A method for forming a photomask is provided. The method includes forming a light blocking layer over a transparent substrate. The light blocking layer has a first portion, a second portion, and a connection portion. The method includes forming a mask layer over the first portion and the second portion of the light blocking layer. The method includes removing the connection portion. The method includes removing the mask layer. The second portion of the light blocking layer is removed during removing the mask layer, while the first portion remains. The method includes after removing the mask layer and the second portion, removing the third portion of the transparent substrate to form a first recess in the transparent substrate. The method includes forming a light blocking structure in the first recess.