Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session ER4: Capacitively Coupled Plasmas II |
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Chair: Li Wang, Ruhr University Bochum, Germany Room: Sendai International Center Hagi |
Thursday, October 6, 2022 1:30PM - 1:45PM |
ER4.00001: Experimental and computational study of the electron power absorption in capacitively coupled neon-oxygen plasmas Aranka Derzsi, Peter Hartmann, Mate Vass, Benedek Horvath, Marton Gyulai, Ihor Korolov, Julian Schulze, Zoltan Donko Phase Resolved Optical Emission Spectroscopy measurements combined with 1d3v Particle-in-Cell/Monte Carlo Collisions simulations were used to study the electron power absorption in capacitively coupled plasmas in mixtures of neon and oxygen. A wide pressure range (15 Pa - 500 Pa) and a wide mixing range of Ne and O2 gases (10% - 90%) were considered for a geometrically symmetric plasma reactor with a gap length of 2.5 cm, operated at a driving frequency of 10 MHz and a peak-to-peak voltage of 350 V. Based on the emission / excitation patterns, multiple operation regimes were identified. Localized bright emission features at the bulk boundaries, caused by local maxima in the electronegativity were found at high pressures and high O2 concentrations. The relative contributions of the ambipolar and the Ohmic electron power absorption were found to vary strongly with the discharge parameters. It was found that the power deposition within the gas causes only a slight increase of the gas temperature above the temperature of the electrodes, which was, however, found to be significant due to the heating of the electrodes by the particles from the plasma. |
Thursday, October 6, 2022 1:45PM - 2:00PM |
ER4.00002: Effect of voltage waveform tailoring and an additional 60 MHz frequency on the ion flux energy distribution function in a low pressure capacitively coupled radio frequency plasma Gerrit Hübner, Ihor Korolov, Stefan Ries, Soheil Karimi Aghda, Jochen M Schneider, Jan Trieschmann, Thomas Mussenbrock, Julian Schulze, Peter Awakowicz, Tobias Gergs Low pressure capacitively coupled radio frequency plasmas are widely used for etching and coating of large-area substrates, e.g., photovoltaic solar cell panels and coated glass windows for skyscrapers. The main challenges are to control the ion energy distribution at the electrode and to achieve a high uniformity of the coating properties at high process rates. In this work we use a multi frequency CCP apparatus. The plasma is ignited between two plane parallel electrodes with diameter of 490 mm and a gap of 75 mm. The discharge is operated in an Ar/N2 mixture at pressures ranging from 0.5 Pa -2 Pa and driven by a tailored voltage waveform (13.56 MHz and 27.12 MHz) with an additional 60 MHz frequency to control the ion flux. We use an array of retarding field energy analysers to measure the ion energy distribution function (IEDF) and the ion flux at the grounded electrode and study the uniformity over the surface. Utilizing the electrical asymmetry effect via voltage waveform tailoring, the uniformity and the properties of the coatings can be controlled, as confirmed by simulations of the gas-phase transport and the surface kinetic processes. Furthermore, by applying the additional 60 MHz voltage, further control over the ion flux at the electrode can be achieved without noticeably influencing the uniformity of the IEDF. |
Thursday, October 6, 2022 2:00PM - 2:15PM |
ER4.00003: Stratification of Capacitively Coupled Plasma in Noble Gases Vladimir I Kolobov, Robert Arslanbekov Standing striations previously observed experimentally in Capacitively Coupled Plasma (CCP) in noble gases have been reproduced in self-consistent computer simulations using the recently developed hybrid kinetic-fluid code [1]. The plasma model assembled in COMSOL contains a kinetic equation for electrons in (x,u) phase space (u is the electron kinetic energy), drift-diffusion equations for ions, and the Poisson equation for the electric field. The radial loss of the particles to the wall via ambipolar diffusion is included, and periodic boundary conditions are used to simulate the stratified positive column plasma. For the first time, we obtained standing striations in CCP due to nonlocal electron kinetics. We confirmed the kinetic nature of these striations at low currents, which resemble moving s striations in DC discharges. They are associated with enhanced electron heating by the RF electric field in the regions of low plasma density and the electron diffusion in phase space with conservation of total energy (kinetic plus potential). The nonlocal kinetics in phase space results in the maximum excitation/ionization rates at the points of maximal plasma density. We have shown that lower average electric fields can maintain stratified plasma compared to striation-free plasma. This substantiates the principle of minimal power for the kinetic striations in DC and RF discharges. |
Thursday, October 6, 2022 2:15PM - 2:30PM |
ER4.00004: The mechanism of frequency coupling in low pressure dual-frequency capacitively coupled plasmas revisited based on the Boltzmann term analysis Máté Vass, Li Wang, Sebastian Wilczek, Trevor Lafleur, Ralf Peter Brinkmann, Zoltan Donko, Julian Schulze The electron power absorption dynamics is investigated for radio-frequency (RF) argon capacitively coupled plasmas (CCPs) at low pressure excited by a dual frequency waveform with frequencies of 27.12 MHz and 1.937 MHz. Based on the spatio-temporal dynamics of the ambipolar electric field outside the sheath, a novel interpretation of the mechanism of frequency coupling is given, which is not based on electron reflection from a Hard Wall sheath edge model, as in previous explanations. |
Thursday, October 6, 2022 2:30PM - 2:45PM |
