A method of forming a pattern includes forming an etching object layer on a substrate. A photoresist layer including a metal, oxygen and an organic material is formed on the etching object layer. An exposure process is performed on the photoresist layer. A developing process is performed on the photoresist layer to form a photoresist pattern including a metal oxide. Ozone is provided onto the substrate to remove a residue of the photoresist layer that includes the organic material. The etching object layer is etched using the photoresist pattern as an etching mask.