Comprehensive understanding of the ignition process of a pulsed capacitively coupled radio frequency discharge: the effect of power-off duration

Abstract

The effect of the pulse-off duration on the time evolution of the plasma and electrical parameters during the ignition phase in a pulsed capacitively coupled radio frequency argon discharge operated at 450 mTorr and 12.5 MHz is investigated synergistically by multifold experimental diagnostics, particle-in-cell/Monte Carlo collision simulations and an analytical model. In the experiment, the electron density is measured time-resolved by a hairpin probe, the spatio-temporal distribution of the electron impact excitation dynamics is studied by phase resolved optical emission spectroscopy, and the amplitudes and the relative phase, φ vi, of the discharge voltage and current are determined based on the waveforms measured by a voltage and a current probe. The experimental results show that the plasma and electrical parameters during the ignition process depend strongly on the duration of the afterglow period, T off, primarily because of the dependence of the remaining charge density on this parameter. Computed values of φ vi show a similar time-dependence compared to the experiment, if the simulations are initialized with specific initial charged particle densities, n ini. This allows us to further understand the time evolution of φ vi for different values of T off based on the simulation results together with an analytical model. In particular, the optical emission intensity is found to change with time in the same fashion as the power deposition into the system at T off ⩾ 100 μs, suggesting that the power is primarily absorbed by the electrons, which dissipate their energy via inelastic collisions. The system goes through different mode transitions of electron power absorption during the ignition phase depending on T off. Specifically, for short T off (high n ini), the α mode dominates during the entire ignition process, as the electric field is largely shielded by the abundant charge located in the interelectrode space. For intermediate values of T off (moderate n ini), another excitation pattern caused by an enhanced drift electric field at the center of the gap is observed, since a large fraction of the externally applied potential can penetrate into the central region in the absence of high charged particle densities. For longer T off (very low n ini), the ignition of the pulsed plasma behaves like a gas breakdown.

On the breakdown process of capacitively coupled plasma in carbon tetrafluoride

“…It is still unclear how the plasma parameters are involved during the breakdown process. The evolution of the plasma parameters and the transformation of the heating mode were recently observed in experiments by Liu et al [25] and Wang et al [26].…”

“…However, the above research all focused on the breakdown process of argon, a well-studied electropositive gas [25][26][27][28][29]. Compared to argon, discharges in electronegative gases such as CF 4 are quite different [9,[11][12][13][14].…”

Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

“…It was found that during the initial stage of the pulse-on period, the input power exhibits two maxima, and meanwhile the electron density was observed to exhibit an overshoot at a high power and a low pressure. Wang et al [109] investigated the effect of the power-off duration on the plasma ignition process of a pulse modulated CCP operated in 450 mTorr Ar by a combination of experiments, PIC/MCC simulations, and an analytical model. They found that the time evolution of the plasma and electrical parameters during the ignition process depend strongly on the duration of the afterglow period, T off , due to the dependence of the remaining (or initial) charge density on this parameter.…”

“…Previous studies on the ignition process of a pulse modulated CCP mostly focused on the time evolution of the axially resolved or even spatially averaged plasma parameters (e.g., the plasma emission, the electron density and temperature, etc. ), [104,105,[109][110][111][112][113][114] however, a 300 mm-diameter electrode is used in current semiconductor industries and, therefore, time evolution of various plasma parameters is highly radius-dependent during the ignition process in a pulse modulated plasma. Su et al [115] studied, for the first time, the time evolution of discharge parameters at different radial positions over a 300 mm-diameter electrode during the ignition process of a pulse modulated CCP in argon by multi-fold experimental diagnostics.…”

Computational analysis of direct current breakdown process in SF6 at low pressure

“…Yong-Xin Liu et al find a sequence of distinct electron power absorption modes in gas discharge system [19]. The effect of the pulse-off duration on the plasma and electrical parameters in a pulsed capacitively coupled radio frequency argon discharge is investigated synergistically through experiment and simulation by Xiang-Yu Wang et al [20]. Only a few works observed the entire process of breakdown to identify the changes in it by means of computational analysis.…”