US Patent 7314690 Photomask producing method and photomask blank

In a method of producing a photomask (10) in which a light-transmissive substrate (1) is formed thereon with a chromium pattern (21) having a global opening ratio difference in its plane on the light-transmissive substrate (1), use is made, as an etching mask for a chromium film (2), of an etching mask pattern (31) made of an inorganic-based material having a resistance against etching of the chromium film (2). Dry etching of the chromium film (2) is carried out under a condition selected from conditions that cause damage to a resist pattern (41) to a degree which is unallowable when etching the chromium film (2) using the resist pattern (41) as a mask.