The Hybrid Simulation Of A Dual-frequency Capacitively Coupled Plasma

Dual-frequency capacitively coupled plasma (DF-CCP) is one of the crucial components for etching in microelectronic manufacturing, and has been widely used in the next generation etching applications due to its simple structure and ability to control the plasma density, the ion energy distributions(IEDs), and the ion angle distributions(IADs) separately. Because the etching process is determined directly by the physical process and the plasma parameters such as plasma density, electric field, potential, IEDs, and IADs, it is important to investigate the phenomena in a dual frequency CCP. However, the traditional theory models have their own shortcomings in accuracy and in efficiency respectively. Therefore, we use a hybrid model based on a fluid model used in the entire region for the fast calculation and a Monte-Carlo model in the sheath for the simulation of the IEDs and IADs to achieve a accurate and efficient simulation of the DF-CCP discharge.In Chapter 2, the plasma parameters, concerned in etching process, such as plasma density, sheath potential, and electric field have been studied based on a fluid model. It finds that, the plasma density is mainly controlled by the high-frequency (HF) source and can be increased effectively by increasing either the frequency on the HF source or the pressure. The low-frequency (LF) source has little affect on it, however, when the low frequency is getting higher and the two sources begin to couple with each other, the LF source starts to affect the plasma density. The electron and ion densities remain the same value at the bulk region and begin to separate in the sheath region, which leads to an increase of the electric field at the sheath region. The electron temperature also increases in the sheath due to the acceleration to the electron by the strong electric field in this region.In Chapter 3, a one-dimensional hybrid model has been developed to investigate the characteristics of energy and angular distributions of the ions and fast neutrals impinging on the rf-biased electrode in a dual frequency capacitively coupled Ar discharge. It shows that, the IEDs appear to have multiple peaks in the dual frequency capacitively coupled rf discharge rather than bimodal shape in a conventional single frequency rf discharge. With the decrease of the pressure, the maximum energy of IEDs and the peaks of IADs increase. The parameters of the two sources have a significant effect on the structures of IEDs. By decreasing the frequency of the LF source, more ions can be accelerated by the LF field effectively which increases the maximum energy in the IEDs. With the increase of the LF voltage, the ions gain more energy from the sheath region, therefore, they strike the process surface with a much higher energy. The IADs have a significant peak at the small angle region, and most ions strike the process surface with the angle less than 3 degrees. More ions strike the electrode with a small angle by increasing either the voltage of LF source or the frequency of HF source. The energy and angular distributions of the fast neutrals are correlative with that of the ions. Compared with the ions, the fast neutrals have a much lower energy and the scattering effect becomes more prominent. In the end we provide a group of experiment results for comparison. The position and the width of the energy peaks, and the average energy are in agreement in general, and by changing the discharge parameters, the evolution of the simulation and experiment result is almost the same.In Chapter 4, a one-dimension hybrid model has been used to study the CF4 discharge, which is frequently used in the etching process. It shows that, the CF4 discharge has a large proportion of negative ions, and the density of F is much larger than the density of electron. Because the negative ions are constrained in the plasma region by the strong electric field in the sheath, their densities decrease apparently near the sheath region, where the density of positive ions and electrons get closer. The minimum energy in the IEDs of the positive ions correspond to a higher energy region, and in the condition of low pressure, the values of IEDs are near zero in the low energy region (typically 0-100eV). The shapes of IEDs change among the species of positive ions. The ions with a small mass traverse the sheath in a short period, which allows these ions sense the influence of the HF source, therefore, the IEDs remain some small peaks in the characteristic bimodal distribution. For the much massive ions, the transit time is much longer, resulting these ions sense a more average sheath potential, therefore, the influence of the HF source becomes less prominent on these ions, and the small peaks in the IEDs disappear while the mass of ions increases. Because an ion after a chemical reaction may consume the total energy or convert to other species, the ions with higher chemical activity which has a higher probability of reacting with other particles have a lower energy in the IEDs.In Chapter 5, a two-dimensional hybrid model is used to study the 2D characters of the plasma parameter in axial and redial direction and the influence of the geometry structure. It finds that, the sheath structure and the electric field near the side wall are different with that near the electrode, due to the influence of the electrode, the electric field in the axial direction is much stronger than radial electric field, and the sheath in the top and the bottom region are much thicker than in the side wall of the reacting chamber. The IEDs and the ion flux incident on the electrode have little change over the electrode region, however, the electric field decreases from the edge of electrode to side wall, which leads a decrease in the ion flux in this region. IADs are almost the same at the center of the electrode, however, in the edge of the electrode, the radial electric field increases which leads more ions strike the electrode with a much larger angle.