Papers

ICMCTF2002 Session F3-1: Surface and Thin Film Analysis

Wednesday, April 24, 2002 8:30 AM in Room San Diego

Wednesday Morning

Start	Invited?	Item
8:30 AM		F3-1-1 The Use of XPS in Thin Film and Multilayer Characterization of Binary and Ternary Oxides D. Leinen (Universidad de Málaga, Spain) In this contribution, different examples of ex-situ control for film composition will be presented in order to show the strength of XPS for thin film analysis at laboratory level as well as its ability for compositional control in industrial processes. As an example of the latter, it will be reported how XPS analysis has been applied to manufacturing control of monocrystalline silicon solar cells. Carbon and phosphor impurities as well as the silver distribution versus depth, crucial for the front contact of the solar cell device, could be monitored by XPS combined with Ar ion depth profiling. As an example of compositional control in mixed oxides and interfaces, XPS results from the multilayer system of Ca modified PbTi0₃3 ferroelectric devices are reported. It is shown that a compositional control of the ferroelectrical films is possible by XPS depth profiling if previous knowledge on Ar ion etching effects, i.e. preferential sputtering, in the material under study is available. Besides, when reaching during profiling the Ca-PbTi0₃3 / Pt back contact interface, Pt interdiffusion could be revealed in some cases. On the other hand, in our laboratory thin film oxides have been prepared by spray pyrolysis and characterized by XPS combined with Ar ion depth profiling. The general interest is not only the control of stoichiometry but also to monitor impurities originating from the sprayed precursor solutions. As an example of mixed oxide, the results of BaTiO3 films are presented. In that case, C atoms originating from the alcoxide used in the precursor solution remain as impurities in the ferroelectric film. In addition, several case studies of compositional and chemical control in single oxide films and bilayers prepared in our laboratory by spray pyrolysis are presented using XPS surface analysis and XPS depth profiling.
9:10 AM		F3-1-3 Ultrathin Oxides: Real-time XPS Study of Corrosion Resistance ¹ J.F. Moore (Argonne National Laboratory); M.P. McCann (Sam Houston State University); M.J. Pellin, J.N. Hryn (Argonne National Laboratory) We are exploring the regime of oxidation where diffusion is rapid and pressures are low. Kinetic effects under these conditions are minimized and a near-equilibrium composition protective oxide may be formed that is a few nanometers thick. These ultrathin oxides (<10 nm) have great potential for addressing corrosion resistance of metals, since they may not craze upon thermal cycling, and can be reformed under high temperature, oxidizing environments. The oxide films are also ideal for electrochemical applications due to their thickness. To study the growth of these oxide films, we have developed a high signal x-ray photoelectron spectrometer (XPS). The instrument can measure near-surface composition during growth under oxygen partial pressures of up to 10^-6 mBar with surface temperatures up to 800C. Under these conditions, film growth is typically complete in under 10 minutes. Experiments with alloys show rapid segregation of reactive alloy components to the surface upon oxygen exposure at high temperatures, while lower temperatures often result in a mixed oxide, typically understood to be internal oxidation. The instrument is also capable of studying oxide films exposed to a corrosive gas such as chlorine. Oxide film growth results for selected single crystals and alloys, and for thermal cycling studies will be presented, along with measurements of the grown oxide films exposed to corrosive atmospheres. ¹ Work supported by the U.S. Department of Energy, BES-Materials Sciences, under contract W-31-109-ENG-38.
9:30 AM		F3-1-4 Analysis of Sputter Deposited ITO-layers by XPS H. Steffen, T.M. Tun, M. Quaas, R. Hippler, H. Wulff (University of Greifswald, Germany) Tin-doped indium oxide (ITO) films were deposited on Si(100) substrates without external heating by means of DC-planar magnetron sputtering. A metallic In/Sn (90/10) target and an argon oxygen gas mixture were used. The flow of the reactive gas oxygen was varied between 0 and 2 sccm. Bias voltages between 0 and -100 V were used. Discharge power, Ar-flow, and pressure were kept constant. The samples were transferred into the surface analyses system through a probe handler at a background pressure ≤ 10 ^-8 mbar. Chemical composition and bonds were strongly influenced by the oxygen flow. With increasing oxygen flow film composition changed from metallic In/Sn to ITO. The oxygen content will be reduced with increasing external bias voltage. The reason for this behavior is the reduction of the flow of negative oxygen ions to the growing layer by the negative bias voltage. The O 1s peak of ITO may be divided into three single peaks. Two of these peaks belong to In-O bonds. The ratio of these two peaks depends on the cristallinity of the surface. The connection between cristallinity and XPS results will be discussed. Because of the used target an In/Sn ratio of 9/1 was expected. This ratio was observed only in case of metallic or completely oxidized layers. In other samples the In/Sn ratio reached values as low as 2/1. The reason is the migration of Sn to the surface after film deposition. This was proofed by in-situ XPS during oxidation of metallic In/Sn layers.
