Radio Frequency Plasma Etching Research Articles

Ar/NH3 Radio‐Frequency Plasma Etching and N‐doping to Stabilize Metallic Phase 1T‐MoS2 for Fast and Durable Sodium‐Ion Storage

AbstractMetallic phase 1T‐MoS2 is considered a prospective anode material for sodium‐ion batteries (SIBs) due to its remarkable electrical conductivity and unique layered structure. However, 1T‐MoS2 is thermodynamically unstable and prone to phase transition to the 2H‐MoS2 phase. Herein, self‐supporting nitrogen‐doped and carbon‐coated 1T/2H mixed‐phase MoS2 nanosheets with rich sulfur vacancies on carbon cloth (C@N‐MoS2‐p/CC) are synthesized through a hydrothermal method and Ar/NH3 radio‐frequency (RF) plasma treatment process. Density‐functional‐theory (DFT) calculations demonstrate that after Ar/NH3 RF plasma treatment, nitrogen‐doping and etching effects are realized, which combine with carbon‐coating significantly reduce the phase transition energy of 1T‐MoS2, thus triggering the phase transition and enabling the stable existence of the highly active 1T‐MoS2. As a result, the C@N‐MoS2‐p/CC exhibits outstanding sodium storage performance, with initial charge–discharge capacities of 701.0/797.0 mAh g−1 at 1 A g−1, respectively. It also demonstrates exceptional rate capabilities and ultra‐high cyclic stability, maintaining a discharge capacity of 404.2 mAh g−1 after 910 cycles at a high rate of 2 A g−1. In a full cell with Na3V2(PO4)3/CC cathode, it exhibits excellent initial charge–discharge capacities of 102.3/102.9 mAh g−1 and maintains satisfactory cycling stability after 350 cycles (86.7 mAh g−1) at 0.1 C.

Ar/NH3 Plasma Etching of Cobalt-Nickel Selenide Microspheres Rich in Selenium Vacancies Wrapped with Nitrogen Doped Carbon Nanotubes as Highly Efficient Air Cathode Catalysts for Zinc-Air Batteries.

This work utilizes defect engineering, heterostructure, pyridine N-doping, and carbon supporting to enhance cobalt-nickel selenide microspheres' performance in the oxygen electrode reaction. Specifically, microspheres mainly composed of CoNiSe2 and Co9Se8 heterojunction rich in selenium vacancies (VSe·) wrapped with nitrogen-doped carbon nanotubes (p-CoNiSe/NCNT@CC) are prepared by Ar/NH3 radio frequency plasma etching technique. The synthesized p-CoNiSe/NCNT@CC shows high oxygen reduction reaction (ORR) performance (half-wave potential (E1/2) = 0.878V and limiting current density (JL) = 21.88mA cm-2). The JL exceeds the 20wt% Pt/C (19.34mA cm-2) and the E1/2 is close to the 20wt% Pt/C (0.881V). It also possesses excellent oxygen evolution reaction (OER) performance (overpotential of 324 mV@10mA cm-2), which even exceeds that of the commercial RuO2 (427 mV@10mA cm-2). The density functional theorycalculation indicates that the enhancement of ORR performance is attributed to the synergistic effect of plasma-induced VSe· and the CoNiSe2-Co9Se8 heterojunction. The p-CoNiSe/NCNT@CC electrode assembled Zinc-air batteries (ZABs) show a peak power density of 138.29mW cm-2, outperforming the 20wt% Pt/C+RuO2 (73.9mW cm-2) and other recently reported catalysts. Furthermore, all-solid-state ZAB delivers a high peak power density of 64.83mW cm-2 and ultra-robust cycling stability even under bending.

