A method of forming fine patterns of a semiconductor device by using carbon (C)-containing films includes forming an etching target film on a substrate including first and second regions; forming a plurality of first C-containing film patterns on the etching target film in the first region; forming a buffer layer which covers top and side surfaces of the plurality of first C-containing film patterns; forming a second C-containing film; removing the second C-containing film in the second region; exposing the plurality of first C-containing film patterns by removing a portion of the buffer layer in the first and second regions; and etching the etching target film by using the plurality of first C-containing film patterns, and portions of the second C-containing film which remain in the first region, as an etching mask.