Mikrowellen‐PECVD für kontinuierliche Großflächenbeschichtung bei Atmosphärendruck

Microwave PECVD for continuous wide area coating at atmospheric pressure Plasma processes are applied for a variety of surface modifications. Examples are coatings to achieve an improved corrosion and scratch protection, or surface cleaning. Normally, these processes are vacuum based and therefore suitable to only a limited extend for large area industrial applications. By use of atmospheric pressure plasma technology integration in continuously working manufacturing lines is advantageously combined with lower costs and higher throughput. Microwave plasma sources present powerful modules for plasma enhanced chemical vapour deposition at atmospheric pressure. At Fraunhofer IWS processes and equipment as well as application specific materials are developed. The coatings are suitable for scratch resistant surfaces, barrier and corrosion protective layers or anti‐reflex layers on solar cells. The film properties achieved are comparable with those produced by low pressure processes.     

Plasmachemisches Ätzen und Beschichten bei Atmosphärendruck

Atmospheric pressure plasma‐chemical etching and deposition. Application in crystalline silicon photovoltaics. For industrial processing of wafer based crystalline silicon solar cells a variety of different technologies are applied. The combination of these requires a complex wafer handling; increasing not only investment costs, but also the risk of wafer breakage. Application of plasma technologies offers the possibility to manufacture crystalline silicon solar cells without any wet chemical or vacuum processes. At Fraunhofer IWS all etching steps necessary for the production of solar cells and the deposition of silicon nitride as passivation and anti‐reflection coating were demonstrated successfully using atmospheric pressure plasma technologies.     

Wirtschaftliche Anwendung von Mikrowellen‐Plasmen vom mittleren bis Atmosphärendruck. Economic utilisation of microwave excited plasma in medium to atmospheric pressure

An overview on the potential of medium to atmospheric pressure processes will be given and discussed in context to production applications. The introduction of the medium to atmospheric pressure plasma source is a huge progress and a valuable, attractive tool. The plasma source bases on the concept of cy lindrical r esonator with annu lar s lots (CYRANNUS®). High process speed and reliability are the most important facts for technical applications. Parameters as gas/flow dynamic can be controlled and lead to further improvements of equipment and process design. The CYRANNUS® plasma is used in down‐stream configuration for several applications such as glass films on polymer substrate to reduce oxygen permeation, protective coatings against corrosion or wear and hydrophilic or hydrophobic surface properties. Also etching or cleaning can be done easily because of arbitrary process gas in the plasma source. The advantage of medium pressure is higher supply of reactive species and improved transportation of reaction products. Various processes with plasma surface interaction are discussed from physical and technical viewpoint as plasma enhanced CVD, plasma polymerisation on metal or polymer substrates. Using the advantages of medium pressure plasma processes consequently leads to new design of equipment and material flow. In‐line/on‐line treatment of 3‐D material becomes most efficient and enables competitive plasma processes for mass productions. For diamond deposition a larger size of the plasma at high pressure processes are essential for a device with best economics.     

Low‐Vacuum Low‐Cost Deposition of Tribological Coatings

TiN coatings of some microns in thickness were deposited by different reactive plasma deposition technologies such as Magnetron Sputtering Magnetically Assisted, Arc Source Ion Plating and Sputter Ion Plating Plasma Assisted on various unheated metal parts. The source to substrate distances was between 8 and 25cm. Deposition were performed in specially designed plants in the pressure range between 10^‐3–10^‐1 mbar and under variable vacuum and plasma conditions. The experiments were carried out with the intention of obtaining isotropic coatings on substrates of complex geometry. Thickness distribution, morphology, hardness and tribological properties of these coatings were investigated and correlated with the gas pressures and the measured plasma parameters during deposition. The aim of this work was to find effective processes and conditions for the reliable low cost deposition of hard coatings at relatively high gas pressures. The investigations were supported by the European Union in the TIPCOAT‐Project: Brite EuRam BE‐3815/Contract BRPR‐CT97‐0397     

Kalte Normaldruck‐Jetplasmen zur lokalen Oberflächenbehandlung

Cold non‐thermal plasma jets for local surface treatment under normal pressure Plasmas at normal pressure are of considerable interest for surface technology because the industrial application requires no vacuum devices. Among other approaches, cold non‐thermal plasma jets represent an emerging technique to generate plasmas at normal pressure with attractive advantages. They allow ambient process temperatures and require only moderate operating voltages (1.5‐2.5 kV). They offer the advantage that the treated surfaces are not placed between the electrodes thus favoring local treatment of non flat, structured 3D surfaces. Moreover, the dimension of the sources is scalable and their integration into automated processes is simple. A capacitively coupled version (27.12 MHz) of a cold plasma jet suitable for surface treatment at atmospheric pressure is presented along with its plasma physical and technical properties and a series of successful applications, including plasma activation of surfaces for increasing printability, adhesion control, surface cleaning, microfluidics, decontamination, its use in plasmamedicine and for deposition of thin SiO₂ films as protective coatings. The device allows the operation with rare gases (e.g. Ar) and reactive gases as N₂, air or admixtures of silicon‐containing compounds.     

