Abstract:
A semiconductor integrated circuit includes a first wiring, a second wiring, a third wiring, a fourth wiring, a first overlap area, a second overlap area, a multi-cut via, the multi-cut via including a first via and a second via formed in the first direction, and a single-cut via formed to connect the third wiring to the fourth wiring in the second overlap area. A width of the second portion of the second wiring corresponding to a first direction is longer than a width of the first portion of the second wiring corresponding to the first direction. A distance between the center of the first via and the center of the second via is longer than the width of the first portion of second wiring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation application of U.S. patent application Ser. No. 13/137,461, filed on Aug. 17, 2011 now U.S. Pat. No. 8,271,926, which is a Continuation application of U.S. patent application Ser. No. 12/076,637, filed on Mar. 20, 2008, now U.S. Pat. No. 8,020,133 B2, which are incorporated by reference herein and from which the present application claims priority. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a semiconductor integrated circuit and a design technique for the same, and more particularly to a semiconductor integrated circuit with a multi-cut via and an automated layout design method for the same. 
     BACKGROUND OF THE INVENTION 
     In a semiconductor integrated circuit containing multiple wiring layers, a via is used to connect a wiring of one wiring layer with a wiring of another wiring layer. Generally, for signal lines other than the power lines, one via is provided for each connection point. Such via is called a “single-cut via”. 
     With the increased miniaturization of a semiconductor integrated circuit, the wiring width has been reduced, and also the cross-sectional area of a via has decreased. Accordingly, in the manufacturing process, it has become difficult to form a via of a desired pattern. In a worst case scenario, an open failure occurs in the single-cut via formation part and thus the desired device operation cannot be implemented, resulting in a lower yield. Further, as the cross-sectional area of a via decreases, the delay time in signal lines increases, and disconnection rate also increases due to electronic migration. These cause lowering of device operation reliability. 
     In order to address these problems, multiple vias may be provided in parallel for each connection point. Such via is called a “multi-cut via”. Particularly, when two vias are provided for each connection point, such via is called a “double-cut via”. After the wiring layout, when as many single-cut vias as possible are replaced with multi-cut vias, the device operation reliability improves. This related art has been described in US Patent Application Publication Nos. US2005/0280159A1 and US2006/0101367A1. 
       FIG. 1A  is a view illustrating an exemplary wiring layout using a conventional single-cut via. Wirings are laid out along wiring grids T 1  to T 5 . For example, a first wiring W 1  extending in a Y direction is laid out along the wiring grid T 5 ; a second wiring W 2  extending in an X direction is laid out along the wiring grid T 2 . The wirings W 1  and W 2  lie on different layers, and are connected to each other at an intersection IS of the wiring grids T 2  and T 5 . Accordingly, a single-cut via pattern SV is arranged at the intersection IS. 
       FIG. 1B  shows a layer structure of the single-cut via pattern SV. The single-cut via pattern SV is a combination of three figures A 1  to A 3 . The figure A 1  is a figure on the same wiring layer as the first wiring W 1  and constitutes part of the first wiring W 1 . On the other hand, the second figure A 2  is a figure on the same wiring layer as the second wiring W 2  and constitutes part of the second wiring W 2 . The figure A 3  represents a via. The single-cut via pattern SV is arranged so that the center of the figure A 3  is located at the center of the intersection IS. 
     In view of “grid dislocation” occurring during manufacturing of the via, the both ends of the figure A 1  are made to protrude by a width OH from the figure A 3 . Similarly, the both ends of the figure A 2  are also made to protrude by a width OH from the figure A 3 . This width OH is called an “overhang” or “extension”. That is, the overhang OH is provided as design constraint to ensure manufacturing reliability. According to our study, it is confirmed that overhang OH provided at least one of the first wiring W 1  direction or the second wiring W 2  direction is effective. Particularly, according to the technology where the gate length of a transistor is 90 nm or less, the overhang OH must be set. 
       FIG. 2A  is a view illustrating an exemplary wiring layout using a conventional multi-cut via. Referring to  FIG. 2A , instead of a single-cut via pattern SV, a multi-cut via pattern (double-cut via pattern) DV is provided at an intersection of the first wiring W 1  and second wiring W 2 . 
