Nondestructive and In-Situ Characterization
Thursday, May 3, 2001 1:30 PM in Room San Diego
F2-1-1 Modern Infrared Spectroscopic Methods for the Analysis of the Molecular Structure of Surfaces and Thin Films
Jens Degenhardt, A.J. McQuillan (University of Otago, New Zealand)
Infrared Spectroscopy has for many years been used to investigate molecular structures and, with the introduction of Fourier Transform IR (FTIR) spectroscopy, has become a well established, non-destructive and rapid method of analysis. Recently developed variants of FTIR have made the method also suitable for the analysis of surfaces and thin films. @paragraph@Two methods that have attracted particular attention in the field of surface infrared spectroscopy are Attenuated Total Reflection (ATR) and Specular Reflection (SR) spectroscopy. Both are very well suited for ex situ as well as in situ spectroscopic characterization of thin films. Due to its small and reproducible penetration depth, ATR is particularly useful for in situ measurements in strongly IR absorbing media while SR spectroscopy has high sensitivity to the orientation of molecules at surfaces.@paragraph@In this paper, applications of these two IR spectroscopic methods will be discussed. For ATR spectroscopy this will include the investigation of a model of a stainless steel surface, research on solar cell development and photocorrosion. Examples of the application of SR spectroscopy will be given in regard to the analysis of DLC, CN@sub x@ and metal oxide layers, and in the elucidation of reaction mechanisms at the metal/solvent interface.
F2-1-3 Characterization of Elastic Properties of Hard Coatings Using the Brillouin Light Scattering Technique
T. Wittkowski, J. Jorzick, K. Jung, B. Hillebrands (Universität Kaiserslautern und Schwerpunkt Materialwissenschaften, Germany)
A survey of the determination of elastical and morphological properties with the Brillouin light scattering (BLS) technique is given, illustrated with results of investigations on amorphous carbon and boron nitride films. The main point of the study is the detection of Rayleigh-like surface modes in 180° backscattering geometry. The dispersion of the phase velocity of these modes for film thicknesses smaller than the phonon wavelength (0.3 - 1 µm) bears in general sufficient information to deduce several independent components of the elastic tensor. Characteristic quantities to describe the properties of hard coatings are deduced. The BLS technique provides precise insight in the elastic behavior of the film material such as the variation of the stiffness with increasing film thickness, elastic anisotropy or the appearance of a layered substructure. This often is evidence for a material texture or for the occurence of a phase transition. In the case of graphite-like material the elastic anisotropy is caused by the single crystal anisotropy in a strongly textured nanocrystalline material. In cubic boron nitride films a correlation between the linewidth of the Rayleigh mode and the grain size near the film surface is observed. The damping is due to the internal boundaries, hence the morphology near the surface can be inferred from the linewidth. Work supported by the Deutsche Forschungsgemeinschaft. .
F2-1-4 Superhard Films and Opaque Superhard Materials by Surface Brillouin Scattering
M.H Manghnani, X Zhang, P.V. Zinin (University of Hawaii)
Surface Brillouin scattering (SBS) measures the frequency shifts of the laser light inelastically scattered by thermally induced acoustic phonons in materials or thin films. SBS can probe the acoustic phonons with frequencies up to 200 GHZ and with wavelengths in the submicron range. In this report, recent results for various thin films by the technique are summarized. 1). Silicon nitride films are of particular interest because of their great potential in advanced microchips and SAW device applications. Films on GaAs and on silicon are researched. A pseudo-interfacial mode is identified in this system. The measured velocities of this interfacial wave is smaller than theoretical predictions, indicating that the mode has a valuable potential in the interface characterizations. For films on Silicon substrate, the acoustic behavior and elastic properties of two films with different density are investigated. True surface waves, i.e. the Rayleigh and the Sezawa waves, were observed; pseudo-Sezawa and guided longitudinal pseudo- waves were also observed. The results show that the density of film has a large effect on the elastic properties of the film. 2). The elastic properties of the Silicon Oxynitride films are determined by observing longitudinal and shear horizontal guided surface waves. The obtained values show that he elastic properties of the films are inferior to the silicon nitride films. 3). Cubic boron nitride (cBN) is the one of the hardest materials next to diamond. The dispersion relations of two cBN films with thicknesses of 55 and 200 nm are investigated by SBS technique. Best-fit SBS data give a shear modulus for cBN film, which is 36% of bulk polycrystalline cBN values. 4). Diamond films have great potential in many industrial applications. Elastic properties of diamond films obtained by the heteroepitxial growth are investigated. The obtained elastic constants are comparable to those of natural diamond. @paragraph@ Here, we also report the first successful measurements by SBS the elastic properties of small specimens of amorphous carbon obtained from C60 under high pressure (13 - 13.5 GPa ) and high temperature (800-900 oC). Simultaneous measurements of the Rayleigh and lateral longitudinal wave velocities make it possible to determine shear and bulk elastic moduli of the specimens. Deduced elastic properties of amorphous carbon synthesized under pressure 13.5 GPa and temperature 900oC are close to those for diamond, indicating that bonds in amorphous carbon network are dominated by diamond-like bonding.