ER4.00005: Pressure dependence on spatio-temporal distribution of excitation rates of Ar 2p1 and Ne 2p1 in Ar and Ar/Ne capacitively coupled plasmas Michihiro Otaka, Toshiaki Arima, Jian-syun Lai, Kizuki Ikeda, Kunihiro Kamataki, Naoto Yamashita, Takamasa Okumura, Naho Itagaki, Kazunori Koga, Masaharu Shiratani Plasma processing is used in a lot of semiconductor manufacturing steps today. For ultra-precision nano-fabrication, spatio-temporal structures of plasma must be clarified and controlled. High-energy electrons have important roles of the dissociation and ionization of gas molecules [1]. In this study, We have investigated the spatio-temporal distribution of excitation rates of some ions in a capacitively coupled plasma using Phase Resolved Optical Emission Spectroscopy (PROES) measurement. The input rf frequency was 13.56 MHz and the power was 25 W, respectively. The ICCD camera had a gate width of 3 ns. The excitation rate was a relative evaluation. Spatio-temporal distributions of excitation rates of Ar 2p1 and Ne 2p1 were measured by PROES from gas pressure p = 37.5 mTorr to 900 mTorr. These measurement results showed as follows; as gas pressure increased,1) the excitation rates of Ar 2p1 and Ne 2p1 decreased, 2) the spatio-temporal region of high excitation rate became small, and 3) the sheath expansion width became narrow and the beam velocity of the high energy electron decreased, respectively. These three results considered to affect electron energy distribution function and electron density. Details will be shown at the conference. |
Thursday, October 6, 2022 2:45PM - 3:00PM |
ER4.00006: Generation of surface modes and plasma uniformity in VHF CCP reactors studied with a EM PIC code Denis Eremin, Efe Kemaneci, Masaaki Matsukuma, Thomas Mussenbrock, Ralf Peter Brinkmann CCP reactors represent one of the main instruments in the plasma processing industry, where they are utilized for a large number of different technologies involving etching or deposition processes. To increase the process rates, one can resort to increasing the ion fluxes to electrodes by using very high frequency harmonics in the driving voltage. The nonlinear dynamics of the plasma sheaths can generate even higher harmonics in the current, leading to the excitation of surface modes existing due to the interaction between the plasma sheath and plasma bulk dynamics. If sufficiently strong, the surface modes can significantly affect the plasma ionization radial profile and thus potentially influence radial uniformity of fluxes and IEDFs of ions impinging on electrodes. In this work we investigate the mentioned characteristics in CCPs operated at a low pressure and driven by VHF harmonics by performing kinetic simulations with an implicit electromagnetic energy-conserving PIC/MCC code. In particular, we discuss generation of energetic electrons as a result of the nonlinear sheath dynamics coupled with the surface mode excitation and the related radial nonuniformities. |
Thursday, October 6, 2022 3:00PM - 3:15PM |
ER4.00007: Current and voltage (I-V) characteristics of intermediate pressure plasma Shadhin Hussain, Matthew Goeckner Capacitively coupled RF discharges are often characterized by their operating pressure and the resultant 'heating mode'. The pressure regime between 1-5 Torr remains largely unexplored although this pressure is employed for a number of applications. At these higher pressures, as collision mean free path becomes much smaller than the sheath thickness, ohmic heating becomes important. Specifically, electrons in the sheath gain energy from the oscillating electric field and then heat the plasma by transferring that energy through collisional processes. To understand the heating of these collisional electrons, time-dependent current and voltage (I-V) on the powered electrode were measured for argon, nitrogen and oxygen plasma in the range of 0.5 – 2.5 Torr. Typical plasma control parameters such as electrode voltage, conduction and displacement currents are calculated as a function of frequency, pressure, deposited power and used gas. A design of experiment (DOE) was carried out to find any functional relationships between the system control parameters: electrode gap; pressure; power; and gas composition, and the resulting frequency-dependent currents and voltages. From our measurements, we find that gap has the least impact on any of the resultant I-V parameters. Pressure and power have the most effect on any of the I-V parameters while gas chemistry also plays a role but to a lesser extent. We will present these results and examine some of the mechanisms through which the control parameters impact the measured I-V. |
Thursday, October 6, 2022 3:15PM - 3:30PM |
ER4.00008: Wave Characteristics in E×B Source: Pressure-Dependent Evolution of Plasma Oscillation Phenomena June Young Kim, Cheongbin Cheon, Jinyoung Choi, Y. S. Hwang, Kyoung-Jae Chung, Hae June Lee We have observed a pressure-dependent evolution of plasma oscillation in the E×B source. The wave characteristics of plasma oscillation were thoroughly measured with multi-array probes to investigate the changes in frequency and wavenumber of the oscillations. At relatively high pressure in the range of mTorr, the Simon-Hoh instability with harmonic components was readily observed in the measured frequency-wavenumber resolved power spectrum density. The fundamental frequency of the Simon-Hoh Instability is near 35 kHz, and their harmonics (i.e., second and third harmonics) are distinguishable. As the working pressure decreases, the Simon-Hoh instability and breathing mode (below 30 kHz) co-exist. In contrast, the extinction of the Simon-Hoh instability with a high mode number occurs as the power density of the breathing mode increases. Finally, the evolution of the wave properties has been discussed in detail with the theoretical description of the dispersion relation. |
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