Characterization Of Oxide Thin Films Research Articles

Damage-free X-ray spectroscopy characterization of oxide thin films

Thin polymer or oxide films are ubiquitous components in many devices, including membranes for filtration or electrodes in electrochemical energy storage. High energy electron or x-ray probes for microscopy and spectroscopy are useful to characterize and understand these materials. However, irreversible damage by the probe radiation remains a challenge. Here, we show that graphene serves as an x-ray and electron transparent substrate that substantially reduces radiation damage of an oxide thin film. We demonstrate this using highly focused x-ray beams, which show that compared to oxide thin films supported on a substrate, graphene-supported regions show minimal changes in the x-ray spectra as a function of x-ray dose. These results pave the way for the development of experimental setups that allow for long exposure time measurements with limited sample damage and substrate-directed radiation patterning.

Atomic-scale characterization of oxide thin films gated by ionic liquid.

Ionic liquids (ILs) have received considerable interest for use in electrostatic gating in complex oxide systems. Understanding the ionic liquid/oxide interface, and any bias-induced electrochemical degradation, is critical for the interpretation of transport phenomena. The integrity of the interface between ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate and La1/3Sr2/3FeO3 under various biasing conditions was examined by analytical transmission electron microscopy, and we report film degradation in the form of an irreversible chemical reaction regardless of the applied bias. This results in an intermixing region of 4-6 nm at the IL/oxide interface. Electron energy loss spectroscopy shows La and Fe migration into the ionic liquid, resulting in secondary phase formation under negative bias. Our approach can be extended to other ionic liquid/oxide systems in order to better understand the electrochemical stability window of these device structures.

Influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide layers using an atomic force microscope

Physical and electrical properties of thin oxide films have been studied using the atomic force microscope (AFM). Experiments have been done in three different surroundings: in air and in secondary vacuum (∼10 −6 mbar) without and with a heating stage in order to study the influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide films. It is shown that by applying a positive voltage at the AFM tip and in the presence of a water layer at the oxide’s surface in air ambient, the behavior of the oxide film is very different compared to the same experiment conducted in secondary vacuum. It is thought that in air, H + ions are injected through the oxide, forming attached hydrogen defects in it. These electrically active defects form a path in the oxide between the tip and the substrate facilitating the passage of charges through the oxide, which can be described by a Trap Assisted Tunneling (TAT) mechanism. The results show that working in vacuum with a heating stage is an important condition for the reliability of the characterization of oxides since the breakdown phenomenon is largely reduced due to the absence of the water layer. Moreover, the creation of hillocks (protrusions appearing on the surface after the electrical stress) on the oxide’s surface is decreased under vacuum.

Measurement Procedures for the Electrical Characterization of Oxide Thin Films

This paper describes a measurement system for the electrical characterization of oxide thin films. Such films can be produced using plasma-sputtering processes and permit the realization of a large set of high-performance components, such as capacitors, active devices, sensors, and protective coatings. The electrical properties of the oxide films, which have a thickness of less than 1 mum, are difficult to measure since very high resistances (on the order of giga ohms) and small capacitances (on the order of picofarads) are expected for contact areas smaller than 1 mm2 . The measurement system and the procedures described in this paper represent an alternative solution to the commercial devices, which usually employ a mercury probe for performing the contact with the specimen under characterization. Furthermore, the proposed system can be used not only to estimate the electrical properties of a single point but to evaluate the uniformity of oxide films on large specimens as well. The experimental results reported refer to valve-metal-based oxide films deposited in a lab-scale capacitively coupled parallel-plate reactor and show the effectiveness of the proposed procedures.

