Abstract:
A pattern data processing method comprising, obtaining pattern data on a mask pattern, determining whether a processing time for the mask pattern in a processing software is reduced by rotating the mask pattern by a predetermined angle than a case where the mask pattern is processed in the processing software without being rotated, obtaining pattern data on a rotated pattern formed by rotating the mask pattern by the predetermined angle in the case that the processing time is reduced, processing the pattern data on the rotated pattern by using the processing software, and causing the mask pattern to return to its original direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority of Japanese Patent Application No. 2006-247976 filed on Sep. 13, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a pattern data processing system, a pattern data processing method, and a pattern data processing program. 
     In a process of manufacturing a semiconductor device such as an LSI, a photoresist is exposed in an exposure process. By using a resist pattern obtained by the exposure as a mask for etching, a fine device pattern such as a gate electrode is formed. 
     In the exposure process, a reduced image of a mask pattern formed on a surface of an exposure mask is projected onto a semiconductor wafer, but the image projected onto the wafer is not similar to the mask pattern due to optical proximity effect. Accordingly, in the stage of designing the exposure mask, a processing called OPC (Optical Proximity Correction) is generally carried out on the mask pattern so that the image of the mask pattern can coincide with the device pattern. 
     OPC is roughly classified into two types: rule-based OPC and model-based OPC. In both types, by inputting design data on a device pattern into a workstation or the like in which an OPC tool (software) is installed, the device pattern whose sides are caused to be uneven is outputted as design data on the mask pattern. 
     After the design data on the mask pattern is obtained in this manner, the process proceeds to a process of drawing the mask pattern on the exposure mask by using an EB (Electron Beam) exposure system. 
     However, a format of the above-described design data is different from that of drawing data used in the EB exposure system. For this reason, after carrying out OPC as described above, a processing called fracturing is carried out for converting the design data into the drawing data. 
     In this manner, in the stage of designing an exposure mask, processing such as OPC or fracturing is carried out. However, as semiconductor devices recently become highly integrated, time taken for such processings increasingly becomes longer. For example, compared with processing of obtaining design data on a mask pattern by generating a rectangle, OPC takes processing time longer several times to several tens of times, and a processing time typically is of several days. As for fracturing, it does not take such a longer time like OPC, but a several tens of hours of the processing time is taken. 
     When the processing times for OPC and fracturing are long as described above, a disadvantage is caused that a time period from the designing of an exposure mask to the completing of the exposure mask becomes longer. 
     It is also possible to obtain a resource such as a new facility or a software license to reduce the processing time. However, this causes an increase in developing costs of the exposure mask due to new facility investment. 
     Therefore, it is desired that the data processing time in the design stage of the exposure mask be reduced while the existing resources are effectively utilized. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a pattern data processing method comprising, obtaining pattern data on a mask pattern, determining whether a processing time for the mask pattern in a processing software is reduced by rotating the mask pattern by a predetermined angle than a case where the mask pattern is processed in the processing software without being rotated, obtaining pattern data on a rotated pattern formed by rotating the mask pattern by the predetermined angle in the case that the processing time is reduced, processing the pattern data on the rotated pattern by using the processing software, and causing the mask pattern to return to its original direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically showing a configuration of design data on a mask pattern used in each embodiment of the present invention. 
         FIG. 2  is a configuration diagram of a pattern data processing system according to a first embodiment of the present invention. 
         FIGS. 3A and 3B  are plan views of a test pattern used in the first embodiment of the present invention. 
         FIG. 4  is a plan view of a mask pattern used in the first embodiment of the present invention. 
         FIG. 5  is a flowchart (No. 1) for describing a pattern data processing method according to the first embodiment of the present invention. 
         FIG. 6  is a flowchart (No. 2) for describing a pattern data processing method according to the first embodiment of the present invention. 
         FIG. 7  is a plan view for describing processing contents of Step S 6  in the first embodiment of the present invention. 
         FIG. 8  is a plan view schematically showing processing contents of Step S 3  in the first embodiment of the present invention. 
