Dynamic Variation of the Sticking Coefficient of Oxygen Atoms in Helicon-Wave Excited High-Density Oxygen Plasmas

Abstract

The sticking coefficient of O atoms on a chamber wall was determined by lifetime measurements in afterglow oxygen plasmas using two-photon laser-induced fluorescence spectroscopy. The sticking coefficient was strongly dependent on the discharge conditions. When the discharge duration was short or the oxygen gas pressure was low, the sticking coefficient was close to unity and the lifetime of O atoms was equal to the diffusion time determined by the chamber geometry. However, for a long discharge duration and a high oxygen pressure, the sticking coefficient was considerably lower and saturated at ∼0.1. The decrease in the sticking coefficient can be explained by the increase in the surface coverage due to adsorption of O atoms during the discharge. The number of O atoms which was sufficient to decrease the sticking coefficient to ∼0.1 was determined experimentally to be on the order of 1015 cm-2.