Papers

ICMCTF1998 Session G3: Hollow Cathode Plasma Processing

Tuesday, April 28, 1998 1:30 PM in Room Town & Country

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		G3-1 The Design of Gas Distribution Systems for Large Area Plasma Deposition and Treatment Equipment. F. Jansen (BOC Coating Technology) Gas inlet systems are generally passive and designed to merely distribute the gas in such a way that a specified thickness uniformity is achieved. The design of these systems is well understood and illustrated taking large area sputtering and PECVD systems as examples. Depending on design and operating parameters, gas inlet systems can also be active plasma sources. The design of these active gas inlet systems is discussed in detail. Active gas inlets are mostly used to deliver chemically activated gas over large areas in deposition and plasma treatment systems. Localized active gas inlets are also used to achieve process stability and uniformity tuning in high throughput deposition systems. Practical examples are again taken from the deposition of dielectric films in large area sputtering and PECVD systems.
2:10 PM		G3-3 The Hollow Cathode - a High Performance Tool for Plasma Activated Deposition H. Morgner (Fraunhofer Institut Elektronenstrahl- und Plasmatechnik, FEP, Germany); M. Neumann, S. Straach (Consultant); M. Krug (Fraunhofer Institut Elektronenstrahl- und Plasmatechnik, FEP, Germany) The hollow cathode will be presented as a plasma source for reactive evaporation processes. The hollow cathode generates an arc discharge plasma. This contains a high portion of directed electrons with an enhanced mean energy, the so called low voltage electron beam (LVEB). The mean energy of the LVEB, in the range of 11eV, results in a very effective ionization of the gas and vapor particles. Consequently, very high plasma densities can be achieved, which corresponds to high particle densities in high rate deposition processes. A high self bias potential of about 15V is obtained on insulating substrates. For the coating of heat sensitive substrates with high deposition rates a process with a low ratio between thermal load and deposition rate is necessary. The heat flux on plastic substrates has been measured in the reactive Al evaporation process. The overall thermal load of 4...5W/cm² related to a deposition rate of 100nm/s is low compared to other processes. This makes the hollow cathode to a favorable tool for the plasma activated high rate deposition. The oxide layers deposited in this process show dense and glassy structures even at comparatively low condensation temperatures. This is caused by the high ion current densities in the order of 30mA/cm². The low ion energy determined by the self bias potential results in relatively low compressive stress below 100MPa. The low thermal load and the moderate intrinsic stress of the layers, makes our hollow cathode plasma activated deposition (HAD) process the method of choice for the deposition of oxides as an abrasion resistant layer on plastic films and sheets.
2:30 PM		G3-4 Hollow Cathode-Assisted Arc Plasma Processing R.E.M. Wilberg, T. Lunow, M. Falz (VTD Vakuumtechnik Dresden, Germany) The hollow cathode arc (HCA) is particularly useful for plasma supported coatings, due to the high charge-carrier density in plasma. The high plasma density near the substrate, adjustable under low pressure within wide margins, enables effective substrate cleaning and heating by ion and electron bombardment. More and more perfect coatings and coating systems for decorative, wear retarding, and corrosion resistant applications are resulting from this process. The combination of hollow cathode arc (HCA) and vacuum coating sources, such as thermal and E-beam evaporators, as well as arc and sputter sources, enables, in a reactively conducted process, the building of simple and effective coating systems. The technical design of the hollow cathode can be optimally adjusted in accordance with the various process parameters. The following combinations have been found to be technically reliable: Hollow cathode discharge with - thermal evaporators - sputter guns - cathodic arc plasma evaporators. Hollow cathode discharge can be employed during all phases of the coating process from precleaning and heating of the substrates to influencing the various properties of deposited coatings, regarding stoichiometrics, compression density, and number of defects. Use of the combination: hollow cathode arc discharge and vacuum arc evaporator in industrial coating plants with reactive process conduct, requires high reliability and stability of the coating system. A tungsten/tantalum hollow cathode will safeguard the required long term stability. This paper provides an overview of the current technical state-of-the-art in the use of the hollow cathode arc with a vacuum arc evaporator and other coating sources. It also reports on other applications, which are still under development.
