Abstract:
A soft mold may be manufactured that is used for forming a pattern. Semiconductor devices and flat panel display devices include a plurality of fine patterns on a substrate. The soft mold may be photo-curable and formed of a material with a hydrophobic property similar to heat-curable molds. The photo-curable mold may be created on a master plate with a resin layer that is removed with a back plate and adhesive layer after embossed or depressed portions are formed on the mold that correspond with embossed or depressed portions of the master plate.

Description:
This application claims the benefit of Korean Patent Application No. 2006-0057986, filed in Korea on Jun. 27, 2006, which is hereby incorporated by reference. This application is related the patent application entitled “FABRICATION APPARATUS AND METHOD OF FABRICATING A SOFT MOLD,” Ser. No. 11/811,703, filed currently herewith. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a mold for forming a pattern. 
     2. Discussion of the Related Art 
     Semiconductor devices and flat panel display devices include a plurality of fine patterns on a substrate. A photolithographic method is widely used to form the fine patterns on a substrate, such as wafer or glass. In the photolithographic method, a thin film to be patterned is disposed on a substrate, and a photoresist is applied to the thin film. The photoresist is exposed to light through a photo mask having predetermined patterns. The photoresist is then selectively removed by a developing process to form a photoresist pattern. The thin film is then etched using the photoresist pattern as an etching mask, and the photoresist pattern is removed. Accordingly, a desired pattern is left on the substrate after the photoresist pattern is removed. 
     However, the photolithographic method is a complicated process that includes exposing and developing, and utilizes an expensive photo mask or exposing apparatus. Production yields may be lowered and manufacturing costs increased as a result of the process. In addition, as patterns are formed to have narrower widths, the production yields may be lowered even further. 
     As an alternative to the photolithographic method, several methods, including a nano-imprint lithographic method, a soft lithographic method, a capillary force lithographic method, and a soft molding method, have been proposed. In the alternative methods, a soft mold of a high molecular elastic material may be used to form a pattern. A soft lithographic method according to the related art will be described hereinafter with reference to accompanying drawings. In particular,  FIGS. 1A to 1F  are cross-sectional views illustrating a method for forming a pattern on a substrate using a soft mold according to the related art. 
     In  FIG. 1A , a thin film  11  to be patterned is formed on a substrate  10 , and a resist  13  is applied to the thin film  11 . 
     In  FIG. 1B , a mold  15 , which has depressed portions  17  corresponding to patterns to be formed, is disposed on the resist  13  such that the depressed portions  17  face the thin film  11 . The mold  15  is pressed such that a top surface of the mold  15  contacts the thin film  11 . Several forces are applied to the resist  13 , such as a repulsive force F R  between the mold  15  and the resist  13 , a capillary force F C  that causes the resist  13  to be drawn into the depressed portions  17  of the mold  15 , a gravity force F G  applied to the resist  13 , and a frictional force or adhesion force F V  between the substrate  10  and the resist  13 . As a result of all these forces being applied to the resist  13 , the overall force F pushing the resist  13  out into the depressed portions  17  of the mold  15  may be expressed by F R +F C −F G −F V . In the soft lithographic method, the mold  15  may be formed of a hydrophobic material so that the mold  15  has a relatively low surface energy. Conversely, the resist  13  may be formed of a hydrophilic material. Accordingly, the repulsive force F R  may result from the surface properties of the mold  15  and the resist  13 . 
