BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method for producing a structure composed of a photoreactive resin or a photocurable resin. The photoreactive resin (photosensitive resin) is generally referred to as a resist and subjected to development. The photocurable resin is used for stereolithography. A common point among these resins is that at least a photoreaction is effected using light. Unless otherwise specified, these resins are referred to as “photoreactive resins” in this specification. 
       SUMMARY 
       [0002]    According to an aspect of an embodiment, a method for manufacturing a structure composed of a photoreactive resin comprises the steps of: forming the photoreactive resin on a sheet member soluble in water; exposing the photoreactive resin selectively to a radiation activating the photoreactivity to produce the structure; and dissolving the sheet member in water after the exposing step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  shows the steps in a method for producing a structure according to an embodiment of the present invention; 
           [0004]      FIGS. 2A to 2E  are schematic cross-sectional views in the steps in the production method shown in  FIG. 1 ; 
           [0005]      FIG. 3  shows the steps in a method for producing a structure according to another embodiment of the present invention; 
           [0006]      FIG. 4  illustrates an example of Step  1600  shown in  FIG. 3 ; 
           [0007]      FIGS. 5A to 5D  illustrate the steps in the production method shown in  FIG. 3 ; 
           [0008]      FIG. 6  illustrates another example of Step  1600  shown in  FIG. 3 ; 
           [0009]      FIGS. 7A to 7C  illustrate the steps in the production method shown in  FIG. 6 ; 
           [0010]      FIG. 8  shows the steps in a method for producing a structure according to another embodiment of the present invention; 
           [0011]      FIGS. 9A to 9C  are schematic cross-sectional view illustrating Step  1700  shown in  FIG. 8 ; 
           [0012]      FIG. 10  shows the steps in a method for producing a structure according to another embodiment of the present invention; 
           [0013]      FIG. 11  illustrates an example of details of Step  1800  shown in  FIG. 10 ; 
           [0014]      FIG. 12  illustrates an example of details of Step  1900  shown in  FIG. 10 ; 
           [0015]      FIGS. 13A to 13F  are schematic cross-sectional views of examples corresponding to the steps shown in  FIG. 10 ; 
           [0016]      FIGS. 14A to 14G  are schematic cross-sectional views of other examples corresponding to the steps shown in  FIG. 10 ; 
           [0017]      FIG. 15  illustrates another example of the details of Step  1800  shown in  FIG. 11 ; 
           [0018]      FIG. 16  illustrates another example of the details of Step  1900  shown in  FIG. 12 ; 
           [0019]      FIGS. 17A to 17F  are schematic cross-sectional views of examples corresponding to the steps shown in  FIGS. 14A to 15 ; 
           [0020]      FIG. 18  shows the steps in a method for producing a structure according to another embodiment of the present invention; 
           [0021]      FIGS. 19A to 19E  are schematic cross-sectional views of the steps in the production method shown in  FIG. 18 ; 
           [0022]      FIG. 20  shows the steps in a method for producing a structure according to another embodiment of the present invention; and 
           [0023]      FIGS. 21A to 21C  are schematic cross-sectional views illustrating the production method shown in  FIG. 20 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The demand for microstructures, e.g. biodevices and optical devices, composed of photoreactive resins has been increasing. To produce microstructures, employment of lithography (exposure) in which a mask pattern is transferred to a resin and nanoimprinting in which a mold pattern is transferred has been devised. However, lithography is a technique for transferring a pattern to a substrate under a photoreactive resin through steps of development, etching, and detachment of the photoreactive resin after exposure. Nanoimprinting is a technique for transferring a pattern to a substrate under the photoreactive resin through steps of etching and detachment of the photoreactive resin after imprinting. Thus, these techniques cannot be employed for production of structures composed of photoreactive resins. 
         [0025]    Furthermore, a photoreactive resin before exposure is in a liquid state usually. Thus, to support the photoreactive resin, the photoreactive resin needs to be applied to a substrate. Hence, the photoreactive resin needs to be detached from the substrate after the completion of pattern transfer. However, it is difficult to detach the photoreactive resin. The structure may be damaged. 
         [0026]    In stereolithography, a liquid ultraviolet-curable resin is cured and laminated with an ultraviolet laser of a stereolithography system to form a three-dimensional structure in a short time. However, similarly, it is difficult to detach the three-dimensional structure from a table used for forming the three-dimensional structure. 
