Etching Gas Research Articles

Homoepitaxial growth of β-Ga2O3 by halide vapor phase epitaxy

We demonstrated halide vapor phase epitaxy of β-Ga2O3 on a native substrate, which should be scalable and useful for the formation of vertical fins and trenches with smooth (100)-faceted sidewalls using plasma-free microfabrication techniques, e.g., selective area growth and gas etching, for use in power device applications. No misoriented domains were detected in the epiwafer during x-ray pole figure measurements. The full width at half maximum values of the x-ray rocking curves of the epiwafer were virtually the same as those of the bare substrate. No domain boundaries were found using scanning transmission electron microscopy at the film/substrate interface. The growth rate was as high as 23 μm h−1, which was comparable to the rate for a (001) epilayer that was grown simultaneously.

Study on effective dry etching of InGaZnO thin films under capacitively coupled plasma-reactive ion etching with a nonfluorine-based etching gas

Dry etching of InGaZnO (IGZO) thin films was performed in a capacitively coupled plasma-reactive ion etching (CCP-RIE) mode using hydrochloride (HCl) and argon (Ar) gases. Dry-etching characteristics and surface properties of IGZO films were then investigated according to gas mixture ratio, radio frequency power, and chamber working pressure. With an optimized ratio of HCl : Ar at 20 : 20 SCCM, the IGZO film showed good etch characteristics with a moderate etch rate of 6.0 nm/min and a low roughness of 0.19 nm. During the etching process of IGZO thin films, nonvolatile by-products such as GaClx, InClx, and ZnClx generated on the surface could be effectively removed by physical bombardment with Ar+ ions. As a result, we successfully conducted dry etching of IGZO thin films in the CCP-RIE system under HCl-Ar gas conditions, which demonstrated dry etching on IGZO without needing a fluorine-based etching gas.

Wet Chemical and Plasma Etching of Photosensitive Glass

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF4/H2 etching gas mixture with a constant volumetric flow of 30 sccm and a variable H2 concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ cHF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements.

Effect of the temperature and HCl partial pressure on selective-area gas etching of (001) β-Ga2O3

We investigated the anisotropic selective-area HCl-gas etching behavior of SiO2-masked (001) β-Ga2O3 and its dependence on the temperature T (548 °C–949 °C) and HCl partial pressure P 0(HCl) (25–250 Pa). The cross-sectional width-to-depth aspect ratio of the etched trenches formed under the striped window along [010] decreased with increasing T and decreasing P 0(HCl). Secondary-ion mass spectrometry revealed slight diffusion of Si into β-Ga2O3 at T = 949 °C, while no diffusion was detected at T = 750 °C. These results provide practical guidelines for the fabrication of desired three-dimensional structures, such as fins/trenches, for high-performance β-Ga2O3-based power devices.

A transparent superhydrophobic film with excellent self-cleaning and UV resistance for photovoltaic panels

Photovoltaic (PV) energy as a sustainable environmental-friendly power source is expected to solve the issues of resource scarcity and environment deterioration, but the accumulation of contaminants on surface and the degradation of internal materials induced by ultraviolet (UV) severely affect the power generation efficiency and service life of PV modules. Herein, we have presented a transparent superhydrophobic UV resistant film (TSURF) fabricated via lamination and CHF3 gas etching. The TSURF can withstands external damages and chemical environments and still maintain superhydrophobic after >10,000 wet abrasions by using different surface tension liquids and surfactants. Benefitting from the high UV reduction (99.5 %) and the excellent mechanochemical durability as well as extraordinary weatherability of the TSURF, the annual power generation efficiency of the TSURF covered PV panel increases by 66.89 % higher than that of pristine PV panel. Although the size of TSURF film may be constrained by etching machine, this work is expected to solve the problem of low efficiency in the long-term use of renewable energy PV panels.