9:50 AM		F3-1-5 Microstructure and Chemistry of Annealed AlCuFeCr Quasicrystalline Coatings M.J. Daniels (University of Michigan, Ann Arbor); D. King (Technology Assessment and Transfer); J.S. Zabinski (Air Force Research Laboratory); J.C. Bilello (University of Michigan, Ann Arbor) As-deposited quasicrystalline films with initial grain size < 10nm were annealed for a variety of times and temperatures in flowing Ar at a base pressure of 5x10^-5 Torr to study the evolution of the microstructure. Sputter profile XPS and synchrotron grazing incidence x-ray scattering (GIXS) examined the subsequent chemistry and microstructures, which originated from the same samples. XPS analysis showed oxygen incorporation reached 70 at.% at the surface of the film, but stabilized at 10 at.% at a depth of 160 nm. By varing the incident angle, synchrotron GIXS was used to probe the structure at varying penetration depths. An amorphous layer less than 30 nm thick was present near the termination surface. A crystalline oxide develops below the amorphous surface region, and is the dominant phase to 140 nm. Between 140 nm and 720 nm, the predominant phase is a quasicrystalline approximant, while the bulk of the film is quasicrystalline. Residual strain analysis shows that the crystalline oxide induces a compressive residual stress. Displacement of major quasicrystalline peaks indicates the relative residual strain to be as high as 0.1%. Acknowledgement: Thanks to the AFOSR, DARPA, and DoE for support of this project.
10:10 AM		F3-1-6 Electronic Properties of Cr_1-xAl_xN Thin Films Deposited by Reactive Magnetron Sputtering R. Sanjinés, O. Banakh, C. Rojas, P.E. Schmid, F. Lévy (IPA-DP-EPFL, Switzerland) The basic electronic properties of Cr_1-xAl_xN films is the subject of this work. Cr_1-xAl_xN films with 0≤x≤0.5 were deposited by magnetron sputtering from Cr and Al targets in an Ar/N₂ atmosphere. X-ray diffraction, electrical resistivity, spectroscopic ellipsometry analyses and X-ray photoelectron spectroscopy (XPS) were performed to investigate the crystal structure and the electronic properties of the films. The films crystallise in NaCl fcc structure. The electrical resistivity was measured from 50K to 320K. The electrical resistivity at 320K increases with increasing Al content, and the temperature coefficient of the resistivity is always negative. The values of the activation energy, which also increase with Al content, are typical of "dirty" metallic nanocrystalline films, where the electrical conductivity is limited by grain boundary scattering. The apparent dielectric functions of the films, evaluated by spectroscopic ellipsometry, show an unusual behavior: the real part of the dielectric function is positive in the near infrared and increases as the photon energy decreases. The imaginary part follows the same evolution. Such a behavior is observed in films containing a small fraction of a metallic phase dispersed in an insulating matrix. How such a model can possibly apply to Cr_1-xAl_xN films is under investigation. It might be the result of an extrinsic oxidation at the grain boundaries. A detailed study of XPS valence band (VB) spectra shows that the substitution of Cr atoms by Al atoms leads to local modifications of covalent-ionic bonds between N p and Cr d orbitals. The variations of the VB structure due to the chemical composition changes correlate with the electrical, optical and mechanical properties.
10:30 AM		F3-1-7 Investigation of the Residual Stresses and Mechanical Properties of (Cr,Al)N Arc PVD Coatings Used for Semi Solid Metal (SSM) Forming Dies E. Lugscheider, K. Bobzin, T. Hornig, M. Maes (Werkstoffwissenschaften, RWTH, Germany) In many cases high compressive stresses are an unwanted side effect of deposited PVD coatings, cause they are known to reduce the adhesive strength of the coating on the substrate. However in some applications a main focus of the PVD coatings consists out of bringing the surface of a substrate into a compressive state. A surface being in a compressive state is more likely to withstand thermal and mechanical alternating stresses within the surface and has a higher resistance against forming cracks and increases the lifespan of SSM dies. Arc ion plating is a PVD process which is known to cause high compressive stresses in coatings due to its high ionisation rate and the applied bias voltage to the substrate. Therefore the arc ion plating process is suitable for bringing a surface of a substrate into a compressive state. The investigated (Cr,Al)N coatings were deposited in such an arc ion plating PVD process and the thickness varies from 2.7 µm to 17 µm. The correlation of thickness verses residual stresses of these coatings was investigated an in order to determine these residual stresses a stripe bending test is backed up and compared with a XRD stress analysis. Additionally the coatings were exposed to impact tests to determine the influence of compressive stresses on the wear behavior caused by alternating stresses.
