1998 MRS Fall Meeting & Exhibit

Chairs

Roger Johnson, Pacific Northwest National Lab
Woo Lee, Stevens Inst of Technology
Michael Pickering, Morton Advanced Materials
Brian Sheldon, Brown Univ

Symposium Support 

• Morton Advanced Materials
• Pacific Northwest National Laboratory 
  
  1998 Fall Exhibitor

* Invited paper

SESSION OO1: MULTILAYERED COATINGS 
Chair: Brian W. Sheldon 
Monday Morning, November 30, 1998 
Independence East (S)

8:30 AM *OO1.1 
THERMAL TRANSPORT THROUGH MULTILAYER COATINGS. Daniel Josell , Edurado Gonzalez, Grady White, National Institute of Standards and Technology, Gaithersburg, MD. 

I present measurements and analysis of the thermal transport properties of bimaterial multilayer coatings. Thermal diffusivities (thermal conductivity divided by specific heat per unit volume) at temperatures above 900C are obtained from the results of pulsed-heating experiments. Room temperature thermal diffusivities are determined by mirage-effect experiments. From analysis of the properties of multilayers with different interface densities (i.e. layer thicknesses), the average impact of a single interface on thermal conductivity is determined. Ratios of the thermal diffusivities perpendicular and parallel to the layers, obtained from the mirage-effect experiments, are also presented and analyzed. 

9:00 AM *OO1.2 
COATINGS AND OPTICAL MATERIALS FOR TUNED INFRARED EMITTANCE AND THERMAL CONTROL. Peter Martin , John Johnston and Wendy Bennett, Pacific Northwest National Laboratory, Richland, WA. 

Many thermal control applications require coatings which emit or absorb strongly at near infrared and infrared wavelengths. One of the primary applications for these coatings is thermal control for surfaces and structures of spacecraft, which are exposed to solar radiation during at least 60 of their orbit, causing wide temperature flucuations. Another recent application for this type of coating is infrared emissive imaging employing a fiber optic infrared scene projector. The development of tuned infrared emissivity coatings for these applications will be presented. While single layer coatings can provide high emissivity in a broad wavelength band, multilayer coatings can be used to obtain higher emissivities over a narrow wavelength band. This band can be tuned to a specific range of temperatures and wavelengths. Coatings developed for thermal control have a reflective base layer, either ZrN or a refractory metal boride. These materials have increased durability compared to metal layers. The multilayer coating deposited over the based layer consists of a Al₂O₃/SiO₂ stack with high emittance at 300 K (9.8 m), and solar reflectance near 0.6. Multilayer tuned infrared absorber/emitter coatings are applied to fiber optic infrared scene projectors. The coatings consists of a three layer Si₃N_4/Cr/Si_3N_4absorber tuned at the 1.06m laser wavelength, and a six layer Cr/dielectric/Cr/dielectric/Cr/dielectric coating which emitts strongly in either the 3 - 5m or the 8 - 12m infrared wavelength bands. Absorption bands of the coatings were independently tunable. All coatings are deposited by reactive dc and rf magnetron sputtering onto 2.5 inch fiber optic face plates. Either Si_3N_4

OO 1.3
AND TRANSITION METALS. Hans Hogberg , Lars Norin, Jun Lu, Uppsala University, Dept of Inorganic Chemistry, The ngstr' Laboratory, Uppsala, SWEDEN; Jan Olle Malm, Lund University, National Center of HREM, Dept of Inorganic Chemistry 2, Lund, SWEDEN; Ulf Jansson, Uppsala University, Dept of Inorganic Chemistry, The ngstr' Laboratory, Uppsala, SWEDEN. 