Plasma-relevant fast electron impact study of difluoromethane

Difluoromethane () is a commonly used etching gas in manufacturing very-large-scale integrated circuits as the fluorine source. Electron impact excitation cross sections for are important input data for modeling the reactive etching plasmas. In this work, we present the experimental generalized oscillator strengths for the , , and transitions on the absolute scale. The measurement was realized by employing the crossed-beam based relative flow technique at an angle-resolved electron energy loss spectrometer, operating at an incident energy of 1500 eV and a resolution of 80 meV. The dipole-forbidden transition at around 9.7 eV is identified for the first time. The measured data are fitted with the well-known Lassettre formula to yield analytical expressions and optical oscillator strengths at for dipole-allowed transitions. The analytical expressions enable integrations over momentum transfer to obtain the Born integral cross sections for electron impact excitations from the threshold to 5000 eV. The integral cross sections for dipole-allowed transitions are scaled to a more reliable level by using the BE-scaling method. The experimental data can benchmark theoretical calculations and supplement the molecular database for plasma modelers.

Controllable Fabrication of Silicon Nanopore Arrays by Two-Step Inductively Coupled Plasma Etching Using Self-Assembled Anodic Aluminum Oxide Mask

Silicon nanopore arrays (SiNPs) were prepared by a two-step inductively coupled plasma (ICP) etching process using a self-assembled anodic aluminum oxide film mask. The influence of etching parameters (first-step etching time, Cl2 proportion in the etching gas, etching pressure, ICP power, and radio frequency (RF) power) on the morphology of the SiNPs were systematically investigated. The results revealed that the first step of ICP etching can effectively remove the barrier layer of the mask. Higher Cl2 proportion and lower etching pressure increase the chemical corrosion and physical bombardment of ICP etching, respectively, which may damage the porous morphology. ICP power affects both chemical reaction etching and physical bombardment, but the RF power mainly affects physical etching. The etching rate is positively correlated with Cl2 proportion and RF power, and negatively correlated with etching pressure. The optimized first-step etching time, Cl2/Ar ratio, etching pressure, ICP power and RF power for high-quality SiNPs are approximately 10 s, 60%, 7 mTorr, 900 W and 100 W, respectively. Precise control of the pore size and depth of the SiNPs can be achieved using this controllable growth process. These results demonstrate a simple and controllable way to achieve good quality SiNPs with desired sizes.

Anisotropic non-plasma HCl gas etching of a (010) β-Ga2O3 substrate

We demonstrated the effectiveness of plasma-free HCl gas etching on a SiO2-masked (010) β-Ga2O3 substrate. The etching process proceeded anisotropically in the window areas, resulting in the fabrication of holes or trenches that were surrounded by etching-resistant (100)- and (01)-faceted sidewalls. When we etched in the striped windows along [001], we were able to create fins and trenches with flat (100)-faceted vertical sidewalls and slightly rough {310}-faceted inclined bottom corners. The vertical-to-horizontal etching ratio was as high as ∼11–14. Our findings indicate that HCl etching is a promising method for fabricating high-aspect-ratio fins/trenches on (010) substrates without causing plasma damage.

Sidewall Modification Process for Trench Silicon Power Devices

In this study, trench sidewall modification processes were designed to improve profile uniformity and thereby enhance the electrical performance of silicon power devices in large-scale production. The effects of trench sidewall modification on the morphology, structure and electrical properties were studied. Plasma-induced damage in etching processes was also observed and briefly explained. Straight and smooth sidewall profiles were achieved through adjusting the SF6/CHF3 proportion in a combined etchant gas flow in the main etching procedure. By comparing HRSEM images from different etching protocols, it was evident that an enhanced CHF3 flow formed a proper passivation of the sidewall, eliminating the ion damages that are common in current main etch steps. To address the impurities introduced from the etchant gas and improve the gate oxide uniformity, further steps of depolymerization were applied in a plasma asher chamber, followed by wet clean steps. In the meantime, the plasma-induced charge accumulation effect was reduced by UV curing. Improved trench sidewall profiles and the gate oxide uniformity contributed to a lower leakage current between the gate and source terminals, leading to an overall yield enhancement of device properties in large-scale silicon wafer fabrication.