         [0027]    A technique in which a photoreactive resin is detached from a substrate with a special remover after exposure is proposed. The technique using the special remover is not practical because of the need for a storage environment at about −20° C. and pretreatment of exposure (increase in temperature to room temperature, defoaming, and the like). It is difficult to simply produce a structure composed of a photoreactive resin, e.g. a microstructure device having a through hole pattern. 
         [0028]    Accordingly, it is an exemplary object of the present invention to provide a method for simply producing a structure composed of a photoreactive resin without damaging the structure. 
         [0029]    A method for producing a structure according to an embodiment of the present invention will be described below with reference to the attached drawings.  FIG. 1  shows the steps in the production method. 
         [0030]    A hot-water-soluble sheet  10  is formed (Step  1100 ). The hot-water-soluble sheet  10  is a sheet member soluble in hot water and is composed of one of agar and a polyvinyl alcohol (PVA) resin. These materials are also environmentally friendly. Agar is soluble in hot water having a temperature of about 50° C. or higher. The PVA resin is soluble in hot water having a temperature of about 80° C. or higher. The size and shape of the hot-water-soluble sheet  10  are not particularly limited. 
         [0031]    A photoreactive resin  20  is applied to the hot-water-soluble sheet  10  (Step  1200 ). Examples of the photoreactive resin that can be used include, but are not limited to, polyvinyl cinnamate, cyclized polyisoprene-bisazide, novolac resins, fluorocarbon resins, and alicyclic resins. A coater may be used for application.  FIG. 2A  is a schematic cross-sectional view in this state. 
         [0032]    A pattern  32  of the mask  30  including a light-shading portion  32   a  and a light-transmitting portion  32   b  is subjected to exposure, thereby transferring the pattern to the photoreactive resin  20  (Step  1300 ). A mercury lamp or an excimer laser system may be used as a light source for exposure. The type of exposure light used is not particularly limited. The transferred pattern may have the same size as or a smaller than its original size. An illumination optical system that illuminates the mask  30  by means of light from the light source may be disposed between the light source and the mask  30 . A projection optical system that projects light from the mask  30  on the photoreactive resin  20  may be disposed between the mask  30  and the photoreactive resin  20 . These optical systems include lenses, mirrors, aperture diaphragms, and the like. The mask  30  may be of a transmissive or reflective type.  FIG. 2B  is a schematic cross-sectional view showing a state during exposure. In  FIG. 2B , the mask  30  is in contact with the photoreactive resin  20 , and the transferred pattern has the same size as its original size. The present invention includes the cases in which a projection optical system is disposed and the transferred pattern has the same size as or a smaller size than its original size.  FIG. 2C  is a schematic cross-sectional view showing a state of the photoreactive resin  20  after completion of exposure. The photoreactive resin  20  includes an unexposed portion  22  formed by shielding the portion from light with the pattern and an exposed portion  24  formed by exposing the portion to light to effect curing. After completion of exposure, the mask  30  is detached from the photoreactive resin  20 . 
         [0033]    Development and rinsing (Step  1400 ) are performed. The hot-water-soluble sheet  10  is insoluble in a developing agent or a detergent. As shown in  FIG. 2D , the unexposed portion  22  is removed to form a hole. The exposed portion  24  is left as a cured resin  25 . If the photoreactive resin  20  is a positive resist, a reverse pattern of the negative resist shown in  FIG. 2D  is obtained.  FIGS. 2A to 2E  are schematic cross-sectional views of the structure  1  including the photoreactive resin  20  and the hot-water-soluble sheet  10  after completion of development. 
         [0034]    Hot-water treatment is performed (Step  1500 ). The temperature of water used is about 50° C. or higher for agar and about 80° C. or higher for a PVA resin. As shown in  FIG. 2E , the hot-water-soluble sheet  10  is dissolved in hot water to leave a microstructure  2 . The microstructure  2  includes a pattern of through holes  23 . 
         [0035]    According to the production method, the sheet member is dissolved in hot water to detach the structure from the sheet member. There is no possibility of damage to the structure because the sheet member is only soaked in hot water. Thus, the (micro)structure formed by transferring the pattern by exposure can be obtained simply and stably. Hot water is inexpensive and also environmentally friendly. 
