ICMCTF2004 Session E3/F1-2: Mechanical Properties and Adhesion

Monday, April 19, 2004 1:30 PM in Room California

Monday Afternoon

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1:30 PM E3/F1-2-1 The Dawning of the Advanced Applications Era of Nanomechanical Testing
Oden Warren (Hysitron)
The nanoindentation technique is rapidly gaining acceptance in the broad scientific community for reasons related more to solving challenging technological problems and better characterizing new classes of materials than to deepening the understanding of the nanoindentation process itself. Consequently, the driving force behind associated instrumentation development will inevitably shift from offering the best list of innate system specifications to providing the most comprehensive solution for a specific application. As a case in point, the methodology of combinatorial or high-throughput materials science holds great promise for revolutionizing the timeframe to new materials discovery. This methodology, however, presents a not-before-seen set of challenges ranging from vast quantities of unique but related samples, to the requirement of guaranteed data integrity across many generations of property screening, to the demand for measurement at highest possible speed without a debilitating loss of accuracy. Providing a proper solution for this set of challenges requires adoption of combinatorial principles by the nanoindentation field. This presentation focuses on nanoindentation as a nanomechanical property screening tool for combinatorially-prepared materials in thin-film format on wafer substrates. Specific topics for discussion include basic requirements for compatibility between nanoindentation and combinatorial materials science; the interplay of film thickness, surface roughness, dominant mode of plastic deformation, probe geometry, and nanoindentation control algorithm for soft metals on hard substrates; and microstructure-property correlations for spreads of ternary alloys possessing austenitic, shape-memory, and superelastic compositions at room temperature.
2:10 PM E3/F1-24 Thin Film Stress Measurement by Optical Fibre Displacement Sensor
S. Chowdhury, M.T. Laugier (University of Limerick, Ireland)
Stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film-substrate system. The stress measurement instrument was tested for two different kinds of thin films, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrate deposited by RF magnetron sputtering. Residual stress was found compressive (-0.83 GPa to -0.44 GPa) for CN films and tensile (121 MPa) for Cu films. Stress developed in CN thin films deposited at substrate temperatures in the range 50-550°C was also examined and it was found that stress in CN films decreased from 0.83 GPa to 0.44 GPa with the increase of substrate temperature.
2:30 PM E3/F1-2-5 Hinge Optimisation in a Micro-rotating Structure for Stress Measurement in Integrated Circuit Interconnects
S.J. Bull, J.M.M. dos Santos, A.B. Horsfall, S.M. Soare, N.G. Wright, A.G. O'Neill, A. Oila (University of Newcastle, United Kingdom); A.J. Walton (University of Edinburgh, United Kingdom)
The process-induced stress in interconnects within integrated circuits has a direct influence on their reliability and thus on the mean time to failure of the devices. To satisfy the requirements of a fast developing microelectronics industry, there is a demand for interconnect track widths to decrease and the number of levels of metallisation to increase. This requires researchers to deliver high quality, stress free metallisation since stressmigration can result in voids, open circuits, and hillocks resulting in shorts between adjacent interconnect stripes. Since measurement of stress in individual metallised lines is not possible by existing techniques another approach has been adopted where a test structure is generated during fabrication based on a micro-rotating cantilever sensor. The two fixed beams are connected off-centre to the opposite sides of the central rotating beam, using hinges of 90 degree angle. Thus, the displacement of the fixed beams due to the released residual stress leads to the deflection of the rotating beam. To support the design finite element modelling has been performed. After processing, the sensor rotation was measured from light micrographs. By comparing the rotation predicted by finite element simulation and that observed experimentally, a clear discrepancy is observed which is critically dependent on the details of the sensor design and the pattern transfer of the lithographic process. To obtain more accurate results, a new degree of complexity for the finite element modelling must be implemented. Realistic geometry must be considered, together with the inclusion of good materials data (elasticity, plasticity, and creep which can be obtained by nanoindentation testing). The paper will present details of different sensor geometries (i.e., new hinge designs) used to optimise sensor sensitivity. More complex structures show a lower plastic deformation in the hinge region and enhanced rotation.
2:50 PM E3/F1-2-6 Numerical and Experimental Analyses on the Contact Stresses Developed during Single and Successive Indentations of Coated Systems
E.A. Perez R, R.M. Souza (University of Sao Paulo, Brazil)
The indentation test is a practical and widely used method for the characterization of the mechanical behavior of materials, during which complex stress and strain fields are developed. In this work, experimental and finite element method (FEM) analyses were conducted to study the effects of the amount of substrate plastic deformation on the contact stresses developed during single and successive spherical indentations of a system with AA6061 aluminum substrate and a chromium nitride (CrN) film. A series of indentations was conducted on the specimen, varying the normal load and the diameter of the sphere. FEM analyses provided values such as the height of indentation pile-up and the radial stresses developed along the film surface. In both cases, FEM values could be associated with experimental results, by direct measurement of pile-up and by the amount of circular cracks that propagated during single indentations, respectively. The results indicated that pile-up height plays an important role on the stresses responsible for the propagation of indentation circular cracks. However, a direct correlation between the amount of substrate plastic deformation and pile-up height was not possible. The numerical and experimental analyses of successive indentations provided further insights on the propagation of circular cracks and its relation with the stress fields and the height of pile-ups.
3:10 PM E3/F1-2-7 Effect of Various Microfabrication Processes on Surface Roughness Parameters and Nanotribology of Silicon Surfaces
S. Chandrasekaran, S. Sundararajan (Iowa State University)

