Y2O3 Thin Films Research Articles

Controlled erbium incorporation and photoluminescence of Er-doped Y2O3

A high concentration of erbium doping was achieved in Y2O3 thin films on Si (100) by depositing Y2O3 alternatively with Er2O3 using radical-enhanced atomic layer deposition (ALD). Specifically, the erbium doping level was controlled by varying the ratio of Y2O3:Er2O3 cycles during deposition, and a 10:5 ratio yielded ∼9at.% erbium incorporation in Y2O3, confirmed by the compositional analysis using x-ray photoelectron spectroscopy. Room-temperature photoluminescence was observed in a 320-Å Er-doped (9 at. %) Y2O3 film deposited at 350 °C. This result is very promising, since the film was fairly thin and no annealing at high temperature was needed to activate the erbium ions. This suggests that radical-enhanced ALD was able to preserve the optically active trivalent state of the erbium ion from its precursor state. The effective absorption cross section for Er3+ ions incorporated in Y2O3 was estimated to be on the order of 10−18cm2, about three orders of magnitude larger than the direct optical absorption cross section reported for Er3+ ions in a stoichiometric SiO2 host. These results validate Y2O3 as a promising Er3+ host material and demonstrate that radical-enhanced ALD is a viable technique for synthesizing these materials.

Influence of Zirconia Sol-gel Coatings on the Fracture Strength of Brittle Materials

In this work, the effect of a sol-gel ZrO2–3 mol% Y2O3thin film on the fracture properties of a variety of brittle substrates was investigated. The results suggest that the film does not have any appreciable influence on the fracture behavior of crystalline substrates but dramatically affects the fracture properties of amorphous layers. In particular, a significant reduction of average fracture strength and a major increase of the Weibull modulus were observed on coated glassy slides. The origin of such variations is attributed to the generation of a homogeneous flaw population in the vitreous substrates, and the possible mechanisms for the production of flaws are analyzed. Implications of these results for the practical use of coated glassy layers are discussed.

Crystalline growth of cubic (Eu, Nd):Y2O3 thin films on α -Al2O3 by pulsed laser deposition

In this paper we report on the growth of crystalline, europium- and neodymium-doped cubic yttria ((Eu, Nd):Y2O3) thin films on hexagonal corundum (α-Al2O3) substrates using the pulsed laser deposition (PLD) technique. A KrF excimer laser was used to ablate material from ceramic (Eu, Nd):Y2O3 targets. The yttria films were deposited on the α-Al2O3 (0001) substrates. X-ray diffractometry (XRD) revealed that the films grew in the Y2O3 [111]-direction. The surface topography of the films was investigated using atomic force microscopy (AFM).

Preparation, characterization and mechanical properties of Y2O3 thin film deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

Abstract Silane coupling reagent (3-mercaptopropyl)trimethoxysilane was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monoalyer (MPTS-SAM) and the terminal –SH group in the film was in-situ oxidized to –SO3H group to endow the film with good chemisorption ability. Thus Y2O3 thin film were deposited on the oxidized MPTS-SAM, by enhanced hydrolysis of yttrium nitrate (Y(NO3)3 · 6H2O) solution in the presence of urea (CO(NH2)2) at 80 °C, making use of the chemisorption ability of the –SO3H group. The thickness and refractive index of the films were determined with an ellipsometer. The morphologies of the films were observed on an atomic force microscope. The adhesion strength and friction behavior of the films on the silicon substrate sliding against a steel ball was examined on a UMT-2MT friction and wear test system. It was found that the Y2O3-600 thin film was well adhered to the substrate with a critical load (Lc) of 2.8 N and had excellent antiwear and friction-reduction performance under a low load of 0.2 N. Thus the Y2O3 film might find promising application in the surface-protection of single crystal Si and SiC in microelectromechanical systems (MEMS).

