Yttrium Oxide Thin Films Research Articles

Growth Characteristics and Properties of Yttrium Oxide Thin Films by Atomic Layer Deposition from Novel Y(iPrCp)3 Precursor and O3

A novel atomic layer deposition (ALD) route of Y2O3 thin films was developed and demonstrated utilizing Y(iPrCp)3 and O3. The ALD growth characteristics were investigated by varying precursor dosage, reactor temperature, and number of deposition cycles. The growth rate of Y2O3 was found to be 0.17 {plus minus} 0.01 nm/cycle within the ALD temperature window of 245 - 300 ºC. The resulting films were analyzed with spectral ellipsometry and x-ray photoelectron spectroscopy, in order to determine stoichiometry, impurity, annealing behavior, and refractive index. The results of this work demonstrate the potential for suggesting Y(iPrCp)3 as a suitable ALD precursor and Ar+ beam as an effective means of removing surface Y(OH)3 on Y2O3 films.

Growth Characteristics and Properties of Yttrium Oxide Thin Films by Atomic Layer Deposition from Novel Y(iPrCp)3 Precursor and O3

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Yttrium oxide thin films prepared under different oxygen-content atmospheres: microstructure and optical properties

Yttrium oxide films were prepared on silicon wafers by reactive magnetron sputtering at different oxygen flow rates to investigate the microstructure and optical properties for desirable planar optical waveguiding applications. Under the different conditions of target surface, the deposition rate, structure, and optical properties have great changes. The deposition rate increases to the maximum, and then monotonically decreases. Oxygen content in films increases and the composition of films transforms from stoichiometry to an oxygen-rich state. Y2O3 films grow with the (222) preferred growth orientation at low oxygen flow rate, and then turn into the (622) orientation; the microstructure evolves from crystal structure to amorphous state as oxygen flow rate increases from 2 to 12 sccm. Sufficient oxygen makes films low-order structure and oxygen-rich films have poor crystallinity. Very smooth film has been obtained at oxygen flow rate of 12 sccm. The refractive index can be greatly modulated by the oxygen-content factor. It is convincing that the controllable structure and optical properties of Y2O3 films can be achieved by adjustment the oxygen flow rate for desired optical design and applications.

Evolution of composition, microstructure and optical properties of yttrium oxide thin films with substrate temperature

A series of yttrium oxide films has been fabricated on Si (100) wafers by different substrate temperatures based on reactive magnetron sputtering technology. And the evolution of composition, microstructure and optical properties of Y2O3 films has been investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). It is shown that stoichiometric Y2O3 with much strong YO bond and cubic nanophase with larger size notably enhance the optical properties, especially refractive index. At low substrate temperature, the composition of Y2O3 films has nonstoichiometry feature accompanying with much physisorbed oxygen (Oδ) compared with these at high temperature. Increasing substrate temperature promotes the formation of YO bonds, approaching the stoichiometry with lower Oδ content. The film commences crystallizing at room temperature, and transformation of crystalline phase from monoclinic to cubic occurs, along with preferred (111) orientation and large grain as temperature increases. The results facilitate clear relationship between the characterizations of Y2O3 film and growth parameters, also, it can be realized that adjustment of optical constants of Y2O3 films in a large range having the aid of substrate temperature to obtain desirable composition and structure for optical applications.

Structure, morphology and optical properties of nanocrystalline yttrium oxide (Y2O3) thin films

