PHOTOMASK SUBSTRATE, PHOTOMASK SUBSTRATE FORMING MEMBER, PHOTOMASK SUBSTRATE MANUFACTURING METHOD, PHOTOMASK, AND EXPOSURE METHOD USING PHOTOMASK

摘要

A photomask substrate having a substantially uniform thickness comprises a first surface on which a mask pattern is to be formed and a second surface, each made of a continuous curved surface. The first surface is formed into a quadrangle composed of a first pair of sides facing each other and a second pair of sides facing each other and has supporting portions at end portions along the respective sides of the first pair. When the photomask substrate is held such that the first surface is in a substantially vertical state, a reference plane parallel to a tangent plane of the first surface at a center point of the first surface is defined to be on the side closer to the first surface than the second surface with respect to the photomask substrate. At this time, a first distance along a thickness direction between the center point of the first surface and the reference plane is shorter than a second distance along a thickness direction between midpoints of the respective sides of the second pair and the reference plane.