Spatio-temporal behavior of microwave sheath-voltage combination plasma source

Abstract

Microwave sheath-Voltage combination Plasma (MVP) is a high density plasma source and can be used as a suitable plasma processing device (e.g., ionized physical vapor deposition). In the present report, the temporal behavior of an argon MVP sustained along a direct-current biased Ti rod is investigated. Two plasma modes are observed, one is an "oxidized state" (OS) at the early time of the microwave plasma and the other is "ionized sputter state" (ISS) at the later times. Transition of the plasma from OS to ISS, results a prominent change in the visible color of the plasma, resulting from a significant increase in the plasma density, as measured by a Langmuir probe. In the OS, plasma is dominated by Ar ions and the density is order 10 11 cm -3 . In the ISS, metal ions from the Ti rod contribute significantly to the ion composition and higher density plasma (10 12 cm -3 ) is produced. Nearly uniform high density plasma along the length of the Ti rod is produced at very low input microwave powers (around 30 W). Optical emission spectroscopy measurements confirm the presence of sputtered Ti ions and Ti neutrals in the ISS.

Microplasma thruster powered by X-band microwaves

“…The major feature of SWP is that discharges can be established over a wide pressure range (∼10 −3 -10 3 Pa) by electromagnetic surface waves excited at plasma-dielectric interfaces without electrodes and magnetic fields; [59][60][61][62][63][64] in SWPs, the microwaves penetrate into the plasma along the interfaces even in the overdense mode to heat plasma electrons in a thin (a few mm thick or less) skin-depth layer. The present configuration of SWP source equipped with a rod antenna on the axis was originally developed for plasma materials processing, [65][66][67][68] being applied to etching of large-diameter substrates (using additionally multipole magnetic fields), 66 to coating of inner and/or outer surfaces of small-diameter metal tubes, [69][70][71] and further to the microplasma thruster; [50][51][52][53][54][55][56][57][58] in practice, it has an advantage in efficient plasma generation even in a limited, small space through surface waves excited at annular plasmadielectric interfaces around the rod antenna on the axis.…”