Patent Publication Number: US-2017363966-A1

Title: Display device

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent Application JP 2016-120543 filed on Jun. 17, 2016, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to display devices and particularly to a display device capable of employing a high-density wiring and to a photomask for forming the high-density wiring. 
     2. Description of the Related Art 
     Since liquid crystal display devices and organic electroluminescent (EL) display devices can be made thin and light, they are used as various displays. Because fabricating such display devises individually is inefficient, many such devices are formed on a mother substrate. After the completion of the mother substrate, the display devices on the mother substrate are separated into individual units. 
     Large mother substrates have an advantage in terms of cost because many display devices can be fabricated at a time. To fabricate a display device, many photolithographic processes are performed, but the exposure device and photomasks used in the processes cannot easily be increased in size. Thus, exposure is performed on the entire surface of a large mother substrate by moving a small photomask. In other words, the same photomask is used repeatedly while the mother substrate is moved. 
     JP-A-2008-304716 discloses a mask pattern designing method that facilitates repetition of exposure. Specifically, a corrective wiring patterns are formed in the exposure frame (shot frame), or a blind frame is formed around the exposure frame with a space provided therebetween. 
     The boundary of the shot frame is prone to the problems of wire widening or narrowing due to exposure shortage or double exposure. JP-A-1999-135417 discloses a method for preventing wire widening or narrowing in which the shot frame does not take the form of a straight line but instead meanders, so that the position of the shot frame differs for each wire. 
     SUMMARY OF THE INVENTION 
     The exposure device that performs exposure on a large mother substrate by using a small photomask while moving the mother substrate is also called the stepper, and the mask pattern within the exposure frame is used repeatedly. The exposure frame needs to be set accurately each time the boundary of the mask pattern is moved, that is, each time the mother substrate is moved. However, the limit of the setting accuracy of current steppers is approximately 1 μm. 
     To eliminate the irregularity of the amount of exposure at the shot boundary, a double exposure area having a predetermined width is formed. If a positive photoresist is used, the resist pattern is narrowed in this double exposure area. Conversely, if a negative photoresist is used, the resist pattern is widened in that area. 
     The screen resolution of liquid crystal display devices and an organic EL display devices is now getting higher. Accordingly, the width or pitch of wires is getting smaller. In such display devices, the irregularity of exposure at the mask frame may cause defects such as short circuits or disconnections of the wires. The problem becomes more serious at the oblique wiring portion where the wiring pitch is smaller. 
     An object of the invention is to prevent wire failures at the photomask boundary (shot boundary) in photolithography in which a stepper is used. 
     Means for Solving the Problems 
     The invention is designed to achieve the above object and can be implemented as the following means. 
     (1) A display device includes: a display area; a terminal; and a wire formed between the display area and the terminal and connected to the terminal. In the display device, the wire includes a first part, a second part, and a third part, the first part extending in a first direction, the second and third parts extending in a direction different from the first direction, the first part being located between the second and third parts and including a protruding portion protruding in a second direction perpendicular to the first direction. 
