Abstract:
A soft mold resist for soft-lithography, a method for fabricating a soft mold, and a method for fabricating a liquid crystal display (LCD) device using the same where the soft mold includes a hydrophilic liquid prepolymer, a photoinitiator; and a surface active agent. A soft mold is formed by applying the soft mold resist to a back plate or a master plate and transferring a predefined pattern from the master plate to the soft mold resist. A display is formed by applying the soft mold to an etch resist layer overlying a thin film and transferring the predefined pattern to the etch resist, then etching the thin film using the etch resist as a mask. Additional processing step are carried out to form the LCD device.

Description:
PRIORITY CLAIM 
       [0001]    This application claims the benefit of Korean Patent Application No. 59968/2006, filed Jun. 29, 2006, which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a resist for a soft mold (namely, resistive pattern) used for soft-lithography and a method for fabricating a liquid crystal display (LCD) device using the same. 
       BACKGROUND 
     Description of the Related Art 
       [0003]    Recently, the importance of a display device as a visual information transmission medium has increased, and various types of competitive display devices are being developed. In order to hold an important position, the display devices should meet the requirements of having a low power consumption, being thin and light, and having high picture quality. 
         [0004]    An LCD, a major product among the flat panel displays (FPDs), can be mass produced and still have the performance necessary to satisfy the expectations of the display market. LCDs can be commonly employed in various application fields such as a large TV or a computer monitor, or the like. and is taking hold as a core display device that may eventually replace the existing cathode ray tubes (CRTs) in the market place. 
         [0005]    The LCD is a display device in which data signals according to image information are individually supplied to liquid crystal cells arranged in a matrix form to control light transmittance of the liquid crystal cells to thus display desired images. 
         [0006]    The construction of the related art LCD will now be described. 
         [0007]      FIG. 1  is an exploded perspective view showing the construction of a related art LCD. 
         [0008]    As shown, the general LCD includes a color filter substrate  113 , a TFT array substrate  101 , and a liquid crystal layer  109  formed between the color filter substrate  113  and the array substrate  101 . 
         [0009]    The color filter substrate  113  includes a color filter  117  including a plurality of sub-color filters that implement red, green and blue colors, a black matrix  115  for dividing the sub-color filters and blocking light transmission through the liquid crystal layer  109 , and a transparent common electrode  111  for applying voltage to the liquid crystal layer  109 . 
         [0010]    The array substrate  101  includes a plurality of gate lines  103  and a plurality of data lines  105  which are arranged vertically and horizontally to define a plurality of pixel regions (P), TFTs, switching elements, formed at respective crossings of the gate lines  103  and the data lines  105 , and pixel electrodes  107  formed on the pixel regions (P). 
         [0011]    In the method for fabricating most of the flat panel display devices including the LCD, a thin film material stacked on the substrate is patterned by using a photolithography process. The photolithography process is a type of photo-etching process and the patterning method using the photolithography process is as follows. 
         [0012]    First, a photoresist, such as a photosensitive material, is coated on a thin film to be patterned, a photo mask with a certain pattern is aligned, and an exposing process is performed. In this case, the photo mask includes a certain transmission region and a blocking region, and light which has transmitted through the transmission region chemically changes the photoresist. 
         [0013]    The chemical change of the photoresist varies depending on the type of the photoresist. In case of a positive photoresist, its light-exposed portion is changed to have qualities dissolved by a developer, and in the case of a negative photoresist, its light-exposed portion is changed to have qualities that are not dissolved by the developer. A process using a positive photoresist is taken as an example in the following description. 
         [0014]    Following the exposing process, when the exposed portion of the photoresist is removed using a developer, a certain photoresist pattern is formed on the thin film. Thereafter, the thin film is etched according to the shape of the photoresist pattern and a remaining photoresist pattern is removed to form a certain shape of thin film pattern. Thus, the photolithography process requires a high-priced photomask and is a complicated processes involving exposing and developing processes that result in high processing costs and low production yield. 
       SUMMARY 
       [0015]    In one aspect, a soft mold includes a hydrophilic liquid prepolymer of 96 wt % or greater, a photoinitiator of about 1 wt % to 3 wt %; and a surface active agent of about 0.01 wt % to 1 wt %. 
         [0016]    In a second aspect, a method of fabricating a soft mold includes providing a master plate having depressed or embossed portions. A resin layer containing a hydrophilic liquid prepolymer of 96 wt % or greater, a photoinitiator of about 1 wt % to 3 wt %, and a surface active agent of about 0.01 wt % to 1 wt % is coated on the master plate. The resin layer is cured by irradiating ultraviolet (UV) light to the resin layer. The cured resin layer is detached from the master plate, wherein the soft mold comprises the cured resin layer. 