Etched characteristics of nanoscale TiO2 using C4F8-based and BCl3-based gases

TiO2 is a material used in various fields such as electronics, optics, environment, etc. For the application to electronic and optical devices, TiO2 needs to be patterned using reactive ion etching using halogen-based gases. In this study, a TiO2 masked with ACL pillar pattern was etched using two types of gases namely C4F8-based (C4F8/SF6/Ar) and BCl3-based (BCl3/CF4/Ar), and the effect of etch gas and asynchronous pulsing (separated source power ON time and bias power ON time in a pulse period) on the etch properties such as the etch rates, etch selectivity, and aspect ratio dependent etching (ARDE) were investigated. The use of asynchronous pulsing with decreased bias pulsing ratio (high source power ON time and low bias ON time in a pulse period) improved the etch selectivity and ARDE possibly due to the lower sputter etching time after the removal of reacted species on the TiO2 surface and due to the more similar etch environment for different aspect ratio TiO2 features, respectively. The use of BCl3-based plasma showed higher etch selectivity over ACL compared to C4F8-based plasma, however, it showed the lower etch rate and more severe ARDE due to the stickiness of Cl compared to F to the sidewall during the etching of high aspect ratio TiO2.

Improving Oxygen Reduction Performance of Surface-Layer-Controlled Pt-Ni Nano-Octahedra via Gaseous Etching.

This study demonstrates an atomic composition manipulation on Pt-Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt-Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt-Ni nano-octahedral sample shows a mass activity of 1.50 A/mgPt, exceeding the initial mass activity of the unetched counterpart (1.40 A/mgPt) and outperforming the benchmark Pt/C (0.18 A/mgPt) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features.

Highly active mesoporous Co–Al2O3 sorbents for the efficient destructive sorption of NF3

Nitrogen trifluoride (NF3) is widely used as an etching gas and cleaning agent in the microelectronics industry. However, it is a novel and powerful greenhouse gas. The destructive sorption of NF3 over metal oxides is an efficient route to control its emission. Here, several sorbents of homogeneous Co–Al2O3 oxides were prepared via changing the molar ratios of HNO3 to Al(OPri)3 in the raw materials, whose impact on the structure of sorbents and the reactivity for NF3 destructive sorption was investigated. It is found that the destructive reactivity of sorbents is strongly affected by their surface area and pore volume. Impressively, the optimal Co–Al2O3-2.45 sorbent with the largest surface area and pore volume presents the longest time of NF3 complete destruction, which is clearly more active than most of the results in the literature. Furthermore, the F migration over the solid interfaces between Al2O3 and Co oxides in Co–Al2O3 sorbents enhances the efficient destruction of NF3. These findings well explain the better reactivity of Co–Al2O3 complex oxides than bare Al2O3, and are beneficial to develop more efficient sorbents for NF3 destruction.

High-density plasma etching of cobalt thin films using C2H5OH/O2/Ar gas mixture

In this study, Co thin films were etched using a C2H5OH/O2/Ar gas mixture via high-density plasma etching. As the concentrations of C2H5OH and O2 gases increased, the etch rate of the Co films decreased, whereas the etch profile improved. The addition of O2 to C2H5OH/Ar led to reduced redeposition on the sidewalls of the Co films. According to X-ray photoelectron spectroscopy and optical emission spectroscopy, the formation of Co(OH)2 compounds is critical for obtaining a redeposition-free etch profile, and CoOx may act as a reaction intermediate. Based on these findings, the C2H5OH/O2/Ar gas mixture can be used as a prospective etching gas in the etching of Co thin films.

Reactive ion Etching of SiO2 and Mo Sidewall Profile Process

This paper investigates the process parameters affecting the sidewall angle of Mo and SiO2 films based on the reactive ion etching (RIE) system, firstly, the photoresist mask with a certain sidewall angle was obtained by adjusting the hardening temperature and hardening time of the photoresist during the lithography process, and their effects on the sidewall angle of the photoresist mask were investigated. In the RIE etching of SiO2 and Mo, the etching gas type (CHF3, CF4, SF6), O2 flow rate, and their effects on the sidewall angle of SiO2 were adjusted to obtain the sidewall angle of SiO2 in the range of 15°~53°, During the RIE etching of Mo, the RF power, SF6 flow rate, and O2 flow rate were adjusted and their effects on the Mo sidewall angle were investigated, resulting in a range of 17.3° to 30.2° for the Mo sidewall angle. This is useful for the study of the thin film body acoustic resonator (FBAR) process.

