Abstract:
The present invention discloses a method of forming an orientation film on a substrate, including: providing the substrate on a stage; positioning a slit coater having a slit nozzle on the substrate; and spraying an orientation material on the substrate through the slit nozzle of the slit coater.

Description:
CROSS REFERENCE 
     This application claims the benefit of Korean Patent Application No.  1999-41242 , filed on Sep. 27, 1999, under 35 U.S.C. § 119, the entirety of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a method of forming an orientation film of a liquid crystal display (LCD) device. 
     2. Description of Related Art 
     A typical LCD device includes lower and upper substrates with a liquid crystal layer interposed therebetween. The lower substrate has a thin film transistor (TFT) as a switching element and a pixel electrode, and the upper substrate has a color filter and a common electrode. The pixel electrode serves to apply a voltage to the liquid crystal layer along with the common electrode, and the color filter serves to implement natural colors. 
     A manufacturing process of the LCD device is explained below. First, the lower substrate is prepared. On the lower substrate, a plurality of thin film transistors and pixel electrodes are arranged in a one-to-one arrangement. To form the orientation film on the lower substrate, the surface of the lower substrate is coated with an organic film such as a polyimide, and the orientation film is rubbed in a direction. It is desirable that the orientation film is formed to keep a uniform thickness of the whole surface over the lower substrate. The rubbing is performed normally by using a cloth. Aligned on the orientation film, the liquid crystal molecules orient themselves uniformly in the direction of the rubbing. By the rubbing treatment of the orientation film, liquid crystals can be driven normally, and uniform display characteristics can be obtained. Then, sealant is applied in a picture-frame-like pattern, either by means of screen-printing or dispensing. Sealant is required in order to make a liquid crystal cell from two substrates. In addition to sealing the liquid crystal, sealant protects the liquid crystal from contamination from external sources such as the penetration of water, and from environmental changes. Next, spacers are sprayed to keep a uniform cell gap between the lower and upper substrates. Important requirements are producing uniform spraying over the entire substrate, controlling the spacer density (number of spacers per unit area), and preventing the formation of lumps. The spraying technique includes a wet method of spraying spacers and a dry method of spraying spacers. The wet method of spraying spacers involves the following steps: diffusing spacers in a low-boiling-point organic solvent, such as freon or alcohol, through the use of ultrasonic waves; spraying the spacer-diffused liquid; and drying the panel in order to evaporate the solvent. In the dry method, spacers are applied electrostatically or diffused by means of an air-jet. When TFT-LCDs are handled, measures should be taken to prevent a static electricity. In addition, freon, alcohol, and other organic solvents are subject to density control. Because of this, the dry or air-jet diffusion method is mainly used. Sequentially, two substrates are assembled with and attached to each other. Alignment of the two substrates depends on alignment error, can be several micrometers. When the two substrates are aligned with each other beyond alignment error, since light leakage may occur, desirable display characteristics cannot be obtained. The next step is a cell-cutting process. The liquid crystal cell manufactured through the foregoing five steps is cut into a unit cell. The liquid crystal cell undergoes the cell-cutting process after a plurality of liquid crystal cells is formed on the large-sized glass substrate. The cell-cutting process includes a scribing process that forms a cutting line on a surface of the substrate with a pen of a diamond having a higher hardness than the glass substrate, and a breaking process that breaks the liquid crystal cell into unit cells. Then, a liquid crystal is injected into the gap between the two substrates. The unit liquid crystal cell generally has an area of hundreds of cm 2  and a gap of several micrometers (μm). A vacuum injecting method, which uses a pressure difference between inside and outside of the cell fills the liquid crystal between the two substrates, for example. 
     At this point, the orientation film is essential to the LCD device. The LCD device displays images by using the dielectric constant anisotropy of liquid crystal molecules and by changing their orientation through the application of a voltage. A critical element of the LCD device is the ability to control the orientation and the pretilt angle of the liquid crystal molecules for a given operating mode. The orientation film is designated to perform these functions. 
       FIG. 1  shows a conventional method of forming the orientation film. As shown in  FIG. 1 , an equipment of coating an orientation film includes a doctor roll  11 , an anilox roll  13 , a printing roll  15 , and a rubber pad  17  attached on the printing roll  15 . The doctor roll  11  is geared with the anilox roll  13 , and the anilox roll  13  is also geared with the printing roll  15  for rotation. The anilox roll  13  has fine grooves  13   a  on its surface. The rubber pad  17  has embossment patterns (⊥) on its one surface. 
     In order to form the orientation film, first, an array substrate  10  is provided on a stage  12 . When the coating equipment is operated, the doctor roll  11  rotates with the anilox roll  13  geared therewith, spraying an orientation material. The sprayed orientation material is deposited into the fine grooves of the anilox roll  13  Subsequently, an orientation material deposited in the grooves of the anilox roll  13  is transferred to the rubber pad  17  of the printing roll  15 , with the anilox roll  13  rotating with the printing roll  15  geared therewith. Thereafter, an orientation material transferred to the rubber pad  17  is coated on the glass substrate  10  in the form of the patterns (⊥) of the rubber pad  17  while the printing roll  15  rotates. The orientation material is coated on rest regions of the substrate other than a sealant region and a pad region. 
