Yttrium Oxyfluoride Research Articles

Novel and practical fabrication of pre-seasoned Y2O3 ceramics through surface modification

In the semiconductor industry, the long “seasoning” time required after the installation of new ceramic components in etching equipment restricts the wafer production efficiency. This study proposes a novel and practical method for the fabrication of pre-seasoned ceramics through surface modification of Y2O3 ceramics. Fluorine-containing reactive vapors were produced by utilizing NH4F as the source. Further, the formation of yttrium oxyfluoride layers on the surfaces of Y2O3 ceramics was demonstrated. The modified surface comprises a single-crystalline phase near the interface with the Y2O3 substrate. The change in the composition, crystalline nature of the modified layer, and orientation relationship with the substrate were examined via transmission electron microscopy. The kinetics of the surface modification were studied for the sintered Y2O3 bulk as well as for practical coatings such as plasma-sprayed or PVD coatings. The proposed surface modification approach can be used to fabricate pre-seasoned Y2O3 coatings, which can significantly benefit the semiconductor industry.

Formation of YOF on Y2O3 through surface modification with NH4F and its plasma-resistance behavior

Yttrium oxyfluoride (YOF) is known for exhibiting superior plasma-resistance properties compared to Y2O3, particularly in a fluorocarbon plasma environment. The formation of the YOF layer directly on the surface of Y2O3 via surface modification may be considered as a viable and cost-effective method. In this study, we employed ammonium fluoride (NH4F) salt for the surface modification of Y2O3. By using a 40 wt% NH4F aqueous salt solution, the YOF layer with a thickness of about 8.6 μm was efficaciously formed in-situ on the surface of Y2O3 based on the fluorination mechanism. The composition and microstructure of the modified Y2O3 surface was thoroughly characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis revealed the formation of distinct intermediate ammonium yttrium fluoride phases depending upon the heat treatment temperature (150 − 500 °C) through the fluorination of Y2O3 with NH4F. A stable YOF phase was formed ultimately at 300 °C. Plasma etching tests were performed using a mixture of CF4/Ar/O2 gases for 1 h. The microstructures of specimens are observed by SEM before and after plasma treatments. Plasma exposure tests demonstrated that specimens heat-treated at 500 °C for 2 h exhibit excellent plasma-resistance behavior with minimal surface damage, which is attributed to the presence of stable and dense YOF phase.

The Etching Behaviour and Fluorine-Based-Plasma Resistance of YOF Coatings Deposited by Atmospheric Plasma Spraying

There is a high demand for plasma-resistant coatings that prevent the corrosion of the internal ceramic components of plasma etching equipment, thereby reducing particle contamination and process drift. Yttrium oxyfluoride (YOF) coatings were prepared using atmospheric plasma spraying (APS) with commercially available YOF/YF3 powder mixtures; namely YOF 3%, YOF 6%, and YOF 9%. The etching behaviour of YOF and yttrium oxide (Y2O3) coatings was investigated using an inductively coupled plasma consisting of NF3/He. X-ray photoelectron spectroscopy (XPS) showed that the YOF 6% coating had the thickest fluorinated layer. The scanning electron microscope (SEM) examination revealed that the YOF 6% coating showed exceptional resistance to erosion and generated a reduced quantity of contaminated particles in comparison to Y2O3. Consequently, it is more suitable as a protective material for the inner wall of reactors. The YOF coatings exhibit excellent stability and high resistance to erosion, indicating their appropriateness for use in the semiconductor industry.

