechanical stability thanks to the Si backbone in the design, but on the other hand required careful control of the reaction kinetics for etching verticality. The influence of MACE reaction kinetics was identified by lowering the oxidant concentration, lowering the processing temperature and by isopropanol addition. We report an optimized MACE condition to achieve an aspect ratio of at least 100:1 at room temperature processing by incorporating isopropanol in the etching solution.

Multiscale modeling of plasma–surface interaction—General picture and a case study of Si and SiO2 etching by fluorocarbon-based plasmas

The physics and chemistry of plasma–surface interaction is a broad domain relevant to various applications and several natural processes, including plasma etching for microelectronics fabrication, plasma deposition, surface functionalization, nanomaterial synthesis, fusion reactors, and some astrophysical and meteorological phenomena. Due to their complex nature, each of these processes is generally investigated in separate subdomains, which are considered to have their own theoretical, modeling, and experimental challenges. In this review, however, we want to emphasize the overarching nature of plasma–surface interaction physics and chemistry, by focusing on the general strategy for its computational simulation. In the first half of the review, we provide a menu card with standard and less standardized computational methods to be used for the multiscale modeling of the underlying processes. In the second half, we illustrate the benefits and potential of the multiscale modeling strategy with a case study of Si and SiO2 etching by fluorocarbon plasmas and identify the gaps in knowledge still present on this intensely investigated plasma–material combination, both on a qualitative and quantitative level. Remarkably, the dominant etching mechanisms remain the least understood. The resulting new insights are of general relevance, for all plasmas and materials, including their various applications. We therefore hope to motivate computational and experimental scientists and engineers to collaborate more intensely on filling the existing gaps in knowledge. In this way, we expect that research will overcome a bottleneck stage in the development and optimization of multiscale models, and thus the fundamental understanding of plasma–surface interaction.

Etching of smoothing/without undercutting deep trench in silicon with SF6/O2 containing plasmas

In this article, the effects of He and Ar which are added into SF6/O2 containing plasmas were investigated in deep Si etching. External controllable parameters such as the He or Ar gas flow were used to study the changes of Si etch rate, Si undercut, oxide selectivity and feature shape correlation. The opening width of feature shape is from 0.22 μm to 0.42 μm. The result shows that the Si undercut decreases and the profile of Si trench is more vertical with the increasing He gas flow in all structures. But the Si etch rate and oxide selectivity will decrease. It is noteworthy that Ar and He have similar effects in reducing undercut. After detailed data analysis, it was found that there were some correlations between Si undercut and normalized residence time in both plasmas. The mechanism of this phenomenon is that the F radicals are diluted due to the addition of a large amount of He and Ar. With the decrease of the F radicals, the lateral etching ability decreases and undercut decreases. The concentration of O and F radicals decreases at almost the same rate when He or Ar gas is mixed, the sidewall profile of trench has no change. Due to the additional vertical bombardment of He+ and Ar+ which produces in the plasma with the addition of the He and Ar, the sidewalls of the Si trench become more vertical. Based on this, an optimized trench etching process is proposed and the etch rate is 1.25 um min−1, the selectivity for oxide mask is 9.5, and the undercut is less than 50 nm.

Specific Features of the Kinetics of the Reactive-Ion Etching of Si and SiO2 in a CF4 + O2 Mixture in a Low Power Supply Mode

Specific Features of the Kinetics of the Reactive-Ion Etching of Si and SiO2 in a CF4 + O2 Mixture in a Low Power Supply Mode

Optical Monitoring of the Biodegradation of Porous and Solid Silicon Nanoparticles.