Transition metal carbides have many interesting physical and chemical properties making them excellent candidates for different thin film application. A major problem, however, has been to deposit high-quality epitaxial films of these materials at low substrate temperatures using conventional vapour deposition techniques. We have recently shown that such films can be obtained at very low temperatures in an evaporation process using C₆₀ as carbon source. Polycrystalline VC and TiC films were deposited by co-evporation of C₆₀ and the metal in a UHV system at temperatures as low as 100C.Analyses with LEED, XRD and HREM showed that epitaxial TiC films can be obtained on MgO(100) and 6H-SiC(0001) at 250C, while the deposition of epitaxial VC films seems to require a slightly higher temperature (<300C. Films deposited on MgO(100) exhibited a very good registry with the substrate, while films deposited on 6H-SiC(0001) showed extensive twin formation. Furthermore, by alternating the metal fluxes we have been able to deposit TiC/VC superlattices on MgO(100) at 400C. Such superlattices are likely to exhibit interesting mechanical properties similar to those observed for nitride superlattice structures.Our results also suggest that epitaxial carbide films and superlattice structures can be obtained for a wide variety of carbide-forming metals. 

9:45 AM OO1.4 
THERMAL STABILITY AND MECHANICAL PROPERTIES OF SPUTTER-DEPOSITED Mo/NbN SUPERLATTICES. Anita Madan , Scott A. Barnett, Northwestern University, Department of Materials Science and Engineering, Evanston, IL; Carolina Engstrom, Jens Birch and Lars Hultman, Linköping University, SWEDEN; Michael Nastasti, Los Alamos National Laboratory, NM. 

Mo/NbN superlattices show an enhanced hardness (up to 30 GPa) as compared to the rule-of-mixtures value of 10 GPa. Mo/NbN superlattices were deposited by reactive dual-cathode magnetron sputtering onto MgO(001) substrates at a temperature of 800C. Since Mo and NbN are mutually immiscible, the superlattice may provide good high-temperature stability, which would be useful for various technological applications. The layered structure and mechanical hardness of epitaxial Mo/NbN superlattices with superlattice periods () of 1.4 and 6.5 nm were investigated after annealing in vacuum at 900 -1000C for  1 hr. High- and low-angle x-ray diffraction (XRD), and reciprocal space mapping showed that the layered structure was stable at 1000 C for 1 h. Satellite peak intensities decreased for longer times and decreased to background levels after 3 hrs. XRD for these annealed films showed the formation of an epitaxial, tetragonal, ternary MoNbN-phase for  = 1.4 nm. For the  = 6.5 nm superlattice, there was evidence of coarsening of layers and a polycrystalline MoNbN phase. Nanoindentation hardness of the annealed superlattice films showed no observable change in the hardness. Cross-sectional transmission electron microscopy (XTEM) results for as-deposited and annealed films will be presented. 

SESSION OO2: MECHANICAL PROPERTIES 
Chair: Brian W. Sheldon 
Monday Morning, November 30, 1998 
Independence East (S)

10:30 AM *OO2.1 FAILURE MECHANISMS IN COMPRESSED FILMS AND COATINGS, Tony Evans , Princeton, Materials Institute, Princeton University, Princeton, NJ. 

Compressed films and coatings fail by buckling and spalling. The phenomena are sensitive to imperfections, residual stresses, and interface adhesion. Each of these effects is discussed and interrelated through failure mechanism maps. Imperfections nucleate interfacial separations and cause premature buckling. Buckle propagation is determined by interface toughness, and affected by segregation and roughness. Spalling is determined by mode mixity effects. Maps predicated on the basic mechanisms allow these ideas to be introduced into useful engineering models. 

11:00 AM OO2.2 
LOW STRESS UNDER BUMP METALLIZATIONS FOR DIRECT CHIP ATTACH. T.M. Korhonen , P. Su, S.J. Hong, M.A. Korhonen and C.-Y. Li, Cornell University, Dept. of Materials Science and Engineering, Ithaca, NY. 

