Daniel Szeremley

Ion energy distribution functions behind the sheaths of magnetized and non-magnetized radio frequency discharges

The effect of a magnetic field on the characteristics of capacitively coupled radio frequency discharges is investigated and found to be substantial. A one-dimensional particle-in-cell simulation shows that geometrically symmetric discharges can be asymmetrized by applying a spatially inhomogeneous magnetic field. This effect is similar to the recently discovered electrical asymmetry effect. Both effects act independently, they can work in the same direction or compensate each other. Also the ion energy distribution functions at the electrodes are strongly affected by the magnetic field, although only indirectly. The field influences not the dynamics of the sheath itself but rather its operating conditions, i.e., the ion flux through it and voltage drop across it. To support this interpretation, the particle-in-cell results are compared with the outcome of the recently proposed ensemble-in-spacetime algorithm. Although that scheme resolves only the sheath and neglects magnetization, it is able to reproduce the ion energy distribution functions with very good accuracy, regardless of whether the discharge is magnetized or not.

On the physics of a large CCP discharge

Demands of the plasma processing industry gradually lead to an increase in electrode areas and driving frequency of the commonly used capacitively coupled reactors. This brings about new phenomena which differ from the well known physics of smaller capacitively coupled plasma (CCP) devices. In this work we compare experimental data and results of numerical modeling for a large CCP discharge having a GEC cell-like geometry currently studied in context of a possible use as a sputtering device. Using an electrostatic implicit particle-in-cell code with Monte-Carlo collisions (PIC/MCC), we have been capable of reproducing all main features of the experimental discharges, which have strong relevance for the processing applications, such as the plasma uniformity and the self-bias. The side chamber proves to play an essential role in defining the physics of the whole device, featuring substantial production of plasma particles and participating in establishing the self-bias due to the telegraph effect observed for higher frequencies.

A global model of cylindrical and coaxial surface-wave discharges

A volume-averaged global model is developed to investigate surface-wave discharges inside either cylindrical or coaxial structures. The neutral and ion wall flux is self-consistently estimated based on a simplified analytical description both for electropositive and electronegative plasmas. The simulation results are compared with experimental data from various discharge setups of either argon or oxygen, measured or obtained from literature, for a continuous and a pulse-modulated power input. A good agreement is observed between the simulations and the measurements. The calculations show that the wall flux often substantially contributes to the net loss rates of the individual species.

Numerical simulations of a microwave driven low pressure plasma

Summary form only given. The market shows in recent years a growing demand for bottles made of polyethylene terephthalate (PET). Therefore, fast and efficient sterilization processes as well as barrier coatings to decrease gas permeation are required. A specialized microwave plasma source - referred to as the plasmaline - has been developed to allow for depositing thin films of e.g. silicon oxid on the inner surface of such PET bottles. The plasmaline is a coaxial waveguide combined with a gas-inlet which is inserted into the empty bottle and initiates a reactive plasma. To optimize and control the different surface processes, it is essential to fully understand the microwave power coupling to the plasma and the related heating of electrons inside the bottle and thus the electromagnetic wave propagation along the plasmaline. In this contribution, we present a fully electromagnetic numerical approach performed by means of the Hybrid Plasma Equipment Model (HPEM). Plasmas at different pressures and input powers are examined. The numerical results are compared with experimentally obtained data and show very good agreement.

A numerical approach for simulations of the mode propagation in a microwave driven plasma discharge

Summary form only given. The market shows in recent years a growing demand for bottles made of polyethylene terephthalate (PET). Therefore, fast and efficient sterilization processes as well as barrier coatings to decrease gas permeation are required. A specialized microwave plasma source - referred to as the plasmaline - has been developed to allow for depositing thin films of e.g. silicon oxid on the inner surface of such PET bottles. The plasmaline is a coaxial waveguide combined with a gas-inlet which is inserted into the empty bottle and initiates a reactive plasma. To optimize and control the different surface processes, it is essential to fully understand the microwave power coupling to the plasma and the related heating of electrons inside the bottle and thus the electromagnetic wave propagation along the plasmaline. In this contribution, we present a detailed dispersion analysis based on a numerical approach. We study how modes of guided waves are propagating under different conditions, if at all.

