The Fluid Simulation Of Argon Discharge And Its Verification With COMSOL Software

Most of the processes in the semiconductor integrated circuit technology depend directly on the low-temperature plasma discharge technique, such as etching, stripping, deposition, cleaning and doping process. The properties of the plasma play a key role in those processes. For example, high density, good uniformity and controllable energy are required to achieve better process control. Three different ways, i.e. theoretical analysis, numerical simulation and experimental diagnosis can be used to study the plasma properties, and among these the numerical simulation is the most convenient means. The fluid dynamic model, the PIC/MC (Particle in cell/Monte Carlo) model and the hybrid model are methods commonly adopted in the numerical simulation. Fluid dynamics simulation is the best choice for the simulation of the large area PECVD (Plasma enhanced chemical vapor deposition) chamber discharge. The fluid dynamic model can give us the macro-parameters of plasmas include density, temperature and so on. Depending on the application needs, one can create a one-dimensional, two-dimensional or three-dimensional fluid dynamic model. The fast calculation and the high calculation efficiency are the significant advantages of the fluid dynamic model. So the macroscopic parameters of the ion can be determined quickly and accurately.In this paper, a two-dimensional fluid model is used to investigate capacitively coupled argon plasmas produced by a combination of two RF sources. In this model the momentum balance equation and the drift-diffusion approximation are used to solve the equation of ions. In order to verify the feasibility and correctness of the model, a comparison test with the two algorithms is developed by means of the commercial software COMSOL. COMSOL is the commercial software which is mainly used in the calculations of structural mechanics, and it adopts the finite element method. A separate plasma module is also provided in this software. We give the electron and ion density, the electron temperature and the potential drop in the three different cases. Meanwhile a brief analysis is taken.The first chapter briefly introduces the concept of the plasma, the way of generating plasma, the application in the semiconductor industry as well as the most widely used models of plasma discharge.Chapter II systematically introduces equations involved in the fluid dynamic model, and details corresponding to electrons, ions and neutral particles are listed. The chamber structure is given in the end. Chapter III takes a test of argon plasma discharge detailed under the fluid dynamic model. The COMSOL software is used for the comparison test to verify the correctness of the momentum equation and the drift-diffusion approximation algorithm. First of all, a group of commonly used parameters of the actual PECVD technology are selected for the validation process. Subsequently, the influences of different pressure and high-frequency voltage on the plasma parameters (the density of electron and ion, the electrical potential and the electron temperature) are studied. The simulation results show that:the increased pressure, high frequency and high-frequency voltage can effectively improve the plasma density. The high frequency has the strongest modulation to plasma density. Further, increasing the pressure, increasing the high frequency, or to reduce the high-frequency voltage could improve the uniformity of the radial distribution of plasma. The effect of the low-frequency on the plasma density is small, and can be ignored. The plasma potential has a direct relationship with the high-frequency voltage. When the pressure increases, the collision probability of particles increases; also the energy loss increases, and it causes a decrease of the electron temperature. The simulation results suggest that our software platform shows the same tendency with COMSOL. After the verification of the feasibility and correctness of our simulation platform the influences of different high-frequency and low-frequency on the plasma parameters are studied. The results show that:the increase of high frequency can significantly improve the plasma density, and low-frequency frequency has little effect on the plasma density.Chapter IV simulates the effect of the chamber structure, the time step and the space step on plasma parameters. The results show that:the increase of the electrode radius causes deterioration of uniformity of the plasma. To increase distance between two plates within a certain range is possible to effectively improve the plasma density, and the edge effect will be gradually weaken, so that the peak of plasma density at the edge of electrode will be relatively reduced, and then the uniformity of the radial plasma is improved. Time step has little effect on the plasma density. Time step should have a good correspondence with the space step in order to get a more accurate simulation results. The decrease of space step is equivalent to the increase division of the grid. Then the smoothness of the plasma density distribution curve becomes better. Less approximation improves the accuracy of the result. Plasma density increases and the uniformity of the radial distribution is also improved. But if the grid is too dense, it will seriously affect the calculation speed, so according to the actual situation, appropriate grid number should be selected.