     In  FIG. 1C , the resist  13  of  FIG. 1B  is moved into the depressed portions  17  by applying pressure to the mold  15 . The resist  13  in the depressed portions  17  is then cured to form resist patterns  13   a . The resist patterns  13   a  correspond to the depressed portions  17  and are created by applying pressure to the mold  15 . 
     In  FIG. 1D , the mold  15  is removed after curing the resist  13 . The resist patterns  13   a  remain on the thin film  11  after the curing of the resist  13  and removing the mold  15 . 
     In  FIG. 1E , the thin film  11  of  FIG. 1D  is etched using the resist patterns  13   a  as an etching mask. The etching results in the formation of patterns  11   a  that correspond with the resist patterns  13   a . The patterns  11   a  are formed by patterning the thin film  11 . 
     In  FIG. 1F , the resist patterns  13   a  of  FIG. 1E  are removed by a stripping process. The removal of the resist patterns  13   a  leaves the patterns  11   a  on the substrate  10 . 
     Generally, the separation of the mold from the resist pattern may be accomplished easier when the surface energy of the mold is lower than the surface energy of the resist. The surface energy is the energy per unit area required to interface between a solid or liquid phase material and a gas phase material. As the solid or liquid phase material has a larger surface energy, it becomes more difficult to interface with the gas phase material. 
     Accordingly, in the soft lithographic method, such as with an in-plane printing (IPP) method, to adequately form a predetermined resist pattern, the surface energies of the mold, the resist and the substrate, which may be referred to as γ MOLD , γ ER  and γ substrate , respectively, should satisfy the following relation: γ MOLD &lt;γ ER &lt;γ substrate    
     If the surface energy of the resist γ ER  is lower than the surface energy of the substrate γ substrate , the resist may be more easily applied to the substrate. If the surface energy of the resist γ ER  is higher than the surface energy of the mold γ MOLD , a repulsive force may be induced between the mold and the resist pattern, and the mold may be more easily separated from the resist pattern. Since the repulsive force of the mold to the resist increases as the surface energy of the mold γ MOLD  is lowered, it is advantageous for the formation of a pattern to lower the surface energy of the mold γ MOLD . 
     Generally, polydimethylsiloxane (PDMS) may be used as a material for the soft mold of the soft lithographic method. In the PDMS mold, uncured chains come out of a surface of the mold, and the PDMS mold keeps a hydrophobic property. Additionally, since the PDMS mold has an elastic property, the PDMS mold may uniformly contact a surface of a substrate to be patterned. The PDMS mold has a relatively low surface energy, and as a result the PDMS mold can be easily detached from the substrate. However, PDMS is heat-curable, and thus the PDMS mold is cured by heat. Accordingly, when the PDMS mold is fabricated, the heat may result in deformations of the mold. In particular, changes in dimensions of mold patterns may be caused due to a shrinking transformation. In addition, PDMS has relatively high viscosity, and as a result, the PDMS material that is deposited through a dispensing method has a relatively large thickness. Further, it may be difficult to reduce the thickness of the PDMS mold. 
     SUMMARY 
     In a first aspect, a soft mold includes a photo-curable material and a photo-initiator combined with the photo-curable material. Each surface of the soft mold satisfies an equation 
                     (     0.3   ×       γ   M   d       γ   L         )       1   /   2       +       (     0.7   ×       γ   M   p       γ   L         )       1   /   2         ≤   0.5     ,         
wherein γ d   M  is a dispersion term of a surface energy of the soft mold, γ p   M  is a polar term of a surface energy of the soft mold, and γ L  is a surface energy of deionized water.
 