Processing of Y2O3 Thin Films by Atomic Layer Deposition from Cyclopentadienyl-Type Compounds and Water as Precursors

Y2O3 thin films were grown onto Si(100) substrates by atomic layer deposition (ALD) using organometallic precursors, viz. tris(cyclopentadienyl)yttrium, Cp3Y, and tris(methylcyclopentadienyl)yttriu...

Photo-formation of interfacial layers during pulsed laser deposition of high-k dielectrics on silicon

ZrO2 and Y2O3 thin films were deposited on Si substrates using pulsed laser deposition in vacuum or oxygen ambient. Angle resolved X-ray photoelectron spectroscopy investigations showed that there was always some oxidation of the Si substrate resulting in the formation of an interfacial layer that could have a deleterious effect on the overall capacitance of the resulting MOS devices. The positions and shape of the metal, the oxygen and the Si XPS peaks suggest that at the temperatures used for deposition (<650 °C) the SiO2 layer is physically mixed with the deposited oxide layer without forming silicate compounds. X-ray reflectivity investigations confirmed the presence of the interfacial layer whose density was found to be higher than that of pure SiO2 but lower than that of the corresponding silicate, corroborating the XPS results. To slow down the substrate oxidation, a low temperature UV-assisted nitridation treatment was performed prior to the deposition of the oxide layer. This UV-assisted treatment resulted in thinner and denser surface passivation layers than those obtained without any treatments indicating an incorporation of nitrogen into the SiO2 network. High-k dielectric layers deposited on such samples exhibited thinner interfacial layers.

Structural characterization of epitaxial Y2O3 on Si (0 0 1) and of the Y2O3/Si interface

The search for high dielectric constant (high-k) oxides to replace silicon dioxide for future CMOS devices is a formidable task. Key issues are definitely good structural and electrical properties as well as high quality interfaces between the high-k and the semiconductor substrate. In this work we study the local structure of ultra thin Y2O3 films and Y2O3/Si interface, by using Y k-edge X-ray absorption spectroscopy (XAS) in grazing incidence geometry. Y2O3 epilayers (2–20nm thick) are grown on Si (001) by MBE at 450°C and some of them are in-situ annealed at 500°C for 30min. In the as grown epilayer, XAS reveals the presence of Y–Si and Y–O correlations at the Y2O3/Si interface. The in-situ annealing produces a rearrangement of the local atomic environment at the interface and only Y–O correlations are detected. The local structural quality of the epilayers improves with thickness and annealing.

Y2O3 thin films: internal stress and microstructure

Thin films of yttrium oxide, Y2O3, were deposited on Si (100), MgO and SrTiO3 substrates by ion beam sputtering. The as-deposited samples are under a strong compressive stress whatever the substrates are. Furthermore the in-plane (222) or (400) Bragg peaks are shifted and non-symmetric. The high-resolution transmission electron microscopy investigations on the epitaxially grown Y2O3 thin films lead to the conclusion that the ion beam deposition process promotes a strong disorder on the oxygen network. The crystallographic symmetry of the Y2O3 structure which is Th7 becomes a fluorite related symmetry which is Fm3m. Annealing treatments or deposition involving a secondary ion beam assisted deposition process re-orders the Fm3m structure which comes back to the equilibrium Th7 symmetry.

Multiple Bit Operation of MFISFET With Pt/SrBi2Ta2O9/Y2O3/Si Gate Structure

A single transistor type ferroelectric memory with multiple bit operation was presented. This cell has a metal ferroelectric insulator semiconductor field effect transistor structure. Y2O3 thin film was used as a buffer insulating layer to improve the memory characteristics and SrBi2Ta2O9 was used as a ferroelectric gate material. The multi-level characteristics of four levels with one order of drain current difference were measured according to the writing voltage step of two volt. This multi-level memory cell enables to increase the density of memory in the same space and lower the cost.

