Abstract:
A method for fabricating a mold includes the steps of forming a photo-polymerizable resin layer between a master substrate and a transparent mold substrate, wherein a first pattern is formed on the master substrate; solidifying the resin layer by exposing the resin layer to a UV light through the transparent mold substrate; and forming a mold having a second pattern by separating the resin layer from the master substrate, wherein the second pattern is in a form of a recess on the resin layer at a portion corresponding to the first pattern and the resin layer being engaged with the mold substrate.

Description:
This application claims the benefit of Korean Patent Application No. 10-2006-0061020 filed in Korea on Jun. 30, 2006, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for fabricating a mold that is used in fabricating a semiconductor integrated circuit and a flat panel display. 
     2. Discussion of the Related Art 
     A general integrated circuit and a flat panel display include a plurality of electrical circuits formed by a plurality of thin films made of a semiconductor material, an insulation material, a conductive material, and a filter material. Some of the plurality of thin films are patterned on a substrate. A patterning process using an etching mask (i.e., resist pattern) provides the patterned thin film. The resist pattern is formed by coating a resist material to an etched thin film, exposing the resist material, and developing the resist material. 
     The exposure process requires an exposure mask and exposure equipment to selectively expose the resist material. Thus, an additional handling step (i.e., arranging the exposure mask) is performed. Accordingly, the patterning process of the resist material including the exposure process has complex processing orders. Therefore, the yield rates of a semiconductor integrated circuit chip and the flat panel display can be compromised. In addition, since the prices of the exposure mask and the exposure equipment increases as desired the pattern requires more accuracy and the pattern area becomes larger. As a result, the patterning process, including the exposure process, increases the fabricating costs of the semiconductor integrated circuit chip and the flat panel display. 
     In order to solve the above problems, an IPP (In-Plane Printing) method without an exposure process is suggested. The IPP method forms a patterned thin film by transferring a desired pattern to a pattern object thin film. In addition, the IPP method can form a resist pattern by transferring the desired pattern to a resist material using a mold. The mold includes a resilient material where detailed patterns are depressed/stamped. 
     The mold is prepared by a related art fabricating method as shown in  FIGS. 1A and 1B . Referring to  FIG. 1A , a thermally cured resin  15  such as PDMS (polydimethylsiloxane) is formed on a master substrate  111  where a first pattern  13  is formed. The master substrate  11  is formed of silicon or glass and the first pattern  13  is formed of one of inorganic materials, such as silicon dioxide, silicon nitride, and metals and organic materials, such as a resist and a wax. 
     The resin layer  15  on the master substrate  11  is solidified by heat. Molecular chain of the PDMS in the resin layer  15  not solidified by the heat is released to a surface of the resin layer  15  contacting the master substrate  11 . This is to maintain the surface energy of the resin layer  15  at a constant value. In other words, the resin layer  15  has only a constant surface characteristic (i.e., a lipophile property). 
     As shown in  FIG. 1B , the thermally cured resin layer  15  is separated from the master substrate  11 . The separated resin layer  15  has a recess  19  on the lower surface thereof, which is formed by the shape of the first pattern  13 . Accordingly, the resin layer  15  having the recess  19  is used as a mold  17  to pattern a pattern object thin film or a resist material. 
     However, the IPP patterning method requires a mold having a different surface energy depending on the material of the pattern object thin film, the process condition, and the desired pattern. In order to satisfy the requirements of the IPP patterning method, an additional handling may be performed to reform the surface of the resin layer (i.e. the mold) using an SAMS (Self-assembled monolayers). This surface reforming work contributes to the more complex fabricating method of the mold. Further, since the related art mold fabricating resin layer is solidified thermally in a single process, the interior material not solidified by heat (i.e., solvent) is released outside the resin layer to deform the shape of the mold. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method for fabricating a mold that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method of fabricating a mold having a desired surface characteristic by changing the surface energy thereof. 
     Another object of the present invention is to provide a method for fabricating a mold that prevents deformation of the mold. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as claimed and broadly described, a method of fabricating a mold includes the steps of forming a photo-polymerizable resin layer between a master substrate and a transparent mold substrate, wherein a first pattern is formed on the master substrate; solidifying the resin layer by exposing the resin layer to a UV light through the transparent mold substrate; and forming a mold having a second pattern by separating the resin layer from the master substrate, wherein the second pattern is in a form of a recess on the resin layer at a portion corresponding to the first pattern and the resin layer being engaged with the mold substrate. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIGS. 1A to 1B  shows cross-sectional views of a related art method of fabricating a mold; and 