Comparison of a numerical and analytical model for the simulation of the mode propagation in a microwave driven plasma discharges

Summary form only given. The market shows in recent years a growing demand for bottles made of polyethylene terephthalate (PET). Therefore, fast and efficient sterilization processes as well as barrier coatings to decrease gas permeation are required. A specialized microwave plasma source - referred to as the plasmaline - has been developed to allow for depositing thin films of e.g. silicon oxid on the inner surface of such PET bottles. The plasmaline is a coaxial waveguide combined with a gas-inlet which is inserted into the empty bottle and initiates a reactive plasma. To optimize and control the different surface processes, it is essential to fully understand the microwave power coupling to the plasma and the related heating of electrons inside the bottle and thus the electromagnetic wave propagation along the plasmaline. In this contribution, we present a detailed dispersion analysis based on a numerical approach. We study how modes of guided waves are propagating under different conditions, if at all.

Numerical study of the mode propagation in a microwave driven plasma

Summary form only given. The market shows in recent years a growing demand for bottles made of polyethylene terephthalate (PET). Therefore, fast and efficient sterilization processes as well as barrier coatings to decrease gas permeation are required. A specialized microwave plasma source - referred to as the plasmaline - has been developed to allow for treatment of the inner surface of such PET bottles The plasmaline is a coaxial waveguide combined with a gas-inlet which is inserted into the empty bottle and initiates a reactive plasma. To optimize and control the different surface processes, it is essential to fully understand the microwave power coupling to the plasma inside the bottle and thus the electromagnetic wave propagation along the plasmaline. In this contribution, we present a detailed dispersion analysis based on an analytical approach. We study how modes of guided waves are propagating under different conditions (if at all). The analytical results are supported by a series of self-consistent numerical simulations of the plasmaline and the plasma.

Ion energy distribution functions in magnetized capacitively coupled RF discharges

Summary form only given. The influence of a spatially inhomogeneous static magnetic field on the characteristics of capacitively coupled radio frequency discharges is investigated. In particular, the focus is placed on the sheath dynamics and the ion energy distribution functions (IEDFs) of ions impinging the electrodes. For this study we employ two different kinetic models. The first is the Particle-in-Cell (PIC) code yapic [1], which takes into account the entire discharge; the second code is the Ensemble-in-Spacetime (EST) model [2] which resolves the plasma boundary sheath only. We make a comparison of the two models by using the sheath voltage and the ion flux through the sheath calculated with PIC as input for EST. [3] We find excellent agreement of the IEDFs calculated with both methods. In addition, good qualitative agreement of the sheath dynamics is observed. However, a quantitative discrepancy between the models can be identified, caused by different collision processes implemented in both models. While it is found that electrons are strongly affected by the applied magnetic field, ions are only indirectly influenced in terms of the asymmetry of the discharge. In addition, we find that EST may be used as an efficient postprocessing tool to obtain the IEDFs even in magnetized cases, in particular if only simplified (i.e., global or fluid-dynamic) models are available.

Collisionless spectral-kinetic simulation of the multipole resonance probe on GPU

Summary form only given. Plasma resonance spectroscopy is a well established plasma diagnostic method realized in several designs. One of these designs is the multipole resonance probe (MRP). In its idealized geometrically simplified version it consists of two dielectrically shielded, hemispherical electrodes to which an RF signal is applied. A numerical tool is under development, which is capable of simulating the dynamics of the plasma surrounding the MRP in electrostatic approximation.In the simulation the potential is separation in an inner and a vacuum potential. The inner potential is influenced by the charged particles and is calculated by a specialized Poisson solver. The vacuum potential fulfills Laplaces equation and consists of the applied voltage of the probe as boundary condition. Both potentials are expanded in spherical harmonics. For a practical particle pusher implementation, the expansion must be appropriately truncated. Compared to a PIC simulation a grid is unnecessary to calculate the force on the particles. To reduce the simulation time the code is parallelized and used on a GPU. This work purpose is a collisionless kinetic simulation, which can be used to investigate kinetic effects on the resonance behavior of the MRP.

Kinetic simulations of a large-sized multifrequency CCP-based sputtering source with a PIC/MCC darwin code

Summary form only given. A novel concept of a sputtering source based on a CCP multifrequency large-sized discharge is currently under experimental investigation [1]. The physics of such a discharge is quite complex and includes phenomena taking place on several time and spatial scales. In particular, because of the size and the high frequency harmonics in the driving voltage of such a discharge, the electromagnetic effects may play a significant role. Moreover, use of the electrical asymmetry effect (EAE) to create a self-consistent bias complicates the problem even more. In the present work we report results of our studying such a discharge with a recently developed self-consistent kinetic 2d3c PIC/MCC GPU-parallelized code which uses Darwin approximation [2] for description of the electromagnetic field components. The simulations are made in a geometry close to that of the sputtering source used in the experiments. We discuss interesting features of the discharges arising in the main and the side chambers and compare the simulation results and the experimental data.