Abstract:
A method for manufacturing a printing plate is realizes a precise and fine pattern by minimizing a variation of etching critical dimension. The method includes forming a hard mask having an opening on an insulating substrate; forming a first trench having a first depth in the insulating substrate using the hard mask; coating, patterning and developing a first photoresist over an entire surface of the insulating substrate including the hard mask; and forming at least a second trench having a second depth in the insulating substrate using the hard mask, wherein the second depth is deeper than the first depth.

Description:
[0001]     This application claims the priority under 35 U.S.C. §119 of the Korean Patent Application No. 10-2005-58303, filed on Jun. 30, 2005, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to a method for manufacturing a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing a printing plate to realize a fine pattern.  
         [0004]     2. Description of the Related Art  
         [0005]     Various displays that can substitute for a cathode ray tube (CRT) have recently been developed, which have various advantages of portability, light weight, thin profile, small size, good picture quality, etc.  
         [0006]     In general, an LCD device is includes a thin film transistor (TFT) array substrate, a color filter substrate, and a liquid crystal layer formed between the TFT array substrate and the color filter substrate. On the TFT array substrate, multiple gate lines are formed in perpendicular to multiple data lines, so as to define multiple pixel regions arranged in a matrix. Also, multiple TFTs are formed on unit pixel regions of the TFT array substrate, wherein the TFTs serve as switching devices. In addition, a pixel electrode of a transparent metal material is formed on the unit pixel regions. Then, RGB color filter layers and a black matrix layer are formed on the color filter substrate to correspond to the pixel electrode.  
         [0007]     The TFT array substrate and the color filter substrate are separately manufactured. Before bonding the TFT array substrate and the color filter substrate to each other, steps of alignment coating, rubbing, spacer dispensing, and seal printing are sequentially performed.  
         [0008]     After completing the above steps, the TFT array substrate and the color filter substrate are positioned opposite to each other, and then they are bonded to each other by heat and UV irradiation. At this time, a seal printing step is performed to bond the two substrates to each other and to prevent the outflow of liquid crystal molecules during injection of liquid crystals.  
         [0009]     The seal printing step includes three methods or sub-steps of 1) a printing method, 2) a sandblasting method and 3) a dispensing method.  
         [0010]     First, the printing method is generally used for manufacture of LCDs and plasma display panels (PDPs) because production facilities are simple and material efficiency is high. That is, after positioning a patterned screen above a substrate, a paste for formation of a wall is printed on the substrate by pressing. Through one printing process, it is possible to obtain a height of about 20 μm before firing. To form a wall having a height of 50 μm to 100 μm, it is necessary to perform the printing process 5 to 10 times, thereby requiring several drying steps. Accordingly, the printing method has low yield. In addition, since the glass substrate is deformed, it is difficult to realize high resolution.  
         [0011]     Second, the sandblasting method is used to produce a fine wall of a large-sized panel. In the sandblasting method, a wall material is coated on a substrate, and is selectively removed to thereby form a wall. For example, a wall material is screen printed on an entire surface of a substrate. Then, a photoresist film is coated on the wall material and selectively patterned by exposure and development. After that, an abrasive material is sprayed onto the substrate so as to physically remove the substrate having no photoresist film, thereby forming the wall. At this time, the abrasive material may be used of Al 2 O 3 , SiC or glass particles, which is sprayed using compressed air or nitrogen gas. By the sandblasting method, it is possible to form the wall of 70 μm or less on the large-sized substrate. However, the glass substrate may be broken due to physical impact during firing. Also, the process of sandblasting is complicated, whereby the manufacturing cost increases. Further, an environmental pollution may be generated due to dust.  
         [0012]     Third, the dispensing method is generally used for sealing a large-sized LCD or PDP. In the dispensing method, a paste is directly dispensed on a substrate by air pressure using line data from computer-assisted design (CAD) used for manufacture of a mask. In the dispensing method, it is possible to reduce the manufacturing cost of the mask, to obtain great degree of freedom for formation of a thick film, and to realize the simplified process and various applications.  
         [0013]      FIG. 1  shows a schematic view illustrating a printing apparatus according to the related art. As shown in  FIG. 1 , the related art printing apparatus includes a printing table  11  supporting a substrate  10 , a printing plate  1  having a convex (or concave) pattern  2  (for printing a pattern  4  on the substrate  10 ), a plate body  12 , an anilox roll  16 , a dispenser  18 , and a doctor roll  15 .  
         [0014]     Then, a printing material  17  (for example ink) is supplied to the anilox roll  16  by the dispenser  18 . The anilox roll  16  and the plate body  12  are formed in shape of cylindrical roll. The anilox roll  16  and the plate body  12  respectively revolve in arrow directions  48  and  46  and are in contact with each other.  