     (2) A photomask including: first sides extending in a first direction; second sides parallel to the first sides; third sides each connecting one end of one of the first sides to one end of one of the second sides, the third sides extending in a second direction perpendicular to the first direction; fourth sides parallel to the third sides and each connecting the other end of one of the first sides to the other end of one of the second sides; and a plurality of wire patterns. In the photomask, the second and third sides meander across a first width in the first direction, each of the plurality of wire patterns includes a first part extending in the first direction and a second part slanted with respect to the second direction at a predetermined angle, and a protruding portion that protrudes in the second direction is formed on the first part at the position where the first part overlaps one of the second sides and one of the third sides. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating part of a mother substrate being exposed to light with the use of a photomask; 
         FIG. 2  is a plan view of one of the many TFT substrates formed on the mother substrate of  FIG. 1 ; 
         FIG. 3  is an enlarged plan view of the terminal area of  FIG. 2  and its nearby area; 
         FIG. 4  is an enlarged plan view of the section of  FIG. 3  that is enclosed by a one-dot chain line; 
         FIG. 5  is a plan view of the mask pattern used for the shot boundary of  FIG. 4 ; 
         FIG. 6  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomask of  FIG. 5  is used; 
         FIG. 7  is an enlarged plan view of the section of  FIG. 3  that is enclosed by a one-dot chain line and that is based on the invention; 
         FIG. 8  is a plan view of the mask pattern of Embodiment 1 that is used for the shot boundary; 
         FIG. 9  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomask of  FIG. 8  is used; 
         FIG. 10A  is a plan view of a second photomask pattern; 
         FIG. 10B  is a plan view of a first photomask pattern; 
         FIG. 10C  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomasks of  FIGS. 10A and 10B  are used; 
         FIG. 11  is a plan view of the mask pattern of another example of Embodiment 2 that is used for the shot boundary; 
         FIG. 12  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomask of  FIG. 11  is used; 
         FIG. 13  is a plan view of the mask pattern of still another example of Embodiment 2 that is used for the shot boundary; 
         FIG. 14  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomask of  FIG. 13  is used; 
         FIG. 15  is a plan view of the mask pattern of yet another example of Embodiment 2 that is used for the shot boundary; 
         FIG. 16  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomask of  FIG. 15  is used; 
         FIG. 17A  is a plan view illustrating a case where the oblique wiring of  FIG. 3  is formed on a single layer; 
         FIG. 17B  is a cross section taken along line A-A of  FIG. 17A ; 
         FIG. 18A  is a plan view illustrating a case where the oblique wiring of  FIG. 3  is formed on two layers; 
         FIG. 18B  is a cross section taken along line B-B of  FIG. 18A ; 
         FIG. 19A  is a plan view illustrating another case where the oblique wiring of  FIG. 3  is formed on two layers; 
         FIG. 19B  is a cross section taken along line C-C of  FIG. 19A ; 
         FIG. 20A  is a plan view of a second photomask pattern; 
         FIG. 20B  is a plan view of a first photomask pattern; and 
         FIG. 20C  is a plan view of the resist pattern (wiring pattern) resulting from exposure in which the photomasks of  FIGS. 20A and 20B  are used. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail. In the embodiments that follow, the direction parallel to the short sides of a TFT substrate  1  is assumed to be a first direction X while the direction parallel to the long sides of the TFT substrate  1  is assumed to be a second direction Y. The first direction X and the second direction Y are perpendicular to each other, but they can also cross each other at an angle other than 90 degrees. 
     Embodiment 11 
       FIG. 1  is a plan view illustrating part of a mother substrate being exposed to light with the use of a photomask. The mother substrate includes thereon many TFT substrates  1  of liquid crystal display panels, but  FIG. 1  illustrates only nine of them. On each of the TFT substrates  1 , a thin film transistor (TFT), a pixel electrode, a common electrode, wiring, and so forth are formed. The lower part of each TFT substrate  1  is a terminal area  120  in which many terminals  130  are formed. The terminal area  120  also includes many wires that connect to the terminals  130 . The TFT substrates  1  of  FIG. 1  are used for liquid crystal display panels, but this is only meant to be an example. The invention can also be applied to substrates for other display panels including organic EL display panels. 
     In  FIG. 1 , the photomask  10  covers multiple TFT substrates  1  (hereinafter referred to also as substrates). If the size of the photomask  10  is a whole number multiple of the size of a substrate, exposure at the boundary of the photomask  10  can be made less irregular. However, there are many different sizes of display panels, and it is impossible to change the stepper or the size of the photomask based on the sizes of the display panels. Thus, the boundary of the photomask  10  needs to be set at an arbitrary position on the wiring pattern formed on the substrates  1 . 