     The multi-cut via pattern DV is a combination of four figures B 1 , B 2 , Ba and Bb.  FIG. 2B  shows a layer structure of the multi-cut via pattern DV. The figure B 1  is a figure on the same layer as the first wiring W 1  and constitutes part of the first wiring W 1 . On the other hand, the figure B 2  is a figure on the same layer as the second wiring W 2  and constitutes part of the second wiring W 2 . The figures Ba and Bb represent two vias constituting the multi-cut via. The center of the figure Ba agrees with the center of an intersection ISa of the wiring grids T 3  and T 5 ; and the center of the figure Bb agrees with the center of an intersection ISb of the wiring grids T 2  and T 5 . 
     In the multi-cut via pattern DV, also, similarly to the single-cut via pattern SV, an overhang OH is provided as design constraint. More specifically, the both ends of the figure B 1  protrude by the overhang OH from the figures Ba and Bb. Similarly, the both ends of the  FIG. 22  also protrude by the overhang OH from the figures Ba and Bb. 
     The present inventor has noted the following point. That is, as described above, when a single-cut via is replaced with a multi-cut via, operation reliability improves. However, as the degree of semiconductor integrated circuit integration increases, the wiring becomes more complex. As a result, there is increased probability that the wirings are in close proximity to the vias. And while the overhang OH is set, the gap between wiring grids has become narrow. Thus, it is difficult to replace a single-cut via with a multi-cut via. For example, referring to  FIG. 2A , after a wiring has been arranged along the wiring grid T 4 , a multi-cut via pattern DV cannot be arranged. In this state, if a multi-cut via pattern DV is arranged, there occurs a design violation between the wiring on the wiring grid T 4  and the multi-cut via pattern DV. Consequently, not the multi-cut via pattern DV but the single-cut via pattern SV illustrated in  FIG. 1A  is arranged. Thus, the improvement in operation reliability cannot be expected so much. 
     SUMMARY 
     The present invention seeks to improve upon those problems at least in part. 
     An embodiment of the present invention discloses a semiconductor integrated circuit described below. The semiconductor integrated circuit includes: a first wiring formed on a first wiring layer; a second wiring formed on a second wiring layer different from the first wiring layer; and a multi-cut via formed in an overlap area in which the first wiring and the second wiring overlap. The multi-cut via includes a first via that connects the first wiring and the second wiring in the overlap area; and a second via that connects the first wiring and the second wiring in the overlap area. The overlap area contains a first end and a second end facing each other. The first end, first via, second via and second end are arranged along a predetermined direction in the described order. Further, the interval between the first end and first via is different from the interval between the second end and second via. According to the present embodiment, a multi-cut via can be used in an area in which no multi-cut via can be arranged according to related art, that is, only a single-cut via can be arranged. Thus, a semiconductor integrated circuit with higher reliability can be provided without increasing the chip area. 
     Further, the present embodiment discloses a semiconductor integrated circuit that includes: a single-cut via; and a multi-cut via including a first via and a second via. In the semiconductor integrated circuit, an overhang with respect to at least one of the first via and second via is smaller than an overhang with respect to the single-cut via. According to the present embodiment, a multi-cut via can be used in an area in which no multi-cut via can be arranged according to related art, that is, only a single-cut via can be arranged. Thus, a semiconductor integrated circuit with higher reliability can be provided without increasing the chip area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a plan view illustrating an exemplary wiring layout using a conventional single-cut via; 
         FIG. 1B  illustrates each layer of the single-cut via portion of  FIG. 1A ; 
         FIG. 2A  is a plan view illustrating an exemplary wiring layout using a conventional multi-cut via; 
         FIG. 2B  illustrates each layer of the multi-cut via portion of  FIG. 2A ; 
         FIG. 3A  is a conceptual view illustrating a multi-cut via pattern according to one embodiment of the present invention; 
         FIG. 3B  illustrates each layer of  FIG. 3A ; 
         FIG. 4A  is a plan view illustrating an exemplary wiring layout using the multi-cut via according to the one embodiment of the present invention; 