         FIG. 9  is a plan view schematically showing processing contents of Step S 4  in the first embodiment of the present invention. 
         FIG. 10  is a plan view schematically showing processing contents of Step S 5  in the first embodiment of the present invention. 
         FIG. 11  is a plan view of a mask pattern used in a second embodiment of the present invention. 
         FIG. 12  is a plan view of a rotated pattern obtained by rotating the mask pattern used in the second embodiment of the present invention. 
         FIG. 13  is a plan view (No. 1) of a mask pattern used in a third embodiment of the present invention. 
         FIG. 14  is a plan view (No. 2) of a mask pattern used in the third embodiment of the present invention. 
         FIG. 15  is a flowchart showing details of Step S 6  in a first example of the third embodiment of the present invention. 
         FIG. 16  is a diagram (No. 1) for describing processing contents of Step S 6  in the first example of the third embodiment of the present invention. 
         FIG. 17  is a diagram (No. 2) for describing the processing contents of Step S 6  in the first example of the third embodiment of the present invention. 
         FIG. 18  is a flowchart showing details of Step S 6  in a second example of the third embodiment of the present invention. 
         FIG. 19  is a diagram describing details of processing contents of Step S 6  in the second example of the third embodiment of the present invention. 
         FIG. 20  is a plan view of a mask pattern used in a fourth embodiment of the present invention. 
         FIG. 21  is a flowchart for describing a pattern data processing method according to the fourth embodiment of the present invention. 
         FIG. 22  is a diagram for describing processing contents of Step S 14  of the fourth embodiment of the present invention. 
         FIG. 23A  is a diagram describing processing contents of Step S 3  in the fourth embodiment of the present invention. 
         FIG. 23B  is a diagram describing processing contents of Step S 5  in the fourth embodiment of the present invention. 
         FIG. 24  is a diagram describing processing contents of Step S 9  in the fourth embodiment of the present invention. 
         FIG. 25  is a diagram describing processing contents of Step S 15  in the fourth embodiment of the present invention. 
         FIG. 26  is a plan view of a mask pattern used to estimate effects of reducing time in the fourth embodiment of the present invention. 
         FIG. 27  is a flowchart for describing a pattern data processing method according to a fifth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (1) First Embodiment 
     In this embodiment, described is a system for carrying out processing such as OPC or fracturing on a mask pattern at the time of designing an exposure mask. 
       FIG. 1  is a diagram schematically showing a structure of design data on a mask pattern used in the present embodiment. 
     Design data D 1  has a hierarchical structure composed of  FIG. 1  to Figure X, and a Topfigure name is given thereto. The Topfigure name is used to identify each of the data D 1  in the case where a plurality of the design data D 1  are present. 
       FIG. 2  is a configuration diagram of a pattern data processing system according to the present embodiment. 
     The system  100  is, for example, a workstation that is briefly divided into a keyboard (input/output unit)  101  with which a designer performs input/output, a monitor  113 , and a control unit  102  connected to the keyboard  101  through a bus  103 . Note that a disk drive  111  for exchanging data with an external recording medium  112  is attached to the control unit  102 . 
     The control unit  102  has an operation unit  104  such as a CPU (Central Processing Unit) and a storage unit  105  such as a hard disk drive or a RPM (Random Access Memory) Of these, the storage unit  105  has a Data information database  106 , a Topfig information database  107 , a Layer information database  108 , and a tool information database  109 . 
     The Data information database  106  has information on which layer of a device corresponds to design data D 1 , e.g., information that design data D 1  is data for an interconnection layer. 
     On the other hand, the Topfigure name of the design data D 1  are stored in the Topfigure information database  107 , and layer numbers of processing targets are stored in the Layer information database  108 . 
     Then, a plurality of tools A to C are stored in the storage unit  105  as software for processing pattern data. 
     In the present embodiment, these tools A to C are software for rule-based OPC, and correction tables  110  needed for OPC are stored in the storage unit  105 . Each of the correction tables  110  comprises, for example, a pair of the gap between adjacent mask patterns and the correction amount of the pattern. 
     Note that the OPC used in the embodiment is not limited to the rule-based OPC, but may be a model-based OPC. 
     The inventor of the present application found out that each of the tools A to C has advantages and disadvantages with respect to figures to be processed. For example, processing time in some tools is faster for a figure having the vertical side longer than the horizontal side than for a figure having the vertical side shorter than the horizontal side. 
     For this reason, in the present embodiment, before OPC is performed on the design data for products, it is investigated for each of the plural tools A to C which of figures takes longer processing time, the figure having a longer vertical side than a horizontal side, or the figure having a longer horizontal side than a vertical side. Then, the obtained results are stored in the tool information database  109  as information D 2  in advance. 
       FIGS. 3A and 3B  are plan views of test patterns  21  and  22  used in this investigation. 
     In the test pattern  21  in  FIG. 3A , a total sum of lengths of vectors along the respective vertical sides is equal to  60 , and a total sum of lengths of vectors along the respective horizontal sides is equal to  12 . Accordingly, the test pattern  21  is a figure which has a longer vertical side. 
     In the following, a figure having a total sum of the lengths of the respective vertical sides larger than a total sum of the lengths of the respective horizontal sides is referred to as a “vertical figure.” 
     On the other hand, in the test pattern  22  in  FIG. 3B , a total sum of lengths of vectors along the respective vertical sides is equal to  12 , and a total sum of lengths of vectors along the respective horizontal sides is equal to  60 . Accordingly, the test pattern  21  is a figure which has a longer horizontal side. 
     In the following, a figure having a total sum of the lengths of the respective horizontal sides larger than a total sum of the lengths of the respective vertical sides is referred to as a “horizontal figure.” 
     In the above-described investigation, it is examined which of test patterns  21  and  22  takes shorter processing time for each of the tools A to C. On the basis of the investigation, decision is made on which figure to be favorite for each of the tools A to C, the vertical figure or the horizontal figure. 
     Next, a method of processing the design data using this system  100  is described. 
       FIG. 4  is a plan view of a mask pattern  10  formed in a chip region R c  of an exposure mask  11 . Note that the outline of the chip region R c  corresponds to an outer periphery of one chip to be formed in a semiconductor wafer. 
     In the following processing flow, as pattern data to be processed in the system  100 , the design data D 1  of this mask pattern  10  is used. Then, the OPC is applied to the design data D 1  by using a tool suitable for a target product, for example, the tool A, among the tools A to C. 
       FIGS. 5 and 6  are flowcharts for describing a pattern data processing method according to the present embodiment. 
     Steps S 0  to S 8  and S 16  in these flowcharts are stored in the form of a program, for example, in the recording medium  112 , and each program is executed by the operation unit  104  by installing the program in the system  100 . 
     At the first Step S 0 , the designer refers to the Data information database  106  to define which layer of the device is a target of the design data D 1  to be processed from now. Moreover, a Topfig name for identifying the data D 1  is defined by referring to the Topfig information database  107 , and a layer number of the processing target is defined by referring to the Layer information database  108 . 
     Next, proceeding to Step S 1 , the design data D 1  recorded in the recording medium  112  is read at the disk drive X 11  under the control of the operation unit  104 . 
     Then, the process proceeds to Step S 2 . Step S 2  is divided into Sub-steps S 6  to S 8 . 
     In the first Sub-step S 6 , on the basis of the design data D 1  obtained in Step S 1 , decision is made on which value to be larger, the total sum of the lengths of the vertical sides of the mask pattern  10 , or the total sum of the lengths of the horizontal sides thereof. The decision result is stored in the storage unit  105  as horizontal to vertical ratio information D 3 . 
       FIG. 7  is a plan view for describing how this decision is made. 
     As shown in  FIG. 7 , for making this decision, vectors along each side of the mask pattern  10  are firstly defined, and then the lengths of the vectors are calculated. The vector length can be obtained from an absolute value of the difference between position coordinates of adjacent vertexes by referring to position coordinates of vertexes included in the design data D 1 , for example. 
     After that, a total sum of the vector lengths in the vertical direction and a total sum of the vector lengths in the horizontal direction are obtained, and then it is determined which of the total sums is larger. 
     In this example, the total sum of the vector lengths in the vertical direction is  10  and the total sum of the vector lengths in the horizontal direction is  14 . Accordingly, the mask pattern  10  can be decided as a horizontal figure in which the total sum of the lengths of the horizontal sides is larger than the total sum of the lengths of the vertical sides. 
     Next, the process proceeds to Step S 7  in  FIG. 5 . 
     In Step S 7 , by referring to the tool information database  109 , the information D 2  is obtained. The information D 2  contains information on which of the vertical and horizontal figures takes shorter processing time in the tool A. In the present embodiment, it is assumed that the vertical figure needs shorter processing time in the tool A than the horizontal figure, and this information is included in the information D 2 . 
     Next, the process proceeds to Step S 8 . In Step S 8 , based on the decision result (the horizontal to vertical ratio information D 3 ) in Step S 6  and the information D 2  referred in Step S 7 , determination is made whether the processing time in the tool A is more reduced by rotating the mask pattern  10  by 90° in a plane than processed without rotation. 
     In this example, since the mask pattern  10  is a horizontal figure, and the processing time in the tool A is shorter for the vertical figure as described above, it is determined that the processing time is reduced (YES). 
     Next, the process proceeds to Step S 3  in  FIG. 6 . 
       FIG. 8  is a plan view schematically showing a processing content in Step S 3 . In Step S 3 , as shown in  FIG. 8 , in the operation unit  104 , pattern data D 4  of the rotated pattern  14  formed by rotating the mask pattern  10  at 90° by using the design data D 1  is generated. 
     Since commercially available OPC software and fracturing software include the function to rotate a pattern, this rotating operation can be performed by using this function. In addition, in  FIG. 8 , the mask pattern  10  is rotated in the clockwise direction to obtain the rotated pattern  14 , but the rotated pattern  14  may be obtained by rotating it in the counterclockwise direction. 
     Then, the pattern data D 4  is stored in the storage unit  105  as pre-correction data. 
     Next, the process proceeds to Step S 4  in  FIG. 6 . With referring to the correction tables  110 , the pattern data D 4  of the rotated pattern  14  is processed in the tool A, and the OPC is applied to the rotated pattern  14 . 
       FIG. 9  is a plan view of the rotated pattern  14  to which the OPC is applied in this manner. The pattern data D 5  of the rotated pattern  14  after the OPC is stored in the storage unit  105  as post-correction data. 
     Next, the process proceeds to Step S 5 . Using the pattern data D 5  in the operation unit  104 , the rotated pattern  14  is reversely rotated by 90°, so that the mask pattern  10  is caused to return to its original direction. 
       FIG. 10  is a plan view of the mask pattern  10  reversely rotated in this manner. The pattern data D 6  of the mask pattern  10  is stored in the storage unit  105  (see,  FIG. 2 ) as corrected and reversely rotated data. In addition, the pattern data D 6  can be stored in the recording medium  112  as necessary. 
     Since the mask pattern  10  is a horizontal figure in this example, it is determined in Step S 8  to rotate (YES) the mask pattern  10 . However, in the case where the mask pattern  10  is a vertical figure, it is determined in Step S 8  not to rotate (No) the mask pattern  10 , and the process proceeds to Step S 16 . 
     In Step S 16 , the OPC is applied to the design data D 1  of the mask pattern  10  by using the correction tables  110 , and the data D 5  after the processing is stored in the storage unit  105  as corrected data. 
     By these steps, main steps of the pattern data processing method according to the present embodiment have completed. 
     According to the present embodiment, information on which of the vertical figure and the horizontal figure needs shorter processing time by the tool A is obtained in advance. Then, by using this information, the mask pattern  10  is rotated in the direction that the tool A is good at processing in Step S 3 . Accordingly, a time required for OPC in Step S 4  can be reduced. 
     In addition, there is a tool among the tools A to C which can reduce the data volume of the output data D 6  by carrying out processing after rotating the mask pattern  10  in a manner described above. Accordingly, time for handling data, such as time for transferring data, can be reduced, and a region in the recording medium  112 , where the output data D 6  occupies, can be reduced. 
     Furthermore, additional facility is not required for this method. Therefore, the existing resources such as workstation and OPC tools are effectively utilized and, at the same time, it becomes possible that the data processing time in the design stage of the exposure mask is reduced. 
     (2) Second Embodiment 
     In the example in  FIG. 4  of the first embodiment, only one mask pattern  10  is formed in one chip region R c . However, in an actual device, as shown in  FIG. 11 , a plurality of mask patterns  10  and  12  are formed in one chip region R c . 
     In the present embodiment, each of the patterns  10  and  12  is considered as one figure, and process is simultaneously performed on these patterns  10  and  12  according to the flows of  FIGS. 5 and 6  of the first embodiment. 
     For example, a total sum of lengths of vertical sides and a total sum of lengths of horizontal sides of the mask pattern  12  are respectively  10  and  8 . Accordingly, a total sum of the lengths of the vertical sides of both patterns  10  and  12  is 20 (=10+10), and a total sum of all the lengths of the horizontal sides thereof is 22 (=14+8). Accordingly, in Step S 6  of  FIG. 5 , the patterns  10  and  12 , as a whole, are decided as a horizontal figure. 
     Accordingly, in Step S 8  of  FIG. 5 , both mask patterns  10  and  12  are collectively rotated by 90° to cause the mask patterns  10  and  12  to be a vertical figure that the tool A is good at processing. 
       FIG. 12  is a plan view of rotated patterns  14  and  16  obtained by rotating the patterns  10  and  12  in this manner. 
     After this step, similar to the first embodiment, process in Steps S 3  to S 5  of  FIG. 6  is performed. 
     According to the above-described present embodiment, even in the case where a plurality of mask patterns  10  and  12  exists in one chip region R c  as shown in  FIG. 11 , it is possible to decide whether the figure is vertical figure or horizontal by regarding the both patterns  10  and  12  as one figure as a whole. With this, it becomes possible that the design data on each of the patterns  10  and  12  is processed in a similar way to that of the first embodiment, and thus the processing time can be reduced. 
     (3) Third Embodiment 
     In the first embodiment, as shown in  FIG. 4 , the target mask pattern  10  is the integral figure. 
     However, as shown in  FIG. 13 , the mask pattern  10  is composed of a group of a plurality of  FIGS. 10   a  to  10   c  because of the designer&#39;s convenience in some cases. Furthermore, shapes of the respective figures constituting the mask pattern  10  may vary depending on the time of designing. Therefore, there is also a case where the mask pattern  10  is formed of  FIGS. 10   d  to  10   g  as shown in  FIG. 14 . 
     In the present embodiment, in such a case, the reduction in the processing time for the design data on the mask pattern  10  is achieved by carrying out Step S 6  described in  FIG. 5  as each of the following examples. 
     FIRST EXAMPLE 
       FIG. 15  is a flowchart showing details of Step S 6  in the present example. Note that Steps other than Step S 6  are the same as those in the first embodiment, so that the description thereof is omitted below. 
       FIG. 16  is a diagram for describing processing contents of Step S 6  in the case where the mask pattern  10  is divided into figures like  FIG. 13 . 
     As shown in  FIG. 15 , Step S 6  is composed of Sub-steps S 9  to S 11 . 
     In the first Step S 9 , as in  FIG. 16 , a sum of lengths of vertical sides and a sum of lengths of horizontal sides are obtained for each of the plural  FIGS. 10   a  to  10   c.    
     In this example, the sum of the lengths of vertical sides and sum of the lengths of the horizontal sides of the  FIG. 10   a  are respectively  10  and  2 . In addition, the sum of the lengths of the vertical sides and the sum of the length of the horizontal sides of the  FIG. 10   b  are respectively  2  and  8 . Moreover, the sum of the lengths of the vertical sides and the sum of the lengths of the horizontal sides of the  FIG. 10   c  are respectively  2  and  4 . 
     Next, the process proceeds to Step S 10  to obtain the total length of vertical sides by adding the sums of the total lengths of the vertical sides of all of the respective FIGS,  10   a  to  10   c  together. In addition, the total length of horizontal sides is obtained by adding the sums of the total lengths of the horizontal sides of all of the respective  FIGS. 10   a  to  10   c  together. 
     In the above-described example, the total length of the vertical side is 14 (=10+2+2), and the total length of the horizontal sides is 14 (=2+8+4). 
     Subsequently, the process proceeds to Step S 11  to obtain a total sum of the lengths of the vertical sides of the mask pattern  10  by subtracting the length of the vertical sides which are shared by the plural  FIGS. 10   a  to  10   c  from the total length of the vertical sides obtained in Step S 10 . 
     In this example, the vertical sides shown by hatching in  FIG. 16  are shared by the plural figures. There are four shared sides in total and each length thereof is 1. Accordingly, a total sum of the vertical sides of the mask pattern  10  becomes 10 (=14−1−1−1−1). 
     In addition, a sum of the horizontal sides of the mask pattern  10  is obtained by subtracting the length of the horizontal sides which are shared by the  FIGS. 10   a  to  10   c  from the total length of the horizontal sides obtained in Step S 10 . 
     In the above-described example, there is no horizontal side which is shared by the  FIGS. 10   a  to  10   c . Accordingly, the above-described total length of 14 per se becomes a total sum of the horizontal sides of the mask pattern  10 . 
     Up to this, Step S 6  in the present embodiment is completed. 
     According to the present embodiment, even in the case where a designer designs the mask pattern  10  with the  FIGS. 10   a  to  10   c  like  FIG. 14 , a total sum of vertical sides and a total sum of horizontal sides of the mask pattern  10  can be obtained. Accordingly, OPC can be performed on the design data D 1  of the mask pattern  10  in short time by following the flows of  FIGS. 5 and 6 . 
     It is to be noted that even in the case where the mask pattern  10  is constructed from  FIGS. 10   d  to  10   g  like  FIG. 17 , the total length of vertical sides and the total length of horizontal sides are calculated for each of the  FIGS. 10   d  to  10   g , and the process is performed by following the above-described flows, so that a total sum of the vertical sides and total sum of the horizontal sides of the mask pattern  10  can be obtained. 
     SECOND EXAMPLE 
     Next, a second example of the present embodiment is described. 
       FIG. 18  is a flowchart showing details of Step S 6  in the present example. It is to be noted that Steps other than Step S 6  are the same as those in the first embodiment, and the description thereof is omitted below. In addition,  FIG. 19  is a plan view for describing process contents of Step S 6  in the present embodiment. 
     As shown in  FIG. 18 , Step S 6  is constructed from Sub-steps S 12  and S 13 . 
     In the first Step S 12 , as shown in  FIG. 14 , in the case where the mask pattern  10  is formed of a group of the plural  FIGS. 10   a  to  10   c , OR operation is performed on data on shapes of these  FIGS. 10   a  to  10   c  to unite the  FIGS. 10   a  to  10   c.    
     With such uniting operation, the mask pattern  10  becomes an integrated figure as shown in  FIG. 19 . 
     Next, the process proceeds to Step S 13  to obtain a total sum of the lengths of respective vertical sides and a total sum of the lengths of respective horizontal sides of the united mask pattern  10 . The way to obtain the total sum is the same as that of the first embodiment, and the description thereof is omitted. 
     Up to this, Step S 6  in the present embodiment is completed. 
     In the present example, even when a designer designs the mask pattern  10  by dividing it into the  FIGS. 10   a  to  10   c , the mask pattern  10  is processed as one integrated shape by uniting these  FIGS. 10   a  to  10   c . Accordingly, OPC can be performed on the mask pattern  10  by following the same flow as that of the first embodiment and time required for OPC can be reduced. 
     (4) Fourth Embodiment 
     In the second embodiment, by following the flows of  FIGS. 5 and 6 , the processing is collectively performed on all of the mask patterns formed in one chip region R c . 
     In contrast, in the present embodiment, on each of a plurality of mask patterns in one chip, process is performed independently as described below. 
       FIG. 20  is a plan view of the mask patterns  10  and  12  to be processed in the present embodiment. Data on the mask patterns  10  and  12  are stored respectively in Figures of design data D 1 , which are different from each other. 
       FIG. 21  is a flowchart of a processing method of design data according to the present embodiment. 
     As shown in  FIG. 21 , in the present embodiment, Steps  14  and  15  are performed in addition to the Steps of the first embodiment, and other than this, the present embodiment is the same as the first embodiment. 
     Firstly, after Steps S 0  and S 1  are performed according to the first embodiment, the process proceeds to Step S 14 . In Step S 14 , as shown in  FIG. 22 , a mask pattern is divided into a plurality of units. In this example, the mask pattern  10  is divided into UNIT-F and the mask pattern  12  is divided into UNIT-U. 
     Next, Steps S 2  to S 5  and S 16  are performed on each of the UNIT-F and the UNIT-U. 
     For example, the mask pattern  10  belonging to the UNIT-F is a horizontal figure, as described above. Accordingly, in Step S 2 , it is determined that the mask pattern  10  should be rotated in a direction that the tool A is good at processing. Then, the mask pattern  10  is rotated by 90° in Step S 3 , and thus becomes a rotated pattern  14  as shown in  FIG. 23A . After that, OPC is performed thereon in Step S 4 , and thereafter, the rotated pattern  14  is reversely rotated by 90° in Step S 5 , and thus the mask pattern  10  as shown in  FIG. 23B  is obtained. 
     On the other hand, in the mask pattern  12  belonging to the UNIT-U (see  FIG. 22 ), a total sum of lengths of respective vertical sides and a total sum of lengths of respective horizontal sides are respectively  10  and  8 . Therefore, the mask pattern  12  is a vertical figure that the tool A is good at processing. Accordingly, in Step S 2 , it is determined that the mask pattern  12  should not be rotated and OPC is performed thereon in Step S 16  as it is to be, so that the state shown in  FIG. 24  is obtained. 
     After the processes completed through Step S 5  on each of UNIT-F and UNIT U, the process proceeds to Step S 15 , in which the UNIT-F and UNIT-U are combined together, so that the state shown in  FIG. 25  is obtained. 
     With this, the main Steps of the present embodiment have been completed. 
     In the above-described present embodiment, the mask patterns  10  and  12  are divided into a plurality of units (UNIT-F and UNIT-U), rotation process is performed only on the mask pattern  10  that the tool A is not good at processing, and the rotation process is not performed on the mask pattern  12 . Accordingly, the design data D 1  of the mask patterns  10  and  12  can be efficiently processed. 
     Note that two mask patterns  10  and  12  are very close to each other in some cases. In this case, if the only one of the patterns is rotated and OPC is performed on the two patterns, the patterns  10  and  12  would overlap each other when the rotated pattern is reversely rotated to bring it into the original state, so that the OPC cannot be properly performed on the patterns. In such a case, it is preferable that the both of the patterns are collectively rotated and applied with OPC, in stead of separately rotating the patterns as in the above. 
     Effects of Time Reduction 
     Next, how much the processing time is reduced in the case where design data is processed according to the present embodiment is described below. 
     It is assumed in the following that mask patterns  30  to  32  shown in  FIG. 26  are respectively divided into UNIT-A to UNIT-C. 
     Table 1 below shows a total sum of lengths of respective vertical sides and a total sum of lengths of respective horizontal sides obtained for each unit. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Total Sum of Lengths 
                 Total Sum of Lengths 
               
               
                   
                 Of Vertical Sides 
                 Of Horizontal Sides 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 UNIT-A 
                 54 
                 88 
               
               
                   
                 UNIT-B 
                 24 
                 12 
               
               
                   
                 UNIT-C 
                 12 
                 10 
               
               
                   
                 TOTAL 
                 90 
                 110 
               
               
                   
                   
               
             
          
         
       
     
     As shown in Table 1, the UNIT-A is a horizontal figure, and the UNIT-B and UNIT-C are vertical figures. 
     Here, it is assumed that processing time by a tool to be used, for example, the tool B, is shorter for a horizontal figure. In this case, the UNIT-B and UNIT-C, which are vertical figures, are to be rotated because the tool is not good at processing them. Table 2 below shows a total sum of lengths of respective vertical length and a total sum of lengths of respective horizontal sides, obtained for each unit after rotating them as described above. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Total Sum of Lengths 
                 Total Sum of Lengths 
               
               
                   
                 Of Vertical Sides 
                 Of Horizontal Sides 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 UNIT-A 
                 54 
                 88 
               
               
                   
                 UNIT-B 
                 12 
                 24 
               
               
                   
                 UNIT-C 
                 10 
                 12 
               
               
                   
                 TOTAL 
                 76 
                 124 
               
               
                   
                   
               
             
          
         
       
     
     As shown in the bottom row of Table 2, a total of the lengths of the respective vertical sides of the respective units becomes “76”, which the tool B is not good at processing, by decreasing by 14, and a total of the lengths of the horizontal respective sides of the respective units becomes 124, which the tool B is good at processing, by increasing by 14. That is, the length of the horizontal sides that the tool B is good at processing is increased approximately 1.18 times (=90/76) and the length of the vertical sides that the tool B is not good at processing is increased approximately 0.887 time (=110/124). 
     Accordingly, when it is assumed that it takes 100 hours for the processing in the case where rotation processing is not performed, it is estimated that the processing can be completed in approximately 88.7 (=0.887×100) hours even when only the reduced amount of the vertical sides is taken into account. 
     It is to be noted that, in the above description, the rotation process is applied to both of the UNIT-B and UNIT-C. However, it is also possible to perform the rotation process only on the UNIT-B. 
     Table 3 below shows a total sum of lengths of respective vertical sides and a total sum of lengths of respective horizontal sides obtained for each of the units in the case where only the UNIT-B is rotated. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Total Sum of Lengths 
                 Total Sum of Lengths 
               
               
                   
                 Of Vertical Sides 
                 Of Horizontal Sides 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 UNIT-A 
                 54 
                 88 
               
               
                   
                 UNIT-B 
                 12 
                 24 
               
               
                   
                 UNIT-C 
                 12 
                 10 
               
               
                   
                 TOTAL 
                 78 
                 122 
               
               
                   
                   
               
             
          
         
       
     
     As shown in the bottom row in Table 3, by rotating only the UNIT-C, a large difference in a total of the lengths of the sides of the respective units does not occur between before the rotation and thereafter. This is because there is not a large difference between the total of the lengths of the respective vertical sides and the total of the lengths of the respective horizontal sides in the UNIT-C. 
     From the result of Table 3, it is understood that, in order to efficiently reduce the processing time, it is effective to perform rotation process on a unit having a large difference between the total length of vertical sides and the total length of horizontal sides. 
     (5) Fifth Embodiment 
     In the above-described first to fourth embodiments, OPC is performed on the design data on the mask patterns, but it is also possible that fracturing process is performed instead of OPC. 
     In this case, in the system  100  shown in  FIG. 2 , the correction tables  110  for OPC are unnecessary, and data conversion software for fracturing is used as tools A to C. 
       FIG. 27  is a flowchart for describing a pattern data processing method according to the present embodiment. It is to be noted that Steps S 0  to S 2  before Step S 3  are the same as those in  FIG. 5  of the first embodiment, so that its explanation is omitted in the following. 
     As shown in  FIG. 27 , a difference between the present embodiment and the first embodiment (see,  FIG. 6 ) is that fracturing is performed in Steps S 4  and S 16  instead of OPC. 
     Fracturing is a process which converts a format of pattern data into a format of data for an electron beam exposure system used for drawing a mask pattern on an exposure mask. 
     In the present embodiment, as the pattern data, the design data on the mask pattern before or after the OPC is performed is employed. Then, similar to the first embodiment, the process in Steps S 1  to S 5  and S 16  are performed on the pattern data. 
     The format of the data includes GDS, OASIS, MEBES, JEOL52, HL-700, HL-800, HL-7000, VSB11, and BEF (Advantest). Among these, data on two different formats respectively become input data and output data in the fracturing. 
     Then, as a result of the processes in Steps S 3  to S 5 , and S 16 , the data D 4  to D 6  are stored in the storage unit  105 , respectively as pre-fracturing data, fractured data, and fractured and reversely rotated data. 
     Even in such a fracturing process, in Step S 3 , by rotating the mask data by 90° in a direction that tools A to C for fracturing are good at processing, it is possible to reduce time required for fracturing in Step S 4  and time required for designing an exposure mask is reduced. 
     The preferred embodiments of the present invention have been described in detail as above, but the present invention is not limited to the above-described embodiments. 
     For example, in the first to fifth embodiments, a case where vertical and horizontal figures are used has been described. However, it is possible to perform the processes on an inclined figure by rotating it in a direction that a tool for OPC or fracturing is good at processing. For example, in the case of processing a figure inclined clockwise by 45° by a tool which is good at processing a horizontal figure, it is possible that the inclined figure is rotated clockwise by 45°, and thereafter the inclined figure is rotated counterclockwise by 45° to return it into its original direction after the processes. 
     As described above, according to the embodiment, since pattern data on a mask pattern is processed by rotating the mask pattern in a direction that the processing software is good at processing, the processing time can be more reduced than the conventional method.