AVS1996 Session TF-WeP: Thin FIlms Poster Session II
Wednesday, October 16, 1996 5:00 PM in Ballroom A
Wednesday Afternoon
Time Period WeP Sessions | Topic TF Sessions | Time Periods | Topics | AVS1996 Schedule
|
TF-WeP-2 Investigation of the Effects of Molecular Weight on the Structure of Polyethylene Oxide
W. Yan (State University of New York, Buffalo); J. Gardella, Jr. (AVS) Polyethylene oxide (PEO) samples were prepared on silver substrates by the Langmuir-Blodgett techniques below the collapse pressure, as determined through force-area isotherm. The PEO films were investigated by Reflection-Absorption Infrared Fourier Transform Spectroscopy (RA-FTIR) and Time of Flight Secondary Ion mass spectroscopy(TOF-SIMS). These analytical methods were applied to study the effects molecular weight(MW) have on the secondary and tertiary structures of the molecular films and the SIMS ion formation mechanism. It is known that in crystalline state, PEO chains contain seven monomers per two helical turns. But it is not known whether the conformation extends to the surface. Previous research showed that the structures of PEO L-B films were influenced by the end group chemistry. RA-FTIR and TOF-SIMS results suggest that structural differences exist in silver adsorbed PEO samples as a function of the molecular weight. |
|
TF-WeP-3 Microcrystalline Silicon Films Deposited at Low Temperatures by ECR Plasma Deposition
R. Knox, V. Dalal (Iowa State University) Microcrystalline silicon films have been deposited on Corning 7059 glass at low temperatures by electron cyclotron resonance (ECR) plasma deposition. Highly diluted silane (1% in hydrogen) plasmas were generated within a microwave ECR source and directed toward a heated substrate. The influence of microwave power (50 to 200 W), chamber pressure (5 to 15 mTorr), and substrate temperature (250-500 C) was investigated. The structural properties were studied using Raman spectroscopy and x-ray diffraction. The electrical and optical properties were characterized by measuring the light and dark conductivity, activation energy, Hall mobility and sub-bandgap absorption. We report the on our attempt to maximize the growth rate without severely degrading the electronic properties of the microcrystalline films. In addition, we report on the microcrystalline to amorphous transition which occurred at substrate temperatures near 300 C. |
|
TF-WeP-4 Trapping Studies in CdS Polycrystalline Thin Films
R. Lozada-Morales (FCFM-BUAP, Mexico); O. Zelaya-Angel, O. Vigil, M. Garcia-Rocha (CINVESTAV, Mexico) Thin films of CdS in the cubic phase were prepared onto glass substrates by the chemical bath deposition method at 80 C. Thermally stimulated currents (TSC), photoluminescence (PL), and photoconductivity measurements were carried out at room temperatur e on as-grown and thermal annealed samples in Ar+S\sub 2\ atmosphere in the 100 to 500 C temperature range during 30 hours. By means of PL a defect induced band, centered at 1.82 \+-\0.02 eV, has been associated to S vacancies. As a result of the thermal treatment (TT) the green emission band (GB) centered at 2.4 eV moves gradually towards lower energies in the 100 - 300 C TT temperature range. At a TT temperature of 300 C, only the yellow band (YB) around 2.2 eV appears. At this temperature the cubic to hexagonal phase transition takes place. Above this TT temperature the YB shifts back to higher energies until the GB is again observed at a TT temperature of 500 C. At this temperature the phase transition is completed [1]. The shifts observed in the peak s of TSC curves are associated to the movement of the band gap of the samples. The photoconductivity experiments clearly show levels at 1.88 and 1.23 eV whose intensities change with TT but the energy positions do not change. The first peak is associated with one of the levels that originate the 1.82 PL defect band, the second one could be attributed to Cd vacancies. [1] O. Zelaya-Angel, J. J. Alvarado-Gil, R. Lozada-Morales, H. Vargas, and A. Ferreira da Silva. Appl. Phys. Lett. 64, 291 (1994) This work was partially suported by CONACYT-Mexico |
|
TF-WeP-6 The Application of PECVD Silicon Nitride as a Double Layer AntiReflection Coating and Passivation Layer for Polysilicon Solar Cells