         FIG. 4B  is a plan view illustrating a configuration of a semiconductor integrated circuit manufactured based an the wiring layout illustrated in  FIG. 4A ; 
         FIG. 5A  is a plan view illustrating another exemplary wiring layout using the multi-cut via according to the one embodiment of the present invention; 
         FIG. 5B  is a plan view illustrating a configuration of a semiconductor integrated circuit manufactured based on the wiring layout illustrated in  FIG. 5A ; 
         FIG. 6A  is a plan view illustrating another exemplary wiring layout using the multi-cut via according to the one embodiment of the present invention; 
         FIG. 6B  is a plan view illustrating a configuration of a semiconductor integrated circuit manufactured based on the wiring layout illustrated in  FIG. 6A ; 
         FIG. 7A  is a plan view illustrating another exemplary wiring layout using the multi-cut via according to the one embodiment of the present invention; 
         FIG. 7B  is a plan view illustrating a configuration of a semiconductor integrated circuit manufactured based on the wiring layout illustrated in  FIG. 7A ; 
         FIG. 8  is a block diagram illustrating an LSI design system according to the one embodiment of the present invention; 
         FIG. 9  is a conceptual view illustrating exemplary via pattern data used in the embodiment of the present invention; and 
         FIG. 10  is a flowchart illustrating a layout design process according to the one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     1. Multi-Cut Via Pattern 
       FIGS. 3A and 3B  illustrate a multi-cut via pattern MV according to an embodiment of the present invention.  FIG. 3A  illustrates a plan view of the multi-cut via pattern MV, and  FIG. 3B  illustrates each layer thereof. The multi-cut via pattern MV according to the present embodiment is a combination of four figures C 1 , C 2 , Ca and Cb. The figure C 1  is a figure on a first wiring layer and constitutes part of a first wiring formed on the first wiring layer. The figure C 2  is a figure on a second wiring layer and constitutes part of a second wiring formed on the second wiring layer. The figures Ca and Cb represent two vias constituting the multi-cut via which connects the first wiring layer with the second wiring layer. Here, the multi-cut via may include three or more vias. 
     Referring to  FIGS. 3A and 3B , WA denotes the wiring width; and WB denotes the via width. Typically, the wiring width WA is greater than the via width WB, and the difference between the wiring width WA and via width WB is expressed as 2×WC. Further, in view of “grid dislocation” occurring during manufacturing of the via, a margin is provided in a direction (wiring direction) orthogonal to the wiring width direction. More specifically, one end of the figures C 1  and C 2  representing the wiring protrude by a width OHa from the figure Ca, and the other end thereof protrude by a width CHb from the figure Cb. That is, the margins OHa and OHb are arranged between the end of the wiring and the via. The margins OHa and OHb provided along the wiring direction are “overhangs”. 
     As illustrated in  FIG. 3A , the “overhang OHa” is provided as design constraint with respect to the one via (Ca); and the “overhang OHb” is provided as design constraint with respect to the other via (Cb). According to the present embodiment, the overhang (OHa or OHb) with respect to at least one via is set smaller than the overhang OH (refer to  FIGS. 1A and 2A ) with respect to the conventional single-cut via SV or multi-cut via DV. More specifically, the overhangs CHa and OHb with respect to the multi-cut via MV according to the present embodiment satisfy the following relation.
 
WC≦OHa≦OH
 
WC≦OHb≦OH
 
     The overhang CHa is set equal to or larger than the width WC and equal to or smaller than the conventional overhang OH. Similarly, the overhang OHb is set equal to or larger than the width WC and equal to or smaller than the conventional overhang OH. The overhangs OHa and OHb may be different from each other, or may be equal to each other. However, if one of the overhangs is equal to OH, the other overhang is not equal to OH. That is, at least one of the overhangs OHa and OHb is set smaller than the conventional overhang OH. In other words, design constraint is reduced with respect to at least one via of the multi-cut via pattern MV. 
     Consequently, the multi-cut via pattern MV can be arranged in an area in which no multi-cut via pattern cannot be arranged according to related art. Thus, the operation reliability of a manufactured semiconductor integrated circuit improves, compared to related art. Here, lowering of reliability caused by reduction of design constraint in the manufacturing process is small, compared to the improvement of operation reliability provided by using the multi-cut via. 
