Phase composition,structural, and plasma erosion properties of ceramic coating prepared by suspension plasma spraying

Y₃Al₅O₁₂ (YAG), Y₂O₃, and Al₂O₃ ceramic coatings were manufactured to investigate the plasma erosion properties. The X‐Ray Diffraction (XRD) analysis confirmed that YAG coating was synthesized successfully by Y₂O₃ and Al₂O₃ mixture suspension using the plasma spraying method. Meanwhile, metastable phases were found in Y₂O₃ and Al₂O₃ coatings due to the quenching in cooling process of melted droplets. The coating surface morphology and microstructure of cross sections were characterized by SEM. The results reveal that coatings are composed by ultrafine splats and exhibit dense lamellar structure. The plasma erosion properties were evaluated at different etching test power under Ar/CF₄/O₂ plasma gas. The experimental results clarify that both of YAG and Y₂O₃ coatings show the better plasma erosion resistance than Al₂O₃ coatings. The formation of fluorination layer surface prevents the coatings from further erosion with plasma gas. Moreover, the etching rate of coatings depended on the fluorination and removing rate of fluoride layer.     

The role of fluorination during the physicochemical erosion of yttria in fluorine-based etching plasmas

A physicochemical mechanism acting between the reactive plasma and the material surface controls the erosion of polycrystalline ceramics in fluorine containing etching plasmas. In this study, a Y₂O₃/YOF composite was exposed to a fluorine etching plasma. Relocalization enables the direct correlation of crystalline orientation with material response. Our study reveals an orientation dependent surface fluorination of Y₂O₃, which controls the etching resistance and morphology formation. Orientations near the low index planes (001), (010) and (100) exhibit the lowest stability due to a homogeneous surface reaction. The presented results help to extend the mechanistic understanding of the plasma-material interaction of Y₂O₃.     

Erosion behavior of Y2O3 in fluorine-based etching plasmas: Orientation dependency and reaction layer formation

Even though advanced ceramics are widely applied as consumables in semiconductor etching processes, the erosion mechanisms and connected surface phenomena are not fully understood. Through the interaction with reactive species and ion bombardment during the plasma exposure, oxide ceramic materials like Y₂O₃ are eroded by a physicochemical mechanism. In this study, fundamental phenomena of surface-plasma interactions were investigated directly at the surface as well as in the near-surface region after exposure to fluorine-based etching plasmas. A straightforward re-localization technique was used to investigate the microstructural features before and after the plasma exposure for up to 2 hours. Electron microscopy methods (scanning electron microscopy, electron backscatter diffraction) were coupled with atomic force microscopy, secondary ion mass spectroscopy, and transmission electron microscopy to study the surface topography and the corresponding reaction layer. Direct correlation of the microstructure before plasma exposure with the surface topography reveals a novel orientation-dependent erosion mechanism that forms plateau-like structures. Furthermore, the in-depth analysis of the near-surface area highlights the influence of the applied bias voltage on the physical damage and chemical gradient formation due to plasma exposure. The combined investigation of surface morphology and near-surface properties reveals new fundamental aspects of the erosion behavior of polycrystalline yttria in CF₄-based etching plasmas.     

Plasma etching properties of various transparent ceramics

The etching properties of four types of transparent ceramics: sapphire (a single crystalline α-Al₂O₃), γ-AlON (γ-aluminum oxynitride), Mg-spinel (MgAl₂O₄), and Y₂O₃, as well as a polycrystalline opaque Al₂O₃ were examined using an inductively coupled plasma etcher under an incident plasma power of 2,000 W for up to 3 h. The transparent γ-AlON and opaque Al₂O₃ showed significant surface morphological changes, whereas sapphire, Mg-spinel, and Y₂O₃ revealed a relatively smooth surface upon etching. However, direct correlation between the surface morphological change and the degree of etching could not be drawn because sapphire showed a uniform surface etching despite its significant mass loss. Even though Y₂O₃ was found to be more plasma-resistant than Al₂O₃, overall, Mg-spinel was the most feasible transparent material for monitoring window application in a semiconductor processing chamber because of its minimal degree of erosion (≤0.4g/m²) and the transmittance change (≤2%) upon 3 h of fluorocarbon (CF₄) plasma etching.     