Physico-chemical Characterization of Thin Oxide Films: Difficulties and Solutions

ABSTRACTOxides have always been an integral part of semiconductor manufacturing both in front and back-end processing. With the necessary increase in performance, the demand on these oxides has been increasing leading to their (future) replacement by more complex materials, such as high-k's in gate oxide and metal gates. With the increasing material complexity, a thorough characterization of all aspects of these materials is necessary, covering, for instance, surfaces and interfaces, nucleation, growth, atomic structure, …This article focuses on the characterization of front-end oxides and their interfaces. It shows that detailed information can be achieved by sophisticated experimental techniques such as synchrotron radiation, high energy ERD or AtomProbe but that adequate sample preparation and/or analysis by a combination of more routinely available techniques may achieve similar results. This is shown through the study of three different systems/problems in the gate stack analysis. We will first focus on the determination of substrate surface preparation conditions before deposition and their influence on growth mode and the growth characteristics by different growth techniques (ALD, MOCVD, …). Second, we present the possibilities of compositional depth profiling of thin layers both with nuclear techniques and Angle-Resolved XPS. Finally, we will show that using conventional XPS and a combination of front and back-side analysis, the interface between high-k oxide and metal gates can be investigated. More examples of gate stack characterization can be found elsewhere

Characterization of oxide thin films using optical techniques

Thin films of oxide materials are playing a growing role as critical elements in optoelectronic devices and nanoscale devices. In this work, thin films of some typical oxides such as WO 3, Ga 2O 3 and SrTiO 3 were investigated. We present measurements of those films, using various optical techniques like photoconductivity transients over a wide time range and photo-Hall measurements. Analysis of the photo-Hall and photoconductivity data permits the determination of the contribution to the photoconductivity made by the carrier mobility and concentration. A model for dispersive carrier transport was proposed to explain the relaxation of the photoconductivity in oxide thin films. In addition, photoluminescence characterization was used to study microstructures and energy band in oxide thin films. The broad emission from oxide host, consisting of several band peaks, was likely due to a recombination process with several possible paths. The dependence of the luminescent intensity on the annealing atmosphere was associated with the presence of oxygen vacancies. It is suggested that our optical analysis efforts have improved the understanding of oxide thin films, and this should lead to the necessary advancements in a variety of devices.

Application of optical and luminescent techniques to the characterization of oxide thin films

The interaction between light and electrons in oxide compounds forms the basis for many interesting and practical effects, which are related to microstructure, energy band, traps, carrier transport and others. Thin films of oxides like WO 3, Ga 2O 3, Y 2O 3 and SrTiO 3 were investigated using various improved optical and luminescent techniques. The home-made systems for optical and luminescent measurements were described in detail. The facilities of photo-Hall and photoconductivity transients have been proven to be powerful tools in the studies, which allow us to perform photoinduced process and relaxation measurements over a wide time range from 10 −8 to 10 4 s. Furthermore, we extended the measurement capabilities of the commercial luminoscope by using an interferometer system with optical fiber and illuminance meter instead of an optical microscope. The cathodoluminescent measurements can be performed at a relative high pressure (20–60 mTorr) compared to ultra-high-vacuum condition of most commercial products. Luminescent characterization was employed as a probe to study doping ions, oxygen vacancies, trap and/or exciton levels in oxide thin films. Our results suggest that various traps and/or excitons in thin films of WO 3, Ga 2O 3 and SrTiO 3 involve in the process of photoconductivity relaxation and emission.

Fabrication and characterization of oxide thin films prepared by MOCVD method

Fabrication and characterization of oxide thin films prepared by MOCVD method

AES characterization of thin oxide films growing on Al foil during oxygen plasma treatment

AbstractThe oxidation phenomenon during exposure of an Al foil to a low‐pressure weakly ionized oxygen plasma was studied by Auger electron spectroscopy (AES). We used a high‐purity Al foil with a thickness of 10 µm. Prior to plasma experiments the samples were analysed by AES depth profiling. The surface composition slightly varied between samples but, generally, a native impurity film with a thickness of approximately 2.5 nm was found on the Al surface. The surface film consisted of Al, O and C. The chemical state of aluminium was determined from the Al (68 eV) and Al (51 eV) peaks. The samples were exposed to weakly ionized oxygen plasma for various periods up to 300 s. Plasma parameters were measured with Langmuir and optical fibre catalytic probes. The electron temperature was about 70 000 K, the density of charged particles was about 1 × 1016 m−3, and the density of neutral oxygen atoms 2.4 × 1021 m−3. The AES depth profiles of plasma exposed samples showed that even after a short exposure to oxygen plasma a thin but stoichiometric Al2O3 layer was formed. With further exposure to oxygen plasma the thickness of the oxide layers and broadening of the oxide/Al interface increased which was explained by thermal effects. Copyright © 2004 John Wiley & Sons, Ltd.