Yttrium oxide (Y2O3) thin films were grown onto Si(100) substrates using reactive magnetron sputter-deposition at temperatures ranging from room temperature (RT) to 500°C. The effect of growth temperature (Ts) on the growth behavior, microstructure and optical properties of Y2O3 films was investigated. The structural studies employing reflection high-energy electron diffraction RHEED indicate that the films grown at room temperature (RT) are amorphous while the films grown at Ts=300–500°C are nanocrystalline and crystallize in cubic structure. Grain-size (L) increases from ∼15 to 40nm with increasing Ts. Spectroscopic ellipsometry measurements indicate that the size-effects and ultra-microstructure were significant on the optical constants and their dispersion profiles of Y2O3 films. A significant enhancement in the index of refraction (n) (from 2.03 to 2.25) is observed in well-defined Y2O3 nanocrystalline films compared to that of amorphous Y2O3. The observed changes in the optical constants were explained on the basis of increased packing density and crystallinity of the films with increasing Ts. The spectrophotometry analysis indicates the direct nature of the band gap (Eg) in Y2O3 films. Eg values vary in the range of 5.91–6.15eV for Y2O3 films grown in the range of RT-500°C, where the lower Eg values for films grown at lower temperature is attributed to incomplete oxidation and formation of chemical defects. A direct, linear relationship between microstructure and optical parameters found for Y2O3 films suggest that tuning optical properties for desired applications can be achieved by controlling the size and structure at the nanoscale dimensions.

Planarization of flexible tape substrate by solution coating process

In this work, the yttrium oxide(<TEX>$Y_2O_3$</TEX>) thin films as the buffer layer were prepared by the simple solution coating and reel-to-reel process on an unpolished metal tape substrate. The <TEX>$Y_2O_3$</TEX> thin films were successfully synthesized by the hydrolysis of yttrium acetate. We have studied the improvement of surface roughness with the concentration of solution(0.1 M, 0.4 M, M) and the number of coatings. The planarization by solution coating process is simple in comparison with the existing polishing process, and it is eco-friendly, and has the benefits of low cost process. The thickness of <TEX>$Y_2O_3$</TEX> films was increased with the <TEX>$Y_2O_3$</TEX> concentration in the solution, and the surface became smoother with the number of coating cycles. Using this process, we have achieved 1.2 nm RMS roughness from a starting roughness of over 31 nm on 25 <TEX>${\mu}m^2$</TEX> area.

Structure and AC conductivity of nanocrystalline Yttrium oxide thin films

Yttrium oxide (Y 2O 3) thin films were grown at substrate temperatures (T s) ranging from room temperature (RT) to 500 °C and their structural and electrical properties were evaluated. The results indicate that Y 2O 3 films grown at RT-100 °C were amorphous (a-Y 2O 3). Y 2O 3 films began to show cubic phase (c-Y 2O 3) at T s = 200 °C. The average grain size varies from 5 to 40 nm as a function of T s. Room temperature ac electrical conductivity increases from 0.4 (Ω-m) − 1 to 1.2 (Ω-m) − 1 with increasing T s from RT to 500 °C. The frequency dispersion of the electrical resistivity reveals the hopping conduction mechanism. Frequency dispersion of the electrical resistivity fits to the modified Debye's function, which considers more than one ion contributing to the relaxation process. The mean relaxation time decreases from 2.8 to 1.4 μs with increasing T s indicating that the effect of microstructure of the Y 2O 3 films is significant on the electrical properties.

Effect of substrate temperature and oxygen partial pressure on microstructure and optical properties of pulsed laser deposited yttrium oxide thin films

Yttrium oxide thin films were deposited on Si (1 1 1) and quartz substrates by pulsed laser deposition technique at different substrate temperature and oxygen partial pressure. XRD analysis shows that crystallite size of the yttrium oxide thin films increases as the substrate temperature increases from 300 to 873 K. However the films deposited at constant substrate temperature with variable oxygen partial pressure show opposite effect on the crystallite size. Band gap energies determined from UV–visible spectroscopy indicated higher values than that of the reported bulk value.