         FIGS. 2A to 2C  shows cross-sectional views of an exemplary method of fabricating a mold according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIGS. 2A to 2C  are cross-sectional views showing an exemplary method of fabricating a mold according to an exemplary embodiment of the present invention. As shown in  FIG. 2A , a photo-polymerizable resin layer  25  is formed on a master substrate  21  on which a first pattern  23  is formed. A mold substrate  27  is formed on the resin layer  25 . In the exemplary embodiment, the resin layer  25  is formed by coating a photo-polymerizable liquid resin on the master substrate  21  having the first pattern  23  thereon. Then, the mold substrate  27  is adhered to the resin layer  25 . Alternatively, the resin layer  25  can be formed on the mold substrate  27  first. Thereafter, the master substrate  21  having the first pattern  23  can be adhered to the resin layer  25 . 
     The master substrate  21  is formed of silicon or glass material and the first pattern  23  is formed of one of inorganic materials such as silicon dioxide, silicon nitride, and metals. The mold substrate  27  can be formed of a transparent material such as glass. The photo-polymerizable resin layer  25  includes a liquefied high molecular precursor material (i.e., one of polyurethane acrylate, glycidyl acrylate, and butyl mathacrylate). Further, a photo initiator such as irgacure 369(2-Benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone) or irgacure 819(phosphine oxide, phenyl bis(2,4,6-trimethyl benzoyl)) can be included in the liquefied high molecular precursor material. In another form, the photo-polymerizable resin layer  25  can include an organic solvent where the photo-polymerizable liquefied high molecular precursor material is diluted. 
     As shown in  FIG. 2B , the resin layer  25  is exposed to UV (ultraviolet) light illuminated through the transparent mold substrate  27 . The UV light is illuminated to the resin layer  25  at the strength of light of 3 to 20 mW/Cm 2  for 5 to 15 seconds. It is preferable that the UV ray is illuminated to the resin layer  25  for approximately 10 seconds. The illumination of the UV light allows the photo-polymerizable high molecular precursor in the resin layer  25  to be cross-linked or solidified by changing the arrangement of the high molecular precursor or the reaction portion. The strength of light of the UV light and the illumination period can be regulated to change the value of the surface energy of the resin layer  25 . Further, the photo initiator included in the resin layer  25  promotes smooth reaction of the photo-polymerizable liquefied high molecular precursor material by the UV light. 
     As shown in  FIG. 2C , the resin layer  25  solidified by the UV light is separated from the master substrate  21 . The resin layer  25  is still adhered to the mold substrate  27 . A second pattern in the form of a recess  31  is provided on a surface of the separated resin layer  25 . The separated resin layer  25  can be exposed to the UV light through the mold substrate  27  and be solidified a second time. Through the second solidifying process, the interior of the resin layer  25  is solidified as well as the surface thereof. 
     In the second hardening process, the UV light is illuminated to the resin layer  25  at the strength of 3 to 20 mW/cm 2  for 20 seconds to 30 minutes. It is preferable that the illumination of the UV light is performed at the strength of approximately 3 or 11 mW/cm 2  for approximately 1 or 10 minutes. The second UV light allows the surface energy of the resin layer  25  to have various values by changing the cross-linking degree in the interior of the resin layer  25 , the reacting portion, or the molecular arrangement. In addition, the photo initiator included in the resin layer  25  promotes smooth reaction of the photo-polymerizable liquefied high molecular precursor material by the UV light. 
     The resin layer  25  solidified by the UV light is used as a mold  29  in an IPP pattern method. Since the resin layer  25  is solidified by UV light twice, the interior and the exterior surface of the resin layer  25  is completely solidified and the shape of the recess  31  (or reaction portion) is maintained. Thus, the deformation of the mold  29  is prevented. The resin layer  25  adhered to the mold substrate  27  allows a thin film pattern to be formed without an exposure process. Similarly, a resist pattern is formed without the exposure process. The thin film pattern is used to fabricate a circuit device and the resist pattern is used as an etching mask. 
     The surface energy of the mold  29  changes according to the first and second illumination conditions. Therefore, the mold  29  can selectively include a lipophile or hydrophile surface characteristic. Actually, when the surface energy of the mold  29  is large, the mold  29  has a hydrophile surface characteristic. On the other hand, when the surface energy thereof is small, it has a lipophile surface characteristic. After the mold  29  is formed, additional UV light is no longer required. 
     The following Table 1 represents the surface energy of the mold  29  obtained experimentally. 
     
