ICMCTF1998 Session FP: F - Posters

Tuesday, April 28, 1998 5:00 PM in Room Atlas Foyer

Tuesday Posters

Time Period TuP Sessions | Topic F Sessions | Time Periods | Topics | ICMCTF1998 Schedule

FP-1 Characterizing and Modeling the Apparent Anomalous Behavior of Resistivity in Cr-Si-O Thin Films
A.F. Jankowski (University of California - Lawrence Livermore National Laboratory)

The Cr-Si-O material system is of interest for use as a thin film resistor. Films are magnetron sputtered onto conducting substrates from metal-oxide compacts using an argon-oxygen working gas mixture. Film compositions that range from 50 to 100 vol.% SiO2 are determined from elemental measurements of Cr, Si and O using Rutherford backscattering. A broad range of resistivities from 101 to 1014 Ohm-cm is found as measured through the 3000Å film thickness. An apparent anomalous behavior is found for the variation of resistivity with elemental Cr, Si and O composition. The anomaly can be interpreted as a discontinuous variation of resistivity for film compositions above 80 vol.% SiO2. The film microstructure is characterized using electron microscopy as a distribution of conducting metal-silicide particles within an insulating matrix. The variation of conductivity with volume percent metal for metal particle - insulator systems can be modelled in terms of an "effective medium" theory. This theory is now used to predictively model the Cr-Si-O resistivity behavior.

This work was performed under the auspices of the United States Department of Energy by Lawrence Livermore National Laboratory under contract #W-7405-Eng-48.

FP-2 Comparative RBS-XRD Studies of Post-implantation Rate on Epitaxial Ge Films Grown on Si Wafer.
V. Richter (Technion-Israel Institute of Technology, Israel)

The post-implantation damage was produced by energetic 100 KeV Ar+ ions at different doses in Ge epitaxial layer grown on Si wafer.

This damage was independently assessed by RBS/channeling and X-ray diffraction (XDR) methods, and an analytical relation between two methods was derived.

It was shown by XRD that an amorphization of the damaged epitaxial layer is reached at much higher irradiation dose than it was estimated trough RBS/channeling measurements.

FP-3 Microstructural Analysis on Plasma Treated Steels using Positron Annihilation Lifetime (PAL) Technique
H.S. Kim, Y.K. Kim, M.-J. Lee, H.Y. Song, D.C. Choi, K.H. Lee (Institute for Advanced Engineering, Korea)
Microstructural analysis has been extensively studied by conventional electron, ion and X-ray techniques for last decades. Recently PAL technique has been used as a powerful tool in defect studies since it is extremely sensitive to the low conce
FP-4 Ambient Dependent Electrical Properties of Bi2 (Te 0.4 Se 0.6)3 Thin Films
V.D. Das, S. Selvaraj (Indian Institute of Technology, India)
Bismuth telluride based chalcogenide materials have been exploited for the development of thermoelectric devices, like refrigerators, small scale power generators etc. In this paper we present the oxygen adsorption studies and the effect of annealing in vacuum on the electrical resi stance of Bi2 (Te0.4 Se0.6 ) 3 thin films. Thin films of Bi2 (Te 0.4 Se 0.6) 3 alloy were prepared onto glass plates held at room temperature in a vacuum of 2 x 10 -5 torr by the flash evaporation technique. It was observed that as air is admitted into the vacuum chamber after cessation of deposition of films, electrical resistance of the films starts to increase rapidly. This is ascribed to the oxygen adsorption on the films. Also it was observed that oxygen adsorption is more in the low thickness films than in the high thickness films. Electrical resistance measurement in vacuum on as-grown films in the temperature range of 300 K - 480 K indicated that resistance of the film during the cooling cycle is lower than that in the heating cycle. This is explained to be dur to the removal of frozen-in defects and desorption of oxygen from the film during the heating cycle. So, to improve the electrical conductivity of the films, the films were annealed at 480 K for a period of one hour. Resistance measurements on these annealed films indicated that resistance during the cooling cycle is higher than the heating cycle. Whereas electrical resistance measurment in the temperature range 300 K - 460 K on the films annealed at 460 K indicated no such behavior. This is explained to be due to the partial evaporatoin of Te from the film as evidenced from the Electron Dispersive Analysis of X-Rays (EDAX). So it is better to anneal these films at lower temperatures for longer time. The films were also structurally characterized using X-Ray Diffraction (XRD) and Selected Area Diffraction (SAD) techniques.
FP-5 Structural Studies of ITO Thin Films With the Rietveld Method
M. Quaas, C. Eggs, H. Wulff (University of Greifswald, Germany)
In recent years grazing incidence x-ray diffraction (GIXRD) has been established as suited method for non destructive investigation of thin films. Many authors use this technique to get chemical and physical information. But there is obviously a lack of crystallographic information, as atomic coordinates, bond lengths, bond angles and occupation number.The application of the Rietveld method to GIXRD patterns increases appreciably information about the crystallographic structure of the films. The aim of this paper is to study structural changes due to tin insertion in tin doped In2O3 (ITO) films. ITO films are of interest due to their good electrical conductivity and high transmittance in the visible region. In2O3 crystallizes in a cubic rare earth oxide structure (Ia3) with two different In sites. Each In(1) is sixfold coordinated by oxygen atoms forming a regular octahedron. Each In(2) is surrounded by a distorted oxygen octahedron with three different distances. The ratio In(1) : In(2) is 1:3. ITO films of about 100 nm were deposited on glass substrates by e-beam evaporation from In2O3/SnO2 pellets with doping concentrations up to 12%. The films were annealed at 450° C for 1h in air and measured by GIXRD. Using Rietveld refinement the lattice constants, bond lengths and occupation numbers were determined. Small tin amounts lead to decreasing lattice constants and also In(1)-In(2) bond lengths. The In(1)-O bond length increases and the distortion of the asymmetric In(2) octahedron becomes stronger. At larger doping concentrations both lattice constants and In(1)-In(2) lengths increase. The In(1)-O bond lengths and the distortion of the In(2) octahedron first decrease, but with further tin insertion an increase of these parameters is observed.The calculated microstrains from xray line profile analysis correspond with the distortion behaviour of the indium octahedrons. Two different insertion mechanisms are discussed.
FP-6 Modeling of a Piezoelectric Film
N.F.J. van Rensburg (University of Pretoria, South Africa); S. Schroeder, H.J. Viljoen, R. Dillon (University of Nebraska-Lincoln)