Stable, amphiphobic, and electrically conductive coating on flexible polyimide substrate

A flexible electrode material, with good surface amphiphobicity and mechanical and chemical stability, was fabricated herein using a simple process. A superhydrophilic nanopillar array with a high aspect ratio was formed on a flexible polyimide substrate by radio-frequency plasma etching using a sputtering system. A superhydrophobic and electrically conductive silver nanopillar array was constructed by sequentially depositing Ag thin films without breaking the vacuum. Good surface amphiphobicity was achieved by fluorination on the Ag nanopillar arrays using 1H,1H,2H,2H-perfluorodecanethiol (PFDT) solution. For the optimal sample, the contact angles for water and ethanol were approximately 166° and 120°, respectively. The water sliding angle and contact angle hysteresis were 3° and 1°, respectively, indicating the potential of the arrays to perform well in self-cleaning tests. Fingerprints were not observed after pressing the thumb on the surface, indicating the excellent anti-fingerprint property. Even after 10,000 bending cycles, the change in the electrical resistance was close to unity, and the surface amphiphobicity was well maintained, indicating the excellent mechanical durability. The superior electrical stability was exhibited even after immersion in different solutions such as water and acid. The superior performances render the Ag nanopillar array with PFDT a good candidate for use as a flexible electrode material.

Room temperature photoluminescence in plasma treated rutile TiO2 (110) single crystals

Defects play a key role in tailoring the functional properties of metal oxides for next generation technologies. A comprehensive understanding and control of defects is therefore of vital importance in order to determine defect engineering strategies in materials and to allow for their technological realization. In this article, we report room temperature photoluminescence from plasma treated rutile TiO2 (110) single crystals. The effect of capacitively coupled radio frequency plasma etching on the luminescence properties of TiO2 (110) single crystals is discussed in detail. The plasma treatment modifies the surface of TiO2 (110) single crystals and introduces oxygen vacancies in the near surface region. The discharge parameters such as treatment time and pressure are correlated with the luminescence properties of treated TiO2 (110) single crystals. The Langmuir probe method is employed to determine the plasma electron density ‘ne‘, ion density ‘ni‘, electron temperature ‘Te’ and electron energy probability function (EEPF) of the plasma used to etch the TiO2 single crystals. Photoluminescence (PL) spectra reveal blue and green-light emission with an intensity dependent on the plasma treatment process. We hope that inducing defects through plasma treatment will be extended to other metal oxides surfaces, which may find utility in various applications.

CoPt/TiN films nanopatterned by RF plasma etching towards dot-patterned magnetic media

CoPt thin films as possible candidates for Bit Patterned magnetic Media (BPM) were prepared and investigated by electron microscopy techniques and magnetic measurements. The structure and morphology of the Direct Current (DC) sputtered films with N incorporation were revealed in both as-prepared and annealed state. Nanopatterning of the samples was carried out by means of Radio Frequency (RF) plasma etching through a Langmuir-Blodgett film of silica nanospheres that is a fast and high throughput technique. As a result, the samples with hexagonally arranged 100 nm size separated dots of fct-phase CoPt were obtained. The influence of the order of nanopatterning and anneling on the nanostructure formation was revealed. The magnetic properties of the nanopatterned fct CoPt films were investigated by Vibrating Sample Magnetometer (VSM) and Magnetic Force Microscopy (MFM). The results show that CoPt thin film nanopatterned by means of the RF plasma etching technique is promising candidate to a possible realization of BPM. Furthermore, this technique is versatile and suitable for scaling up to technological and industrial applications.

Adhesion of diamond-like carbon coated on tungsten carbide by using the RFPECVD method

Diamond-like carbon films were prepared on tungsten carbide by using radio-frequency plasma etching chemical vapor deposition under various conditions: Ar plasma pretreatment with bias voltages of −800, −1000, and −1150 V, Ar gas flows of 62.5, 100, and 130 sccm, and pretreatment times of 15, 30, and 50 min. The surface roughness of the diamond-like carbon film on tungsten carbide was measured using atomic force microscopy. Film adhesion was evaluated using a scratch tester, after which the scratched diamond-like carbon films were inspected by using scanning electron microscopy. An increase in the Ar gas flow or the pretreatment time caused a decrease in film adhesion. However, film adhesion increased with increasing Ar pretreatment bias voltage. The values of the film adhesion under the various conditions were 7–47N, and the maximum normal load of 47N was obtained an Ar plasma pretreatment bias voltage of −1150 V, a pretreatment time of 15 min, an Ar gas flow of 62.5 sccm, and a CH4 bias voltage of −600 V.

