Abstract:
An exposure process using photomasks, the process includes the steps of: providing a plurality of glass photomasks for optical lithography with respect to a target substrate to be processed, the photomasks having identical exposure patterns, and exposing the target substrate a plurality of times using the plurality of glass photomasks.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is related to Japanese Patent Application No. 2005-087588 filed on Mar. 25, 2005, whose priory is claimed and the disclosure of which is incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an exposure process and apparatus using glass photomasks which are used in the field of optical lithography. 
   2. Description of Related Art 
   As conventional exposure processes of a type using a photomask, those shown in  FIGS. 4A-4E  and  FIGS. 5A-5E  are known.  FIGS. 4A-4E  and  FIGS. 5A-5E  are explanatory views of exposure processes for exposing a negative resist and a positive resist, respectively, using glass photomasks. 
   According to the exposure process of  FIGS. 4A-4E , a single glass photomask  10   a  is used in a single exposure apparatus. The photomask  10   a  includes a glass substrate  11  having an exposure pattern composed of a light-blocking area  12  and a light-transmitting area  13 . A glass substrate  3  to be processed (target substrate) having a metal film  31  and a negative resist  4   a  stacked thereon is exposed to exposure light through the light-transmitting area  13  ( FIG. 4A ). 
   Then, the resist  4   a  is developed so that an unexposed area of the negative resist  4   a  is dissolved and removed ( FIG. 4B ). 
   Subsequently, the metal film  31  is etched so that the metal film  31  is removed except for an area under the unremoved resist  4   a  ( FIG. 4C ). 
   The resist  4   a  is then removed so that the metal film  31  of a desired pattern appears ( FIG. 4D  and  FIG. 4E ). 
   The exposure process of  FIGS. 5A-5E  uses a single glass photomask  10   b  in a single exposure apparatus. The glass photomask  10   b  includes a glass substrate  11  having an exposure pattern composed of a light-transmitting area  12  and a light-blocking area  13 . A target glass substrate  3  having a metal film  31  and a positive resist  4   b  stacked thereon is exposed to exposure light through the light-transmitting area  13  ( FIG. 5A ). 
   Then, the resist  4   b  is developed so that an exposed area of the resist  4   b  is dissolved and removed ( FIG. 5B ). 
   Subsequently, the metal film  31  is etched so that the metal film  31  is removed except for an area under the unremoved resist  4   b  ( FIG. 5C ). 
   The resist  4   b  is then removed so that the metal film  31  of a desired pattern appears ( FIG. 5D  and  FIG. 5E ). Such processes as described above are disclosed in, for example, Japanese Unexamined Patent Publication No. HEI 4(1992)-109223. 
   Each of the glass photomasks  10   a ,  10   b  can be disposed in close contact with the target substrate or at a distance of several tens μm to several hundreds μm from the target substrate, or a pattern of the photomask can be projected onto the target substrate. 
   The conventional exposure processes using a glass photomask are carried out in the manner described above. Therefore, where there is a light-blocking defect  100  in the light-transmitting portion  13  in  FIG. 4A , an unexposed area  110  is formed as shown in  FIG. 4B  and  FIG. 4C . Further, where there is the light-blocking defect  100  in the light-transmitting portion  13  in  FIG. 5A , an unexposed area  130  is formed as shown in  FIG. 5B  and  FIG. 5C . 
   As a result, the metal film  31  having a defect  160  of missing a portion of the metal film as shown in  FIG. 4D ,  FIG. 4E  or a defect  150  of having a portion of the metal film remaining as shown in  FIG. 5D  and  FIG. 5E  is formed. In order to prevent such defects  150 ,  160 , the photomasks  10   a ,  10   b  need to be fabricated so as to eliminate the defect  100 , which results in a problem that the fabrication cost of the photomasks increases. In general, the glass photomasks have a structure in which a light-blocking pattern such as a chromium film is formed on a transparent glass substrate. The defects in the photomask  10   a ,  10   b  are caused by, for example, an air bubble or a damage in the substrate  11  as indicated by the defect  100 , a crack in the light-blocking area  12  of the substrate  11 , and adhesion of flying dust or the like during the fabrication process. 
