Abstract:
A method for fabricating a soft mold is disclosed, in which process matching is high regardless of a size of a master mold for forming the soft mold. The method for fabricating a soft mold includes arranging a master mold on a jig, forming a pre-polymer layer in the jig, attaching a back-plane substrate onto the pre-polymer layer, selectively curing the pre-polymer layer to selectively form a polymer layer, stripping the polymer layer and the pre-polymer layer from the jig and the master mold, and removing the pre-polymer layer that is not cured.

Description:
[0001]     This application claims the benefit of the Korean Patent Application No. P2005-0055197, filed on Jun. 24, 2005, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a soft mold, and more particularly, to a method for fabricating a soft mold, in which the soft mold is properly used if a size of a master mold is smaller than that of a substrate to be patterned.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Generally, a soft mold is fabricated by casting a rubber having elasticity in a mold and concaving or embossing a pattern depending on a shape of the mold.  
         [0006]     The soft mold is used to form a fine pattern of a micro unit, such as a concave or embossed pattern. For example, the soft mold is used to form either a color filter on a color filter substrate of a liquid crystal display device or an electrode in an organic electroluminescent (EL) device.  
         [0007]     The soft mold can be fabricated by curing an elastic polymer. Polydimethylsiloxane (PDMS) is widely used as the elastic polymer. In addition to PDMS, polyurethane or polyimide may be used as the elastic polymer.  
         [0008]     Hereinafter, a related art process for fabricating a soft mold will be described with reference to the accompanying drawings.  
         [0009]      FIG. 1A  to  FIG. 1C  are sectional views illustrating related art process steps of fabricating a soft mold.  
         [0010]     As illustrated in  FIG. 1A , a master A is prepared to concave or emboss a predetermined shape on a surface of a soft mold.  
         [0011]     The master A is formed in such a manner that an insulating material such as Si 3 N 4  or SiO 2  is deposited on an insulating substrate  10  such as a silicon substrate to form a preceding layer and the preceding layer is patterned by a photolithographic process to form a desired pattern  12 .  
         [0012]     At this time, the pattern  12  on the insulating substrate  10  may be formed of metal, photoresist or wax in addition to Si 3 N 4  or SiO 2 .  
         [0013]     The master A is formed by the aforementioned process steps.  
         [0014]     As illustrated in  FIG. 1B , if the master A is completed, an elastic polymer (elastic rubber) solution of a pre-polymer state is cast on the master A to form a pre-polymer layer  14 . PDMS is used as the elastic polymer.  
         [0015]     Subsequently, the pre-polymer layer  14  is cured.  
         [0016]     Next, as illustrated in  FIG. 1C , a polymer layer in which the pre-polymer layer  14  is completely cured is referred to as a soft mold  16 . The soft mold  16  is stripped from the master (‘A’ of  FIG. 1B ) so that the soft mold concaved or embossed in a predetermined shape on its surface is fabricated.  
         [0017]     The related art soft mold is fabricated by the aforementioned process steps.  
         [0018]     The soft mold fabricated as above is used in various fields of soft lithography, soft molding, capillary force lithography, and in-plane printing.  
         [0019]     For mass production of the product based on the soft mold used in various fields, it is necessary to exactly align the soft mold.  
         [0020]     Particularly, in the soft mold for in-plane printing, in case where a master mold is smaller than a substrate to be patterned, a threshold is formed in the mold to cause a problem when a fine pattern is formed.  
         [0021]     This case will be described with reference to  FIG. 2A  and  FIG. 2B .  
         [0022]      FIG. 2A  and  FIG. 2B  are structural sectional views illustrating a master mold smaller than a substrate to be patterned.  
         [0023]     As illustrated in  FIG. 2A , after a master mold  22  is arranged on a rectangular mold shaped jig  21 , a cured polymer layer  22  is formed in the jig  21  including the master mold  22 . A back-plane substrate  24  is attached onto the cured polymer layer  22 .  
         [0024]     As illustrated in  FIG. 2B , in a state that the back-plane substrate  24  is attached to the cured polymer layer  22 , the jig  21  and the master mold  22  are stripped from the polymer layer  23  to form a soft mold attached with the back-plane substrate.  