Plasmachemische Gasphasenabscheidung – eine Technologie zur Deposition organischer und anorganischer Schichten. Plasma Enhanced Chemical Vapor Deposition – a Thin Film Technique for Organic and Inorganic Layers

Plasma enhanced chemical vapor deposition (PECVD) has a wide range of interest for thin films up to some μm thickness. It has widespread applications for high quality dielectric and semiconducting silicon alloys at deposition temperatures below 450 °C and pressures at 1 mbar on plane substrates and attracts growing attention for the surface modification of polymers. The PECVD takes advantages of the possibility to alter the film properties in a wide range easily, and the coatings can achieve a variety of useful properties unobtainable by other coating techniques. An environmentally friendly plasma chemical reactor etch cleaning of SiO_x, SiN_x and other film materials can be applied by changing the process gas and without breaking the vacuum. PECVD can be used in a fixed substrate and continuous substrate flow mode. An capacitively coupled parallel‐plate electrode assembly using radio‐frequency (RF) excitation of the discharge is most widely used for substrate areas up to a few square meters. Among the capacitively excitation an inductively and electromagnetically excitation at frequencies in the RF and UHF range has also succeeded in achieving a high rate PECVD. Two applications are presented to show the characteristics and the potential of this technique, the PECVD of semiconducting hydrogenated amorphous silicon, intrinsic or doped, with low power densities using monosilane as a source gas for solar cells, thin films transistors and digital image sensors and the plasma polymerisation of organosilicon protection layers employing the HMDSO monomer and high power densities for mirrors and lenses.     

Kostenstruktur von Plasmaverfahren

Cost Structure of Plasma Processes — The share of investment costs and operating expense in vacuum coating processes At a first glance coating costs of plasma processes seem to be dominated by high investments. Here it is shown that operating costs are at least of the same importance. Thus, it is reasonable to accept coating costs as only one contribution amongst others to the overall production costs. The example ?solar cells”? shows that further enhancement of the coating process is less effective compared to an increase of energy conversion efficiency. On the other hand it appears more effective for cost reduction of hard coatings to decrease energy consumption and to increase the deposition rate instead of minimization of investment costs for the coating machine. The cost structures of depositions from the liquid phase and plasma processes are of the same order but growing environmental demands clearly favor the latter one (no liquid waste, etc.). The commonly used argument, that it is always preferable to run coating processes at atmospheric pressure without the use of (expensive) vacuum equipment rather than under vacuum conditions needs to be reconsidered particularly when noble gases are necessary at atmospheric pressure to obtain equal qualities of the coatings.     

Nanokristalline Werkstoffe hergestellt mit dem Thermischen HF‐Plasma

Nano‐crystalline materials manufactured with the Thermal RF‐Plasma The Inductively Coupled Plasma (ICP) at atmospheric pressure is particularly suited for melting and evaporation of materials. The electrodeless ICP can be generated without limitation of the kind of plasma forming gases. Therefore, using an argon‐oxygen gas mixture as sheath gas of the ICP nanophase coatings can be processed by synthesis with metal‐organic liquid precursors injected in the hot plasma core. For depositions, the plasma jet has to be supersonic. For particles which impinge onto the substrate placed near the nozzle exit of the plasma torch thin and dense coatings are obtained with crystallite sizes of 30‐ 40 nm. The composition and the grain size of as‐deposited coatings are analyzed by XRD.     

Großflächige Quellen f�r die industrielle Plasmatechnik

Plasma‐technological processes in modern thin film technologies for the refinement of surfaces are of constantly growing interest. Plasma‐technical procedures for the surface modification and film deposition mainly are contributed to the low pressure regime and use ion and/or plasma techniques. In particular plasma‐technological process concepts in the industrial field require adapted and scalable large area plasma sources. A new source concept, based on a coaxial structure, unites these specifications and permits plasma arrangements of nearly any required size.     

Großflächige Plasmabeschichtungen: Niederdruck oder Atmosphärendruck?

