ICMCTF2006 Session G5: Large Area Production Coatings, Plasma Cleaning and Pretreatment of Large Surfaces
Thursday, May 4, 2006 8:30 AM in Royal Palm 4-6
G5-1 Plasma-Assisted Electrostatic Cleaning of Contamination for Nanoimprint Lithography
W.M. Lytle, M.J. Neumann, S.N. Srivastava, D.N. Ruzic (University of Illinois at Urbana-Champaign)
Nanoimprint lithography involves a mechanical process of pushing a UV-transmittable quartz mold into a thin film. When the mold is withdrawn, small amounts of contamination from the imprinted area may stay on the mold. When subsequent processing is done with a contaminated mold, feature resolution decreases and there is potential for any film processed with the contaminated mold to be defective. Currently, there is no known way to remove particles with D < 40 nm, yet nanoimprint lithography requires that the minimum defect size in the mask is only 10 nm. Accordingly a new technique has been developed: Plasma-Assisted Cleaning by Electrostatics (PACE). PACE involves using charge imbalance between the particle and the substrate to propel the nanoparticles off the surface. Through applying a pulsed bias to the substrate and using a broad-beam electron gun or pulsed plasma to charge the particles, the contamination is removed from the surface due to the momentary charge imbalance. As the contamination size decreases, the net charge to achieve the same repulsion is reduced and therefore leads to no theoretical limit on the size of the particle removed. The benefit of PACE is the quickness in which a surface may be processed since the entire surface can be cleaned at once. Results of cleaning 30nm polystyrene latex spheres from Si wafers showed nearly complete removal with no residual damage. Cleaning of quartz substrates and damage assessment of features will be reported.
G5-2 Large Area ZnO:Al Contacts for Thin Film Silicon Solar Cells
V. Sittinger, F. Ruske, B. Szyszka (Fraunhofer IST, Germany); B. Rech, G. Schöpe, H. Stiebig (Institute of Photovoltaics, Germany)
Throughout the last years strong efforts have been made to use Al-doped ZnO films on glass as substrates for amorphous or amorphous/microcrystalline silicon solar cells. The material promises better performance at low cost especially because ZnO:Al can be roughened in order to enhance the light scattering into the cell.@paragraph@ The deposition of high quality films by magnetron sputtering or alternative methods such as PLD or LPCVD has been reported repeatedly. Nevertheless the transfer to large areas is accompanied by technological difficulties. One of the most promising candidates for large area deposition of ZnO:Al is reactive magnetron sputtering of Al-doped Zn targets. Despite the need for harsh process control the possible advantages such as high deposition rates and low target cost seem to outweigh the problems.@paragraph@ At Fraunhofer IST the reactive magnetron sputtering process has been optimised in order to meet the requirements for front contacts in thin film silicon solar cells. The most crucial points in this respect are high transmittance in the visible and near-infrared, a reasonable sheet resistance and the etching behaviour. It will be shown how the ZnO material properties can be influenced by choosing adequate deposition conditions and what effects are observed in terms of cell performance.@paragraph@ The developed processes are subsequently scaled up on the In-Line coater A700V at Fraunhofer IST. A-Si/µc-Si tandem modules on 30 x 30 cm@super 2@ substrates reached initial efficiencies of up to 9.8 %.
G5-3 Current Developments Regarding Continuous Industrial Large Area EB-PVD Processes Including the Introduction of Plasma Activated Process Combinations
E. Reinhold, J. Faber, C. Steuer (VON ARDENNE Analegntechnik GmbH, Germany); Ch. Metzner, B. Scheffel (Fraunhofer FEP, Germany)
Electron beam physical vapor deposition (EB-PVD) is a well established large area coating technology. Meanwhile the coating business of finishing industries has been extended widely. This paper presents current developments regarding the deposition of large area mass products in conjunction with matched industrial conceptions of highly productive coaters. Reactive EB-PVD allows the deposition of some important compounds. Requirements on the process guidance will be discussed. Possibilities of process combinations in order to activate (reactive) EB-PVD processes will be considered. Special attention will be paid the ignition of a spotless arc discharge on EB heated materials' a process combination which is introduced as Spotless arc Activated Deposition process (SAD process). The technological capacity of reactive large area SAD will be considered with regard to advantageous applications. Coating costs will be compared with other coating technologies.
G5-5 Experimental Results for the Substrate Cooling During High-Rate PVD
J.-P. Heinss, Ch. Metzner (Fraunhofer FEP, Germany)
The problem of substrate cooling during vacuum processes, especially during high rate PVD, is often discussed in the literature. Because the temperature dominates few of the main layer and substrate properties, it is often an object in view to keep the substrate temperature in a certain level. In dependency on the heat input, the used materials and the substrate dimensions the temperature rise can be a limiting factor for the coating technology itself. In these cases it is necessary to remove the process heat at least partially by an active cooling. We have tested two different configurations: the heat transfer through a solid body contact and through a thin gas layer. We present the experimental results for the achieved heat transfer coefficients in a test device. Furthermore we represent our technical solution for the cooling of sheets and of metal strips we use in our laboratory coating equipments and discuss the cooling effects during high rate electron beam evaporation.