       FIG. 2  is a plan view of one of the many TFT substrates formed on the mother substrate of  FIG. 1 . As illustrated in  FIG. 2 , a frame area  110  is formed around a display area  100 . In the frame area  110  are many wires and the like. As further illustrated in  FIG. 2 , the terminal area  120  is formed outside the display area  100  and the frame area  110 . Disposed in the terminal area  120  is a driver IC that drives the liquid crystal display panel. The driver IC is connected to at least part of the many wires via the terminals  130  formed on the frame area  110 . 
       FIG. 3  is an enlarged plan view of the terminal area  120  of  FIG. 2  and its nearby area. As illustrated in  FIG. 3 , in the frame area  110  adjacent to the terminal area  120 , wires  30  have an oblique wiring portion  35 , which is slanted with respect to the second direction Y. In the terminal area  120 , the wires  30  run parallel to the second direction Y. This, however, is only meant to an example. In the actual product, the wires  30  can have an oblique wiring portion also in the terminal area  120 . 
     In  FIG. 3 , the two-dot chain line  125  represents the exposure boundary (hereinafter referred to also as the shot boundary). This means that the exposure performed for the right side of the shot boundary  125  of  FIG. 3  is different from that performed for the left side. Specifically, the exposure for the left side of the shot boundary  125  is performed with the use of a first photomask pattern while the exposure for the right side is performed with the use of a second photomask pattern. 
       FIG. 4  is an enlarged plan view of the section of  FIG. 3  that is enclosed by a one-dot chain line. At the oblique wiring portion  35 , the pitch or width of the wires  30  is smaller than in other areas, which poses a problem. In  FIG. 4 , the arrow direction denoted by L indicates that the second photomask pattern is used for exposure while the arrow direction denoted by R indicates that the first photomask pattern is used for exposure. 
     As illustrated in  FIG. 4 , in order to prevent exposure shortage at the shot boundary  125 , a double exposure area  50  having a predetermined width d 1  is provided. That is, the double exposure area  50  is the place where overexposure occurs. In the case of a positive photoresist, the resist gets thinner where overexposure occurred, which may cause wire disconnections. 
       FIG. 5  is a plan view of pieces of the mask pattern  11  that are used for the shot boundary  125  of  FIG. 4 . In the double exposure area  50  of  FIG. 5 , a corrective pattern  13  is formed so that the width of the pieces of the mask pattern  11  will become larger at the corrective pattern  13  than in the other portions of the mask pattern  11 . This corrective pattern  13  is used to compensate for the result of the overexposure due to the double exposure. 
       FIG. 6  illustrates the resist pattern  20  resulting from exposure in which the photomask of  FIG. 5  is used. The resist pattern  20  is equivalent to a wiring pattern. The width of the wiring pattern pieces in the double exposure area  50  is kept the same as that in the other portions. 
     However, such divided exposure at the oblique wiring portion  35  as illustrated in  FIG. 6  involves difficulties in forming the corrective pattern  13  because that is formed in an oblique direction, as is similar to the wiring forming direction. In other words, because a mask pattern is formed by combining grids, it requires time to form and adjust the corrective pattern  13 , which is slight correction in an oblique direction. As a result, the number of steps required to draw the mask pattern will increase. 
     Also, since the wiring pitch is smaller at the oblique wiring portion  35 , the formed pieces of the corrective pattern  13  are likely to be connected to each other, which may cause short circuits of the wires. Moreover, due to the small wiring pitch, the oblique wiring portion  35  is more subject to the influence of shot-to-shot variation of the exposure amount. As a result, the wiring pitch needs to be increased, and the wiring cannot be formed densely. 
