VARIATION OF CF3, CF2 AND CF RADICAL DENSITIES WITH RF CHF3 DISCHARGE DURATION

We have measured CF3, CF2 and CF radical densities in a RF discharge CHF3 plasma using infrared diode laser absorption spectroscopy and have observed the variation of radical densities with passage of time after discharge initiation. The results show that the CF, radical densities increased with discharge time and then became stable. The thickness of fluorocarbon polymer films grown on the electrodes was also measured to investigate the influence of fluorocarbon polymer formation on CF, radical densities in the plasma. It was considered from these results that the radical density continues to increase until the electrodes are covered with a certain thickness of fluorocarbon polymer film. Moreover, the CF2 radical showed a different dependence on discharge duration to CF3 and CF radicals because of its longer lifetime.