In order to use a flip chip method for bonding the Si chip directly to an organic substrate, compatible under bump metallizations (UBM's) must be available. Conventional schemes with a copper-based solderable layer are not well compatible with the high-tin solders (such as eutectic Pb-Sn) used with organic substrates. This is due to the rapid reaction between Sn and Cu which depletes the UBM of copper. Ni-based schemes show slower reaction with the solder and have been identified by the semiconductor industry as preferable replacements to Cu-based UBM's. However, Ni-containing metallurgies are often associated with high stresses, which result in a poor practical adhesion between the silicon chip and the metallization, leading to interfacial failure during fabrication or service. In this research, several nickel-containing UBM schemes are studied experimentally. Stress measurements are made for each metallization before patterning of UBM pads. Flip chip bonded test chips are then fabricated and the practical adhesion between solder/UBM and UBM/Si interfaces is assessed by micro-mechanical tests. The performance of the UBM schemes in shear and fatigue is contrasted to the stresses present in the metallization. 

11:15 AM OO2.3 
DIRECT DETERMINATION OF STRAINS IN AMORPHOUS THIN FILMS. J. Hershberger ^a, Z.U. Rek^b, S.M. Yalisove^a, and J.C. Bilello^a; ^aDepartment of Materials Science & Engineering, University of Michigan, Ann Arbor, MI; ^bStanford Synchrotron Radiation Laboratory, Stanford, CA. 

Two X-ray scattering techniques have been used to determine strains in thin films of sputter deposited amorphous B₄C and SiC. Direct measurements from Grazing Incidence X-ray Scattering (GIXS) provided radial distribution functions. These were used to determine average interatomic spacings and elasticity was used to calculate strain. The results were compared to strains from substrate curvature data obtained using Double Crystal Diffraction Topography (DCDT). The difference may be attributable to an interface stress measured by DCDT but not GIXS. 

11:30 AM OO2.4 
INTRINSIC STRESSES AND INTERNAL INTERFACES IN AMORPHOUS Cu-Ti AND Co-Tb FILMS. U. Geyer , U. von Huelsen, M. Bicker, I. Physikalisches Institut and Sonderforschungsbereich, Universitaet Goettingen, Goettingen, Germany, M. Seibt, IV. Physikalisches Institut and Sonderforschungsbereich, Universitaet Goettingen, Goettingen, GERMANY. 

Amorphous metallic films are usually regarded as frozen-in liquid films with smooth surfaces and free of internal interfaces and macroscopic intrinsic stresses- properties which are advantageous for many applications. In contrast to this, amorphous Cu_xTi_100-x and Co_xTb_100-x films, prepared by physical vapor deposition, develop during growth large intrinsic stresses (0.5-1GPa) over a broad range of compositions. In-situ intrinsic stress measurements show compressive stresses in the early stages of film growth and, with increasing film thickness, a crossover to tensile stresses. The compressive stresses are possibly caused by a positive surface stress. The tensile stresses decrease with increasing reduced substrate temperature, T_S/T_M, of the alloy films. Scanning tunneling microscopy and transmission electron microscopy studies indicate kinetic surface roughening during the film growth (growth exponent ) which finally leads to the formation of a columnar microstructure with a high density of internal interfaces. This formation of growth columns (typical diameter 20nm) coincides with the change from compressive to tensile stress formation. These tensile stresses can be understood in terms of disturbed short range atomic order relations at the column interfaces. With increasing T_S/T_M the column diameters increase, and the analysis of this temperature dependence reveals the activation energy of surface diffusion. During linear temperature ramps (), compressive stresses due to differential thermal expansion of the film/substrate combination and tensile stresses due to annealing out of excess volume in the films are observed. In films with internal interfaces the volume relaxation starts at lower temperatures than in films without internal interfaces, indicating that the interfaces are annihilation sites for the excess volume. 

11:45 AM OO2.5 
THICKNESS EFFECT ON CRACKING PHENOMENA AND MECHANICAL PROPERTIES OF SUBMICRON GLASS THIN FILMS DEPOSITED ON A POLYMER SUBSTRATE. Masa-aki Yanaka , Yutaka Kato, Yusuke Tsukahara, Toppan Printing Co., Ltd., Technical Research Institute, Saitama, JAPAN; Nobuo Takeda, The University of Tokyo, Center for Collaborative Research, Tokyo, JAPAN. 