Function of aluminum coating on fabrication of nanowhiskers by radio frequency plasma etching

Diamond nanowhiskers could be obtained by anisotropic etching of as-grown and aluminum coated diamond films in a radio frequency (RF) Ar/O 2 plasma. The distributions of diamond nanowhiskers were on the presence of Al coatings. For the Al-coated diamond film, the distribution of the whiskers was almost same as that of the coated Al particles. However, for the as-grown diamond film, the whiskers randomly formed on the diamond surface with higher etching rate. Comparing these two situations, we found that Al coating was a critical factor in the etching process which served as mask contributing to restraining etching the film underneath. The whiskers (1 μm in height and 50 nm in diameter) could be obtained under optimum etching conditions. In addition, the dependence of the distribution of the whiskers on Al coating time was demonstrated.

Preparation of diamond whiskers using Ar/O 2 plasma etching

Radio frequency (RF) plasma etching of chemical vapor deposition (CVD) diamond film has been investigated in Ar/O 2 plasmas, with an emphasis to elucidate the effects of reacting gas on the fabrication of diamond whiskers. Diamond whiskers were formed on diamond films pre-coated with Al. It was found that diamond whiskers preferentially formed at the diamond grain boundaries. The densities of diamond whiskers increased with O 2 / Ar ratio. Whiskers obtained in pure O 2 plasma etching were 50 nm in diameter and 1 μm in height. The etching rate was increased by mixing Ar with appropriate volume of O 2. Al coated on the diamond surface reacted with O 2 to form Al 2O 3, serving as mask to restrain the etching underneath. Raman spectroscopy measurement confirmed that the whiskers kept sp 3 diamond bonding structure after RF plasma etching. The field emission characteristics of the whiskers were also inspected.

Collisional effects on characteristics of asymmetric radio-frequency sheaths

For most reactive radio-frequency plasma etching processing, the plasma sheaths near two electrodes are asymmetric due to the powered electrode area being smaller than the grounded electrode area. Taking collisional effects of ions with neutrals in the sheaths into account, a selfconsistent dynamic model is proposed here to describe the characteristics of radio-frequency sheaths. Numerical results show the collisional effects on some physical quantities, such as instantaneous voltages on the electrodes, instantaneous thicknesses of the electron sheathes, spatial distributions of the ion density and the electric field in the sheaths, and instantaneous voltage difference between two electrodes.

Scale-up of a Parallel Plate RF Plasma Etching Reactor by Using Reactive Gas Flow Simulations

A parallel plate/narrow gap radio frequency (RF) (400 kHz)-plasma etching reactor for a 200 mm diam wafer was scaled up to that for a 300 mm diam wafer according to numerical simulations of gas flow and mass transfer for the etching gas Experimental measurements of this reactor (for a 300 mm diam wafer) agree well with the simulated etching rate and etching uniformity on the 300 mm diam wafer. It was shown that the reactor for a 300 mm diam wafer could be scaled up only in the radial direction. It was also clarified that gas inlet showerhead radius and plasma radius correlatively affect the etching rate at the edge of the wafer; they are therefore key parameters that must be controlled to get better uniformity of etching rate. © 2001 The Electrochemical Society. All rights reserved.

Generation of positively charged particles at an anode and transport to device wafers in a real radio frequency plasma etching chamber for tungsten etch-back process

The transport path of particles, that have flaked off a grounded anode of a real parallel-plate radio frequency (rf) plasma etching equipment for tungsten etch-back processing to device wafers on the cathode, is measured by using an in situ monitoring system that measures laser light scattered by the particles. A few particles appear constantly only near the grounded anode while rf power is being supplied. These particles have parabolic trajectories that open upward. Few particles are observed near the wafer. On the other hand, at the timing of the turning off of rf power, many particles appear near the anode. Their trajectories from the anode to the chamber wall are sharply curved. Near the wafer, which has a negative self-bias voltage, almost all the particles’ trajectories are from the chamber wall to the wafer. Therefore, the particles move from the anode to the device wafer on the cathode and keep away from the after-glow plasma as well as from the bulk plasma. These particles are then attracted to the wafer by its negative self-bias voltage. These phenomena indicate that the particles generated at the anode have positive charges.