       
         
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Solidifying condition 
                   
               
             
          
           
               
                 First illumination 
                 Second illumination 
                 Experimental result 
               
             
          
           
               
                 condition 
                 condition 
                 Surface energy 
                   
               
             
          
           
               
                 Strength 
                   
                 Strength of 
                   
                 Total 
                   
                   
                   
               
               
                 of light 
                   
                 light 
                   
                 sum 
                 Distribution 
                 Polarity 
               
               
                 (mW/cm 2 ) 
                 Period (sec) 
                 (mW/cm 2 ) 
                 Period (sec) 
                 (T) 
                 (D) 
                 (P) 
                 D/P 
               
               
                   
               
             
          
           
               
                 3 
                 10 
                 None 
                 50.3 
                 41.0 
                 9.3 
                 4.4 
               
             
          
           
               
                 3 
                 10 
                 3 
                 60 
                 38.3 
                 31.4 
                 6.9 
                 4.5 
               
               
                 3 
                 10 
                 3 
                 300 
                 32.6 
                 26.4 
                 6.2 
                 4.3 
               
               
                 3 
                 10 
                 11 
                 60 
                 32.7 
                 26.6 
                 6.1 
                 4.3 
               
               
                 3 
                 10 
                 11 
                 300 
                 28.1 
                 23.1 
                 5.0 
                 4.6 
               
             
          
           
               
                 11 
                 10 
                 None 
                 47.6 
                 39.4 
                 8.2 
                 4.8 
               
             
          
           
               
                 11 
                 10 
                 3 
                 60 
                 34.6 
                 29.4 
                 5.3 
                 5.6 
               
               
                 11 
                 10 
                 3 
                 300 
                 26.5 
                 23.7 
                 2.8 
                 8.5 
               
               
                 11 
                 10 
                 11 
                 60 
                 30.4 
                 26.5 
                 3.8 
                 6.9 
               
               
                 11 
                 10 
                 11 
                 300 
                 23.5 
                 20.8 
                 2.6 
                 7.9 
               
               
                   
               
             
          
         
       
     
