1. A method for fabricating an exposure mask, the method comprising: decomposing a designed pattern layout that includes a plurality of line patterns and pad patterns overlapped with the line patterns into a first mask layout having a first pattern defined between two neighboring line patterns and a connection portion connecting the two neighboring line patterns, a second mask layout having a second pattern that defines the pad pattern, and a third mask layout having a third pattern that opens the connection portion; verifying the first mask layout by comparing the first mask layout with the designed pattern layout; forming a spacer over a contour image formed with the first mask layout; verifying the spacer; verifying the second mask layout by verifying an overlay margin with the first mask layout; verifying the third mask-layout by verifying an overlay margin with the first and second mask layout; combining the first mask layout, the second mask layout, and the third mask layout to perform a simulation, by a computer, to obtain a simulated image; comparing the simulated image with the designed pattern layout, re-designing the first, second, or third mask layouts after verifying the first mask layout, the second mask layout, and the third mask layout until the simulated image is identical with the designed pattern layout and a final mask layout is formed; and, fabricating a mask using the final mask layout.