Application of similarity laws to dual-frequency capacitively coupled radio frequency plasmas with the electrical asymmetry effect

The Electrical Asymmetry Effect (EAE) provides control of the mean ion energy at the electrodes of multi-frequency capacitively coupled radio frequency plasmas (CCP) by tuning the DC self bias via adjusting the relative phase(s) between the consecutive driving harmonics. Depending on the electron power absorption mode, this phase control affects the ion flux in different ways. While it provides separate control of the mean ion energy and flux in the α-mode, limitations were found in the γ- and Drift-Ambipolar modes. In this work, based on experiments as well as kinetic simulations, the EAE is investigated in the striation-mode, which is present in electronegative CCPs driven by low frequencies. The discharge is operated in CF4 and is driven by two consecutive harmonics (4/8 MHz). The simulation results are validated against measurements of the DC self bias and the spatio-temporally resolved dynamics of energetic electrons. To include heavy particle induced secondary electron emission realistically, a new computationally assisted diagnostic is developed to determine the corresponding secondary electron emission coefficient from a comparison of the DC self bias obtained experimentally and from the simulations. Based on the validated simulation results, the EAE is found to provide separate control of the mean ion energy and flux in the striation mode, while the axial charged particle density profiles and the number of striations change as a function of the relative phase. This is understood based on an analysis of the ionization dynamics.

Section: Pic/mcc Simulationmentioning

confidence: 99%

The electrical asymmetry effect in electronegative CF₄ capacitive RF plasmas operated in the striation mode

Wang

Masheyeva

Liu

et al. 2023

“…Compared to a single-frequency sinusoidal excitation, the application of more harmonics in a TVW allows for better control over the ion flux and ion energy [21]. Another advantage of TVWs is that it can produce a strong electrical asymmetry effect even in a geometrically symmetrical reactor, and is considered to have great application prospects [23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Kinetic simulations of capacitively coupled plasmas driven by tailored voltage waveforms with multi-frequency matching

Yu,

Wu,

Yang

et al. 2024

Impedance matching is crucial for optimizing plasma generation and reducing power reflection in capacitively coupled plasmas (CCP). Designing these matchings is challenging due to the varying and typically unknown impedance of the plasma, especially in the presence of multiple driving frequencies. Here, a computational design method for impedance matching networks (IMNs) for CCPs is proposed and applied to discharges driven by tailored voltage waveforms (TVW). This method is based on a self-consistent combination of particle in cell/Monte Carlo collision simulations of the plasma with Kirchhoff’s equations to describe the external electrical circuit. Two Foster second-form networks with the same structure are used to constitute an L-type matching network, and the matching capability is optimized by iteratively updating the values of variable capacitors inside the IMN. The results show that the plasma density and the power absorbed by the plasma continuously increase in the frame of this iterative process of adjusting the matching parameters until an excellent impedance matching capability is finally achieved. Impedance matching is found to affect the DC self-bias voltage, whose absolute value is maximized when the best matching is achieved. Additionally, a change in the quality of the impedance matching is found to cause an electron heating mode transition. Poor impedance matching results in a heating mode where electron power absorption in the plasma bulk by drift electric fields plays an important role, while good matching results in the classical α-mode operation, where electron power absorption by ambipolar electric fields at the sheath edges dominates. The method proposed in this work is expected to be of great significance in promoting TVW plasma sources from theory to industrial application, since it allows designing the required complex multi-frequency IMNs.

“…A variety of experimental and computational studies focused on different aspects of CCP operation has been conducted in the past. These include computational investigations based on fully kinetic particle-in-cell simulations complemented with the Monte Carlo treatment of collision processes (PIC/MCC) [6][7][8][9][10][11][12][13][14][15][16][17][18][19] as well as hybrid fluid/kinetic simulations [19][20][21] and experimental studies based on different plasma diagnostics.…”

Section: Introductionmentioning

confidence: 99%

Experimental validation of particle-in-cell/Monte Carlo collisions simulations in low-pressure neon capacitively coupled plasmas

Park,

Horváth,

Derzsi

et al. 2023

Plasma simulations are powerful tools for understanding fundamental plasma science phenomena and for process optimization in applications. To ensure their quantitative accuracy, they must be validated against experiments. In this work, such an experimental validation is performed for a 1d3v particle-in-cell simulation complemented with the Monte Carlo treatment of collision processes of a capacitively coupled radio frequency plasma driven at 13.56 MHz and operated in neon gas. In a geometrically symmetric reactor the electron density in the discharge center and the spatio-temporal distribution of the electron impact excitation rate from the ground intothe Ne 2p1 state are measured by a microwave cutoff probe and phase resolved optical emission spectroscopy, respectively. The measurements are conducted for electrode gaps between 50 mm and 90 mm, neutral gas pressures between 20 mTorr and 50 mTorr, and peak-to-peak values of the driving voltage waveform between 250 V and 650 V. Simulations are performed under identical discharge conditions. In the simulations, various combinations of surface coefficients characterising the interactions of electrons and heavy particles with the anodized aluminium electrode surfaces are adopted. We find, that the simulations using a constant effective heavy particle induced secondary electron emission coefficient of 0.3 and a realistic electron-surface interaction model (which considers energy-dependent and material specific elastic and inelastic electron reflection, as well as the emission of true secondary electrons from the surface) yield results which are in good quantitative agreement with the experimental data.