A mathematical model is presented for a thin piezoelectric film sputtered onto a substrate. The film is modeled as a network of springs and nodes and the substrate determines the boundary conditions at the interface. Springnode models (SNM) have been used to model local phenomena, like stress concentrations at crack tips, stress intensity factors and dynamic crack growth. However, the spring layout of existing models have restricted their application to isotropic materials with specific ratios of Lame constants. One feature of SNM which is particularly attractive, is the ease with which the model can inclue the effect of existing cracks on the stress distribution and the formation of new cracks, albeit in a qualitative sense.

In this work the model is generalized to describe not only general isotropic materials, but also anisotropic ones. The spring constants are selected so that a Taylor expanision of the equations match the constitutive equations of the continuum description and the model can now be employed to study piezoelectric materials. In this work the response of a ZnO film to mechanical perturbations is modeled. These results are compared with a film that has a distribution of fine cracks.

In the latter case, the waves are scattered and the cracks also act as focusing points for the potential distribution. These models provide insightful information on the aging effects as well as the performance of piezoelectrics under loading that could lead to local cracking.

FP-7 On the Energy Influx to the Substrates During Sputter Deposition of Thin Metal Films
H. Kersten (University of Greifswald, Germany); G.M.W. Kroesen (Technical University of Eindhoven, the Netherlands); R. Hippler (University of Greifswald, Germany)

The thermal conditions at the substrate surface influence essentially the elementary processes (adsorption, diffusion, desorption) as well as the structure and composition of the surface layers during deposition of thin metal and metal-oxide films. Besides an external heating or cooling, respectively, the energy balance of a substrate is determined by the plasma process itself.

The integral energy influx during sputtering mainly consits of the kinetic energy of charge carriers and sputtered particles, and the released condensation heath. By variation of the substrate potential the contribution of ions and electrons could be separated. The electron density was measeured by Langmuir-probes and self-excited electron resonance spectroscopy. The contribution of the electrons has been calculated for different energy distributions, too. The influence of the ions as well as of the sputtered particles on the energy balance was studied by energy-resolved mass spectrometry. The contributions of both components could be distinguished by variation of the potentials and the distance between target and substrate.

The measured intergral energy influx which has been determined from the raise of the surface temperature at the sputtering process is in good accordance with the proposed model.