The multiple cracking phenomena in thin SiOx films deposited on a 12micron-thick polyethylene terephthalate (PET) substrate during the tensile test were investigated. SiOx thin films were deposited on a PET substrate by electron beam vacuum evaporation method. Oxygen content x was about 1.7 measured by X-ray photoelectron spectroscopy. Five kinds of specimens with different SiOx film thicknesses of 43, 67, 90, 120 and 320 nm were prepared. The multiple cracking progress was observed in-situ by optical microscopy and from which the crack density in SiOx films was obtained as a function of the applied strain. With the appropriate estimation of the residual strain in the film, the crack onset strain was nearly proportional to the minus one-half power of the thickness. After the cracking is sufficiently developed, on the other hand, thinner specimens showed higher crack density than thicker ones. The development of the crack density was predicted by both the modified shear lag analysis and the fracture mechanics analysis. Both analyses explained reasonably well the experimental results. The validity of stress states assumed in analyses were also evaluated by comparing with the finite element calculations. In the fracture mechanics analysis, the critical energy release rate G_c for the film cracking was estimated. The best fitting of the theory to the thickness dependence of the crack onset strain was obtained when G_c=14.5 J/m² which seems to be admissible value for the bulk silica glass. 

SESSION OO3: PROPERTIES AND PROCESSING OF PVD COATINGS 
Chair: Roger N. Johnson 
Monday Afternoon, November 30, 1998 
Independence East (S)

1:30 PM *OO3.1 
PROPERTY AND PROCESSING COMPARISON OF OPTICAL COATINGS MADE BY ION ASSISTED EVAPORATION AND MAGNETRON SPUTTERING. Walter T. Pawlewicz , Barr Associates, Inc., Westford, MA. 

Ion Assisted Evaporation and Magnetron Sputtering are the two most important industrial physical-vapor-deposition processes used for optical coatings today. Each has strengths and weaknesses, and each is best for different coating jobs. This paper provides a comprehensive comparison of the two. Starting with introductory sketches and pictures, the two processes are compared point-by-point and graded in scorecard fashion. Included are issues like materials compatibility, deposition rate, thickness uniformity, layer thickness accuracy, amenability to modeling, mechanical stress control, durability, environmental stability, refractive indices, absorption, scatter, scalability (substrate size and shape), equipment, and ease of use and automation. The comparison is illustrated with examples from the author's 24 years of optical coating experience at 3 different companies, with 40+ coating chambers (small and very large), in research, development and production coating environments. 

2:00 PM OO3.2 
PREPARATION, CHARACTERIZATION AND PROPERTIES OF SPUTTERED VANADIUM OXIDE COATINGS. Yeon-Gon Mo , R. O. Dillon, P. G. Snyder, Center for Microelectronic and Optical Materials Research, Dept of Electrical Engineering, University of Nebraska, Lincoln, NE. 

Magnetron reactive sputtering has been shown to allow fabrication of large area, uniform coatings of both metallic and metal oxide materials. A wide variety of technological applications for vanadium oxides have been suggested such as electrical switches, holographic storage media, thermal switches and thermal control devices. The vanadium oxide films were prepared by magnetron dc reactive sputtering as a function of oxygen partial pressure. Optical properties of the films were investigated by ellipsometry and spectroscopy in the visible and infrared wavelength regions. Optical constants, n and k were measured by ellipsometry. The X-ray and infrared spectroscopic data revealed the relation between optical properties and deposition conditions such as the oxygen partial pressure and the substrate temperature. 

2:15 PM OO3.3 
PROCESS WINDOWS AND PROPERTIES OF TUNGSTEN- AND VANADIUM-OXIDES DEPOSITED BY MSIP-PVD-PROCESS. Univ.-Prof. Dr. techn. E. Lugscheider, Univ.-Prof. Dr. techn. O. Knotek, Dipl.-Ing. C. Barimani , Dipl.-Ing. St. Baerwulf, Materials Science Institute, University of Technology, Aachen, RWTH-Aachen, Aachen, GERMANY. 

