Basic investigations of an integrated modulator for plasma immersion ion implantation

The replacement of the external high voltage modulator by an integrated plasma based modulator recently presented, would appreciably reduce the costs of plasma immersion ion implantation equipment. Hence an inherent restriction of the integrated modulator is the limited maximum current supplied by the integrated modulator during the application of the high voltage pulse to the sample. The aim of the present publication is to investigate possibilities to overcome this limitations. Detailed investigations are presented on the response of a plasma if electrons are extracted by a large electrode with special emphasis on the processes near the wall and near the control grid of the modulator.
Switching off the negative bias voltage of the grid, controlling the electron flow to the anode, results in an increase of the plasma floating potential from -8V to about 60V, as revealed by probe measurements. All electrons leaving the plasma are collected by the anode. Further during the off - time of the grid voltage a 2 to 3 fold increase of the plasma density was observed.