Carbon nanocoils and/or microcoils were synthesized using C2H2 as the source gas along with the injection of SF6 as an incorporated additive gas under the thermal chemical vapor deposition (TCVD) system. To control the geometries of the carbon coils, we varied the SF6 flow injection time at different reaction temperature ranges. At the lowest reaction temperature (550°C), carbon microcoils were dominantly formed within a relatively short initial SF6 flow injection time (less than 5 min). By increasing the SF6 flow injection time, carbon nanocoils could be well developed on the entire surface of the sample. At 750°C, the formation of carbon microcoils dominated over the entire sample surface, irrespective of the SF6 flow injection time. Based on these results, the growth mechanism for the dominantly formed carbon coils was suggested and discussed. In addition, the causes for the dominant formation of carbon nanocoils and/or microcoils according to the SF6 flow injection times with the different reaction temperatures were analyzed.