Patent Document

The present invention claims the benefit of Korean Patent Application No. P2002-077949 filed in Korea on Dec. 9, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of fabricating a display device, and more particularly, to a method of fabricating a color filter substrate for a liquid crystal display device. 
     2. Discussion of the Related Art 
     With rapid development within the information technology field, display devices have evolved to be able to process and display increasingly large amounts of information. Flat panel display technologies recently have been developed for display devices having small thickness, light weight, and low power consumption. Among these technologies, liquid crystal display (LCD) devices commonly have been used in notebook computers and desktop computer monitors due to their superior image resolution, color image display, and image quality. 
     In general, an LCD device includes an upper substrate, a lower substrate, and a liquid crystal layer disposed between the upper and lower substrates. The LCD device makes use of optical anisotropy of liquid crystal material and produces images by varying light transmittance according to the alignment of liquid crystal molecules by an electric field. 
     The lower substrate, which is commonly referred to as an array substrate, includes thin film transistors and pixel electrodes, and is fabricated using repeated photolithographic processes to pattern thin films. The upper substrate, which is commonly referred to as a color filter substrate, includes a color filter layer for displaying color images. The color filter layer commonly includes sub-color filters of red (R), green (G), and blue (B), and is formed by various methods including, for example, a dyeing method, an electro-deposition method, a pigment dispersion method, and a printing method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility. 
       FIGS. 1A  to  1 D are cross sectional views of a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art. Here, the pigment dispersion method is used. 
     In  FIG. 1A , a black matrix  15  is formed on an insulating substrate  10  by depositing a metal material or coating a resin, and patterning the metal material or the resin through a photolithographic processes. The black matrix 15 blocks light leakage, which is caused by irregular operation of liquid crystal molecules, within regions except for pixel electrodes of an array substrate (not shown). The black matrix  15  also prevents light from being transmitted into a channel of a thin film transistor of the array substrate. 
     In  FIG. 1B , a color resist  17 , which may be one of red, green, and blue resists, for example a red one, is coated onto the substrate  10  including the black matrix thereon by spin coating. A mask  20  having a light transmitting portion and a light blocking portion is disposed over the red resist  17 , and the red resist  17  is exposed to light using the mask  20 . Here, the red resist  17  is shown to have a negative property, i.e., a portion of the red resist  17  that is not exposed to light is removed. 
     In  FIG. 1C , the red resist  17  (in  FIG. 1B ) is developed, and a red color filter pattern  17   a  is formed. Then, the red color filter pattern  17   a  is cured and hardened. 
     In  FIG. 1D , green and blue color filter patterns  17   b  and  17   c  are formed on the black matrix  15  through similar processes, as shown in  FIGS. 1B and 1C . Next, an overcoat layer  23  and a common electrode  25  are subsequently formed on the substrate  10  including the color filter patterns  17   a ,  17   b , and  17   c . The overcoat layer  23  protects the color filter patterns  17   a ,  17   b , and  17   c , and flattens the surface of the substrate  10  having the color filter patterns  17   a ,  17   b , and  17   c . The common electrode  25  is made of a transparent conductive material, such as indium-tin-oxide and indium-zinc-oxide. 
     During the fabrication method of the color filter substrate using the pigment dispersion, since the color filter substrate is fabricated by repeated processes of coating, exposing, developing, and curing of a color resist, the fabrication method is complicated and requires significant amounts of time and numerous pieces of equipment. To solve the above problem, a fabrication method of a color filter substrate using thermal imaging has been proposed, as disclosed for example in U.S. Pat. No. 6,242,140, which is hereby incorporated by reference. 
       FIGS. 2A  to  2 D are cross sectional views of another method of fabricating a color filter substrate using thermal imaging according to the related art. In  FIG. 2A , a black matrix  35  is formed on an insulating substrate  30  by depositing a metal material or coating a resin, and patterning the metal material or the resin by photolithographic processes. 
     In  FIG. 2B , a first color transcription film  40  is disposed over the substrate  30  including the black matrix  35 . The first color transcription film  40  includes a supporting film  40   a , a light-to-heat conversion (LTHC) layer  40   b , and a color filter layer  40   c.    
