Measurements of dioxygen fluoride (O2F) in an atmospheric pressure plasma jet

Abstract

When etching tantalum with a coaxial-cylinder-type atmospheric pressure plasma jet (APPJ) in a He∕CF4∕O2 gas mixture, we found that the etch rates vary little with the distance between the plasma region and the substrate. Etch rates decrease by less than a factor of 3 when the distance increases from 0.3to20.3cm in a closed tube that carries the APPJ effluent. These results indicate that reactive species may last up to 40ms in the effluent. Ultraviolet absorption spectroscopy was employed to measure possible reactive species, specifically dioxygen fluoride (O2F) and ozone (O3), in a parallel-plate type APPJ. O2F was found to be a significantly long-lived species, lasting up to 10ms in the effluent with a constant density of about 1015cm−3. Using a measured O3 density profile, the concentration of atomic fluorine (F) was estimated to be about 1013cm−3, which is two orders of magnitude lower than that of O2F at a distance of 1cm away from the APPJ exit. In summary, F atoms produced inside the APPJ combine with O2 molecules, producing O2F molecules, which can live long enough to reach and possibly etch metal surfaces.