         [0025]     Afterwards, a substrate  25  for a fine pattern is arranged below the soft mold.  
         [0026]     At this time, the master mold has a size greater than that of the substrate to be patterned.  
         [0027]     However, if the substrate  25  to be finely patterned is greater than the master mold as illustrated in  FIG. 2B , a threshold is formed at the corner of the mold.  
         [0028]     The mold is not closely attached to the substrate  25  due to the threshold. Thus, the mold is spaced apart from the substrate  25  at a certain interval. Particularly, the mold is used for in-plane printing, a problem occurs in that the fine pattern is not formed.  
       SUMMARY OF THE INVENTION  
       [0029]     Accordingly, the present invention is directed to a method for fabricating a soft mold, which substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0030]     An advantage of the present invention is to provide a method for fabricating a soft mold, in which process matching is high regardless of a size of a master mold for forming the soft mold.  
         [0031]     Additional advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0032]     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for fabricating a soft mold according to the present invention includes arranging a master mold on a jig, forming a pre-polymer layer in the jig, attaching a back-plane substrate onto the pre-polymer layer, selectively curing the pre-polymer layer to selectively form a polymer layer, stripping the polymer layer and the pre-polymer layer from the jig and the master mold, and removing the pre-polymer layer that is not cured.  
         [0033]     The pre-polymer layer is thermally cured or UV-cured.  
         [0034]     The thermal curing is performed in a microwave oven.  
         [0035]     The UV curing is performed using a mask having a light-transmitting portion and a light-shielding portion.  
         [0036]     In another aspect of the present invention, a method for fabricating a soft mold includes arranging a master mold on a jig, forming a pre-polymer layer, which can be thermally cured, in the jig, attaching a back-plane substrate onto the pre-polymer layer, loading the master mold, the pre-polymer layer and the jig into a microwave oven, selectively thermal-curing the pre-polymer layer in the microwave oven to selectively form a polymer layer, stripping the polymer layer and the pre-polymer layer from the jig and the master mold, and removing the pre-polymer layer that is not cured.  
         [0037]     The pre-polymer layer is formed of one selected from PDMS, polyimide, and epoxy.  
         [0038]     The method further includes treating the back-plane substrate with a coupling agent before attaching the back-plane substrate onto the pre-polymer layer.  
         [0039]     The coupling agent treatment is performed using a primer.  
         [0040]     The pre-polymer layer that is not cured is dipped in a normal nucleic acid (n-Hxan) solution and then removed.  
         [0041]     The master mold is formed in such a manner that an insulating material such as Si 3 N 4  or SiO 2  is deposited on an insulating substrate such as a silicon substrate to form a preceding layer and then the preceding layer is patterned by a photolithographic process to form a desired pattern. The preceding layer is formed of metal, photoresist, or wax.  
         [0042]     In other aspect of the present invention, a method for fabricating a soft mold includes arranging a master mold on a jig, forming a pre-polymer layer, which can be UV-cured, in the jig, attaching a back-plane substrate onto the pre-polymer layer, selectively UV-curing the pre-polymer layer using a mask having a light-transmitting portion and a light-shielding portion to selectively form a polymer layer, stripping the polymer layer and the pre-polymer layer from the jig and the master mold, and removing the pre-polymer layer that is not cured.  
         [0043]     The pre-polymer layer is formed of one selected from polyurethane, polyurethane-acrylate, epoxy, and novolac. The pre-polymer layer that is not cured is dipped in a normal nucleic acid (n-Hxan) solution and then removed.  
         [0044]     The master mold is formed in such a manner that an insulating material such as Si 3 N 4  or SiO 2  is deposited on an insulating substrate such as a silicon substrate to form a preceding layer and then the preceding layer is patterned by a photolithographic process to form a desired pattern. The preceding layer is formed of metal, photoresist, or wax.  
         [0045]     The method further includes treating the back-plane substrate with a coupling agent before attaching the back-plane substrate onto the pre-polymer layer.  