Surface roughness parameters affect the real contact area and hence the tribology in micro/nano systems1. Few studies have addressed the interplay between surface roughness and tribological behavior of processed surfaces using prevalent microfabrication processes2. In this study, the effect of several popular etching processes in silicon micromaching on the nanotribological properties of the resulting surfaces of Si(100) are investigated. The etchants studied are KOH solution (6M, 8M and 10 M at 80°C), and TMAH (25% aqueous at 90°C). Deep reactive ion etching (DRIE) is also employed for comparison. Etching rates are evaluated using a profilometer. Quantitative surface roughness parameters (RMS, peak-to-valley, skewness, kurtosis and autocorrelation distance) are measured using an atomic force microscope as a function of scan size for the various fabrication processes. Micro/nanoscale friction and wear experiments are also performed using an AFM and a reciprocating tribometer. Based on the results these experiments, guidelines for fabricating surfaces with optimum friction/wear are proposed. @paragraph 1B. Bhushan, Modern Tribology Handbook, Vol. 1, CRC Press, New York, 2000.

2 S. Sundararajan and B. Bhushan, Static Friction Force and Surface Roughness Studies of Surface Micromachined Electrostatic Micromotors Using an Atomic Force/Friction Force Microscope, Journal of Vacuum Science and Technology A vol. 19 (2001), pp. 1777-1785.

3:30 PM E3/F1-2-8 Enhancement of Micro/nano Tribological Characteristics by Topographically Roughened Thin Fluorocarbon Films
E.S. Yoon, H.J. Oh, H.G. Han, H. Kong (Korea Institute of Science and Technology, South Korea)
Micro/nano tribological characteristics of thin fluorocarbon films were experimentally evaluated in the work. Polytetrafluoroethylene (PTFE) modified polyethylene, low molecular weight PTFE and polyethylene were used as coating materials. These films were deposited on Si-wafer (100) by ion beam assisted deposition (IBAD) method. The coating parameters of IBAD method were controlled in order to change the bond strength of the coated films. Ar ion beam sputtering was performed to change the surface topography of films using a hollow cathode ion gun under different Ar ion dose conditions in a vacuum chamber. The chemical composition and bond structure of the coated surfaces were analyzed with X-ray Photoelectron Spectroscope (XPS). The water contact angle of the films was measured with a sessile-drop contact anglemeter. Also the micro- and nano-tribological characteristics of the coated films were evaluated with a micro-tribometer and an atomic force microscope (AFM). The durability of the films was also evaluated with a macro tribotester. Results showed that the fluorocarbon films converted the Si-wafer surface to be hydrophobic. The durability, the water contact angles and surface roughness of coated surfaces increased with the coating thickness. Among the test specimens, low molecular weight PTFE film showed the best performance in terms of the durability and micro/nano tribological characteristics. The surface roughening of the film increase by Ar sputtering resulted in the decrease of nano adhesion and friction. Therefore, it was found that the micro/nano tribological characteristics of surfaces were much enhanced by the synergistic effect of both thin fluorocarbon film coating and the surface roughening. These results were discussed in terms of the capillary force according to the change of surface topography.
3:50 PM E3/F1-2-9 Molecular Dynamics Simulation of Subsurface Deformation Due to Sliding Friction in Al-si Alloys
V.M. Stoilov, A. Alpas (University of Windsor, Canada)
Plastic deformation and damage accumulation below the contact surface are the two important aspects of sliding wear of ductile materials. In this study, a molecular dynamics simulation technique was used to predict the sliding friction induced plastic deformation state of the material below the contact surface of an Al-Si alloy. The modeled system was restricted to 2D single crystal Al matrix containing spherical inclusions represented by the Si particles. The modified embedded atom model (MEAM) potential was used in performed molecular-dynamic simulation. It was shown that the intrinsic deformation behavior of the subsurface layer arises from the continuous nucleation of dislocations and their glide motion through the crystal. Results illustrate that that inclusion size plays very important role in determining the tribological properties of the material. It was shown that the presence of inclusion boundaries actually stops the migration of dislocations and therefore the hardness of material increases with reduction of the dimensions of the inclusion until a certain critical inclusion size. Below that threshold mechanism of propagation of the dislocations is unaffected by the presence of the inclusion. Therefore further decrease in the size of the inclusions leads to softening of the material.
4:10 PM E3/F1-2-10 Effect of Deposition Method on the Development of Residual Stress in PVD TiCN Coatings on Cemented Carbide Inserts*
D. Bhat (University of Arkansas); O.B. Cavin, T.R. Watkins (Oak Ridge National Laboratory); M.H. Staia (Universidad Central de Venezuela); S.J. Bull (University of Newcastle, United Kingdom)