         [0036]    The structure  2  shown in  FIG. 2E  may be used alone. The structure  2  may be used together with a support member  40 . The support member  40  may be attached to the structure  2  in order to merely support or reinforce the structure  2 . The support member  40  may have an optical effect. An embodiment will be described below with reference to  FIGS. 3 to 5D .  FIG. 3  shows a modification of the steps in the production method shown in  FIG. 1 .  FIG. 3  differs from  FIG. 1  in that Step  1600  is provided between Steps  1400  and  1500 . Referring to  FIG. 3 , the support member  40  is fixed to the developed photoreactive resin  20  (Step  1600 ) subsequent to Step  1400 . 
         [0037]    Step  1600  will be described below in detail with reference to  FIG. 4 .  FIG. 4  illustrates Step  1600  shown in  FIG. 3 . The support member  40  is formed (Substep  1602 ). As shown in  FIG. 5A , the support member  40  according to this embodiment has hollow rectangular columns when viewed in plan. However, the shape and size thereof are not particularly limited. The support member  40  includes posts  42  and openings  44 . The posts  42  support the photoreactive resin  20 . The thickness and shape of each post  42  are not limited. The openings  44  communicate with through holes  23 . The length and size of each opening  44  are not limited. 
         [0038]    An adhesive  46  is applied to the bottom face  41  of the support member  40  (Substep  1604 ). The material constituting the adhesive  46  is not limited. The adhesive  46  is required not to be detached during the hot-water treatment. The support member  40  is positioned and attached on the upper face  20   a  of the developed resin  20  to form a structure  1 A (Substep  1606 ). An upper face  20   a  is disposed opposite a lower face  20   b  to which the hot-water-soluble sheet  10  is attached. In the structure  1 A, the hot-water-soluble sheet  10  is fixed to the lower face  20   b  of the photoreactive resin  20 , and the support member  40  is fixed to the upper face  20   a  of the photoreactive resins  20 .  FIG. 5B  is a schematic cross-sectional view showing a state after positioning. The center line C 1  of each opening  44  and the center line C 2  of a corresponding one of the through holes  23  are aligned with a center line C. Each post  42  is positioned in the center of a corresponding one of the cured photoreactive resin  25 .  FIG. 5C  is a schematic cross-sectional view of the hot-water-soluble sheet  10  and the photoreactive resin  20  having the upper face  20   a  to which the support member  40  is bonded. 
         [0039]    Step  1500  is performed to obtain a structure  2 A as shown in  FIG. 5D . In the structure  2 A, the support member  40  is fixed to the upper face  20 A of the photoreactive resin  20  with the adhesive  46 . According to this embodiment, the resin structure supported by or reinforced with the support member can be obtained. 
         [0040]    A modification of Step  1600  will be described below with reference to  FIG. 6 .  FIG. 6  illustrates Step  1600 . In  FIG. 6 , formation and mounting of the support member  40  are performed in a single step. 
         [0041]    The developed photoreactive resin  20  and the hot-water-soluble sheet  10  are attached to a mold  50  (Substep  1612 ). The mold  50  is attached to the upper face  20   a  of the photoreactive resin  20 .  FIG. 7A  shows a state of a cavity in the mold  50  clamped. The mold  50  has channels  54 ,  56 , and  58 . The channel  54  defines the shape of the support member  40 . The channels  56  taper and are provided in response to the channel  54 . A resin  60  is separated between the channels  54  and  56 . The mold  50  may be separated between the channels  54  and  56  into an upper mold section and a lower mold section. Each of the channels  56  is connected to the channel  58 . The channel  58  supplies the channels  56  with the thermoplastic resin  60 . Non-limiting examples of the thermoplastic resin include polycarbonate and polyether imide. A metal element and an organic material may be incorporated. 
         [0042]    After clamping, the thermoplastic resin  60  is fed into the mold  50  (Step  1614 ). In this embodiment, the temperature-controlled thermoplastic resin  60  is fed from a supply source (not shown) into the mold  50  through the channel  58  by injection molding. An injection molding apparatus as is well known to those skilled in the art may be used. The support member  40  can be produced by injection molding with high accuracy. The thermoplastic resin  60  is integrated with the photoreactive resin  20  when the resin  60  is fed. Thus, the adhesive  46  shown in  FIG. 5B  does not need. 
