ICMCTF2006 Session F1: In Situ Characterization

Tuesday, May 2, 2006 8:30 AM in Room Royal Palm 1-3

Tuesday Morning

Start	Invited?	Item
8:30 AM	Invited	F1-1 Controlling Residual Stresses in Thin Films C.V. Thompson (M.I.T.) The performance of thin films in most applications is affected by residual stresses that develop during deposition. This is especially true in microelectromechanical systems, for which continuous and patterned films are released by etching of underlying layers to create beams and membranes that can be actuated for mechanical functions. Residual stress gradients can cause beam curling, compressive stresses can cause beam or membrane buckling, and tensile stresses can lead to poorly controlled beam or membrane stiffness. The residual stress in metallic films can range from highly compressive (-1GPa) to highly tensile (+1GPa), depending on the technique and conditions of deposition. Experiments involving in situ stress measurements made during film deposition as well as during interruptions of deposition have revealed a rich phenomenology that, when coupled with structural analyses, has led to greatly improved insights into the origins of residual stresses. Tensile stresses are primarily associated with coalescence processes and compressive stresses are thought to be associated with non-equilibrium surface structures that develop during deposition. Both mechanisms can be controlled through the use of growth interruptions and/or control of the deposition temperature and rate.
9:10 AM		F1-3 Raman Mappings of Vanadium-Alloyed Al_1-xCr_xN Coatings: A New Kind of Thin Film Analysis R. Kaindl, B. Sartory, R. Tessadri (University of Innsbruck, Austria); R. Franz, C. Mitterer (University of Leoben, Austria) Ternary Al_1-xCr_xN hard coatings show significantly increased hardness, wear and oxidation resistance compared to simple binary coatings like TiN or CrN. They are applied to e.g. metal cutting and forming tools at the industrial scale. A further improvement of friction properties is obtained by alloying Al_1-xCr_xN with V, which forms V₂O₅ layers at high-temperatures acting as solid lubricant. The tribological properties of hard coatings are strongly influenced by their structure and chemistry, i.e. phase composition, size and orientation of individual crystallites as well as oxidation and diffusion. Micro-Raman spectroscopy in general is limited to non-destructive analysis of lattice, size, defects, impurities and orientation of the respective crystallites of hard coatings at the µm scale. Combining the spectrometer with a piezo-autofocus, a heating stage and a motorized, computer-controlled X-Y stage enables coating analyses at room and elevated temperatures up to several hundred °C in three dimensions. Newly grown phases and structural changes of coating and substrate within wear tracks produced by tribological ball-on-disk tests were identified. Electron microprobe X-ray distribution images combined with Raman mappings confirmed the presence of the iron oxides maghemite and hematite in the tracks. Colour coded Raman maps allowed unambiguously identification of coating and underlying substrate. High-temperature mapping at 700°C showed partly removed coating on silicon-wafer substrates due to stress and/or recrystallisation. Oxidations of Al-Cr-V-N coatings to V₂O₅ and AlVO₄ around 650°C were monitored "in situ". In conclusions, Raman mappings are a powerful tool for the analysis of advanced hard coatings in the process of their development.