     In a second aspect, a method of fabricating a soft mold includes providing a master plate having depressed or embossed portions. A resin layer is disposed on the master plate and cured by irradiating UV light to the resin layer. The cured resin layer is detached from the master plate. Each surface of the soft mold satisfies an equation 
                     (     0.3   ×       γ   M   d       γ   L         )       1   /   2       +       (     0.7   ×       γ   M   p       γ   L         )       1   /   2         ≤   0.5     ,         
wherein γ d   M  is a dispersion term of a surface energy of the soft mold, γ p   M  is a polar term of a surface energy of the soft mold, and γ L  is a surface energy of deionized water.
 
     In a third aspect, a soft mold for creating a pattern includes a photo-curable material that comprises one or more of diethylene glycol dimethacrylate (DGDMA), ethylene glycol dimethacrylate (EGDMA), ethylene glycol phenyletheracrylate (EGPEA), 2-ethoxy-(2-ethoxy)ethyl acrylate (EOEOEA), 1,6-hexanediol (EO) diacrylate (HD(EO)DA), polyurethane acrylate, glycidyl acrylate, or butyl methacrylate. A photo-initiator is combined with the photo-curable material. 
     In a fourth aspect, a method for producing a photo-curable soft mold includes disposing a resin layer including a photo-curable material on a master plate that comprises one or more of diethylene glycol dimethacrylate (DGDMA), ethylene glycol dimethacrylate (EGDMA), ethylene glycol phenyletheracrylate (EGPEA), 2-ethoxy-(2-ethoxy)ethyl acrylate (EOEOEA), 1,6-hexanediol (EO) diacrylate (HD(EO)DA), polyurethane acrylate, glycidyl acrylate, or butyl methacrylate. A back plane is contacted with the resin layer, which is cured using a photo-initiator by irradiating ultraviolet light on the resin layer. The resin layer is removed from the master plate to form the photo-curable soft mold. 
     In a fifth aspect, a method of forming a pattern using a soft mold includes forming a thin film on a substrate, and applying a resist to the thin film on the substrate. A soft mold is disposed on the resist that includes at least one depressed pattern. The soft mold has a hydrophobic property and is removed from the substrate to form at least one desired pattern on the substrate. 
     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. Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. Nothing in this section should be taken as a limitation on those claims. Further aspects and advantages are discussed below in conjunction with the embodiments. 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The system and/or method may be better understood with reference to the following drawings and description. Non-limiting and non-exhaustive embodiments are described with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like referenced numerals designate corresponding parts throughout the different views. The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIGS. 1A to 1F  are cross-sectional views illustrating a method for forming a pattern on a substrate using a soft mold according to the related art; and 
         FIGS. 2A to 2F  are cross-sectional views illustrating a method of fabricating a photo-curable soft mold according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present disclosure, an example of which is illustrated in the accompanying drawings. In the present embodiments, a photo-curable soft mold is proposed rather than a heat-curable soft mold, such as the PDMS mold. The photo-curable soft mold according to the present embodiments may be formed of one or more material selected from diethylene glycol dimethacrylate (DGDMA), ethylene glycol dimethacrylate (EGDMA), ethylene glycol phenyletheracrylate (EGPEA), 2-ethoxy-(2-ethoxy)ethyl acrylate (EOEOEA), 1,6-hexanediol (EO) diacrylate (HD(EO)DA), polyurethane acrylate, glycidyl acrylate, and butyl methacrylate. The materials have a relatively low viscosity. A photo-initiator may be added to the selected material. In one embodiment, the photo-initiator may be one of IRGACURE 369, IRGACURE 184 or IRGACURE 379 of Ciba Specialty Chemicals. 
     In the present embodiments, the photo-curable soft mold made of the above-mentioned material satisfies a condition defined by equation (1) such that the photo-curable soft mold has a similar value for its surface energy as that of the heat-curable soft mold made of PDMS. 
     
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           0.3 
                           × 
                           
                             
                               γ 
                               M 
                               d 
                             
                             
                               γ 
                               L 
                             
                           
                         
                         ) 
                       
                       
                         1 
                         / 
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           0.7 
                           × 
                           
                             
                               γ 
                               M 
                               p 
                             
                             
                               γ 
                               L 
                             
                           
                         
                         ) 
                       
                       
                         1 
                         / 
                         2 
                       
                     
                   
                   ≤ 
                   0.5 
                 
               
               
                 
                   equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     As defined in equation (1), γ M  is a surface energy of the soft mold and γ L  is a surface energy of deionized water. In addition, γ d  is a dispersion term and γ p  is a polar term. Hereinafter, the left side of the equation (1) may be referred to as a coefficient A. 
     The equation (1) is derived from the following equations:
 
γ ML =γ M −γ L  cos θ  equation (2)
 
γ ML −γ M +γ L   −W   a   equation (3)
 
     The equation (2) is Young&#39;s equation, and equation (3) is Good-Girifalco&#39;s theory. In equation (3), Wa is a work of adhesion. The following equation (4) is derived from equations (2) and (3):
 
γ L (1+cos θ)= W   a   equation (4)
 
     In general, a surface is regarded as hydrophobic when a contact angle of a water droplet on it is larger than 90 degrees. Therefore, the following equation (5) must be satisfied to establish that the surface of the soft mold has a hydrophobic property. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       1 
                       + 
                       
                         cos 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                     ) 
                   
                   = 
                   
                     
                       
                         W 
                         a 
                       
                       
                         γ 
                         L 
                       
                     
                     ≤ 
                     1 
                   
                 
               
               
                 
                   equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     5 
                     ) 
                   
                 
               
             
           
         
       
     
     If the following equation (6) for Owens and Wendt&#39;s hypothesis is substituted for equation (5), then equation (1) may be derived.
 
 W   a =2(γ L   d γ M   d ) 1/2 +2(γ L   p γ M   p ) 1/2   equation (6)
 