X-ray photoelectron spectroscopy and NIR self-quenching emission behavior in Ho3+ doped YOF and V-YOF

Stoichiometric (YOF) and non-stoichiometric yttrium oxyfluoride (Y7O6F9) also known as the vernier phase (V-YOF) were investigated for possible optical applications. Both structures were prepared from a single source through the pyrolysis method. The V-YOF and YOF structures decomposed at 900 °C and 950 °C, respectively. X-ray photoelectron spectroscopy revealed four different yttrium sites in the V-YOF structure. The visible holmium ions emission doped in both consisted of three regions due to the 5S2,5F4 → 5I8, 5F5 → 5I8, and 5S2,5F4 → 5I7 transitions. The YOF structure's visible lifetime was also longer than in the V-YOF structure. The near-infrared photoluminescence emission originated from 5S2,5F4 → 5I6, 5I6 → 5I8 in both structures. The 5S2,5F4 → 5I6 near-infrared lifetimes for both decreased, indicating an energy transfer process. The 5I6 → 5I8 lifetime in both fluctuated due to the possibility of self-quenching through photon-trapping processes. The lifetimes were in the microseconds range.

Surface analysis of yttrium oxyfluoride deposited via air plasma spraying for Erosion resistance against NF3 plasma

Surface analysis of yttrium oxyfluoride deposited via air plasma spraying for Erosion resistance against NF3 plasma

Synergistic regulation of the formation of yttrium oxyfluoride layer on yttrium oxide substrate by fluoride-chloride molten salts

Fluoride molten salt (KAlF4) can modify Y2O3 to form YOF, but the reaction degree of this process is difficult to control and tends to form a large amount of yttrium fluoride (YF3) with low-strength. The reaction degree of the modification process of fluoride molten salt with Y2O3 can be suppressed by the synergistic effect of chlorides (KCl-CaCl2), which is mainly determined by the diffusion of fluorine-containing complex ions (AlF4-) in the fluoride-chloride mixed molten salts (FCMMS). The low diffusion rate of AlF4- in FCMMS directly leads to the decrease of the fluorination reaction rate and delays or even prevents the deeper fluorination process. After the synergistic modulation of Y2O3 by FCMMS, only YOF is formed, and the formation of YF3 is completely avoided. The strategy and mechanism may be applied to the economical preparation of YOF protective layer or YOF powder on low-cost Y2O3 template.

The near-infrared emission of Er3+-doped yttrium oxy-fluoride ceramic powders: Temperature reading using uncoupled and thermally coupled energy levels

The performance of Er3+-doped yttrium oxy-fluoride (YOF) powders for optical temperature sensing is examined in this paper. YOF: Er3+ ceramic powders with near-infrared fluorescent emissions were synthesized via the combustion method. After heat treatment at 800 °C, the crystalline material shows strong near-infrared (NIR) fluorescence when excited with CW laser at 808 nm. The Er3+ emission bands found in the NIR region, centered at 970 and 1526 nm, correspond to excited levels 4I11/2 and 4I13/2, which relax to the ground state 4I15/2. YOF: Er3+ fluorescent powders are used to explore the optical thermometer sensitivity in the NIR region at 980–1650 nm in the temperature range from 298 to 523 K. Under the assumption of a quasi-equilibrium Boltzmann population distribution, the temperature sensing properties of thermally linked Stark sublevels derived from (4I11/2 and 4I13/2)→ 4I15/2 transitions have been thoroughly investigated using the FIR variation readout between these thermally connected Stark sublevels. The thermal sensing performance has also been investigated based on the FIR approach between non-thermally coupled levels (NTCL). The FIR readout of 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 NTCL transitions were used to calculate the relative sensitivity in the NIR spectral range. The performance comparison of the TCL and NTCL FIR techniques reveals the possibility of this ceramic powder being employed as a ratiometric thermal sensor for remote temperature readings.

Eu3+-doped Y7O6F9 ceramic powder phosphor for optical thermometry based on fluorescence spectral techniques

In recent years, optical thermometry performance of europium (Eu3+) doped phosphors has been studied by probing the temporal and spectral change of the fluorescence with temperature. In this scenario, the choice of the host material is important to maximize the temperature sensitivity. Yttrium oxyfluoride is an interesting host candidate because it combines low phonon energy of fluorides with high chemical and thermal stability of oxides. In this work, the combustion synthesis approach was used to produce Eu3+-doped Y7O6F9 powder phosphors. The Judd-Ofelt intensity parameters of the samples were calculated by the analysis of the fluorescence. When exposed to an externally-controlled change of the temperature, the fluorescence spectral profile of the sample changed. We observed that the relative temperature sensitivity estimated by the full-width at half-maximum and the valley-to-peak ratio methods were 0.08 and 0.35% K−1, respectively, at a temperature of 318 K, validating the phosphor for temperature sensing application.