   Particularly in plasma display panels with screens of increasing size, when the photomasks  10   a ,  10   b  are used for forming display electrodes (transparent electrodes, bus electrodes), address electrodes or barrier ribs, the substrate  11  would be defective even with only one air bubble in its large area. This results in problems that a defect-free substrate  11  increases the cost and a defective substrate  11  cannot be effectively used. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in order to solve the above problems, and it provides an exposure process using glass photomasks which allows for reduction in fabrication cost of the photomasks and effective use of a defective glass substrate. 
   According to an aspect of the present invention, there is provided an exposure process using glass photomasks, the process comprising the steps of: providing a plurality of glass photomasks for optical lithography with respect to a target substrate to be processed, the photomasks having identical exposure patterns, and exposing the target substrate a plurality of times using the plurality of glass photomasks. 
   In the above-mentioned exposure process, each glass photomask may have a light-transmitting area and a light-blocking area defined by each exposure pattern, and at least one of the photomasks may have a defect that blocks light in the light-transmitting area. 
   Further, in the above-mentioned exposure process, the exposure patterns are preferably identical within a range of tolerance. 
   According to another aspect of the invention, provided is an exposure apparatus comprising: a supporter for supporting a plurality of glass photomasks for optical lithography; a mount for mounting a target substrate to be processed; a moving unit for moving the supporter and the mount relative to each other; a light source for exposing the substrate through one of the photomasks when the photomask faces the substrate; and a controller for controlling the moving unit and the light source, wherein the plurality of glass photomasks have identical exposure patterns and the target substrate is exposed a plurality of times using the plurality of glass photomasks. 
   The mount may be movable with respect to the supporter or the supporter may be movable with respect to the mount. 
   According to the present invention, the exposure is performed the plurality of times using the plurality of glass photomasks having the same pattern. Therefore, even when there is a defect that blocks light in at least one of the photomasks, formation of an unexposed area can be eliminated by multiple exposure. This allows for minimization of the fabrication cost and effective use of a defective glass substrate as well as prevention of exposure errors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
       FIG. 1  is an explanatory view of an exposure process of a negative resist according to a first embodiment of the invention; 
       FIG. 2  is an explanatory view of an exposure process of a positive resist according to the first embodiment of the invention; 
       FIG. 3A  and  FIG. 3B  are explanatory views of exposure processes using glass photomasks according to second and third embodiments of the invention, respectively; 
       FIG. 4A  to  FIG. 4E  are explanatory views of a conventional exposure process of a negative resist; 
       FIG. 5A  to  FIG. 5E  are explanatory views of a conventional exposure process of a positive resist; 
       FIG. 6  is an explanatory view illustrating a detailed structure of an exposure apparatus for performing the exposure process of  FIG. 3A ; 
       FIG. 7  is a block diagram of a control system of the apparatus of  FIG. 6 ; 
       FIG. 8  is an explanatory view illustrating a detailed structure of an exposure apparatus for performing the exposure process of  FIG. 3B ; and 
       FIG. 9  is a block diagram of a control system of the apparatus of  FIG. 8 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
   With reference to  FIG. 1  and  FIG. 2 , an exposure system for performing an exposure process using glass photomasks according to a first embodiment of the invention will be described below.  FIG. 1  is an explanatory view of an exposure process of a negative resist using glass photomasks, and  FIG. 2  is an explanatory view of an exposure process of a positive resist using glass photomasks. 
   According to the exposure process of  FIG. 1 , a first exposure apparatus  1  and a second exposure apparatus  2  are arranged in parallel along a transfer direction (a direction of arrow A) of a substrate  3  to be processed (hereinafter referred to as a target substrate  3 ). The exposure apparatuses  1 ,  2  have glass photomasks  10   a ,  20   a . The photomask  10   a  includes a glass substrate  11  having an exposure pattern composed of a light-blocking portion (light-blocking area)  12  and a light-transmitting portion (light-transmitting area)  13 . The photomask  20   a  includes a glass substrate  21  having an exposure pattern composed of a light-blocking portion  22  and a light-transmitting portion  23 . The photomasks  10   a ,  20   a  may be formed of, for example, a glass substrate having a light-blocking film corresponding to the exposure pattern formed on or under the substrate, or a glass substrate including therein a light-blocking material corresponding to the exposure pattern. The light-blocking portion (light-blocking film) may be a chromium film. The exposure pattern of the photomask  10   a  and the exposure pattern of the photomask  20   a  are identical within a range of tolerance. The target substrate  3  is subjected to a first exposure with the first exposure apparatus  1  and then a second exposure with the second exposure apparatus  2 . It is supposed that the photomasks  10   a ,  20   a  have light-blocking defects  100 ,  200  in their light-transmitting portions, respectively, due to air bubbles. 
   In the exposure using the photomask  10   a , a negative resist  4   a  on the target substrate  3  is irradiated with exposure light through the light-transmitting portion  13  of the mounted photomask  10   a  so that a portion of the resist (a hatched portion of the resist  4   a  in  FIG. 1 ) is insolubilized to a developer. However, the defect  100  in the light-transmitting portion  13  blocks the exposure light, rendering a part of the resist  4   a  unexposed to light. Thus, an unexposed portion  110  is formed. 
   The target substrate  3  which includes the resist  4   a  having the unexposed portion  110  is moved in a direction of arrow A to the second exposure apparatus  2  and is exposed again using the exposure apparatus  2 . The resist  4   a  is then irradiated with exposure light through the light-transmitting portion  23  of the photomask  20   a  mounted in the exposure apparatus  2 . The light-transmitting portion  23  has the defect  200  caused by an air bubble as does the light-transmitting portion  13  of the photomask  10   a . However, the defects  100 ,  200  are formed in different positions of their respective photomasks  10   a ,  20   a , and there is almost no possibility that the defects  100 ,  200  are formed in the same position of the respective photomasks. Thus, the unexposed portion  110  can be exposed to exposure light through the light-transmitting portion  23  so that the unexposed portion  110  can be changed into an exposed portion  120  and be insolubilized. 
   As described above, even with the photomasks  10   a ,  20   a  formed of the glass substrates  11 ,  21  having the air-bubble defects  100 ,  200 , respectively, a complete pattern of the resist  4   a  can be accurately formed by performing the exposure twice in such a manner that the photomasks  10   a ,  20   a  complement each other. 
   According to the exposure process of  FIG. 2 , which is contrary to the process of  FIG. 1 , a positive resist  4   b  is irradiated with exposure light through a light-transmitting portion  13  of a glass photomask  10   b  so that the resist is solubilized to a developer in a first exposure apparatus  1 . However, the exposure light emitted through the light-transmitting portion  13  is blocked by an air bubble that forms a light-blocking defect  100  in the light-transmitting portion  13 . This hinders a part of the resist  4   b  from being solubilized, and thereby an unexposed portion  130  is formed (see  FIG. 2 ). 
   A target substrate  3  including the resist  4   b  having the unexposed portion  130  is moved in a direction of arrow B and placed inside a second exposure apparatus  2 . The exposure apparatus  2  emits exposure light to the resist  4   b  including the unexposed portion  130  through a light-transmitting portion  23  of a photomask  20   b  so that the unexposed portion  130  is surely exposed. Thus, whole area of the resist  4   b  corresponding to the light-transmitting portion  23  can be solubilized to the developer. 
   According to the exposure process of  FIG. 2  for the formation of a positive resist pattern, even when the photomasks  10   b ,  20   b  having the air-bubble defects is used as in the case of the negative resist, a complete pattern of the resist  4   b  can be accurately formed by performing the exposure twice in such a manner that the photomasks  10   b ,  20   b  complement each other. 
   Second Embodiment 
   In the first embodiment, the exposure is performed twice separately using two apparatuses, that is, the first and second exposure apparatuses  1 ,  2 . Now, referring to  FIG. 3A , an exposure process using glass photomasks according to a second embodiment of the invention is described. In this process, two light sources for emitting exposure light to two glass photomasks  10   a ,  20   a , respectively, are provided in a single exposure apparatus  1   a . In the exposure apparatus  1   a , a target glass substrate  3  having a negative resist  4   a  formed thereon is transported in a direction of arrow B in  FIG. 3A  so as to sequentially receive exposure light emitted from the two light sources through the photomasks  10   a ,  20   a , respectively. Thus, a complete pattern of the resist  4   a  can be accurately formed by performing the exposure twice in such a manner that the photomasks  10   a ,  20   a  complement each other as in the first embodiment. 
   Third Embodiment 
   According to the first and second embodiments, the target substrate  3  having the negative or positive resist  4   a  or  4   b  stacked thereon is moved relative to the photomasks  10   a ,  20   a  or  10   b ,  20   b . However, in an exposure process using glass photomasks according to a third embodiment of the invention shown in  FIG. 3B , a target glass substrate  3  having a negative resist  4   a  stacked thereon is fixed in a single exposure apparatus  1   b , and glass photomasks  10   a ,  20   a  are moved in directions of arrow C and arrow D in  FIG. 3B , respectively, to perform exposure. 