     Accordingly, in equation (1), the coefficient A is determined by the dispersion term γ d  and the polar term γ p  of the surface energy. A method of fabricating a photo-curable soft mold using a material satisfying the above-mentioned conditions will be described hereinafter with reference to accompanying drawings.  FIGS. 2A to 2F  are cross-sectional views illustrating a method of fabricating a photo-curable soft mold according to one embodiment. 
     In  FIG. 2A , a master plate  20  is prepared. The master plate  20  has predetermined embossed portions  22  on its surface. The master plate  20  may have depressed portions, rather than embossed portions  22 . Alternatively, the portions between embossed portions  22  may be referred to as depressed portions. The master plate  20  may be formed by depositing an insulating layer, such as silicon nitride or silicon oxide, on an insulating substrate. The insulating layer may then be patterned through a photolithographic process in one example. Alternatively, the master plate  20  may be formed by selectively patterning the surface of the master plate  20 . 
     In  FIG. 2B , a resin layer  30  is formed on the master plate  20 . The resin layer  30  may include at least one material selected from diethylene glycol dimethacrylate (DGDMA), ethylene glycol dimethacrylate (EGDMA), ethylene glycol phenyletheracrylate (EGPEA), 2-ethoxy-(2-ethoxy)ethyl acrylate (EOEOEA), 1,6-hexanediol (EO) diacrylate (HD(EO)DA), polyurethane acrylate, glycidyl acrylate, or butyl methacrylate. In one embodiment, the resin layer  30  is chosen to satisfy the equation (1). Additionally, since the resin layer  30  is cured by UV light, the resin layer  30  may include a photo-initiator. The photo-initiator may be used to improve the curing of the resin layer  30  by the UV light. 
     In  FIG. 2C , a back-plane  50  is coupled with a top surface of the resin layer  30 . Herein, the phrase “coupled with” is defined to mean directly connected to or indirectly connected through one or more intermediate components. In one embodiment, an adhesive material  40  may be applied to a surface of the back-plane  50 . The surface of the back-plane  50  with the adhesive is contacted with the top surface of the resin layer  30 . The adhesive material  40  may operate to couple the resin layer  30  with the back-plane  50 . In alternative embodiments, the attaching of the back-plane  50  may be omitted. 
     The back-plane  50  may be formed of a transparent material, such as glass, quartz, polyethyleneterephthalate (PET), polymethylmethacrylated (PMMA), or polycarbonate (PC). In one example, the adhesive may be EC-2320 of 3M Co., Ltd. The adhesive material  40  may be formed on the back-plane  50  by a spray coating method, a spin coating method, a slit coating method or a bar coating method. 
     In  FIG. 2D , UV light is irradiated on the resin layer  30  to cure the resin layer  30 . The resin layer  30  is cured by activating physical cross-linking reactions of linear chain polymers due to the photo-initiator. As described above, a photo-initiator applied to the resin layer  30  may be used to improve the curing of the resin layer  30  by UV light. 
     In  FIG. 2E , the cured resin layer  30  with the back-plane  50  is detached from the master plate  20 , and thus, in  FIG. 2F , a soft mold  100  is completed. In particular, the back-plane  50  may be removed from the master plate  20  and because the adhesive material bonds the resin layer  30  with the back-plane  50 , the removal of the back-plane  50  also removes the resin layer. The back-plane  50  with the resin layer  30  forms the soft mold  100  as shown in  FIG. 2F . The soft mold  100  has depressed or embossed portions, which correspond to the embossed or depressed portions of the master plate  20  of  FIG. 2E . To strengthen the hydrophobic property of the soft mold  100 , a post-treatment process may be performed using UV light on the soft mold  100 . In the post-treatment process, the intensity of the UV light may be within a range of 2 to 15 mW/cm 2 , and the irradiation time may be within a range of 10 seconds to 20 minutes in one embodiment. 
     For example, when the UV light having an intensity of about 11 mW/cm 2  is irradiated to the soft mold for about 5 minutes, the soft mold has a dispersion term of the surface energy of about 20.8 and a polar term of the surface energy of about 2.6. Accordingly, the coefficient A of the soft mold is about 0.45 with the above dispersion and polar values. The coefficient A of the soft mold is similar to that of a heat-curable soft mold, such as a PDMS. A heat-curable soft mold which is made of PDMS may have a dispersion term of the surface energy of about 18.8, a polar term of the surface energy of about 1.6, and the resulting coefficient A becomes about 0.4. Alternatively, another photo-curable soft mold made of polyurethane may have a coefficient A of about 0.6 and does not possess the hydrophobic property. 
     In the present embodiments, since the soft mold is photo-curable, dimensions of the mold patterns are not deformed by the process of curing. In addition, the soft mold is formed of one or more materials having a similar hydrophobic property to a heat-curable soft mold, such as a mold made from PDMS. Finally, the soft mold may be easily detached from a substrate for forming desired patterns. Because the material for the soft mold has relatively low viscosity, the soft mold may be created with a small thickness of several micrometers and a lighter weight. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the soft mold for an in-plane printing process that a method of manufacturing the same of the present invention without departing from the spirit or scope of the invention. The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive. The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention.