1. A method of repairing a mask, the method comprising: inspecting the mask using a mask inspection tool to identify a defect on a circuit pattern of the mask; repairing the defect using a mask repair tool to form a repaired pattern; forming, using a point source, a first group of diffraction images of the repaired pattern and a second group of diffraction images of a reference feature; and validating the mask by comparing the first group of diffraction images with the second group of diffraction images.