11:10 AM		F3-1-9 New Residual Stress Measurement in Textured Thin Film by Grazing Incidence X-ray Diffraction C.H. Ma (University of Illinois at Urbana Champaign); J.-H. Huang (National Tsing Hua University, Taiwan, ROC); H. Chen (University of Illinois at Urbana Champaign) Measurements of residual stresses in textured thin films have always been problematic. In this study, a new experimental approach using grazing-incidence X-ray diffraction (XRD) is presented with its principles based upon the conventional sin square phi method. Instead of using the Bragg-Brentano (B-B) or the Seemann-Bohlin (S-B) geometry, the proposed method utilizes an asymmetrical diffraction geometry for which X-rays were incident at a grazing angle gama to the sample surface, while the angle Phi is the tilt angle of the sample surface as defined by the conventional sin square phi method. For an isotropic medium measured strain using this grazing incidence geometry assumes a linear relationship with the geometrical parameter, cosin sqare alpha sin square phi, where the angle alpha equals to the Bragg angle theta minus the grazing angle gama. The cosin square alpha sin square phi method is employed to measure the residual stress in highly textured transition metal nitride (TiN, VN, CrN) thin films with the thickness less than 0.5 micrometer.
11:30 AM		F3-1-10 Growth and Structure of Silica Films Deposited by Plasma-enhanced CVD on Polymeric Materials K. Teshima, Y. Inoue, H. Sugimura, O. Takai (Nagoya University, Japan) The fact that silica is ecologically benign has received much attention recently since it is harmless to human beings and the environment, and is abundant in nature. There is now a strong demand for silica coatings on polymeric materials. Among various deposition methods, plasma-enhanced CVD is most promising for the low-temperature deposition of silica. In this work, silica films have been prepared on polymeric materials by low-temperature plasma-enhanced CVD (PECVD) using organosilane compounds and oxygen as raw materials. The chemical bonding states and compositions of the films deposited were evaluated with FT-IR and XPS. Furthermore, silica growth processes on polymer substrates were studied by means of SEM and AFM observations. The SEM images clearly show that the silica growth processes in the early stage of the deposition depend on the deposition conditions, such as substrate surface conditions and an oxygen fraction. Organosilane fragments are thought to adsorb selectively on energetically advantageous surfaces of polymer substrates. It is considered that silica clusters are formed on the polymer surface in the early stage of the deposition. In this study, silica films were found to grow on polymer substrates in an island-like, discontinuous manner, rather than layer-by-layer.
11:50 AM		F3-1-11 Localized Deformation of Multicomponent Thin Films D.V. Shtansky, E.A. Levashov, S.A. Kulinich, A.N. Sheveiko, F.V. Kiriuhancev (Moscow Steel and Alloys Institute, Russia); J.J. Moore (Colorado School of Mines) Recent fracture investigations have revealed that there are two types of deformation mechanism of nanostructured thin films: homogeneous deformation and localized inhomogeneous deformation with the formation of shear bands. However, the nature of this phenomenon remains unclear. A comparative analysis of fracture of various films is presented. Films of Cr-B, Ti-Si-N, Ti-B-N, Ti-Cr-B-N, Ti-Al-B-N and Ti-Si-Zr-N-O were deposited on Si substrate by DC magnetron sputtering of composite SHS-targets. The indentation of the as-deposited films was made using Vickers microhardness tester at a load of 10, 25 and 50 g. The SEM and AFM studies were fulfilled for investigating the film behavior during localized deformation. Both homogeneous and localized inhomogeneous deformations of the fracture surface were observed and described. Isolated particles located within the area of deformation were frequently observed. The films were characterized in terms of their structure, chemical composition, microhardness, elastic modulus, elastic recovery and surface topography. The mechanism of deformation of multicomponent nanostructured thin films is discussed.