S. Winderbaum (University of South Australia); O. Reinhold (Defence Science and Technology Organisation); F. Yun (University of New South Wales) Reflection losses in PESC polycrystalline silicon solar cells have been reduced by the application of a double layer antireflection coating of plasma enhanced chemical vapour deposition silicon nitride (PECVD SixNyHz ). The layer was deposited in a single wafer parallel plate reactor powered by a 13.56 Mhz RF power supply using SiH4 and NH3 as the reactive gases. Refractive indexes and extinction coefficients of the films were measured thoughout the solar spectrum during the process chararacterisation. The layers deposited had refractive indexes of 2.48 and 1.95 at HeNe wavelength and thicknesses of 42.5 and 64.5 nm respectively. The overall reflectance measured using a Cary-5 spectrophotometer in the wavelength range between 350 to 1150 nm was 7.4 %. The extinction coefficient of the high refractive index film showed a significant increase in absorption for short wavelengths. However, the improvement in current collection was higher than expected from the overall reflectance and absorption of the film. Short circuit current was increased by 49 % and open circuit voltage increased by 3.3 % when compared with uncoated cells. These results imply a passivation effect which increased the open circuit voltage beyond the value expected solely from the current collection addition |
|
TF-WeP-7 Tungsten Silicide Thin Films for Resistors
C. Backhouse (University of Alberta, Canada); G. Este (Nortel Technology, Canada); J. Sit, S. Dew, M. Brett (University of Alberta, Canada) We have produced and characterized thin films of stoichiometric and non-stoichiometric tungsten silicide in order to produce highly resistive films (about 1 k-ohm/square), with temperature coefficients of resistivity (TCR) less than 0.2 per cent/K, by a technique that we believe is more reproducible, and has better uniformity than comparable techniques involving cermets. Although there are a variety of materials which are capable of producing highly resistive films (of about 1 k-ohm/square or more), in our experience these tend to involve very thin films (in the case of metals), reproducibility and uniformity problems (in the case of cermets), or have large TCRs (in the case of semiconductors). We applied a variety of physical vapour deposition techniques for the sputter deposition of tungsten and silicon films ranging from pure silicon to pure tungsten. In doing so we have identified a range of compositions and thicknesses in which the TCR and resistivity are independent of thickness, suggesting that these films do not suffer from any significant changes in microstructure at any critical thickness in the range of 70 to 1000 nm. These results were also independent of the type of sputter deposition used. These factors suggest that such films will be useful in the manufacture of stable resistors on the order of 1 k-ohm or more. |
|
TF-WeP-8 Sputter Deposition of High Resistivity Boron Carbides
N. Ianno, A. Ahmad (University of Nebraska, Lincoln) We have succeeded in the rf magnetron sputter deposition of high resistivity boron carbide (B\subl-x\C\subx\). This has been accomplished by sputter depositing the boron carbide from a methane saturated high density pure boron target. We will show that the composition and optical band gap of the sputter deposited material are a function of the applied rf power. Boron-carbide/n-Si(111) heterojunction diodes can be fabricated from closo-1,2-dicarbadodecaborane by using synchrotron radiation induced chemical vapor deposition (SR-CVD) and plasma enhanced chemical vapor deposition (PECVD). The success of these devices is based on the fact that these two deposition methods yield high resistivity (\rho\ \>\ 10\super8\ \Omega\-cm)B\sub5\C films. To date films deposited via sputtering have low resistivities, \rho\ \<\ 10 \Omega\-cm, and thus do not form rectifying junctions with silicon. In this work, the B\sub5\C was sputter deposited from a boron target previously saturated in a methane plasma. This yielded B\sub5\C films with resistivities greater than 10\super7\ \Omega\-cm and rectifying junctions with n-Si(111), n-Si(100), p-Si(100), and p-Si(111). Furthermore, boron carbide/silicon heterojunction diodes fabricated via sputtering compare favorably with those fabricated from borane cage molecule sources using plasma enhanced chemical vapor deposition (PECVD). |
|
TF-WeP-9 Nanoscale Crystalline Thin Films for Capacitive Gas Sensors
M. Gimon-Kinsel, K. Balkus, Jr (University of Texas, Dallas) Molecular sieves are attractive materials for use in discriminating chemical sensors. Microporous (pore diameter <20\Ao\) and mesoporous (pore diameter 20-500 \Ao\) metal oxides offer size and shape selective adsorption as well as chemical and thermal stability. We have developed a capacitance-type chemical sensor that exploits the selectivity of molecular sieves. This device relies on a thin continuous layer of molecular sieve which serves as the dielectric phase. Pulsed laser deposition allows the generation of well dispersed polycrystalline thin films of the molecular sieves with thickness on the order of several hundred nanometers. The molecular sieve dielectric constant is sensitive to the polarity and quantity of an adsorbed gas. Thus, the sensor response is a change in capacitance upon exposure to specific gases. The sensor response has been shown to be highly dependent on the particular molecular sieve. Other parameters which are expected to affect sensor response are temperature, humidity, and capacitor design. In this presentation we describe recent studies which examine the influence of temperature on the sensor response to a variety of combustion gases including CO and CO\sub 2\. |
|
TF-WeP-10 Metal Vapor Sources for Scientific Research and Thin Films Technology: Review
A. Zolkin (Novosibirsk State University, Russia) Continuos and pulse sources of metal vapor for application in physics, chemistry and technologies, are described. The flow of vapor through the nozzle into vacuum is close to continuous regime. The maximum temperature and vapor pressure are: T\ The goal of the Review is to demonstrate how to create a reliable metal vapor source with high optical density (\>\10\super 15\atom/cm\super 2\) for use in and high (>10\super 21\atom/cm\super 2\c) intensity in Materials Technology for Thin Films Source classification. Metal vapor sources involving thermal heating can be graded according to the similarity of features (thermophysics or constructional) [1]. The first group includes the sources involving the expansion of vapor into vacuum from the saturated state (or close to it). The nozzle region in the sources of this type is, as a rule, poorly protected from emissive heat losses. These sources are The second group includes the sources in which vapor is superheated before expansion in order to decrease or eliminate condensation in the nozzle region. These sources allow to handle the characteristics of vapor expanding into vacuum (with superhe The application of two-temperature sources in scientific research and technologies for Thin Films Deposition allows one to control the metal gas dynamic flow, produce atomic, cluster beams or vapor jets without microdroplet phase in it. References 1. A.S.Zolkin. Metal vapour Sources for Scientific Research and Technologies. Academy of Science, Institute of Thermophysics, Novosibirsk. Russia.1993. 75p. |
|
TF-WeP-12 Molecular Dynamics Simulations of Void Formation during Film Growth
H. Helbig, J. Beasock, G. Ramseyer, L. Walsh (Rome Laboratory) Recent molecular dynamics simulations of thin film deposition in two dimensions by Smith and Srolovitz\super 1\ show that voids are formed when fissures that occur by chance are bridged over by atoms adhering to their side walls. We have reproduced this result, under somewhat different simulation conditions, in two dimensions, and extended the simulation to three dimensions. A comparison of the two- and three-dimensional results will be presented. \super 1\ R.W. Smith and D.J. Srolovitz, J. Appl. Phys. 79 (3), 1 Feb. 1996. |
|
TF-WeP-13 Ti-based Superconducting Films Deposited from Ultrasonic Aerosol
A. Conde-Gallardo (CINVESTAV-IPN, Mexico); M. Garcia (UNAM, Mexico); M. Jergel, C. Falcony (CINVESTAV-IPN, Mexico) Thallium-Based Superconducting Films were grown by spray pyrolysis technique where the aerosol is ultrasonically generated. The films are grown in two steps. First a Ba, Ca and Cu precursor films are deposited by spray pyrolysis and after that, in a thermal diffusion process the thallium is introduced at the same time that the sinterization of the film is achieved. Different starting materials, which have different thermodynamic behavior were used for the precursor film. The EDS Analysis and the scanning electron microscopy (SEM) show that the composition and the surface morphology of the precursor film depend a lot from the starting materials. The same techniques are used for studing the effect of silver when it is introduced as dopant in such Tl-base superconducting films. Electrical and optical characterization of these films are also presented and discussed as well as the chemical composition and the thallium profile measured by RBS technique |
