Patent ID: 8293432

Claim:
A pellicle comprising: a rectangular pellicle frame including four side bars, at least one side bar having a ventilation hole with two side openings for adjusting a pressure inside a space defined by the pellicle frame equal to an atmospheric pressure; and a filter disposed to cover an external opening of the ventilation hole for preventing entrance of a foreign substance into said space, wherein at least an edge around one of said side openings of the ventilation hole is chamfered to a degree selected from a group consisting of C0.5 to C1.0 and R0.5 to R1.0, where C0.5 means that an edge intersected by two planes at a right angle is chamfered by an inclined surface from a position 0.5 mm inward from the edge in one plane and a position 0.5 mm inward in another plane from the edge and C1.0 means that the edge is chamfered by the inclined surface from positions 1.0 mm inward from the edge at the two planes, respectively; and R0.5 means that an edge intersected by two planes at a right angle is rounded by 0.5 mm radius and R1.0 means that the edge is rounded by 1.0 mm radius.