Synthesis of Diamond Using RF Magnetron Methanol Plasma Chemical Vapor Deposition Assisted by Hydrogen Radical Injection

A new plasma chemical vapor deposition (P-CVD) system was developed for synthesis of diamond. This system consisted of a parallel-plate radio frequency (RF) (13.56 MHz) plasma reactor, with a radical source using a microwave (2.45 GHz) discharge plasma and substrate heating using a cw-CO2 laser. In this system, hydrogen (H) radicals were generated in the microwave H2 plasma and preferentially injected near the substrate in the parallel-plate RF magnetron methanol ( CH3OH) plasma region. By scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, it was found that diamond was successfully synthesized using this system. The effects of H radical on the diamond formation were also investigated from the results of optical emission measurements in the RF plasma region, thin-film deposition and etching of the nondiamond phases by varying amounts of H radical injection.

Investigation of modulated radio frequency plasma etching of GaAs using Langmuir probes

Radio frequency ClCH3/H2 plasma etching of GaAs is examined in the 10–140 mTorr pressure range using square-wave modulation of the excitation source to control the etching. A Langmuir probe is used to measure time-resolved electron density, characteristic temperature, and floating potential during the plasma afterglow period. The ClCH3/H2 plasma electron energy is found to be 1.2±0.3 eV. The near afterglow plasma density decay has a time constant in the order of τ=30 μs at 140 mTorr for 10%–20% ClCH3 in H2 and τ=100 μs for H2. The floating potential continues to decay into the far afterglow, with a characteristic time of the order of milliseconds. The Langmuir probe measurements indicate that in ClCH3 plasmas the near afterglow is dominated by electron attachment, whereas the far afterglow is dominated by ambipolar diffusion. The GaAs etch rate experiments show that surface reactions continue into the far afterglow, dominating the behavior of the time average etch rate.

Analysis of diamond phase in hydrogenated hard carbon film using radio frequency plasma etching

The hydrogenated hard carbon films prepared in CH4 radio frequency (rf) discharge, have been examined to characterize the film structure by means of several spectroscopic measurements combined with CF4 rf plasma etching. The CF4 plasma etching can selectively remove the amorphous phase with graphite structure, and can retain the diamond structure in the film. After the CF4 plasma etching for a long time, cylindrical structures and/or particles were formed on the substrate. The top of the cylindrical structure or the particle was diamond, and the bottom part was the Si substrate. It was confirmed that most of the components in the hard carbon film is amorphous phase, and the diamond phases exist at the interface between the film and the substrate.

Radio frequency plasma etching of Si/SiO2 by Cl2/O2: Improvements resulting from the time modulation of the processing gases

The etching of poly-Si and its selectivity over gate oxide SiO2 were measured for both Cl2 and Cl2/O2 plasmas and the experimental data indicate that modulation of the processing gases increases the Si/SiO2 selectivity while decreasing the unwanted deposition. The best results to date have been Si etch rates of ∼1000 Å/min and Si/SiO2 selectivities of ∼50. It has also been demonstrated that the Si/SiO2 selectivity is strongly dependent on the presence of photoresist. A qualitative model for these results is proposed, which appears to fit these observations. In this model, hydrocarbon fragments from sputtered photoresist reduces the SiO2 to Si, with a corresponding decrease in the Si/SiO2 etching selectivity. This carbonaceous material can be removed by the oxygen before it causes etching damage to the SiO2. Oxygen, unfortunately, can also react with the etching reaction products (e.g., SiCl4) to form SiO2 and the Si oxychlorides (Si2OCl6, Si3OCl8), which deposit on the wafer. The experimental evidence indicates, however, that this unwanted deposition can be minimized by alternating the Cl2 and O2 gases, rather than by running them both at a constant pressure, as is typically done. Of most immediate interest is the fact that this improvement by modulation can be achieved on time scales (≳1 s), which are attainable with the fairly long residence times in present generation hex etchers.

Radio frequency plasma etching of Si/SiO2 by Cl2/O2 : Improvements resulting from the time modulation of the processing gases

The etching of poly-Si and its selectivity over gate oxide SiO2 were measured for both Cl2 and Cl2/O2 plasmas and the experimental data indicate that modulation of the processing gases increases the Si/SiO2 selectivity while decreasing the unwanted deposition. The best results to date have been Si etch rates of ∼1000 Å/min and Si/SiO2 selectivities of ∼50, and it has been demonstrated that the Si/SiO2 selectivity is critically related to the presence of photoresist. A qualitative model for these results is proposed which appears to fit these observations. In this model, hydrocarbon fragments from sputtered photoresist reduces the SiO2 to Si, with a corresponding decrease in the Si/SiO2 etching selectivity. This carbonaceous material can be removed by the oxygen before it causes etching damage to the SiO2. Oxygen, unfortunately, can also react with the etching reaction products (e.g., SiCl4 ) to form SiO2 and the Si oxy-chlorides (Si2OCl6, Si3OCl8 ) which deposit on the wafer. The experimental evidence indicates, however, that this unwanted deposition can be minimized by alternating the Cl2 and O2 gases, rather than by running them both at a constant pressure as is typically done. Of most immediate interest is the fact that this modulation improvement can be achieved on time scales (≳1 s) which are attainable with the fairly slow residence times available in present generation hex etchers.

Large-area microwave and radiofrequency plasma etching of polymers

We have investigated O2/CF4 plasma etching of five commercial polymers: polyimide, polyamide, polyethylene terephthalate, polycarbonate and cured epoxy resin. A new large-area microwave plasma apparatus has been used in this work, but the same apparatus can also be used as a capacitively coupled radiofrequency (13.56 MHz) discharge reactor. The effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics has been examined. We have observed distinct maxima in the etch rate as functions of pressure and CF4 concentration. Activation, energies evaluated from the Arrhenius plots fall in the range 0.04-0.2 eV, in agreement with data in the literature. Dry etch susceptibility of a given polymer correlates strongly with the degree of unsaturation in the polymer's structure

Transmission electron microscopy studies of plasma-etched silicon nitride/silicon carbide composites.

Transmission electron microscopy has been used to isolate and examine the intergranular glass phase in hot-pressed silicon nitride/silicon carbide composites. Previously there have been difficulties in locating a suitable region for studies of this nature because the interfering nitride and carbide grains inhibit isolation of the glass for examination. Radiofrequency plasma etching of thinned sections of 6 wt% Y2O3, 2 wt% A12O3 in Si3N4 containing 30 vol% of SiC proved to be fruitful in isolating the glass phase. A mixture of CF4 and O2 quantitatively remove the acicular nitride phase without any evidence of attack on either the glass or carbide. Composites containing ceria and magnesia as substitutes for yttria behave similarly. This indicates that glasses containing minor to major concentrations of elements forming stable fluorides inhibit the attack of fluoride ions on silica glasses containing these elements.

Ultrastructural comparison of ion beam and radiofrequency plasma etching effects on biological tissue sections.

Three dry etching techniques (Ar+ ion beam, O2+ ion beam, O2 radiofrequency electrodeless discharge) were compared with respect to preferential etching and damage to the ultrastructure of glutaraldehyde-fixed Epon-embedded frog skeletal muscle sections. SEM and TEM studies were performed on both unstained and stained (osmium tetroxide, uranyl acetate) sections. Etching effects were observed to differ for the various ion beam or plasma etching techniques. Whereas selective retention of electron dense structures (e.g. Z lines, nuclear heterochromatin) was observed for oxygen plasma etching, preferential etching of these components was observed using O2+ ion beam bombardment. Selectively etched Z lines and etch-resistant nucleoli were observed for both reactive (O2+) and inert (Ar+) ion beam sputtering after sufficiently high ion doses. The above suggest that selective etching under keV ion beam irradiation is related more to physical sputtering processes (momentum transfer) than to the chemical reactivity of the incident ion. Heavy metal post-fixation and staining had no qualitative effect on the nature of the selective etching phenomena. The above findings are significant in that they potentially influence both electron and ion microprobe measurements of etched biological specimens.