F2-1-5 Characterization of Thin Films by Light Scattering Ellipsometry
T.A. Germer, M.J. Fasolka (National Institute of Standards and Technology)
Angle-resolved light scattering has, in the past, proven to be an efficient, sensitive, and non-invasive method for measuring roughness of single material interfaces, when they are sufficiently smooth. The results of first-order perturbation theory relate the angle-resolved scattering function to the power spectral density (PSD) of the surface height function. Information contained in the polarization of the scattered light extends the method to measurement of roughness of two interfaces of a dielectric film. While traditional specular ellipsometry provides sufficient information to determine film thickness, extending ellipsometry to the scattering regime allows one to determine the PSD function of each interface and the cross-PSD function between the interfaces. In this talk, the method and theory of scattering ellipsometry will be described, examples will be given, and limitations will be discussed. The examples will include conforming, non-conforming, and anti-conforming films, conditions which can be found amongst silicon dioxide and polymer films on rough silicon. These examples illustrate how the degree of conformity between two interfaces depends upon the spatial frequency of the roughness and can reflect the underlying mechanisms of roughness propagation. For anti-conformal interfaces, first-order perturbation theory has difficulty describing the results, but qualitative information can still be inferred. .
F2-1-6 Surface Melting on Nanoparticles and Some Implications to Growth
K. Peters (European Synchrotron Radiation Facility, France and Northwestern University); P. Steadman (European Synchrotron Radiation Facility, France); J.D. Almer (Linkoping University, Sweden and Advanced Photon Source); M. Oden, J. Birch (Linkoping University, Sweden); Y.-W. Chung, J.B. Cohen (Northwestern University)
Dear Dr. Peters: You requested a copy of your abstract for review. When I went to do that for you I realized that I did not have a copy. I received the title information from Dr. Grant via Jens Birch. Could you please supply me with one or two paragraph of your invited talk. Thank you, Mary Gray ICMCTF Conference Administrator
F2-1-8 Characterization of Nitride Films Grown by Surface-Reconstruction-Induced Epitaxy
M.R. Sardela Jr (University of Illinois at Urbana); M. Jenkins, R. Hanfoug, M.-A. Hasan (C.C. Cameron Applied Research Center & University of North Carolina at Charlotte)
AlN is a wide-band gap material used in alloying with GaN compounds for band gap engineering of optoelectronic devices or used as a seed layer for the growth of nitrides on sapphire substrates. The growth of epitaxial group-III nitrides directly on Si substrates is very attractive since it offers the advantages of the established Si microelectronics technology. However epitaxial growth in this case is difficult due to the large lattice mismatch and the formation of amorphous Si nitride at the Si/AlN interface. This work investigates structural properties of AlN films grown on Si substrates by molecular beam epitaxy using atomic N flux from RF plasma source fitted with dual ionization chambers. AlN epitaxy was possible after changing the Si surface reconstruction by the deposition of 0.3 ML of Al on the surface. In-situ surface electron diffraction, electron microscopy and a combination of different x-ray diffraction methods confirmed the formation of single crystalline AlN. Film texture, strain and mosaic distribution were determined as function of growth parameters. Two-dimensional mapping of the x-ray scattering distributions were used to determine in-plane and out-of-plane lattice parameters of the films and the crystallographic orientation of the film relative to Si. Strain and mosaicity were shown to be strong function of the growth temperature (T@sub s@ ). Films with negligible strain and low mosaic distribution were obtained at T@sub s@ ~ 700 @super o@C and no evidence of crystallographic tilt relative to the substrate was observed. The ratio of hexagonal to cubic AlN phases was also quantified in the films as a function of Al/N flux ratio and growth temperature.
F2-1-9 An Analysis of the TiN PCVD Process Based on OES Measurements
S. Peter, H. Giegengack, F. Richter (Technische Universität Chemnitz, Germany); R. Tabersky, U. König (Widia-Valenite, Germany)
Optical emission spectroscopy measurements were performed for better understanding and control of the PCVD process used in the coating production of Widia/Valenite. First of all, film deposition experiments on cemented carbides and in-situ OES measurements were made with successively modified process parameters. Thereby we investigated the influence of the titanium chloride flow, the nitrogen flow, the mean discharge current, the pressure and the pulse repetition frequency. The coatings were characterized with respect to the deposition rate, composition, crystallographic structure and microhardness. In particular, the dependence on process parameters of emission signals (lines/bands) from 12 species (Ti, Ti@super +@, Cl, Cl@super +@, H@sub 2@, H, N@sub 2@, N@sub 2@@super +@, N, N@super +@, Ar and Ar@super +@) involved into the TiN deposition process was analyzed. Interesting insights into the PCVD system were received from additional time (over the period of the pulsed DC) and space (between the cathode and the negative glow) resolved OES measurements. Especially the mostly different behavior of the emission intensities from atomic and ionized titanium led us to new knowledge of the decisive plasmachemical reactions.