Silicon nanoparticles (SiNP) are currently of great interest, especially in biomedicine, because of their unique physicochemical properties combined with biodegradability. SiNPs can be obtained in various ways and can have either a non-porous solid (sol-) or porous (por-) structure. In this work, we carry out detailed optical monitoring of sol- and por-SiNP biodegradation using Raman and photoluminescence (PL) micro-spectroscopy. SiNPs were obtained by ultrasound grinding of sol- or por-silicon nanowires, created by silver-assisted chemical etching of crystalline Si with different doping levels. In this case, sol-SiNPs consist of nanocrystals 30 nm in size, while por-SiNPs consist of small 3 nm nanocrystals and 16 nm pores. Both SiNPs show low in vitro cytotoxicity towards MCF-7 and HEK293T cells up to 800 μg/mL. The appearance of the F-band (blue–yellow) PL, as well as a decrease in the intensity of the Raman signal, indicate the gradual dissolution of the sol-SiNPs during 20 days of incubation. At the same time, the rapid dissolution of por-SiNP within 24 h is identified by the quenching of their S-band (red) PL and the disappearance of the Raman signal. The obtained results are important for development of intelligent biodegradable drug delivery systems based on SiNPs.

Molecular dynamics simulation for reactive ion etching of Si and SiO2 by SF5+ ions

Silicon (Si)-based materials such as Si and silicon dioxide (SiO2) are commonly used as basic components of advanced semiconductor devices. For example, alternating stacks of poly-Si and SiO2 layers are used in three-dimensional (3D) NAND flash memory devices. Fabrication of high-aspect-ratio deep holes through such stacked materials by plasma etching may be achieved by highly energetic and chemically reactive ion injections to the surface. Etching by sulfur hexafluoride (SF6) plasmas can produce ions carrying multiple fluorine (F) atoms and therefore exhibit high etch rates for both Si and SiO2. In this study, reactive ion etching of Si and SiO2 materials by SF5+ ions was examined with the use of molecular dynamics (MD) simulation. For this purpose, a simplified interatomic potential functions model for sulfur (S) was developed that approximately represents molecular moieties or molecules SFn (n≤6) based on density-functional-theory (DFT) calculations. The etching yields of Si and SiO2 by SF5+ ions evaluated by MD simulations with these new potential functions were found to be in good agreement with those obtained from multibeam injection system experiments, which implies that the etching process is essentially due to sputtering enhanced by chemical reactions of F atoms with the surface materials. Analyses of the depth profiles of atomic concentrations of etched surfaces and desorbed species obtained from MD simulations also indicate that the presence of excess F atoms on the surface enhances the etching yield of Si and SiO2 significantly over corresponding physical sputtering.

Achieving high-responsivity near-infrared detection at room temperature by nano-Schottky junction arrays via a black silicon/platinum contact approach

A room temperature sub-bandgap near-infrared ( λ > 1100 nm ) Si photodetector with high responsivity is achieved. The Si photodetector features black Si made by wet etching Si (100), Si/PtSi nano-Schottky junction arrays made from black Si/Pt contacts, and chemical and field-effect passivation of black Si. Responsivities are 147.6, 292.8, and 478.2 mA/W at reverse voltages of − 1.0 , − 1.5 , and − 2.0 V for 1550 nm light, respectively, with corresponding specific detectivities being 9.79 × 10 8 , 1.88 × 10 9 , and 2.97 × 10 9 cm · Hz 1 / 2 / W . This work demonstrates a practical room temperature sub-bandgap near-infrared Si photodetector that can be made in a facile and large-scale manner.

Near-infrared detection in Si/InP core-shell radial heterojunction nanowire arrays

We have explored the photodetection properties of a core-shell nanowire (NW) heterojunction based device consisting of p-Si/n-InP with an aim to provide an alternative to Si based photodetector by integrating a III-V material, viz. InP with silicon. The core is p-Si NWs, prepared by metal assisted chemical etching of p-type Si (100) substrate at room temperature using Ag nanoparticles, whereas n-type InP shells were deposited by metal organic chemical vapor deposition. The current-voltage characteristics of the device resemble that of a p-n junction with good rectification ratio in the dark, and provides photoresponse under visible and near-infrared (NIR) spectral region at low reverse bias condition. In the NIR regime, it shows an on/off ratio of 23 with a rise and fall time of 387 ms and 424 ms, respectively, at a reverse bias voltage of 2 V. The device exhibits a peak responsivity and detectivity of 2.749 A/W and 5.52 × 1011 Jones, respectively, at 920 nm under the same reverse bias voltage. Thus p-SiNW/n-InP core-shell based device could have the potential to be developed as an optoelectronic device beyond the traditional p-n junction exploiting its radial heterojunction based structure.