FP-8 Reverse Engineering of Multi-layered Hard Coatings Using Sputter Depth Profiling and Scanning Auger Spectroscopy
R.L. Moore (Evans East)
A protocol for the analysis of hard coatings of unknown composition using ion-sputtered depth profiling and Auger spectroscopy is presented. Through the use of rapid depth profiling, elemental line scans and high spatial resolution survey analysis complete characterization of multi-layered systems is possible. By monitoring a major surface component and a substrate tag the profiling routine is optimized for expediency. Line scans, elemental mapping and point surveys are subsequently used to identify layer components. Individual layer thickness is calculated by applying the correct sputter rate for each layer identified in the line profile. When the actual sputter rate is unknown profilometry is implemented to determine crater depth and the respective layer thickness approximated using simple mathematics. Other analytical procedures that utilize ball cratering and low-angle taper sectioning to expose buried layers and interfaces are discussed.
FP-9 Raman Microscopy Study of Pulsed Laser Ablation Deposited Silicon Carbide Films
F. Neri (University of Messina - Istituto Nazionale per la Fisica della Materia, ITALY); S. Trusso, C. Vasi (Consiglio Nazionale delle Ricerche, Italy); F. Barreca (University of Messina, Italy); P. Valisa (I.S.A. Italia s.r.l., Italy)
Silicon carbide films have been deposited by pulsed laser ablation of SiC targets. A Nd:YAG laser beam was focused onto the target surface with a typical irradiated area of 1 mm2. The duration of the laser pulse was 8 ns and the energy was adjustable in the range 50-100 mJ. The deposition takes place in a high vacuum chamber with a residual pressure of 1x10-7 mbar. Films were deposited on both c-Si and 7059 Corning glass substrates. The samples microstructure was studied by means of SEM imaging and spatially resolved Raman spectroscopy. Raman spectra were acquired by a Dilor LabRam equipment with a spectral resolution of 1 cm-1 and a laser focalization spot diameter of about 0.7 μm. Some inhomogeneities, on an otherwise structureless sample surface, were evident in the SEM images. Their regular and almost circular shape suggests they arise from particulate material generated by the ablation process. A detailed Raman imaging study was carried out over a properly selected area (30x30 μm) including some inhomogeneous spots. Analysis of the spectral features relative to phonon modes revealed a variety of structural configurations. In particular, in the homogeneous region, the amorphous phases of silicon carbide, graphitic carbon and silicon were identified. On the other hand the inhomogeneous spots contained predominantly microcrystalline phases of both silicon and graphitic and tethrahedral carbon species. Micro-Raman spectroscopy provided an excellent tool, in giving local structural informations, by selectively probing a microscopic scattering volume.
FP-10 Electrical Conduction Studies on (Bi0.5Sb0.5)2Te3 Thin Films
V. Damodara Das, P. Gopal Ganesan (Indian Institute of Technology, Madras, India)

The semiconducting alloys of bismuth antimony tellurid are the best materials currently available for thermoelectric applications near room temperature. Increasing interest in thin film thermoelectrtic devices stimulates the study on (Bi 1-x Sb x) 2 Te 3 alloy thin films. In this paper the electrical conduction studies on (Bi 0.5 Sb 0.5 ) 2 Te 3 alloy films are presented. These films have been prepared by the flash evaporation method on clean glass plates in a vacuum of 1 x 10 -5 torr. The thickness of the films was monitored by a quartz crystal thickness monitor. The rate of deposition was also controlled to 10 a+- 1 ao A. As using the quartz crystal thickness monitor. Electrical resistance measurement was carried out in a vacuum of 1 x 10 -5 torr.

The structural analysis, which was carried out by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques revealed that all the films were polycrystalline with hexagonal structure. The compositional analysis was carried out by Energy Dispersive Analysis by X-rays (EDAX). From, the resistance vs temperature plots for as-grown and annealed films of thickness 1000 ao A, it is observed that resistance variation during the heating cycle of the as-grown film is entirely different from that in the cooling cycle. But the resistance variation in the heating and cooling cycles of the annealed films is the same. This indicates that during heating of the as-grown films most of the frozen in non-equilibrium defects are annealed out. The plots of in (σ) vs 1000/T for the films of two different thicknesses are near-linear which indicates that these films are semiconducting. The activation energy of the films is calculated to be 55 meV and 50 meV for the films of thickness 1000 ao A and 2000 ao A respectively. It is also found that the resistivity of the films is dependent on the film thickness and the thicker film has a low resistivity value while the thinner film has a high resistivity value. This variation of resistivity with thickness is due to the classical size effect.

