Patent ID: 7314690

Claim:
A method of producing a photomask in which a light-transmissive substrate is formed thereon with a chromium pattern having a global opening ratio difference in its plane on the light-transmissive substrate, said method characterized by comprising the steps of: preparing a photomask blank having, on said light-transmissive substrate, at least a chromium film for forming said chromium pattern, an etching mask film made of an inorganic-based material having a resistance against etching of said chromium film, and a resist film; exposing and developing said resist film with a desired pattern to form a resist pattern; applying dry etching to said etching mask film using said resist pattern as a mask to form an etching mask pattern; and applying dry etching to said chromium film using said etching mask pattern as a mask to form said chromium pattern, wherein the dry etching of said chromium film is carried out under a condition selected from conditions that cause damage to said resist pattern to a degree which is unallowable when etching said chromium film using said resist pattern as a mask, wherein, in the step of forming said chromium pattern, an etching rate of said chromium film is ten or more times an etching rate of said etching mask pattern, and selection ratio of etching rate of inorganic-based etching mask pattern material/etching rate of resist is two or more.