Simulation of standing wave effects in large-area capacitively coupled silane mixture discharges

In PECVD processes for solar cell and display manufacturing, with the increase of the chamber size and driving frequency for the purpose of higher production efficiency, the non-uniformity of deposited film induced by standing wave effects becomes severe. Based on a fluid model coupled with a transmission line model, the potential amplitude between electrodes as well as the plasma characteristics in a capacitive plasma sustained in a silane/hydrogen mixture driven at 27.12 MHz, with 2 m square electrodes, are investigated. The simulation results are validated by industrial experimental results, confirming the relationship between the distributions of the potential amplitude on the powered electrode and the film thickness. In the case of high silane content and low power, significant radial attenuation of the surface wave leads to noticeable weakening of the standing wave effect due to higher electron-neutral collision frequency. In addition, the density distributions of electrons and positive ions are primarily related to their generation rates as well as axial transport. However, radial transport is more important for negative ions, especially near the electrode edges at which a negative ion density peak is observed, although the local negative ion generation rate is very low. Finally, strategies such as using multiple power inputs and shaped electrode are studied to improve uniformity.