         [0017]    In a third aspect, a method of forming a pattern using a soft mold includes forming a thin film on a substrate. A resist is applied to the thin film on the substrate. A soft mold is disposed on the resist. The soft mold includes at least one depressed pattern and has a hydrophilic property. The soft mold is removed from the substrate to form at least one desired pattern on the substrate. 
         [0018]    In a fourth aspect, a method for forming a liquid crystal display (LCD) device using a soft mold includes providing a first substrate and a second substrate. A black matrix is formed on the first substrate. A color filter is formed on the black matrix. An overcoat and column spacers is patterned with a soft mold. The soft mold has a hydrophilic property. A gate electrode is formed on the second substrate. A gate insulating layer is formed on the gate electrode. A TFT including a source electrode, a drain electrode, an active pattern, and a semiconductor layer is formed on the second substrate. A passivation layer and pixel electrode are formed on the second substrate. A liquid crystal layer is disposed between the first substrate and the second substrate. The first substrate is attached with the second substrate. 
         [0019]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0020]    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. 
           [0021]    In the drawings: 
           [0022]      FIG. 1  is an exploded perspective view showing the structure of a related art liquid crystal display; 
           [0023]      FIGS. 2A to 2C  are sectional views sequentially showing a method for patterning a thin film according to an exemplary embodiment of the present invention; 
           [0024]      FIGS. 3A to 3E  are sectional views sequentially showing a method for fabricating a soft mold according to one exemplary embodiment of the present invention; and 
           [0025]      FIGS. 4A to 4E  are sectional views sequentially showing a method for fabricating a soft mold according to another exemplary embodiment of the present invention. 
           [0026]      FIGS. 5A to 5C  are sectional views sequentially showing a method for fabricating an overcoat layer including a column spacer using the soft mold according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The resist for a soft mold and a method for fabricating a liquid crystal display (LCD) device using the same according to the exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. 
         [0028]      FIGS. 2A to 2C  are sectional views sequentially showing a method for patterning a thin film according to the exemplary embodiment of the present invention. Specifically,  FIGS. 2A to 2C  show a method for patterning a thin film by using soft-lithography which allows formation of a pattern without using a photolithography process. 
         [0029]    As shown in  FIG. 2A , a thin film  203   a  is formed on a substrate  201 , on which an etch resist  205   a  is then formed with a liquid resin. 
         [0030]    Thereafter, a soft mold  207   a  including a depressed pattern (B) and an embossed pattern (A) is brought into contact with a surface of the etch resist  205   a  from above the substrate  201  on which the thin film  203   a  and the etch resist  205   a  are formed. In this case, the soft mold  207   a  can be formed by curing a resist for a soft mold. 
         [0031]    When the soft mold  207   a  contacts the surface of the etch resist  205   a  that corresponds to a portion where a pattern is to be formed, the etch resist  205   a,  which is a liquid resin, transfers to the depressed pattern (B) of the soft mold  207   a  by virtue of a capillary action and the high surface energy of the soft mold  207   a.  In this case, the soft mold  207   a  is pressed when it contacts with the surface of the etch resist  205   a  as necessary. 
         [0032]    After a certain amount of time lapses, the soft mold  207   a  is separated from the substrate  201 . Then, as shown in  FIG. 2B , an etch resist pattern  206   a  in the same shape as the depressed pattern (B) remains on the thin film  203   a.  A certain amount of etch resist may remain at other portions in addition to the etch resist pattern  206   a,  and in this case, an ashing process can be performed to remove the remaining etch resist. 
         [0033]    Next, as shown in  FIG. 2C , the thin film  203   a  is selectively etched by using the etch resist pattern  206   a  as a mask, and then the etch resist pattern  206   a  is removed to form a certain thin film pattern  203 . 
         [0034]    As mentioned above, the soft photolithography process according to the present invention includes the process of allowing the etch resist and the soft mold to contact with each other to form the etch resist pattern. In this case, the etch resist transfers to the depressed pattern of the soft mold pattern to form the etch resist pattern corresponding to the pattern formed at the soft mold pattern. 
