Creation and Evaluation of Construction Guidelines Using CFD for Low Pressure Plasma Gas Feed-in Systems to Homogenize the Precursor Gas Flow

The local gas-flow behavior is almost unknown for low pressure plasma systems, except parallel plate reactors for semiconductor purposes. To overcome this lack of knowledge, this study starts with the influence investigation of the gas feed-in systems technical layout on the homogeneity of the gas supply for large volume plasma enhanced chemical vapor deposition (PECVD) chambers. Computational fluid dynamics (CFD) simulations are used as a tool to determine velocity and pressure distribution inside the gas feed-in pipe as well as in the PECVD-chamber itself. The parameters varied were: flow rate, pipe length, number of holes, hole diameter and aspect ratio of the pipe section. The calculated pressure values are compared with the experimentally measured ones to validate the simulation results. An excellent conformity of the calculated and measured pressures is observed. With the aim to evaluate the homogeneity of gas distribution through the pipe holes the nonuniformity coefficient (Φ) was created. The results show the influence of each layout parameter in the homogeneity of the gas distribution. Hence in future correct technical layouts of gas feed-in systems can easily be applied. With these results construction guidelines has been formulated.

Introduction of a New Baffle-Plate Concept to Control the Gas Flow Behavior in a Large Volume PECVD Chamber

Achieving a reasonable homogeneity of the coating deposition rate within a low-pressure plasma process is a challenge, especially in large volume chambers. The local gas flow behavior is one key parameter in the coating deposition. Basically, with the exception of the product geometry and the electrode design, there are two main influences on the gas flow distribution inside a large volume chamber: 1) gas feed-in system and 2) gas exhaustion system. This work focuses on the gas exhaustion system with the aim to reduce its influence on the gas flow behavior inside a large plasma coater. In this sense, a solution with a perforated plate, named “Baffle-Plate”, is created. Thereby relevant construction parameters are identified and investigated to understand their influence in respect to the homogeneity of the gas exhaustion. Number of holes, hole diameter, distance of the Baffle-Plate to the top of the chamber, gas flow and chamber volume are evaluated parameters. Computational fluid dynamics (CFD) simulations are used as a tool to determine velocity and pressure distribution inside the PECVD-chamber and, consequently, to evaluate the layout parameters of the Baffle-Plate. Additionally, practical coating experiments with and without the Baffle-Plate installed are performed. The results show a correlation between the gas flow distribution and the homogeneity of the coating deposition rate. With these results construction guidelines have been formulated. Hence in future developments correct technical layouts of the Baffle-Plate can be applied, easily.