         [0015]     The printing plate  1  adheres on an outer surface of the plate body  12 , wherein the printing plate  1  has the convex (or concave) pattern  2  having a desired shape. The convex pattern  2  is positioned to be in contact with the substrate  10 .  
         [0016]     Also, the printing material  17  is supplied from the anilox roll  16  to the convex pattern  2 , and then the printing material  17  of the convex pattern  2  is printed on the substrate  10 . The substrate  10  is positioned on the printing table  11 . During printing, the substrate  10  is moved to an arrow direction  47 .  
         [0017]     The printing material  17  printed on the substrate  10  has a shape or pattern  4  corresponding to the convex pattern  2 , which is referred to as the printing result. Here, the printing result is formed in shape of frame.  
         [0018]     The anilox roll  16  is in contact with the doctor roll  15  as well as the convex pattern  2 . The doctor roll  15  uniformly coats the printing material  17  supplied from the dispenser  18  onto the outer surface of the anilox roll  16 . Accordingly, the doctor roll  15  is in contact with the anilox roll  16  within a range between a portion of supplying the printing material  17  and a portion being in contact with the convex pattern  2 . Instead of the doctor roll  15 , a plate-shaped doctor blade may be used. Also, instead of the dispenser  18 , another cylindrical roll may be used so as to provide the printing material  17  to the anilox roll  16 .  
         [0019]     Generally, the printing apparatus is used to form letters or figures on packing paper. However, the printing apparatus may be used to form various patterns on thin films. For example, an alignment layer or a sealant may be printed on a glass substrate of an LCD device by printing a polyimide thin film.  
         [0020]     Hereinafter, a method for manufacturing a printing plate according to the related art will be described with reference to the accompanying drawings.  
         [0021]      FIGS. 2A  to  2 E are cross sectional views illustrating a related art method for manufacturing a printing plate.  
         [0022]     As shown in  FIG. 2A , a metal layer  52  for a hard mask is deposited on an insulating substrate  51 , and photoresist  53  is coated on the metal layer  52 . The metal layer  52  is formed of Cr or Mo. Then, the photoresist  53  is selectively patterned by exposure and development to thereby define a pattern area.  
         [0023]     Referring to  FIG. 2B , the metal layer  52  is selectively removed using the patterned photoresist  53  as a mask to thereby form a metal layer pattern  52   a.    
         [0024]     As shown in  FIG. 2C , the photoresist  53  is removed. The photoresist  53  is removed using oxygen gas plasma or various oxidizers to form the metal layer pattern  52   a . When using oxygen gas plasma, oxygen gas plasma is generated by providing oxygen gas under vacuum and high voltage conditions, and the oxygen gas plasma decomposes the photoresist, whereby the photoresist is removed.  
         [0025]     As shown in  FIG. 2D , the exposed insulating substrate  51  is selectively etched using the metal layer pattern  52   a  as a mask to thereby form a trench  54  having a depth of about 20 μm. When etching the insulating substrate  51 , an isotropic etching method using HF-based etchant is used.  
         [0026]     As shown in  FIG. 2E , the metal layer pattern  52   a  is removed, thereby completing the printing plate.  
         [0027]     The completed printing plate is then installed on the printing apparatus shown in  FIG. 1 . Then, after the printing material is coated on the anilox roll, the anilox roll is in contact with the printing plate. Thus, the printing material is printed on the predetermined pattern of the printing plate, and the printing material of the printing plate is printed on the substrate to thereby obtain the printing result of the predetermined pattern.  
         [0028]     However, the related art method for manufacturing the printing plate has the following disadvantages.  
         [0029]     In the method for manufacturing the printing plate according to the related art, the trench having the predetermined depth is formed by the isotropic etching method of etching the insulating substrate using the metal layer pattern as the mask, whereby the etching critical dimension (CD) is large. As a result, it is difficult to manufacture a precise printing plate. That is, if the etching thickness of the insulating substrate is about 5 μm, it is impossible to obtain a line width of 10 μm or less (‘A’ of  FIG. 2D ).  
       SUMMARY OF THE INVENTION  
       [0030]     Accordingly, the invention is directed to a method for manufacturing a printing plate that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0031]     An object of the invention is to provide a method for manufacturing a printing plate to realize a precise and fine pattern by minimizing a variation of etching critical dimension (CD).  
         [0032]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for manufacturing a printing plate includes, in part, forming a hard mask having an opening over an insulating substrate; forming a first trench having a first depth in the insulating substrate using the hard mask; coating a first photoresist over an entire surface of the insulating substrate including the hard mask; patterning the first photoresist by entire exposure and development using the hard mask; forming a second trench having a second depth in the insulating substrate using the hard mask, wherein the second depth is deeper than the first depth; coating a second photoresist over the entire surface of the insulating substrate including the hard mask; patterning the second photoresist by entire exposure and development using the hard mask; forming a third trench having a third depth in the insulating substrate using the hard mask, wherein the third depth is deeper than the second depth; and removing the hard mask.  
