Patent ID: 11971653
Assignee: SHIN-ETSU CHEMICAL CO., LTD.
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 9:
10. A method of manufacturing, from the photomask blank of claim 3, a photomask having a circuit pattern in a film made of a silicon-containing material, which method comprises the steps of:
(A) forming a resist film on the side of the film made of a chromium-containing material that is away from the substrate;
(C) patterning the resist film to form a resist pattern;
(D) patterning the film made of a chromium-containing material by dry etching the film with an oxygen-containing chlorine-based gas using the resist pattern as an etching mask so as to form a pattern in the film made of a chromium-containing material;
(E) patterning the film made of a silicon-containing material by dry etching the film with a fluorine-based gas using the pattern in the film made of a chromium-containing material as an etching mask so as to form a pattern in the film made of a silicon-containing material; and
(F) following step (E), leaving a portion of the film made of a chromium-containing material located at an outer peripheral edge of the substrate that is a region where a circuit pattern is not formed in the film made of a silicon-containing material and removing the pattern in the film made of a chromium-containing material in areas other than at the outer peripheral edge of the substrate by dry etching with an oxygen-containing chlorine-based gas.