Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session QR1: Capacitively Coupled Plasmas |
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Chair: Julian Schulze, Ruhr University Bochum Room: Oregon Convention Center A103-A104 |
Thursday, November 8, 2018 2:00PM - 2:30PM |
QR1.00001: Electron heating in electronegative capacitively coupled discharge of complex chemistry Invited Speaker: Jon Tomas Gudmundsson A brief overview is given on the development of a comprehensive reaction set for the oxygen discharge for particle-in-cell Monte Carlo collision (PIC/MCC) simulations. A particular attention is given to the creation and destruction of the negative ion O$^-$. Then the one-dimensional object-oriented PIC/MCC code {\tt oopd1}, using this comprehensive reaction set, is applied to explore the charged particle density profiles, the electron heating mechanism and the electron energy probability function (EEPF) in a single frequency capacitively coupled oxygen discharge. We explore how including and excluding detachment by the singlet metastable molecules O$_2$(a$^1\Delta_{\rm g}$) and O$_2$(b$^1\Sigma_{\rm g}$) influences the electron heating mechanism and the discharge electronegativity. We demonstrate that the detachment processes have a significant influence on the discharge properties, in particular at the higher operating pressures ($> 30$ mTorr) [1,2]. We show that for low driving frequency and low pressure (5 and 10 mTorr), a combination of stochastic ($\alpha$-mode) and drift ambipolar (DA) heating in the bulk plasma (the electronegative core) is observed and the DA-mode dominates the time averaged electron heating [3]. As the driving frequency or pressure are increased, the heating mode transitions into a pure $\alpha$-mode, where electron heating in the sheath region dominates [3]. This transition coincides with a sharp decrease in electronegativity. Furthermore, we demonstrate that the electrodes surface quenching coefficient has a significant influence on the density of the singlet metastable O$_2$(a$^1\Delta_g$) and thus the discharge electronegativity and electron heating mechanisms [4]. [1] J. T. Gudmundsson and M. A. Lieberman, Plasma Sources Sci. Technol. {\bf 24}, 035016 (2015) [2] J. T. Gudmundsson and B. Vent{\'e}jou, J. Appl. Phys. {\bf 118}, 153302 (2015) [3] J. T. Gudmundsson, D. I. Snorrason and H. Hannesdottir, Plasma Sources Sci. Technol. {\bf 27}, 025009 (2018) [4] A. Proto and J. T. Gudmundsson, Plasma Sources Sci. Technol. accepted for publication 2018 [Preview Abstract] |
Thursday, November 8, 2018 2:30PM - 2:45PM |
QR1.00002: Spatio-temporal analysis of the electron power absorption in electropositive capacitive RF plasmas based on moments of the Boltzmann equation Julian Schulze, Zoltan Donko, Trevor Lafleur, Sebastian Wilczek, Ralf Peter Brinkmann We present an analysis that provides a detailed understanding of the spatio-temporal electron power absorption dynamics in low pressure electropositive capacitive RF plasmas. The method is based on the moments of the Boltzmann equation, takes input quantities from kinetic PIC/MCC simulations, and does not use any ad-hoc assumptions. It allows the identification of \textit{all} physical mechanisms and an accurate quantification of their contributions. In contrast to some widely accepted previous models we find that high space- and time-dependent ambipolar electric fields outside the sheaths play a key role in the electron power absorption. This ambipolar field is time-dependent within the RF period and temporally asymmetric, i.e., the sheath expansion is not a 'mirror image' of the sheath collapse. This time-dependence is mainly caused by a time modulation of the electron temperature resulting from the energy transfer to electrons by the ambipolar field itself during sheath expansion. This mechanism of electron power absorption, which is markedly different from the Hard Wall Model, is of key importance for energy transfer to electrons on time average and is essential for the generation of capacitively coupled plasmas. [Preview Abstract] |
Thursday, November 8, 2018 2:45PM - 3:00PM |
