Photomask substrate, photomask substrate forming member, photomask substrate fabrication method, photomask, and exposing method that uses the photomask

A photomask substrate fabricating method, comprising the steps of:

• preparing a plate shaped member with a substantially uniform thickness that comprises a first surface, whereon a mask pattern is to be formed, and a second surface, which opposes the first surface;
• disposing the plate shaped member and the forming member in a heat treatment furnace in the state wherein end part areas along one set of sides of two sets of opposing sides that constitute the second surface of the plate shaped member are supported by support parts such that the plate shaped member is substantially horizontal;
• and
• after heating the interior of the heat treatment furnace such that the temperature of the plate shaped member reaches a prescribed temperature, lowering the temperature of the plate shaped member.

A photomask substrate, wherein a first surface for forming a mask pattern is a rectangle with a diagonal line length of 1,200 mm or greater;

• the thickness of the photomask substrate is 8 mm or greater;
• the photomask substrate is held in the state wherein the first surface is substantially vertical;
• and
• if a reference plane is defined as an arbitrary plane that is parallel to the vicinity of the center of the first surface and is located at a position that is sufficiently spaced apart from the first surface on the near side of the first surface, then distances from the vicinities of end parts of a first centerline, which is one of two centerlines that constitute the first surface, to the reference plane are longer by 30-100 μm than a distance from the vicinity of the center of the first centerline to the reference plane.

A photomask substrate fabricating method, comprising the steps of:

• preparing a plate shaped member that has a thickness of 8 mm or greater and wherein a surface for forming a mask pattern is a rectangle with a diagonal line length of 1,200 mm or greater;
• disposing the plate shaped member and the forming member in a heat treatment furnace in the state wherein areas in the vicinities along one set of sides of two sets of opposing sides that constitute the lower surface of the plate shaped member are supported by support parts such that the plate shaped member is substantially horizontal;
• and
• after heating the interior of the heat treatment furnace such that the temperature of the plate shaped member reaches a prescribed temperature, lowering the temperature of the plate shaped member.