For large area deposition of amorphous hydrogenated silicon (a-Si:H), capacitively coupled plasma-enhanced chemical vapor deposition with an excitation frequency of 13.56 MHz (RF-PECVD) has been predominantly used to date. Due to the good layer properties that can be achieved using RF-PECVD, this is the most common process, particularly for thin, high-quality a-Si:H layers on planar substrates.

In this project, however, extremely thick (> 30µm) a-Si:H coatings are to be deposited on planar and non-planar substrates with a deposition rate greater than 5 µm/h. For this purpose, an alternative plasma-assisted coating process is used in this project: microwave-assisted chemical vapor deposition with a plasma excitation frequency of 2.45 GHz (MW-PECVD). The basic advantage of microwave excitation over other types of discharge is that it is a plasma source and therefore the substrate does not form an electrode directly involved in the current flow. Furthermore, higher deposition rates can be achieved with MW-PECVD due to higher electron energies and electron and ion concentrations.