MEASUREMENT OF THE GAS TEMPERATURE IN FLUOROCARBON RADIO-FREQUENCY DISCHARGES USING INFRARED-ABSORPTION SPECTROSCOPY

The translational gas temperature was measured in 13.56 MHz radio-freq uency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temp erature was deduced from the linewidths of the absorption lines of the se molecules. It is shown that linewidth measurements yield a simple a nd direct method to determine the gas temperature, with an accuracy up to similar to 10 K. The results obtained in CF4 and CHF3 plasmas indi cate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The t emperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased h eating rate of the gas. Moreover, it was found that the temperature ri se is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by c hemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4 plasma. (C) 1996 American Vacuum Society.