ICMCTF2006 Session B2-2: Arc and E-Beam Coatings and Technologies

Wednesday, May 3, 2006 8:30 AM in Room Golden West

Wednesday Morning

Start	Invited?	Item
8:30 AM	Invited	B2-2-1 Filtered Vacuum Arc Deposition of Undoped and Doped ZnO Thin Films: Electrical, Optical, and Structural Properties S. Goldsmith (Tel Aviv University, Israel); R.L. Boxman (Tel-Aviv University, Israel) Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50 - 400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, Sn:In₂O₃ (ITO), Al:ZnO (AZO), Ga:ZnO, Sb:ZnO, Mg:ZnO and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄, and ZnO-SnO₂), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post deposition treatment has also been applied to improve the properties of TCO films. The deposition rate of FVAD ZnO and M:ZNO thin films, where M is a doping or alloying metal, is in the range of 1 -15 nm/s. The films are generally nonstoichiometric, poly-crystalline n-type semiconductors. In most cases, ZnO films have a Wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as deposited n-type thin ZnO film is in the range (0.2 - 6)×10^-5 Ωm, carrier electron density is 10²³ - 5x10²⁵ m^-3, and electron mobility is in the range 10 - 40 cmsupper 2V^-1s^-1; depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ~3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission at 500 nm wavelength of a 500 nm thick ZnO film is ~0.90.
9:10 AM		B2-2-3 Effects of Oxygen Partial Pressure on Film Growth and Electrical Properties for Undoped ZnO Films with a Thickness Below 100 nm T. Yamamoto, S. Kishimoto (Kochi University of Technology, Japan); K. Inaba (Rigaku Corporation, Japan); M. Yamaguchi (Casio Computer Co., Ltd., Japan); K. Ikeda, H. Makino, T. Yamada (Kochi University of Technology, Japan) Very recently, ZnO has been extensively studied for various applications such as transparent conducting electrodes, sensors and thin film transistors. While polycrystalline ZnO thin films are commonly used in these conventional applications, there has been a growing interest in obtaining them with a thickness below 100 nm on various substrates. In our previous works, for undoped ZnO films prepared by rf-plasma-assisted electron beam deposition, we established that the resistivity of ZnO films decreases with increasing a film thickness up to 100 nm. Our object in this study is to discuss what determine the dependence of electrical properties on film thickness; and to give a solution to improve the electrical properties. A series of ZnO thin films were deposited on glass substrates using the ion plating system with O₂-gas flow rates ranging from 0 to 60 sccm. The thickness of the ZnO films changes from 5.8 to 105 nm. For ZnO films prepared under the condition that O₂-gas flow rates is fixed to be 5 sccm, from Hall-effect measurements, we find that resistivity decreases from 0.2 to 0.02 Ωcm with increasing film thickness: While carrier concentration remains to be almost constant, 1.65 - 2.0 e+19 cm^-3, the Hall mobility increases from 1.7 to 16.7 cm²/Vs with increasing film thickness. From in-plane XRD data and AFM measurements, both in-plane grain size and averaged surface roughness increases with increasing film thickness. Thus, the above findings indicate that the dominant scattering mechanism which determines electrical properties described above is a boundary scattering mechanism. To enhance the grain size and orientation along the c-axis, we prepared the ZnO thin films under O₂-gas flow rates of 30 sccm. From cross-sectional TEM images, we established the improvement of the orientation; consequently, the enhancement of the Hall mobility decreases the resistivity of ZnO thin films.
9:30 AM		B2-2-4 Effects of Oxygen Partial Pressure on Doping Properties for Ga-Doped ZnO Films Prepared by Reactive Plasma Deposition with a Traveling Substrate T. Yamamoto, T. Yamada, K. Ikeda, S. Kishimoto, H. Makino, M. Yamaguchi (Kochi University of Technology, Japan) Very recently, ZnO has been extensively studied for various applications such as transparent conducting electrodes in flat display panel and solar cells. In our previous works, for Ga-doped ZnO (GZO) films (Ga content of 3 wt%; film thickness of 200 nm; substrate temperature of 200 degree C) prepared by reactive plasma deposition, we established low resistivity of 2.8 Ωcm on glass substrates with a size of up to 1 m². Our object in this study is to discuss effects of oxygen partial pressure on doping properties. A series of ZnO thin films (Ga content ranging from 1 to 11 wt%, substrate temperature of 200 degree C) were deposited on glass substrates using the reactive plasma deposition with a traveling substrate technique. O₂-gas flow rates were varied from 0 to 20 sccm. Deposition time was fixed. For GZO films with a film thickness of 235 nm prepared under the condition that Ga content was 4 wt% and O₂-gas flow rates was 10 sccm, we find a minimum sheet resistance of 9.6 Ω/square with resistivity of 2.27 Ωcm, carrier concentration of 9.7 e+20 cm^-3, and the Hall mobility of 28.4 cm²/Vs. We find that while carrier concentration increases with increasing Ga contents of up to 5 wt%, they decreases with further increasing the Ga contents. With increasing O₂-gas flow rates, growth rates of GZO films increase from 2.0 to 3.5 nm/sec. On the other hand, we find different changes of carrier concentration and Hall mobility dependent on O₂-gas flow rates from that of growth rates described above. We will discuss what happens on GZO films prepared under oxygen-rich condition from a view point of microstructure.
9:50 AM		B2-2-5 Carbon Based Tribological Coatings - Deposited with Stationary Rates of 100 nm/s B. Scheffel, J.-P. Heinss, Ch. Metzner (Fraunhofer FEP, Germany) A permanent demand for the coating industry is the reduction of costs by the increase of the deposition rate. That's why we tested the possibilities of the high rate electron beam evaporation to produce carbon based tribological coatings. We present in detail the used experimental technique, which allowed us to deposit with remarkable high rates of 100 nm/s and the results of the analytical investigations. In the case of strong plasma activation dense layer structures were achieved. In dependency on the composition the measured micro hardness reached values up to 35 GPa in maximum. We discuss the results of the structure analyses. In different evaporation configurations we obtained hydrogen free as well as hydrogen containing amorphous carbon. Furthermore we modified the evaporation process to deposit titanium and tungsten containing amorphous carbon coatings. The experiments and results give a new impression about the possibilities and the variability of the high-rate electron beam evaporation.