       FIG. 7  is an enlarged plan view of the section of  FIG. 3  that is enclosed by a one-dot chain line and that is based on the invention. As illustrated in  FIG. 7 , the oblique wiring portion  35  includes a horizontal wiring portion  36 . The horizontal wiring portion  36  is parallel to the direction in which the photomask or the substrate moves relative to each other (hereinafter referred to also as the shot moving direction), that is, parallel to the first direction X. The length or width of the horizontal wiring portion  36  is represented by d 2 . The angle θ of the oblique wiring portion  35  in  FIG. 7  is more than 0 degrees and less than 90 degrees. As illustrated in  FIG. 7 , the wiring pitch P 2  of the horizontal wiring portion  36  can be made larger than the wiring pitch P 1  at the oblique wiring portion  35 . Thus, the width of each wire can also be made larger at the horizontal wiring portion  36 . As a result, it is possible to reduce the influence of exposure amount variation at the shot boundary. In this embodiment, the corrective pattern  13  corresponds to protruding portions, the horizontal wiring portion  36  corresponding to a first part, the oblique wiring portion  35  connected to the horizontal wiring portion  36  corresponding to second and third parts. 
     In  FIG. 7 , the arrow direction denoted by L indicates a second photomask pattern is used for exposure while the arrow direction denoted by R indicates that a first photomask pattern is used for exposure. The width of the double exposure area  50  is d 1 . The width d 1  of the double exposure area  50  in  FIG. 7  is 2 μm or greater, which is larger than the minimum distance across which the stepper can move. The width d 2  of the horizontal wiring portion  36  needs to be larger than the width d 1  of the double exposure area  50  (i.e., d 1 &lt;d 2 ). The width d 2  is preferably 3 μm or greater, more preferably 9 μm or greater. The upper limit of the width d 2  of the horizontal wiring portion  36  is determined based on wiring layout conditions because too large a width d 2  may affect the wiring layout. 
       FIG. 8  is a plan view of the mask pattern of Embodiment 1 that is used for the shot boundary  125 . In  FIG. 8 , the arrow direction denoted by L indicates a second photomask pattern is used for exposure while the arrow direction denoted by R indicates that a first photomask pattern is used for exposure. As illustrated, the corrective pattern  13  is formed in the double exposure area  50 . The mask pattern pitch is P 2 , and the width of each piece of the mask pattern  11  is Wm. Also, the height of each piece of the corrective pattern  13  is Wr, and the minimum distance between the two pieces of the mask pattern  11  (in this case, the distance between adjacent two pieces of corrective pattern  13 ) is Sm. In this case, P 2  is equal to Wm+2Wr+Sm. The height Wr of the pieces of the corrective pattern  13  is 0.5 μm or thereabout, and the minimum distance Sm between the two pieces of the mask pattern  11  is 3.0 μm or thereabout. 
       FIG. 9  is a plan view of the resist pattern  20  resulting from exposure in which the photomask of  FIG. 8  is used. The resist pattern  20  is equivalent to a wiring pattern. Due to the presence of the corrective pattern  13 , the width of the pieces of the wiring pattern in the double exposure area  50  is the same as that in the other portions. In other words, the width is the same in the double exposure area  50  and in the other portions of the wires. According to the invention, the wiring pattern width and wiring pitch at the double exposure area  50  can be kept the same as those in the other portions, as illustrated in  FIG. 9 . Therefore, wire short circuits and wire disconnections can be prevented. 
     Embodiment 2 
     Embodiment 1 is an example in which the double exposure area  50  extends along a straight line. However, when the double exposure area  50  is disposed on a straight line, problems associated double exposure occur at the upper and lower portions of wires as viewed in plan view. As a result, wire short circuits and wire disconnections may be likely to occur. 
     Therefore, in Embodiment 2, the double exposure area  50  is caused to meander so that the position of the double exposure area  50  at the upper portion of a wire is different from that at the lower portion of the wire. 