Stability and plasma etching behavior of yttrium-based coatings by air plasma spray process

In recent days, many studies have focused on fluorine-saturated yttrium-based coatings for better material performance in semiconductor processing chambers. In this investigation, yttrium oxide (Y2O3) and yttrium oxyfluoride (YOF) powders were synthesized using a simple solid-state wet chemical process. Then, the Y2O3 and YOF powder feedstocks were coated on an aluminum (Al) substrate using the atmospheric plasma spraying (APS) technique at different plasma powers of 25.6, and 25.2, 33.2 kW, respectively. Microstructure, macroscopic property, and chemical stability of dense Y2O3 and YOF-coated samples were analyzed. The Vickers hardness values of Y2O3 and YOF coated samples were 369.2 ± 32, and 267.1 ± 25, 241.9 ± 31 at plasma powers of 25.6, and 25.2, 33.2 kW, respectively. Y2O3 sample was showed higher hardness value due to less porosity. The etching behavior of the Y2O3 and YOF coatings was analyzed using PECVD- NF3 plasma. X-ray photoelectron spectrum analysis (XPS) has confirmed the fluorination on the etched surfaces. The relative intensity ratios of the YF to YO peaks on the Y2O3 and YOF coatings after exposure to NF3 plasma were 1.30 and 1.48, respectively. This indicated that the YOF coating showed a strong fluorination layer and superior resistance for fluorine-plasma exposure compared to Y2O3, which is more appropriate for use as a protective material for the inner wall reactors. Therefore, YOF coated samples have good stability with high erosion resistance, which is highly suggested for applications in the semiconductor industry.

Tunable Ho3+ co-doped YOF:Bi3+ emission through cathodoluminescence

The tunability of holmium (Ho3+) emission was achieved with bismuth (Bi3+) as a co-dopant in an yttrium oxyfluoride (YOF) host for optoelectronic applications. Cathodoluminescence (CL) studies were investigated under electron beam irradiation (5 keV) for both YOF: x mol % Bi3+ (x = 0.3, 0.4, 0.5, 0.6, 0.8) and YOF: 0.4 mol % Bi3+, x mol % Ho3+ (x = 0.8, 1.4, 2, 3, 4, 5) samples. The samples were synthesized by the pyrolysis technique followed by annealing in ambient air at 900 °C. The structure of all samples exhibited pure rhombohedral YOF. The morphology studies showed small particles that agglomerated into bigger particles after annealing. Ultraviolet CL emission for the single doped Bi3+ samples were attributed to the emission of Bi3+ around 316 nm and the visible emission around 624 nm was attributed to Bi2+. The presence of Bi2+ emission was a result from ionization during electron beam bombardment. The samples co-doped with Bi3+ and Ho3+ ions showed the same emission components of Bi3+ and Bi2+ as well as Ho3+ emission at 540 nm. X-ray photoelectron spectroscopy confirmed the samples’ composition with the presence of Bi2+ as well as the existence of an intermediate Y-O-F layer that must have formed during electron bombardment. The fitted CIE coordinates of the co-doped samples showed that the CL emission can be tuned from green to yellow and to orange.