F2-1-10 Thin-Film Elastic Property Measurements Using Laser-Ultrasonic SAW Spectrometry
D.C. Hurley, V.K. Tewary (National Institute of Standards and Technology); A.J. Richards (CSIRO Telecommunications and Industrial Physics, Australia)
We have developed noncontact methods to evaluate the elastic properties of thin films using laser ultrasonics. Our technique is based on the optical generation and detection of surface acoustic waves (SAWs) over a broad frequency range - from approximately 10 MHz to over 200 MHz. The SAWs are generated using a line-focused, 200-ps pulsed laser and detected by a Michelson interferometer with a nominal bandwidth of 800 MHz. The SAW phase velocity is determined by measuring the wave displacement over a range of propagation distances. Since the phase velocity depends on the SAW frequency in thin-film systems, the phase velocity spectrum (dispersion relation) provides information about the system's mechanical properties. Quantitative elastic-property information is obtained by comparing the data to analytical models for wave propagation in layered anisotropic systems. We will present dispersion relations for a variety of specimens to illustrate our techniques, including a series of Si wafers with TiN films 0.2-1.3 micrometers thick and containing residual stress. Results for the samples' elastic properties obtained with our analysis will also be presented, and such effects as film anisotropy and residual stress will be discussed.
F2-1-11 Quality Control of Ultra-Thin and Super-Hard Coatings by Laser-Acoustics
D. Schneider (Fraunhofer Institute for Material and Beam Technology IWS Dresden, Germany); T. Schuelke (Fraunhofer USA - Center for Surface and Laser Processing); D. Schultrich (Fraunhofer Institute for Material and Beam Technology IWS Dresden, Germany)
Non-destructive testing of hard-coatings is highly desirable. The available test methods are permanently confronted with manifold new demands of the surface engineering arising from reducing film thickness, more complicated film composition and extreme mechanical requirements as high hardness, stiffness and adhesion. The laser-acoustic technique based on surface acoustic waves is a relatively new surface test method, but its capability for testing thin and hard coatings has already been demonstrated. The laser-acoustic method yields the Young’s modulus revealing the effect of varying bonding structure of the material, porosity and other micro-defects, including insufficient adhesion. Efforts have been done to adapt the method to the requirements of testing ultra-thin and multi-layer films. The special methodical aspects of testing these films are discussed, such as the effect of measuring accuracy, bandwidth and sample dimension. For nano-meter thick films, the theoretical assumption of a homogenous film hardly applies. The gradient interlayer and the non-complete micro-structural development in the process region at the surface evidently influence the calculated film modulus for the thickness of the carbon films lower than 4 nm. Although the output value for elastic film parameter only represents a averaged effective value for the film thickness put in, it can be used as indirect indicator for the processes taking place at the first stage of the film formation. The results presented illustrate the way the laser-acoustic results can help to optimize the deposition processes. Ultra-thin amorphous carbon films deposited by high current pulsed vacuum arc have been tested. The effects of the substrate temperature during the deposition, the contents of nitrogen and the film thickness were studied. The minimum film thickness was 3 nm. The coherent trend of elastic and plastic deformability, frequently reported for thicker carbon films as correlation of hardness with Young’s modulus, was found for the ultra-thin carbon films too. The plastic behavior was studied by means of measuring the nano-scratch resistance. The effect of nano-meter inter-layers in micro-meter thick multi-layer films made of diamond-like carbon and metal layers is presented. A long-wave theoretical approach is used for describing the anisotropic elastic behavior of such multi-layers.
F2-1-12 Study of Thin Film-Edge Induced Stresses in Silicon Substrate by Infrared Photoelasticity Method
H.J. Peng, S.P. Wong (The Chinese University of Hong Kong, China); S.N Zhao (South China University of Technology, China)
Stresses induced in the substrate by thin film edge are of great practical interest in silicon process technology. There has been extensive theoretical and experimental work to study this problem in recent years. For example, micro-Raman method has been used to study the substrate stress induced by silicide thin film edge though only an average value of the stress within a certain penetration depth can be obtained and not the whole stress field in the substrate. There are also a number of theoretical studies of this problem using finite element method but so far a satisfactory analytical solution of the problem is still lacking. In this work, we shall report the direct observation of the stress field in the silicon substrate induced by an oxide thin film edge using the infrared(IR) photoelasticity(PE) method. Our experimental results showed that the earlier analytical solutions cannot give a satisfactory description of the observed IR PE stress fringe patterns. We also developed a new analytical model for this film edge induced stress with good agreement between the simulated and experimental stress fringe patterns. In addition, the effects of film thickness and substrate thickness on the stress distribution in this structure were also investigated. This work is supported in part by the Research Grants Council of Hong Kong SAR (Ref. No. CUHK 4155/97E).