1. A method of compensating for a 3-D mask effect using a compensating mask, comprising: generating a first kernel corresponding to a normal mask used for forming a minute pattern; generating a second kernel corresponding to a compensating mask; mixing the first kernel corresponding to the normal mask with the second kernel corresponding to the compensating mask; generating a multi-optical system kernel corresponding to mixing the first kernel and the second kernel; calibrating standard optical parameters and a pupil surface function of a projection lens positioned under a mask of an optical system to generate the first kernel and the second kernel corresponding to the normal and the compensating masks, respectively; and forming the multi-optical system kernel according to a weighting function of the kernel of the compensating mask, wherein the weighting function expresses the extent to which the compensating mask is to be used to effectively exclude the 3-D mask effect.