Plasma-Etched Vertically Aligned CNTs with Enhanced Antibacterial Power.

The emergence of multidrug-resistant bacteria represents a growing threat to public health, and it calls for the development of alternative antibacterial approaches not based on antibiotics. Here, we propose vertically aligned carbon nanotubes (VA-CNTs), with a properly designed nanomorphology, as effective platforms to kill bacteria. We show, via a combination of microscopic and spectroscopic techniques, the ability to tailor the topography of VA-CNTs, in a controlled and time-efficient manner, by means of plasma etching processes. Three different varieties of VA-CNTs were investigated, in terms of antibacterial and antibiofilm activity, against Pseudomonas aeruginosa and Staphylococcus aureus: one as-grown variety and two varieties receiving different etching treatments. The highest reduction in cell viability (100% and 97% for P. aeruginosa and S. aureus, respectively) was observed for the VA-CNTs modified using Ar and O2 as an etching gas, thus identifying the best configuration for a VA-CNT-based surface to inactivate both planktonic and biofilm infections. Additionally, we demonstrate that the powerful antibacterial activity of VA-CNTs is determined by a synergistic effect of both mechanical injuries and ROS production. The possibility of achieving a bacterial inactivation close to 100%, by modulating the physico-chemical features of VA-CNTs, opens up new opportunities for the design of self-cleaning surfaces, preventing the formation of microbial colonies.

The role of silanol groups on the reaction of SiO2 and anhydrous hydrogen fluoride gas

AbstractIt is essential to etch SiO2 for producing silica glass components, semiconductor devices, and so on. Although wet‐etching with hydrogen fluoride (HF) solutions is usually employed for this purpose, it faces a drawback that microstructures stick during the drying of the solution. To overcome this problem, we have developed a dry‐etching technique with gaseous HF at high temperatures. In the present study, an interesting phenomenon was found that silicon thermal oxides were much less etched than vitreous silica by gaseous HF. Such difference had not been found in wet‐ or humid HF gas etching. Because their bulk chemical formulae are the same (SiO2), it was suggested that the surface species affected the reaction rate. In fact, preprocessing with water vapor plasma remarkably increased the etching rate on the thermal oxides layer, and vacuum heating almost completely suppressed the reaction on the vitreous silica and the plasma‐treated thermal oxides. These results indicate that the surface silanol groups enhance the reaction between SiO2 and gaseous HF. Based on the results, a model of chain reaction for SiO2 and gaseous HF was proposed, where the surface silanol groups act as the reaction center.

Graphene: Preparation, tailoring, and modification.

Graphene is a 2D material with fruitful electrical properties, which can be efficiently prepared, tailored, and modified for a variety of applications, particularly in the field of optoelectronic devices thanks to its planar hexagonal lattice structure. To date, graphene has been prepared using a variety of bottom-up growth and top-down exfoliation techniques. To prepare high-quality graphene with high yield, a variety of physical exfoliation methods, such as mechanical exfoliation, anode bonding exfoliation, and metal-assisted exfoliation, have been developed. To adjust the properties of graphene, different tailoring processes have been emerged to precisely pattern graphene, such as gas etching and electron beam lithography. Due to the differences in reactivity and thermal stability of different regions, anisotropic tailoring of graphene can be achieved by using gases as the etchant. To meet practical requirements, further chemical functionalization at the edge and basal plane of graphene has been extensively utilized to modify its properties. The integration and application of graphene devices is facilitated by the combination of graphene preparation, tailoring, and modification. This review focuses on several important strategies for graphene preparation, tailoring, and modification that have recently been developed, providing a foundation for its potential applications.