     However, the conventional method of forming the orientation film requires preparatory proceedings including attaching the rubber pad to the printing roll and cleaning the rolls. If the cleaning process is not cleanly carried out, owing to contamination, spots may take place on the substrate on which the orientation film is formed, or pinholes may occur during a hardening process, thereby lowering manufacturing yields. Further, since the anilox roll  13  has the fine grooves on its surface, the anilox roll  13  is badly worn if it is used during a certain period, so that a shape of the fine grooves may be transformed. Therefore, after a certain period, the doctor roll  11  and the anilox roll  13  should be replaced. Therefore, during replacement of the doctor roll  11  and the anilox roll  13  subsequent processes cannot be performed. Besides, since the rubber roll  17  is lower in hardness than other components of the coating equipment, the life span of the rubber pad is short and also its emboss patterns should be changed according to the model. Therefore, operation efficiency becomes lowered and a production cost also becomes high. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide a method of forming an orientation film of a liquid crystal display device, which has a high manufacturing yield, a high operation efficiency and a low production cost. 
     In order to achieve the above object, a preferred embodiment of the present invention provides a method of forming an orientation film on a substrate, including providing the substrate on a stage; positioning a slit coater having a slit nozzle and an orientation material, the slit nozzle being at a predetermined distance from the substrate; and spraying the orientation material on the substrate through the slit nozzle of the slit coater. 
     A thickness of the orientation film is about 0.8 μm to about 1.0 μm. The slit coater sprays an orientation material out of the slit nozzle to have a surface tension. 
     The method of forming an orientation film on a substrate further includes providing at least one laser device irradiating a laser beam; and patterning predetermined portions of the orientation film using the laser beam. The laser beam is an eximer laser. 
     By using a method of coating the orientation film on the substrate according to the preferred embodiment of the present invention, defective rates such as a spot of the orientation film and a pinhole are lowered. Further, an operating rate is improved because a continuous production is possible. Since components replaced are small in number, a production cost is low and a manufacturing yield is high. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which: 
         FIG. 1  shows a conventional method of coating an orientation film on a substrate; 
         FIG. 2  shows a method of coating an orientation film on a substrate according to a preferred embodiment of the present invention, 
         FIG. 3A  is a side view illustrating a slit coater according to the preferred embodiment of the present invention; 
         FIG. 3B  is a perspective view illustrating the a slit coater according to the preferred embodiment of the present invention; and 
         FIG. 4  shows a method of forming a pattern of the orientation film according to the preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to a preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings. 
       FIG. 2  is a side view illustrating a method of coating an orientation film according to the preferred embodiment of the present invention. As shown in  FIG. 2 , a slit coater  101  is used as coating equipment. The slit coater  101  is a general coating device that has been usually used to coat a photoresist, a pigment of color filter, an organic insulating layer and the like. As an example of the slit coater  101 , there is a model “CFPR R-119S” available from a Japanese company “TOK (Tokyo Ohka Kogyo)”. As shown in  FIGS. 3A and 3B , the slit coater  101  includes a slit nozzle  103 . The slit coater  101  sprays an orientation material through the slit nozzle  103 . Preferably, an orientation material  105  is sprayed to keep a surface tension. To keep a surface tension of the orientation material, a speed that the orientation material is effused is preferably greater than one that a slit coater  101  moves. Therefore, when the orientation material  103  is coated on a substrate  100 , due to a surface tension, the orientation material is not separated from the substrate  100  and keeps its uniform thickness. 
     To coat the orientation material on the substrate  100 , first the substrate  100  is located on a stage  120  and then is turned upside down. The slit coater  101  is located to be at a predetermined distance from the substrate  100  in the light of a thickness of the orientation film. Thereafter, the slit coater  101  moves along the substrate  100 , spraying the orientation material on the substrate  100 . Preferably, a thickness of the orientation film formed is about 0.8 μm to about 1.0 μm in the light of a surface tension of the orientation material. Preferably, a uniformity error of the orientation film is ±5%. 
       FIG. 4  shows a process of forming a predetermined pattern on the substrate on which the orientation film is formed. The patterning process is one which removes orientation film  104  on regions that the pad portion is formed and that a sealant is printed. As shown in  FIG. 4 , an eximer laser device is usually used to form a predetermined pattern  307  of the orientation film  103  on the substrate. However, as a device to form a pattern of the orientation film, any other high-power laser beam device(s) may be used.  FIG. 4  shows only a beam head  305  of the eximer laser device. The beam head  305  irradiates a laser beam  303  to form the pattern  307  with a predetermined angle. A robot programmed to move along a pattern controls the beam head  305 . A plurality of the beam heads  305  may be used for formation of the patterns  307 . Since the laser beam  303  processes the orientation film on the substrate  100  non-thermally and only the orientation film of a certain pattern can be removed without any damage of portions of the orientation film other than a pattern and the substrate  100 , it is easy to form the pattern  307  of the orientation film compared with the conventional art. Since the laser beam is not affected by the surroundings, a process of forming the pattern of the orientation film is possible in the atmosphere. 
     As described herein before, by using a method of coating the orientation film on the substrate according to the preferred embodiment of the present invention, defects such as a spot of the orientation film and a pinhole are lowered. Further, operation efficiency is improved because a continuous production is possible. Since replaced components are small or few, a production cost is low and a manufacturing yield is high. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.