Plasma Chemical Processes
The research topic of “plasma chemical processes” focusses on the physics and chemistry of reactive plasma. The team develops approaches and methods for control of plasma chemical processes. This particularly also includes the determination of concentrations of charged and uncharged plasma species, its energy distribution, as well as the analysis of emissions by the plasma and the interaction of plasma with the adjacent surfaces. For this purpose, state-of-the-art infrared absorption spectroscopy methods are available, which represent a highly sensitive and accurate way for (in situ) determining molecule concentrations in plasmas and which are also capable of measuring the plasma kinetics. For examination of the processes during electric breakdown and morphology of plasmas, fast spectroscopic or imaging methods are used. The diagnostic work is supplemented by modelling and is performed in close cooperation with partners from science and industry. Its priority is the development of new methods for the control of plasmas in surface treatment or plasma chemical synthesis.
Reactive plasmas are among the most important working mediums in the industry. Plasma processes are state-of-the-art, particularly for activation, cleaning, coating and etching. Careful use of resources and compliance with ever more rigorous quality requirements are necessary for economical and environmental reasons and these aspects require research and development activities. Measuring the concentration of important plasma components, such as radicals or stable byproducts, and ascertaining their temporal behavior, enables statements to be made concerning the dominant processes, e.g. for layer deposition or for etching. Monitoring of key species, which due to their high reactivity are extremely short-lived and occur in small concentrations, gives users a unique tool for controlling plasmas with which the process is optimized and the treatment results become reproducible. This approach has already been successfully implemented in the semiconductor industry.
The plasma nitriding method is one of the most important methods for mediating a higher surface hardness of workpieces. Higher surface hardness increases resistance to abrasive, adhesive and corrosive wear of these components. Together with our partner Freiburg University of Mining and Technology, at the INP a new procedure for nitriding is being developed that should overcome the disadvantages of the existing technology. Through an innovative process design, so-called active screen plasma nitriding avoids effects (hollow cathode effect, arcing, boundary effects) that result in an inhomogeneous machining of the workpiece, e.g. through localized melting or sputtering. For this procedure the INP is working out a new process control based on infrared laser absorption spectroscopy, that is coupled with the electrical power supply. The essential main species in this process has already been identified. Its concentration constitutes a control parameter that enables active adaptation of process conditions, and thus the optimization of the hardening process.
High-accuracy verification of gases in very low concentrations is important in the medical sector, for environmental protection, in safety technology and in many other areas. Unlike other measurement methods in special laboratories, analysis of trace gases via laser absorption spectroscopy offers many advantages, such as fast measuring times and low detection limits. This method also offers clear measurement results without interfering cross-sensitivities. For realization of high sensitivities, extending down into the ppt range, methods are used at the INP that combine modern infrared laser light sources and optical resonators. After successfully validating the suitability of this technology for provision of compact transportable, ultra-sensitive, multi-component trace gas sensors, currently a prototype based on this technology is being developed at the INP as part of a transfer project.
Atmospheric pressure plasmas are increasing in significance, and are opening up new application fields, such as plasma synthesis, plasma medicine or decontamination. However, due to their characteristics, it is difficult to make statements concerning composition of these plasmas, and other important plasma parameters. Classic plasma diagnostic methods are either unusable or they can only be used with limitations due to the high density, high collision rates and short lifetimes. Modern imaging and spectroscopy methods (e.g. streak camera, time-correlated single-photon counting) offer the possibility of analyzing electrical breakdown and making statements concerning the strength of the electric field. Here important contributions can be made towards interpreting and controlling these sources. Moreover, in cooperation with Oxford University, the INP succeeded in detecting the hydrogen peroxl radical in the effluents of a non-thermal argon plasma jet in air, via optical feedback cavity-enhanced absorption spectroscopy method. This method makes available the high sensitivity desired for detection of reactive, short-lived species, and consequently should be further extended in the future, to help explain the active mechanisms and develop approaches for process control.
As part of the DFG-funded project "Development of new plasma-assisted processes for thermochemical surface treatment of ferrous materials with an active grid made of carbon", the basics for the development of a new process for the surface treatment of ferrous materials with an active grid made of carbon-reinforced carbon (CFC) are to be developed in cooperation with the TU Bergakademie Freiberg. The aim of the project is to investigate the main mechanisms of this plasma diffusion treatment in various media, especially carbon-containing media. For this purpose, IR absorption and optical emission spectroscopy are applied to a laboratory reactor at the INP as well as to an industrial plant at the TU Freiberg in order to analyze the plasma-chemical reactions in connection with the achieved treatment results. Based on this in situ parameters for the controlled generation of carburized and nitrocarburized boundary layers with defined properties and for safe process control will be deduced.
Prof. Jürgen Röpcke
Phone: +49 3834 - 554 444
In its research and innovation funding program KMU-Innovativ Photonik, the BMF supports the collaborative project "Innovative plasma nitriding through dynamic process control using optical frequency combs (InPro-F)". At the INP, the sub-project "High-resolution VIPA detection system for dynamic process control" is being processed. The network consists of the companies Menlo Systems GmbH, neoplas control GmbH and RÜBIG GmbH & Co. KG. The aim of the project is to develop a demonstrator of an optical measurement and control system based on frequency comb laser spectroscopy, which is suitable for the process control of a plasma-assisted nitriding or nitrocarburizing process under industrial conditions. The project result is intended to bring about a technological leap forward for the plasma-assisted nitriding and nitrocarburizing processes by introducing a controlled procedure based on in-situ concentration measurements of molecular plasma species for the first time.