     In  FIG. 2C , the first color transcription film  40  is adhered to the substrate  30  without bubbles. A laser head  50 , from which a laser beam is generated, is disposed over the first color transcription film  40 . Then, the laser beam is applied to the first color transcription film  40  within a portion where a first color filter pattern will be formed later while the laser head  50  is reciprocated along a straight line. In the first color transcription film  40  exposed to the laser beam, the LTHC layer  40   b  transforms light absorbed from the laser beam into thermal energy and emits the thermal energy. Accordingly, the color filter layer  40   c  is transferred onto the substrate  30  due to the emitted thermal energy. Here, the color filter substrate may be a stripe type where color filter patterns are disposed along a line each having the same color. Thus, a first line is exposed to the laser beam by moving the laser head along a straight line, but second and third lines are skipped. Similarly, a fourth line is exposed to the laser beam. Using these processes, all the lines of the first color filter pattern are exposed, and the first color transcription film  40  is removed. 
     In  FIG. 2D , the first color filter pattern  45   a  is formed between the adjacent black matrixes  35  on the substrate  30 , wherein the first color filter pattern  45   a  may be a red color filter. A second color filter pattern  45   b  and a third color filter pattern  45   c  are formed through the same process, as shown in  FIGS. 2B and 2C , wherein the second and third color filer patterns  45   b  and  45   c  may be green and blue color filters, respectively. The substrate  30  having the color filter patterns  45   a ,  45   b , and  45   c  is placed in a hardening furnace, and the color filter patterns  45   a ,  45   b , and  45   c  are hardened. An overcoat layer  47  is formed on the color filter patterns  45   a ,  45   b , and  45   c  in order to protect the color filter patterns  45   a ,  45   b , and  45   c , and to flatten the surface of the substrate  30  otherwise having steps. Next, a common electrode  49  is formed on the overcoat layer  47  by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide. 
     During the thermal imaging method, manufacturing throughput of the color filter substrate is influenced by an application direction of the laser beam, wherein the laser beam is applied to the transcription film along a direction parallel to a pixel length of the LCD device. For example, in a color filter substrate of a video graphic array (VGA) LCD device, which has a resolution of 640 by 480, the VGA LCD device has sub-pixels of 640 by 3 lines (i.e., 1920 lines). Thus, the laser head  50  must scan 640 times for each color filter pattern, and a total number of scans is 1920. In addition, a size of the pixel depends on the resolution being used (e.g., VGA, SVGA (super video graphic array), XGA (extended graphic array), and so on), thereby making it problematic to have a laser beam fit for each different pixel size. 
     The scanning of the laser head  50  may be accomplished along a direction parallel to a pixel width of the LCD device, thereby reducing the scanning times. This may be referred to as a horizontal laser scan. The manufacturing throughput of the color filter substrate is improved due to reduction of the scanning times. However, in this case, there is a problem that scanning traces may be formed at pixel regions, thereby reducing image quality. 
       FIG. 3  is a plan view of a color filter substrate fabricated by a thermal imaging method using a horizontal laser scan according to the related art. In  FIG. 3 , a substrate  30  includes a black matrix  35  and a color filter pattern  45  thereon, wherein the black matrix  35  has an opening in which the color filter pattern  45  is placed. The color filter pattern  45  is formed by the above-described thermal imaging method using a horizontal laser scan. A laser head  50  having a plurality of laser pixels  52  first scans the substrate  30  along a horizontal direction of the substrate  30  repeatedly turning the laser pixel  52  ON and OFF. After the first scan, the laser head  50  is moved along the vertical direction of the substrate  30  by a width of the first scan, and a second scan is accomplished. Here, a scanning trace  55  is formed along a border between first and second scanning regions, and is situated on the color filter pattern  45 . 
       FIG. 4A  is an enlarged view of a region A in  FIG. 3  according to the related art, and  FIG. 4B  is a cross sectional view along IV—IV of  FIG. 4A  according to the related art. 