9:30 AM		F1-4 Spinodal Decomposition of Ti_1-xAl_xN: Experiments and Modeling P.H. Mayrhofer (RWTH Aachen University, Germany); H. Clemens (Montanuniversität Leoben, Germany); H. Eckerlebe (GKSS Research Center Geesthacht, Germany); J. Sjölén (SECO Tools AB, Germany); F.D. Fischer (Montanuniversität Leoben, Austria); H. Böhm (Vienna University of Technology, Austria); D. Music, J.M. Schneider (RWTH Aachen University, Germany); C. Mitterer (University of Leoben, Austria); L. Hultman (Linkoping University, Sweden) Recently we have reported, that metastable NaCl-structured (c) Ti_1-xAl_xN exhibits spinodal decomposition during annealing before phase transformation into the stable constituents c-TiN and wurtzite-structured (w) AlN. Here, we present results for the details of the decomposition process using a combination of experimental (small-angle neutron scattering (SANS), TEM, XRD, DSC, and nanoindentation) and theoretical (ab initio, thermodynamic and kinetic) methods. During annealing of c-Ti_1-xAl_xN at 900 °C for 1.5 h coherent ~ 3-nm-sized c-AlN and c-TiN precipitates are formed initiated by fully coherent Al-rich and Ti-rich domains. These intermediate metastable phases act as additional obstacles for dislocation movement, which is consistent with the hardness increase observed during annealing. As soon as the equilibrium phases are obtained and the precipitates coarsen, the film hardness decreases. Thus, age hardening and tempering is demonstrated for a ceramic thin film system. The calculated temperature-composition phase diagram shows a huge spinodal miscibility gap. At ~ 900 °C the chemical driving force for the decomposition of c-Ti_0.34Al_0.66N into c-AlN and c-TiN is ~ 7.83 kJ/mol (1.46 kJ/cm³). Continuum mechanical investigations show that the average value of stored elastic strain energy for the decomposition is ~ 0.24 kJ/cm³ (as c-AlN and c-TiN have different specific volumes and elastic constants). The coherent surface energy contribution related to 3-nm-sized precipitates is ~ 0.10 kJ/cm³. Thus, the overall driving force of the decomposition is reduced to ~ 1.12 kJ/cm³. The theoretical results are in excellent agreement to the corresponding exothermic reactions of ~ 0.99 kJ/cm³, as detected by DSC. These ingredients allow developing a simple kinetic model for the decomposition process of c-Ti_1-xAl_xN.
9:50 AM		F1-5 Glass Forming Ability and Crystallization of Co_1-xC_x Sputtered Films A. Aouni (FSTT Tanger, Maroc/LSGS EMN, France); E. Bauer-Grosse (LSGS EMN, France) In this work, the cobalt-carbon system was explored in a wide range x of carbon content (0.07 3C and δ-Co₂C interstitial carbides, permitting a complete crystallization up to x = 0.33 and only a partial crystallization due to the presence of amorphous carbon beyond this value.
10:10 AM		F1-7 Spectroscopic Ellipsometry of Films on Rough Surfaces T.E. Tiwald (J. A. Woollam Co., Inc.); R.E. Lakis (Los Alamos National Laboratory); B. Johs (J. A. Woollam Co., Inc.) On optically specular surfaces, In Situ Spectroscopic Ellipsometry is known to provide highly detailed, accurate and repeatable information about film thickness, growth rates, refractive index and other properties. We demonstrate that Spectroscopic Ellipsometry can quantify film thickness on rough, diffusely-scattering surfaces that are generally considered non-ideal for ellipsometric measurements. It is also relatively insensitive to changes in substrate height and incident angle that accompany moving substrates, which means it can be used for real-time monitoring of web coaters and other industrial-scale coating processes. Three film-rough-surface combinations were studied: silicon nitride on large-grained poly-crystalline silicon, oil films on latex paint, and sputtered SiO₂ on nickel surfaces machined to 13 different standard finishes (such as 2L, 8G, 32BL, 125P, 125M, etc.). Reference films were simultaneously deposited on single-crystal silicon substrates located adjacent to the rough surface samples. Film thickness on rough surfaces were obtained by fitting ellipsometric Delta data only, using a simple single-film-substrate model and the film refractive index values determined from the reference data. (Delta data are more sensitive to the film thickness-index product and less sensitive to substrate and interface properties.) Using this method, film thicknesses from rough-surfaces linearly correlate to the reference thicknesses, with 0.9 ≤ R² ≤ 0.99, with the more specular surfaces producing the best results. With the exception of Si₃N₄ on polysilicon, it was difficult to reliably extract the film refractive index from the rough surface data. These difficulties are related to the sensitivity of ellipsometric Psi to variations in substrate and interface optical properties.