     In the experiments, distinct UV light strengths and illuminating periods were applied to the resin layer  25 . One of the first illumination conditions were UV light strength of approximately 3 mW/cm 2  and an illuminating period of about 10 seconds. Another one of the first illumination conditions were UV light strength of about 11 mW/cm 2  and an illuminating period of about 10 seconds. Then, one of the second illumination conditions were 3 mW/cm 2  for about 1 min or 5 min, and another one of 11 mW/cm 2  for about 1 or 5 minutes. 
     In a first case, only a first illumination of 3 mW/cm 2  for 10 seconds was performed (i.e., no second illumination), the results included distribution D=41.0, polarity P=9.3, total sum T=50.3, and D/P ratio=4.4. In a second case, first illumination of 3 mW/cm 2  for 10 seconds and second illumination of 3 mW/cm 2  for 60 seconds were performed, the results included the distribution D=31.4, the polarity P=6.9, the total sum T thereof=38.3, and the D/P ratio=4.5. In a third case, first illumination of 3 mW/cm 2  for 10 seconds and second illumination of 3 mW/cm 2  for 300 seconds were performed, the results included the distribution D=26.4, the polarity P=6.2, the total sum T thereof=32.6, and the D/P ratio=4.3. In a fourth case, first illumination of 3 mW/cm 2  for 10 seconds and the second illumination of 11 mW/cm 2  for 60 seconds were performed, the results included distribution D=26.6, the polarity P=6.1, the total sum T=32.7, and the D/P ratio=4.3. In a fifth case, first illumination 3 mW/cm 2  for 10 seconds and the second illumination of 11 mW/cm 2  for 300 seconds, the results included the distribution D=23.1, the polarity P=5.0, the total sum T=28.1, and the D/P ratio=4.6. 
     From Table 1, the surface energy of the mold  29  was largest when no second illumination was performed. Then, given the same first illumination condition, the surface energy became lower as the strength of UV light and/or the illuminating period were increased in the second illumination. Further, given the same first illumination condition and the same illuminating period in the second illumination, the surface energy of the mold  29  became lower as the strength of the UV light was increased. As shown in Table 1, the distribution D, the polarity P, the total sum T, and the D/P ratio of the surface energy of the mold  29  are all decreased as compared to the result of first illumination at the strength of 3 mW/cm 2 . For example, when only the first illumination of 11 mW/cm 2  for 10 seconds was performed, the results included distribution D=39.4, polarity P=8.2, total sum T=47.6, and the D/P ratio=4.8. In other words, when a first illumination of 11 mW/cm 2  for 10 seconds and a second illumination of 3 mW/cm 2  or 11 mW/cm 2  for 1 to 5 minutes were performed, values of the distribution D, the polarity P, the total sum T, and the D/P ratio were all lower than those in the case when the first illumination of 3 mW/cm 2  for 10 seconds and the second illumination of 3 mW/cm 2  or 11 mW/cm 2  for 1 to 5 minutes were performed. 
     As mentioned above, the surface energy of the mold  29  according to the first and second illumination conditions can have various values ranging from 23 to 50. Generally, if the surface energy of the mold  29  is large, the mold  29  has a hydrophile surface characteristic. On the contrary, if the surface energy is small, the mold  29  has a lipophile surface characteristic. Therefore, the mold  29  includes the hydrophile property if the strength of second UV light is small and the second illuminating period is short given the same first illumination condition. On the other hand, the mold  29  includes the lipophile property when the strength of second UV light is large and the second illuminating period is long. In addition, the mold  29  has a hydrophile property if the strength of UV light in the first illumination is small and has a lipophile property if it is large given the same second illumination condition. 
     As mentioned above, the resin layer is formed by coating a resin having a photo-polymerizable characteristic on the master substrate having the first pattern formed thereon. The resin layer is adhered to a transparent mold substrate, then, the surface of the resin layer is solidified by illuminating the first UV light. The mold is formed by separating the solidified resin layer from the master substrate with the resin layer being adhered to the mold substrate. 
     In the exemplary embodiment of the present invention, a UV light can be additionally illuminated on the firstly illuminated resin layer. The interior of the resin layer is solidified by illuminating the resin layer with UV light twice. Accordingly, deformation of the shape of the mold can be prevented. Further, since the surface energy of the mold can be regulated by the first and second illumination conditions, the surface characteristic of the mold can be easily selected. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the method of fabricating the mold of the present invention without departing from the spirit or scope of the invention. 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.