Effects of precursor evaporation temperature on the properties of the yttrium oxide thin films deposited by microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition

Yttrium oxide thin films are deposited using indigenously developed metal organic precursor (2,2,6,6-tetra methyl-3,5-hepitane dionate) yttrium, commonly known as Y(thd) 3 (synthesized by ultrasound method). Microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition process was used for these depositions. Depositions were carried out at a substrate temperature of 350 °C with argon to oxygen gas flow rates fixed to 1 sccm and 10 sccm respectively throughout the experiments. The precursor evaporation temperature (precursor temperature) was varied over a range of 170–275 °C keeping all other parameters constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and refractive index of the coatings are measured by the spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. C-Y 2O 3 phase is deposited at lower precursor temperature (170 °C). At higher temperature (220 °C) cubic yttrium oxide is deposited with yttrium hydroxide carbonate as a minor phase. When the temperature of the precursor increased (275 °C) further, hexagonal Y 2O 3 with some multiphase structure including body centered cubic yttria and yttrium silicate is observed in the deposited film. The properties of the films drastically change with these structural transitions. These changes in the film properties are correlated here with the precursor evaporation characteristics obtained at low pressures.

Structural and optical properties of yttrium oxide thin films for planar waveguiding applications

Thin films of yttrium oxide, Y2O3, were deposited by reactive sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The optical properties, structure, and crystalline phase of the films were found to be dependent on the deposition method and process parameters. X-ray diffraction analysis on the “as-deposited” thin films revealed that the films vary from amorphous to highly crystalline with a small broad peak at 29° corresponding to the ⟨222⟩ reflections of Y2O3. The samples with the polycrystalline structure had a stoichiometry close to bulk cubic Y2O3. Scanning electron microscopy imaging revealed a regular column structure confirming their crystalline nature. The thin film layers which allowed guiding in both visible and infrared regions had lower refractive indices, higher oxygen content, and a more amorphous structure. Higher oxygen pressures during the deposition lead to a more amorphous layer.

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y2O3:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm2 and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y2O3:Eu was formed. The Y2O3:Eu film irradiated by the ArF laser at 80 mJ/cm2 and 500°C showed typical PL spectra of Eu3+ ions with cubic symmetry and a 5D0→7F2 transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.

Effect of argon ion activity on the properties of Y 2O 3 thin films deposited by low pressure PACVD

Yttrium oxide thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition process using an indegeneously developed Y(thd) 3 {(2,2,6,6-tetramethyl-3,5-heptanedionate)yttrium} precursor. Depositions were carried out at two different argon gas flow rates keeping precursor and oxygen gas flow rate constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GIXRD) and infrared spectroscopy. Optical properties of the films are studied by spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. Stability of the film and its adhesion with the substrate is inferred from the nanoscratch test. It is shown here that, the change in the argon gas flow rates changes the ionization of the gas in the microwave ECR plasma and imposes a drastic change in the characteristics like composition, structure as well as mechanical properties of the deposited film.

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Abstract Yttrium oxide (Y2O3) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)3 synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y2O3 on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.

A Modified Moving Horizon Estimator for In Situ Sensing of a Chemical Vapor Deposition Process

A modified moving horizon estimator (mMHE) was developed to estimate thin film thickness, growth rate, and refractive indices in situ from a dual-wavelength reflectance measurement during chemical vapor deposition. In this application, mMHE combines the advantage of high speed of the recursive least squares estimator (RLS) and the accuracy of the moving horizon estimator (MHE). A simulated deposition process with drifting growth rate was used as a benchmark to compare the performance of RLS, MHE, mMHE, and the extended Kalman filter (EKF). The results indicate that mMHE yields more accurate estimates than RLS by incorporating a priori estimates in the optimization function. Improved accuracy of mMHE over EKF was obtained due to the horizon of data used at each time step. In addition, mMHE provided similar accuracy to MHE for short horizons, and it was much faster than MHE. RLS, MHE, mMHE, and EKF were also compared on an experimental chemical vapor deposition system where a yttrium oxide thin film was deposited on a silicon substrate. The ex situ ellipsometry characterization indicated that a more accurate and robust estimate was obtained by MHE and mMHE, compared to the RLS and EKF estimates.

