입자 및 유체 시뮬레이션을 활용한 고압 마이크로 방전과 저압 대면적 플라즈마에 관한 연구

Abstract

Cylindrical microhollow-cathode discharges with diameter D of 100 um are analyzed by two dimensional (2d3v) axisymmetric particle-in-cell Monte-Carlocollision simulations. Argon discharges at pressure p of 10 and 100 Torr are generated with a DC current source of 1-10 mA. Under these conditions (pD = 0.1 and 1 Torr.cm), the discharges extend inside the hollow cathode and createa virtual anode along the symmetry axis. Due to the resulting radial electric field, secondary electrons emitted from the cathode surface acquire a pendular motion within the hollow cathode and populate the high energy tail of theelectron-energy-probability function. The characteristics of the microhollowcathode discharge for different secondary electron-emission models are compared. When driven by a constant current source, a low effective secondary electron-emission coefficient results in higher plasma density and discharge voltages.Secondly, the results of simulations using a fluid model and a PIC-MCC model are compared, and the PIC-MCC is used to explore the kinetics of energetic ions and electrons in high-pressure microplasmas. The kinetics are studiedunder helium discharges at 760 Torr and Ne/Xe DBD discharges at 300 Torr with various driving currents and geometries. While EEPFs of microplasmas at high pressure show strong nonequilibrium behavior near the sheath region, EEDFs on the powered and grounded electrodes have qualitatively different features depending on input power. The effective temperature and energy fluxof charged particles can be obtained from the slopes in EEPFs and IEPFs. The effects of input power, discharge length, and mixture gas concentration on the IEDFs on each electrode are discussed.Thirdly, microdischarges at atmospheric pressure were studied by two computational methods. The first method is a typical one-dimensional fluid model in which the electron velocity distribution function is assumed to be Maxwellianand the energy equation is solved to determine the spatial profile of the electron temperature. The second method is a particle-in-cell (PIC) model with Monte-Carlo collisions (MCC). We compared the time-averaged density, electricfield and power consumption profiles of helium microdischarges driven at 13.56 MHz and 2.45 GHz obtained with the two models. The agreement between thetwo models depends on the driving frequency. The kinetic information obtained from the PIC-MCC model indicates that the improved agreement at higher frequency is due to the evolution of the electron energy distribution function froma three-temperature distribution at 13.56 MHz to a close-to-Maxwellian distribution at 2.45 GHz.Finally, the relations between the plasma and growth processes of hydrogenated microcrystalline silicon (uc-Si:H) from monosilane/hydrogen (SiH4/H2) glow discharge are studied by using the zero-dimensional global model. In order to reduce production costs for silicon thin film solar cells, high-rate deposition must be achieved without polysilicon, so-called DUST. For this achievement,it is necessary to discuss the characteristics of plasmas with respect to some kinds of external plasma parameters like total pressure, input power, excitation frequency, and gas mixture composition. We compared the densities ofreactive species which are well known as precursors for the film growth to the growth processes such as the deposition rate, the polymerization reaction andthe crystallinity of film structure. As a result, we confirmed that the radicals were closely related to the film growth processes and their production in the bulk plasma was convolutedly dependent on the external plasma parameters.In order to develop efficient multidimensional simulation tools for more detailed analysis, a large number of chemical reactions considered in the global model must be reduced. The main reactions were selected from the analysis of generation rate of precursors for the film growth.