   Thus, according to the exposure process of the third embodiment, a complete pattern of the resist  4   a  can be accurately formed by performing the exposure twice in such a manner that the photomasks  10   a ,  20   a , one or both of which have a defect, complement each other as in the previous embodiments. 
     FIG. 6  is an explanatory view illustrating a detailed structure of the exposure apparatus  1   a  of  FIG. 3A . In  FIG. 6 , the apparatus  1   a  includes a support table  53  having openings  51 ,  52 . The support table  53  has stages  54 ,  55  disposed on the peripheries of the openings  51 ,  52 , respectively. The stages  54 ,  55  are two-dimensionally movable and slightly rotatable in a horizontal plane and are adapted to horizontally support the photomasks  10   a ,  20   a , respectively. Below the support table  53 , a sliding rail  56  is horizontally placed. The sliding rail  56  slidably supports a slider  57  in a direction of arrow B or in an opposite direction. The slider  57  has a stage  59  disposed thereon. The stage  59  is two-dimensionally movable and slightly rotatable in a horizontal plane and is adapted to horizontally support the target substrate  3 . Above the support table  53 , two light sources  60 ,  61  for emitting exposure light and collimator lens  62 ,  63  for collimating light emitted from the light sources  60 ,  61 , respectively, are provided. The light sources  60 ,  61  are adapted to vertically illuminate, through the lens  62 ,  63 , the photomasks  10   a ,  20   a  with light emitted from the light sources  60 ,  61 , respectively. The resist  4   a  on the target glass substrate  3  (see  FIG. 3A ) is then exposed to the light transmitted through the photomask  10   a  or  20   a . The support table  53  is equipped with motors  64 ,  65  for driving the stages  54 ,  55 , respectively, and the slider  57  is equipped with a motor  66  for driving the stage  59 . 
   The support table  53  includes alignment sensors  67 ,  68  for detecting alignment marks of the photomask  10   a  at positions opposed to the periphery of the photomask  10   a . The support table  53  also includes alignment sensors  69 ,  70  for detecting alignment marks of the photomask  20   a  at positions opposed to the periphery of the photomask  20   a . The slider includes alignment sensors  71 ,  72  for detecting alignment marks of the target glass substrate  3  at positions opposed to the periphery of the substrate  3 . Further, on the slider  57 , a motor  73  for driving the slider  57  is provided. The motor  73  is equipped with a rotary encoder  76  which detects the position of the slider  57  on the sliding rail  56 . 
     FIG. 7  is a block diagram illustrating a control system of the exposure apparatus  1   a  of  FIG. 6 . In  FIG. 7 , a controller  74  receives outputs from the sensors  67 - 72  and the rotary encoder  76  of the motor  73  to control a driver circuit  75 . The driver circuit  75  drives the light sources  60 ,  61  and the motors  64 - 66 ,  73 . The controller  74  includes a microcomputer composed of a CPU, ROM and RAM, and the driver circuit  75  includes a power circuit for lighting the light sources and a power circuit for driving the motors. 
   In the exposure apparatus  1   a  of  FIG. 6  and  FIG. 7 , when the photomasks  10   a ,  20   a  are mounted on the stages  54 ,  55 , respectively, the alignment marks of the photomasks  10   a ,  20   a  are detected by the alignment sensors  67 ,  68  and  69 ,  70 , respectively. Then, the stages  54 ,  55  are driven to align each of the photomasks  10   a ,  20   a  at a predetermined position. 
   Subsequently, when the target glass substrate  3  is mounted on the stage  59 , the alignment marks of the substrate  3  are detected by the alignment sensors  71 ,  72 . The stage  59  is then driven to align the substrate  3  at a predetermined position. On the other hand, the position of the slider  57  on the sliding rail  56  is detected by the rotary encoder  76  and the slider  57  is driven to be aligned at a predetermined position shown in  FIG. 6 . 
   Next, the light source  60  is lit for a predetermined period of time and the substrate  3  is exposed to light through the photomask  10   a.    
   The slider  57  is then moved in the direction of arrow B. When the slider  57  reaches a predetermined position below the photomask  20   a , the light source  61  is lit for a predetermined period of time so that the substrate  3  is subjected to a second exposure through the photomask  20   a.    
