A New Technology for Negative Ion Detection and the Rapid Electron Cooling in a Pulsed High-Density Etching Plasma

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Abstract
Time-resolved measurements of key parameters in an inductively-coupled pulsed discharge in chlorine are carried out to elucidate a feature of pulsed plasma etching. Langmuir probe diagnostics in the afterglow phase show a very fast decrease in the electron temperature from 3.5 eV to 0.8 eV within 10 µs, along with a plasma potential drop from 22 V to 5 V. A new technique for measuring the time-varying absolute negative ion density is developed, which is based on laser-induced photodetachment and electron-beam excited instabilities at plasma frequency. This novel method reveals that the dissociative electron attachment yields a large increase in the chlorine negative ion density of up to 2×1010 cm-3 (∼50 % of the positive ion density) at an afterglow time of 20 µs.