Ashing Properties in a Surface-Wave Mode Plasma with a Quartz Window

Abstract

Relationship between microwave oxygen plasma and ashing properties is studied at pressures from 13.3 Pa to 133 Pa and a microwave power of 1 kW with a quartz disk-plate window. In the pressure range, electron density increases with reducing pressure. At 13.3 Pa, a produced plasma, whose electron density exceeds the cutoff density of 7.6×1010 cm-3, is in a surface-wave mode. In the surface-wave mode, plasma is confined to the window surface area and an activation energy of the ashing reaction in a downstream is 0.48 eV which is comparable to 0.5 eV with an ashing condition by oxygen atoms [O(3P)] (the so-called downstream state). On the contrary, a plasma at 133 Pa is in the volume mode and an intensity profile of a microwave electric field shows an existence of a significant standing-wave. In the volume mode, activation energy profiles depended on the intensity profile. From these comparisons, it is concluded that the surface-wave mode plasma can provide the ashing condition by the oxygen atoms. Radial uniformity of ashing rate in the surface-wave mode is much better than that in the volume mode.