Large-area capacitively coupled discharges are widely used in plasma enhanced chemical vapor deposition (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 and deserves more attention and in-depth studies. Based on a fluid model coupled with transmission line model, the potential amplitude distribution on the powered electrode as well as the plasma characteristics in a capacitive plasma sustained in a silane/hydrogen discharge driven at 27.12 MHz, with 2 m square electrodes, are investigated. This work identifies three critical control parameters: pressure, silane content, and input power, with particular emphasis on radial wave attenuation caused by electron-neutral elastic collisions. The simulation results are validated by industrial experimental results, confirming the relationship between the distributions of potential amplitude on the powered electrode and the film thickness.
Two distinct mechanisms emerge from the analysis. Under low silane content with high power conditions, the surface wave radial attenuation is not significant and the surface wave wavelength variations dominate the potential amplitude distribution on the powered electrode. Conversely, 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. Neglecting the radial attenuation of the surface wave would result in significant deviations in the potential amplitude distribution on the powered electrode, as shown in the following figure.
Strategies such as adjusting power input positions or using multiple power input are studied to improve uniformity, but the improvements are still limited. Although it requires strict parameter control and machining precision, the shaped electrode demonstrates remarkable uniformity improvement of the potential distribution. In future work, it is necessary to further analyze the impact of the standing wave effects on the radial distributions of electron, ions, and neutral radicals under complex conditions, such as different chamber structures, gas flows, and temperature distributions, as well as the impact on the quality of deposited films. This will enable a more comprehensive and accurate study of standing wave effects, providing support and guidance for solving real industrial problems.