|
TF-WeP-14 Determining the Refractive Index of Photoresist Thin Films using Spectroscopic Ellipsometry
R. Synowicki, J. Woollam (J.A. Woollam Co., Inc.) Variable Angle Spectroscopic Ellipsometry (VASE\superR\) is a powerful technique for determining the film thickness and refractive index of photoresists and other dielectric organic materials. However, like all optical analysis methods, ellipsometry uses optical models to extract useful information from the experimental data. This makes the choice of analysis model critical to the quality of the results obtained. General modeling techniques for the analysis of organic films will be reviewed. These techniques include modeling the film optical constants (n and k) using mathematical dispersion models such as the Cauchy, Sellmier, and Lorentz models. New fitting techniques will be introduced, including the use of a very flexible dispersion model developed by Herzinger and Johs, as well as direct fits for n and k by direct inversion of the experimental psi and delta data. The merits and shortcomings of all techniques will be discussed. Also, effects of film non-idealities such as surface roughness, index grading within the film, thickness nonuniformity, and optical anisotropy will also be discussed. |
|
TF-WeP-15 Plasma-assisted Deposition of Polycrystalline-Si (poly-Si) Thin Films on SiO\sub 2\ by a Low-temperature Two-step Plasma Process
D. Wolfe, F. Wang, G. Lucovsky (North Carolina State University) As gate oxide thickness decrease to ~3 nm to scale with short FET channel lengths (< 0.1\mu\m), microstructure of poly-Si gate electrodes must be controlled. This paper presents a two-step, low-temperature plasma-assisted process for deposition of in-situ doped poly-Si thin films on SiO\sub 2\. The process separates interface formation from bulk film growth providing a way to obtain a mechanically smooth interface between poly-Si layers and SiO\sub 2\ surfaces by first depositing a microcrystalline-Si (\mu\c-Si) template, and then a poly-Si layer with larger grain size. This approach is based on studies in which process conditions were optimized for remote PECVD of i) smooth \mu\c-Si films with crystallites nucleating directly on SiO\sub 2\, and ii) homoepitaxial growth of Si. Without using a \mu\c-Si template, the second deposition produces an amorphous film on SiO\sub 2\ substrates. When a \mu\c-Si template is used, the same deposition process results in a poly-Si film with a grain size approaching 100 nm. For each process, the Si source gas silane is injected downstream from the plasma generation region to prevent direct plasma-assisted dissociation. Dopant gases, e.g., phosphine or diborane, are premixed with downstream injected silane. The concentrations of dopants in deposited layers are proportional to source gas ratios of phosphine (or diborane) to silane. Dopants are activated in the as-deposited films; however, optimization of FET gate stacks with deposited dielectrics requires post deposition rapid thermal annealing (RTA), typically for 30 s at 900=B0C. The microstructure and electrical conductivity of doped \mu\c-Si/poly-Si films are characterized as-deposited and after RTAs for different template layer thicknesses. Dopant profiles are obtained by secondary ion mass spectrometry and microstructure is characterized by transmission electron microscopy, reflection high energy electron diffraction, x-ray diffraction and Raman scattering. |
|
TF-WeP-16 Rutherford Backscattering and Channeling Studies of TiO\sub 2\ Substrate, Epitaxially Grown Pure and Nb Mixed TiO\sub 2\ Films
R. Smith, N. Shivaparan (Montana State University); S. Thevuthasan, Y. Gao, S. Chambers (Pacific Northwest National Laboratory) There is a growing interest in the preparation of oxides as thin films on various oxide and metal substrates to obtain high quality-surfaces. Ultrathin oxide films grown on metal substrates permit the current to tunnel to the metal through the film so that charged-particle surface science probes can be used to characterize the films without charging difficulties. Another way of reducing the charging effects in semiconductor oxides is to introduce dopants to increase the number of free carriers. In addition, it is of interest to grow mixed metal oxides in order to obtain enhanced surface catalytic properties. We have recently pursued the MBE growth of Nb-mixed TiO\sub 2\ to form Nb\sub x\Ti\sub 1-x\O\sub 2\ phases, where x is as