         [0035]    In this respect, however, if the repulsive force is strong between the etch resist and the surface of the soft mold, namely, if adhesion between the etch resist and the soft mold is weak because of a low surface energy of the soft mold, the etch resist will not sufficiently transfer to the depressed pattern of the soft mold, making it difficult to form the etch resist pattern. In subsequent processes that use the etch resist pattern, the etch resist pattern will not be properly formed in the underlying layers. Thus, it is necessary to improve the adhesion between the soft mold and the etch resist, and with improved adhesion, contact between the two materials can be improved and it is possible to form a high quality pattern. 
         [0036]    The adhesion and spreading characteristics between the two contacting materials depend on the surface energy, and the stronger the surface energy of the soft mold, the better the adhesion and spreading characteristics with the etch resist. In addition, the adhesion between the two materials depends on hydrophilicity of the two materials, and the more a material has hydrophilicity, the more the adhesion increases. In contrast, the higher the hydrophobicity of the material, the more the adhesion decreases. 
         [0037]    Thus, in the exemplary embodiment of the present invention, a soft mold with hydrophilicity and high surface energy is formed by using a photocurable (UV curable) material and an LCD is fabricated by using the soft mold. 
         [0038]      FIGS. 3A to 3E  are sectional views sequentially showing a method for fabricating a soft mold according to a first exemplary embodiment of the present invention. 
         [0039]    As shown in  FIG. 3A , a resist  305  for a soft mold is coated to form a soft mold on a substrate  301 . In this case, the material for forming the soft mold is a UV curable liquid material for forming a pattern, which will be called a resist for a soft mold hereinafter. 
         [0040]    The substrate  301  can be made of glass or PET (Polyethylene Terephthalate). 
         [0041]    Next, as shown in  FIGS. 3B and 3C , a master plate  307  with a certain pattern formed at a region corresponding to a pattern desired to be formed on the soft mold is prepared and allowed to contact with an upper surface of the resist  305 . In this case, the resist  305  can be pressed or heated to increase its mobility, as necessary. 
         [0042]    The master plate  307  includes a certain pattern such as a depressed pattern or an embossed pattern formed on the master plate  307 . The master plate  307  can be a glass plate or a glass plate with a metal formed thereon. Alternatively, the master plate  307  may be a flexible plate, such as plastic, or may be a flexible plate with a metal formed thereon. The material for forming the certain pattern can be made of one of a metal, silicon oxide/silicon nitride, photoresist, and wax. 
         [0043]    When the master plate  307  contacts with the resist  305 , the resist  305 , which is in a liquid state, transfers to the depressed pattern of the master plate  307 . 
         [0044]    Next, as shown in  FIG. 3D , the resist  305  is cured by exposure to light to create a soft mold. The resist  305 , according to an exemplary embodiment of the present invention, is a material that can be cured when light is irradiated thereto. In a preferred embodiment, the resist  305  is cured using ultraviolet light having a wavelength of about 300 nm˜500 nm. 
         [0045]    As shown in  FIG. 3E , after a soft mold  305 ′ is formed, the master plate  307  is separated from the substrate  301 . 
         [0046]      FIGS. 4A to 4E  are sectional views sequentially showing a method for fabricating a soft mold according to another exemplary embodiment of the present invention. 
         [0047]    First, as shown in  FIG. 4A , a master plate  407  with a certain pattern formed at a region corresponding to a pattern desired to be formed on the soft mold is prepared. 
         [0048]    As mentioned above, the master plate  407  includes a certain pattern such as a depressed pattern or an embossed pattern formed on the master plate  407 . The master plate  407  can be a glass plate or a glass plate with a metal formed thereon. Alternatively, the master plate  407  may be a flexible plate, such as plastic, or may be a flexible plate with a metal formed thereon. The material for forming the certain pattern can be made of one of a metal, silicon oxide/silicon nitride, photoresist, organic material and wax. 
         [0049]    Thereafter, as shown in  FIG. 4B , a resin layer  405  for forming a soft mold is coated on the master plate  407  by using a spin coating or the like. In this case, the material for forming a soft mold can be a UV curable liquid material for forming a pattern. 
         [0050]    Next, as shown in  FIG. 4C , a back plane  401  is brought into contact with an upper surface of the resin layer  405 . In this case, if necessary, a certain attachment material (not shown) can be interposed between the resin layer  405  and the back plane  401 . 
         [0051]    The back plane  401  can be made of glass or PET (Polyethylene Terephthalate), or the like. 
         [0052]    Next, as shown in  FIG. 4D , light is irradiated through the back plane  401  to cure the resin layer  405  and to form a soft mold  405 ′. 