Dr. Norbert Lang
Phone: +49 3834 - 554 452
The aim of the joint project funded by Eurostars is a new compact optical sensor system in the mid infrared for in-situ process monitoring in the semiconductor industry, environmental and exhaust gas monitoring. The innovative approach is based on the use of special Fabry-Perot quantum cascade lasers with previously unattainable properties in terms of spectral tuning range and tuning rate. The consortium consists of the companies Alpes Lasers SA and neoplas control GmbH as well as the research centers Center Suisse d’Electronique et de Microtechnique (CSEM) and INP. The aim of the sub-project is to utilize and evaluate the desired innovative tuning properties of this new type of laser for a spectroscopic measuring system. On the one hand, this requires the development of a control method for the laser that is specifically tailored to the level-crossing chirp behavior. Furthermore, special requirements with regard to the detection of these lasers must be taken into account and implemented. The demonstration setup to be developed will enable both in-situ measurements on plasma processes, such as etching processes in the semiconductor industry, and extractive measurements on gas samples, as are common in environmental monitoring or breathing gas control.
Dr. Norbert Lang
Phone: +49 3834 - 554 452
In this project funded by the DFG, the INP is working with the Institute for Energy Technology at the TU Berlin on the detailed and quantitative analysis of the pyrolysis of wood particles. These basic data are intended to close gaps in the understanding of the pyrolysis mechanism, which are of great importance for every thermochemical conversion process. The main result will be to include heterogeneous side reactions in the pyrolysis kinetics mechanism of wood particles, i.e. to determine not only the influence of these reactions on the volatile composition, but also on the reaction enthalpies and the process kinetics. In-situ laser spectroscopic methods such as infrared laser absorption spectroscopy and laser-induced fluorescence are used to determine the gas composition in close vicinity of the surface of a pyrolyzing wood particle (on a technically relevant cm scale) in a spatially and time-resolved manner.
Prof. Jürgen Röpcke
Phone: +49 3834 - 554 444
The project "Terahertz Detection of Atoms in Plasma Processes" aims at the development of spectroscopic methods in the terahertz (THz) spectral range for the determination of the absolute density of atoms and ions for a variety of species in technologically relevant plasma processes such as plasma-aided deposition of AlN and Si-based films. The joint proposal brings together the expertise of the Paul-Drude-Institut für Festkörperelektronik in the field of manufacturing customized THz quantum-cascade lasers for spectroscopic applications and of the Leibniz-Institut für Plasmaforschung und Technologie in the field of spectroscopic plasma diagnostics. Our novel approach is based on the detection of hyperfine transitions of the ground state in metal atoms and ions in the THz spectral range using quantum-cascade lasers. These lasers can be conveniently used in coolant-free Stirling coolers allowing for a compact setup. For the detection of Si, Al, N+, and O, single-mode quantum-cascade lasers emitting at 2.31, 3.36, 3.92, and 4.75 THz, respectively, will be developed and manufactured. Frequency combs spanning the spectral range from 3.3 to 4.0 THz will be developed for the simultaneous detection of Al and N+ allowing for a compact process control system based on dual-comb spectroscopy for the deposition of AlN films.
Dr. Jean-Pierre van Helden
Phone: +49 3834 - 554 3811
The aim of this DFG-funded project is the investigation of individual discharges in dielectric barrier discharges (DBDs) in multi-filament arrangements. For this purpose, individual discharges in a multi-filament arrangement will be characterized and the interaction of the filaments will be analyzed, while to entire discharge, i.e. the sum of all filaments is considered. Since the plasma chemical reactions are initiated by the physical processes in the single filaments, pulsed DBDs offer the possibility to influence and control certain plasma parameters in such a way that plasma chemical processes can be initiated more selectively and efficiently. Since a large number of filaments occur simultaneously in DBD reactors used in applications, it has to be clarified whether the existing knowledge from the single filament can be transferred to such arrangements. Furthermore, it has to be investigated how the electrical breakdown and the discharge development are influenced by the mutual influence of volume and surface processes in multifilament arrangements in order to work out possible correlations of discharge physics and plasma chemistry.
Dr. Hans Höft
Phone: +49 3834 - 554 3926
The subject of this DFG project is the model-based analysis of spatial layer structures as well as spontaneous mode transitions and instabilities in dielectric barrier discharges at atmospheric pressure. For this purpose, a self-consistent hydrodynamic plasma model for the time-dependent, spatially two-dimensional description of a single-filament discharge in argon at atmospheric pressure is developed and used to explore experimentally observed phenomena. The main aim is to gain a deeper physical understanding of the influence and mode of action of external discharge parameters such as voltage amplitude and frequency as well as the effect of gas impurities on the stability of the discharge by means of parameter studies based on statistical test planning. Finally, the input sizes can be optimized and various discharge modes can be controlled and therefore, be used for applications.
Dr. Markus Becker
Phone: +49 3834 - 554 3821