         [0043]    After opening the mold, a structure  1 B as shown in  FIG. 7B  is obtained (Substep  1616 ). The structure  1 B includes the hot-water-soluble sheet  10  attached to the lower face  20   b  of the photoreactive resin  20  and the support member  40  attached to the upper face  20   a  of the photoreactive resin  20 . Unlike the structure  1 A, the structure  1 B does not include the adhesive  46  between the support member  40  and the upper face  20   a  of the photoreactive resin  20 . The shape and size of the support member  40  are the same as those in the structure  1 A. 
         [0044]    Step  1500  is then performed to obtain a structure  2 B attached to the support member  40  as shown in  FIG. 7C . The structure  2 B includes the support member  40  fixed to the upper face  20   a  of the photoreactive resin  20 . Unlike the structure  2 A, the structure  2 B does not include the adhesive  46  between the support member  40  and the upper face  20   a  of the photoreactive resin  20 . 
         [0045]    The structures  2 A and  2 B may be used as they are. Alternatively, a single or plurality of structures formed by cutting the structures  2 A and  2 B may be used. Such an embodiment will be described below with reference to  FIGS. 8 to 9C .  FIG. 8  shows the steps in a modification of the production method shown in  FIG. 3 .  FIG. 8  differs in Step  1700  provided between Steps  1500  and  1600  from  FIG. 3 . 
         [0046]    Referring to  FIG. 8 , the structure  1 A or  1 B is cut (Step  1700 ) subsequent to Step  1600 . As shown in  FIG. 9A , cutting is performed with a dicing blade  70 . The dicing blade  70  includes a rotational component  71  and a blade  72  fixed to the rotational component  71 . The dicing blade  70  cuts the structure  1 B into pieces. The structure  1 B shown in  FIG. 9A  may be replaced with the structure  1 A. As shown in  FIG. 9B , each of the resulting pieces is a structure  1 C including the hot-water-soluble sheet  10 , the photoreactive resin  20  having one of the through holes  23 , and the support member  40 . 
         [0047]    The back surface  10   b  side of the hot-water-soluble sheet  10  faces to the dicing blade  70  side before the structure  1 B is cut with the dicing blade  70 . The blade  72  cuts the structure  1 B along the center line D of each post  42  of the support member  40 . A coolant  75  is supplied from a tank  74  to a cutting position of the blade  72 . The hot-water-soluble sheet  10  prevents the entry of chips into the posts  42 . 
         [0048]    The structure  1 C shown in  FIG. 9B  may be immediately subjected to Step  1500  to form a structure  2 C shown in  FIG. 9C . The structure  2 C includes the support member  40  fixed to the photoreactive resin  20 . In the case where the structure  2 C is packed, transported, and unpacked, it is preferred that the structure  1 C be subjected to these steps and then Step  1500  immediately before use as a device. Thus, the hot-water-soluble sheet  10  prevents the entry of foreign matter into the posts  42  during these steps. That is, according to this embodiment, the sheet can prevent the entry of chips into the photoreactive resin and the support member during cutting. 
         [0049]    In the production method according to  FIG. 1 , from the viewpoint of handling, the hot-water-soluble sheet  10  is preferably supported with a support structure until exposure is completed. Such an embodiment will be described below with reference to  FIG. 10 .  FIG. 10  shows the steps in a modification of the production method shown in  FIG. 1 . The modification method shown in  FIG. 10  differs from the production method shown in  FIG. 1  in that Step  1800  is provided between Steps  1100  and  1200  and in that Step  1900  is provided between Steps  1300  and  1400 . Referring to  FIG. 10 , the hot-water-soluble sheet  10  is supported (Step  1800 ) subsequent to Step  1100 . 
         [0050]    Step  1800  will be described in detail with reference to  FIGS. 11 to 14G .  FIG. 11  illustrates details of Step  1800 . 
         [0051]    A base substrate  80  is formed (Substep  1802 ). As shown in  FIG. 13A , the base substrate  80  according to an embodiment is a flat plate having a groove  82  on a surface  80   a  and is composed of a resin or glass. The base substrate  80  has a rectangular shape when viewed in plan. The groove  82  is in the form of a rectangle larger than the outside shape of the structure  2 . The groove  82  is formed outside an exposure region. In this embodiment, the base substrate  80  is formed by injection molding with a thermoplastic resin. According to another embodiment, as shown in  FIG. 14A , a base substrate  80 A having a bump  81  is used in place of the base substrate  80 . A plat plate including the bump  81  covers the exposure region. The height of the bump  81  is higher than that of a surrounding flat portion. 
