Papers

ICMCTF2003 Session G3: Hollow Cathode, Hybrid and Atmospheric Plasma Processing

Monday, April 28, 2003 1:30 PM in Room Sunrise

Monday Afternoon

Start	Invited?	Item
1:30 PM		G3-1 Hollow Cathode Based Multi-component Depositions J. Felts (Nano Scale Surface Systems, Inc.) Thin film technologies are evolving from single component structures to multi-component (nano composite) structures. Nano composites incorporate at least two structural and chemical groups and offer novel properties for today's marketplace. Thin films are also being deposited at higher and higher deposition pressures, with several claims of depositions at atmospheric pressures (760 Torr). Depositions based on hollow cathodes can deposit composite thin films at high rates and pressures up to at least 10 Torr. Oxide and nitride structures can be doped with metallic or polymeric groups offering the properties of both components. For example, a silicon dioxide with a dispersed fluoropolymer offering the lubricity of Teflon^® with the mechanical and thermal properties of SiO₂ was fabricated. FTIR data and deposition rate information will be presented along with configurations for in-line depositions for roll coating applications.
2:10 PM		G3-3 Deposition of High Quality Amorphous Silicon, Germanium and Silicon-Germanium Thin Films by a Hollow Cathode Reactive Sputtering System N.J. Ianno, R.J. Soukup, G. Pribil (University of Nebraska-Lincoln); Z. Hubicka (Institute of Physics, Academy of Sciences ASCR, Czech Republic) High quality hydrogenated amorphous silicon (a-Si:H), germanium (a-Ge:H), and silicon-germanium (a-SiGe:H) thin films have been deposited by means of a dc hollow cathode system with magnetic field confinement. High purity single-crystal silicon and germanium nozzles were reactively sputtered in a high density hollow cathode discharge of argon and hydrogen. This process avoids the use of the toxic and pyrophoric gases, germane and silane. The amorphous silicon thin films had light to dark conductivity ratios >10⁶ with light conductivity in the 10^-5 S/cm range. The best a-Si:H films have a Tauc band gap near 1.8 eV with an atomic hydrogen concentration of about 14%. The growth rate was in the 2 - 3 µm/h range. The a-Ge:H films were deposited in a similar manner in the same vacuum system. Measurements of FTIR, Tauc bandgap, and conductivity were also made on these films. The FTIR results indicate that these films have hydrogen bonding as a single atom, as did the hydrogenated silicon films. The Tauc bandgap was about 1.0eV for all the germanium films. A slight photoresponse was noted for these films which were deposited at a rate of from 2 to 6 µm/h. The a-SiGe:H films are also deposited by the same method in the same vacuum system. Here, two hollow cathodes of single crystal Si and Ge are reactively sputtered simultaneously. A description of the complete system will be presented. The optical and electronic properties of the initial films are promising. The photoresponse is dependent upon the bandgap, germanium content, as expected. A light to dark ratio of 2600 has been achieved for a film with a bandgap of 1.53eV. The FTIR data indicates that SiH bonds dominate over GeH bonds by the absence of peaks at 570 and 1880 cm^-1.
2:30 PM		G3-4 Large Area Plasma Processing System Based on Electron Beam Ionization D. Leonhardt (US Naval Research Laboratory); C. Muratore (US Naval Research Laboratory/ASEE Postdoctoral Research Associate); S.G. Walton (US Naval Research Laboratory); D.D. Blackwell (SFA, Inc.); R.F. Fernsler, R.A. Meger (US Naval Research Laboratory) Electron beam (e-beam) ionization has been shown to be both efficient at producing plasma and scalable to large area (square meters). NRL has developed a number of hollow cathodes to generate sheets of electrons culminating in a 'Large Area Plasma Processing System' (LAPPS) based on the e-beam ionization process. We have demonstrated that the beam ionization process is fairly independent of gas composition and capable of producing low temperature plasma electrons (<0.5 eV in molecular gases) in high densities (10⁹-10¹² cm^-3). This system should offer increased control of plasma-to-surface fluxes and the ability to modify materials' surface properties uniformly over large areas. The system discussed consists of a pulsed planar plasma distribution generated by a magnetically collimated sheet of 2-3kV, < 1 mA/cm² electrons injected into a neutral gas background (oxygen, nitrogen, sulfur hexafluoride, argon). Typical operating pressures range from 20-150 mtorr with beam-collimating magnetic fields (100-200 Gauss) for plasma localization. Results of surface modification tests of materials including anisotropic removal of polymeric material (photoresist) and silicon as well as thin film deposition.¹ Complementary time-resolved in situ plasma diagnostics (Langmuir probes, microwave transmission and mass spectrometry) of these pulsed plasmas will be shown to illustrate the general plasma characteristics. The attributes of this beam-generated planar plasma make it ideal for many materials applications, particularly when large areas are important. Work supported by the Office of Naval Research. ¹ See additional presentations by co-authors at this conference.
