Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session PW2: Capacitively Coupled Plasmas IILive
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Chair: Xiaopu Li, Applied Materials |
Wednesday, October 7, 2020 1:00PM - 1:30PM Live |
PW2.00001: Electron power absorption in capacitive RF plasmas based on a moment analysis of the Boltzmann equation Invited Speaker: Mate Vass Low temperature capacitively coupled RF plasma sources (CCPs) are important tools for various industrial applications. Efficient knowledge-based optimisation of these plasma processes requires a detailed understanding of the complete electron power absorption mechanisms. In this work, a spatio-temporally resolved and self-consistent analysis of the electron power absorption dynamics is presented for various gases and discharge conditions. We apply our analysis to unmagnetized electropositive (argon) [1-2] and electronegative (oxygen) [3], as well as to magnetized low pressure CCPs [4]. The analysis is based on a study of the first velocity moment of the Boltzmann-equation using information taken from 1d3v Particle-In-Cell/Monte Carlo Collision simulations. We revisit some of the well known models of electron power absorption in CCPs (e.g. {\it `collisionless'/`stochastic' heating}, {\it `Ohmic heating'}, etc.) and show that they do not provide a full and self-consistent understanding, and can lead to misleading results. To obtain a full understanding, the total electron power absorption is divided into four mechanisms: pressure, Ohmic, inertial and magnetic power absorption. Surprisingly, at very low pressure we find {\it `Ohmic heating'} to be the dominant power absorption mechanism as a consequence of the attenuation of {\it `Pressure heating'}. The power absorption dynamics of secondary electrons are studied and the effect of externally applied magnetic fields on the acceleration of electrons is also addressed. \noindent This work has been conducted in close cooperation with Sebastian Wilczek, Li Wang, Trevor Lafleur, Ralf Peter Brinkmann, Zolt\'an Donk\'o and Julian Schulze.\\ \noindent [1] Schulze J et al. 2018 {\it Plasma Sources Sci. Technol.} {\bf 27}(5) 055010\\ \noindent [2] Vass M et al. 2020 submitted to PSST\\ \noindent [3] Vass M et al. 2020 {\it Plasma Sources Sci. Technol.} {\bf 29} 025019\\ \noindent [4] Wang L et al. 2020 submitted to PSST [Preview Abstract] |
Wednesday, October 7, 2020 1:30PM - 2:00PM Live |
PW2.00002: Kinetic Modeling of Low-Pressure Multi-Frequency Capacitively Coupled Plasmas Invited Speaker: Shahid Rauf Low pressure (\textless 20 mTorr) capacitively coupled plasmas (CCP) are widely used for dielectric etching in the semiconductor industry. These plasma discharges are often used with multiple radio frequency (RF) generators and RF power can be high. Kinetic effects dominate the behavior of these discharges due to the low gas pressure and high voltages. This paper focuses on particle-in-cell modeling of low-pressure multi-frequency CCPs. A combination of 1-dimensional (1D) and 2-dimensional (2D) models in both Cartesian and cylindrical geometry are used to understand the physics of these plasmas and examine technological issues. 2D model of the Gaseous Electronics Conference (GEC) reference cell is first used to validate the underlying model using experimental measurements of electron density and DC self-bias voltage at 100 mTorr. The plasma density peaks at the electrode edge at 100 mTorr in the GEC reference cell. The model is then extended to lower pressures and it is shown that enhanced diffusion leads to the peak in plasma density moving to the chamber center at pressures below 50 mTorr. A larger plasma system is next modeled with a combination of very high frequency (VHF) and medium frequency (MF) RF sources. As expected, application of the MF voltage increases the ion energy at the substrate. However, the MF source also influences plasma density and uniformity. 1D models are used to understand some of the kinetic effects that dominate the operation of low pressure CCPs. 1D model of a single frequency discharge is first used to illustrate the transition of electron transport from fluid-like at 100 mTorr to fully ballistic at sub-25 mTorr pressures. 1D models of multi-frequency discharges are then used to examine issues related to ion energy distribution function (IEDF) control. The use of non-sinusoidal MF voltages for IEDF control is also studied. [Preview Abstract] |
Wednesday, October 7, 2020 2:00PM - 2:15PM Live |
PW2.00003: Fluid Modeling of Capacitively Coupled Radio-frequency Discharge Over a Wide Range of Frequencies Han Luo, Andrei Khomenko, Sergey Macheret A parallel-plate capacitively coupled radio-frequency (CCRF) discharge in air and argon in a wide range of frequencies (25-165 MHz) was simulated with fluid model using drift diffusion approximation and local mean energy assumption. Different combinations of the boundary conditions and reaction mechanisms were used and the results compared with in-house experimental results. The calculated electron number densities, reactances and sheath thicknesses are in good agreement with the experimental results. A decoupled simulation of chemistry of neutral species in air plasma on a long (millisecond) time scale shows that under the conditions of experiments at a pressure on the order of 1 Torr the losses of atomic oxygen are due to diffusion and surface recombination, and that the mole fraction of atomic oxygen reaches about 1{\%}. [Preview Abstract] |
Wednesday, October 7, 2020 2:15PM - 2:30PM Live |
PW2.00004: Simulation of a capacitively coupled plasma micro-thruster using the particle-in-cell method. Michael May, Andrew Powis, Igor Kaganovich A radio-frequency (13.56MHz) capacitively coupled plasma (CCP) micro-thruster was simulated in two dimensions by an electrostatic particle-in-cell (PIC) method, using a PPPL-modified version of the commercial LSP code [1]. At the gas valve, the gas pressure is high, up to 5 Torr, and the discharge can operate at high voltages, up to 400 V in argon. Results were benchmarked against the previous 2D fluid simulations of ref. [2] and validated by comparison with the experimental data of ref. [3]. Results show plasma properties depend strongly on the secondary electron emission from walls and dielectric thickness separating electrodes from the plasma. [1] A.T. Powis, J.A. Carlsson, I.D. Kaganovich, Y. Raitses, and A. Smolyakov, \textit{Physics of Plasmas}~\textbf{25}, 072110 (2018). [2] A. Greig, C. Charles, and R. W. Boswell, \textit{Frontiers in Physics}~\textbf{2}, 80 (2015). [3] C. Charles and R. W. Boswell,~\textit{Plasma Sources Sci. Technol~}\textbf{21,~}022002 (2012). [Preview Abstract] |
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