     In  FIGS. 4A and 4B , after repeated laser scans, the scanning trace  55  is formed on the color filter pattern  45  because of scanning borders of the first and second scans. When a laser beam is applied to a light-to-heat conversion (LTHC) layer of a transcription film, photo energy from the laser beam applied to the LTHC layer is transformed into thermal energy. Accordingly, a color filter layer is transferred onto the substrate due to the thermal energy, wherein the color filter layer is actually transferred onto a larger area than the region actually exposed to the laser beam. In addition, due to difference in scanning times, spontaneous hardening of the color filter film, and the expansion rate of the color filter layer, the scanning trace  55  may have a certain thickness that protrudes over the surface of the color filter pattern  45 . Thus, the scanning trace  55  on the color filter pattern  45  lowers image quality. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method of fabricating a color filter substrate for a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that improves image quality. 
     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. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of fabricating a color filter substrate for a liquid crystal display device includes forming a black matrix on a substrate, adhering a color transcription film to the substrate, disposing a laser head over the color transcription film, repeatedly scanning a laser beam across a surface of the color transcription film using the laser head, removing the color transcription film so that a color filter pattern remains within color filter pattern regions defined by the black matrix, and polishing a surface of the color filter pattern to planarize a surface of the color filter pattern. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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  1 D are cross sectional views of a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art; 
         FIGS. 2A  to  2 D are cross sectional views of another method of fabricating a color filter substrate using thermal imaging according to the related art; 
         FIG. 3  is a plan view of a color filter substrate fabricated by a thermal imaging method using a horizontal laser scan according to the related art; 
         FIG. 4A  is an enlarged view of a region A in  FIG. 3  according to the related art; 
         FIG. 4B  is a cross sectional view along IV—IV of  FIG. 4A  according to the related art; 
         FIG. 5A  is a plan view of an exemplary laser head according to the present invention; 
         FIG. 5B  is a plan view showing an exemplary laser pixel of the laser head of  FIG. 5A  according to the present invention; 
         FIG. 6  is a cross sectional view of an exemplary color transcription film according to the present invention; and 
         FIGS. 7A  to  7 E are cross sectional views of an exemplary method of fabricating a color filter substrate according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 5A  is a plan view of an exemplary laser head according to the present invention, and  FIG. 5B  is a plan view showing an exemplary laser pixel of the laser head of  FIG. 5A  according to the present invention. In  FIGS. 5A and 5B , a laser head  160  may have about 224 laser pixels  162  arranged along a line, wherein each of the laser pixels  162  may have a length L of about 5 μm to about 20 μm and a width W of about 3 μm to 5 μm. Of course, the laser pixel  162  may have a different size, i.e., larger or smaller, than the laser pixels  162  when the power of each of the laser pixels  162  is considered. For example, an entire size of the laser pixels  162  within the laser head  160  may be about 4480 μm by about 31 m, and a scan width of the laser head  160  may be about 4480 μm. The laser pixels  162  of the laser head  160  may be automatically operated by a computer system such that each of the laser pixels  162  turn ON and OFF according to red, green, and blue color filter patterns. 
       FIG. 6  is a cross sectional view of an exemplary color transcription film according to the present invention. In  FIG. 6 , a color transcription film  110  may include three layers: a supporting film  110   a ; a light-to-heat conversion (LTHC) layer  110   b ; and a color filter layer  110   c . The supporting film  110   a , which may support the LTHC layer  110   b  and the color filter layer  110   c , may include a high molecular substance, such as polyester and polyethylene, having transparent and high transmittance characteristics in order to transmit a laser beam to the LTHC layer  110   b . The LTHC layer  110   b  may be formed on the supporting film  110   a  and may be made of a material that can efficiently convert light into heat energy. Accordingly, the LTHC layer  110   b  may convert light energy from a laser head into heat energy. The LTHC layer  110   b  may include an organic material, such as carbon black and IR (infrared) pigments, or an inorganic material, such as a metal material (i.e., aluminum (Al), metallic oxide, or alloy of the above materials). The color filter layer  110   c , which may be the layer to be transferred, may be formed on the LTHC layer  110   b  and may include one of red, green, and blue colors. 
       FIGS. 7A  to  7 E are cross sectional views of an exemplary method of fabricating a color filter substrate according to the present invention. Here, a color filter substrate of  FIGS. 7A  to  7 E shows pixels along a line having the same color, for example red, and for convenience of explanation, a laser head may be illustrated to be shortened as compared with a region between black matrixes of a substrate. 