     2. Example of Application 
     Various examples of application of the multi-cut via pattern MV according to the present embodiment illustrated in  FIGS. 3A and 3B  will be described below. 
     2-1. First Example 
       FIG. 4A  illustrates an exemplary wiring layout using the multi-cut via pattern MV. A first wiring W 1  on a first wiring layer extending in a Y direction is laid out along a wiring grid T 5 . A second wiring W 2  on a second wiring layer extending in an X direction is laid out along a wiring grid T 2 . The multi-cut via pattern MV is arranged at an intersection of the first wiring W 1  and second wiring W 2 . The center of the figure Ca representing the one via lies on an intersection ISa of the wiring grids T 3  and T 5 ; and the center of the figure Cb representing the other via lies on an intersection ISb of the wiring grids T 2  and T 5 . 
     According to the present example, one overhang OHa is set smaller than the conventional overhang OH (OHa&lt;OH). The other overhang OHb is set equal to the conventional overhang OH (OHb=OH). Therefore, the overhangs OHa is smaller than the overhang OHb (OHa&lt;OHb). In this case, referring to  FIG. 4A , no design violation occurs between a third wiring W 3  laid out along a wiring grid T 4  and the multi-cut via pattern MV. 
     For example, consider a case where, after all wirings have been laid out using a single-cut via pattern SV, the single-cut via pattern SV is replaced with a multi-cut via pattern MV. Referring to  FIG. 4A , after a third wiring W 3  has been laid out along the wiring grid T 4 , the multi-cut via pattern DV according to related art cannot be used. In contrast, according to the present embodiment, the single-cut via pattern SV can be replaced with the multi-cut via pattern MV. That is, the probability of replacement with the multi-cut via increases. Consequently, the operation reliability of a manufactured semiconductor integrated circuit improves. 
     Wirings may be laid out using the multi-cut via pattern MV in the first place. In this case, also, the probability of placement of the multi-cut via increases. Consequently, the operation reliability of a manufactured semiconductor integrated circuit improves. Also, consider a case where, when the wirings W 1  and W 2  are laid out, the third wiring W 3  has not been laid out yet. In this case, according to related art, after the multi-cut via pattern DV has been arranged, the third wiring W 3  cannot be additionally arranged. That is, when the operation reliability is raised, the easiness in wiring arrangement lessens. However, according to the present embodiment, as illustrated in  FIG. 4A , even after the multi-cut via pattern MV has been arranged, the third wiring W 3  can be additionally arranged. That is, the easiness in wiring arrangement improves, compared to related art. In other words, lessening of the easiness in wiring arrangement can be suppressed while maintaining operation reliability. 
       FIG. 4B  is a plan view illustrating a configuration of a semiconductor integrated circuit  1  manufactured based on the wiring layout illustrated in  FIG. 4A . Referring to  FIG. 4B , a first wiring  10  is formed on a first wiring layer M 1 ; and a second wiring  20  is formed on a second wiring layer M 2 . The first wiring  10  and second wiring  20  are connected via a multi-cut via  30 . To be more in detail, the first wiring  10  and second wiring  20  overlaps with each other in a “overlap area OVL”, and the multi-cut via  30  is formed in the overlap area OVL. The multi-cut via  30  includes a first via  30   a  and a second via  30   b  connecting the first wiring  10  and second wiring  20 . 
     The shape of the first wiring  10  is a combination of the pattern of the first wiring W 1  of  FIG. 4A  and the figure C 1  contained in the multi-cut via pattern MV. The shape of the second wiring  20  is a combination of the pattern of the second wiring W 2  of  FIG. 4A  and the figure C 2  contained in the multi-cut via pattern MV. Thus, the overlap area OVL of  FIG. 4B  reflects the entire shape of the multi-cut via pattern MV of  FIG. 4A . A first via  30   a  and second via  30   b  of  FIG. 4B  correspond to the figures Ca and Cb of the multi-cut via pattern MV, respectively. Accordingly, after manufacturing of the semiconductor integrated circuit  1 , overhangs OHa and OHb can be measured and compared. In this example, the overhang OHa with respect to the first via  30   a  is smaller than the overhang OHb with respect to the second via  30   b  (OHa&lt;OHb). 
     The overhangs OHa and OHb can also be defined as follows. As illustrated in  FIG. 4B , Ea and Eb denote facing ends of the overlap area OVL. The facing ends Ea and Eb of the overlap area OVL are ends arranged in a direction (Y direction) orthogonal to the wiring width direction (X direction) in the overlap area OVL. The end Ea, first via  30   a , second via  30   b  and end Eb are arranged in the Y direction in the described order. The gap between the end Ea and first via  30   a  is the overhang OHa; the gap between the end Eb and second via  30   b  is the overhang OHb. 
     When the semiconductor integrated circuit  1  includes a single-cut via, an overhang OH with respect to the single-cut via can also be measured. For example, referring to  FIG. 4B , a wiring  40  is formed on a first wiring layer M 1 ; and a wiring  50  is formed on a second wiring layer M 2 . The wiring  50  corresponds to the third wiring W 3  of  FIG. 4A . The wirings  40  and  50  are connected to each other via a single-cut via  60 . OH denotes an overhang with respect to the single-cut via  60 . In this example, the overhang OHa with respect to the first via  30   a  is smaller than the overhang OH with respect to the single-cut via  60  (OHa&lt;OH). The overhang OHb with respect to the second via  30   b  is substantially equal to the overhang OH with respect to the single-cut via  60  (OHb=OH). 
     2-2. Second Example 
       FIG. 5A  illustrates another exemplary wiring layout using a multi-cut via pattern MV;  FIG. 5B  is a plan view illustrating a configuration of a semiconductor integrated circuit  1  manufactured based on the wiring layout illustrated in  FIG. 5A . The same reference characters are applied to constituent elements corresponding to the first example, and hence an explanation thereof is omitted. 
     As illustrated in  FIG. 5A , in this example, one overhang OHa is set equal to the conventional overhang OH (OHa=OH). The other overhang OHb is set smaller than the conventional overhang OH (OHa&lt;OH). Therefore, the overhang OHb is smaller than the overhang OHa (OHb&lt;OHa). In this case, even after a third wiring W 3  has been laid out along a wiring grid T 1 , a multi-cut via pattern MV can be arranged. Alternatively, after the multi-cut via pattern MV has been arranged, the third wiring W 3  can be laid out along the wiring grid T 1 . Accordingly, operation reliability and the easiness in wiring arrangement improve, compared to related art. 
     As illustrated in  FIG. 5B , in this example, the overhang OHa with respect to the first via  30   a  is substantially equal to the overhang OH with respect to the single-cut via  60  (OHa=OH); and the overhang OHb with respect to the second via  30   b  is smaller than the overhang OH with respect to the single-cut via  60  (OHb&lt;OH). Therefore, the overhang OHb with respect to the second via  30   b  is smaller than the overhang OHa with respect to the first via  30   a  (OHb&lt;OHa). 
     2-3. Third Example 
       FIG. 6A  illustrates another exemplary wiring layout using a multi-cut via pattern MV;  FIG. 6B  is a plan view illustrating a configuration of a semiconductor integrated circuit  1  manufactured based on the wiring layout illustrated in  FIG. 6A . The same reference characters are applied to constituent elements corresponding to the above examples, and hence an explanation thereof is omitted. 
     This example is a combination of the first and second examples. That is, the overhangs OHa and OHb are both set smaller than the conventional overhang OH (OHa&lt;OH, OHb&lt;OH). As a result, the highest probability of placement of the multi-cut via pattern MV is provided. Accordingly, when the multi-cut via pattern MV according to this example is used, operation reliability and the easiness in wiring arrangement significantly improve. On the other hand, when a certain degree of manufacturing reliability must be ensured, the multi-cut via pattern MV illustrated in the first example or second example is preferably used. 
     2-4. Fourth Example 
       FIG. 7A  illustrates another exemplary wiring layout using a multi-cut via pattern MV;  FIG. 7B  is a plan view illustrating a configuration of a semiconductor integrated circuit  1  manufactured based on the wiring layout illustrated in  FIG. 7A . The same reference characters are applied to constituent elements corresponding to the above examples, and hence an explanation thereof is omitted. 
