Direct measurements of sheath-accelerated secondary electrons formonitoring the incident ion flux in plasma immersion ion implantation

Abstract

This paper reports direct measurements of sheath-accelerated secondary electrons, with a semiconductor detector, during plasma immersion ion implantation in an energy range of several keV. This new method is not essentially affected by a displacement current caused by sheath expansion immediately after a negative high voltage pulse is applied to a target. The technique enables us to obtain the absolute secondary electron flux as well as the secondary electron emission coefficient (SEEC) during the process in a plasma environment for monitoring the incident ion flux. The measured SEEC is rather high, probably because the target surface is oxidized by residual oxygen impurities in a discharge chamber. The incident ion flux estimated from the measured secondary electron flux and the SEEC is in the same order as the expected Bohm flux to the target.