Remotely floating wire-assisted generation of high-density atmospheric pressure plasma and SF₆-added plasma etching of quartz glass

High-density and large-volume atmospheric pressure plasma can be extended remotely by placing a long floating wire inside an Ar-gas flowing quartz tube connected with an inductively coupled coil. The discharge quartz tubes were categorized into three I-shaped tubes and one L-shaped tube. The influence of the geometrical design on plasma properties was investigated. Using the floating wire-assisted L tube, an electron density of 10¹⁴ cm⁻³ and a gas temperature less than 850 K were obtained at the downstream remote region. That is where the Ar plasma plume blew out from the slit at the bottom of the floating wire-assisted L tube at a distance of 140 mm from the coil center, when 100 W of a very high-frequency power (100 MHz) was applied to the inductively coupled coil. The applicability of this new L-type plasma source for large-area glass etching with a high etch rate was explored. At the remote region where the Ar plasma plume blew out of the slit of the L tube, SF₆ gas was added for etching a quartz glass plate. Glass etching could be obtained over a large area of 15 mm × 20 mm with a maximum etch rate of 2 μm/min and a volume etch rate of 0.3 mm³/min.