       FIGS. 10A to 10C  are plan views illustrating an exposure method according to Embodiment 2.  FIG. 10A  is a plan view illustrating a second photomask pattern. In  FIG. 10A , the left side corresponds to a light blocking portion  12  while the right side corresponds to the mask pattern  11  used to form wiring by exposure. As illustrated in  FIG. 10A , the double exposure area  50  meanders. In other words, the position where double exposure occurs differs between the upper and lower portions of a wire. The first part of the double exposure area  50  used for double exposure at the upper portion of a wire and the second part of the double exposure area  50  used for double exposure at the lower portion of the wire are displaced from each other by d 3  in the shot moving direction, that is, the first direction X. In other words, d 3  is the width across which the double exposure area  50  meanders. The meander width d 3  of the double exposure area  50  is preferably larger than the width d 1  of the double exposure area  50 , for example, more than twice as large as the width d 1 . In addition, the width d 3  of the double exposure area  50  is smaller than the width d 2  of the horizontal wiring portion  36  of  FIG. 6 . 
     A corrective pattern  13  is formed between the first part and the second part, so as to prevent wire narrowing. This middle portion between the first part and the second part, that is, the portion parallel to the horizontal wiring portion  36 , is also subjected to double exposure. This portion is formed so as to overlap a mask pattern  11 , which corresponds to a wiring pattern, for the purpose of preventing diffraction of light. 
       FIG. 10B  is a plan view illustrating a first photomask pattern. In  FIG. 10B , the right side corresponds to the light blocking portion  12  while the left side corresponds to the mask pattern  11  used to form wiring by exposure. As illustrated in  FIG. 10B , the double exposure area  50  meanders. That is, the first part of the double exposure area  50  used for double exposure at the upper portion of a wire and the second part of the double exposure area  50  used for double exposure at the lower portion of the wire are displaced from each other by d 3  in the shot moving direction, that is, the first direction X. 
     Similar to  FIG. 10A , a corrective pattern  13  is formed between the first part and the second part, so as to prevent wire narrowing. This middle portion between the first part and the second part, that is, the portion parallel to the horizontal wiring portion  36 , is also subjected to double exposure. This portion is formed so as to overlap a mask pattern  11 , which corresponds to a wiring pattern, for the purpose of preventing diffraction of light. 
       FIG. 10C  illustrates the resist pattern  20  resulting from exposure in which the photomasks of  FIGS. 10A and 10B  are used. The resist pattern  20  is equivalent to a wiring pattern. As illustrated in  FIG. 10C , the width of each piece of the wiring pattern at the first and second parts of the double exposure area  50  is kept similar to that in other portions where double exposure is not performed. On the other hand, the width of each piece of the wiring pattern is made larger on one side in the region where the double exposure area  50  runs parallel to the shot moving direction, or the first direction X. 
     The reason for the larger width is that by doing so, the middle portion of the double exposure area  50  between the first and second parts can be formed easily on a mask pattern  11 , which corresponds to a wiring pattern, when the double exposure area  50  is caused to meander. The larger width is also for reducing the influence of light diffraction on patterning. In the present embodiment, the double exposure area  50  is formed so as to overlap the horizontal wiring portion  36 , at which the wiring pitch is larger than that at the oblique wiring portion  35 . Thus, the one-sided width increase of the middle portion does not have much influence. 
     On the side where the corrective pattern  13  is not formed, slight wire narrowing may occur. However, coupled with the wire width increase on the side where the corrective pattern  13  is formed, the width of each piece of the wiring pattern at the double exposure area  50  can at least be made equal to that at portions where double exposure is not performed. It should be noted that, in the present embodiment, slightly narrowed wire portions on the side where the corrective pattern  13  is not formed correspond to recessed portions. 
       FIG. 11  is a plan view of the mask pattern of another example of Embodiment 2 that is used for the shot boundary  125 . In  FIG. 11 , the arrow direction denoted by L indicates a second photomask pattern is used for exposure while the arrow direction denoted by R indicates that a first photomask pattern is used for exposure. The mask pattern pitch is P 2 , and the width of each piece of the mask pattern  11  is Wm. Also, the height of each piece of the corrective pattern  13  is Wr, and the minimum distance between the two pieces of the mask pattern  11  (in this case, the distance between adjacent two pieces of corrective pattern  13 ) is Sm. In this case, P 2  is equal to Wm+2Wr+Sm. 
