Most plasma sources have to undergo a breakdown process, during which, energy is injected, and particles are ionized. However, we still know little about this fast evolution process. In this work, a one-dimensional direct implicit particle-in-cell/Monte-Carlo collision (PIC/MCC) program is used to study the breakdown process of a capacitively coupled plasma (CCP) driven by dual radio frequencies. The results show that the breakdown process can be divided into three phases: the pre-breakdown, transition, and post-breakdown phases. In the pre-breakdown phase, the plasma density and heating power grow exponentially. The electric field can penetrate the whole discharge region without any shielding, resulting in a higher-than-average electron energy. Secondary electron emission is critical to grow the electron numbers under these discharge conditions. During the transition phase, the formation of sheaths maximizes the electron generation rate and heating power. The formation of sheaths also causes a drastic change in the electrical characteristics of CCP devices. In the post-breakdown phase, the plasma parameters gradually evolve until a steady state is reached. The decreasing rate of generation and the increasing rate of particle loss gradually equalize. The trends of the power gain and plasma loss are similar to the curves for the particle generation and loss rates, and a dynamic equilibrium is finally reached in the last steady state.

Because of the larger surface-area-to-volume ratio, micro-discharges can be sustained by surface emission processes. If the cathode is heated, micro-discharge can be sustained mainly by thermionic emission. However, we still knew little about how this kind of plasma is ignited and sustained. In order to explore the breakdown process of dc-driven micro-discharge sustained by thermionic emission, a one-dimensional implicit particle-in-cell/Monte Carlo collision method is adopted, coupled with the external circuit and thermionic emission model. The breakdown process of micro-discharge lasts about 8μs, and this process can be roughly divided into two phases, i.e., pre-breakdown and breakdown phase. The dynamic plasma parameters during the evolution process are analyzed, such as particle density, electron energy distribution function, electric potential, average particle temperature, and particle current density. The plasma electrical characteristics as well as the article and power balance, are also presented to show the evolutionary features of the whole gas breakdown process.

The breakdown of SF6 gas at low pressure is of vital importance to both aerospace and microelectronics industries. However, the breakdown characteristics of SF6 in direct current at low pressure are still seldom studied. In this work, one-dimensional implicit particle-in-cell/Monte-Carlo collision algorithm is used to study the entire direct current breakdown process of low-pressure SF6. The ion-molecule collision, recombination, and external circuit are considered in the model. According to the results, the breakdown process can be divided into three stages: pre-breakdown stage, breakdown stage, and post-breakdown stage. In the pre-breakdown stage, the cathode sheath is not yet formed so the constant electric field exists in the entire area. In the breakdown stage, the formation mechanism of the cathode sheath is analyzed and the electrodes as a whole changes from capacitive to resistive, sharing the voltage with the external resistance. In the post-breakdown stage, the continued growth of positive ions leads to the formation of a thin anode sheath, which further causes the negative plasma potential, different from electropositive gas. The energy production terms including heating power and secondary electron emission (SEE) power are equal to the energy loss terms including collision loss power and boundary loss power, where collision loss power and boundary loss power are almost equal, while SEE power is negligible. In the final, plasma parameters gradually evolve to the last steady-state.

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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.