FP-11 Study on Chromium Oxide Synthesized by Unbalanced Magnetron Sputtering
D.Y. Wang, C.H. Lin, C.-C. Chang (National Chung Hsing University, Taiwan, ROC); W.Y. Ho, J. Chang (Surftech Corp., Taiwan, ROC)
Due to the superior heat resistance and high temperature hardness, alumina thin films were applied as the protective coating for cutting inserts and other heavy machining tools. However, the conventional CVD process can not satisfy the increasing demands for coatings on substrates of lower tempering temperatures and on high precision tools requiring tight dimension control. In this study, fully densified aluminum oxide thin films were deposited reactively on high-speed steel substrates by unbalanced magnetron sputtering (UBM) technique. Due to the high ion current density attributed to the UBM design, high rate deposition of alumina thin films was achieved. The target poisoning due to the reactive process was effectively eliminated by using a pulsed power supply, which operated between 0-40 kHz. The phase formation of alumina was found a function of deposition temperature, ion current density, and the substrate bias. The interfacial analysis and tribological properties were studied with XRD, TEM, scratch, and pin-on-disk tribo-testers.
FP-12 UHV Apparatus for Very Low Energy Ion Beam Deposition of Thin Films and In Situ Surface and Thin Film Analysis
T. Sikola, J. Spousta, J. Zlamal, F. Lopour, S. Prusa, R. Kalousek, J. Jiruse, M. Triskala, P. Tichopadek, P. Babor, R. Roucka, S. Voborny (Technical University of Brno, Czech Republic); A. Nebojsa (Masaryk University Brno, Czech Republic); B. Lencova (Academy of Sciences of the Czech Republic)
Direct deposition of thin films by very low energy ion beams has become a useful tool for synthesis of metastable ultra-thin films of unique properties. In our group an UHV apparatus for this novel technique is being developed. Additionally, the UHV conditions will enable us to apply several in situ monitoring techniques in the apparatus and thus to improve a direct control over deposi tion processes and properties of thin films. The apparatus produces focused ion beams of very low (hyperthermal) energies (101 eV) and low energies (102 - 103 eV).The ion beam generated in a simple plasma ion source is mass selected by a Wien filter. The three-stage-differential pumping provided by 3 turbo pumps makes it possible to keep the operational pressure in the deposition chamber in the range of 10-5 Pa. Concerning technologies, the apparatus will be particularly applied for direct ion beam deposition of metal nitrides (ZrN, MoN), Si3N4, diamondlike carbon, carbon nitride and other metastable films (e.g. galium nitride). The in-situ monitoring methods such as low energy ion scattering (LEIS), secondary ion mass spectrometry (SIMS), scanning force and tunnelling microscopy (SF M/STM), and ellipsometry are being developed by the group and will be fully at our disposal in 1998 year. Further, the spectrum of the in situ analytical methods will be completed by XPS and LEED. The monitoring and analytical techniques will be applied as real time feedback for optimising characteristics and properties of the growing films (e.g. chemical composition, structure, morphology, optical properties) and for a study of processes responsible for thin film growth (e.g. nucleation and surface reactions). In the contribution the principles of both direct deposition and in-situ analytical methods, their basic design features and the first results achieved in the development and testing of the apparatus will be discussed in detail.
FP-13 Microstructure Analysis of MoS2 Codeposited with Diamondlike Carbon Films for Wear Improvement
D.Y. Wang, C.L. Chang (National Chung Hsing University, Taiwan, ROC); W.Y. Ho, J. Chang (Surftech Corp., Taiwan, ROC)
A compound lubricating film composed of an MoS2 thin film deposited over DLC interlayer by the unbalanced magnetron (UBM) sputtering technique was investigated for potential usage in severe environments. Compared with typical metal nitrides, DLC showed strong affinity to MoS2 as the supporting hard coating for advanced wear applications. TEM and XRD revealed the amorphous nature of the as-deposited MoS2 lattice structure. Due to the advantage of the abundant ion bombardment during the UBM deposition process, MoS2 showed a dense morphology with a well-bonded interface to DLC. The results demonstrated that the inclusion of a supportive DLC interlayer effectively improved the wear behavior of MoS2under various loading conditions. However, MoS2is very susceptible to hydration and oxidation, which resulting in significantly higher friction coefficients (0.05-0.07) and lower wear life in humid environments. Wear debris and the oxidized transfer layer on both MoS2 and its counterpart caused excessive abrasive wear. The TEM and GDS analysis demonstrated the formation of loose molybdenum oxide whiskers on the surface of MoS2 as a result of atmospheric oxidation. Additional mechanism is required to stabilize the MoS2 for wear applications in humid atmosphere.
FP-14 Effect of Excess PB and O Contents on the Ferroelectric Properties of Sputter Deposited Pb(Zr0.52Ti0.48)O3/Pt System
H.H. Park, D.H. Kim, I.S. Jin (Yonsei University, Korea); T.S. Kim (KIST, Korea)

The electrical properties of ferroelectric devices are mainly depended on the microstructure of ferroelectric film and the interfacial state with electrodes. Concerning with the interface, the formation of depletion region is a dominant cause to degrade the electrical properties. Even though a lot of works have been done on the relationship between depletion region and the electrical property, but there is no clean explanation on the origin of the depletion region. And the suppressing methodology to the formation of depletion region was not given for the amelioration of ferroelectric properties.

