Characterization of Thin Film Growth Mechanism and Evolving Film Properties
Thursday, May 3, 2001 8:30 AM in Room San Diego
F5-1-1 Preparation of Extremely Thin Aluminum Oxide and Nitride Films Using a Novel Low Energy Plasma Beam Process
B. Hillebrands, B.F.P. Roos, S.O. Demokritov (Universitaet Kaiserslautern, Germany)
Reaction processes in the preparation of thin insulating barriers for magnetic tunnel junctions are studied. The barriers were prepared by means of a new technique using a highly dissociated low energy (30 eV-80 eV) ionized oxygen/nitrogen atom beam. The reaction depth was determined by the combined in-situ resistivity and optical reflectivity measurements. The depth variates from 1.5 to 2 nm in agreement with performed Monte Carlo simulations. The reaction process is found to be self limiting. Two different reaction mechanisms (diffusive and ion-imbedding) are separated. The electrical and magnetotransport properties of obtained junctions are studied. The values of the barrier parameters are determined.
F5-1-3 Plasma Diagnostics and the Evolution of a TiN Deposition Process
C. Muratore, J.J. Moore (Colorado School of Mines); J.A. Rees (Hiden Analytical Ltd., United Kingdom); D. Carter, G. Roche (Advanced Energy Industries Inc.)
Film deposition processes employing remotely generated plasmas to deliver reactive species to a substrate, such as ion beam assisted deposition (IBAD) or inductively coupled reactive plasma (ICRP) enhanced deposition, are recognized for their ability to increase deposition rates and modify the (micro- and/or lattice) structure of thin film compounds. Manipulation of extrinsic process conditions (e.g., gas flow, source power, etc.) in IBAD and ICRP processes produces measurable changes in intrinsic process conditions such as ion and electron energy distributions and densities. Intrinsic deposition conditions, when correlated to film properties, yield useful information about processing/structure/property relationships. This information continues to change the way we design our deposition processes and equipment. For example, we can measure the reactive ion density and energy distributions of the ICP and ion beam sources. By varying the source gas composition and power conditions it is possible to optimize the number density (for maximum deposition rate) and energy distributions (for desirable film microstructure) of all species present in the chamber. "It is evident from the measurements of intrinsic chamber conditions that the behavior of the reactive sources is such that an optimization of this kind would be difficult to achieve using an "intuitive" approach, in which one makes educated guesses about optimum extrinsic processing conditions, and that plama diagnostics facilitate intelligent process design."
F5-1-4 Structures and Properties of the SiNC Films on Si Wafer at Different Deposition Stage
JinYu Wu, ChengTzu Kuo, TzuLung Liu (National Chiao Tung University, Taiwan)
The SiNC films were deposited on Si wafer by a microwave plasma chemical vapor deposition (MPCVD) system with CH@sub 4@, N@sub 2@ and additional Si chips as the sources. The films were examined at different deposition times to explore different growth stages of deposition. Based on the structures and the properties of the films, the film deposition can be roughly divided into two stages. In the first stage or the early deposition stage, the structure of the films is essentially nano-crystals embedded in ternary SiNC amorphous matrix. In contrast, in the second stage, the films are further covered by the binary SiN crystalline phases. At 6-hr deposition time, the first amorphous and the second crystalline stages or layers of the films are about 100 nm and 2 @micro@m in thickness, respectively. The structures of the second crystalline layer of the films are matched much closer to @alpha@-Si@sub 3@N@sub 4@ than @beta@-Si@sub 3@N@sub 4@ and tetragonal Si@sub 3@N@sub 4@ type structures. Its nano-hardness and reduced modulus are around 26~33 GPa and 271~381 GPa, respectively, which are about the same order of magnitude to the reported values for Si@sub 3@N@sub 4@ crystals. In contrast, the corresponding values for the first layer, including the substrate effect due to much smaller film thickness, are around 15 ~ 22 GPa and 151 ~ 201 GPa, respectively. The peak positions of the CL spectra for the first and second layers of the films are obviously located at 3.88 eV, and 2.82 eV, respectively. In summary, at the present deposition conditions, the ternary silicon carbon nitrides can only be obtained in nano-crystalline forms and during the early stage of deposition. Effect of adding hydrogen in the source gases on structures and properties of the films will be discussed.