         [0052]    The hot-water-soluble sheet  10  is positioned and then bonded to the base substrate  80  with a double-sided tape  83  (Substep  1804 ). 
         [0053]    In an embodiment, as shown in  FIG. 13A , after positioning, the hot-water-soluble sheet  10  is bent at edges of the surface  80   a  of the base substrate  80 . Ends  11  of the hot-water-soluble sheet  10  are bonded to the back surface  80   b  of the base substrate  80 . Thereby, the flatness of the hot-water-soluble sheet  10  can be maintained on the surface  80   a  side of the base substrate  80 .  FIG. 13A  is a schematic cross-sectional view showing a state in which the hot-water-soluble sheet  10  is positioned with respect to the base substrate  80 . 
         [0054]    According to another embodiment, as shown in  FIG. 14A , after the hot-water-soluble sheet  10  is positioned, the ends  11  of the hot-water-soluble sheet  10  are bonded to ends of the base substrate  80 A outside the groove  82  on the surface  80   a  with a double-sided tape  83 . That is, a bonding portion is formed in a peripheral portion which has a small height and is located outside the exposure region.  FIG. 14A  is a schematic cross-sectional view showing a state in which the hot-water-soluble sheet  10  is positioned with respect to the base substrate  80 A.  FIG. 14B  is a schematic cross-sectional view showing a state in which the hot-water-soluble sheet  10  is bonded to the base substrate  80 A. 
         [0055]    The photoreactive resin  20  is applied to the hot-water-soluble sheet  10  (Step  1200 ).  FIGS. 13B and 14C  are schematic cross-sectional views showing the state. The photoreactive resin  20  is applied to a region of the hot-water-soluble sheet  10  interior to the groove  82 . In particular, in  FIG. 14C , the height of the peripheral region is lower than the central exposure region. Thus, in the case where the photoreactive resin  20  is applied by spin coating, a stable thickness can be ensured. 
         [0056]    The pattern  32  of the mask  30  is transferred to the photoreactive resin  20  by exposure (Step  1300 ).  FIGS. 13C and 14D  are schematic cross-sectional views showing a state during exposure. 
         [0057]    Support for the hot-water-soluble sheet  10  is removed (Step  1900 ). As shown in  FIG. 12 , in this embodiment, the hot-water-soluble sheet  10  is cut along the groove  82  with a cutter  84  to separate the sheet from the base substrate  80  (Substep  1902 ).  FIGS. 13D and 14E  are schematic cross-sectional view showing a state during cutting. A method shown in  FIG. 13D  is useful for exposure treatment utilizing a substrate having a polygonal outer shape. 
         [0058]    Development and rinsing are performed (Step  1400 ) to form the substrate  1  similar to that shown in  FIG. 2D , as shown in  FIGS. 13E and 14F . Hot-water treatment is performed (Step  1500 ) to form the structure  2  similar to that shown in  FIG. 2E , as shown in  FIGS. 13F and 14G . According to the embodiment with reference to  FIGS. 13A to 14G , the sheet member is easily supported with the base substrate. According to the embodiment with reference to  FIGS. 14A to 14G , a stable thickness of the photoreactive resin is ensured. 
         [0059]    Examples of modifications of Step  1800  shown in  FIG. 11  and Step  1900  shown in  FIG. 12  will be described in detail with reference to  FIGS. 15 to 17F .  FIG. 15  illustrates an example of a modification of the details of Step  1800  shown in  FIG. 11 .  FIG. 16  illustrates an example of a modification of the details of Step  1900  shown in  FIG. 12 . 
         [0060]    A support structure  85  is formed (Substep  1812 ). The support structure  85  includes a porous member  87  mounted on a box  86 . The box  86  is composed of aluminum or the like and is in the form of a cylinder or a substantially rectangular parallelepiped. The box  86  includes a bump  86   a  and an exhaust port  86   c . The bump  86   a  protrudes from the inner surface toward the inside of the box  86 . The bump  86   a  is provided along the internal circumference of the box  86  at a constant height from the bottom face  86   d  of the box  86 . The bump  86   a  serves as a support for the porous member  87 . When the porous member  87  is attached to the bump  86   a , a exhaust space  86   b  is formed between the back surface  87   b  of the porous member  87  and the bottom face  86   d . The exhaust space  86   b  communicates with the exhaust port  86   c . The exhaust port  86   c  is connected to a vacuum pump (not shown) through a line  88  and a valve  89 . The exhaust space  86   b  is thus evacuated from the exhaust port  86   c . The exhaust space  86   b  is maintained at reduced pressure during the hot-water-soluble sheet  10  is supported. The porous member  87  is composed of a ceramic material or the like and is in the form of a cylinder or a substantially rectangular parallelepiped. A surface  87   a  of the porous member  87  is flush with the top face  86   e  of the box  86 . Reducing the pressure in the exhaust space  86   b  begins to suck from the surface  87   a  of the porous member  87 . 
