A NEW TECHNOLOGY FOR NEGATIVE-ION DETECTION AND THE RAPID ELECTRON COOLING IN A PULSED HIGH-DENSITY ETCHING PLASMA

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 mu s, 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 x 10(10) cm(-3) (similar to 50% of the positive ion density) at an afterglow time of 20 mu s.