QR1.00003: Striations in dual-frequency capacitively coupled CF\textunderscore 4 plasmas Yong-Xin Liu, Ihor Korolov, Edmund Schungel, Zoltan Donko, Julian Schulze, You-Nian Wang Striations in dual-frequency (8/40 MHz) capacitively coupled CF\textunderscore 4 plasmas have been investigated by Phase Resolved Optical Emission Spectroscopy (PROES) and via particle in cell/Monte Carlo collision (PIC/MCC) simulations. The properties of the striated structures as a function of the high-frequency voltage amplitude, $\phi $\textunderscore H, have been analyzed. The measured spatiotemporal electronic excitation patterns at different $\phi $\textunderscore \textunderscore H showed good agreement with the simulation results. As $\phi $\textunderscore H increased, the width of each ion density peak increased, while the striation gap (i.e., the distance between adjacent ion density peaks) remained nearly unchanged, leading to a decrease in the number of striations and, finally, to their disappearance at a certain $\phi $\textunderscore H. In the presence of striations, the maximum ion density inside the bulk was found to increase slightly with $\phi $\textunderscore H, while the minimum ion density was almost independent of $\phi $\textunderscore H, as it is primarily determined by the lower excitation frequency, and is almost unaffected by $\phi $\textunderscore H. A hysteresis associated with the striated - DA (drift ambipolar) mode transition induced by increasing and decreasing $\phi $\textunderscore H has been observed both in the experiments and in the simulations. [Preview Abstract] |
Thursday, November 8, 2018 3:00PM - 3:15PM |
QR1.00004: Self-excited plasma series resonance driven by Gaussian type pulses in capacitively coupled plasmas Li Wang, De-Qi Wen, Yuan-Hong Song, You-Nian Wang Using a Particle In Cell/Monte Carlo collision (PIC/MCC) model, we investigate the effects of PSR oscillations on the discharge properties in a Gaussian type pulse driven Argon plasma. The effects of the gas pressure, voltage amplitude, and pulse width on the resonance characteristics are also examined. When appropriate parameters are imposed, high frequency oscillations are excited between the capacitive sheaths and the inductive bulk plasma, which could greatly enhance the spatiotemporal performances of the electron power absorption, ionization rate, and electric field. It is further found that the PSR oscillations exhibit a strong dependence on the plasma properties, such as the sheath width and electron density. This dependence gives rise to the control of the resonance frequency by the external parameters. By applying Fourier analysis on the sheath voltage, the resonance frequency is found to increase with the enlargement of the voltage amplitude, while approximately be inversely proportion to the Gaussian pulse width. Besides, the PSR oscillations decay rapidly as the pressure increases due to the enhanced collisional damping. [Preview Abstract] |
Thursday, November 8, 2018 3:15PM - 3:30PM |
QR1.00005: Breakdown at chamber wall in ICP/CCP PECVD plasma caused by higher harmonics Michael Klick A serious problem in ICPs at low pressure for deposition of dielectric layers (HDP-PECVD) is the occurrence of electrical breakdowns at the inner wall of the process chamber. In a production chamber where this was found, such an event has a strong influence on the yield of the wafer. Chamber materials, mainly Al, is melted out of the chamber wall, negatively charged in the plasma, jumps as a hot, liquid Al ball across the wafer and remains finally at the wafer surface. This is shown by REM pictures and breakdown movies. Due to the loss of yield, it is important to detect arcing in real time and to eliminate its root cause. The occurrence of arcing is verified by an asymmetry parameter of the plasma which is calculated from the chamber wall current within the SEERS algorithm. It can be understood as the ratio of the RF voltages across the boundary sheath at the grounded chamber wall and the wafer at hot (RF driven) electrode. The asymmetry responds with a strong peak if the arcing occurs which enables arcing detection in real-time. It was found that the probability of this plasma-driven breakdown is higher at low pressure process conditions, i.e. this method should be also applicable on dry etch processes which run with lower pressure usually. It will be demonstrated that this was driven by higher harmonics of the 13.56 MHz potential of the wafer electrode. The exchange of RF components, strictly RF matchbox, influences the amount of harmonics and so the probability of the breakdowns. There are some potential mechanisms, there discussed which in simple 2d plasma model showing a spatial variation of the harmonic content of the sheath voltage at the wall. [Preview Abstract] |