Effect of charge-up of surfaces of sintered Y2O3 and yttrium oxyfluoride on their erosion rates due to ion bombardment

The erosion rate of sintered Y2O3 and yttrium oxyfluoride (Y-O-F) due to Ar ion bombardment was investigated for use in the plasma process chamber. The Ar ion bombardment was performed by irradiations of Ar plasma and Ar ion beam. In addition, charge-up behavior of these ceramics was investigated by two methods. One was the measurement of the surface voltage during the plasma irradiation (the so-called self-bias voltage), and the other was the measurement of the surface voltage generated due to the accumulation of static electricity in the clean room air. It was found that the negative self-bias voltage of the Y2O3 surface was smaller than that of Y-O-F. It was also found that Y2O3 was easily positively charged by the accumulation of the static electricity compared to Y-O-F, which was consistent with the observed relationship of the self-bias voltages between Y2O3 and Y-O-F. For the evaluation of the erosion rate due to Ar ion bombardment, it was found that the material and setting of masks to make the erosion step for evaluating the rate greatly affected the results. When electrically conductive masks with electrically connecting to a substrate were used, the erosion rate of Y-O-F was smaller than that of Y2O3. The results suggested that the intrinsic ion-bombardment-induced erosion rate of Y-O-F was smaller than that of Y2O3, because the ion bombardment energy was expected to be almost the same due to the existence of the conductive masks. On the other hand, when insulating masks were used, the rates of Y2O3 and Y-O-F were almost the same level. Considering the aforementioned charge-up behavior, the results suggested that a relatively larger positive charge-up of the Y2O3 surface during the ion bombardment decelerated injecting ions, resulting in the decrease in ion bombardment energy and, thus, the erosion rate.

Fabrication of Al-YOF/TiB2 composites by molten-salt-assisted stirring casting

The poor wettability between oxides and Al melt and presence of alumina film on Al melt surface seriously limits the fabrication of Al matrix composites (AMCs) reinforced by oxides via casting method. The wettability of oxides can be improved by modification with fluorine, and the oxyfluoride is more feasible to incorporate into Al melt, but the strength of the oxides may decrease after modification. Therefore, it is necessary to assess the strengthening effect of oxyfluoride by comparison with classical reinforcement. In this work, AMCs reinforced with yttrium oxyfluoride (YOF) and TiB2 were successfully fabricated by molten-salt-assisted stirring casting. YOF particles exhibit a better distribution in Al matrix than TiB2 particles, and the YOF particles show better bonding strength with Al matrix than TiB2 due to reactive wetting. Al-YOF composite shows higher hardness, tensile strength, and ductility than Al-TiB2 composite. The values of microhardness, yield strength (σ0.2) and ultimate tensile strength (σb) of Al-YOF composite are 27.2 HV, 55 MPa and 81 MPa, which are 25.9 %, 62 % and 53 % higher than that of pure Al.

Microstructure and mechanical properties of Al matrix composite reinforced with micro/nano-sized yttrium oxyfluoride

Aluminum matrix composites (AMCs) are widely studied because of their low density, high strength, and castability. Since the high strength and low cost of oxide, it is considered to be a suitable kind of reinforcements for AMCs. However, due to the poor wettability between Al melt and oxide, AMCs reinforced with oxides is usually difficult to be prepared by casting method. Al melt wets better with fluoride than with oxide, but the strength of fluorides is lower than oxides. Oxyfluoride may be a feasible choice for reinforcing AMCs with both good wettability and enough strength. In this study, nano-yttrium oxyfluoride (YOF)-reinforced AMCs were fabricated by employing molten-salt-assisted stirring casting for the first time. The microstructures and mechanical properties of the resulting AMCs with various contents of YOF were investigated in detail. The results indicated that YOF significantly improved the mechanical properties of the Al matrix. The morphology and distribution of the Y-rich phase evolved with an increase in the YOF content, and the formation of casting defects was promoted, these affected the strengthening effect of AMCs. The Al–0.06 vol% YOF composite exhibited optimal mechanical properties while maintaining favorable ductility. Its microhardness, yield strength, and ultimate tensile strength were 20%, 65.6%, and 62.8% higher than those of pure Al, respectively. Therefore, nano-YOF can act as a favorable reinforcement material for AMCs. Refining the coarse Y-rich particles in the composite with high YOF content, minimizing segregation and eliminating casting defects could further improve the mechanical properties of the Al–YOF composites, which can be investigated in future works.