         [0046]     The present invention is intended to solve a problem in which a fine pattern is not formed as a master mold is not closely attached to a substrate and thus is spaced apart from the substrate at a certain interval due to a threshold formed at a corner of the mold if the mold is smaller than a substrate for the fine pattern. In the present invention, the size of the mold is controlled regardless of the size of the master mold so that the threshold is not formed when the mold is in contact with the substrate for the fine pattern.  
         [0047]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0048]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention.  
         [0049]     In the drawings:  
         [0050]      FIG. 1A  to  FIG. 1C  are sectional views illustrating related art process steps of fabricating a soft mold;  
         [0051]      FIG. 2A  and  FIG. 2B  are structural sectional views illustrating a master mold smaller than a substrate to be patterned;  
         [0052]      FIG. 3A  to  FIG. 3F  are sectional views illustrating process steps of fabricating a soft mold according to the first embodiment of the present invention; and  
         [0053]      FIG. 4A  to  FIG. 4F  are sectional views illustrating process steps of fabricating a soft mold according to the second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0054]     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0055]     A method for fabricating a soft mold according to the first embodiment of the present invention will be described.  FIG. 3A  to  FIG. 3F  are sectional views illustrating process steps of fabricating a soft mold according to this first embodiment of the present invention.  
         [0056]     In the first embodiment of the present invention, if a size of a master mold is smaller than that of a substrate for a fine pattern, a thermal curing material is used as a material of a soft mold so that a desired portion of the soft mold is selectively thermal-cured in a microwave oven and a portion of the soft mold which is not cured is removed, thereby fabricating the soft mold.  
         [0057]     In the method for fabricating a soft mold according to the first embodiment of the present invention, as illustrated in  FIG. 3A , a master mold  31  is arranged on a rectangular mold shaped jig  30 . The master mold  31  is to concave or emboss a predetermined shape on a surface of a soft mold.  
         [0058]     The master mold  31  is formed in such a manner that an insulating material such as Si 3 N 4  or SiO 2  is deposited on an insulating substrate such as a silicon substrate to form a preceding layer and then the preceding layer is patterned by a photolithographic process to form a desired pattern.  
         [0059]     At this time, the pattern on the insulating substrate may be formed of metal, photoresist or wax in addition to Si 3 N 4  or SiO 2 .  
         [0060]     As illustrated in  FIG. 3B , a pre-polymer layer  32  that can be thermally cured is formed in the jig  30  including the master mold  31 .  
         [0061]     The pre-polymer layer  32  may be formed of any one selected from PDMS, polyimide, and epoxy.  
         [0062]     Afterwards, as illustrated in  FIG. 3C , a back-plane substrate  33  is attached onto the pre-polymer layer  32 .  
         [0063]     Although not illustrated, the back-plane substrate  33  is treated with a coupling agent to improve adhesion between the pre-polymer layer  32  and the back-plane substrate. The coupling agent may be performed using a primer.  
         [0064]     Next, the resultant is loaded into the microwave oven.  
         [0065]     As illustrated in  FIG. 3D , a coordinate for a thermal curing portion is set so that the pre-polymer layer  32  is selectively heated in the microwave oven to undergo a curing process. The heated pre-polymer layer  32  is varied to a polymer layer  32   a . At this time, the thermal curing portion is formed with an area smaller than that of the substrate for a fine pattern.  
         [0066]     A portion where the pre-polymer layer is not heated in the microwave oven is not cured and remains as the pre-polymer layer  32 .  
         [0067]     Next, as illustrated in  FIG. 3E , the polymer layer  32   a  and the pre-polymer layer  32  are stripped from the jig  30  and the master mold  31 .  
         [0068]     Afterwards, as illustrated in  FIG. 3F , the pre-polymer layer  32  that is not cured is dipped in a normal nucleic acid (n-Hxan) solution and then is removed. Thus, the soft mold attached with the back-plane substrate  33  is completed.  
         [0069]     As described above, the pre-polymer layer  32  is selectively thermal-cured to form the polymer layer  32   a  and the pre-polymer layer  32  that is not cured is removed. In this case, even though the master mold  31  is smaller than a substrate  34  for a fine pattern, a threshold is not formed between the soft mold and the substrate  34 . Therefore, it is possible to desirably form the fine pattern.  
