Patent ID: 8426087

Claim:
A photomask comprising four main features formed based on design information of a circuit feature to be formed on a substrate in order to form an exposure feature corresponding to the circuit feature on the surface of the substrate, wherein each of the main features is formed into a square or rectangular shape and has a first side extending in a first direction and a second side extending in a second direction perpendicular to the first direction, and the four main features are annularly arranged so that a quadrangle is formed by four vertices inside the four main features, when viewed from the center of the four main features, the photomask further comprising a first sub-feature laid at a predetermined position in the quadrangle defined based on the positions of the four vertices of the quadrangle in order to increase a depth of focus of the exposure feature, wherein the first sub-feature is formed into a square or rectangular shape and has a third side extending in the first direction and a fourth side extending in the second direction.