Driving frequency dependence of capacitively coupled plasmas in atmospheric argon (original) (raw)
Related papers
Physics Letters A, 2013
The influence of excitation frequency (13.56-96 MHz) on the characteristics of capacitively coupled argon plasma is investigated by means of Langmuir probe and a high-voltage probe. Measurements are performed in argon pressure of 40 and 60 mTorr at a fixed discharge voltage V pp = 200 V. The measured electron energy distribution function EEPFs are a bi-Maxwellian type irrespective of the driving frequency and gas pressure. The electron density and temperatures show peak over frequency range of 54-72 MHz, beyond which it decreases. The non-monotonic dependences of plasma parameters with driving frequency were interpreted in terms of excited surface wave excited at the powered electrode.
Physics of Plasmas, 2018
A capacitively coupled radio frequency discharge driven by two harmonics substantially different from each other allows some degrees of independent control of the ion energy and ion flux. The low frequency (x LF) source controls the ion energy, while the ion flux is controlled by the high frequency (x HF) source. The choices of the driving frequencies can influence the properties of the dual frequency capacitively coupled plasmas (2f CCP). Here, we study the effect of the driving frequencies on the properties of the 2f CCPs, i.e., on the generation of a DC self-bias, the excitation of the non-linear Plasma Series Resonance (PSR) effect as well as the independent control over the mean ion energy and the flux in three different 2f CCP experiments: namely (2.26 þ 13.56) MHz, (2.26 þ 27.12) MHz, and (13.56 þ 27.12) MHz. We also use a non-liner global model that consists of a description of the plasma bulk based on a fluid dynamic approach coupled to a separate model of the sheath. We use argon and cover a wide range of operating conditions. We find the choices of different x LF and x HF 's result in substantial changes of the decoupling of the mean ion energy from the ion flux. We also observe that increasing x HF decreases the DC self-bias at a fixed value of x LF. The PSR effect and, therefore, the electron power deposition strongly depend on the high frequency source. The experimental results are consistent with the predictions of the non-linear global model which proves the usefulness of such a rather simplistic model to study of 2f CCP discharges.
Fundamental investigations of capacitive radio frequency plasmas: simulations and experiments
Plasma Physics and Controlled Fusion, 2012
Capacitive radio frequency (RF) discharge plasmas have been serving hi-tech industry (e.g. chip and solar cell manufacturing, realization of biocompatible surfaces) for several years. Nonetheless, their complex modes of operation are not fully understood and represent topics of high interest. The understanding of these phenomena is aided by modern diagnostic techniques and computer simulations. From the industrial point of view the control of ion properties is of particular interest; possibilities of independent control of the ion flux and the ion energy have been utilized via excitation of the discharges with multiple frequencies. 'Classical' dual-frequency (DF) discharges (where two significantly different driving frequencies are used), as well as discharges driven by a base frequency and its higher harmonic(s) have been analyzed thoroughly. It has been recognized that the second solution results in an electrically induced asymmetry (electrical asymmetry effect), which provides the basis for the control of the mean ion energy. This paper reviews recent advances on studies of the different electron heating mechanisms, on the possibilities of the separate control of ion energy and ion flux in DF discharges, on the effects of secondary electrons, as well as on the non-linear behavior (self-generated resonant current oscillations) of capacitive RF plasmas. The work is based on a synergistic approach of theoretical modeling, experiments and kinetic simulations based on the particle-in-cell approach.
2010
A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5-70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar-He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500-2100 K), He (3000-3500 K) and H (2500-3200 K), the rotational temperature of the OH band (1300-2900 K), the electron temperature (5500-6500 K) and the electron number density (8 • 10 13-2 • 10 14 cm − 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.
