PURPOSE: To shorten a time required for an etching process, and to obtain a glass mask having a minute and high-accuracy pattern with good reproducibility, by removing a chromium oxide layer by wet etching and the remaining chromium layer by plasma etching in etching a chromium layer having 2 layer structure and low reflectivity.

CONSTITUTION: A resist film 4 is patternwise exposed with electron beams, to form a pattern on a plate, the plate is subjected to wet etching to remove the image lines of a chromium oxide film 3, then, the resist film is removed, and finally, a chromium film 2 is etched by plasma etching to obtain the remaining chromium oxide film 3' as a mask for etching.