ICMCTF1998 Session F3: Surface and Thin Film Analysis

Thursday, April 30, 1998 1:30 PM in Room San Diego

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	F3-1 Characterization of Metal Coatings and Thin Films Using a Synchrotron Light Source T.K. Sham (University of Western Ontario, CANADA) When charge particles, such as electrons and positrons, are circulated around an orbit at relativistic speed, they emit light tangential to their orbit. This light is now commonly known as synchrotron radiation (light). However, synchrotron light is no ordinary radiation for it contains a continuous spectrum of bright electromagnetic radiation with energies varying from infrared to gamma rays. To-day, second and third generation synchrotron light sources are becoming readily available. and around the world. Thus these facilities offer new and unprecedented, yet accessible opportunities for materials characterization for general users. In this talk, the properties of a synchrotron light source will be discussed. Emphasis is placed on techniques that can have profound implications to advanced characterization of metal coating and thin films. Techniques to be discussed include x-ray absorption fine structures (XAFS) using multi-element multi-core levels, photoemission spectroscopy with variable photon energy, and x-ray reflectivity measurements among others. These techniques take advantage of the tunability and brightness of the synchrotron source which allows for a much bigger range of element, sampling depth and even chemical sensitivity in thin film characterization. The nature of the interface can also be revealed. The application of these techniques to thin film problems will be illustrated with studies of metal thin films (magnetic and non magnetic) on metal, metal thin films on silicon, metal silicide films on silicon and the effect of diffusion barrier TiN films in Al(Cu)/TiN/Si systems. Other useful techniques such as imaging and diffraction will also be noted
2:10 PM		F3-3 Reaction of CO with the Ion-Bombarded Ni(111) Surface J.R. Yang, H.-Y. Hwang, C.-C. Chang (National Taiwan University, Taiwan); W.-H. Hung (Synchrotron Radiation Research Center, Taiwan) We report on the effect of ion bombardment and synchrotron radiation on the chemical reactions occurring on the surface. The chemical reactivity of metal and semiconductor surfaces with chlorine and carbon monoxide is enhanced under ion bombardment. The degree of the reactivity perturbation may be controlled by subjecting surfaces of different temperature to particle beams of different energy, irradiation time, and flux. Isotopic studies reveal that the change of the surface reactivity is caused not only by the alteration of the surface structure but also by the formation of new surface states. Synchrotron-radiation-induced core-level spectroscopy and temperature-programmed desorption studies show that the binding energy of molecules on the new states may be governed by the electronic distribution of the particle-perturbed surface and by the electron-donating or -accepting characteristics of the adsorbing molecules. Molecular dynamics calculations are used to understand the atomistic mechanism of the surface reaction affected by ion irradiation.
2:30 PM		F3-4 Depth-Profiling of Nonconductive Oxidic Multilayers with Plasma-based SNMS in HF Mode J. Goschnick, C. Natzeck, T. Schneider, M. Sommer, F. Zudock (Forschungszentrum Karlsruhe GmbH, Germany) Multilayer structures to be used as gas sensor microsystems were prepared on oxidized silicon substrates with reactive magnetron sputtering techniques and Ion Beam Assisted Chemical Vapor Deposition. Some 100 nm thick semiconducting metal oxide layers with gas-sensitive conductivity, such as tin dioxide (SnO₂) or tungsten trioxide (WO₃), are deposited on the substrate and coated by additional layers of Al₂O₃, CuO, or SiO₂ to obtain gas sensors with customized gas selectivity. The latter are restricted in thickness to less than 50 nm, otherwise the gas permeability would be too low. However, the electrical conductivity of the set-up is too low to avoid charge-up during depth-profiling by DC sputtering techniques. Plasma-based Secondary Neutral Mass Spectrometry (SNMS) has been found well suited to analyze such multilayers, provided a high frequency module is employed. The latter periodically applies with 500 kHz a negative potential and ground potential to the sample. In the first half cycle, bombarding ions are accelerated towards the sample, while electrons are allowed to compensate an upcoming charge-up during the other half cycle. In this way, a depth resolution of Δz/z = 0.1 (e.g. 10 nm at a depth of 100 nm) was obtained. Multilayer structures of the types CuO/Al₂O₃/SnO₂/SiO₂/Si-substrate and SiO₂/WO₃/SiO₂/Si-substrate were analyzed concerning the thickness, the stochiometry, and the purity of the layers as well as the thermal stability of the interfaces to optimize the gas-selective membrane layers. Intermediate annealing after each deposition step turned out to be a prerequisite to avoid interdiffusion as a consequence of the ca. 300°C operating temperature of such metal oxide gas sensors.
2:50 PM		F3-5 In Situ Analysis of the Nucleation and Initial Growth of Multi-Component Oxide Films Using Mass Spectroscopy of Recoiled Ions J. Im, A.M. Dhote, A.R. Krauss, O. Auciello, D.M. Gruen (Argonne National Laboratory); R. Ramesh (University of Maryland); R.P.H. Chang (Northwestern University); J.A. Schultz (Ionwerks); E. Irene (University of North Carolina) Thin oxide films such as YBa₂Cu₃O_7-x (YBCO), SrBi₂Ta₂O₉ (SBT) and ZrO₂ can be fabricated via physical vapor-deposition methods in a background of ambient oxygen, typically at a pressure of 5x10-4 Torr or greater, which prevents the use of most surface analytical methods during film growth. We have developed Mass spectroscopy of Recoiled Ions (MSRI) as a means of determining the elemental composition and structure of the uppermost 2-3 atomic layers under the ambient oxygen background required for the growth of single and multicomponent thin oxide films. By comparing the time evolution of the signals corresponding to the substrate and film during growth, it is possible to determine whether growth occurs via the Frank van der Merwe or Volmer-Weber process. In general, it is found that for relatively refractory materials such as ZrO₂, initial growth occurs via the Volmer-Weber process. For films which contain a relatively volatile component such as YBCO and SBT, 2-dimensional growth occurs at room temperature, but, at the temperatures required for crystallization, oxygen is necessary to stabilize the volatile film components, and growth occurs via the Volmer-Weber mechanism. The local density of electronic states at the surface gives rise in general to a "fingerprint analysis" which can be used to determine the chemical phase of a growing film. This method is used to study the effect of substrate temperature and oxygen partial pressure on the surface composition and chemical phase of these oxides. *Work supported by the US Dept. of Energy, Office of Basic Energy Sciences under contract W-31-109-ENG-38, and by the Office of Naval Research under contract 852E1.
