ICMCTF2002 Session G3-1: Hollow Cathode, Hybrid and Atmospheric Plasma Processing

Monday, April 22, 2002 1:30 PM in Room Sunrise

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	G3-1-1 The Removal of Organic Impurities with Spray Type Plasma Reactor at Atmospheric Pressure M. Kogoma (Sophia University, Tokyo) Some organic impurities on the printing wiring surfaces have a bad influence on the metal contacts and to make the soldering failure. The plasma treatment or ashing in a low pressure is one of the useful method to remove such impurities on the surfaces. However to insert this method in to an assembly line is hardly used in the atmosphere. We had already reported that the Atmospheric Pressure Glow Plasma (APG) had very high ashing rate to remove the organic impurities with using cylindrical spray type discharge reactor to treat the small area. Now we propose new type reactor that can treat wider area than that of the recent one. First, we tried to test the effect of the treatment gases (oxygen in helium and oxygen in argon) for increase the densities of active species(oxygen atom) in the after glow stream. Consequently, we found that the oxygen /argon system has much higher rate than the former system. Next, we changed the reactor dimension to know what size of the electrode is the best to treat the surface. We will discuss more details in the symposium.
2:10 PM		G3-1-3 Hollow Cathode Cold Atmospheric Plasma Source with Monoatomic and Molecular Gases H. Baránková, L. Bardos (Uppsala University, Sweden) Performance of the radio frequency (rf) hollow cathode at atmospheric pressure was tested for neon, argon, nitrogen and air. Non-equilibrium (cold) atmospheric plasma was generated in the gas flowing through the rf hollow cathode. The electrode system was installed in a chamber open to ambient atmosphere. Two rf frequencies of 13.56 MHz and 27.12 MHz were compared. Similarly to the low pressure hollow cathodes the higher frequency was found to be more suitable for all tested gases, due to a lower rf voltage and related power for ignition and sustaining a stable plasma. The Fused Hollow Cathode (FHC) source powered by 27.12 MHz generator produces a stable uniform plasma over large area in monoatomic gases, suitable for surface cleaning and activation applications. However, a substantial difference was found in discharge performance when using molecular gas. An optimization of impedance matching network enabled to generate stable cold plasma at rf powers around 100 W in both air and nitrogen flowing through the single cylindrical hollow cathode with diameters ≤ 400 µm. Possibilities of a stable uniform air (or nitrogen) plasma generation over large areas by the FHC sources are discussed, too. $.
2:30 PM	Invited	G3-1-4 From mbar to Atmospheric Plasma Processing: Progress in Hardware and Large Area Applications J. Engemann (FMT, University-GH Wuppertal, Germany) The majority of all plasma processes still refers to low-pressure non-equilibrium plasmas. Over the years scaleable high density plasma sources have been developed for a wide variety of different applications. Meanwhile there is a whole range of plasma excitation schemes available including advanced capacitively/inductively coupled rf-sources, helicons and a variety of microwave plasma sources. As an example the so-called SLot ANtenna 2.45 GHz microwave plasma source SLAN with active plasma diameters of up to 67 cm will be presented. The smallest of these sources with a plasma diameter of 4 cm (μmSLAN) allows for the formation of a free standing plasma beam with extraordinary properties. Using argon as a feed gas electron temperatures of well below 1 eV with plasma densities in the range of 10¹³ cm^-3 have been observed more than 30 cm downstream the source outlet. With such a system high quality DLC films with deposition rates close to 40 µm/hour have been deposited for automotive applications. Maximum plasma densities, excellent homogeneity, contamination issues, scaleability and reduced cost of ownership were the most important driving forces for “traditional” low pressure plasma sources. Because of the relatively high power levels needed for a homogenous stable plasma generation and the widespread energy distribution functions of charged plasma particles a more selective plasma chemistry is difficult to achieve. A major step to overcome this barrier relates to the use of time-modulated power coupling or the operation at extremely low average cw-power levels. As a consequence a substantial retention of the original monomer structure is possible as well as the incorporation of dopants/additives in certain limits. This is especially important for the deposition of highly functionalised polymer thin films for biomedical applications. A novel 13.56 rf Hollow Cathode Plasma Source developed at the Microstructure Research Center fmt has been proven to satisfy those requirements including scaleability and very low parasitic contamination. Process examples spanning from optical SiO_x hard coatings, SiN_x thin films for photovoltaics to DLC for optical and biomedical applications. Increasing the workable pressure range to atmospheric pressure without loosing the technological benefits of low-pressure non-equilibrium plasmas is highly attractive and has stimulated massive research worldwide. Because of their comparable low lifetime charged plasma particles play a less significant role in atmospheric pressure plasma processing. Instead, metastable engineering on a molecular level is becoming more important. Here so-called surface and coplanar discharges operating (at least partially) in the glow discharge regime without any restricion to the use of molecular gases are promising. This talk will address some novel innovative schemes together with process examples, too.