     In  FIG. 11 , the corrective pattern  13  is formed corresponding to the double exposure area  50 . Unlike  FIGS. 10A to 10C , the width of the corrective pattern  13  in  FIG. 11  is the same as that of the double exposure area  50 . In other words, the width of the corrective pattern  13  in the first direction X is not made larger. 
       FIG. 12  is a plan view illustrating the resist pattern  20  resulting from exposure in which the photomask of  FIG. 11  is used. The resist pattern  20  is equivalent to a wiring pattern. Due to the presence of the corrective pattern  13 , the width of the pieces of the wiring pattern in the double exposure area  50  is the same as that in the other portions. As further illustrated in  FIG. 12 ,  FIG. 12  is different from  FIG. 10C  in that the width of the pieces of the wiring pattern stays the same across the regions where the double exposure area  50  extends in the first direction X. In this case, short circuits of the wires are less likely to occur although the influence of light diffraction in the double exposure area  50  is more likely to emerge depending on the accuracy of the stepper. 
       FIG. 13  is a plan view of the mask pattern of still another example of Embodiment 2 that is used for the shot boundary  125 . The photomask layout and mask pattern pitch of  FIG. 13  is the same as in  FIG. 11 . However,  FIG. 13  differs from  FIG. 11  in that, in the former, two pieces of the corrective pattern  13  are formed on one side of each piece of the mask pattern  11  at the interval equal to the meander width of the double exposure area  50 . The width of the corrective pattern  13  of  FIG. 13  is the same as that of the double exposure area  50 . 
       FIG. 14  is a plan view illustrating the resist pattern  20  resulting from exposure in which the photomask of  FIG. 13  is used. The resist pattern  20  is equivalent to a wiring pattern. In the double exposure area  50  of  FIG. 14 , wire narrowing will occur on the side where the corrective pattern  13  is not formed. However, due to the presence of the corrective pattern  13  on the other side, the width of each wire can at least be made equal to that of the pieces of the wiring pattern at portions where double exposure is not performed. Further in  FIG. 14 , because the width of the corrective pattern  13  is smaller than in  FIGS. 10A to 10C , short circuit of the wires is less likely to occur. 
       FIG. 15  is a plan view of the mask pattern of yet another example of Embodiment 2 that is used for the shot boundary  125 . The photomask layout and mask pattern pitch of  FIG. 15  is the same as in  FIGS. 11 and 13 . However,  FIG. 15  differs from  FIG. 13  in that, in  FIG. 15 , a piece of the mask pattern  11  has pieces of the corrective pattern  13  formed on its first and second parts (i.e., two pieces of the corrective pattern  13  are formed at portions overlapping the double exposure area  50 ) and a piece of the mask pattern  11  located below the former has pieces of the corrective pattern  13  formed on the opposite sides of its first and second parts. The width of the corrective pattern  13  of  FIG. 15  is the same as that of the double exposure area  50 . 
       FIG. 16  is a plan view illustrating the resist pattern  20  resulting from exposure in which the photomask of  FIG. 15  is used. The resist pattern  20  is equivalent to a wiring pattern. In the double exposure area  50  of  FIG. 16 , wire narrowing will occur on the side where the corrective pattern  13  is not formed. However, due to the presence of the corrective pattern  13  on the other side, the width of each wire can at least be made equal to that of pieces of the wiring pattern at portions where double exposure is not performed. Further in  FIG. 16 , because the width of the corrective pattern  13  is smaller than in  FIGS. 10A to 10C , short circuit of the wires is less likely to occur. Moreover, in  FIG. 16 , because the minimum distance Sm between two pieces of the mask pattern  11  is larger than in  FIG. 11 , short circuit of the wires is less likely to occur. 
