A method of forming an opening pattern including the following steps is provided. An ultra low dielectric constant layer, a dielectric hard mask layer and a patterned metal hard mask layer are sequentially formed on a substrate. A portion of the dielectric hard mask layer is removed to form a patterned dielectric hard mask layer by using the patterned metal hard mask layer as a mask. The patterned metal hard mask layer is removed after forming the patterned dielectric hard mask layer. A portion of the ultra low dielectric constant layer is removed to form a first opening by using the patterned dielectric hard mask layer as a mask.