Method of forming photomask and method of manufacturing semiconductor device

A method of forming a photomask, comprising the steps of:

• successively laminating a light shielding film and a first resist film on a surface of a transparent substrate;
• patterning said first resist film to form a first resist film pattern;
• etching said light shielding film with the first resist film pattern used as a mask so as to form a single light shielding film pattern of said light shielding film in a form of an independent arrangement pattern and a plurality of light shielding film patterns of said light shielding film in a form of a collective arrangement pattern in a first region of the surface of the transparent substrate and a dummy pattern of said light shielding film in a second region of the surface of the transparent substrate;
• removing the first resist film pattern;
• forming a second resist film on the surface of the transparent substrate to cover said light shielding film patterns in the first regions and the second regions of the surface of the transparent substrate;
• patterning said second resist film to form a second resist film pattern on the first region of the surface of the transparent substrate;
• and
• removing by etching the dummy pattern in said second region with the second resist film pattern used as a mask.