CO2 sensing behavior of vertically aligned Si Nanowire/ZnO structures

Metal oxide nanostructures are highly attractive for the fabrication of gas sensors due to their high surface‐to‐volume ratios. The design of novel structures has great importance to improve sensing behavior. Atomic layer deposited ZnO thin film on vertically aligned silicon nanowire (Si NW) arrays were used to understand the influence of etching time on CO2 sensing behavior of the SiNW/ZnO structure. The metal-assisted chemical etching method was used to realize SiNW arrays. The etching processes were performed for 5, 10, 30, and 60 min. The linear relationship between etching time and Si NW length was reported. 30 nm ZnO thin films were deposited on Si NWs by atomic layer deposition (ALD) method using diethyl Zinc and H2O as Zn and O2 sources, respectively. The CO2 sensing properties of the SiNW/ZnO structures were examined at ambient temperature and low CO2 concentration. The testing measurement results reveal that the sensor realized on un-etched Si does not exhibit any sensitivity. While the SiNW/ZnO was sensitive to CO2, the sensor sensitivity increase with the etching time due to the increase in the specific reactive surface. Moreover, the realized sensors have a relatively low response and recovery times, in the range of 2–7 s, by comparison to the reported ones in the literature.

Development of Virtual Metrology Using Plasma Information Variables to Predict Si Etch Profile Processed by SF6/O2/Ar Capacitively Coupled Plasma.

In the semiconductor etch process, as the critical dimension (CD) decreases and the difficulty of the process control increases, in-situ and real-time etch profile monitoring becomes important. It leads to the development of virtual metrology (VM) technology, one of the measurement and inspection (MI) technology that predicts the etch profile during the process. Recently, VM to predict the etch depth using plasma information (PI) variables and the etch process data based on the statistical regression method had been developed and demonstrated high performance. In this study, VM using PI variables, named PI-VM, was extended to monitor the etch profile and investigated the role of PI variables and features of PI-VM. PI variables are obtained through analysis on optical emission spectrum data. The features in PI-VM are investigated in terms of plasma physics and etch kinetics. The PI-VM is developed to monitor the etch depth, bowing CD, etch depth times bowing CD (rectangular model), and etch area model (non-rectangular model). PI-VM for etch depth and bowing CD showed high prediction accuracy of R-square value (R2) 0.8 or higher. The rectangular and non-rectangular etch area model PI-VM showed prediction accuracy R2 of 0.78 and 0.49, respectively. The first trial of virtual metrology to monitor the etch profile will contribute to the development of the etch profile control technology.

Effect of Convection on Chirality of Spatiotemporal Patterns Observed in the Reduction of Hydrogen Peroxide