     FIG. 8  is an explanatory view illustrating a detailed structure of the exposure apparatus  1   b  of  FIG. 3B . In  FIG. 8 , the exposure apparatus  1   b  includes a sliding table  53   a  having openings  51 ,  52 . The sliding table  53   a  has stages  54 ,  55  disposed on the peripheries of the openings  51 ,  52 , respectively. The stages  54 ,  55  are two-dimensionally movable and slightly rotatable in a horizontal plane. 
   The stages  54 ,  55  are adapted to horizontally support the photomasks  10   a ,  20   a , resepctively. Below the sliding table  53   a , a sliding rail  56   a  is placed. The sliding rail  56   a  slidably supports the sliding table  53   a  in directions of arrow C and arrow D. A mount  57   a  provided below the sliding table  53   a  includes a stage  59  which is two-dimensionally movable and slightly rotatable in a horizontal plane. The stage  59  is adapted to horizontally support the target substrate  3 . 
   Above the sliding table  53   a , a light source  60  for emitting exposure light and a collimator lens  62  for collimating light from the light source  60  are disposed. The light source  60  is adapted to vertically illuminate, through the lens  62 , the photomask  10   a  or  20   a  with light emitted from the light source  60 . 
   The resist  4   a  on the target glass substrate  3  (see  FIG. 3B ) is sequentially exposed to light that is transmitted through the photomasks  10   a  and  20   a . The sliding table  53   a  includes motors  64 ,  65  for driving the stages  54 ,  55 , respectively, and the mount  57   a  includes a motor  66  for driving the stage  59 . 
   The table  53   a  also includes alignment sensors  67 ,  68  for detecting alignment marks of the photomask  10   a  at positions opposed to the periphery of the photomask  10   a . Similarly, the sliding table  53   a  includes alignment sensors  69 ,  70  for detecting alignment marks of the photomask  20   a  at positions opposed to the periphery of the photomask  20   a.    
   The mount  57   a  includes alignment sensors  71 ,  72  for detecting alignment marks of the target substrate  3  at positions opposed to the periphery of the substrate  3 . 
   Further, the sliding table  53   a  includes a motor  73  for driving the sliding table  53   a . The motor  73  is equipped with a rotary encorder  76   a  which detects the position of the sliding table  53   a  on the sliding rail  56   a.    
     FIG. 9  is a block diagram illustrating a control system of the exposure apparatus  1   b  of  FIG. 8 . In  FIG. 9 , a controller  74   a  receives outputs from the alignment sensors  67 - 72  and the rotary encoder  76   a  of the motor  73   a  to control a driver circuit  75   a . The driver circuit  75   a  drives the light source  60  and the motors  64 - 66 ,  73   a . The controller  74   a  includes a microcomputer composed of a CPU, ROM and RAM, and the driver circuit  75   a  includes a power circuit for lighting the light source and a power circuit for driving the motors. 
   In the exposure apparatus  1   b  of  FIG. 8  and  FIG. 9 , when the photomasks  10   a ,  20   a  are mounted on the stages  54 ,  55 , respectively, the alignment marks of the photomasks  10   a ,  20   a  are detected by the alignment sensors  67 ,  68  and  69 ,  70 , respectively. 
   Then, the stages  54 ,  55  are driven to align each of the photomasks  10   a ,  20   a  at a predetermined position. 
   Subsequently, when the target glass substrate  3  is mounted on the stage  59 , the alignment marks of the substrate  3  are detected by the alignment sensors  71 ,  72 . 
   The stage  59  is then driven to align the substrate  3  at a predetermined position. On the other hand, the position of the table  53   a  on the sliding rail  56   a  is detected by the rotary encorder  76   a , and the sliding table  53   a  is driven to be aligned at a predetermined position shown in  FIG. 8 . 
   Next, the light source  60  is lit for a predetermined period of time so that the substrate  3  is exposed through the photomask  10   a.    
   The sliding table  53   a  is moved in the direction of arrow D. When the photomask  20   a  reaches a predetermined position above the substrate  3 , the light source  60  is lit for a predetermined period of time so that the substrate  3  is subjected to a second exposure through the photomask  20   a.    
   According to the third embodiment of the invention, the resist  4   a  on the target substrate  3  is thus exposed. 
   The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.