Passivation effect on the surface characteristics and corrosion properties of yttrium oxide films undergoing SF6 plasma treatment

This study investigates the structures, compositions and fluorocarbon-plasma etching behaviors of yttrium oxyfluoride (YOF) passivation films fabricated on sputter-deposited yttrium oxide (Y₂O₃) by high-density SF₆ plasma irradiation. High-resolution transmission electron microscopy and nano-beam electron diffraction confirmed a YOF passivation film containing multiple phases of (104) and (006) crystal planes was formed on the fluorinated Y₂O₃ surface. X-ray photoelectron spectroscopy revealed few changes in the chemical compositions and surface roughness of the YOF passivation film after fluorocarbon plasma etching, confirming the chemical stability of the SF₆ plasma-treated Y₂O₃ sample. The etching depth was ～20% lower on the SF₆ plasma-treated Y₂O₃ film than on the commercial Y₂O₃ coating. These results showed that the SF₆ plasma-treated Y₂O₃ films have an excellent erosion resistance properties compared to the commercial Y₂O₃ coatings.     

Plasma etching behavior of yttrium-aluminum oxide composite ceramics

In order to get a general regularity of erosion performance in alumina-strengthened yttria ceramics, High-quality yttrium-aluminum oxide composite ceramics with different alumina/yttria molar ratios were fabricated, and the as-prepared specimens were named Y₂O₃, YAG, YAGA, and Al₂O₃. The erosion behavior of the ceramics was examined and explained. The etching morphologies of the ceramics revealed that the multi-phase composite ceramic (YAGA) was etched selectively, whereas the single-phase ceramics were corroded homogeneously. The weight loss rate of the ceramics after etching was not proportional to the Al₂O₃ content, and it conformed to the percolation theory. As the alumina content in yttrium-aluminum oxide composite ceramics was below the minimum value of percolation transition in two-phase system the erosion resistance of the strengthened composite ceramics demonstrated excellent as well yttria ceramics.     

Evaluation of halogenated polyimide etching for optical waveguide fabrication by using inductively coupled plasma

Oxygen plasma etching of a series of halogenated polyimides was carried out for low‐loss waveguide fabrication by using inductively coupled plasma (ICP). The effects of etching parameters such as ICP power, rf power, and O₂ flow rate on the etching rate and etching profile of polymer films were investigated. The increase in the etch rate with the ICP power and the rf power was observed. Both the vertical profile and sidewall roughness were found to be related to the ion energy (dc bias). By optimizing these parameters, a vertical profile and a smooth sidewall were obtained by 500 W of ICP power, 150 W of rf power, 5 mTorr of chamber pressure, and 40 sccm of the O₂ flow rate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 176–182, 2001     

Microstructure and plasma corrosion behavior of yttria coatings prepared by the aerosol deposition method

Particle contamination arising from inner ceramic components of the plasma etching equipment has become a serious issue. Yttria (Y₂O₃) coatings prepared via aerosol deposition (AD) have demonstrated superior plasma resistance in the reduction of particle contamination. The superior particle contamination performance of Y₂O₃ coatings prepared by AD has been speculatively attributed to its unique microstructure; however, the relationship between the coatings’ microstructure and plasma corrosion behavior has been insufficiently clarified. Herein, we investigated the relationship between the microstructure and plasma corrosion behavior of Y₂O₃ coatings prepared by the AD method and compared the results with those for coatings prepared by other coating methods. When internal pores are present, these internal pores were selectively plasma corroded; plasma corrosion marks reflecting their pore shape were formed, and the surface roughness increased with increasing plasma exposure time. However, when no internal pores were present, as in the case of the AD coating, the surfaces were homogeneously corroded and maintained their initial surface. As the risk of particle contamination caused by the corrosion of the plasma-resistant coatings is greatly increased with surface roughness, we concluded that the Y₂O₃ coating prepared via AD will contribute greatly to reducing particle contamination.     

Preparation of diamond whiskers using Ar/O2 plasma etching

Radio frequency (RF) plasma etching of chemical vapor deposition (CVD) diamond film has been investigated in Ar/O₂ 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 O₂ / Ar ratio. Whiskers obtained in pure O₂ plasma etching were 50 nm in diameter and 1 μm in height. The etching rate was increased by mixing Ar with appropriate volume of O₂. Al coated on the diamond surface reacted with O₂ to form Al₂O₃, serving as mask to restrain the etching underneath. Raman spectroscopy measurement confirmed that the whiskers kept sp³ diamond bonding structure after RF plasma etching. The field emission characteristics of the whiskers were also inspected.     

