ICMCTF2008 Session F1-2: Advances in Characterization of Coatings and Thin Films

Monday, April 28, 2008 1:30 PM in Room Royal Palm 4-6

Monday Afternoon

Start	Invited?	Item
1:30 PM		F1-2-1 RF Glow Discharge Plasma Opens New Possibilities for the Characterization of Thin Films P. Hunault, J. Malherbe, P. Chapon (HORIBA Jobin Yvon, France); M. Ganciu (NILPRP, Romania, - LPGP, France); O. Hirsch (HORIBA Jobin Yvon, France) Radio Frequency Glow Discharge Optical Emission Spectrometry (RF GD-OES) is an established technique capable of Ultra Fast Elemental Depth Profiling of thin films down to the nanometer. As the name suggests, RF GD-OES relies on the sputtering of a large area of a material with a Glow Discharge Plasma capacitively coupled to the sample and the subsequent excitation of the sputtered species in the plasma and their analysis with a spectrometer. It is an extremely rapid technique (erosion rate of several microns/minute), that provides elemental depth profile composition of all elements (including H, N, O, and C) and it is applicable to conductive and non-conductive materials. Recent results published on ultra thin films have shown that the depth resolution can be even better than a nanometer. Other research has revealed the minimal surface damage that the GD plasma induces when compared to ion guns. Expertise from plasma deposition together with theoretical and experimental characterizations of the RF GD plasma, are used to propose several new findings and improvements with immediate practical benefits. Three new topics will be presented: a) The new "plasma cleaning" concept applied to GD assures outstanding surface results even on contaminated industrial samples. b) The benefit of the deposition of metallic thin films on polymer coatings will be illustrated. c) Finally, speciation results on chromated coatings will be introduced opening a new area to GD analysis.
1:50 PM	Invited	F1-2-2 Residual Stresses in Thin Films Characterized by High Temperature X-ray Diffraction J. Keckes (University of Leoben, Austria); C. Kirchlechner, K.J. Martinschitz (Austrian Academy of Sciences, Austria) Virtually all types of thin films are expected to contain some amount of residual stress decisively influencing their mechanical behavior and performance. The residual stresses represent very important issue especially in the case of modern electronic packages representing nowadays complicated composites of semiconductors, metals, dielectrics and plastics with specific thermal expansion coefficients, manufacturing temperatures and geometry. The main aim of this contribution is to demonstrate an application of high-temperature XRD to characterize thermo-mechanical behaviour of thin films. At first, basic principles of the approach will be introduced. As a next, an application of XRD to study selected phenomena like size-effects, annealing of intrinsic stresses, plastic flow, annealing of implantation damage, development of stresses in multilayered structures and effects in the substrate will be discussed. Additionally, a new self-consistent diffraction technique allowing for a determination of X-ray elastic constants (XECs) on an absolute scale will be presented. The new method is based on the combination of sin₂psi and curvature techniques. The basic idea resides in the fact to use a monocrystalline substrate with known mechanical properties as an internal standard to determine a relationship between the measured elastic strain and the macroscopic stress. The knowledge of experimental XECs can be used to perform XRD characterization of residual stresses in thin films on an absolute scale. The new approach is demonstrated on a variety of thin film systems measured using laboratory and synchrotron sources (BESSY and Hasylab) at room and at high temperatures. This work was supported by Austrian NANO Initiative within the project "StressDesign - Development of Fundamentals for Residual Stress Design in Coated Surfaces.
2:30 PM		F1-2-4 Advanced Characterisation of Plasma Electrolytic Oxidation Coatings on Aluminium: Effects of Direct Current Density and Electrolyte Concentration on Residual Stresses R.H.U. Khan, A.L. Yerokhin, A. Matthews (University of Sheffield, United Kingdom) Plasma Electrolytic Oxidation (PEO) represents significant interest as an ecologically friendly alternative to acid-based anodising processes for light metals. During PEO, the oxide film formation is influenced by multiple heating-cooling cycles initiated by surface plasma microdischarge events; this affects the coating structure, phase composition and stress state. In this work, effects of current density and KOH electrolyte concentration on structure, phase composition and residual stresses in the oxide coatings produced on aluminium using DC PEO mode are studied. The residual stresses are evaluated by X-ray diffraction using the Sin² method. Nanoindentation studies are conducted to evaluate nanohardness and global Young modulus values for the PEO coatings using a Hysitron triboscope. SEM and TEM techniques are utilised to study surface morphology and nano-scale features of the PEO coatings. Correlations between internal stress and coating thickness, morphology and phase composition are discussed. Regimes of PEO treatment favourable for the production of the coatings with minimal stress level are identified.
2:50 PM		F1-2-5 Residual Stress Depth Profiling in Complex Hard Coating Systems by X-ray Diffraction M. Klaus, Ch. Genzel (Hahn-Meitner-Institut Berlin, Germany); H. Holzschuh (Walter AG, Tübingen, Germany) Cutting tools and many highly stressed technical components are usually coated by CVD- and PVD methods to protect them from abrasive wear and to increase lifetime. To prevent crack propagation, the films are often not uniform but consist of stacks of alternating sublayers with different chemical structure and crystallographic texture. The mechanical properties of the systems are strongly influenced by the material inherent residual stresses (RS). By means of RS engineering beneficial compressive stresses can be generated within the films either during the deposition process itself or by a subsequent mechanical surface treatment like grit blasting. The introduced stresses are not uniform with respect to the coating system but occur in form of steep intralayer or rather long-range interlayer in-plane stress gradients. In the first case compressive and tensile stresses are at least partially balanced within the topmost sublayer, whereas in the second case mechanical equilibrium is developed between various sublayers and the interfacial substrate zone. The presentation is on the evaluation of RS distributions in complex hard coating systems by X-ray diffraction. By the example of cutting tools made of cemented carbide which are CVD coated with multilayer stacks consiting of TiCN and Al₂O₃ sublayers, a new methodical approach is introduced that allows for analyzing the RS distribution even in buried sublayers. Furthermore, accompanying simulations based on the kinematical diffraction theory are shown to be helpful to explain the experimental results and to find out the optimum experimental set-up for special measuring problems.
3:10 PM		F1-2-6 A New Non-Destructive Method of Determining the Modulus of Nanoscale Thin Films J.W. Paggett, J.C. Bilello (MetaGlass Coatings, LLC) Measuring the elastic modulus of nanoscale thin films presents a significant technical challenge. One can compute modulus values from nanohardness data, but this method has its drawbacks for amorphous coatings and is especially difficult when a particular film has a variable surface finish. A unique method of measuring the elastic modulus of amorphous metallic thin films is presented. This procedure is entirely non-destructive and depends on being able to independently determine the stress and the strain in a thin film deposit. The stress in the amorphous film is measured using a laser curvature method applied to a coating on a Si wafer. This well known technique does not depend on the mechanical properties of the film when the film is thin compared to the substrate. The elastic strain in the film is found via grazing angle incidence scattering (GIXS) data. In the GIXS geometry, the scattering vector, Q, is (nearly) within the plane of the film. The strain is calculated from the relative positions of the first nearest neighbor maxima of the sample and a reference standard. Once the stress and strain in the amorphous film have been independently measured, the modulus of the film is found as usual from Hooke’s Law. This procedure has been carried out for a series of amorphous metallic films of various thicknesses and the results compared to the modulus determined from nanoindentation.