         [0033]     The invention in part, pertains to a method for manufacturing a printing plate that includes forming a hard mask having an opening over an insulating substrate; forming a first trench having a first depth in the insulating substrate using the hard mask; forming at least one subsequent trench having a subsequent depth in the insulating substrate using the hard mask, the depth of the subsequent trench being deeper than that of the previous trench, each subsequent trench being formed by: coating a photoresist over an entire surface of the insulating substrate including the hard mask, patterning the photoresist by exposing and developing using the hard mask, forming the subsequent trench in the insulating substrate using the hard mask, wherein the subsequent depth is deeper than the previous depth; and removing the hard mask. In the invention, the photoresist remaining may be removed after forming each subsequent trench. Alternately, all photoresists may be removed together after removing the hard mask.  
         [0034]     It is to be understood that both the foregoing general description and the following detailed description of the invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     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. In the drawings:  
         [0036]      FIG. 1  shows a schematic view illustrating a printing apparatus according to the related art;  
         [0037]      FIGS. 2A  to  2 E show cross sectional views illustrating a method for manufacturing a printing plate according to the related art; and  
         [0038]      FIGS. 3A  to  3 H show cross sectional views illustrating a method for manufacturing a printing plate according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     Additional advantages, objects, 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.  
         [0040]     Reference will now be made in detail to the preferred embodiments of the 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.  
         [0041]      FIGS. 3A  to  3 H show cross sectional views illustrating a method for manufacturing a printing plate according to the invention.  
         [0042]     As shown in  FIG. 3A , a metal layer  62  for a hard mask is deposited on an insulating glass substrate  61 , and a first photoresist  63  is coated over the metal layer  62 . The metal layer  62  may be formed of Cr, Mo or any other suitable material. Then, the first photoresist  63  is selectively patterned by exposure and development to thereby define a pattern area.  
         [0043]      FIG. 3B  shows the metal layer  62  being selectively removed using the patterned first photoresist  63  as a mask, thereby forming a metal layer pattern  62   a . The first photoresist  63  is then removed.  
         [0044]     To form the metal layer pattern  62   a , the first photoresist  63  that was used as the mask is removed using oxygen gas plasma or any other suitable oxidizing technique. When using oxygen gas plasma, oxygen gas plasma is generated by providing oxygen gas under vacuum and high voltage conditions, and the oxygen gas plasma decomposes the photoresist, whereby the photoresist is removed.  
         [0045]     As shown in  FIG. 3C , the exposed insulating substrate  61  is selectively etched using the metal layer pattern  62   a  as a mask, thereby forming a first trench  64  having a first depth of about 2 μm to 6 μm. When etching the insulating substrate  61 , an isotropic etching method using HF-based etchant may be preferably used. However, any other suitable etching technique may be used. On forming the first trench  64  by the isotropic etching method, etched portions extend to lateral sides of the first trench  64 . As the depth of the first trench  64  decreases, it is possible to decrease the etched portions at the lateral sides of the first trench  64 .  
         [0046]     As shown in  FIG. 3D , a second photoresist  65  is coated over the entire surface of the insulating substrate  61  including the first trench  64 . The second photoresist  65  may be formed by a spin coating method, by a spray coating method or by a dip coating method. The spin coating method rotates the wafer at high speed under a vacuum chuck, and is most generally used owing to advantageous characteristics of stability and uniformity.  
         [0047]     Generally, photoresists are categorized into positive type and negative type photoresists.  
         [0048]     A negative type photoresist is typically formed by adding a mixture of hard rubber resin and bis-diazide based compound to a photosensitive organic solvent formed of a bridging material. In negative photoresists, the portion irradiated with light is hardened into a net-like mesh by the bridging material, and a solubility differential is generated between the portions irradiated and not irradiated by light, to thereby form a pattern.  
         [0049]     In positive type photoresists, the portion irradiated with light is dissolved by a developer (typically an alkali-based material), and the portion not irradiated with light is not dissolved, to thereby form the pattern using the solubility difference.  
         [0050]     Generally, the positive type photoresist is formed of a mixture of quinone-diazide based photoresist, alkali-soluble phenol-based resin and organic solvent, wherein the mixture is insoluble. However, the mixture becomes soluble in the alkali etchant by light irradiation. However any appropriate chemical system can be used to form the photoresists.  
         [0051]     In the method for manufacturing the printing plate according to the invention, a positive type photoresist is preferably used.  
