PURPOSE: To obtain the photomask blank and photomask having good light shieldability and low reflectivity by forming a thin film of a material specified in the atomic number ratios of the ranges of the respective contents of chromium, nitrogen and oxygen on a light transmissive substrate and patterning this thin film, thereby forming the photomask.

CONSTITUTION: The thin film 12 is formed on the light transmissive substrate 10 by a sputtering method, etc., using the material which consists of the chromium, nitrogen and oxygen and has 40 to 60%, 30 to 50% and 5 to 25% atomic number ratios of the ranges of the respective contents, by which the photomask blank is obtd. An electron beam resist or photoresist 14 is then applied on the thin film 12 and is exposed with desired patterns by using an electron beam or light and is then subjected to development processing, by which resist patterns 14 are obtd. The thin film 12 is then etched with the resist 14' as an etching mask and the resist layer 14 is peeled to obtain the photomask 12'. The photomask blank having the good light shieldability and low reflectivity at the wavelength of an excimer laser beam and the photomask formed by using this blank are obtd. in this way.