About the EDF formation in a capacitively coupled argon plasma
Plasma Sources Science and Technology, 2006
The formation of the electron distribution function (EDF) in the bulk plasma of a capacitively coupled radio-frequency (rf) discharge in argon generated in the plasma-chemical reactor PULVA-INP is investigated experimentally and theoretically. Measurements of the EDF and internal plasma parameters were performed by means of a Langmuir probe at pressures of 0.5-100 Pa and discharge powers of 5-100 W. The observed EDFs have revealed a two-temperature behaviour at low pressures and evolved into a Maxwellian distribution at high gas pressures and large discharge powers. Theoretical determination of the EDF is based on the numerical solution of the Boltzmann kinetic equation in the local and non-local approaches under experimental conditions. The model includes elastic and inelastic electron-atom collisions and electron-electron interactions. Low electron temperatures and relatively high ionization degrees are the features of the PULVA-INP rf discharge. This leads to significant influence of the electron-electron collisions on the EDF formation. The modelled and measured distributions show good agreement in a wide range of discharge parameters, except for a range of low gas pressures, where the stochastic electron heating is intense. Additionally, mechanisms of the EDF formation in the dc and rf discharge were compared under similar discharge conditions.
2011
Theoretical and experimental study of the microwave cut-off probe for electron density measurements in lowtemperature plasmas J. Appl. Phys. 110, 073308 (2011) Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS) J. Appl. Phys. 110, 073303 (2011) Measurements of electron avalanche formation time in W-band microwave air breakdown Phys. Plasmas 18, 080707 Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster Phys. Plasmas 18, 080701 Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and realtime Tokamak control Rev. Sci. Instrum. 82, 063508 (2011)
The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas
Plasma Sources Science and Technology, 2014
We investigate the electron heating dynamics in electropositive argon and helium capacitively coupled RF discharges driven at 13.56 MHz by particle-in-cell simulations and by an analytical model. The model allows one to calculate the electric field outside the electrode sheaths, space and time resolved within the RF period. Electrons are found to be heated by strong ambipolar electric fields outside the sheath during the phase of sheath expansion in addition to classical sheath expansion heating. By tracing individual electrons we also show that ionization is primarily caused by electrons that collide with the expanding sheath edge multiple times during one phase of sheath expansion due to backscattering toward the sheath by collisions. A synergistic combination of these different heating events during one phase of sheath expansion is required to accelerate an electron to energies above the threshold for ionization. The ambipolar electric field outside the sheath is found to be time modulated due to a time modulation of the electron mean energy caused by the presence of sheath expansion heating only during one half of the RF period at a given electrode. This time modulation results in more electron heating than cooling inside the region of high electric field outside the sheath on time average. If an electric field reversal is present during sheath collapse, this time modulation and, thus, the asymmetry between the phases of sheath expansion and collapse will be enhanced. We propose that the ambipolar electron heating should be included in models describing electron heating in capacitive RF plasmas.
AIP Advances, 2018
The behavior of a single frequency capacitively coupled plasma (CCP) driven by 13.56 MHz rf source is investigated using an approach that integrates a nonlinear global analytical model and experimental data. The non linear model consists of a description of the plasma bulk, based on a fluid dynamics approach coupled to a separate model of the sheath. The parameters used in the model are obtained by operating the single frequency CCP experiment (13.56 MHz) in argon at working pressures 73 to 400m torr. Experimentally measured plasma parameters such as the electron density, electron temperature, the discharge symmetry parameter as well as the rf voltage waveforms are the inputs of the theoretical model. Model results of the DC self bias and rf current for various operating pressures and powers are shown. A comparison of the outputs of the numerical results is done with the experimentally obtained values of the DC self bias and rf current. A good quantitative correspondence between the...
Plasma Sources Science and Technology, 2020
A particle-in-cell simulation study is performed to investigate the discharge asymmetry, higher harmonic generations and electron heating mechanism in a low pressure capacitively coupled plasma excited by a saw-tooth like current waveform for different driving frequencies; 13.56 MHz, 27.12 MHz, and 54.24 MHz. Two current densities, 50 A m−2 and 100 A m−2 are chosen for a constant gas pressure of 5 mTorr in argon plasma. At a lower driving frequency, high frequency modulations on the instantaneous sheath electric field near to the grounded electrode are observed. These high frequency oscillations create multiple ionization beam like structures near to the sheath edge that drives the plasma density in the discharge and responsible for discharge/ionization asymmetry at lower driving frequency. Conversely, the electrode voltage shows higher harmonics generation at higher driving frequencies and corresponding electric field transients are observed into the bulk plasma. At lower driving f...