         [0070]     A method for fabricating a soft mold according to the second embodiment of the present invention will be described.  FIG. 4A  to  FIG. 4F  are sectional views illustrating process steps of fabricating a soft mold according to the second embodiment of the present invention.  
         [0071]     In the second embodiment of the present invention, if a size of a master mold is smaller than that of a substrate for a fine pattern, a UV curing material is used as a material of a soft mold so that a desired portion of the soft mold is selectively UV-cured using a mask and a portion of the soft mold which is not cured is removed, thereby fabricating the soft mold.  
         [0072]     In the method for fabricating a soft mold according to the second embodiment of the present invention, as illustrated in  FIG. 4A , a master mold  51  is arranged on a rectangular mold shaped jig  50 . The master mold  51  is to concave or emboss a predetermined shape on a surface of a soft mold.  
         [0073]     The master mold  51  is formed in such a manner that an insulating material such as Si 3 N 4  or SiO 2  is deposited on an insulating substrate such as a silicon substrate to form a preceding layer and then the preceding layer is patterned by a photolithographic process to form a desired pattern.  
         [0074]     At this time, the pattern on the insulating substrate may be formed of metal, photoresist or wax in addition to Si 3 N 4  or SiO 2 .  
         [0075]     As illustrated in  FIG. 4B , a pre-polymer layer  52  that can be UV-cured is formed in the jig  50  including the master mold  51 .  
         [0076]     The pre-polymer layer  52  may be formed of any one selected from polyurethane, polyurethane-acrylate, epoxy, and novolac.  
         [0077]     Afterwards, as illustrated in  FIG. 4C , a back-plane substrate  53  is attached onto the pre-polymer layer  52 .  
         [0078]     Before the back-plane substrate  53  is attached onto the pre-polymer layer  52 , although not illustrated, the back-plane substrate  53  is treated with a coupling agent to improve adhesion between the pre-polymer layer  52  and the back-plane substrate. The coupling agent may be performed using a primer. If the UV-cured material is used as the pre-polymer layer, the coupling agent treatment may be omitted.  
         [0079]     Next, as illustrated in  FIG. 4D , a mask  54  that transmits light only in a UV-curing portion and shields light in the other portion is arranged on the resultant, and UV is irradiated from a UV lamp  55 . Then, the UV is selectively irradiated to the pre-polymer layer  52  to selectively cure the pre-polymer layer  52 . The pre-polymer layer  52  to which the UV is irradiated constitutes a polymer layer  52   a . At this time, the UV-curing portion is set to be smaller than a substrate for a fine pattern. A portion where the pre-polymer layer is not UV-cured remains as the pre-polymer layer  52 .  
         [0080]     Next, as illustrated in  FIG. 4E , the polymer layer  52   a  and the pre-polymer layer  52  are stripped from the jig  50  and the master mold  51 .  
         [0081]     Afterwards, as illustrated in  FIG. 4F , the pre-polymer layer  52  that is not cured is dipped in a normal nucleic acid (n-Hxan) solution and then is removed. Thus, the soft mold is completed, in which the polymer layer  52   a  is attached to the back-plane substrate  53 .  
         [0082]     After the pre-polymer layer is selectively UV-cured, the portion where the pre-polymer layer is not cured is removed. In this case, even though the master mold  51  is smaller than a substrate  56  for a fine pattern, the soft mold can be fabricated so as not to form a threshold between the soft mold and the substrate  56 . Therefore, it is possible to desirably form the fine pattern using the soft mold.  
         [0083]     As described above, the method for fabricating a soft mold according to the present invention has numerous advantages, including the following.  
         [0084]     After the pre-polymer layer is selectively thermal-cured or UV-cured, the pre-polymer layer that is not cured is removed, so that the soft mold is completed. In this case, even though the master mold is smaller than the substrate for a fine pattern, the soft mold can be fabricated so as not to form the threshold between the soft mold and the substrate. Therefore, it is possible to desirably form the fine pattern.  
         [0085]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.