Characterization of a slot antenna microwave plasma source for hydrogen plasma cleaning

Abstract

A new large volume microwave plasma source has been used for the production of a hydrogen plasma. The source consists of an annular waveguide cavity with axial slots on the inner side which acts as a field applicator to sustain a plasma at 2.45 GHz. The plasma is contained in a fused silica bell jar of 16 cm in diameter and 20 cm in height. The distance between the slots corresponds to a waveguide wavelength. The source is able to generate a highly dissociated (up to 90%) hydrogen plasma for cleaning purposes. Stable operation of the plasma source is shown for a pressure range of 0.1–1.3 mbar and a power range of 600–2000 W. The plasma can be ignited over the entire examined pressure range, and the power needed for discharge ignition is below 1.7 kW. The minimum ignition power is 1050 W for a pressure of 0.7 mbar. A double Langmuir probe and optical emission spectroscopy were used to characterize the hydrogen plasma as a function of microwave power, pressure, and position. The results indicated a typical ion density of 1.5×1011 cm−3 which is an order of magnitude less than that obtained for argon under similar conditions. The typical electron temperature is 2.5 eV for microwave power of 2 kW and pressure of 0.7 mbar.