GLASS SUBSTRATE FOR MASK BLANK, MASK BLANK, AND PHOTOMASK

摘要

PROBLEM TO BE SOLVED: To provide a glass substrate for mask blank, which can improve a measurement accuracy of flatness of a main surface, when an inclined surface is held by a flatness measurement apparatus.SOLUTION: A glass substrate for mask blank includes two main surfaces that are substantially parallel with each other, two side surfaces that are substantially parallel with each other and substantially vertical to the two main surfaces, and substantially flat four inclined surfaces each of which intersects at an obtuse angle with any one of the main surfaces and connects between any one of the main surfaces and any one of the side surfaces, each of the inclined surfaces has a center line that is parallel in the longer direction with each other, when two of the side surfaces are seen from a substantially vertical direction, an angle between a center line of the arbitrary one of the inclined surfaces adjacent to the side surfaces on one side and a center line of arbitrary one of the inclined surfaces adjacent to the side surface on the opposite side is 0 rad or larger and 0.001 rad or smaller.SELECTED DRAWING: Figure 1