Silicon Etching Employing Negative Ion in SF₆ Plasma

Abstract

For a feasibility study of plasma etching employing bipolar ions, Si etching by negative ion was studied in SF 6 plasma. Negative ions were confirmed by Langmuir probe measurements of ion currents, in which the current ratio of both polarity ions became about unity in a down-stream region at 90 mTorr pressure. In these down-stream region, Si etching was observed not only at negative DC bias but also at positive bias, indicating negative ion etching. The activation energy of etching by negative ion was found quite low compared with that by positive ion with the same bias energy. One possible explanation for this result is that the ion species are different for the polarity.