         [0053]    Similar to the exemplary embodiment described above, the resist material for resin layer  405  according to the instant embodiment, is a material that can be cured when light is irradiated thereto. The resin layer  405  is preferably cured using ultraviolet light having a wavelength of about 300 nm˜500 nm. 
         [0054]    As shown in  FIG. 4E , after soft mold  405 ′ is formed, the master plate  407  is separated from the back plane  401 . 
         [0055]    Preferably, the pattern forming resist is in a liquid state assuming UV curability. In addition, the pattern forming resist preferably has hydrophilicity in order to better contact characteristics with an etch resist in forming a pattern in the LCD or the like. 
         [0056]    The material of the soft mold, namely, the resist for the soft mold according to the present invention includes a hydrophilic liquid prepolymer of about 96 wt % or greater; a photoinitiator of about 1 wt % to 3 wt %; and a surface active agent of about 0.01 wt % to 1 wt %, and is a material that can be cured when light is irradiated thereto. In one embodiment, the hydrophilic liquid prepolymer of may be 98 wt %; the photoinitiator may be 1.5 wt %; and the surface active agent may be 0.5 wt %. 
         [0057]    The hydrophilic liquid prepolymer is a prepolymer that can be UV cured and includes acrylate prepolymer. The acrylate prepolymer includes an HEA (2-Hydroxyethyl Acrylate), EGDMA (Ethyleneglycol Dimethacrylate), EGPEA (Ethyleneglycol Phenyltheracrylate), HPA (Hydroxypropyl Acrylate), and HPPA (Hydroxyphenoxypropyl Acrylate), and the like, and includes a hydrophilic acrylate prepolymer that can be UV cured. 
         [0058]    In the soft mold material, one prepolymer can be used, or alternatively, two or more prepolymers can be mixed to be used, as necessary. 
         [0059]    The photoinitiator is a material that forms a radical upon receiving light to start polymerization, including “Irgacure 369,” “Irgacure 184,” “Irgacure 819,” and the like, available from Ciba Speciality Chemicals. [note the chemical composition should be described and claimed] In the soft mold material, one photoinitiator can be used, or alternatively, several can be mixed as necessary. 
         [0060]    The surface active agent is added to change the surface tension or the surface energy. A preferred surface active agent is “FSO-100” available from DuPont Corporation. [note the chemical composition should be described and claimed] 
         [0061]    When the resist for a soft mold according to the present invention is exposed to light, a light-induced reaction occurs in which the photoinitiator forms a radical, whereby the resist is polymerized and cured. In particular, the resist is cured by the light irradiation thereon and molded, and, as described above, UV light of about 300 nm˜500 nm can be used to cure the resist. 
         [0062]    The thin film patterning process using the resist for a soft mold can be used in a process for forming a color filter or a black matrix, or an overcoat layer including a column spacer. In addition, the thin film patterning process using the resist for a soft mold can be also used in a process for fabricating an OLED (Organic Light Emitting Diode) or other flat plane display devices, as well as an LCD device. 
         [0063]    The resist for a soft mold and the method for fabricating an LCD by using the soft mold fabrication method will be described as follows. 
         [0064]    The process for fabricating the liquid crystal display panel can be divided into a driving element array process for forming a driving element on the lower array substrates, a color filter process for forming a color filter on the upper color filter substrate, and a cell process. 
         [0065]    First, a plurality of gate lines and a plurality of data lines arranged to define pixel regions on the array substrate are formed, and a TFT, a driving element, is formed to be connected with the gate lines and the data lines at each of the pixel regions through the array process. In addition, a pixel electrode which is connected with the TFT and drives the liquid crystal layer as a signal is applied thereto through the TFT is formed through the array process. 
         [0066]    A black matrix  412  for discriminating sub-color filters and shielding light passing a liquid crystal layer and a color filter layer  413  comprising red, green and blue sub-color filters implementing colors are formed on the color filter substrate  411  through the color filter process as shown in  FIGS. 5A to 5C . And then, an overcoat layer  415  including column spacers  416  may be formed on the color filter substrate  411 . 
         [0067]    In this case, the pattern of the overcoat layer  415  including the column spacers  416  may be formed by using the soft mold  405 ′ and the soft mold fabrication method according to the present invention. 
         [0068]    Namely, for example, in order to form the pattern such as the overcoat layer  415  including the column spacers  416  on the color filter substrate  411 , a master plate (not shown) with a certain pattern formed at a region corresponding to a pattern desired to be formed on the soft mold  405 ′ is prepared. 
