Silicon etching by alternating irradiations of negative and positive ions

Abstract

Si etching by alternating irradiations of negative and positive ions was studied in plasma. Negative ions were confirmed by a quadrupole mass and energy analyser. The ion was a dominant species and showed a maximum in its density at 40 mTorr pressure. The Si etching rate, which was obtained under 400 kHz RF bias, has a maximum at the same pressure as has the density, confirming that the negative ion etching was effective. In the etching feature, severe side etching was observed at lower pressures such as 20 mTorr, whereas the etching was fairly directional at higher pressures such as 40 mTorr and the directionality was still kept even for width.