Microwave plasma sources of dimensions less than a size of a few millimeters have possible applications as miniature materials processing sources for use in spatially localized deposition applications, deposition and surface treatment on the inside of larger work pieces, formation of arrays of small plasmas for simultaneous processing of localized regions across large areas, portable-low temperature sterilization, incorporation of plasmas in micro-systems for chemical analysis, microreactors, surface treatment, and micro-thrusters for spacecraft propulsion. Accordingly, this investigation is devoted to the design and development of very small microwave plasmas for localized surface treatment.
Two designs of microwave generated microplasma applicators will be presented. The first applicator is based on a microstrip transmission line, and the second one is based on a coaxial cavity. The discharge is created by using 2.45 GHz microwave energy and the diameter of the plasma stream considered in this study ranges from 2 millimeters down to 10’s microns. the microwave power utilized ranges from a few Watts to 100 Watts and the operating pressures range from 0.5 Torr up to an atmospheric pressure.
Several diagnostic techniques were utilized to characterize the miniature discharges. Gas temperature and electron density analysis was performed using optical emission spectroscopy (OES). The electron temperature and electron density measurements were performed using the double Langmuir probe (DLP). The power densities for argon discharges created by these applicators vary from 10's to over 800 Wcm-3 and the plasma densities are are in the range of 1012 to over 1014 cm-3 depending on the pressure, power, and feed gas composition.
An argon/SF6 and an argon/oxygen feed gas mixtures are used to create a plasma stream with radicals for silicon etching and polycrystalline diamond etching respectively. Experimental results for these etching procedures will also be presented.