Double-exposure mask structure and photolithography method thereof

Double-exposure mask structure and photolithography method for performing a photolithography process on a substrate are provided. The substrate has a central region and a margin region. A double-exposure mask structure includes a plurality of parallel and spaced first masks corresponding to the central region, a plurality of parallel and spaced second masks corresponding to the central region, and a plurality of auxiliary masks. The second masks intersect with the first masks to form a plurality of overlapping regions. The auxiliary masks are not in contact with one another, and correspond to the Second masks to assist the overlapping regions neighboring to the auxiliary masks to have sufficient depth of focus for photolithography. With the auxiliary masks, the overlapping regions in the central region and neighboring to the margin region can have preferred photolithography and etching effect.