F5-1-5 Comparative Study of the Properties of Aluminum Nitride Films Prepared by dc and rf Sputter-Deposition
T.P. Drüsedau, K. Koppenhagen, J. Bläsing (Otto-von-Guericke Universität Magdeburg, Germany)
Nanocrystalline aluminum nitride films of typical 200 to 500 nm thickness were prepared by dc- and rf-magnetron sputtering from an Al-target in nitrogen and nitrogen-argon atmospheres. The influence of the N@sub 2@ flow (N@sub 2@ total and partial pressure, respectively) and the sputtering power on the structural and optical properties is investigated. Films prepared in pure nitrogen atmosphere are in general stoichiometric with a density around 94 % of bulk AlN. Most of the films are highly c-axis oriented, i. e. show a 002 texture. Exceptions are films prepared at increased N@sub 2@ pressure. The crystallite size shows a maximum at intermediate N@sub 2@ flow with a maximum value of 90 nm for dc-sputtering. The optical properties static refractive index and optical Tauc gap vary with N@sub 2@ pressure between 1.7 - 2.1 and 4.9 5.4 eV, respectively. As judged by crystallographic and optical properties, dc sputter-deposition results in films of superior properties. It is suggested that the higher target voltage for the dc-discharge resulting in higher energies of the film-forming species and especially the reflected nitrogen neutrals is the origin of this effect.
F5-1-6 Modeling the Surface Concentration During Post-Discharge Nitriding
J. Bernal, F. Castillo (ITESM. CEM., México); J. Ascencio (ININ., México); J. Oseguera (ITESM. CEM., México)
Several studies have demonstrated the advantage of the post-discharge nitriding process over conventional methods. In this process the equilibrium concentration is rapidly obtained between the substrate and the surrounding atmosphere. For atmosphere conditions corresponding to the equilibrium with @epsilon@ and @aa gamma@ precipitates of these phases can be observed on the surface even at short periods of time. In the present work, we present a model to follow the evolution of the surface concentration during the post-discharge nitriding. The proposed model considers the dissociation of the N@sub 2@ molecule and a set of initial and boundary conditions to solve the mass transport equations in the solid. Into the model we perform calculations of the reaction kinetic parameters for the N@sub 2@ molecule dissociation. Experimental results were incorporated into the model to estimate a lower limit for nitride nucleation.
F5-1-7 Modeling the Spatial Surface Concentration During Post-Discharge Nitriding
J. Bernal (ITESM. CEM., México); A. Medina (Instituto de Investigación Nuclear, México); F. Castillo (ITESM. CEM., México); O. Salas (ITESM. CEM. México); J. Oseguera (ITESM. CEM., México)
The purpose of this paper is to describe the spatial distribution of active species in a post-discharge reactor and simultaneously follow the evolution of the surface concentration. Two models were linked to micro structural analysis, the first predicts the atmospheric density evolution of atomic nitrogen along the quartz tube of the reactor and the second follows the evolution concentration on the surface until the equilibrium is reached with the surrounding atmosphere for every analysis position. Experimental results were also analyzed to relate them to the spatial distribution of the active species in terms of the precipitation nitride density along the reactor. For this purpose samples of pure iron were nitrided for short nitriding times in a mixture of N@sub 2@-H@sub 2@-Ar. These results were also used to estimate the lower limit of @epsilon@ and @aa gamma@ nucleation at several positions along the quartz tube. The evolution of the surface concentration quickly reaches the required values to nucleate both @epsilon@ and @aa gamma@. Simulation results could be used to control the process based on calculated the surface nitrogen concentration as a function of position and its relationship with nitride precipitation
F5-1-8 Thin Metal Overlayers on Oxides: Epitaxy and Chemical Reactions
T. Wagner (Max-Planck-Institut für Metallforschung, Germany)
Thin metal films on oxide substrates are used in a variety of technological applications. Ideally, the films should have low defect densities; this prerequisite can be often fulfilled by growing epitaxial films. Recently, epitaxial films have received a great deal of attention for fundamental studies of the structure and bonding of heterophase interfaces. In this paper, a detailed fundamental investigation of the nucleation and growth processes of metals on SrTiO@sub 3@ and TiO@sub 2@ single crystals will be presented. The metal was deposited by MBE. The structure and chemical composition of the metal/oxide interfaces were investigated with different surface science methods and electron microscopy. In addition, nucleation processes were analyzed on the basis of rate equations. In summary, general trends will be given which allow the prediction of the growth behavior of metals on oxides as a function of processing and materials parameters.