10:30 AM		F1-8 Observations of Electroforming and Dielectric Breakdown in Thin Films of Cadmium Arsenide M. Din (University Technology MARA, Malaysia); R.D. Gould (Keele University, United Kingdom) Cadmium arsenide(Cd₃As₂) is one of the group of II-V semiconductors which posseses a high electron mobility µ_n of up to 1.0 - 1.5 m²V^-1s^-1. Potential applications include magnetoresistors, thermal detectors and photodetectors. Cd₃As₂ thin films may be prepared by thermal evaporation, but require further electrical characterisation over a range of deposition conditions. In previous work¹ it was observed that at high electric fields carrier excitation via the Schottky and Poole-Frenkel effects occurred, followed by destructive electroforming and breakdown effects at an electric field F_b of up to 5 x 10⁷ V m^-1. In the present work these effects are more fully explored. Films were deposited at rates of about 0.5 nm s^-1and with thickness in the range 0.2 - 1.2 µm onto substrates maintained at 293 K using planar Ag electrodes. Some samples were prepared with Al or Au electrodes and substrate temperatures of up to 393 K. At a specific voltage there was a catastrophic decrease in the current from typically several hundred to a few mA. The corresponding field was found to depend on the film thickness, and followed a relation of the form F_b = Ad^-b, where d is the film thickness and A and b are constants. For films with Ag electrodes deposited under the standard conditions a calculated value of b = 0.83 was obtained. Similar behaviour was identified previously in films with wider bandgaps. After the breakdown events the samples showed voltage-controlled differential negative resistivity (VCNR) in their current-voltage characteristics, with a peak current of several mA at an operating voltage of a few volts, characteristic of an electroforming process. It has previously been suggested that this type of process may result in the growth of nanowires within the semiconductor. ¹ M. Din and R.D. Gould, Thin Solid Films 340 (1999) 28-32.
10:50 AM		F1-9 Residual Stress Evolution in Magnetron Sputtered TiNi Films O.S. Kirakosyan, G.E. Ayvazyan, A.H. Vardanyan (Engineering Academy of Armenia) Development of residual stress is an intrinsic phenomenon in thin film deposition experiments, and strongly influences the mechanical properties and stability of thin films. TiNi films on silicon substrate produced by the magnetron sputtering technique were used to study the relationship between the most relevant deposition parameters and/or annealing conditions and the residual stress level. Mechanical stresses in TiNi films were evaluated from the measured curvature change using the Stoney equation. In situ wafer curvature was measured between room temperature and 530°C using a laser interferometer with an external thermo-chamber. It was found that the properties of TiNi films could be linked to the residual stress magnitude, which in turn was strongly affected by the deposition process parameters, such as film composition, deposition temperature and working gas pressure. During annealing of as-deposited films, stress evolution is related to residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation. The stress relaxation and generation behavior was significantly affected by Ti/Ni ratios, annealing temperatures and durations. It should be emphasized that independent from the deposition parameters and annealing conditions after the chemical removal of TiNi films, the silicon substrates return to the initial non deformed state. This result shows the elastic nature of their curvature.
11:10 AM		F1-10 Fabrication, Phase Transformation, and Surface Characterization of the NiPAlCu Gradient Coating F.-B. Wu, K.-T. Liu, C.-H. Lin, J.G. Duh (National Tsing Hua University, Taiwan) Multicomponent Ni-P-Al-Cu alloy coating with gradient elemental distribution was deposited by dual gun sputtering technique with novel target design. The elemental gradient distribution in the alloy coating was achieved by sputtering control on the composite target, which was made by an electroplated Ni-P thick film on Cu disc. Elemental distribution was analyzed by the Auger electron spectrum (AES) depth profiling. The Cu content decreased with the increase of Ni and P elements from coating surface. The gradient distribution of Ni, P, and Cu elements was revealed, showing a successful NiP/Cu target design and a useful sputtering strategy. Through X-ray phase identification, the coating showed an amorphous/nanocrystalline feature in the as deposited state. A good thermal stability was revealed for the gradient Ni-P-Al-Cu coating since no significant phase transformation phenomenon was observed under annealing up to 500°C. A smooth surface morphology with roughness around 1 nano was found for the alloy coating. In addition, the immersion corrosion behavior of the gradient Ni-P-Al-Cu coating was intensively discussed by the in-situ electro-chemical atomic force microscopy (ECAFM).