Thursday, November 8, 2018 3:30PM - 3:45PM |
QR1.00006: Electrical Asymmetric Effect in Very High Frequency Capacitively Coupled Plasma Source using Electromagnetic Plasma Model Xiaopu Li, Kallol Bera, Shahid Rauf, Ken Collins Capacitively coupled plasmas (CCP) are widely used for semiconductor material processing. One of the challenges for advanced material processing using CCP discharges is the flexibility of tuning species fluxes and energies. Recently, electrical asymmetric effect (EAE) has been studied [1, 2], where separate control of ion flux and ion energy is achieved by applying a fundamental frequency and its higher harmonics. In the present study, EAE is investigated by tailored-waveform excitations in the very high frequency (VHF) regime where electromagnetic effect becomes significant. A fully coupled electromagnetic plasma model is used to evaluate EAE in a CCP discharge. The fluid plasma model computes species densities and fluxes, as well as the plasma current density. The electromagnetic phenomena are described by the Maxwell equations with the plasma current density updated from the fluid model. The finite difference time domain (FDTD) technique is used to discretize the Maxwell equations. A geometrically asymmetric Ar discharge is excited using the VHF source and its harmonics. The phase between the excitation frequency and its harmonics has been modulated to control the electrical asymmetry for different spacing and pressures. This study provides a fundamental understanding of EAE that is important to achieve flexible control of ion fluxes and energies in VHF CCP discharges. 1. U Czarnetzki et al, J. Phys.: Conf. Ser. 162 012010 (2009) 2. T Lafleur, 2016 Plasma Sources Sci. Technol. 25 013001 (2016) [Preview Abstract] |
Thursday, November 8, 2018 3:45PM - 4:00PM |
QR1.00007: Electromagnetic PIC Simulations of VHF CCP discharges having cylindrical geometry Denis Eremin, Frederick Schmidt Following the needs of plasma processing industry, modern CCP reactors have much larger electrode radius compared to the older analogs to increase the processed area and often include a very high frequency harmonic in the driving spectrum in order to increase the ion flux. Both lead to emergence of new effects not known in the physics of smaller CCPs, such as the excitation of modes intrinsic to such plasma-filled reactors and modification of the field patterns due to the skin effect in high power regimes, which is typically connected to strong plasma nonuniformities. In this work we simulate these effects with a fully implicit energy-conserving electromagnetic PIC code in 2D (r,z) realistic cylindrical geometry and explore them in detail for several typical CCP regimes. [Preview Abstract] |
Thursday, November 8, 2018 4:00PM - 4:15PM |
QR1.00008: A method for coupling lumped element circuits to plasma simulations Frederik Schmidt, Tobias Gergs, Thomas Mussenbrock, Jan Trieschmann External lumped element circuits such as matching networks, filter elements and generators are necessary for most plasma applications to function properly. In various experimental studies it has been shown that these elements interact with the plasma in a nonlinear way. Many plasma simulations do not include external circuits though for various reasons. One of them being, that including the external circuits in the form of Kirchhoff's differential equations can become cumbersome, especially for large circuits. In this work a simulation approach is proposed based on Harmonic Balance Analysis that allows for principally arbitrary plasma simulations to be coupled to external circuits, while avoiding to solve Kirchhoff's equation by hand. The method is studied at the example of an equivalent circuit plasma model and compared to a transient simulation of the system. [Preview Abstract] |
