MEASUREMENTS OF NEUTRAL SPECIES IN LOW-PRESSURE C2F6 DISCHARGES USING DIODE-LASER ABSORPTION-SPECTROSCOPY

We report the first diode laser spectroscopic investigation of low pressure C2F6 discharges which are commonly used for plasma etching of silicon dioxide. A new high sensitivity technique that utilizes combined wavelength and frequency modulation technique has been developed that permits individual species in gas discharges at very low pressures to be monitored. In situ measurements of the relative concentrations of the oxide etchant radicals such as CF3 and CF2 in a pure C2F6 plasma were performed in a production compatible, multiconfiguration, parallel-plate plasma etching reactor. Comparative data for the reactor configured as a diode, a triode, and a magnetic multipole enhanced triode are presented. The total pressure was varied from 0.62 to 87 mTorr. Data obtained show that both the reactor geometry and the total gas pressure have significant effects on the overall species population. The results also show that the magnetic multipole enhanced triode has a much higher efficiency for generating the etchant radicals at lower pressure than the other geometries.