Computational lithography, e.g., inverse lithography technique (ILT) and source mask optimization, is considered necessary for the “extremely low k1” lithography process of sub-20 nm device node. The ideal design of a curvilinear mask for computational lithography requires many changes during photomask fabrication. These range from preparation of the mask data to measurement and inspection. The manufacturability of a photomask for computational lithography is linked to predictable and manageable quality of patterning. Here, we have proposed the use of “inverse e-beam lithography” on photomask for computational lithography, which overcomes the patterning accuracy limits of conventional e-beam lithography. Furthermore, the preferred target design for ILT, a new verification method, and the accuracy required for the mask model are also discussed; with consideration of acceptable writing time () and computing power.