Infrared emission enhancement through holmium(3+) co-doped yttrium oxyfluoride doped with bismuth(3+) phosphor

Infrared (IR) emission was enhanced through holmium (Ho3+) co-doped bismuth (Bi3+) doped yttrium oxyfluoride (YOF). Energy transfer in YOF:Bi3+, Ho3+ was investigated for possible application as a spectral converter material for Si solar cells. Photoluminescence (PL) studies were investigated for energy transfer possibilities for IR emission. YOF: 0.4 Bi3+ mol % samples were co-doped with Ho3+ = 0.8, 1.4, 2, 3, 4 and 5 mol % by using the pyrolysis method. The X-ray diffraction analysis revealed the crystallization of the samples to rhombohedral YOF (space group: R 3‾ m (166)). PL excitation spectra showed an intense 1S0 → 3P1 Bi3+ band at 265 nm that dominated the 4f-4f Ho3+ peaks at 360 nm and 449 nm that were ascribed to the 5I8 → 5G5,3H6 and 5I8 → 5F1,5G6 transitions, respectively. During excitation to the 3P1 level of Bi3+, ultraviolet emission of Bi3+ ions occurred. Partial energy was transferred to the Ho3+3H6 and 5G5 energy levels and this was followed by multiple non-radiative transitions that populated the 5F4 and 5S2 levels of Ho3+. Final PL results showed a tremendous enhancement of Ho3+ emission in the IR region. Sensitizing the Ho3+ emission through Bi3+ ensured that the high energy levels of Ho3+ would be populated first.

Improvement of Yttrium Oxyfluoride Coating with Modified Precursor Solution for Laser-Induced Hydrothermal Synthesis

In the semiconductor manufacturing process, the inner walls of the equipment are coated with yttrium-based oxides for etch resistance against plasma exposure. Yttrium oxyfluoride (YOF) particle synthesis and coating methods have been actively studied owing to their high erosion resistance compared to Y2O3 and Al2O3. Owing to the formation of a rough and porous coating layer by thermal spray-coating, the coating layer disintegrates, as the etching process has been conducted for a long time. Laser-induced synthesis and coating technology offer several advantages, including simplified process steps, ease of handling, and formation of a dense coating layer on the target material. In this study, YOF was coated on an aluminum substrate using a modified precursor solution. The NaF and HMTA were added to the precursor solution, resulting in enhanced synthetic reactivity and stabilizing the oxides. The material coated on the surface was analyzed based on the characteristics of composition, chemical bonding, and phase identification. We found that the coating properties can be improved by using an appropriate combination of modified precursor solutions and laser parameters. Therefore, the findings in this study are expected to be utilized in the field of coating technology.

Thermal sensing in NIR to visible upconversion of Ho3+ and Yb3+ doped yttrium oxyfluoride phosphor

Rare-earth (RE) oxyfluorides compatible for RE doping make a path for efficient near-infrared (NIR) to visible upconversion (UC). This paper describes the efficient use of YOF:Ho3+/Yb3+ phosphor nanoparticles synthesised by the Pechini sol-gel method as thermal sensors using UC in the visible region. Material characterisations such as X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM), revealed the structural information of the material and its prominence for RE doping. Average size of 44 nm obtained from SEM with maximum phonon energy of 480 cm−1 observed from Raman measurements assure the use of RE doped YOF for UC. Excitation of YOF:Ho3+/Yb3+ with NIR (980 nm) revealed intense UC emission in the visible and DS in the NIR region. Although Ho3+ and Yb3+ ions do not have resonance energy levels at 980 nm, three two-photon UC emission bands centred at 538, 655 and 755 nm from 5F4+5S2→5I8, (5F5→5I8+5F3→5I7) and 5F4+5S2→5I7 transitions were obtained through phonon-assisted energy transfer. For the evaluation of thermal sensitivities using 980 nm excitation, fluorescence intensity ratio (FIR) was used based on the thermally non-coupled levels in the visible UC bands between the temperatures 20–300 K. The relative sensitivities (SR) which is the measure of temperature sensing ability of YOF materials with 1 mol % Ho3+ and 10 mol % Yb3+ was found to be 0.32 for UC in visible region was achieved with 980 nm excitation at 300 K.