3:10 PM		G3-6 RF Hollow Cathode Arrays for Low Temperature Plasma Procesing D. Theirich, K.P. Ningel, M. Mildner, D. Korzec, J. Engemann (University of Wuppertal, Germany) Hollow Cathodes are well known as power efficient sources of high density plasmas. Most of the hollow cathodes currently used are single cathodes. For large area plasma treatment suitable arrays of hollow cathodes are highly needed. This paper deals with 13.56 MHz rf hollow cathode arrays and their applications for low temperature plasma processing. Linear arrays of 30 cm length and planar arrays of 20x30 cm² have been developed. Due to their modular design these arrays can be fitted together to yield extended linear plasma sources. The arrays can be equipped with two gas inlets: one feeding gas through the cathode directly, the other feeding gas downstream into the vacuum chamber where the jets expand. Therefore remote type of plasma processing becomes possible. Due to the absence of dielectric windows and the variety of possible bulk materials (aluminium, steel, etc.) almost all types of gases can be used in the Pa to kPa pressure range. Several types of plasma processing like plasma activation, plasma polymerization, plasma CVD and others have been successfully demonstrated using these plasma sources. For example CF-, CH-, SiO_x- and SiN-films can be deposited with excellent homogeneities up to ± 2 %. The absolute values of the deposition rates (e. g. up to more than 1,500 nm/min for HMDSO) are very competitive to deposition rates achieved by microwave plasma sources. Moreover the rf hollow cathodes seem to be up to five times more efficient than microwave plasma sources in terms of energy efficiency. Generally the rf hollow cathodes are scaleable, efficient and reliable tools for plasma processing.
3:30 PM		G3-7 Effect of Magnetic Field Configuration on the Performance of the Hollow Cathode Linear Arc Discharge (LAD) Source. H. Baránková, L. Bardos (Uppsala University, Sweden) The Linear Arc Discharge (LAD) source based on the linearly scalable radio frequency (rf) generated parallel plate hollow cathode in a focusing magnetic field was examined for film deposition both in PVD and PE CVD regimes. The component of the focusing magnetic field perpendicular to the cathode plates promotes the pendulum motion of the hot electrons thereby enhancing the hollow cathode effect and the ion bombardment of the cathode walls. However, the density profile of ions generated in the cathode outlet depends not only on magnetic field but also on the distribution of electric fields in the rf and hollow cathode discharges and on ion velocity components controlled by both discharge parameters and gas dynamics. The distribution of ions in the outlet slit affects the erosion zone geometry and heating of cathode plates. Consequently it is reflected by the uniformity of deposited films. Experimental examination of different configurations of magnetic field near the outlet of the LAD source and of an auxiliary field in the substrate area was performed. Optimization of the magnetic field arrangement for different LAD regimes is discussed and illustrated by examples.
3:50 PM		G3-8 Experiments and Modelling of Combined PVD- and CVD-Processes Using a Hollow Cathode Arc Discharge Plasma H. Bolt, A. Buuron, F. Koch, M. Noethe (Forschungszentrum Juelich, Germany) A plasma based deposition method was developed which allows the deposition of non-metallic coatings with a graded metal interlayer to improve the substrate adhesion of the non-metallic coating. For this a plasma enhanced PVD-process was combined with a CVD-process using a hollow cathode arc discharge plasma produced from a LaB₆ cathode as thermal electron emitter. In the present experiments a combination of an Al-interlayer with a graded transition to an a-C:H top coating was selected. During the process the dense plasma of the hollow cathode arc discharge was magnetically confined and guided to the deposition substrate. The metal atoms for the interlayer formation were introduced into the plasma by evaporation and ionised by the plasma. Subsequently the a-C:H coating was deposited by introducing hydrocarbon precursor gases into the same discharge. During the deposition the energy of these ions can be controlled by applying a negative bias potential to the substrate. Parallel to the experimental work a numerical model was developed to analyze the plasma and surface processes which lead to the deposition of the coating. Applying a diffusion approach, transport and inelastic collision reactions between neutrals, the background plasma species and the reactive species were modeled. The results of the calculations were density profiles of the various relevant gas phase species which could be compared with diagnostic measurements as well as calculated profiles of the deposition rates on substrates. In addition to the comparison of the modeled and the measured deposition rates, the coatings were subjected to extensive characterization.