Plasma synthesis of oxygen vacancy-rich CuO/Cu2(OH)3NO3 heterostructure nanosheets for boosting degradation performance.

Defect regulation and the construction of a heterojunction structure are effective strategies to improve the catalytic activity of catalysts. In this work, the rapid conversion of CuO to Cu2(OH)3NO3 was achieved by fixing nitrogen in air as NO3- using dielectric barrier discharge (DBD) plasma. This innovative approach resulted in the successful synthesis of a CuO/Cu2(OH)3NO3 nanosheet heterostructure. Notably, the samples prepared using plasma exhibit thinner thickness and larger specific surface area. Importantly, oxygen vacancies are introduced, simultaneously forming heterojunction interfaces within the CuO/Cu2(OH)3NO3 structure. CuO/Cu2(OH)3NO3 using plasma effectively degraded 96% of methyl orange within 8 min in the dark. The degradation rate is 81 and 23 times that of CuO and Cu2(OH)3NO3 using hydrothermal methods, respectively. The high catalytic activity is attributed to the large specific surface area, the abundance of active sites, and the synergy between oxygen vacancies and the strong heterojunction interfacial interactions, which accelerate the transfer of electrons and the production of reactive oxygen species (˙O2- and ˙OH). The mechanism of plasma preparation was proposed on account of microstructure characterization and online mass spectroscopy, which indicated that gas etching, gas expansion, and the repulsive force of electrons play key roles in plasma exfoliation.

Scanning electron microscope analysis to evaluate the effect of pretreatment with ozone and sodium hypochlorite on pits and fissures of primary teeth.

The cornerstone of preventative therapy is made up of pit and fissure sealants and fluorides. Resin sealants have been shown to help reduce fissure decay in both primary and permanent teeth. Etching of primary molars is not effective due to prismless enamel, higher organic content, and diversity in fissure shape. Methods of pretreatment of pits and fissures have been hypothesized to promote microporosities in etched enamel and hence sealant adherence. Examining the etching pattern and surface roughness of the enamel surface can be used to gauge these. This study aimed to evaluate the effect of pretreatment with ozone gas and 5.25% sodium hypochlorite solution on pits and fissures of primary teeth to check for the etching pattern and surface roughness. Thirty noncarious primary molars were sectioned to retain the crowns, and randomly divided into three groups, sodium hypochlorite, ozone gas, and control. Each sample was pretreated with the agent, washed, followed by etching with 37% phosphoric acid. Samples were sectioned and subjected to scanning electron microscope analysis to evaluate the etching pattern and surface roughness. Comparison of the etching pattern in three groups showed a statistically insignificant difference (P=0.364). Surface roughness was highest in the hypochlorite group followed by ozone and control which showed a statistically significant difference (P = 0.001). The surface area between the three groups showed a statistically insignificant difference. Sodium hypochlorite is a better pretreatment agent compared to ozone gas and acid etching alone. However, as all results were not statistically significant further research must be carried out to prove the effectiveness of these agents.

Efficient fabrication of single-wall carbon nanotube nanoreactors by defect-induced cutting.

Single-wall carbon nanotubes (SWCNTs) with ultra-thin channels are considered promising nanoreactors for confined catalysis, chemical reactions, and drug delivery. The fabrication of SWCNT nanoreactors by cutting usually suffers from low efficiency and poor controllability. Here we develop a defect-induced gas etching method to efficiently cut SWCNTs and to obtain nanoreactors with ultrasmall confined space. H2 plasma treatment was performed to generate defects in the walls of SWCNTs, then H2O vapor was used as a "knife" to cut SWCNTs at the defect sites, and short cut-SWCNTs with an average length of 175 nm were controllably obtained with a high yield of 75% under optimized conditions. WO3@SWCNT derivatives with different morphologies were synthesized using short cut-SWCNTs as nanoreactors. The radiation resistance of WO3@SWCNT hybrids improved obviously, thus providing a platform for the synthesis of novel SWCNT-based derivatives with fascinating properties.