In a cell array of a conventional semiconductor memory device, a memory cell may include a switching element and a data storage element, and a cell may have an 8F2 configuration (F being a feature size based on a design rule). Many efforts have been made to provide increased integration of devices. More particularly, an area occupied by a memory cell has been reduced. For example, semiconductor memory devices are changing from 8F2 configurations to 6F2 configurations. Active regions of a 6F2-type cell array recently developed may be diagonal.
Portions of a conventional cell array having diagonal active regions is illustrated in FIG. 1 and FIG. 2. The conventional cell array has a plurality of diagonal active regions. Adjacent active regions are arranged face to face in a major axis direction. To define diagonal shapes on a reticle, a to-be-exposed portion is divided into segments S and S′ of a predetermined width which are exposed discontinuously. Therefore, more time may be required to fabricate a reticle than a square configuration having vertical and horizontal axis directions. Further, a segment size may be determined according to pattern-to-pattern distances B and B′ and a pattern inclination so that correcting patterns may be difficult. If patterns are disposed face to face in a major direction, a bridge may occur at patterns transcribed to a substrate if a distance between adjacent patterns is a feature size A. In the case where patterns are diagonally disposed face to face, as illustrated in FIG. 2, a pattern-to-pattern distance A′ may become narrower than a feature size increasing a possibility that a bridge may occur.
To form a normal pattern during an exposure process, an optical requirement for a light source of a direction corresponding to an inclined axis of a pattern may be provided. Thus, an optical system may adopt a unique aperture to select and irradiate light in the direction corresponding to a pattern axis.