large as ~ 0.4. A recent x-ray photoelectron diffraction (XPD) study by Gao and co-workers [1], including reflection high-energy and low-energy electron diffraction (RHEED/LEED), shows that Nb mixed TiO\sub 2\ epitaxial films possess excellent short- and long-range structural order, and that Nb atoms substitutionally incorporate at cation sites. We have investigated the crystalline quality of the TiO\sub 2\(100) substrate, epitaxially grown pure and Nb-mixed TiO\sub 2\ films using Rutherford Backscattering (RBS) and channeling experiments. The minimum yield obtained from the angular scans for Ti and Nb shows that the film crystalline quality is reasonably good and that most Nb atoms occupy the cation sites. We will discuss these results along with the results of theoretical simulations. [1] Y. Gao and S.A. Chambers, Surf. Sci. 348, 17 (1996) |
|
TF-WeP-17 In-Situ XPS Characterization of Cubic Boron Nitride Thin Films Grown by Dual Beam Sputter Deposition
K. Park, D. Lee (Korea University); K. Kim, D. Moon (Korean Research Institute of Standards and Science) Cubic boron nitride thin films were grown on a silicon(100) substrate by dual ion beam sputter depopsition. Boron was sputter deposited by 1 keV argon ion beams from a boron target and the substrate was simultaneously bombarded with low energy mixed ion beams of nitrogen and argon. We developed a substrate heating and transfer system with which the thin films grown at an elevated substrate temperature can be transferred to a XPS analysis chamber without being exposed to the air. The effects of substrate temperature, bombarding ion flux and ion energy were studied with in-situ XPS, FT-IR, XRD and high resolution-TEM analysis. The optimum conditions for c-BN growth were 460\super o\C, B/N\sub 2\\super +\ ratio of 1.0 and 400 eV assist ion energy. In this work, the growing process of c-BN film was studied by in-situ XPS. The \pi\ plasmon(\pi\p) loss peak at about 9 eV higher binding energy than the B 1s and N 1s core level peaks was used to identify the hexagonal BN phase because it is observed only in h-BN phase. From in situ XPS analysis as a function of deposition time, it was observed that an initial amorphous BN layer and a h-BN layer were grown sequentially before the growth of a c-BN layer of high quality. These results have been found to be consistent with the FT-IR and TEM results. Angle resolved in-situ XPS analysis showed that the surface layer of the c-BN film is always in the h-BN phase, which can be direct evidence for the stress model for c-BN growth where h-BN is converted to c-BN by stress accumulation at the subsurface region. |
|
TF-WeP-18 The Fine Structures in the Valence-Band, Auger Electron, and Plasmon Energy Loss Spectra Obtained using X-ray Photoelectron Spectroscopy of Diamond-like Carbon Films
S. Seo, D. Ingram (Ohio University) The electronic structures of diamond, graphite, and Diamond-Like Carbon (DLC) films were examined using X-ray Photoelectron Spectroscopy (XPS). DLC films were deposited on Si (100) substrates with 4 to 10 mTorr argon gas pressure in an Unbalanced Magnetron (UBM) sputtering system. Using a monochromatized X-ray source Al K\alpha\, the valence-band region (-5 to 40 eV in BE), Auger electron transition region (230-290 eV in KE), plasmon energy loss region (275-360 eV in BE) were obtained. The DLC spectra of X-ray excited Auger Electron Spectroscopy (XAES) have the similar feature as of diamond, not showing the characteristic shoulder feature of graphite. In addition, the plasmon peaks (24-25 eV) observed in XAES of DLC films are close to the surface plasmon peak of diamond (25.5 eV). The valence-band region contains four bands at 6 eV (p-like state), 13 eV (s+p state), 19 eV (s-like state), and 26 eV (seen from oxygen containing carbon material) in binding energy. For DLC deposited at low argon gas pressure (4 mTorr), the relative growth of the p-like state with respect to s+p and s-like states indicates that the average sp\super 3\ bonding configuration is large in the film. Moreover, the optical band gap obtained using UV-VIS spectroscopy becomes wide, 0.8 eV, in this film. In plasmon loss energy spectra from DLC films, there are several characteristic plasmon losses at the 22, 25, and 28 eV shifts as in microcrystalline graphite, diamond (surface plasmon energy loss), and graphite, respectively. For the DLC film deposited at 4 mTorr argon gas, the plasmon loss at 25 eV becomes dominant indicating the enhancement of diamond-like structure. |