Surface and Thin Film Analysis

Tuesday, May 1, 2001 8:30 AM in Room San Diego

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8:30 AM F3-1-1 Profile Reconstruction in Sputter Depth Profiling
S. Hofmann (Max-Planck-Institute for Metals Research, Germany)
Ultra high depth resolution of about 1-2 nm is now frequently achieved in sputter depth profiling of thin layers. However, quantification of measured profiles in terms of atomic monolayer accuracy and better can only be accomplished by applying appropriate methods of deconvolution or profile reconstruction. Usually, reconstruction of the original in depth distribution of composition is performed by convolution of an assumed depth distribution with the correct, experimentally or theoretically determined depth resolution function. The result is compared with the measured profile and the input depth distribution iteratively varied until an optimum fit is obtained. Of the different approaches developed to adequately describe the depth resolution function, the so called mxing-roughness-information depth (MRI)-model has proved its usefulness in many applications including both SIMS and AES @footnote 1@. The MRI model is governed by three fundamental and physically well-defined parameters: atomic mixing length, roughness and information depth. Some application examples are presented for depth profiling of oxide multilayers using AES and SIMS, and for comparison of SIMS and AES in profiling of GaAs/AlAs delta layers and thick layers, where an accuracy of @±@ 0.2 monolayers is obtained. First order non-linear effects like preferential sputtering can be corrected by a composition dependent sputtered depth/sputtering time relation. However, segregation and compound formation effects causing inhomogeneous elemental distribution in the mixing zone are difficult to include and are the main reason for the present limitations. @FootnoteText@ @footnote 1@ S. Hofmann and J. Schubert, Determination and application of the depth resolution function in sputter profiling with SIMS and AES, J. Vac.. Sci. Technol. A 16, 1096 (1998).
9:10 AM F3-1-3 Silicon Diffusion on LiF Films Deposited on Si(100) Induced by Electron Beam
M. Cremona (Pontifícia Universidade Católica do Rio de Janeiro, Brazil); C.A. Achete, P.I. Guimarães (Universidade Federal do Rio de Janeiro, Brazil)
Alkali fluoride films containing color centers are promising systems for applications in new integrated optical devices like waveguides and lasers. Ionizing radiation, usually electron beams, allows the creation of high concentrations of defects forming thin active channels with controlled depth. Recently several investigations were made about the production of lithium fluoride (LiF) active waveguide using low energy electron beam irradiation. @paragraph@In this work, a Scanning Auger Microprobe was used in order to investigate the modifications induced by the electron bombardment on LiF films of different thickness deposited on Si(100) substrates and on LiF single crystals. The current density of the primary electron beam was determined using a Faraday cup. 1 KeV argon-ion sputtering was used only for few seconds in order to produce a carbon-free surface at the very beginning. The Auger spectra suggest that electron bombardment induces alkali metal accumulation and halogen depletion at the surface, in agreement with the results obtained for single crystals[1]. For long time exposition to the electron beam (~20 min.) it is possible to observe the growth of the large crystallites of Li on the films surface. The dimension of this crystallites were determined by ex situ AFM measurements. Moreover depending on the primary energy of the electron beam used and on the thickness of the LiF films, unexpected results revealed from this analysis show a strong diffusion of the silicon from the substrate to the free surface. An explanation for these effects is given in terms of diffusion of the halogen ion with subsequent color center formation and chemical reaction with the Si of the substrate. @paragraph@The results reveal that Li agglomeration and Si diffusion can contribute significantly to the LiF surface alteration and consequently degrade the performance of the waveguide device. @FootnoteText@ @footnote 1@E. Paparazzo, N. Zema, Surf. Sci. 372 (1997) L301-L308
9:30 AM F3-1-4 Study the Resivity of TaxNy Films by Implementing OES in the Magnetron DC Sputtering System
Y.M. Lu (Kung-Sen University of Tecnnology, Taiwan, ROC); R.J. Weng, W.S. Hwang (National Cheng Kung University, Taiwan, ROC); Y.S. Yang (Metal Industries Research and Development Centre, Taiwan, ROC)
Tantalum nitrides have been found to be promising materials for many applications, such as diffusion barriers, wear and corrosion-resistant materials, and precise and stable resistors used in active silicon integrated circuits. In this paper, the effect of the amount of tantalum ions existing in the plasma on the electrical and structural properties of the tantalum nitride films had been studied. The films were deposited on silicon substrates by d.c. magnetron sputtering system. Post heat treatment in the nitrogen atmosphere was employed to increase nitrogen content in the films. The film thickness was measured by an a-step profilometer. The sheet resistance of all samples was detected by four-probe meter, and the XRD pattern was used to analysis the crystal structure of the films. The Results reveal that when OES is set between 53% and 70%, the resistivity variations of tantalum nitride films are small which imply a practical useage for this material . Increasing the OES values, the crystal phases will transit from ß-Ta, Ta2N, and finally to TaN.Post heat treatment in nitrogen atmosphere can effectively increase nitrogen content in the film and induce Ta5N6 phase which lead to increase resivity of the films. Y. M. Lu1, R. J. Weng2, W. S. Hwang2, Y. S. Yang3 1. Department of Electronic Engineering, Kun Shan University of Technology, Tainan, Taiwan 2. Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan 3. Metal Industries Research and Development Centre, Kaohsiung, Taiwan e-mail:
9:50 AM F3-1-5 Influence of Environmental Factors on the Chemical Integrity of Protective Coatings
T.L. Barr, T.H. Dugall (University of Wisconsin-Milwaukee); N. Heimann, R. Heimann (Elisha Technologies)
Recently we have become concerned with the chemical details of the influence of various environmental factors on the character of coatings, including select oxides and nitrides, that are esteemed for their integrity. The environmental influences include those induced both during and following the coating process as a result of exposure to water and/or atmosphere under differing conditions of temperature, pressure and ph. Critical factors in these chemical influences include their depth of field, their involvement with the integrity of the coating species and the temporal behavior. In many cases the environmental effects produce just superficial coatings of the intended coating, merely dulling the aesthetics, but not altering the principal property desired for the coating. In other cases, however, the effects can be damaging or even catastrophic. The first process considered is to view what may by the most prolific chemical reaction on our planet: every surface exposed to Earth's atmosphere at room temperature suffers from some degree of low temperature (Cabrera-Mott) oxidation from O@sub2@. This is a feature detailed by our group in the 1970's, where the mechanism and extent of the process for metals, alloys, and even dielectrics were described. Subsequent studies demonstrated its involvement with biological systems, in fact, it has been shown to occur on essentially all air-exposed surfaces. The present study expands on these arguments and demonstrates their involvement in the processing and integrity of select nitrides, where segregations play an important role affecting both use and longevity. Additional studies are presented in which other common environmental reactions are explored, particularly those that compete directly with the additives intended to form more complex protective coatings, such as silicates. These reactions include aquation and carbonation and are suspected to sometimes aid and sometimes to undermine the integrity of the coating.
10:10 AM F3-1-6 Measuring and Correlating Variations of Hardness, Composition and Microstructure on the Nanometer-Scale
M. Kunert (Max-Planck Institut fuer Metallforschung, Germany); S.P. Baker (Cornell University); B.B. Baretzky, E.J. Mittemeijer (Max-Planck Institut fuer Metallforschung, Germany)
Ion implantation generates a complex microstructure within less than 500 nanometer of the sample surface. Sharp gradients in composition and defect concentration can occur, in addition to the formation of compounds of the implanted species and elements of the original alloy. As a result, pronounced changes of the mechanical properties are induced in the ion implanted region. An understanding of the relations among the ion implantation parameters and the resulting composition and microstructure on the one hand, and the relations among composition, microstructure and properties on the other hand is the key for tayloring near-surface properties of a workpiece by ion implantation. @paragraph@ In this work, the variations of hardness, chemical composition, and microstructure within a carbon implanted region of a Ti-6Al-4V alloy were measured using nanoindentation, Auger electron spectroscopy, and transmission electron spectroscopy, respectively. These variations with depth were, for the first time, correlated with a depth accuracy of about +/- 20 nm. The hardnessdepth profile can quantitatively be explained by means of the formation of an almost continuous TiC layer within the implanted region and precipitation hardening.
10:30 AM F3-1-7 Analysis of Amorphous Boron Carbide Thin Films for Potential Applications as Hard Coatings
D.N. McIlroy, D. Zhang (University of Idaho); G. DeStasio (University of Wisconsin-Madison); D. Bahr (Washington State University)
The stoichiometry and morphology of boron-carbon alloy thin films grown by plasma enhanced chemical vapor deposition can be significantly modified by changing the deposition rate. Using the technique of imaging photoelectron spectromicroscopy we can simultaneously image the surface of the sample while obtaining near edge x-ray absorption fine structure spectra (NEXAFS). Films grown at a rate of 55Ã…/min. are characterized by an amorphous-like matrix with carbon-rich and dome-like inclusions. Films grown at a deposition rate of 330Ã…/min. are found to be much more homogeneous and free of carbon-rich and dome-like inclusions. An excitation at 191.7 eV in the B 1s absorption spectrum has been associated with amorphous growth. The relative intensities of the p* and s* excitations across the C 1s absorption edge of these boron-carbon alloys indicate that carbon bonding is predominantly through sp3 hybridization, while boron bonding is a mix of sp2 and sp3 hybridization. The NEXAFS measurements qualitatively explain the observed increase in hardness of amorphous boron carbide, as measured by nanoindentation, as a function of increased substrate temperature during deposition.