         [0069]    Thereafter, a certain thin film such as a resin layer for forming the soft mold  405 ′ is formed on the master plate by using a spin coating or the like. In this case, the resin layer for forming the soft mold  405 ′ may be a UV curable liquid material containing a hydrophilic liquid prepolymer of about 96 wt % or greater; a photoinitiator of about 1 wt % to 3 wt %; and a surface active agent of about 0.01 wt % to 1 wt %. 
         [0070]    Next, the color filter substrate  411  with the black matrix  412  and color filter layer  413  formed thereon is brought into contact with an upper surface of the resin layer. In this case, if necessary, a certain attachment material may be interposed between the resin layer and the color filter substrate  411 . 
         [0071]    And then, light is irradiated through the color filter substrate  411  to cure the resin layer and to form the soft mold  405 ′. 
         [0072]    After the soft mold  405 ′ is formed, the master plate is separated from the color filter substrate  411 . Then, the overcoat layer  415  including column spacers  416  is formed on the color filter substrate  411 . 
         [0073]    Subsequently, after alignment films are coated on the array substrate and the color filter substrate, they are aligned to provide an anchoring force or a surface fixing force (namely, a pretilt angle and an alignment direction) to liquid crystal molecules of a liquid crystal layer formed between the array substrate and the color filter substrate. 
         [0074]    After finishing the aligning process, spacers are formed to uniformly maintain a cell gap between the array substrate and the color filter substrate, a sealant is coated on an outer edge portion of the color filter substrate, and then, the array substrate and the color filter substrate are attached by pressing the substrates together. 
         [0075]    The array substrate and the color filter substrate are large-scale mother substrates. In other words, a plurality of panel regions are formed on the large-scale mother substrates, and the TFT, the driving element, and the color filter layer are formed on each panel region, so in order to fabricate unit liquid crystal panels, the mother substrates should be cut and processed. 
         [0076]    The liquid crystal is injected by using a vacuum injection method using a pressure difference. That is, according to the vacuum injection method, the liquid crystal injection opening of the unit liquid crystal display panel separated from the large-scale mother substrates is put in a container filled with liquid crystal in a chamber with a certain degree of vacuum, and then, the degree of vacuum is changed to allow liquid crystal to be injected into the interior of the liquid crystal display panel according to a pressure difference between the interior and the exterior of the liquid crystal display panel. When the liquid crystal is filled within the liquid crystal display panel, the liquid crystal injection opening is sealed to form the liquid crystal layer of the liquid crystal display panel. Thus, in order to form the liquid crystal layer at the liquid crystal display panel through the vacuum injection method, a portion of the seal pattern needs to be opened to serve as the liquid crystal injection opening. 
         [0077]    Where a dropping method is used to form the liquid crystal layer, after finishing the aligning process, a seal pattern is formed with a sealant on the color filter substrate and at the same time liquid crystal is dropped to the array substrate. 
         [0078]    According to the dropping method, after liquid crystal is dropped and dispensed on image display regions of the large-scale first mother substrate where a plurality of array substrates are disposed or on image display regions of the second mother substrate where the plurality of color filter substrates are disposed, the first and second mother substrates are attached by applying a certain pressure thereto to thereby make the liquid crystal uniformly distributed to the entire image display regions to thus form a liquid crystal layer. 
         [0079]    Thus, in the case where the liquid crystal layer is formed in the liquid crystal display panel through the dropping method, the seal pattern should be formed as a closed pattern surrounding the outer edges of pixel part regions in order to prevent a leakage of liquid crystal to outside of the image display regions. 
         [0080]    The dropping method allows dropping of liquid crystal within a relatively short time compared with the vacuum injection method and can quickly form the liquid crystal even when the liquid crystal display panel is large. 
         [0081]    In addition, because the only required amount of liquid crystal is dropped on the substrate, such an increase in the unit cost of the liquid crystal display panel according to discarding of the high-priced liquid crystal as in the vacuum injection method can be prevented, and thus, the price competitiveness of the product can be enhanced. 
         [0082]    Thereafter, in a state that the array substrate and the color filter substrate on which liquid crystal has been dropped and the sealant has been coated are aligned, pressure is applied thereto to attach the array substrate and the color filter using the sealant and at the same time the dropped liquid crystal is spread uniformly on the entire portion of the panel. 
         [0083]    In the fabrication process, the plurality of liquid crystal panels with the liquid crystal layer formed therein are formed from the large-scale mother substrates. The glass substrates are processed and cut separate them into a plurality of liquid crystal panels, which are then inspected to thereby finish the fabrication of the liquid crystal display panels. 
         [0084]    It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.