Measurement of nc-Si:H film uniformity and diagnosis of plasma spatial structure produced by a very high frequency, differentially powered, multi-tile plasma source

This paper presents the characterization of a very high frequency, differentially powered, capacitively coupled, multi-tile plasma source, MAMELUKE. Specifically, this work concentrates on the plasma enhanced chemical vapor deposition of nano-crystalline silicon suitable for application in thin film solar manufacturing. The use of a differentially-fed multi-tile source has several benefits, but imposes a spatial structure on the plasma. Sections of dielectric insulator between the differentially-fed tiles interrupt both the electrode structure and the local gas delivery to the plasma volume, both of which contribute to the gas phase chemistry uniformity profile. We investigate the affect of these factors on the plasma spatial structure by measuring the uniformity of deposited films. We examine films deposited using the MAMELUKE source focusing on the ability to produce uniform, high quality films over large areas, with high deposition rates. Spatially resolved measurements of film thickness and crystalline fraction are presented. These measurements are then used in combination with the known behaviors of very high frequency plasma systems established by previous research to draw conclusions regarding the behavior of plasma uniformity with changing process parameters. The measurements indicate that changes in the uniformity of film properties are primarily driven by gas phase chemistry effects. Changes in local gas phase chemistry are attributed to a combination of non uniformities in both the power and gas delivery in the MAMELUKE source.