Crystal field analysis of erbium doped yttrium oxide thin films in C2 and C3i sites

AbstractFluorescence measurements on Er ions in Y2O3 thin films have been analyzed with crystal‐field Hamiltonians of C2 and C3i symmetries including J‐mixing effects. Crystal‐field parameters have been determined based on the Racah theory, that minimize the rms deviation between calculated and experimentally found energy. This theoretical analysis confirms the dominance of the C2 symmetry site in the fluorescence spectrum; however in the infrared emission spectrum, the contribution of the two sites C2 and C3i is comparable.

Buckling phenomena in Y2O3 thin films on GaAs substrates

Worm-like buckling structures have been investigated by atomic force microscopy to estimate the relevant parameters for the mechanical stability of Y2O3 thin films deposited by ion beam sputtering technique on GaAs substrates. The internal stresses involving in the observed buckling phenomena have been estimated to be around 8.5 GPa in compression. The critical thicknesses up to which the various damaging mechanisms occur have also been determined.

Silicate interface formation during the deposition of Y2O3 on Si

ABSTRACTThe interface behaviour during PE-MOCVD deposition of Y2O3 thin films on Si/SiO2 (8 Å) substrates has been investigated by XPS, TEM and OES analysis. The deposition process involves the sequential injection of MO precursors into the CVD chamber and is assisted by an O2 plasma. The injection frequency greatly influences the interface behaviour in terms of thickness and composition. The O2 plasma and the solvent also greatly affect substrate oxidation, and subsequently interface formation during deposition. Several mechanisms are discussed to account for substrate oxidation in view of a careful control of interface formation.

High epitaxial quality Y2O3 high-κ dielectric on vicinal Si(001) surfaces

Thin films of Y2O3 were grown by molecular-beam epitaxy on silicon aiming at material with adequate crystal quality for use as high-κ gate replacements in future transistors. It was found that Y2O3 grows in single-crystalline form on 4° misoriented Si(001), due to an in-plane alignment of 〈110〉Y2O2 to the silicon dimer direction. The Y2O3 layers exhibit a low degree of mosaicity, a small proportion of twinning and sharp interfaces. This represents a significant improvement compared to material grown on exact silicon surfaces.

Preparation of Y2O3 thin films deposited by pulse ultrasonic spray pyrolysis

Thin films of Y2O3 with a preferred (101) orientation were deposited by a spray pyrolysis method. Ethanol solution of yttrium acetylacetonate were ultrasonically nebulized and thermally decomposed onto Si(100) in the temperature range 350–400°C. The films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. An appropriate ratio of pulse time to interval time between pulses was found to be necessary for obtaining homogeneous and uniform nanostructural Y2O3 thin films.

Evidence for the physical basis and universality of the elimination of particulates using dual-laser ablation. I. Dynamic time-resolved target melt studies, and film growth of Y2O3 and ZnO

The application of a dual-laser ablation process, incorporating the addition of a synchronized CO2 laser to the traditional excimer (KrF) laser used for the ablation of targets in thin film deposition, has been previously demonstrated to be effective in the elimination of particulates in films of Y2O3 [J. Vac. Sci. Technol. A 13, 1171 (1995)]. It has been hypothesized that the efficacy of particulate removal is related to phase transformation from the solid to liquid phase prior to excimer laser ablation of the target material. In this series of two articles we present direct physical evidence of the dynamics of the phase transformation occurring on the target surface and its effect on the morphology of film growth. Pump–probe experiments have been conducted using the CO2 laser to probe the dynamic reflectivity of the target surface on the nanosecond timescale. These experiments were conducted for a range of materials spanning a wide range of thermal conductivity including a low thermal conductivity insulator (Y2O3), and a sublimating oxide (ZnO), as well as a high thermal conductivity metal (Zn) to assess the universal applicability of the results. In this article (Part I) the results of these dynamic reflectivity experiments are correlated with previously reported particulate-free deposition of thin films of Y2O3. Similar experiments are conducted for ZnO. In both cases, the reflectivity measurements yielded times for the onset of melt at a variety of CO2 laser fluences. Synchronization of the KrF laser to coincide with the onset of melt resulted in particulate-free film growth. The effect of mistiming on the quality of the deposited film is presented for ZnO.

