Glass substrate for an electron device, photomask blank and photomask using the same

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 surface of the 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 the principal surface and at least one side surface, said principal and said side surfaces being subjected to precision polishing;
• the glass substrate being such that, where the dimension of a damage present on the principal surface of the glass substrate and having a particular directivity is represented by a first length in a major-axis direction and a second length in a minor-axis direction perpendicular to the major-axis direction, the second length of the damage in the minor-axis direction is equal to 1 μm or less when the damage is cut along a plane perpendicular to the principal surface
• wherein:
• the second length of the damage in the minor-axis direction is not greater than 0.5 μm.

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 surface of the 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 the principal surface and at least one side surface;
• a laser beam being introduced in the manner such that 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;
• the glass substrate being such that no stain within the glass substrate is detected when detection of a defect is carried out in accordance with optical change of the laser beam leaking from the surface of the glass substrate,
• wherein:
• the laser beam is introduced through the chamfered surface;
• the laser beam being emitted only from the chamfered surface when the light path of the glass substrate is optically uniform.