1. A mask forming method comprising: preparing design data of a mask including a plurality of tri-tone regions and a plurality of pattern regions, the plurality of pattern regions including identical repetition patterns; generating mask pattern data of the mask based on the design data; generating inspection control information for controlling inspection of a defect on the mask based on the mask pattern data, the inspection control information including information including coordinates of the identical repetition patterns, coordinates of the plurality of tri-tone regions, and inspection sensitivity information of the identical repetition patterns and of the plurality of tri-tone regions; generating an item of drawing-inspection data having the mask pattern data and the inspection control information by combining the inspection control information with the mask pattern data, wherein the item of drawing-inspection data is for use in forming and in inspecting a mask pattern of the mask; forming the mask pattern of the mask based on the item of drawing-inspection data which is generated before forming the mask pattern; and inspecting the mask pattern based on the item of drawing-inspection data, wherein the inspecting the mask pattern comprises: inspecting a first portion in the mask pattern which is different from the plurality of pattern regions by a Die-to-Database comparison method, selecting a second portion corresponding to one of the identical repetition patterns in the plurality of pattern regions based on the positional information in the item of drawing-inspection data, and inspecting the second portion by a Die-to-Die comparison method at an inspection sensitivity corresponding to the inspection sensitivity information in the item of drawing-inspection data.