Sheath dynamics and dose analysis for planar targets in plasma source ion implantation

Abstract

A comparison of the experimental measurements and numerical calculations of temporal and spatial sheath evolution for planar targets is presented. The propagating sheath edge initially emanates in an ellipsoidal shape elongated along the plane of the target, then transforms to a spherical shape at a distance of about one diameter from the target, and ultimately the sheath becomes stationary at a distance that depends on the plasma parameters and target dimensions. To complement sheath expansion measurements with dose uniformity in planar targets, silicon wafers were implanted with nitrogen. Surface profilometry and scanning Auger microprobe measurements showed greater sputtering and shallower implantation depths at the edge of the wafer, relative to the centre, in qualitative agreement with the sheath expansion measurements.