     Embodiment 3 
     In Embodiments 1 and 2, wires are formed on a single layer. However, the invention can also be applied to the case of multilayer wiring. In that case as well, such photomasks as mentioned in Embodiments 1 and 2 can be used to perform exposure on each layer. 
       FIG. 17A  is a plan view illustrating a case where the oblique wiring portion  35  of  FIG. 3  is formed on a single layer while  FIG. 17B  is a cross section taken along line A-A of  FIG. 17A . In  FIG. 17B , the wires  30  are formed on a substrate  40 , and a first insulating film  41  is formed to cover the wires  30  and the substrate  40 .  FIG. 18A  is a plan view illustrating a case where the oblique wiring portion  35  of  FIG. 3  is formed on two layers while  FIG. 18B  is a cross section taken along line B-B of  FIG. 18A . In  FIG. 18B , lower wires  31  are formed on the substrate  40 , and the first insulating film  41  is formed to cover the lower wires  31  and the substrate  40 . Further, upper wires  32  are formed on the first insulating film  41 , and a second insulting film  42  is formed to cover the upper wires  32  and the first insulating film  41 . In  FIGS. 18A and 18B , the upper wires  32  are formed between the lower wires  31 .  FIG. 19A  is a plan view illustrating another case where the oblique wiring portion  35  of  FIG. 3  is formed on two layers while  FIG. 19B  is a cross section taken along line C-C of  FIG. 19A . In  FIG. 19B , the lower wires  31  are formed on the substrate  40 , and the first insulating film  41  is formed to cover the lower wires  31  and the substrate  40 . Further, the upper wires  32  are formed on the first insulating film  41 , and the second insulting film  42  is formed to cover the upper wires  32  and the first insulating film  41 . In  FIGS. 19A and 19B , the upper wires  32  are formed so as to overlap the lower wires  31 . 
     In the cases of  FIGS. 18A through 19B , the exposure methods explained in Embodiments 1 and 2 can be used to form either of the upper wires  32  or the lower wires  31 . Alternatively, as illustrated in  FIGS. 20A to 20C , the mask pattern used for the shot boundary  125  can be changed in forming the lower wires  31  and the upper wires  32 . 
       FIGS. 20A to 20C  are plan views illustrating an exposure method for forming the lower wires  31 . The upper wires  32  are formed by the same exposure method as that of  FIGS. 10A to 10C .  FIGS. 20A to 20C  are the same as  FIGS. 10A to 10C  except that the meander width d 4  of the double exposure area  50  of  FIGS. 20A to 20C  is smaller than the meander width d 3  of the double exposure area  50  of  FIGS. 10A to 10C . 
     In  FIGS. 20A to 20C , the meander width of the double exposure area  50  for the lower wires  31  is larger than that for the upper wires  32 . However, the invention can also be applied in the same manner to the opposite case where the meander width of the double exposure area  50  for the lower wires  31  is smaller than that for the upper wires  32 . Further, if separate photomasks are to be used to form the lower wires  31  and the upper wires  32 , the position of the shot boundary  125  can be changed. It should be noted that, in the present embodiment, the meander width d 3  of the double exposure area  50  corresponds to a first width and that the meander width d 4  of the double exposure area  50  corresponds to a second width. 
     In the above explanation, the shot moving direction is assumed to be a horizontal direction, that is, the first direction X. However, a similar explanation apples when the shot moving direction is the second direction Y. Also, although the photoresist is assumed to be of the positive type in the above explanation, a similar explanation applies when it is a negative photoresist. At portions where resist widening will occur in the case of the positive photoresist, resist narrowing will occur in the case of the negative photoresist. Conversely, at portions where resist narrowing will occur in the case of the positive photoresist, resist widening will occur in the case of the negative photoresist. Furthermore, the invention can be applied not only to liquid crystal display panels but also to organic EL display panels.