3:10 PM		G3-1-6 The Hollow Cathode Arc Discharge - a Key to Excellent Layer Properties in Plasma Activated High Rate Deposition H. Morgner, G. Mattausch, M. Neumann, O. Zywitzki (Fraunhofer Institut Elektronenstrahl- und Plasmatechnik (FhG-FEP) Dresden, Germany) Employing thermal evaporators, very high deposition rates can be achieved. However, layer properties lack sufficient density typically. This drawback can be overcome by introduction of a suitable plasma activation. Plasma properties like plasma density in the range of 10¹²/cm³ and electron temperature of about 3 eV in the positive plasma column as well as the very wide operation parameter range including different evaporation materials and different gases in a wide pressure range between 0.1 Pa to 30 Pa make the hollow cathode arc sources to be first choice tools for plasma activation. A wide variety of configurations for different applications and process conditions has been developed and optimized. Most configurations are dedicated to web coating. For uniform plasma activation of the vapor generated by a line evaporator, the hollow cathode plasma sources are arranged side by side and are equipped with ring anodes. Directed electrons from the cathodes pass through the ring anodes and activate the vapor cloud close to the substrate. The resulting ion current density impinging on the substrate amounts to 5...10 mA/cm². For higher degree of activation, the plasma electrons can be drawn towards additional anodes arranged close to the crucible. In combination with an external transversal magnetic field, an internal electrical field within the plasma is generated. It accelerates ions towards the substrate. In this setup, ion current densities from 30 to 60 mA/cm² can be achieved. In directed vapor deposition (DVD) technology developed recently, vapor stemming from a point source is focused by a carrier gas to propagate as a tight beam. Operation pressures up to 30 Pa are typical for this process. The hollow cathode arc source has to be adapted to these conditions. Furthermore, the drop of the self bias voltage due to electron collision processes in dense atmosphere has to be compensated by an external bias voltage applied to the substrate which enhances the energy of the condensing ions. For deposition of non-conductive layers, this bias voltage must be AC pulsed.
3:30 PM		G3-1-7 Performance of Radio Frequency Hollow Cathodes at Low Gas Pressures L. Bardos, H. Baránková (Uppsala University, Sweden); Y.A. Lebedev (Russian Academy of Science, Russia) Typical hollow cathodes have distances between opposite inner walls in a milimeter range and can operate at gas pressures of about 0.1 - 10 Torr. This is because the pressure and the cathode geometry must fulfill condition for the hollow-cathode effect, based on electron exchange between opposite walls. In this paper, we report on the performance of the radio frequency (rf) powered cylindrical and linear hollow cathodes, with the gas flowing through the cathode, at mTorr pressure range typical for magnetron sputters or arc evaporators. Operation of simple cylindrical hollow cathodes with inner diameter exceeding 10 mm was possible at pressure down to 0.9 mTorr in argon. The plasma ion density did not exceed magnitude of 10⁹ cm^-3. However, the plasma density as high as 5 x 10¹¹ cm^-3 was measured 15 cm below 16 cm long linear M-M (Magnets-in-Motion) hollow cathodes at 5 mTorr. Measurements of plasma parameters' radial profiles at pressures between 3 and 10 mTorr confirmed that the M-M cathodes produce high-density plasma in both argon and nitrogen and can be used as a sputtering/evaporation source for large area PVD of films at mTorr pressure region. Moreover, the M-M sources can be used in different hybrid PVD and PE CVD plasma systems with conventional sources, which extends application potential of these sources substantially.
3:50 PM		G3-1-8 Improvement of the Interfacial Characteristics of Ethylene-vinyl Acetate /Polyurethane Composites Using Atmospheric Pressure Plasma J.M. Baek, J.-G. Kim, K. Hoon Lee, K. Ho Lee (Institute for Advanced Engineering, KOREA) Plasma treatment is frequently used to increase surface functionality and surface activity, and, it enables to improve various surface properties such as catalytic selectivity, printability, and interfacial adhesion between various materials. In this work, the surface of ethylene-vinyl acetate (EVA) is exposed under an atmospheric pressure plasma torch (APPT), which is generated by dielectric barrier discharge (DBD), and the results are systemically investigated. As a processing gas, air, and O₂ are used. The surface energetics of the treated EVA surfaces are investigated by contact angle measurements of sessile drop method using the van Oss equation, and mechanical adhesion strength are estimated by 180° peeling test. The adhesion properties between EVA and polyurethane (PU) are much improved after the plasma treatment, and the adhesion energy (GIC) is increased up to above 100%. It is thought that the plasma treatment leads to a drastic increase of surface free energy of EVA, mainly due to the increase of its specific polar component. And, APPT process seems to be effective solution for improving adhesion of EVA/PU interface.
4:10 PM		G3-1-9 Deposition of Fluorinated Amorphous Carbon Films by Atmospheric Pressure Plasma Glow Discharge D.J. Kim, H.R. Lee, K. Hoon Lee, K. Ho Lee (Institute for Advanced Engineering, Korea) Fluorinated amorphous carbon films(a-C:F) were deposited on glass and indium doped tin oxide(ITO) by dielectric barrier discharge (DBD) at medium frequencies of 5~100kHz in an atmosphere. And, effects of interlayer on the adhesion and film properties were investigated. CH₄, CF₄ and C₂F₆ were used for deposition, and Ar or He was introduced for stabilizing glow discharge. Dielectric material and electrode design including gas feeding system were main factor of stable atmospheric glow plasma generation and successful deposition. It is known that deposition of hydrophobic film like a-C:F films on the hydrophilic substrates by chemical vapour deposition method is not easy. In this work, we tested oxygen deficient silicon oxide, silicon contained polymer and a-C:H films as intermediate layers. Tetraethylorthosilicate(TEOS), Hexamethyldisilane(HMDS), and CH₄ were used as main deposition gases, respectively. Among these, a-C:F film using a-C:H or polymer as an interlyer showed excellent adhesion and hydrophobicity(contact angle with water, 125°). And, with a-C:H adhesion layer, there was much increase of surface hardness compared to substrate. However, the films with oxygen deficient silicon oxide as an adhesion layer showed poor uniformity. Also, there was an optimal flow rate of C₂F₆ or CF₄ for hydrophobic coating. With excessive flow rate of C₂F₆ or CF₄, substrate were etched instead of being coated. Surface morphology was best at higher temperature using AFM.