A method of forming fine patterns includes forming an upper mask layer on a substrate, forming preliminary mask patterns on the upper mask layer, and forming upper mask patterns by etching the upper mask layer using the preliminary mask patterns as etch masks. Forming the upper mask patterns includes etching the upper mask layer by performing an etching process using an ion beam. The upper mask patterns include a first upper mask pattern formed under each of the preliminary mask patterns, and a second upper mask pattern formed between the preliminary mask patterns in a plan view and spaced apart from the first upper mask pattern.