Diagnostics of a hexamethyldisiloxane/oxygen deposition plasma

The study presents diagnostic results from a hexamethyldisiloxane/oxygen/argon deposition plasma. The plasma was excited by microwaves using a slot-antenna device. We mainly used Fourier transform infrared spectroscopy to monitor molecule/radical concentrations. Additionally cavity ringdown spectroscopy was set up to determine absolute atomic silicon densities. The measurements were performed in the downstream region of the reactor. By studying the correlation between radical concentrations in the plasma and different input gas compositions we could identify relevant reaction pathways. It is concluded that oxygen is not only involved in the usual oxidation channels but also in breaking the siloxane bond. Consequently, siloxane polymerization occurs mainly on the surface and not in the plasma volume. Another unexpected feature concerns the indirect production of methane by reactions, which can also be controlled through the oxygen concentration.