     In this example, the via position is different from that of the first example. More specifically, the center of a figure Ca representing one via is located at an intersection ISa of wiring grids T 2  and T 5 ; and the center of a figure Cb representing the other via is located at an intersection ISb of wiring grids T 1  and T 5 . In this case, no design violation occurs between a third wiring W 3  laid out along a wiring grid T 3  and the multi-cut via pattern MV. In other aspects, this example is similar to the first example. With regard to the second example and third example, also, a similar layout is possible. 
     3. Design System 
     Layout design according to the present embodiment is performed using a computer.  FIG. 8  is a block diagram illustrating an exemplary LSI design system  100  according to the present embodiment. The LSI design system  100  includes a processor  110 , storage apparatus  120 , input apparatus  130  and output apparatus  140 . The processor  110  processes data. Examples of the storage apparatus  120  include HDD and RAM. Examples of the input apparatus  130  include a keyboard and mouse. Examples of the output apparatus  140  include a display and printer. 
     In the storage apparatus  120 , there are stored net list NET, layout data LAY and via pattern data VIA. The net list NET is data indicating a connection relation between elements in an LSI for which a layout is to be designed. The layout data LAY is data indicating an LSI layout obtained by carrying out a layout design processing. The via pattern data VIA is data used during layout design processing. 
       FIG. 9  illustrates an exemplary via pattern data VIA. The via pattern data VIA indicates multiple via patterns. For example, as the multiple via patterns, there are included the single-cut via pattern SV (refer to  FIG. 1A ), the conventional multi-cut via pattern DV (refer to  FIG. 2A ) and the multi-cut via patterns MV 1  to MVn (refer to  FIG. 3A ) according to the present embodiment. Of the multi-cut via patterns MV 1  to MVn according to the present embodiment, at least one of them is prepared (n being one or more). When the multi-cut via patterns MV 1  to MVn are prepared, the overhangs OHa and OHb with respect to each pattern are set to various values. 
     Referring to  FIG. 8  again, in the storage apparatus  120 , there is also stored a layout tool  200 . The layout tool  200  is a computer program executed by the processor  110 . Using the command of the layout tool  200 , the processor  110  carries out a layout design processing according to the present embodiment. More specifically, the processor  110  reads the net list NET and via pattern data VIA from the storage apparatus  120  and carries out a wiring processing and via arrangement processing by using the data. As a result, the layout data LAY is produced. 
     The computer program code and data structures described in this detailed description are typically stored on a computer readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. This includes, but is not limited to, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs) and DVDs (digital versatile disk), and semiconductor memory devices. 
       FIG. 10  is a flowchart illustrating an exemplary wiring processing and via arrangement processing according to the present embodiment of the present invention. Firstly a routing (layout) of the first wiring W 1  on the first wiring layer is carried out (step S 10 ) Subsequently, a routing of the second wiring W 2  on the second wiring layer is carried out (step S 20 ). Subsequently, a via pattern to be arranged at an intersection of the first wiring W 1  and second wiring W 2  is selected (step S 30 ). In this case, that via pattern is selected from among multiple via patterns indicated by the via pattern data VIA according to the surrounding wiring state. 
     Firstly a multi-cut via pattern having a largest overhang is selected from the via pattern data VIA (step A 1 ). In the example of  FIG. 9 , the conventional multi-cut via pattern DV is selected. Subsequently, it is verified whether the selected multi-cut via pattern satisfies the design rule. That is, in view of the surrounding wiring state, it is verified whether the selected multi-cut via pattern can be arranged (step S 32 ). If so (step S 32 ; Yes), the selected multi-cut via pattern is used. 
     If not so (step S 32 ; No), another multi-cut via pattern is selected (step S 33 ; No). In this case, a multi-cut via pattern MV having a second largest overhang is selected (step S 34 ). Thereafter, step S 32  is executed again. If no multi-cut via patterns are arrangeable (step S 33 ; Yes), a single-cut via pattern SV is selected (step S 35 ). 
     Thereafter, the one via pattern selected in step S 30  is arranged (step S 40 ). When such processing is repeated, the layout design according to the present embodiment is implemented. 
     It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.