Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session VF2: Capacitively Coupled Plasmas III |
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Chair: Thomas Mussenbrock, Ruhr University Room: 2a |
Friday, October 14, 2016 11:00AM - 11:15AM |
VF2.00001: On the Significance of Metastable States in Low Pressure Capacitively Coupled Oxygen Discharges Jon Gudmundsson, Holmfridur Hannesdottir We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code {\tt oopd1} to explore the spatio-temporal evolution of the electron heating mechanism in a capacitively coupled oxygen discharge in the pressure range 10 -- 200 mTorr. The electron heating is most significant in the sheath vicinity during the sheath expansion phase. We explore how including and excluding detachment by the singlet metastable states O$_2$(a$^1\Delta_{\rm g}$) and O$_2$(b$^1\Sigma_{\rm g}^+$) influences the heating mechanism, the effective electron temperature and electronegativity, in the oxygen discharge. We demonstrate that the detachment processes have a significant influence on the discharge properties, in particular for the higher pressures. At 10 mTorr the time averaged electron heating shows mainly ohmic heating in the plasma bulk (the electronegative core) and at higher pressures there is no ohmic heating in the plasma bulk, that is electron heating in the sheath regions dominates. [Preview Abstract] |
Friday, October 14, 2016 11:15AM - 11:30AM |
VF2.00002: Plasma Instability in Radio-Frequency Capacitively Coupled Discharge Kallol Bera, Ankur Agarwal, Shahid Rauf, John Forster Stationary and moving striations with spatial periodic structure have been observed in radio-frequency (RF) capacitively coupled plasmas (CCP). To understand the striation mechanism, we have incorporated thermoelectric electron energy transport effect$^{\mathrm{1}}$ in our fluid plasma model. The thermoelectric coefficient is calculated using Bolsig$+^{\mathrm{2}}$ for different chemistries, and is found to be the largest for Ar plasma. The thermoelectric effect reduces electron energy diffusion, which can localize the plasma and lead to periodic structures. To examine striations in capacitive plasmas, 2-dimensional Ar plasma at 13.5 MHz is first simulated without the thermoelectric effect. The charged species densities are then perturbed and growth or decay of different modes with time is observed. The periodicity of the structure is determined by the relative instability of different modes. Intermediate modes with periodicity of 4 to 15 cm are observed to grow while higher order modes decay. We will discuss effect of chemistry, power, pressure, and rf frequency to illustrate regimes where plasma instability may occur in typical CCP reactor geometries. $^{\mathrm{1}}$D. Mackey et. al, Appl Math Lett, p. 865, 2005. $^{\mathrm{2}}$G. J. M. Hagelaar and L. C. Pitchford, Plasma Sources Sci. Technol., p. 722, 2005. [Preview Abstract] |
Friday, October 14, 2016 11:30AM - 11:45AM |
VF2.00003: High bias voltage plasma with electron beam Inshik Bae, Hongyoung Chang A deep trench with high aspect ratio is required in the etch process, and it is well known that ion flux and energy can be independently controlled by means of dual or triple frequency. However, multi frequency capacitively coupled plasma (CCP) has a few problems to achieve high aspect ratio, such as surface charging and power coupling to bias voltage as well as interference between the frequencies. In this study, a new type of CCP, which is modified by using electron beam, is introduced. Low frequency of 400 kHz is used to generate plasma and to achieve high bias voltage in CCP. Electron beam, which is generated by thermal tungsten filament, is used to provide excess electrons. Because of excess electrons, the bias voltage of the powered electrode becomes extremely high to balance between electron and ion fluxes at the electrode. The effects of pressure, electron beam current, beam energy, and RF power in this phenomenon are carefully examined. A bias voltage which is almost same as a voltage amplitude of the RF power is obtained when enough number of electrons are supplied. This method can be used to generate high energy ions in etching process, and provides a more convenient and independent control of ion energy. [Preview Abstract] |
Friday, October 14, 2016 11:45AM - 12:00PM |
VF2.00004: Voltage vs. Current Driven CCRF Discharges: Differences in Electron and Ion Dynamics Sebastian Wilczek, Jan Trieschmann, Julian Schulze, Ralf Peter Brinkmann, Aranka Derzsi, Peter Hartmann, Zoltan Donko, Thomas Mussenbrock In numerical simulations of capacitively coupled radio frequency (ccrf) discharges the following fundamental question is unanswered: What are the implications of driving the discharge with a sinusoidal current source vs.\ a sinusoidal voltage source? Several analytical models as well as simulations use current sources as boundary conditions. Especially at low pressures, however, the theory of the self-excitation of the plasma series resonance (PSR) by the nonlinearity of the plasma sheath is eliminated when using a current source (as no harmonics in the current are allowed). In contrast, a sinusoidal voltage source can strongly enhance the power dissipation via the self-excitation of the PSR (nonlinear electron resonance heating). In this work, we investigate the differences between voltage and current driven sources with respect to the electron and ion dynamics. By means of Particle-In-Cell simulations, we analyze both scenarios for identical input powers coupled into the system. Significant differences are discussed for different parameter sets, e.g. input power (voltage and current amplitude), driving frequency and pressure. [Preview Abstract] |
Friday, October 14, 2016 12:00PM - 12:15PM |
VF2.00005: Investigation of plasma-sheath resonances in low pressure discharges Schabnam Naggary, Efe Kemaneci, Ralf Peter Brinkmann, Mustafa Megahed Plasma sheath resonances (PSR) arise from a periodic exchange between the kinetic electron energy in the plasma bulk and the electric field energy in the sheath and can easily be excited by the sheath-generated harmonics of the applied RF. In this contribution, we employ a series of models to obtain a well-defined description of these phenomena. In the first part, we use a global model to study the influence of the nonlinear charge-voltage characteristics on the electron dynamics. However, the global model is restricted to the assumption of spatially constant potential at each driven and grounded electrode and thus delivers only the fundamental mode of the current. In order to remedy the deficiency, we introduce a spatially resolved model for arbitrary reactor geometries with no assumptions on the homogeneity of the plasma. An exact evaluation of the analytical solution is realized on the assumption of a cylinderical plasma reactor geometry with uniform conductance. Furthermore, the spatially resolved model is capable of being utilized for a more realistic CCP reactor geometry and non homogeneous plasma provided the conductance distribution is known. For this purpose, we use the CFD-ACE+ tool. The results show that the proposed multi-mode model provides a significant improvement. [Preview Abstract] |
Friday, October 14, 2016 12:15PM - 12:30PM |
VF2.00006: Effect of driving frequency on the electron-sheath interaction and electron energy distribution function in a low pressure capacitively coupled plasmas Sarveshwar Sharma, Nishant Sirse, Predhiman Kaw, Miles Turner, Albert R. Ellingboe The effect of driving frequency (27.12-70 MHz) on the electron-sheath interaction and electron energy distribution function (EEDF) is investigated in a low pressure capacitive discharges using a self-consistent particle-in-cell simulation. At a fixed discharge voltage the EEDF evolves from a strongly bi-Maxwellian at low frequency, 27.12 MHz, to a convex type distribution at an intermediate frequency, 50 MHz, and finally becomes a weak biMaxwellian above 50 MHz. The EEDF evolution leads to a two-fold increase in the effective electron temperature up to 50 MHz, whereas the electron density remains constant in this range. After 50MHz, the electron density increases rapidly and the electron temperature decreases. The transition is caused by the transient electric field excited by bursts of high energy electrons interacting strongly with the sheath edge. Above the transition frequency, high energy electrons are confined between two sheaths which increase the ionization probability and thus the plasma density increases. [Preview Abstract] |
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