The tungsten and vanadium oxides are well known to be usable as solid lubricants at elevated temperatures. As a matter of fact metal-oxides are interesting for tribological insets at atmospheric conditions because of their `oxidation.stability'.The presentation is going to report about various investigations made to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive and non-reactive mode by the MSIP-PVD-process. One focus of the study is on the metal oxide-phases generated in the MSIP-process under various conditions and their mechanical and metallographic properties. Therefore the coatings were deposited, developed and analyzed by standard testing methods to characterize the mechanical and structural properties, like SEM, microhardness, scratch testing and pin on disk. 
Further stable process windows will be presented for the reactive mode as well as the influence of different process parameters to the microstructure and the material properties. Especially the influence of process-parameters on the deposition rate (d.c. versus r.f mode, reactive versus non-reactive mode) is of big interest to evaluate the economic relevance.It will be shown, that it is possible to deposit vanadium-oxides despite target contamination effects in wide ranges by adapting the gas-flow. 

2:30 PM OO3.4 
TOOLCOATINGS DEPOSITED BY PVD-PROCESSES FOR THE PROTECTION AGAINST CORROSION AND WEAR OF THE THIXOFORMING-PROCESS. E. Lugscheider, O. Knotek, C. Wolff, S. Baerwulf, Materials Science Institute, University of Technology Aachen, RWTH-Aachen, Aachen, GERMANY. 

The publication is going to report about various PVD-hard material coatings deposited on thixoforming-tools. The focus of the study is on the protection against corrosion and wear occuring in the thixoforming-process of aluminium alloys. 
Especially the extreme corrosive problems caused by the molten and partial congealed phases of the aluminium alloys, which interact with the tool steels have to be reduced by new composite concepts to increase the tool-life. For that purpose AIP-PVD-hard material coatings (arc-ion-plating physical-vapor-deposition) on Ti- and Cr-basis were deposited, developed and analyzed by standard testing methods to characterize the mechanical and structural properties, like SEM, microhardness, scratch testing and pin on disk. Further an adhesion test was established to get a quantitative dimension of the toolcoating adhesion force against the aluminum counterbody. To receive detailed information about the corrosive reactions two methods were used a) a dipping test and b) an annealing test, which characterize the conditions in the thixoforming-process. 
It will be shown, that it is possible to inhibit corrosion effects completly by using previously optimized PVD-coatings on tool-steels. Further a multiple adhesion force reduction of aluminium alloys could be reached by the use of PVD-hard material coatings. 

SESSION OO4: COATINGS FOR HARSH ENVIRONMENTS 
Chair: Roger N. Johnson 
Monday Afternoon, November 30, 1998 
Independence East (S)

3:15 PM *OO4.1 
CORROSION-RESISTANT COATINGS FOR HIGH-TEMPERATURE APPLICATIONS. T. M. Besmann , J.A. Haynes, and K.M. Cooley, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN. 

Efforts to increase the efficiency of energy conversion devices has required their operation at ever high temperatures. This has forced both substitution of lower temperature materials for higher temperature ceramics. Many of those materials will require protection from high temperature corrosion caused by combustion gases and atmospheric contaminants. This paper will explore the development of some examples of such coatings for potential application in fuel combustion and other harsh environments. 
Research sponsored by the U. S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the Advanced Automotive Propulsion Materials Program, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation. 

3:45 PM OO4.2 
THE OXIDATION OF CHROMIA THIN FILMS DEPOSITED VIA COMBUSTION CHEMICAL VAPOR DEPOSITION. A. Alexiou , J. M. Hampikian, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA. 

