The present invention provides a method for forming an opening, including: first, a hard mask material layer is formed on a target layer, next, a tri-layer hard mask is formed on the hard mask material layer, where the tri-layer hard mask includes an bottom organic layer (ODL), a middle silicon-containing hard mask bottom anti-reflection coating (SHB) layer and a top photoresist layer, and an etching process is then performed, to remove parts of the tri-layer hard mask, parts of the hard mask material layer and parts of the target layer in sequence, so as to form at least one opening in the target layer, where during the step for removing parts of the hard mask material layer, a lateral etching rate of the hard mask material layer is smaller than a lateral etching rate of the ODL.