         [0052]      FIG. 3E  shows that exposure and development are performed for the second photoresist  65  using the metal layer pattern  62   a  as a mask. Here, if the second photoresist  65  is coated over the entire surface of the insulating substrate  61 , a lower portion of the metal layer pattern  62   a  is partially etched by the isotropic etching process for forming the first trench  64 . In this case, the second photoresist  65  buries the etched lower portion of the metal layer pattern  62   a.    
         [0053]     The development of the second photoresist  65  may be performed by deposition or spraying. If the second photoresist  65  is developed by deposition, it is difficult to control the conditions of temperature, density and variations by time passage. However, in the case of the spraying, it becomes easier to control the above-mentioned conditions.  
         [0054]     If the entire surface of the second photoresist  65  is exposed, the second photoresist  65  positioned under the metal layer pattern  62   a  remains without undergoing exposure, and the remaining second photoresist  66  (that is not under the metal layer pattern  62   a ) is completely removed by the exposure.  
         [0055]     Then, as shown in  FIG. 3F , the insulating substrate  61  is selectively removed using the metal layer pattern  62   a  as a mask, so that a second trench  66  is formed in the first trench  64 . The second trench  66  has a second depth that is deeper than the first depth of the first trench  64 .  
         [0056]     As explained above, when isotropic etching forms the second trench  66 , etched portions extend into lateral sides of the second trench  66 . However, since the depth of the second trench  66  becomes low, it is thus possible to decrease the etched portions in the lateral sides of the second trench  66 . Also, the second photoresist  65  remains in the lateral sides of the first trench  64 , that is, under the metal layer pattern  62   a , so that decreasing the etched portions in the lateral sides of the second trench  66  becomes possible.  
         [0057]     In  FIG. 3G , a third photoresist (not shown) is coated over the entire surface of the insulating substrate  61  including the second trench  66 . Then, exposure and development are performed whereby the third photoresist remains under the metal layer pattern  62   a . The insulating substrate  61  is selectively etched to thereby form a third trench  67  having a third depth which is deeper than the second depth.  
         [0058]     Similar to the first and second trenches, when the third trench  67  is formed by the isotropic etching, etched portions are extended into the lateral sides of the third trench  67 . However, since the depth of the third trench  67  is low, it is possible to decrease the etched portions in the lateral sides of the third trench  67 .  
         [0059]     Also, a positive photoresist may preferably be used as the second photoresist  65  or the third photoresist. However, any suitable photoresist may be used.  
         [0060]     Coating of the photoresist, exposure and development are repeatedly performed to form a complete trench having a desired depth using the metal layer pattern  62   a  and the remaining photoresist as masks.  
         [0061]     As shown in  FIG. 3H , after removing the metal layer pattern  62   a , the entire surface of the insulating substrate  61  is cleaned so as to remove the remaining photoresist and foreign particles generated by etching, thereby completing the printing plate according to the invention.  
         [0062]     In the method for manufacturing the printing plate according to the invention, positive photoresist is repeatedly coated, and then patterned by the exposure and development. Also, the etched depth of the insulating substrate is controlled for each etching process using the metal layer pattern  62   a  and the remaining photoresist as masks so as to form a trench having the desired depth in the insulating substrate  61 .  
         [0063]     When the first, second and third trenches  64 ,  66  and  67  are formed, the first to third photoresists remaining under the metal layer pattern  62   a  may be simultaneously removed by the final cleaning process, or may be respectively removed after each of the trenches is formed.  
         [0064]     The complete printing plate is provided to the printing apparatus shown in  FIG. 1 . Then, after a desired pigment material is coated on the anilox roll, the anilox roll is contacted with the printing plate. Thus, the pigment material is printed on the predetermined pattern of the printing plate, and the pigment material of the printing plate is printed on a substrate, thereby obtaining the printing result of the predetermined pattern.  
         [0065]     In contrast, the related art method for manufacturing the printing plate forms a trench of the desired depth in the insulating substrate by one etching process using the photoresist or hard mask. However, in the method for manufacturing the printing plate according to the invention, the trench of the desired depth is formed in the insulating substrate with the several etching processes using a hard mask, repeated deposition of photoresist, and entire exposure and development.  
         [0066]     In one preferred embodiment of the invention, the three steps are performed so as to form a trench of the desired depth. However, the invention is not limited to the three steps. For example, any number of steps between two and ten steps may preferably be used.  
         [0067]     As described above, the method for manufacturing the printing plate according to the invention has the following advantages.  
         [0068]     A trench of a desired depth is formed in the insulating substrate by several etching processes utilizing the formation of the hard mask, deposition of the photoresist and entire exposure and development. That is, the etched depth of the trench for each etching process is controlled so as to minimize error due to the etching critical dimension, thereby forming a fine and precise pattern of a printing plate.  
         [0069]     It will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the spirit or scope of the inventions. Thus, it is intended that the invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.