CORRELATION BETWEEN CH3 RADICAL DENSITY AND CARBON THIN-FILM FORMATION IN RF DISCHARGE CH4 PLASMA

The CH3 radical density and the deposition rate of carbon thin film were measured under the same conditions in RF-discharge CH4 and CH4/rare gas plasmas. The behavior of the CH3 radical density showed a similar tendency as the deposition rate of carbon thin film as a function of power and CH4 pressure in CH4 plasma. In CH4/Xe plasma, where a selective formation mechanism increases the CH3 radical density with increasing Xe dilution whereas other CHx radicals are expected to decrease, the carbon deposition rate increased with increasing Xe dilution. These results strongly suggest that the CH3 radical is the dominant precursor in the him formation. The increase of film formation rate in CH4/Xe plasma was slower than that of the CH3 radical density with increasing Xe dilution. This could be attributed to the sputtering of the film by heavy Xe ions. In CH4/He plasma, where the effect of sputtering is expected to be small, the film deposition rate and the CH3 density varied in a much more similar manner.