         [0061]    The hot-water-soluble sheet  10  is positioned and placed on the support structure  85  (Substep  1814 ) Dimensions of the hot-water-soluble sheet  10  at this point correspond to dimensions of the hot-water-soluble sheet  10  shown in  FIGS. 13D and 14E  after cutting. The valve  89  is closed during positioning and placing; hence, the pressure of the exhaust space  86   b  is atmospheric pressure. Thus, the hot-water-soluble sheet  10  is merely placed on the top face  86   e  of the box  86  and on the surface  87   a  of the porous member  87  of the support structure  85  and is not fixed.  FIG. 17A  is a schematic cross-sectional view showing the hot-water-soluble sheet  10  and the support structure  85  after positioning. 
         [0062]    Evacuation is initiated (Substep  1816 ). The valve  89  is opened during evacuation; hence, the pressure in the exhaust space  86   b  is reduced. Thus, the hot-water-soluble sheet  10  is sucked and fixed to the surface  87   a  of the porous member  87  of the support structure  85 .  FIG. 17B  is a schematic cross-sectional view showing a state of the hot-water-soluble sheet  10  fixed to the support structure  85  after evacuation. 
         [0063]    The photoreactive resin  20  is applied to the hot-water-soluble sheet  10  while the evacuation is continued (Step  1200 ).  FIG. 17C  is a schematic cross-sectional view showing this state. The pattern  32  of the mask  30  is transferred to the photoreactive resin  20  by exposure while the evacuation is continued (Step  1300 ).  FIG. 17D  is a schematic cross-sectional view showing a state during exposure. 
         [0064]    Support of the hot-water-soluble sheet  10  is removed (Step  1900 ). In this embodiment, evacuation is terminated, and then the hot-water-soluble sheet  10  is detached from the support structure  85  (Substep  1912 ).  FIG. 17E  is a schematic cross-sectional view showing a state after separation. Cutting operation with the cutter  84  shown in  FIGS. 13D and 14E  is not required, thereby improving workability. 
         [0065]    Development and rinsing are performed (Step  1400 ). Thereby, the substrate  1  similar to that shown in  FIG. 2D  is obtained. Hot-water treatment is performed (Step  1500 ). Thereby, the structure  2  similar to that shown in  FIG. 2E  is obtained, as shown in  FIG. 17F . According to this embodiment, the sheet member is easily supported by the porous member and evacuation. Furthermore, the sheet member is easily detached from the porous member by terminating evacuation. 
         [0066]    In Step  1300  shown in  FIG. 1 , pattern transfer is performed by exposure. In another embodiment, pattern transfer is performed by nanoimprinting. In this case, a mold  35  having a relief pattern  36  is used in place of, the mask  30 . This embodiment will be described below with reference to  FIG. 18 to 19E .  FIG. 18  shows the steps in a production method according to this embodiment. 
         [0067]    The hot-water-soluble sheet  10  is formed (Step  1100 ). As shown in  FIG. 19A , the photoreactive resin  20  is applied to the hot-water-soluble sheet  10  as in the step shown in  FIG. 2A  (Step  1200 ). The pattern of the mold  35  is transferred to the photoreactive resin  20  by nanoimprinting (Step  1350 ). Specifically, as shown in  FIG. 19B , the hot-water-soluble sheet  10  and the photoreactive resin  20  are mounted to a nanoimprinting apparatus (not shown) and positioned with respect to the mold  35  mounted on a pressure plate  38 . As shown in  FIG. 19C , the mold  35  is pressed against the photoreactive resin  20  with the pressure plate  38  and irradiated with ultraviolet rays. The pressure plate  38  and the mold  35  are each composed of a light-transmitting material such as quartz. The photoreactive resin  20  can be irradiated with ultraviolet rays through the pressure plate  38  and the mold  35  so as to effect curing. Then the mold  35  is detached from the photoreactive resin  20 .  FIG. 19D  is a schematic cross-sectional view showing a structure  1 D including the photoreactive resin  20  and the hot-water-soluble sheet  10 . The hot-water-soluble sheet  10  is dissolved by hot-water treatment to obtain a structure  2 D shown in  FIG. 19E  (Step  1500 ). 
