Abstract:Electric characteristics of capacitively coupled discharges were calculated, including their nonlinear behaviour and generation of higher harmonic frequencies of discharge current and voltage. The discharge was modelled as a series combination of the bulk plasma, two nonlinear sheaths and a radio frequency generator. Comparison of the results of the model with an experiment is discussed. The model was used for studying the waveforms of discharge current and sheath voltages and generation of higher harmonic fre… Show more
“…The origin of this distortion is the presence of high-harmonic components. These harmonics, observed also in symmetric discharge geometries, are known to be induced by the nonlinearity of the sheath in capacitive discharges 13 , 14 . Figure 1 Electrical and electron characteristics of single-rf argon capacitive discharges.…”
Determining the electron properties of weakly ionized gases, particularly in a high electron-neutral collisional condition, is a nontrivial task; thus, the mechanisms underlying the electron characteristics and electron heating structure in radio-frequency (rf) collisional discharges remain unclear. Here, we report the electrical characteristics and electron information in single-frequency (4.52 MHz and 13.56 MHz) and dual-frequency (a combination of 4.52 MHz and 13.56 MHz) capacitive discharges within the abnormal α-mode regime at atmospheric pressure. A continuum radiation-based electron diagnostic method is employed to estimate the electron density (ne) and temperature (Te). Our experimental observations reveal that time-averaged ne (7.7–14 × 1011 cm−3) and Te (1.75–2.5 eV) can be independently controlled in dual-frequency discharge, whereas such control is nontrivial in single-frequency discharge, which shows a linear increase in ne and little to no change in Te with increases in the rf input power. Furthermore, the two-dimensional spatiotemporal evolution of neutral bremsstrahlung and associated electron heating structures is demonstrated. These results reveal that a symmetric structure in electron heating becomes asymmetric (via a local suppression of electron temperature) as two-frequency power is simultaneously introduced.
“…The origin of this distortion is the presence of high-harmonic components. These harmonics, observed also in symmetric discharge geometries, are known to be induced by the nonlinearity of the sheath in capacitive discharges 13 , 14 . Figure 1 Electrical and electron characteristics of single-rf argon capacitive discharges.…”
Determining the electron properties of weakly ionized gases, particularly in a high electron-neutral collisional condition, is a nontrivial task; thus, the mechanisms underlying the electron characteristics and electron heating structure in radio-frequency (rf) collisional discharges remain unclear. Here, we report the electrical characteristics and electron information in single-frequency (4.52 MHz and 13.56 MHz) and dual-frequency (a combination of 4.52 MHz and 13.56 MHz) capacitive discharges within the abnormal α-mode regime at atmospheric pressure. A continuum radiation-based electron diagnostic method is employed to estimate the electron density (ne) and temperature (Te). Our experimental observations reveal that time-averaged ne (7.7–14 × 1011 cm−3) and Te (1.75–2.5 eV) can be independently controlled in dual-frequency discharge, whereas such control is nontrivial in single-frequency discharge, which shows a linear increase in ne and little to no change in Te with increases in the rf input power. Furthermore, the two-dimensional spatiotemporal evolution of neutral bremsstrahlung and associated electron heating structures is demonstrated. These results reveal that a symmetric structure in electron heating becomes asymmetric (via a local suppression of electron temperature) as two-frequency power is simultaneously introduced.
“…The discharge parameters need to be estimated. From the plasma impedance calculation [34] the plasma resistance is determined as…”
Section: Oscillationsmentioning
confidence: 99%
“…Note thatthe resistance calculation was simplified using the dcapproach as the collision frequency is two orders of magnitude higher compared to the frequency of the oscillations. Similarly from impedance calculation [34] the plasma inductance is derived as…”
Thispaper reports on the oscillations both on the cathode voltage and on the discharge current which emerged suddenly and simultaneously during ahigh-power impulse magnetron sputtering pulse. Detailedexperiments identified the pressure and the discharge current ranges to detect these oscillations. The oscillationsoriginatedfrom the magnetized plasma and their frequency ranged from 225 kHz to 400 kHz depending on the experimental conditions. Simultaneous measurement of both oscillations and spokes was conducted to find mutual correlations. The oscillations always accompanied the spokes and no particular conditions to detect oscillations in theabsence ofspokes were found. The oscillations were not caused by the rotational motion of the spokes butemerged when acertain threshold amount of spokes was overreached.
“…can be used instead of equations (3)- (5). Since equation (7) does not depend on electron temperature, the proposed method is independent of the value of electron temperature at sufficiently low probe biasing.…”
Section: Sensitivity To Input Parametersmentioning
confidence: 99%
“…As a result, while the DC value of the plasma potential is routinely measured by compensated Langmuir probes, there is a lack of data describing the temporal evolution of plasma potential during a discharge period, in spite of the fact that it is a fundamental electric characteristic of plasma. This fact is valid, especially in capacitively coupled discharges where the plasma potential comprises not only the DC and the one RF component supplied from the RF power generator, but it also includes numerous higher harmonic frequencies created by plasma due to the nonlinear nature of sheaths [3][4][5].…”
A method for the measurement of plasma potential waveforms is presented that is based on measurement with a high-impedance probe and an electric model of the sheath around the probe. The method was verified and compared with methods that were previously used for measurement of the temporal development of plasma potential during an RF period of capacitive discharges. The sensitivity of the method to the values of required input parameters (mean plasma potential value, electron concentration and temperature) was analyzed and it was found that with a lower precision, the method can be used even without the knowledge of these input parameters. Finally, plasma potential waveforms were measured in a low-pressure capacitively coupled discharge. In agreement with theoretical models, the generation of higher harmonic frequencies of plasma potential and their sensitivity to electron concentration were observed.
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