Spatially resolved ion energy distribution measurements in a large-area planar microwave plasma

Abstract

By employing a movable retarding field analyser, ion energy distribution (IED) functions have been measured in a large-area microwave plasma at pressure, ranging from 0.3 to 0.8 mbar which are typical for the use of this plasma source. It can be shown that the IED functions are fully developed with decreasing exponential shapes. For a given microwave power, the IED function extends towards higher energies with increasing pressure. The mean ion energy also increases with increasing pressure and decreases with increasing distance from the active plasma region. The relationships between microwave power and mean ion energy are complex, but it is clear that the influence of microwave power on the IED and mean ion energy decreases at lower pressures and larger distances from the active plasma region. The mean ion energy near the active plasma region decreases strongly with the distance from the centre of the microwave coupling window and this implicitly shows that the plasma possesses a strongly inhomogeneous internal field structure in this direction.