10:50 AM F3-1-8 Junction Properties of Nickel Phthalocyanine Thin Film Devices Utilizing Gold and Indium Electrodes
T.S Shafai, T.D. Anthopoulos (Staffordshire University, United Kingdom)
The DC electrical properties of Gold/Nickel Phthalocyanine/Indium (Au/NiPc/In) thin sandwich film structures have been investigated. The three-layered devices were fabricated utilizing a novel sequential vacuum evaporation technique. At low voltages, current density in the forward direction obeys the diode equation, while for higher voltages conduction is dominated by a SCLC mechanism. In the reverse bias a transition from electrode-limited to bulk limited conduction process has been identified. After prolonged exposure of the sample to dry air, diode characteristics were absent, with current density exhibiting weak polarity dependence. Analysis of experimental data suggests a conduction mechanism dominated by the Poole-Frenkel effect. A strong rectifying effect was apparent after heat treatment of the sample in vacuum for approximately one hour at a temperature of 393 K. Results are interpreted in terms of an oxygen adsorption process at the NiPc/In interface. Calculation of barrier height, rectification ratio, and diode ideality factor for both freshly prepared and heat-treated samples are also reported.
11:10 AM F3-1-9 Phase Changes of CrN Films at High Temperature Under Controlled Atmosphere
H.Y. Chen (National Chung Hsing University, Taiwan, ROC); F.-H. Lu (National Chung Hsing University, Taiwan, R.O.C.)
The CrN films were deposited onto Si substrates by a cathodic arc plasma deposition technique. After that, the films were annealed at temperatures ranging from 300°C to 1000°C for 2 hr in air, N@sub 2@ and N@sub 2@/H@sub 2@=9 atmosphere. XRD results show that the @beta@-Cr@sub 2@N phase appeared at 500°C in all cases. It seems that low nitrogen partial pressures would not enhance the formation of Cr@sub 2@N phase. The Cr@sub 2@O@sub 3@ phase occurred at 700°C meanwhile the @beta@-Cr@sub 2@N phase diminished. CrN was completely transformed into Cr@sub 2@O@sub 3@ at 1000°C both in air and N@sub 2@. Nevertheless, only a small amount of CrN was oxidized in N@sub 2@/H@sub 2@=9 even at 1000°C. The Gibbs free energy changes @DELTA@G for the oxidation of CrN films in these gases were calculated from thermodynamic data. At constant temperature, @DELTA@G(air)<@DELTA@G(N@sub 2@)<<@DELTA@G(N@sub 2@/H@sub 2@=9), which is consistent with our experimental results. The color changes of the films associated with the phase changes were also discussed and analyzed.
11:30 AM F3-1-10 Scratch and Mar Resistance of Paint Coatings and Polymer Films Using the Nanoscratch Technique: Viscoelastic Behavior and Relaxation Effects
R. Consiglio (CSEM Instruments SA, Switzerland)
Viscoelastic response in polymeric materials are highly dependent on both strain rate and temperature. We have studied different polymer coatings and have determined a methodology to quantitatively determine the viscoelastic response of coatings applicable to automotive applications under scratch and mar test conditions. This Nano-Scratch test applied here has proven to be versatile in measuring elastic and plastic deformations, as well as friction and fracture. We show here the influence of strain rate (scratch speed) on elasto-plastic deformations, the effect of time on elastic relaxation and the effects of heating or weathering on the residual deformation. The interest is to give keys which will help in understanding material behavior and improving the mechanical properties of polymer coatings, especially in scratch and mar resistance.
11:50 AM F3-1-11 Effect of Laser Irradiation on I-V Characteristics of Pulse-Electrodeposited Ag/Hg:1212/CdSe Hetero-Nanostructures
S.H. Pawar, D.D. Shivagan, P.M. Shirage, L.A. Ekal, N.V. Desai (Shivaji University, India)
For the realization of most cryoelectronic devices based on the use of superconducting thin films, the development of multilayer deposition techniques will be crucial. The fabrication of layered structures of superconducting and normal metallic, insulating or semiconducting films presents interesting challenges for a wide range of electronic applications. The advantage of high operating temperature brings an increased feasibility of hybrid semiconductor-superconductor devices, circuits and systems. In the present investigation, the pulse electrodeposition technique has been employed for the fabrication of Ag/Hg:1212/CdSe heterostructures. Pulse-potential deposition gives non-porous, fine grained and dense deposit. Pulsating potential with 25 Hz frequency and 50% duty cycle was used and synthesis parameters were individually optimized for deposition of Hg:1212 and CdSe on silver substrate, and for deposition of CdSe on Ag/Hg:1212. The XRD pattern of Ag/Hg:1212/CdSe shows presence of both tetragonal Hg:1212 and hexagonal CdSe structures with standard lattice parameters. The HgBa@sub 2@CaCu@sub 2@O@sub 6+delta@ (Hg:1212) thin film is found to be superconducting below 104 K. By studying FWHM and applying Scherrer’s formula it is found that particle size of CdSe film is 30-50 nm . I-V characteristics is important in determining the built in junction potential and energy discontinuties in the conduction and valance band edge at the interface of the heterojunctions. The photoinduced changes in I-V characteristics of these hetero-nanostructures were studied at room temperature with and without laser irradiations ( HeNe Red laser @lambda@= 632.8 nm, Power 2 mW and photon energy 2.01 eV). Results are attributed to formation of heterojunction and reported.