Characterization of thin oxide films on GaAs substrates by optical methods and atomic force microscopy

AbstractIn this paper the results of optical and atomic force microscopy characterization of oxide thin films prepared by thermal oxidation of GaAs single crystal wafers at a temperature of 500°C in air are presented. The optical characterization is performed using multi‐sample modification of the method based on combining variable angle spectroscopic ellipsometry and near‐normal spectroscopic reflectometry. It is shown that the films exhibit the rough lower boundaries and refractive index profile inhomogeneities. The spectral dependences of the refractive index and extinction coefficient of these films are presented within the wide spectral region, i.e., 210–900 nm. The values of the thicknesses and roughness parameters characterizing the oxide films are introduced as well. Copyright © 2004 John Wiley & Sons, Ltd.

Surface analysis of nickel-oxide films modified by a reactive element

The surface morphology of oxide grown in the temperature range of 873–1173K on modified high-purity nickel has been observed and quantitatively analyzed by atomic-force microscopy. The modifications included one of two finishing techniques and either CeO2 sol-gel coatings or Ce-ion implantation. There is an essential difference in the surface morphology and grain size for oxides formed on Ce/CeO2-modified nickel in comparison to pure NiO. The oxide topography also depends on the substrate-surface-finishing technique and the method of applying the cerium. Both Auger electron spectroscopy and Rutherford backscattering spectrometry were used to evaluate the depth composition of the oxide. In the modified oxide formed on chemically polished substrates the Ce generally appeared to be located close to the outer surface, even after long oxidation times. In oxide grown on mechanically polished substrates Ce was detectable by these techniques only during the very early stages of oxidation. A general correlation exists between the parameters describing the oxide-surface morphology and the Ce-depth distribution, and the reduction of the NiO growth rate achieved by applying the reactive element. Detailed analysis of the oxide surface, internal microstructure, and chemistry gives new insights into the problem of the characterization of thin oxide films and the mechanism of oxide formation.

AES/GDS characterization of thin oxide films on FeCr sheet steels

AbstractThin oxide films on four kinds of commercial sheet were characterized with Auger electron spectroscopy (AES) and glow discharge optical emission spectroscopy (GDS). Enrichment of alloying elements was noticed in the thin oxide films formed in air. The depth profiles obtained by AES with ion sputtering showed that enrichment of chromium occurred at the interface between the oxide and the matrix. It was difficult with AES to obtain the profiles of silicon and manganese because of overlap of their peaks with the iron peaks on the spectrum. On the other hand, with GDS, silicon and manganese could be analysed quantitatively in thin films that are <0.05 μm thick.

X-ray Diffraction of Thin Oxide Films on Soldered Module Pins

AbstractThe presence of metal oxide films from wave solder baths on timed module pins are partly responsible for non-wet problems in subsequent soldering steps. The cylindrical geometry of the pins lends itself to the characterization of thin oxide films by using the highly sensitive Debye-Scherrer camera method. As confirmed by Electron Hicroprobe Analysis (EMA), pins containing thin oxide films were used to obtain the diffraction patterns. A software program was developed that subtracts the diffraction angles of an oxids-free control pin from the pattern of the contaminated pin, and tabulates the residual d-spacing (interplanar distance) of the contaminant film.

Characterization of thin oxide films for FET applications

Electronic transport in thin silicon dioxide films used for field effect transistor (FET) devices is controlled by the metal-oxide barrier height rather than by bulk defect centers. The presence of charged ions (i.e., sodium) or interface states at the injecting electrode can lower the barrier height and thereby increase the electronic conduction. In addition, the transport of sodium ions is generally believed to be emission-limited from traps located at the metal-oxide interface. When present in large concentrations (>10 12/cm 2), Na ions can alter the internal space charge field, markedly enhance the current, and even lead to dielectric breakdown. Instabilities in the current at high electric fields (∼10 7V/cm) as a result of ionization processes were observed prior to breakdown. The degradation of metal-oxide-semiconductor capacitors as a result of electrothermal stressing can be retarded by the incorporation of hydrogen in the SiO 2.