Correlation between CH3Radical Density and Carbon Thin-Film Formation in RF Discharge CH4Plasma

The CH3radical density and the deposition rate of carbon thin film were measured under the same conditions in RF-discharge CH4and CH4/rare gas plasmas. The behavior of the CH3radical density showed a similar tendency as the deposition rate of carbon thin film as a function of power and CH4pressure in CH4plasma. In CH4/Xe plasma, where a selective formation mechanism increases the CH3radical density with increasing Xe dilution whereas other CHxradicals are expected to decrease, the carbon deposition rate increased with increasing Xe dilution. These results strongly suggest that the CH3radical is the dominant precursor in the film formation. The increase of film formation rate in CH4/Xe plasma was slower than that of the CH3radical 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 CH3density varied in a much more similar manner.