Patent ID: 6555273
Filing Date: 2003-04-29
Classification: G03F

Abstract:
A method of manufacturing a photomask blank by preparing a glass substrate for the photomask blank and depositing a thin film having at least a light shielding function on a principal surface of the glass substrate, wherein:the glass substrate is selected based upon a predetermined reference set value using a method for detecting a defect for said glass substrate in accordance with optical change of an inspecting laser beam emitted from a laser source; the surface of said glass substrate including at least a pair of principal surfaces parallel to each other, at least a pair of side surfaces perpendicular to the principle surfaces, and at least one chamfered surface interposed between a principal surface and at least one side surface, said principal and said side surfaces being subjected to precision polishing; the defect being detected by introducing the laser beam in the manner such that, when a light path in the glass substrate is optically uniform, the laser beam propagates through the glass substrate to cause total reflection on the principal surfaces and the side surfaces and propagates reciprocally between at least a pair of side surfaces so that the laser beam travels throughout an inspected region surrounded by the principal surfaces, the side surfaces, and the at least one chamfered surface and by detecting the laser beam leaking from the principal surfaces, wherein: the laser beam is introduced through a chamfered surface; the laser beam being emitted only from a chamfered surface when the light path of the glass substrate is optically uniform.