Large area plasma coatings: low pressure or atmospheric pressure? Research in the field of atmospheric pressure plasma is often motivated by the expectation of cost‐saving compared to low pressure plasma processes. A cost analysis based on plasmachemical processes which can also be performed at atmospheric pressure, however, reveals a different picture: high gas flow rates that are required for atmospheric pressure plasmas were found to cause increased costs for large‐area plasma deposition.     

Mikrowellen‐Plasmabrenner bei Atmosphärendruck

Microwave Plasma Torch at Atmospheric Pressure The development of the microwave plasma torch shows that a combination of two resonators is targeting for a reliable ignition under atmospheric pressure and stable continuous operation at high power conditions. An adapted gas management with jacket flow and good mixing can be produced by the coaxial design. The spectroscopic investigation of the torch gives information about the spatial temperature distribution in the plasma. The distribution of the OH‐rotation‐vibration band is observed in the line of sight with a high spectroscopic resolution. In an air plasma a constant core gas temperature of 3600 K is determined. It is independent of the outside parameters, like microwave power or gas flow. Only the plasma volume adapts, in order to keep the energy content constant.     

Plasmagestützte Flascheninnenbeschichtung

Application of substrate biasing for plasma enhanced inner coating of plastic bottles to improve barrier properties The article summarizes the results of a research project aiming at the improvement of the barrier performance of plastic beverage bottles by means of plasma enhanced barrier coatings. A pilot plant for the biased barrier coating of PET‐bottles was designed and successfully commissioned within the scope of the investigations. In the process, two excitation types are examined: the so‐called in‐plasma process and a single‐sided plasmaline process for the deposition of barrier coatings. Advantages as well as draw backs of both processes are investigated with respect to an industrial implementation. As a result, improvement of the barrier performance by adjustment of the substrate bias is estimated by a factor of 2‐3. At the same time, substantial challenges for the realization of the processes as well as possible approaches for their solution are identified with the support of gas flow simulations.     

Die Hochleistungsmikrowellenquelle Miro

The high‐performance microwave source Miro – Plasma characterization and applications in PECVD and combination sputtering processes To evaluate the potential of the high‐efficiency microwave source Miro 200 CI the properties of plasma processes were investigated focusing at PECVD coatings of a‐C:H‐ and SiO_x as relevant applications. The sources were also intensively characterized by plasma diagnostic methods, e.g. by optical emission spectroscopy and electrical plasma probes. The analysis of the real efficiency of individual sources with slight changes in construction could be used to come to an optimized design. The Miro sources are able to create an extensive working volume showing relative homogeneous deposition rates of currently 35μm/h for a‐C:H and 25 μm/h for SiO_x. An arrangement of multiple sources enables PECVD processes for large area coating at a pressure level close to those commonly used with PVD sources. So, post‐oxidation of sputtered layers with the Miro source could be used beneficially to obtain optical oxide layers with lower absorption. Combinations with HIPIMS sputter sources lead to efficient deposition processes of coatings for tribological applications.     

Plasmamessungen und Schichteigenschaften

Plasma Analysis and Thin Film Properties of Sputter‐ and Ionplating PVD‐Processes For a large number of thin film applications just few thin film coating processes are used in industrial scale production. For example, Magnetron Sputtering (MS), Ionplating (IP), Arc Source Ablation (AS) and technical variations of them. Recent developments allow beside traditional dc modes also the use of pulsed dc modes, as for instance in magnetron sputtering and arc source deposition. In this work the Reactive Low Voltage Ionplating (RLVIP) with pulsed substrate bias (Ionplating Plasma Assisted IPPA), DC and DC‐pulse Magnetron Sputtering and Arc source deposition in DC‐ and DC‐pulse mode is of interest concerning their plasma. Pulsing the substrate‐bias of the RLVIP (IPPA) influences film stress and optical absorption but is not easy to handle in industrial production. Pulsing the sputter processes leads to massive changes in the coating plasma and the coatings itself. And finally pulsing the arc‐current of the Arc Source Ablation processes implements advantages for lower cathode temperatures, for use of less conducting cathode materials, less droplet formation and improved chemical reactivity with oxygen.     

Beidseitige Innen‐ und Außenbeschichtung von PET‐Getränkeflaschen

Double‐sided interior and exterior coating of PET beverage bottles Plasma‐enhanced methods for the interior coating of PET beverage bottles have already been put into practice in the industry. Thereby the achieved barrier properties are limited due to defects in the coating, which emerge during the layer growth and allow a higher permeability. One possible way to improve barrier properties is the double‐sided coating. The implementation of the concept in form of a demonstrator plant is presented. By means of optical emission spectroscopy (OES) as a very versatile and easy to use method for the surveillance of industrial plasma processes, the influence of the gas composition on the plasma homogeneity and barrier properties of the coating is demonstrated. Permeation measurements are carried out, showing the potential of the combined coating process for the deposition of effective coatings.     