3:10 PM		F3-6 Break
3:30 PM		F3-7 Growth of C60 Films on Metal Surfaces S. Rusponi, E. Giudice (CSFBT-CNR and INFM, Genova, Italy); C. Boragno (Universita di Genova, Italy); U. Valbusa (CSFBT-CNR and INFM, Genova, Italy); E. Magnano (Laboratorio TASC-INFM, Trieste, Italy) C60 thin films grown on metal substrates have attracted great interest in the past as they show peculiar electronic and chemical properties. In this study, we present recent results on the growth of C60 films on Ag(001),Ag(110) and Cu(110) obtained by a variable temperature UHV-STM . At low temperature, the C60 molecules nucleate on terraces, forming hexagonal islands. Increasing T, the nucleation takes place preferentially at descending steps and in a second time large islands are created. After high temperature annealing, peculiar quasi-periodic structures are observed, in which some molecules appear brighten than the surrounding ones. This effect is not due to a surface reconstruction, but to the large charge transfer from the metal surface. Second layer islands show a different arrangement. The STM results will be related with recent observations obtained at the synchrotron radiation facility ELETTRA (Italy) on the same systems.
3:50 PM		F3-8 FIB Machined Sub-Micron Thickness Cantilevers for the Study of Thin Film Properties M. Becker, J. McCarthy, D. Atteridge, Z. Pei (Oregon Graduate Institute of Science and Technology) When a thin film is deposited on a cantilever, residual stresses due to thermal expansion and lattice parameter mismatches lead to deflection of the beam. This response has been used as the basis for measuring residual stress, and the product of biaxial modulus and expansion coefficient differential. Typical application restricted to thick substrates has the advantage of yielding information independent of substrate properties, but has two disadvantages. One is that it does not yield values for modulus and expansion coefficient separately. The second is that for film-substrate combinations of interest, the deflection of the beam may be small, limiting the accuracy of the results. For substrates of known properties, varying finite ratios of thicknesses permits measuring both modulus and expansion coefficient. Thinner ubstrates can provide increased deflection and improved accuracy. Micron and sub-micron cantilevers have been fabricated at OGI from thin single crystal Si machined using a focused ion beam milling workstation. Si cantilevers had essentially zero deflection prior to film deposition. Micron thick Al films were deposited on a number of cantilevers. Beam lengths were in the range of 15 to 20 microns. Film/substrate thickness ratios varied from smaller than one to equal to more than double. Deflections were measured as functions of distance along the lengths of the beams. It has been demonstrated that micro-cantilevers can be made with reproducible geometries and comparable film and substrate thicknesses, so as to produce deflections suitable for accurate measurement and independent determination of separate physical properties.
4:30 PM		F3-10 Electrodeposition of Ni-P-SiC Composites in Replacement of Chromium Six Valance (Cr⁺) Coating J. Zahavi, A. Bodnevas, O. Berkh (Israel Institute of Metals, Technion, Israel) The nature and quantity of the organic compounds significantly influend not only the adsorption potential of the SiC particles and their incorporation rate, but also the nickel-phosphorus electrocrystallization and electrodeposition mechanism. It was found, that the most appropriate additives for Ni-P composite coatings are nitrogenous organic compounds, which weakly inhibit the cathodic process and their influence is mainly determined by their interaction with the particles. In this respect, the best suited additives are amino compounds containing Si atoms in their molecules (I.e. silane). Anion active additive, saccharin unlike these additives is non-stimulator and in fact inhibitis SiC particles codeposition. The different action is the result of loose adsorption of these molecules on the SiC surface and their brightening effect, which decreases the particle capture in Ni-P deposit.
4:50 PM		F3-11 Electrical and Microwave Characterization of Kanthal Thin Films: Temperature and Size Effect K.S. Bhat, S.K. Datta, C. Suresh (Ministry of Defence (DRDO), India) Thin films of kanthal were deposited onto clean glass plates and ceramic substrates by flash evaporation in a vacuum of 3X10^-5 torr. The in-situ resistance of as-grown films measured at various temperatures revealed that these films were stable at high temperatures and had negligible temperature coefficient of resistance. The thickness dependence of conductivity was also measured and it was observed that it obeyed Fuch-Sondheimer theory of electrical conduction of metallic films. The surface resistivity of these films was estimated from the ac conductivity measurements carried out using an LCR meter. One of the important applications of kanthal films is as a microwave absorber in Coupled-Cavity Traveling-Wave Tubes. To characterize these films for their microwave absorption behavior Kanthal films of various thicknesses were coated onto the walls of a Ku-Band cavity and the transmission loss of the cavity was measured at 17 GHz. The skin depth of the film (which is different from that of bulk material) has been estimated in the light of the measured values of the dc and ac conductivities of the films and a theoretical explanation for the observed thickness dependence of microwave loss has been presented.