F5-1-10 Initial Deposition of Calcium Phosphate Coatings on Polystyrene and Polytetrafluorethylene
B. Feddes (University of Nijmegen, The Nertherlands); A.M. Vredenberg (University of Utrecht, The Netherlands); G.J.C. Wolke, J.A. Jansen (University of Nijmegen, The Netherlands)
Calcium phosphate (CaP) coatings can be applied to improve the biological performance of polymeric medical implants. On the other hand, a strong interfacial bond between ceramic and polymer is required for clinical applications. Consequently, this study focuses on the development of the interface during deposition of CaP (1-20 nm) on polystyrene (PS) and polytetrafluorethylene (PTFE). @paragraph@ Coatings were deposited using RF magnetron sputtering in argon. Some of the samples received an oxygen plasma pretreatment. Composition and thickness of the coatings were measured using RBS. Morphology was probed by AFM and the presence of chemical bonds at or nearby the interface was determined using XPS. @paragraph@ Initially, as a result of oxygen incorporation during pretreatment, the number of C-O bonds nearby the interface is higher for pretreated than for untreated PS. This difference disappears after deposition of 1.5 nm CaP. Based on AFM and RBS results, this is roughly the thickness at which a continuous CaP layer is formed on pretreated PS. Then, 25% of the probed C atoms are present in a C-O bond. AFM shows that the nucleation site density on PS increases from 1*10@super 10@ to 13*10@super 10@ sites/cm@super 2@ as a result of the plasma pretreatment. @paragraph@ In PTFE, the pretreatment does not incorporate oxygen in the material. However, during CaP deposition C-F bonds are broken and F escapes from the PTFE. Ca-F bonds form at the interface. Initially, almost no P is deposited. Presumably, P reacts with F and escapes as PF@sub 3@ gas. @paragraph@ Thus, the two substrates possess strongly different reactivity towards CaP. The final structure of the interface seems to be influenced by energetic Ar from the plasma, and not by the pretreatment.
F5-1-11 Characterization of PVD-TiCN-Layers by Physical and Electrochemical Methods.
C.A. Achete, L.F. Senna (Universidade Federal do Rio de Janeiro, Brazil); T. Hirsch (Stifitung Institut für werkstofftechinik/IWT Bremen, Germany)
The aim of this work was to study the steel/TiCN- coating system, since the TiCN coatings provide the advantage to study the chemical and physical as well as the mechanical properties for a range of different chemical compositions. TiCN coatings were deposited by the magnetron sputter ion plating technique, onto High Speed Steel S 6-5-2 (M2) and a simple medium carbon steel C45 (AISI 1045). The PVD TiCN coatings were produced with a variation of the partial pressures of nitrogen and methane, for a constant substrate bias (0, 50 or 100V) and a constant deposition temperature (300, 350, 400 or 450 °C). Next, the substrate bias was varied for a constant ratio of partial pressures and for constant temperature. X-Ray analysis of phase composition and texture showed that all diffraction lines were only Ti(C,N). The residual stresses and textures in the coating had also clarified the differences to standard TiN coatings, mainly with high carbon sample and high bias voltage deposition. It is analyzed the correlation between the electrochemical behavior of the TiCN coatings measured by Electrochemical Impedance Spectroscopy (EIS) and the X-rays measurements.
F5-1-12 Characterization of AgInTe@sub 2@ Films Grown by Hot Wall Epitaxy Technique on KCl Substrate
A. Singh, R.K. Bedi (Guru Nanak Dev University, India)
AgInTe@sub 2@ films have been grown by Hot wall epitaxy technique onto the KCl substrate kept at different temperatures in a vacuum of 10@super@-@5@ torr. Experimental conditions are optimised to obtain better crystallinity of the films. The films so prepared are studied for their electrical resistivity, Hall mobility , carrier concentration, structural and optical properties. Observations reveal that the electrical conductivity and carrier concentration of films increases with the increase in temperature, while the Hall mobility decreases. The results indicates that the films are p-type, thus indicating holes as dominant charge carriers. The scanning electron micrographs of the films show an increase in grain size with increase in substrate temperature . Analysis of optical absorption studies on the films indicate the band gap energies lie in the range 0.93- 0.95eV.