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search.filters.applied.f.access: openAccess × Author: van Helden, Jean-Pierre H. × End date: 2022 × Start date: 2021 × DDC: 530 × Type: Text × Version: publishedVersion × WGL Institute: INP ×

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    On the relationship between SiF4plasma species and sample properties in ultra low-k etching processes
    (New York, NY : American Inst. of Physics, 2020) Haase, Micha; Melzer, Marcel; Lang, Norbert; Ecke, Ramona; Zimmermann, Sven; van Helden, Jean-Pierre H.; Schulz, Stefan E.
    The temporal behavior of the molecular etching product SiF4 in fluorocarbon-based plasmas used for the dry etching of ultra low-k (ULK) materials has been brought into connection with the polymer deposition on the surface during plasma treatment within the scope of this work. For this purpose, time-resolved measurements of the density of SiF4 have been performed by quantum cascade laser absorption spectroscopy. A quantification of the non-linear time dependence was achieved by its characterization via a time constant of the decreasing SiF4 density over the process time. The time constant predicts how fast the stationary SiF4 density is reached. The higher the time constant is, the thicker the polymer film on top of the treated ultra low-k surface. A correlation between the time constant and the ULK damage was also found. ULK damage and polymer deposition were proven by Variable Angle Spectroscopic Ellipsometry and X-ray Photoelectron Spectroscopy. In summary, the observed decay of the etching product concentration over process time is caused by the suppressed desorption of the SiF4 molecules due to a more dominant adsorption of polymers. © 2020 Author(s).
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    Effects of Plasma-Chemical Composition on AISI 316L Surface Modification by Active Screen Nitrocarburizing Using Gaseous and Solid Carbon Precursors
    (Basel : MDPI, 2021) Jafarpour, Saeed M.; Pipa, Andrei V.; Puth, Alexander; Dalke, Anke; Röpcke, Jürgen; van Helden, Jean-Pierre H.; Biermann, Horst
    Low-temperature plasma nitrocarburizing treatments are applied to improve the surface properties of austenitic stainless steels by forming an expanded austenite layer without impairing the excellent corrosion resistance of the steel. Here, low-temperature active screen plasma nitrocarburizing (ASPNC) was investigated in an industrial-scale cold-wall reactor to compare the effects of two active screen materials: (i) a steel active screen with the addition of methane as a gaseous carbon-containing precursor and (ii) an active screen made of carbon-fibre-reinforced carbon (CFC) as a solid carbon precursor. By using both active screen materials, ASPNC treatments at variable plasma conditions were conducted using AISI 316L. Moreover, insight into the plasma-chemical composition of the H2-N2 plasma for both active screen materials was gained by laser absorption spectroscopy (LAS) combined with optical emission spectroscopy (OES). It was found that, in the case of a CFC active screen in a biased condition, the thickness of the nitrogen-expanded austenite layer increased, while the thickness of the carbon-expanded austenite layer decreased compared to the non-biased condition, in which the nitrogen- and carbon-expanded austenite layers had comparable thicknesses. Furthermore, the crucial role of biasing the workload to produce a thick and homogeneous expanded austenite layer by using a steel active screen was validated.
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    High-Performance GaAs/AlAs Terahertz Quantum-Cascade Lasers for Spectroscopic Applications
    (New York, NY : IEEE, 2020) Schrottke, Lutz; Lü, Xiang; Röben, Benjamin; Biermann, Klaus; Hagelschuer, Till; Wienold, Martin; Hübers, Heinz-Wilhelm; Hannemann, Mario; van Helden, Jean-Pierre H.; Röpcke, Jürgen; Grahn, Holger T.
    We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm$^2$. These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications. © 2011-2012 IEEE.