Phase diagram study and thermodynamic assessment of the Y2O3-YF3 system

The phase diagram of the Y2O3-YF3 system up to 1973 K was investigated using a classical equilibration/quenching experiment and differential thermal analysis (DTA). Equilibrium phases were confirmed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analysis. For the very first time, the entire range of the phase diagram of yttrium oxy-fluoride system up to 1973 K was experimentally determined. Cubic-Y2O3 phase dissolves more than 5 mol% of YF3 at 1973 K. The melting points of YOF and vernier phases are found to be higher than 1973 K and their steep liquidus in the YF3-rich region are determined. Based on new experimental phase diagram data and thermodynamic property data in the literature, the Y2O3-YF3 system was thermodynamically modeled by the CALculation of PHAse Diagram (CALPHAD) method. As applications of the thermodynamic database, metastable solubilities of YF3 in Y2O3 during plasma etching process were calculated.

Yttrium Oxyfluoride Coating Deposited with a Y5O4F7/YF3 Suspension by Suspension Plasma Spraying Under Atmospheric Pressure

Yttrium Oxyfluoride Coating Deposited with a Y5O4F7/YF3 Suspension by Suspension Plasma Spraying Under Atmospheric Pressure

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.

Two-step synthetic route towards Er3+/Yb3+ co-doped vernier yttrium oxyfluoride phosphor with high optical temperature sensing sensitivity

Exploring an up-conversion (UC) phosphor for the fluorescence intensity ratio (FIR) technique has been a great challenge in the field of optical temperature sensors. In this paper, a two-step synthetic route [Y(OH)CO 3 →Y(OH) 1.63 F 1.37 →Y 6 O 5 F 8 ] was designed to successfully synthesize Y 6 O 5 F 8 :Yb 3+ /Er 3+ UC phosphors for optical temperature sensing. The phase and morphology of the samples at various stages of the synthetic route were investigated. Under 980 nm excitation, two green emission bands centered at 522 nm and 547 nm and a red emission band centered at 670 nm were observed. Y 6 O 5 F 8 :10%Yb 3+ /1%Er 3+ exhibited the strongest UC emission under 980 nm excitation and was selected for further characterizations. The absorption and emission processes (a two-photon process) of photons in Y 6 O 5 F 8 :10%Yb 3+ /1%Er 3+ were elucidated based on the UC luminescence mechanism. Among them, the ET occupies a key position, which was also confirmed by the decay curves. In addition, the optical temperature sensing behavior of Y 6 O 5 F 8 :10%Yb 3+ /1%Er 3+ was explored using the FIR technique. The maximum absolute and relative sensitivities were determined to be 0.0074 K -1 (518 K) and 1.39% K −1 (293 K), respectively. The results show that Y 6 O 5 F 8 :10%Yb 3+ /1%Er 3+ phosphor has promising application potentials in optical temperature sensors with excellent sensitivity. A two-step synthetic route [Y(OH)CO 3 →Y(OH) 1.63 F 1.37 →Y 6 O 5 F 8 ] was designed to successfully synthesize Y 6 O 5 F 8 :Yb 3+ /Er 3+ UC phosphors. The optical temperature sensing performance of Y 6 O 5 F 8 :0.1Yb 3+ /0.01Er 3+ was evaluated based on the FIR technique, and its maximum absolute and relative sensitivities were determined to be 0.0074 K -1 (518 K) and 1.39% K −1 (293 K), respectively. • A two-step synthetic route was designed to successfully synthesize Y 6 O 5 F 8 . • The possible UC pathways of photons in Y 6 O 5 F 8 :0.1Yb 3+ /0.01Er 3+ were proposed. • High sensitivity for optical temperature sensing was found in this host material.