Beschichtung und Reinigung von Oberflächen mit Atmosphärendruck‐Plasmen. Coating and cleaning of surfaces with atmospheric pressure plasmas

Since long time dielectric barrier discharges have been in use for technical applications such as ozone synthesis and surface activation treatment of polymers for subsequent printing, pasting, or laquering. A new field of applications for these discharges is opened by their use for plasma‐based coating and cleaning processes at atmospheric pressure. By introducing gaseous monomers (like hydrocarbons, fluorocarbons, silicon‐organic compounds) into the discharge zone, coatings can be deposited on electrically conductive or insulating substrates. Barrier discharges in oxygen containing gases can also be used for the degreasing of surfaces. Owing to the possibility, to sustain barrier discharges in very small volumes, new perspectives are opened for the geometrically structured modification of chemical and physical properties of surfaces as well as for the modification or coating of internal surfaces in microfluidic devices.     

Anorganisch‐organische Hybridschichten für die Entspiegelung optischer Oberflächen

Inorganic‐organic hybrid coatings for antireflection of optical surfaces The application of nanostructures for optical surfaces has been discussed since antireflective nanostructures have been discovered on the eyes of night‐flying insects. On injection molded plastic lenses, antireflective nanostructures can easily be produced by plasma etching. The procedure has now been adapted to vacuum evaporated organic layers. Complex coatings composed of inorganic layers and organic nanostructures are especially suitable for realizing broadband antireflection properties on glass lenses.     

Abscheidung,Charakterisierung und Anwendung von Plasma‐Polymerschichten auf HMDSO‐Basis

Deposition, Characterisation and Application of HMDSO‐based Plasma Polymer Films High quality organosilicone coatings can be produced via plasma enhanced chemical vapor deposition of hexamethyldisiloxane (HMDSO). In this article aspects of deposition, analysis and application of HMDSO/O₂ processes are presented. The coatings’ organic/inorganic character can be adjusted by an appropriate combination of plasma power and gas mixture which is shown by XPS. Particularly multi layer and gradient layer systems can be deposited within the same process. Quantitative chemical depth profiling of such layer systems can be performed by secondary neutral mass spectrometry (SNMS). AFM investigations exhibit that the surface roughness of the coatings is determined by the appearance of hemispherical agglomerates, which is more pronounced, the more glass‐like the coatings are. As an example of use it is shown, that an appropriate HMDSO plasma treatment can distinctly improve the tribological behavior of elastomer devices. The presented work is done within a project of the German Federal Ministry of Education and Research (BMBF) entitled: “nano functionalization of interfaces for data‐, textile‐, building‐, medicine‐, bio‐, and aerospace‐ technology”.     

Hochselektive Absorberschichten für thermische Sonnenkollektoren

High‐selective absorber coatings for solar thermal collectors Highly selective absorber coatings are necessary for the effective operation of state‐of‐the‐art solar thermal collectors. The thin film gradient optical coating with its spectrally selective characteristics achieves high solar absorptance combined with low thermal emittance. Such complex multi‐layer systems are produced in modular vacuum coating processes. Industrial air‐to‐air coating lines allow the continuous coating of metal bands in a pass‐through process and provide absorber coatings which meet highest demands for efficiency, durability and esthetics.     

Fabrication of a Large‐Area Hierarchical Structure Array by Combining Replica Molding and Atmospheric Pressure Plasma Etching

A novel approach to produce a large‐area hierarchical structure array is presented. The method combines replica molding and atmospheric pressure plasma (APP) etching processes. Liquid blends consisting of siliconized silsesquioxane acrylate (Si‐SSQA), polyethylene glycol dimethacrylate (PEGDMA), and photoinitiator are used as roughness formable materials during APP etching. Microstructures composed of the Si‐SSQA/PEGDMA mixtures are fabricated by replica molding. Nanoroughness is realized on the microstructures by argon/oxygen (Ar/O₂) APP etching in air. The nano­roughness on molded microstructures is efficiently controlled by varying the weight ratio of Si‐SSQA to PEGDMA and the etching time. The hierarchical structures fabricated by combining replica molding and Ar/O₂ APP etching show superhydrophilicity with a long‐term stability, resulting in the formation of hydroxyl‐terminated silicon oxide layer with the reorientation limit. On the other hand, the hierarchical structures treated with a perfluorinated self‐assembled monolayer (SAM) show increased the water contact angles of up to 161° depending on the morphology of the hierarchical structures. The increment of water contact angles is consistent with increment of the nano‐/microroughness of hierarchical structures.