1. A method of manufacturing a mask, the method comprising: designing a second mask data pattern for forming a first mask data pattern; creating a first emulation pattern, which is determined from the second mask data pattern, using a first emulation; creating a second emulation pattern, which is determined from the first emulation pattern, using a second emulation; comparing a pattern, in which the first and second emulation patterns overlap, with the first mask data pattern; and manufacturing a mask layer, which corresponds to the second mask data pattern, according to results of the comparison.