Experimental demonstration of multifrequency impedance matching for tailored voltage waveform plasmas

Absolute atomic oxygen densities measured space resolved in the active plasma volume of a COST microplasma reference jet operated in He/O2 and driven by tailored voltage waveforms are presented. The measurements are performed for different shapes of the driving voltage waveform, oxygen admixture concentrations, and peak-to-peak voltages. Peaks- and valleys-waveforms constructed based on different numbers of consecutive harmonics, N, of the fundamental frequency f 0 = 13.56 MHz, different relative phases and amplitudes are used. The results show that the density of atomic oxygen can be controlled and optimized by voltage waveform tailoring (VWT). It is significantly enhanced by increasing the number of consecutive driving harmonics at fixed peak-to-peak voltage. The shape of the measured density profiles in the direction perpendicular to the electrodes can be controlled by VWT as well. For N > 1 and peaks-/valleys-waveforms, it exhibits a strong spatial asymmetry with a maximum at one of the electrodes due to the spatially asymmetric electron power absorption dynamics. Thus, the atomic oxygen flux can be directed primarily towards one of the electrodes. The generation of atomic oxygen can be further optimized by changing the reactive gas admixture and by tuning the peak-to-peak voltage amplitude. The obtained results are understood based on a detailed analysis of the spatio-temporal dynamics of energetic electrons revealed by phase resolved optical emission spectroscopy.

Section: Plasma Sourcementioning

confidence: 99%

“…This is a powerful technique which can be used in combination with any existing plasma source without modifying the source itself, but only the external power supply. Impedance matchings for VWT have been developed and are available [60][61][62]. In this sense, VWT is a modular technique.…”

Section: Introductionmentioning

confidence: 99%

Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O₂

Korolov

Steuer

Bischoff

et al. 2021

“…Indeed, for SF CCP, simplified CCP models already provide a good estimate of the nominal inductor and capacitor values needed, and the variable capacitors anyway have a range of values that allows the user to compensate for any differences compared with theory or any non-ideal effects. However, for some more complex cases like pulsed CCP [17,18] and CCP driven by TVWs [19][20][21][22][23], the design of matching circuit based on these simplified CCP models is hard or even impossible, due to the complexity and non-linearity. Our model thus may provide a feasible solution to these more complicated cases.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, design of the matching networks is one of the key issues in some new CCP configurations, to achieve better control over specific plasma characteristics. Recent efforts include dual-frequency CCP [9,[13][14][15][16], pulsed CCP [17,18] and CCP driven by tailored voltage waveforms (TVWs) [19][20][21][22][23] used in etching at low pressure, as well as CCP at atmosphere [24], or even using CCP as a tunable impedance element for RF systems [25].…”

Section: Introductionmentioning

confidence: 99%

Self-consistent simulation of the impedance matching network for single frequency capacitively coupled plasma

Gao¹,

Yu²,

Wu³

et al. 2022

Matching networks are of vital importance for capacitively coupled plasmas to maximize the power transferred to the plasma discharge. The nonlinear interaction between the external circuit and plasma has to be considered to design suitable matching networks. To study the effect of the matching circuit, we coupled PIC/MC model and nonlinear circuit equations based on Kirchhoff’s laws, in a fully nonlinear and self-consistent way. The single-frequency capacitively coupled discharge with ”L”-Type matching networks are simulated. Fully self-consistently results of circuit and plasma parameters are presented and then power absorbed by the plasma and efficiency are calculated. With the tune of the matching network, the efficiency can reach 28.7 %, leading to higher potential as well as higher electron density at fixed source voltage. Besides, only very small components of the third harmonics are found in the plasma voltage and current while surface charge densities have multiple harmonics on account of the strong plasma nonlinearity. Finally, the effects of matching capacitors on discharge are analyzed, results show that smaller Cm1 and Cm2 of 500 pF to 1000 pF may be a proper choice for better matching, resulting in higher voltage across the CCP, and thus higher electron density and power absorption efficiency are obtained.

“…VWT was demonstrated to provide control of (i) the dc self-bias voltage via the Electrical Asymmetry Effect to improve the control of ion properties [8,[38][39][40][41][42], (ii) the sheath dynamics to control the electron power absorption dynamics and the electron energy distribution function [43][44][45][46], and (iii) nonlinear electromagnetic effects to optimize plasma uniformity [47][48][49][50][51]. Based on existing multi-frequency impedance matchings [52][53][54], VWT is a modular technology. Any existing capacitive RF plasma source can be upgraded to use VWT by modifying only the external circuit.…”

Section: Introductionmentioning

confidence: 99%

Control of electron velocity distributions at the wafer by tailored voltage waveforms in capacitively coupled plasmas to compensate surface charging in high-aspect ratio etch features

Hartmann

Wang

Nösges

et al. 2021

Low pressure single- or dual-frequency capacitively coupled radio frequency (RF) plasmas are frequently used for high-aspect ratio (HAR) dielectric etching due to their capability to generate vertical ion bombardment of the wafer at high energies. Electrons typically reach the wafer at low energies and with a wide angular distribution during the local sheath collapse. Thus, in contrast to positive ions, electrons cannot propagate deeply into HAR etch features and the bottom as well as the sidewalls of such trenches can charge up positively, while the mask charges negatively. This causes etch stops and distortion of profile shapes. Here, we investigate low pressure, high voltage capacitively coupled RF argon gas discharges by Particle-In-Cell/Monte Carlo collisions simulations and demonstrate that this problem can be solved by Voltage Waveform Tailoring, i.e. the velocity and angular distribution of electrons impacting on the electrodes can be tuned towards high velocities and small angles to the surface-normal, while keeping the energies of the impacting ions high. The applied voltage waveforms consist of a base frequency of 400 kHz with 10 kV amplitude and a series of higher harmonics. A high frequency component at 40 or 60 MHz is used additionally. Square voltage waveforms with different rise-times are examined as well. We show that high fluxes of electrons towards the wafer at normal velocities of up to 2.2 × 107 m s−1 (corresponding to 1.4 keV energy) can be realized.