Effect of ZnO and TiO2 doping on the sintering behavior of Y2O3 ceramics

Full densification of Y₂O₃ is challenging and requires a very high sintering temperature (above 1700 °C). In this study, the effect of ZnO and TiO₂ dopants on its densification was investigated, showing that both dopants lowered the sintering temperature and improved the process. Moreover, ZnO promoted the grain growth, while TiO₂ inhibited it; hence, the ZnOTiO₂ co-doping and the change in the ZnO/TiO₂ ratio allowed the control of the sintered body microstructure while maintaining high densification. Since Y₂O₃ has a higher plasma erosion resistance than conventional Si-based materials, the plasma dry etching resistance of the sintered Y₂O₃ was also evaluated and found superior due to the improved densification and controlled grain size of the doped samples.     

Conversion of Pyrolysis Fuel Oils by a Dielectric Barrier Discharge Reactor in the Presence of Methane and Ethane

Pyrolysis fuel oil cracking by low‐temperature plasma was investigated in a dielectric barrier discharge reactor at ambient pressure. The promoting effect of methane and ethane in the formation of products was evaluated by altering the working gas from methane to ethane. In addition, the production of hydrocarbons and hydrogen was analyzed. The main parameters were working gas type, flow rate, and applied voltage. Increasing the applied voltage enhanced the production rate of valuable petrochemical compounds like gas and liquid. Alteration of the working gas flow rate led to a higher production rate of H₂, C₂, C₃, and C₄. Chemical investigations were performed by optical emission spectroscopy of plasma and the main mechanisms are described.     

Comparative analysis of barium titanate thin films dry etching using inductively coupled plasmas by different fluorine-based mixture gas

In this work, the inductively coupled plasma etching technique was applied to etch the barium titanate thin film. A comparative study of etch characteristics of the barium titanate thin film has been investigated in fluorine-based (CF₄/O₂, C₄F₈/O₂ and SF₆/O₂) plasmas. The etch rates were measured using focused ion beam in order to ensure the accuracy of measurement. The surface morphology of etched barium titanate thin film was characterized by atomic force microscope. The chemical state of the etched surfaces was investigated by X-ray photoelectron spectroscopy. According to the experimental result, we monitored that a higher barium titanate thin film etch rate was achieved with SF₆/O₂ due to minimum amount of necessary ion energy and its higher volatility of etching byproducts as compared with CF₄/O₂ and C₄F₈/O₂. Low-volatile C-F compound etching byproducts from C₄F₈/O₂ were observed on the etched surface and resulted in the reduction of etch rate. As a result, the barium titanate films can be effectively etched by the plasma with the composition of SF₆/O₂, which has an etch rate of over than 46.7 nm/min at RF power/inductively coupled plasma (ICP) power of 150/1,000 W under gas pressure of 7.5 mTorr with a better surface morphology.     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

Electrochemical properties of polypropylene membranes modified by the plasma polymerization coating of SO2/acetylene

Polypropylene membranes were modified by the plasma etching of SO₂, SO₂? O₂, or SO₂? H₂O, followed by the plasma polymerization coating of SO₂/acetylene. The conditions for SO₂ plasma etching were optimized by the measurement of the ion‐exchange capacity (IEC) as a function of the plasma‐etching power (10–30 W), gas pressure (40–60 mTorr), and treatment time (15–120 s). For the plasma etching of SO₂? O₂ and SO₂? H₂O, only the pressure ratio (SO₂/O₂ and SO₂/H₂O) was optimized under the optimized conditions determined from SO₂ plasma etching. Plasma etching was then combined with the plasma polymerization coating of SO₂/acetylene, for which the conditions were again optimized by the measurement of the IEC as a function of the plasma power (10–40 W), chamber pressure (50–200 mTorr), SO₂/acetylene ratio (15/135–60/90), and treatment time (0–10 min). Next, the electrical resistance and water uptake were evaluated. The modified membranes were also analyzed with scanning electron microscopy, whereas plasma polymer coatings were characterized with Fourier transform infrared/attenuated total reflection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3692–3699, 2006     

Transparent ultrafine Yb3+:Y2O3 laser ceramics fabricated by spark plasma sintering

Conventional ceramic processing techniques do not produce ultrafine‐grained materials. However, since the mechanical and optical properties are highly dependent on the grain size, advanced processing techniques are needed to obtain ceramics with a grain size smaller than the wavelength of visible light for new laser sources. As an empirical study for lasing from an ultrafine‐grained ceramics, transparent Yb³⁺:Y₂O₃ ceramics with several doping concentrations were fabricated by spark plasma sintering (SPS) and their microstructures were analyzed, along with optical and spectroscopic properties. Laser oscillation was verified for 10 at.% Yb³⁺:Y₂O₃ ceramics. The laser ceramics in our study were sintered without sintering additives, and the SPS produced an ultrafine microstructure with an average grain size of 261 nm, which is about one order of magnitude smaller than that of ceramics sintered by conventional techniques. A load was applied during heating to enhance densification, and an in‐line transmittance near the theoretical value was obtained. An analysis of the crystal structure confirmed that the Yb³⁺:Y₂O₃ ceramics were in a solid solution. To the best of our knowledge, this study is the first report verifying the lasing properties of not only ultrafine‐grained but also Yb‐doped ceramics obtained by SPS.     