         [0068]    According to the production method, the sheet member is dissolved in hot water to detach the structure from the sheet member. There is no possibility of damage to the structure because the sheet member is only soaked in hot water. Thus, the (micro)structure formed by transferring the pattern by nanoimprinting can be obtained simply and stably. Hot water is inexpensive and also environmentally friendly. 
         [0069]    An embodiment in which the hot-water-soluble sheet  10  is applied to stereolithography will be described below with reference to  FIGS. 20 to 21C .  FIG. 20  shows the steps in a production method according to this embodiment.  FIG. 21A  is a schematic cross-sectional view of a stereolithography system. The hot-water-soluble sheet  10  is formed (Step  2100 ) as in Step  1100 . The hot-water-soluble sheet  10  is mounted on a table  136  of an elevator  130  of the stereolithography system  100  and then immersed (Step  2200 ). 
         [0070]    The stereolithography system  100  includes a light source  110 , a scanner  120 , the elevator  130 , a tank  140 , and a controlling unit  150 . The light source  110  is constituted by ultraviolet laser such as KrF excimer laser. The scanner  120  includes an optical system  122  having a lens and a mirror. The scanner  120  guides laser light L emitted from the light source  110  and scans a photoreactive resin in the xy-plane. The elevator  130  includes a post  132 , an L-shaped arm  134  that moves along the post  132  in the z-direction, and the table  136  attached to the arm  134 . The hot-water-soluble sheet  10  is placed on the top face  137  of the table  136 . The tank  140  has a box shape, contains the photoreactive resin (photocurable resin)  20 , and includes a lid  142  composed of a light-transmitting material. As the photocurable resin of this embodiment for stereolithography, TSR820 may be used. The controlling unit  150  controls operations of the light source  110 , the scanner  120 , and the elevator  130  on the basis of information of an object to be shaped. The stereolithography system  100  may have a structure as is well known to those skilled in the art. Thus, description in detail is omitted. 
         [0071]    The controlling unit  150  initiates stereolithography by scanning the resin with laser light L and lowering the elevator  130  (Step  2300 ). Specifically, a three-dimensional model is divided into slices and converted into contour-line data. The controlling unit  150  controls the scanner  120  on the basis of the contour-line data. Thereby, laser light L scans across the surface of the photoreactive resin  20  in the tank  140  through the lid  142  so as to draw the cross-sectional shape. A portion irradiated with laser light L is cured to form one cross-sectional layer of the shape on the table  136 . The controlling unit  150  lowers the arm  134  attached to the elevator  130  by one layer at a time. A plurality of thin cross sections are continuously laminated, thereby forming a three-dimensional object corresponding to the three-dimensional model. By repeating this procedure, a three-dimensional object  4  is formed. After completion of stereolithography, the controlling unit  150  terminates the irradiation of laser light L form the light source  110  (Step  2400 ). 
         [0072]    The controlling unit  150  lifts the arm  134  to remove the three-dimensional object  4  and the hot-water-soluble sheet  10  from the stereolithography system  100 .  FIG. 21B  is a schematic cross-sectional view of the three-dimensional object and the hot-water-soluble sheet  10  removed from the stereolithography system after shaping. 
         [0073]    The hot-water-soluble sheet  10  is dissolved by hot-water treatment. Thereby, the three-dimensional object  4  is obtained shown in  FIG. 21C . According to the production method, the sheet member is easily detached from the table for supporting the sheet member. Furthermore, the three-dimensional object is easily detached from the sheet member by means of hot water. Thereby, the three-dimensional object can be produced simply and stably. 
         [0074]    The embodiments of the present invention have been described above. The present invention is not limited to these embodiments. Various modifications and changes can be made without departing from the scope of the invention. 
         [0075]    The present invention provides a method for simply producing a structure composed of a photoreactive resin without damaging the structure.
According to an aspect of an embodiment, a method for manufacturing a structure composed of a photoreactive resin comprises the steps of: forming the photoreactive resin on a sheet member soluble in water; exposing the photoreactive resin selectively to a radiation activating the photoreactivity to produce the structure; and dissolving the sheet member in water after the exposing step.