In this work, PZT thin film was deposited on the Pt and RuO2 electrode by RF-magnetron sputtering system. For the investigation of excess lead and oxygen role to the formation of depletion region, various PZT targets containing 10, 30, 50, and 100% of excess PbO contents were used. The phase and composition analyses using X-ray diffractometer, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy and interfacial analysis of PZT/Pt and PZT/RuO2 using angle-resolved XPS were performed . From the analyses, we observed that non-perovskite α - PbO2 phase in as-deposited PZT film decomposes and compensates the Pb and O losses at near interface region during the inevitable post-anneal process. And the improvement of fatigue property after post-anneal depending on the excess contents of PbO was observed. From the above results, the degradation of electrical property of ferroelectric film is explained and the optimum preparative condition could be given.

FP-15 A Study on the Structural Distribution Se Passivated GaAs Surfaces
H.H. Park, J.W. Kim, S.H. Sa, M.G. Kang (Yonsei University, Korea)

For the development of compound semiconductor technology, passivation of the surface to stabilize it during the device process is a crucial issue. It has been announced that the improvement of electronic properties of GaAs device is obtained by passivating the surface with chalcogen atoms such as S and Se. However the nature of S or Se passivating the GaAs surfaces was not same and the characterization of the passivated surface structure on an atomic scale was urgently needed.

In this work, we performed the study on the structure of S and/or Se passivated GaAs surfaces using angle resolved X-ray photoelectron spectroscopy (ARXPS), low energy electron diffraction (LEED), and ion scattering spectroscopy (ISS). S and Se passivations of GaAs has been done using (NH4)2Sx, (NH4)2S+Se, and Na2Se/NH4OH solutions, respectively. The passivated GaAs surface structures were estimated with layer attenuation model from ARXPS results by varying the take-off angle. Photoemission studies showed that the surface is terminated with about a monolayer of sulfur and selenium. LEED patterns showed the regular distribution of passivating species on the S and Se terminated surfaces. ISS was used to confirm the distributional model for passivated surfaces. Through the above analyses, acceptable structural models were proposed for S and/or Se treated GaAs surfaces.

FP-16 EPMA of Multilayer Multicomponent Coatings
A.V. Moshnikov, A.I. Rumyantseva (The Polzunov Central Boiler and Turbine Institute, Russia); I.I. Krukov (The Polzunov Central Boiler and Turbine Institute)
The techniques for EPMA of multicomponent multilayer coatings were developed. Software permiting to carry out qualitative and quantitative analysis of layers was compiled. These programs also take into account the existance of long-active fluoresence effect. The software for analysis of high-resistance layers was developed. It permits to take account the effect of charge accumulation in local regions of interaction between electron beam and the sample. Procedure of inversion mathematic convolution for composition analysis of microinclusion at the layer boarder was used.
FP-17 Dielectric Studies in Cellulose Acetate-Polyvinyl Acetate Polymer Blend Films
S.K. Ashok, S. Doddapaneni (S.V. University, India)
The dielectric capacitance and loss behaviour of cellulose acetate (CA), polyvinyl acetate (PVAc) and their blends were studied as a function of temperature (range 300-440 K), frequency (range 10 KHz-10 MHz) and blend ratio. Pure CA and PVAc films showed an increase in capacitance with temperature leading to a peak and then drop with further increase in temperature. This has been explained on the basis of facilitation of orientation of dipoles present in the polymer. In blend films the peak temperature shifted towards lower temperatures with increasing blend composition showing plasticization effect. Tan? Vs 1/T plots showed two loss peaks at low and high temperatures. The high temperature peak (? peak) was attributed to the rotation of the polar units due to segmental motion while the low temperature peak (β peak) was assigned to the orientation of polar groups themselves. There was a slight shift in the position of the loss peaks due to blending which has been attributed to plasticization effect which enhances the molecular interaction between constituent polymers.
Time Period TuP Sessions | Topic F Sessions | Time Periods | Topics | ICMCTF1998 Schedule