G5-6 Combination of Hollow Cathode- and Vacuum Arc Plasma for TiAlN- Thin Film Deposition
M. Holzherr, B. Bücken, M. Falz (VTD VAKUUMTECHNIK Dresden GmbH, Germany)
In order to provide a sufficient wear protection on tools which finally supports to increase productivity in manufacturing processes, the substrates can be coated with hard material layers. Because of its high hardness and oxygen resistance Titanium-Aluminium-Nitride (TiAlN)- hard material coatings have been applied usually for high speed cutting and minimal lubrication applications. @paragraph@ In the past many attempts to increase the performance of TiAlN- coatings had been carried out. One approach e.g. was the optimisation of the Al- content in TiAlN- thin films. The performance of the coating increases with aluminium content until a maximum value is reached when the structure changes from face centred cubic (fcc) to body centred cubic (bcc).@paragraph@ The aluminium content can be modified by the target material composition itself as well as by process parameters. E.g. it is well-known that through decreasing substrate voltage (BIAS) the Al- content in TiAlN coating is increased.@paragraph@ In the standard hard material coating process of the DREVA 600 coating plant two hollow cathode (HC -) plasma sources are being used for the in-situ pre-treatment of the substrates i.e. for electron impact heating and Ar- ion etching. Six vacuum arc (VARC-) sources provided as metal evaporation sources operate in the subsequent reactive thin film deposition process.@paragraph@ Thus, both hollow cathode plasma sources of the DREVA 600 are completely integrated into the deposition process itself. By means of optical emission spectroscopy (OES-) measurements it can be demonstrated that the additional hollow cathode plasma provides an increase of excitation and ionisation degree of the evaporated aluminium in the new TiAlN deposition process. Results, how effectively this additional HC- plasma influences the TiAlN-thin film properties will be shown.
G5-7 New Trends and Developments in Large Area PVD Coating of Metal Strips in Europe
Ch. Metzner (Fraunhofer FEP, Germany)
World wide activities for the introduction of vacuum coating in the field of surface finishing of metal strips and sheets are steadily growing. The applications are wide diversified from corrosion protection coatings e.g. for car bodies via abrasion protection layers up to optical layer stacks onto large metal surfaces. Based on new developments for PVD coating technologies and techniques especially high value products are coming more and more in the focus. In the last years our institute and European companies have developed new technologies and new layer systems for different applications. The paper gives an overview about these activities. Great progress was reached concerning our plasma activated high-rate electron beam deposition by the so called SAD and HAD processes. It was possible to develop basics for an active cooling of metal strips and sheets during the PVD coating. A continuous challenge is the process stability and the quality assurance during long term deposition. We have started new developments to solve this problem with In-situ Advanced Process Control (APC). The investigations concerning new layer stacks reach from hard coatings via transparent abrasion and scratch resistant layers up to selective solar absorbing films. The new process technologies and available equipment's are depicted. The paper gives an overview about new trends and developments in large area PVD coating of metal strips in Europe.
G5-8 Electron Beam Induced Bias for High Speed, High Conductivity Coating of Ultra Thin Capacitor Web
S. Kueper, H. Hagemann (Leybold Optics GmbH, Germany)
The main challenges in capacitor web coating are the decreasing web thickness, the increasing conductivity and the competition for higher web speeds, i.e. higher productivity. All trends require a better transfer of the heat of condensation from the evaporated material to the coating drum in order to prevent thermal damage to the web. Applying a bias voltage to the web after the actual coating is used in most of today´s coaters, but is limited by the break through voltage of the web itself. Furthermore, pinholes cause a frequent collapse of the bias and the corresponding enhanced heat transfer, which results in patches of thermally damaged web or ultimately in web tear. @paragraph@ Modern coaters use an elaborate system of charge management of the web throughout the coating system. A pre treatment station neutralizes the (changing) inherent static charge on the web and creates a steady ground state of the web from the unwinder. At the same time a surface modification of the web can be performed to promote adhesion. A scanning electron beam then applies a very high, but immobile (static) charge before coating. The resulting difference in potential between web and coating drum is an order of magnitude higher than conventional bias and results in a much higher adhesion force of the web to the drum. In consequence, the heat transfer from web to the drum is enhanced during the entire time of contact to the coating drum. This allows coating of thinner web at higher speeds with higher thickness. Finally, a post treatment station assures the complete discharge of the web on the rewinder. @paragraph@ This paper explains the principle of electron beam bias, quantitatively compares the electrical forces at work and the experimental results of web coating with traditional and electron beam bias systems. The necessary hardware is explained and production data are discussed.