Thursday, November 8, 2018 4:15PM - 4:30PM |
QR1.00009: Analysis of the power dissipation in a lumped element model for capacitive discharges Dennis Engel, Laura Kroll, Schabnam Naggary, Ralf Peter Brinkmann Capacitively coupled plasmas (CCPs) are widely used in material processing and other applications. Despite several decades of research, not all important physical processes are fully understood. Modelling and simulation approaches help to get a better insight. Spatially resolved models like particle-in-cell simulation, kinetic, or fluid models are generally computational expensive. Global models, in contrast provide a simple understanding of CCPs with comparatively little effort. \\ This work revisits an existing lumped element model [1], in which the plasma bulk is represented by a lossy inductor and the sheath by a non-linear capacitive diode, employing a matrix sheath model. Ziegler et al. [2] used this model to calculate the power dissipation inside the plasma bulk. However, a closer analysis shows that the matrix sheath assumption leads to inconsistencies. Here, an improved sheath model applied to analyze the power dissipation. The outcome is remarkably different from that of the former model. \\[1ex] [1] T. Mussenbrock et al., PSST \textbf{16}, 377–385 (2007)\\{} [2] D. Ziegler, T. Mussenbrock, R. P. Brinkmann, Physics of Plasmas \textbf{16}, 023503 (2009) [Preview Abstract] |
Thursday, November 8, 2018 4:30PM - 4:45PM |
QR1.00010: Investigation of the electron and the ion kinetics in a capacitively coupled Ar plasma of intermediate pressue regime Jin Seok Kim, Ho Jun Kim, Hae June Lee In semiconductor fabrications, capacitively coupled plasmas (CCPs) are widely used to etching and deposition processes. However, they have non-uniform plasma density and temperature distributions with a high plasma density near the edge which results in non-uniform etching or deposition profiles. In this study, we investigate the electron energy probability function (EEPF) from the center to the edge of ~a CCP at a pressure of Torr regime using a two-dimensional particle-in-cell simulation. In a narrow gap CCP, the EEPFs in the center of the CCP have three temperatures. However, Druyvesteyn-like EEPFs occur with lots of step-ionizations which result in high plasma density near the edge. In a long gap CCP, the shapes of EEPFs are similar to those of a short gap CCP at different locations. However, the mean energy of low-energy electrons at the edge is higher than that at the center. It is caused by a lateral electric field near the edge of CCPs. Also, the ion energy distribution functions on the wafer are analyzed wih the change of electrode gap spacing. [Preview Abstract] |
Thursday, November 8, 2018 4:45PM - 5:00PM |
QR1.00011: Dynamics of Multiple Ion Species in Low Pressure Capacitively Coupled Argon-Xenon Discharges Maximilian Klich, Sebastian Wilczek, Ralf Peter Brinkmann, Jesper Janssen, Thomas Mussenbrock, Jan Trieschmann Industrial plasma applications require an accurate control of the ion energy at the substrate surfaces. At the same time, these plasmas contain various gas and ion species, which may imply a complex chemistry. The control of the kinetics of multiple gas and ion species is a topic of current research. We investigate a low pressure argon-xenon discharge by means of Particle-In-Cell/Monte Carlo Collision (PIC/MCC) simulations. The advantage of this noble gas mixture lies in its feasible amount of species and a corresponding simple chemistry. A symmetric capacitively coupled radio-frequency (CCRF) discharge is investigated for a variety of discharge parameters. It is found that a separate control of argon and xenon ions cannot unconditionally be achieved under these conditions. This conclusion is drawn from simulated quantities such as the plasma and ion densities, the fluxes toward the surfaces, the discharge energy balance and, in particular, the ion energy distribution functions (IEDFs) at the electrodes. With the obtained knowledge, it is possible to obtain insight into the formation of complex structures in the IEDFs in plasmas with multiple ion species (e.g., influence of charge transfer collisions). [Preview Abstract] |
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