4:10 PM		G3-9 Surface Functionilization of Polymer Films and Webs using Atmospheric and Subatmospheric Plasmas W. Decker (Sigma Labs, Inc.); A. Yializis (Sigma Labs., Inc.) Plasma treatment is a common process for cleaning, etching and chemically functionalizing surfaces of polymer films. High speed plasma treatment is performed at atmospheric and subatmospheric pressure with a treatment device combining magnetic and hollow cathode effects, which enhance the gas ionization and focus and direct the plasma energy onto the surface of the moving web. Plasma treated polymer films show highly increased micro roughness. Polymer films metallized after plasma treatment exhibit highly improved adhesion between polymer and metal and better oxygen and water vapor barrier behaviour. Fabrics can be treated to attain hydrophilic or hydrophobic properties.
4:30 PM		G3-10 Optimisation of Reactive Deposition in a Hollow Cathode Arc Equipment G. Rohrbach, K.-L. Barth, J. Kallo, A. Lunk (University of Stuttgart, Germany) The effective application of the Hollow Cathode Arc (HCA) in plasma activated PVD processes is based on twofold properties: a) production of an isotropic high density plasma, b) generation of suprathermal beam electrons. The paper deals with investigations on the generation as well on the relaxation processes of the electrons in a HCA equipment. The parameters of the electron component in the plasma were measured by directional resolved Langmuir probe, magnetic spectrometer, microwave interferometer and optical emission spectroscopy. In the gases and gas mixtures used, three groups of electrons could be detected: isotropic distributed electrons, high energetic and low energetic beam electrons. The energy and concentration of these three groups depend on gas mixture and pressures. By the results obtained a model of electron beam generation inside of the hollow cathode is developed. The results of the electron parameter measurements are compared with data resulting from evaporation experiments. Titanium, boron and silicon were evaporated in different gas mixtures in dependence on power and time. The properties of the films deposited depend sensitive on plasma parameter in reactive processing. Stabilisation of the deposition process can be achieved by in situ diagnostics of the film growth. As an example the deposition of cubic boron nitride (c-BN) in a hollow cathode arc deposition equipment is discussed in detail.
4:50 PM		G3-11 Double Layer Coating by Hollow Cathode Discharge Ion Plating M. Minato (Vacuum Metallurgical Co., Ltd., Japan); M. Sato, M. Oishi (Tigold Corporation, Japan) For a decorative appearance, gold (alloy) film is generally deposited on TiN or TiCxNy film by the vacuum evaporation or sputtering methods. It is sometimes however difficult to obtain good adhesion with gold (alloy) film because gold atoms are not sufficiently ionized in these methods. We have developed in-situ double layer coating equipment using Hollow Cathode Discharge (HCD) ion plating. An HCD gun and a crucible were used for the evaporation of titanium and resistive heater for the evaporation of gold. The two sources faced each other. Plowing nitrogen as a reactive gas, titanium was evaporated by the HCD gun and TiN film (1 micron meter in thickness) was deposited on the substrate. Then reducing the power of the HCD gun, the argon plasma from the hollow cathode was irradiated to gold vapor which was evaporated by resistive heating from a tantalum boat. The voltage of the HCD gun was set to 30 V corresponding to the argon gas flow rate. The electrical current of HCD gun was changed and the adhesion of the gold layers were investigated. A good adhesion was obtained with the HCD current between 110 A and 150 A. As the very smooth surface of TiN film can be obtained by HCD ion plating, this method gives a functional decorative film with a high quality.