Patent ID: 7139064

Claim:
An optical system, comprising: a light source for generating a first light beam; an optical element for forming the first light beam into an off-axis illumination beam having a hexapole, wherein the hexapole of the off-axis illumination beam incident upon the illumination lens includes, four first poles having a first size, and symmetrically disposed with respect to an x-axis and a y-axis, which are substantially perpendicular and intersect each other, wherein the x-axis and the y-axis are arranged on a plane that is substantially perpendicular with respect to an optical axis of the illumination lens, and two second poles having a second size equal to or greater than the first size, and disposed in the x-axis so as to be symmetric with respect to the y-axis; an illumination lens for directing the off-axis illumination beam onto a photo mask having a mask pattern; and a projection lens for receiving a second light beam transmitted through the photo mask and projecting the second light beam onto a substrate so as to form a photoresist pattern corresponding to the mask pattern on the substrate, wherein the photoresist pattern comprises a plurality of first holes arranged in rows and columns and a plurality of second holes arranged in a zigzag along a row direction and a column direction, and each second hole is arranged at a center of an imaginary rectangle limited by four first holes and has a cross-sectional area greater than those of the first holes.