Background The spatiotemporal patterns have been reported in many electrochemical systems. Most of the patterns disappear when the reactions stop. This is because they originate from the spatial distribution of the local current and potential during the reactions. However, it is possible to inscribe the patterns into materials by utilizing the pattern formation in the material processing. This process enables to fabricate materials with unique shapes reflecting the pattern profile and is expected to be a new method for the production of such highly sophisticated materials. As one of the materials formed in this process, we have focused on the helical nanopore formed in the Platinum-assisted chemical etching of Si induced by the oxidation of Si and the reduction of H2O2. In this phenomenon, the helical pores are spontaneously formed by immersing the Si substrate modified with Pt nanoparticles into the etchant. We reported that the formation of helical pores originates from a spatiotemporal pattern emerging in the reduction reaction of H2O2 on the Pt particle. Our recent paper on helical nanopore formation in the etching of silicon implies that it is possible to fabricate chiral materials by utilizing the spatiotemporal pattern. In order to utilize the chiral material formed by the spatiotemporal pattern formation in the field of chiral chemistry, it is an inevitable task to control the chirality of the material. Because it is determined by the chirality of the pattern, we have to understand the effect of spatial symmetry breaking on the chirality of the spatiotemporal pattern. In this report, we focus on convection as the chiral condition introduced to the system and investigate its effect on the chirality of the spatiotemporal pattern. Among the several spatiotemporal patterns, we focus on the rotating waves (RW), where active and inactive sites rotate on the ring electrode because it is considered that this pattern emerges during the helical pore formation.Experimental In order to investigate the effect of the convection on the RW, we simulate the formation of the RW during the electrochemical reduction of H2O2 on the Platinum ring electrode based on the model constructed by Fukushima. In this model, we deal with the local electrode potential (E) and the local concentration of H2O2 (c) on the electrode surface as the variables. The differential equations governing E and c ware obtained by considering the equivalent circuit and the consumption and diffusion of H2O2, respectively. Since RWs have two different modes, which are the right-handed rotating wave (R-RW) and the left-handed rotating wave (L-RW), either may appear preferentially in the system where convection is considered. We conducted the simulation several times in a certain condition with random perturbation, and examined the percentage of R-RW in all RWs formed (R-RW%). In this simulation we always introduced the right-handed convection.Result and discussion The R-RW% changed depending on the velocity of the convection (v). When the convection was strong and v was 10 m/s, the R-RW was 0%, meaning that only the L-RW was formed. It should be emphasized that the RWs in the opposite direction to that of the convection, i.e. upstream RWs were formed in this condition. In contrast, when convection was mild and v was 0.1~1 m/s, the direction of the preferential RW was different from that of the RW formed when v was 10 m/s. In other words, the RW whose direction was the same as that of the convection (the downstream RW) was preferentially formed under mild convection. These results suggest that the formation of downstream RWs under mild convection is governed by the nonlinear dynamics. The observation of the change in the distribution of c and E showed that E in some area of the electrode got out of the potential region, where a negative differential resistance (NDR) appeared in the current-potential curve, at the initial stage of the RW formation. As a result, the double concavities emerged in the distribution of c. Therefore, we concluded that the competition of the effects of the convection on the double concavities and the whole concavity caused the change of the preferential RW with v.

Gas‐phase chemistry and reactive‐ion etching kinetics for silicon‐based materials in C4F8 + O2 + Ar plasma

AbstractIn this study, we investigated the effects of C4F8/O2 and Ar/O2 component ratios in C4F8 + O2 + Ar gas system on plasma parameters, gas‐phase chemistry, and etching kinetics for Si, SiO2, and Si3N4 under the condition of inductively coupled radiofrequency (13.56 MHz) plasma. The use of plasma diagnostics by Langmuir probes, together with the zero‐dimensional plasma modeling, allowed one to compare two different gas mixing regimes in respect to (a) electrons‐ and ions‐related plasma parameters; (b) steady‐state densities of plasma active species; and (c) formation and decay kinetics for F atoms and polymerizing radicals. It was shown that variations in both C4F8/O2 and Ar/O2 mixing ratios result in nonmonotonic (with maximums at ∼10% to 15% O2) Si, SiO2, and Si3N4 etching rates as well as in opposite changes in corresponding effective reaction probabilities. The model‐based analysis of etching mechanisms allowed one to suggest that the net effect from all heterogeneous (i.e., appeared on the etched surface) interaction pathways may be controlled either by the fluorocarbon radical flux (in the case of Ar/O2 mixing ratios at constant fraction of C4F8) through the polymer film thickness or by the O atom flux (in the case of C4F8/O2 mixing ratios at constant fraction of Ar) through the balance of adsorption sites.