Studies on the influence of lithium incorporation in the photoluminescence of Y 2O 3:Eu 3+ thin films

Nanostructured europium-doped yttrium oxide thin films with lithium as a co-dopant were prepared using pulsed laser ablation technique. X-ray diffraction studies of the films indicated amorphous nature of the as deposited films and a transformation to crystalline phase with increase of annealing temperature. In this transformation, lithium co-doped films showed early crystallization. Lithium substitution resulted not only in enhancement of photoluminescence at 612 nm, resulting from 5D 0– 7F 2 transition within europium, but also found to reduce the required processing temperature for intense photoemission. The deviation observed in the value of lattice constant of films annealed at different temperatures is found to be sensitive to annealing temperature. In the light of this, the dependence of photoluminescence intensity on the magnitude of lattice imperfection is also discussed. The morphology and transmittance of the films are also found to be sensitive to annealing process and lithium doping.

Optical and structural characteristics of Y2O3 thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)3). The decomposition of Y(acac)3 was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)3. The rest of the complex is then dissociated or degraded partially until Y2O3 is obtained in the final step with the presence of carbon related residues. Then the Y(acac)3 was used to synthesize Y2O3 thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.

Deposition of yttrium oxide thin films in supercritical carbon dioxide

A synthetic avenue for the formation of yttrium oxide thin films on Si native oxide surfaces is demonstrated by the reaction of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) yttrium(III) with inorganic (H 2O 2) and organic (tert-butyl and di-tert-amyl) peroxides in supercritical carbon dioxide. The reactions are carried out in a hot wall reactor at temperatures below 130 °C and pressures ranging from 13.10 to 22.75 MPa. Spectroscopic Ellipsometry verifies thin film formation and X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements confirm formation of yttrium oxide films and the presence of carbonate and hydroxide species which are removed after high temperature anneals.

Site-Selective Deposition and Micropatterning of Visible-Light-Emitting Europium-Doped Yttrium Oxide Thin Film on Self-Assembled Monolayers

We have developed a novel process for preparing a micropattern of europium-doped yttrium oxide thin films using a patterned self-assembled monolayer. The thin film was transformed into the crystalline phase by annealing at 800 °C for 1 h. Europium-doped yttrium oxide films showed red emission (611 nm) due to photoluminescence excited by 266 nm. The deposition and micropatterning of visible-light-emitting europium-doped yttrium oxide was successfully realized in an aqueous solution under environmentally friendly conditions.

Yttrium oxide thin films: Influence of the oxygen vacancy network organization on the microstructure

Y 2O 3 thin films are deposited by ion beam sputtering on Si, SrTiO 3 and MgO substrates. In order to obtain a better knowledge on the phase transition mechanisms in yttrium oxide, the effects of ion implantation have been studied as a function of the initial microstructure of thin films. The different microstructures for the as-deposited and implanted samples have been studied and characterized by means of X ray diffraction, High Resolution Transmission Electron Microscopy and Electron Energy Loss Spectroscopy and are compared to the cubic-C and monoclinic-B phase of Y 2O 3. The experimental results show clearly the presence of non-equilibrium phases in the implanted and non-implanted thin films. A particular attention is paid to the understanding of the relationship between the oxygen vacancy network organization, the stoichiometry and the formation mechanisms of these crystallographic phases.

Reactive Ion Etching of Y2O3 Films Applying F-, Cl- and Cl/Br-Based Inductively Coupled Plasmas

Reactive ion etching of yttrium oxide thin films was investigated using CF4/O2, BCl3, HBr and Cl2 inductively coupled plasmas. For all gas combinations, with the exception of Cl2, the etch rate was found to be similar, indicating a primarily physical etch process, enhanced in Cl2 by an additional chemical-etching component. The highest observed etch rate was 53 nm/min in Cl2, suitable for controlled etching of optical ridge waveguide structures several hundred nm in height. Overall, the surface quality of the etched Y2O3 films was the highest after etching in CF4/O2 plasmas, indicating a trade-off in etch rate and film quality between the various process gases. Preliminary selectivity measurements show that Ni is a suitable material for etch-masking of high resolution structures in Y2O3.