Modeling of Atmospheric-Pressure Dielectric Barrier Discharges in Argon with Small Admixtures of Tetramethylsilane
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Modeling of Atmospheric‑Pressure Dielectric Barrier Discharges in Argon with Small Admixtures of Tetramethylsilane Detlef Loffhagen1 · Markus M. Becker1 · Andreas K. Czerny2,3 · Claus‑Peter Klages2 Received: 30 June 2020 / Accepted: 19 August 2020 © The Author(s) 2020
Abstract A time-dependent, spatially one-dimensional fluid-Poisson model is applied to analyze the impact of small amounts of tetramethylsilane (TMS) as precursor on the discharge characteristics of an atmospheric-pressure dielectric barrier discharge (DBD) in argon. Based on an established reaction kinetics for argon, it includes a plasma chemistry for TMS, which is validated by measurements of the ignition voltage at the frequency f = 86.2 kHz for TMS amounts of up to 200 ppm. Details of both a reduced Ar-TMS reaction kinetics scheme and an extended plasma-chemistry model involving about 60 species and 580 reactions related to TMS are given. It is found that good agreement between measured and calculated data can be obtained, when assuming that 25% of the reactions of TMS with excited argon atoms with a rate coefficient of 3.0 × 10−16 m3 ∕s lead to the production of electrons due to Penning ionization. Modeling results for an applied voltage Ua,0 = 4 kV show that TMS is depleted during the residence time of the plasma in the DBD, where the percentage consumption of TMS decreases with increasing TMS fraction because only a finite number of excited argon species is available to dissociate and/or ionize the precursor via energy transfer. Main species resulting from that TMS depletion are presented and discussed. In particular, the analysis clearly indicates that trimethylsilyl cations can be considered to be mainly responsible for the film formation. Keywords Dielectric barrier discharges · Tetramethylsilane · Numerical modeling · Plasma polymerization
* Detlef Loffhagen loffhagen@inp‑greifswald.de 1
Leibniz Institute for Plasma Science and Technology, Felix‑Hausdorff‑Str. 2, 17489 Greifswald, Germany
2
Institute for Surface Technology, Technische Universität Braunschweig, Bienroder Weg 54 E, 38108 Braunschweig, Germany
3
Present Address: Institute of Applied Materials ‑ Applied Material Physics, Karlsruhe Institute of Technology, Herrmann‑von‑Helmholtz‑Platz 1, 76344 Eggenstein‑Leopoldshafen, Germany
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Plasma Chemistry and Plasma Processing
Introduction Tetramethylsilane (TMS, (CH3 )4 Si ), one of the most simple organosilicon compound (organosilane, alkylsilane), has frequently been used as a precursor for plasma-enhanced chemical vapor deposition (PECVD) of silicon- and carbon-containing thin films [1–11]. The deposition process is also termed “plasma polymerization”—and the deposits “plasma polymer”—if a relatively large “organic” character of the precursor (monomer) is retained in the film, observable, e.g., as a major content of CHx moeities. Aside from other potential purposes, TMS-derived thin films have been of interest as insulators with low dielectric constants for microelectronic applications (“lo
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