An experimental and analytical study of an asymmetric capacitively coupled plasma used for plasma polymerization

Plasma processing is widely used to provide novel surface modifications to materials for a variety of applications. Typically, the systems used to carry out these modifications are poorly characterised. Here we describe the basics of a global model for a capacitively coupled asymmetric parallel plate radiofrequency plasma system routinely used to produce plasma polymers. An analytical global model was developed for argon, for which cross-sections are known, at a constant pressure of 1 Pa, and includes an electrical model and a power balance. The main parameters of interest were ion flux and self-bias voltages. The argon modelling results were then compared to experimental results for a range of operating gases (argon, oxygen, amines, acids, alcohols, ethers, siloxanes) including both saturated and unsaturated compounds with molecular weights ranging from 40 to 162 g.mol^-1, for different inter-electrode separations and from 2 to 50W using an Impedans OctIV probe. Importantly, it is shown that the RF power transfer efficiency is dependent on the gas. The results show that the argon model results can be used to predict the plasma parameters for other gases when the RF power transfer efficiency is taken into account.