Abstract:
A method of dividing the exposure region for a liquid crystal display panel. This method is characterized in that the exposure region is divided into a first shot, a second shot, a third shot, and a fourth shot, wherein each of the shots is adjacent to any other two shots, and the overlap region of the first to fourth shots is designed by two-dimensional gradation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the manufacture of a liquid crystal display panel (LCD panel), more particularly, to a method of dividing the exposure region into four shots for the pixels of the liquid crystal display panel. The method is capable of eliminating shot Mura by using two-dimensional gradation at the center overlap region of the four shots.  
           [0003]    2. Description of the Related Art  
           [0004]    An active matrix type liquid crystal display panel comprises an array substrate, an opposite substrate, and a liquid crystal material. A pixel electrode array is formed on the array substrate. An opposite electrode is formed on the opposite substrate. The liquid crystal material is disposed between the array substrate and the opposite substrate. The TFTs and the pixel electrodes connected thereto are formed on the array substrate in a matrix shape. These electrodes and TFTs are conventionally fabricated by photolithography followed by etching.  
           [0005]    As the display areas of the liquid crystal display panel increase, needs of patterning technologies for fabricating the electrode and TFTs become stronger. When the panel area is larger than that of the photo mask, so-called division exposure (stepper) is employed. That is to say, one display area is divided into a plurality of shots followed by exposure using the stepper. Traditionally, a 14-inch liquid crystal display panel is divided into six shots.  
           [0006]    When the same image signal is input to pixels in different exposure areas, the luminances thereof may be different from each other. In particular, when the difference in luminances in adjacent exposure areas is large, the boundary line of each exposure area is viewed as a seam, namely shot Mura. That is to say, the difference in luminances is easily observable.  
           [0007]    U.S. Pat. No. 5,784,135 to Inada, et al. discloses a display device in which display regions have non-linear boundaries, solving the luminance defect viewed as a “seam”. In the display device, so-called one-dimensional gradation cut is utilized. The liquid crystal display device has a screen for equally displaying an image. According to the method of the prior art, the non-linear boundary line is formed so that pixels in different exposure areas are mixed in a boundary area thereof so as to equalize the apparent difference in luminances of pixels in the vicinity of the boundary line.  
           [0008]    However, luminance defects are still perceived in the overlap region of four shots using the method of one-dimensional gradation.  
           [0009]    Therefore, improved methods of dividing the exposure region for a liquid crystal display panel are needed.  
         SUMMARY OF THE INVENTION  
         [0010]    In view of the above disadvantages, an object of the invention is to provide a method of dividing the exposure region for a liquid crystal display panel. According to the method, the difference in luminances in adjacent exposure areas, especially in the overlap region of four shots, is minor and not obvious. As a result, when the same image signal is input to pixels in different exposure areas, the image viewed is the same.  
           [0011]    In accordance with one aspect of the invention, there is provided a method of dividing the exposure region of a liquid crystal display panel, characterized in that the exposure region is divided into a first shot, a second shot, a third shot, and a fourth shot, wherein each of the shots is adjacent to any other two shots, and the overlap region of the first to fourth shots are designed by two-dimensional gradation.  
           [0012]    In accordance with another aspect of the invention, the overlap width of each adjacent shot is about 2 to 20 mm.  
           [0013]    In accordance with a further aspect of the invention, the pixels in the overlap region are randomly exposed by any one of the first to fourth shots. Preferably, the exposed density distribution of the pixels in the overlap region is gradually reduced toward to the diagonal shot.  
           [0014]    In accordance with yet another aspect of the invention, any two of the adjacent shots are designed by one-dimensional gradation.  
           [0015]    In accordance with a still further aspect of the invention, the overlap region of the first to fourth shots can be cross-shaped.  
           [0016]    In accordance with a still further aspect of the invention, the liquid crystal display panel is preferably an active matrix liquid crystal display panel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The preferred embodiment of the invention is hereinafter described with reference to the accompanying drawings in which:  
         [0018]    [0018]FIG. 1 is a diagram showing a liquid crystal display panel having six shots and their overlap regions according to the embodiment of the invention.  
         [0019]    [0019]FIG. 2 is an enlarged diagram of Z portion of FIG. 1 showing the concepts for dividing the exposure region near a part of overlap region according to the embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 and FIG. 2 show a liquid crystal display panel having six shots and their overlap regions according to the embodiment of the invention.  
         [0021]    Electrodes and semiconductor devices are formed on the array substrate for the active matrix type liquid crystal display device. These electrodes and semiconductor devices such as TFTs are conventionally fabricated by thin film pattern forming technologies, namely deposition, photolithography, and etching.  
         [0022]    In a conventional thin film pattern forming process, a thin film material is formed on a substrate by a particular film forming method such as sputtering or chemical vapor deposition (CVD). The thin film is patterned in a desired shape by photolithography and etching. In other words, a photoresist layer is coated on the thin film formed on the substrate. Afterward, a photomask is aligned on the upper surface of the substrate. Rays of light are exposed to the substrate through the photomask. Thereafter, the exposed photoresist is developed. With a mask of the developed photoresist, the undesired portion of the thin film formed on the substrate is etched out and a desired pattern is obtained. By repeating these processes a number of times corresponding to the number of layers of thin films that construct the electrodes and semiconductor devices, the desired device can be fabricated.  
         [0023]    As shown in FIG. 1, the liquid crystal display panel  100  is divided into six shots S 1 , S 2 , S 3 , S 4 , S 5 , and S 6 . Overlap region OL between each adjacent shot has a width of about 2 to 20 nanometers. Z portion is the overlap region among the shots S 1 , S 2 , S 3 , and S 4 .  
         [0024]    [0024]FIG. 2 is an enlarged diagram of Z portion of FIG. 1 showing the concepts for dividing the exposure region near a part of overlap region. Z portion of the panel  100  includes a plurality of small squares having numerals of  1 ,  2 ,  3 , and  4 . The small squares with numeral  1  denote the region of shot S 1  adjacent to shots S 2  and S 4 . The small squares with numeral  2  denote the region of shot S 2  adjacent to shots S 1  and S 3 . The small squares with numeral  1  denote the region of shot S 3  adjacent to shots S 2  and S 4 . The small squares with numeral  4  denote the region of shot S 4  adjacent to S 1  and S 3 . Also, each square comprises R, G, and B pixels.  
         [0025]    When the first exposure for shot S 1  is conducted, the small squares with numerals  2 ,  3 , and  4  are shielded and masked. When the second exposure for shot S 2  is conducted, the small squares with numerals  1 ,  3 , and  4  are shielded and masked. When the third exposure for shot S 3  is conducted, the small squares with numerals  1 ,  2 , and  4  are shielded and masked. When the fourth exposure for shot S 4  is conducted, the small squares with numerals  1 ,  2 , and  3  are shielded and masked.  
         [0026]    The exposure density of one of the shots S 1 , S 2 , S 3 , and S 4  is gradually reduced toward the shot positioned in its diagonal line. For example, the exposure density of shot S 1  is gradually reduced toward shot S 3  which is not adjacent to shot S 1 .  
         [0027]    As shown in Y portion, in the shape of a cross, of FIG. 1, the pixels in the Y portion are made of shots S 1  to S 4 . Namely, the pixels in the Y portion are fabricated by one of the shots S 1  to S 4 , so that the difference in luminances in adjacent exposure areas is minor and not obvious. As a result, when the same image signal is input to pixels in different exposure areas, the image viewed is the same.  
         [0028]    While the invention has been described with reference to various illustrative embodiments, the description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as may fall within the scope of the invention defined by the following claims and their equivalents.