Chromia thin films were deposited onto alloy substrates by combustion chemical vapor deposition. The substrates chosen for testing were Ni and Ni-20Cr. The chemical precursor utilized to achieve chromia films was chromium nitrate and the depositions took place within the flame at temperatures between 200 and 550C. Amorphous coatings were deposited between 200 and 375C, whereas crystalline coatings were deposited between 400 and 550C. The crystalline chromia, eskolaite, Cr₂O₃, was deposited at a rate of approximately 2 m/hr, whereas the amorphous coating was deposited at a lower rate, approximately 0.4 m/hr. Coatings containing 2 wt yttrium were also formed. The deposition temperature necessary to form crystalline chromia/yttria coatings was slightly higher (50C) than those containing chromia only. The ability of the various coatings to provide oxidation protection was characterized using thermogravimetric analysis (TGA). The chromia crystalline coatings reduce the oxidation behavior of Ni-20Cr by nearly a factor of ten, whereas the amorphous chromia coating does not demonstrate such an improvement. Characterization of the coatings was accomplished using a variety of techniques, including SEM, TEM, EDS, and x-ray diffraction. 

4:00 PM OO4.3 
OXIDATION OF PECVD SIC DEPOSITED FROM TRIMETHYLSILANE. Peter A. DiFonzo , Mona Massuda, Microelectronics Research Laboratory, Columbia MD; James T. Kelliher, Applied Materials, Richmond, VA. 

The stoichiometric composition and the oxidation rates ( wet or dry ) of plasma enhanced chemical vapor deposition (PECVD) of silicon carbide (SiC) films are effected by the deposition conditions of trimethylsilane (3MS) and ambient gas. We report the oxidation kinetics of SiC when deposited by (PECVD) using flows (25-100 sccm) of (3MS) and a constant carrier gas flow of 85 sccm of either argon or nitrogen. Oxidations were conducted in an horizontal Bruce Technologies International BDF-41 atmospheric furnace in the temperature range of 925-1000C in an oxygen(1HCl) environment for dry and 975-1050C by pyrogenic steam for wet. All samples were annealed in pure nitrogen for 20 minutes at 1100C prior to oxidation. Oxidized films were measured optically by an nk Technologies 1200 and mechanically by an Tencor P210 profilometer. Activation energies were calculated by the Arrhenius behavior of the oxidation parameters. Films deposited in an argon ambient revealed a lower oxidation rate ( wet or dry ) than those deposited in an nitrogen ambient. Films deposited in an nitrogen ambient showed unstable oxidation characteristics which is believed to be due to the nitrogen content as measured by X-ray Photoelectron Spectrography (XPS). For dry oxidation, films deposited in an argon ambient have parabolic activation energies of 41 and 57 kcal/mol for 3MS flows of 25 and 50 sccm respectively. Films deposited with 100 sccm in argon have dry parabolic rates of approximatly 17.32  10^3 2/min at 925C, similar to samples deposited with nitrogen except no unstable characteristics were observed. In the case of wet oxidation, films deposited in argon gave parabolic activation energies of 29 and 105 kcal/mol for 3MS flows of 25 and 50 sccm respectively. Similarly, for wet oxidation unstable results were found for films deposited in an nitrogen environment. 

4:15 PM OO4.4 
MULLITE DIFFUSION BARRIERS FOR SiC-C/C COMPOSITES PRODUCED BY PULSED LASER DEPOSITION. H. Fritze , G. Borchardt, Institut für Allgemeine Metallurgie, Clausthal-Zellerfeld, GERMANY; T. Witke, B. Schultrich, Fraunhofer-Institut für Werkstoffphysik und Strahltechnologie, Dresden, GERMANY; C. Rüscher, Institut für Mineralogie, Universität Hannover, Hannover, GERMANY; S. Weber, S. Scherrer, Ecole des Mines de Nancy, Nancy, FRANCE. 

Pulsed Laser Deposition (PLD) allows the ablation of nonconductive and high melting point target materials and the preparation of films with complex composition. High energy impact leads to melting and evaporation of the target material in a single step. In case of mullite ablation, the flux of the metal components is stoichiometric. Under reduced pressure the oxygen content in the layers decreases. However, after a short oxidation treatment, the formation of mullite in the coating is completed, as confirmed by IR spectroscopy and XRD investigations.