2:50 PM		G3-5 Hybrid Cold Atmospheric Plasma Source H. Baránková, L. Bardos (Uppsala University, Sweden) Due to a short mean free path of particles at atmospheric pressure and an influence of ambient air, the plasma in open systems has typically a short-range impact of about a few milimeters. Therefore most sources employ considerably high noble gas flows, of the order of tens slm. Moreover, many sources need expensive helium for stabilization of the plasma. We designed a new type of cold atmospheric plasma source that combines microwave plasma with the hollow cathode plasma generated simultaneously by a common hollow electrode. A laboratory prototype of such a hybrid source with simple cylindrical electrode will be presented. The source is capable to generate even several tens of centimeters long plasma plume in open air at less than 500 sccm of argon flow. The hollow cathode plasma is generated either by the radio frequency (Rf) power or by pulsed DC power. Parameters of the hybrid plasma plume are controlled by both the microwave and the hollow cathode powers. The latest prototype of the Hybrid Hollow Electrode Activated Discharge (H-HEAD) cold atmospheric plasma source represents an upscaled modification of hybrid sources with linear outlet for large area plasma treatments of 3d substrates. Performance of H-HEAD sources in processing experiments will be briefly described.
3:10 PM		G3-6 Atmospheric Pressure Microwave CVD for Barrier Layers on Steel Sheets V. Hopfe, R. Liske, D. Rogler, G. Maeder, C. Schreuders (Fraunhofer Institute Material and Beam Technology Dresden, Germany); B. Schuhmacher, C. Piehl (ThyssenKrupp Stahl AG / Dortmunder OberflächenCentrum, Germany) Atmospheric pressure CVD processes are promising for the development of cost effective technologies for wide area coating on steel sheets. For this purpose, it is necessary to build up reactors which are applicable for continuous coating processes. In the present study, a microwave plasma CVD reactor was developed on a laboratory scale for continuous coating on temperature sensitive metallic substrates of widths up to 150 mm. The up-scaling of this approach into the meter range is currently under development. A non-thermal volume source with microwave activation was applied which is capable to deposit both oxide and non-oxide coatings. The reactor design was established and optimised by computational fluid dynamical simulations. High deposition rates were achieved being typically in the range of 20 - 80 nm/s. Different methods comprising optical emission and in-situ FTIR spectroscopy were applied for process characterisation. A range of atomic and molecular intermediates, precursor fragments, and reaction products were identified leading to conclusion that a complete conversion of the element-organic precursors into an inorganic layer takes place. The microwave plasma CVD reactor is currently applied to deposit oxide layers on galvanised steel sheets. The coatings are designed to be used as interface layers to improve the adhesion of organic coatings. The complete layer system must fulfil severe specifications, i.e. concerning the forming properties and the corrosion resistance. The coatings were characterised concerning their structure (FTIR reflection, spectro-ellipsometry, AFM, XPS, FE-SEM) and electrochemical/corrosion protection properties (cyclovoltammetry, weathering tests).
3:30 PM		G3-7 Atmospheric Pressure PE-CVD of Silicon Based Coatings using a Glow Dielectric Barrier Discharge S. Martin, F. Massines, N. Gherardi, C. Jimenez (LGET-CNRS, France) The aim of this work is to determine the properties of silicon-based coatings realised with an atmospheric pressure glow dielectric barrier discharge and to understand the growth mechanisms. Mixtures of SiH₄ and N₂O diluted in N₂ to reach the atmospheric pressure are used to obtain silicon oxide thin films. A longitudinal gas injection allows studying the coating properties as a function of the reactive gas decomposition and transformations level. The other parameters of this study are the silane rate and the plasma power. The thickness profile as a function of the gas residence time in the discharge clearly presents 2 maximum. MEB observations, ellipsometry and infrared results show that the first maximum which typically corresponds to a 1ms residence time is due to radicals directly interacting with the surface while the second one observed for 10ms residence time is due to the accumulation of aggregates formed in the gas phase due to the radicals interaction in the gas bulk. The first mechanism leads to dense silicon oxide coatings. Higher is the plasma power, denser is the coating, values of 98% of SiO₂ are reached. The growth rate increases with the silane concentration and the plasmas power but saturation is observed around some ten of nanometer per minute. The second mechanism leads to porous deposit typically made of 30 % of SiO₂ and 70% of void. The growth rate increases like the square of the silane concentration. The maximum coating roughness is observed when the two mechanisms significantly contribute to the film growth leading to the formation of "cauliflower" type structure.
