Patent ID: 7889910

Claim:
A character pattern extracting method comprising: ranking character patterns the number of which is larger than a maximum number of character patterns which are formed in an aperture by a ranking unit depending on the number of times of reference in design data of a semiconductor device to store the character patterns in a ranking storage unit; reading the larger number of character patterns from the ranking storage unit and extracting a plurality of first extraction patterns the number of which is smaller than the maximum number by a first extracting unit from the large number of read character patterns in a descending order of the number of times of reference; defining a plurality of character patterns except the first extraction patterns out of the large number of character patterns by the first extracting unit as candidate patterns to store the candidate patterns in a candidate storage unit; reading the plurality of candidate patterns from the candidate storage unit, selecting from the read candidate patterns a plurality of candidate patterns the number of which corresponds to a difference obtained by subtracting the number of extracted patterns from the maximum number, and creating a plurality of combinations of the plurality of selected candidate patterns by a combination unit to store the combinations of the plurality of selected candidate patterns in a combination storage unit; and reading the plurality of combinations of selected candidate patterns from the combination storage unit and extracting a plurality of second extraction patterns included in a combination among the plurality of combinations of selected candidate patterns by a second extracting unit, in which a manufacturing time of the semiconductor device is most shortened.