Study on carbon contamination and carboxylate group formation in Y2O3-MgO nanocomposites fabricated by spark plasma sintering

For Y₂O₃-MgO nanocomposites fabricated by spark plasma sintering (SPS), the strong absorption peaks, which are assigned to the stretching vibrations of carboxylate group (OCO), are commonly observed in IR spectra. These absorption peaks can negatively affect military applications such as IR windows or domes. In order to suppress the formation of these absorption peaks, therefore, it is important to understand how the carboxylate group in the SPSed Y₂O₃-MgO nanocomposite originated. In this study, it is demonstrated that the formation of the carboxylate group is related to the carbon contamination during SPS processing. The carbon phase transforms into CO₂ gas by annealing and this leads to a reaction with metal oxide phases, resulting in the formation of carbonate phase. This carbonate phase contributes to the absorption peaks of the carboxylate group.     

Anisotropic dry etching of boron doped single crystal CVD diamond

Semiconducting boron doped single-crystal CVD diamond has been patterned using aluminum masks and an inductively coupled plasma (ICP) etch system. For comparison insulating HPHT diamond samples were also patterned using the same process. Diamond etch rates above 200 nm/min were obtained with an O₂/Ar discharge for a gas pressure of 2.5 mTorr using 600 W RF power. We have accomplished the fabrication of structures with a minimum feature size of 1 μm with vertical sidewalls in both CVD and HPHT diamond. The ICP etching produced smooth surfaces with a typical root-mean-square surface roughness of 3 nm. The dependence of etch rate on bias voltage was somewhat different for the two types of diamond. However, for all samples both the etch rate and anisotropy were found to improve with increasing bias voltage.     

Wear properties of α- and α/β-SiAlON ceramics obtained by gas pressure sintering and spark plasma sintering

In this study, α- and α/β-SiAlON materials, doped with Y₂O₃ and Nd₂O₃, were sintered using two different sintering processes: spark plasma sintering (SPS) and gas pressure sintering (GPS). The wear and mechanical properties of the samples were compared related to the composition, additives and sintering processes. The results show that the hardness was not affected by the processing type whereas the toughness values were lower for spark plasma sintered materials than gas pressure sintered materials. This can be explained by the changed microstructure of the two different types of material. Additionally, α/β-SiAlON materials, sintered using gas pressure sintering, showed a lower wear than the spark plasma sintered materials. The results of the wear test were compared with β-Si₃N₄ materials and it was observed that α/β-SiAlON, sintered by GPS, has better wear properties than the tested β-Si₃N₄ materials.     

Rapid synthesis of Y3Al5O12 powders via plasma electrolysis

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) is an important functional material. However, the strict and complicated preparation has limited its wide application. This study aimed to rapidly synthesize Y₃Al₅O₁₂ by plasma electrolysis for the first time. The prepared powder was studied from topography, structure and elements by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The powder had a good crystal form with a spherical shape. The single kind of diffraction peak of Y₃Al₅O₁₂ in XRD revealed the high purity of the synthesized powders. The study of the relationship between the applied voltage and the synthesized powder revealed a threshold voltage of 210 V under the present condition. The higher voltage led to the damage of the electrode due to excessive heat. The synthesis of the YAG powder had a melt-quench process. The two processes were carried out at the same time.     

Liquid phase formation in the system Al2O3–Y2O3–AlN: Part II. Thermodynamic assessment

The mixing parameters of liquid phase in the Al₂O₃–Y₂O₃–AlN system were assessed based on differential thermal analysis (DTA) and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDX) investigations of selected compositions. Phase diagram of the Y₂O₃–AlN system was calculated. Liquidus surface of the Al₂O₃–Y₂O₃–AlN system was constructed and compared with experimental results on primary crystallisation fields. Calculated temperatures of invariant reactions were in agreement with DTA results. Vertical sections of the Al₂O₃–Y₂O₃–AlN system were calculated and compared with experimental data