3:50 PM		G3-8 Investigation of the Low Temperature Atmospheric Deposition of TCO Thin Films on Polymer Substrates O. Churpita, Z. Hubicka, M. Cada, L. Jastrabik, L. Soukup (Institute of Physics, Academy of Sciences ASCR, Czech Republic) Atmospheric barrier-torch discharge was used as a source for deposition of TCO thin films on polymer substrates. Atmospheric high-density plasma jet was created at the outlet of a quartz nozzle which was supplied by either He or Ar gas flow. RF power was capacitively connected to the plasma by stainless steel ring electrode via dielectric wall of the quartz tube. There was not a direct contact of the atmospheric plasma with the metallic electrode in this configuration. Two working modes were distinguished during the deposition process. In the first one, the power absorption was very low and interaction of the plasma jet with the substrate did not appear. In the second one, plasma jet was in interaction with the substrate surface. In_xO_y and SnO_x conductive thin films were already deposited on polymer substrates by this technique at atmospheric pressure. As growth precursors, vapors of solid phase of In-acetylacetonate and Sn-acetylacetonate were used for deposition of In_xO_y and SnO_x thin films, respectively. These solid precursors vapors were carried by nitrogen gas flow to the atmospheric plasma jet body. Furthermore, the use of precursors as Sn₂ - acetylacetonate and In₃ - tetramethylheptanedionate in the form of liquid solution were investigated. A possibility to prepare vapors of these precursors by a flash evaporator working up to atmospheric pressure is being investigated. This technique is able to provide very precise and reproducible control of vapors precursors delivery to the plasma jet channel. Atmospheric plasma jet parameters were controlled by emission spectroscopy. Furthermore, the planar Langmuir probe working up to atmospheric pressure was used for the measurement of electron temperature in the position of the substrate by different deposition conditions. Deposited films were analyzed by means of electron microprobe system, XRD diffraction and spectroscopic ellipsometry.
4:10 PM		G3-9 The Application of Atmospheric Pressure Plasma for Display Industry Y.H. Lee, C.H. Yi, C.H. Jeong, B.J. Park, G.Y. Yeom (Sungkyunkwan University, South Korea) Plasma treatment for the surface modification has been used to produce hydrophobic or hydrophilic surface on metals, plastics, glass, or polymers in various industries. In this study, a novel large area atmospheric pressure plasma apparatus has been used to generate a large area and high density atmospheric pressure plasma (plasma larger than 700mm in width) and the effects of this type of plasma apparatus on the removal of organic contaminants of large area glass substrates, printed circuit boards, and plasma display panels have been carried out. A low frequency AC power supply with a sine wave voltage (3-100kHz) was used to generate the plasmas under atmospheric pressure. Helium was used as the ignition and discharge gas and O₂/Ar mixtures were used as the reactive gas. The sample was mounted just below the plasma region formed by the electrodes. The size of the electrodes was 20mm(L) x 760mm(W). Using this type of atmospheric pressure plasma apparatus, dense, uniform, and very stable plasma could be obtained on the entire area of the electrode. Using this apparatus, organic materials such as photoresist were etched to estimate the cleaning rate and uniformity of organic materials. Characteristics of the cleaned sample surface were investigated by X-ray photoelectron spectroscopy and also by measuring contact angle of water drops. For all of the materials, the contact angle decreased significantly after the plasma treatment and the effect of the plasma treatment was sustained about one week for PCB.
4:30 PM		G3-10 Effect of an Atmospheric Plasma Treatment on the Characteristics of Indium Tin Oxide (ITO) Surface C.H. Jeong, C.H. Yi, Y.H. Lee, G.Y. Yeom (Sungkyunkwan University, South Korea) Recent studies on the surface treatment of various materials are concentrated on the atmospheric pressure plasmas instead of low pressure plasmas due to the various advantages of atmospheric pressure plasma. In this study, atmospheric pressure glow discharges generated by low frequency (kHz) power supply between dielectric covered electrodes were used to remove contamination on the ITO surface and the change of surface composition, optical transmittance, surface roughness, and resistivity of ITO after the atmospheric plasma treatment were investigated. Surface characteristics after the plasma treatment were investigated using X-ray photoelectron spectroscopy (XPS) and showed the decrease of carbon contaminants by the atmospheric pressure plasma treatment. The decrease of contact angle from near 90degree to less than 10degree was also obtained by the plasma treatment. Other properties such as surface roughness, optical transmittance, and resistivity were measures using an atomic force microscopy, a UV-spectrometer, and a four point probe, respectively after the plasma treatment.