Hard, wear-resistant coatings of transition-metal carbides, nitrides and carbonitrides are routinely used to enhance the machining performance and life of cutting tools. The increased hardness and wear-resistance of the coatings, deposited by physical vapor deposition (PVD) methods, is attributed in part to the fine structure and development of compressive residual stresses in the films. The compressive stress is thought to be responsible for discouraging microcracking and failure of sharp edges of the cutting tool. However, a high compressive stress may also promote unexpected delamination of the coating during machining. In this paper, we present the room-temperature residual stress measurement data on PVD TiCN coatings on cemented carbide, deposited using various techniques, such as unbalanced magnetron sputtering, arc ion plating, conventional and filtered cathodic arc processes. Prior studies1,2 of the microhardness and tribological behavior of these coatings showed a strong dependence on the C/C+N ratio. The present results show a wide variation in the compressive residual stress in the coatings, which is consistent with the known characteristics of the deposition methods. These results are discussed in the context of the coating methods and composition, and correlated with the previous data on hardness and tribological performance.

1 Bull, S.J., Bhat, D.G. and Staia, M.H., Surface and Coatings Technol., 163-164 (2003) 499 paragraph 22Bull, S.J., Bhat, D.G. and Staia, M.H., Surface and Coatings Technol., 163-164 (2003) 507 *The residual stress analysis: Research sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract number DE-AC05-00OR22725.

4:30 PM E3/F1-2-11 Composition and Characteristics of Ta-Al Resistance Material by Magnetron Cosputtering
P.J. Su, C.K. Chung (National Chung Kung University, Taiwan, R.O.C.)
This paper presents the composition and characteristics of the cosputtered Ta-Al alloy heater material, which has been used as the resistance layer of the ink jet printhead or micro -thermal actuator. Three Ta-Al films were sputtered by increasing the Al power from 1 kW to 4 kW, and the Ta power was fixed at 2.68 kW. The composition of Ta-Al films are characterized by grazing incident angle X-ray diffractometer (GIAXRD) and Rutherford backscattering spectrometry (RBS), and the hardness of the film is measured by nanoindenter. The composition of Al in Ta-Al alloy increases non-linearly with increasing the Al power, while the hardness of the film decreases with increasing the Al power. The hardness reduction is due to increasing of the Al composition. The composition of the three films is Ta, Al, Ta2Al, which may be the mixture of these compounds. When the Al power is 2 kW, the film is identified to be TaAl compound, which is more stable than other films, while there are mixed phases in other films. Resistivity of the Ta-Al was measured by the four-point probe. The better resistivity of heater in inkjet application is generally larger than 150µΩ-cm. The Ta-Al film for the 2 kW Al power has very suitable resistivity about 164µΩ-cm for the resistance heater film. After post thermal treatment, the hardness of the film can be enhanced. This will be good for the anti-cavitation ability of the inkjet heater material.
4:50 PM E3/F1-2-12 Computation of Young's Modulus and Residual Stress of Hard Surface Coatings on Elasto-plastic Substrates through Indentation Experiments, Finite Element (FE) Simulations and Inverse Modeling Technique.
B.S. Anantha Ram, J. Danckert, T.G. Faurholdt (Aalborg University, Denmark)
This paper presents the idea of a new way of identifying the residual stress (compressive in nature) and the Young's modulus of a hard coating like TiN (Titanium Nitride) on elasto-plastic substrates like HSS (High Speed Steel). The method involves low load micro-indentation experiments, axi-symmetric Finite Element (FE) simulation of the same and inverse modeling technique. The basic idea of inverse modeling is to combine the experiments and the FE-simulations through an optimization scheme, so as to identify the optimum design parameters/variables which minimize the error between the experimental data and the FE-data. In this case the design parameters/variables represent the residual stress and the Young's modulus of the coating. The experimental data and the FE-data are the profiles obtained under a selected critical load by Atomic Force Microscope (AFM) scanning. The FE-simulation involves a coupled thermal and structural analysis. The thermal part creates a equi-biaxial-residual stress in the coating and the structural part only involves the mechanical loading. The paper only presents the idea, i.e., the numerical part and the experimental data is presently assumed as synthetic data. One of the objectives of this study is to collaborate with interested researchers/company who could contribute in developing the experimental data and to extend the idea into reality. If it could be done, the new way of identifying the key parameters, viz., the residual stress and the Young's modulus of the coating with one single experiment can be determined much faster and can be implemented in quality control routines.
Time Period MoA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2004 Schedule