Influence of Oxygen Vacancies on the Luminescence Spectra of Y 2 O 3 Thin Films

Luminescence spectra of Y2O3 thin films annealed in air and in vacuum are investigated. It is established that the presence of oxygen vacancies leads to a decrease in the intensity of the luminescence band with a maximum at 3.4 eV (related to emission of self‐localized Frenkel excitons describing the excited state of a molecular ion (YO6)9−) and of the luminescence band with a maximum at 2.9 eV (related to the anion sublattice). It is revealed that the oxygen vacancies also lead to a decrease in the luminescence intensity in the 2.60, 2.35, 2.10. 1.90, and 1.70 eV bands that are related to radiative recombination in the donor–acceptor Y3+–O2− pairs. The donor–acceptor distances are calculated.

Preparation and characterization of sol–gel Y2O3 planar waveguides

Abstract Y2O3 thin film waveguides were prepared using a sol–gel method and a dip-coating procedure. Multicoating operations were necessary to produce multimode and low attenuation coefficient waveguides. Thickness and refractive index were determined by m-lines spectroscopy. X-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) were used for structural investigations and nanocrystals size determination as a function of the annealing temperature. The Y2O3 amorphous phase was observed at low heat-treatment temperature (300°C) and the layers turn to cubic nanocrystalline form when the annealing temperature reached 400°C. An annealing treatment at 600°C was necessary to provide more densified and good optical planar waveguides exhibiting an attenuation coefficient lower than 2 dB/cm.

Direct heteroepitaxy of crystalline Y2O3 on Si (001) for high-k gate dielectric applications

This work focuses on the microstructural characteristics of Y2O3 thin films and interfaces, which is related to their suitability as high-k replacement for SiO2 gate dielectrics in future transistor devices. The films were grown directly on silicon (001) substrates by electron-beam evaporation in a molecular beam epitaxy chamber under ultrahigh vacuum conditions. At an optimum growth temperature, ∼450 °C, high crystalline quality films were obtained, albeit with a heteroepitaxial relationship Y2O3 (110)//Si (001) and Y2O3 [001]//Si 〈110〉, which favors the formation of a potentially harmful complex microstructure. The latter consists of large (submicron-sized) domains containing smaller (10–30 nm) inclusions with perpendicular crystal orientations. Despite predictions for thermodynamic stability and low O2 partial pressure in the chamber, the chemical reaction of Y2O3 with Si could not be avoided. Indeed, a nonuniform interfacial amorphous layer with thickness 5–15 Å was observed, while YSi2 was formed at a moderate growth temperature (610 °C).

Etching mechanism of Y2O3 thin films in high density Cl2/Ar plasma

In this study Y2O3 thin films were etched with an inductively coupled plasma. The etch rate of Y2O3 and the selectivity of Y2O3 to YMnO3 were investigated by varying the Cl2/(Cl2+Ar) gas mixing ratio. The maximum etch rate of Y2O3 and the selectivity of Y2O3 to YMnO3 were 302 Å/min and 2.4, respectively, at a Cl2/(Cl2+Ar) gas mixing ratio of 0.2. Based on x-ray photoelectron spectroscopy analysis, it was concluded that the Y2O3 thin film was dominantly etched by Ar ion bombardment and was assisted by the chemical reaction of a Cl radical. This result was confirmed by secondary ion mass spectroscopy analysis with the presence of a Y–Cl bond at 124.4 (amu).

Y 2 O 3 Thin Films Characterized by XPS

Y2O3 thin films were synthesized by chemical vapor deposition (CVD) using Y(acac)3.xH2O (Hacac= 2,4-pentanedione) as precursor. This work is focused on the x-ray photoelectron spectroscopy (XPS) characterization of an Y2O3 thin film deposited on glass substrate at 450 °C in N2+O2 atmosphere and subsequently annealed in air at 1000 °C. Besides the wide scan spectrum, charge corrected binding energies for the Y 3d5/2, O 1s, and C 1s surface photoelectron signals are reported.