     In  FIG. 7A , a black matrix  105  may be formed on an insulating substrate  100  by depositing a metal material, such as chromium (Cr), or coating a resin, such as an epoxy. Then, the metal material or resin may be patterned through photolithographic processes. 
     In  FIG. 7B , a first color transcription film  120 , which may include a supporting film  120   a , a light-to-heat conversion (LTHC) layer  120   b , and a color filter layer  120   c , may be disposed over the substrate  100  including the black matrix  105  with the color filter layer  120   c  facing the substrate  100 . The first color transcription film  120  may be adhered to the substrate  100  without bubbles, and a laser head  160  may be disposed at a distance over the first color transcription film  100 . Then, a laser beam of the laser head  160  may be applied to the first color transcription film  120  in a portion where a first color filter pattern will be formed later as the laser head  160  scans the substrate  130  by reciprocating the laser head  160  along a straight line or moving a stage fixing the substrate  100  thereon along a straight line. In the first color transcription film  120  exposed to the laser beam, the LTHC layer  120   b  may transform light absorbed from the laser beam into thermal energy, thereby emitting thermal energy. Then, the color filter layer  120   c  may be transferred onto the substrate  100  due to the emitted thermal energy. 
     In  FIGS. 7A  to  7 E, the color filter substrate may be a stripe-type, wherein color filter patterns along a line may have the same color. Accordingly, a first line may be exposed to the laser beam by moving the laser head along a straight line. However, second and third lines may be skipped. Similarly, a fourth line may be exposed to the laser beam. In this manner, all the lines of the first color filter pattern may be exposed. After a first scan, one of the substrate  100  and the laser head  160  is transferred, and the second, third, and fourth scans may be sequentially performed. 
     In  FIG. 7C , the first color transcription film  120  (in  FIG. 7B ) may be removed after the whole substrate  100  is scanned. Here, the color filter layer  120   c  corresponding to the LTHC layer  120   b  exposed to the laser beam may be transferred onto the substrate  100 , while the color filter layer  120   c  corresponding to the LTHC layer  120   b  not exposed to the laser beam may be removed together with the color transcription film  120  (in FIG.  7 B). Accordingly, a first color filter pattern  125  may be formed both between the adjacent black matrixes  105  on the substrate  100  and on the black matrixes  105 . In the example shown, the first color filter pattern  125  may be a red color filter. 
     Scanning traces  130  may be formed along borders between the first, second, third, and fourth scans on the color filter pattern  125 . The scanning traces  130  protrude over the color filter pattern  125 . Next, although not shown in the figures, a second color filter pattern and a third color filter pattern may be formed through the same process shown in  FIGS. 7B and 7C . The second and third color filter patterns may be green and blue color filters, respectively. Next, the substrate  100  having the color filter pattern  125  may be placed into a hardening furnace, and the color filter pattern  125  may be hardened under temperatures within a range of about 200 degrees of Celsius to about 300 degrees of Celsius. 
     In  FIG. 7D , the substrate  100  including the hardened color filter pattern  125  may be situated onto a stage (not shown), and the surface of the color filter pattern  125  may be polished by a chemical mechanical polishing (CMP) process using a polisher  150  moved along the surface of the color filter pattern  125  or by moving the stage. Accordingly, the scanning traces  130  may be removed and the surface of the color filter pattern  125  may be flattened (or planarized). In addition, a surface roughness of the color filter pattern  125  may be improved. The polishing process may be accomplished along an entire surface of the color filter pattern  125 , or may be performed within specified portions of the color filter pattern  125 . 
     In  FIG. 7E , a common electrode  140  may be formed on the color filter pattern  125  by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide. Thus, an overcoat layer may be formed between the color filter pattern  125  and the common electrode  140  may be omitted since the color filter pattern  125  has a flat surface due to the polishing process. 
     According to the present invention, since the scanning traces formed along a border between adjacent scans may be removed through a polishing process, such as a CMP process, a liquid crystal display device having high quality images may be provided. In addition, manufacturing costs may be reduced since the overcoat layer may be omitted. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the color filter substrate and method of fabricating a color filter substrate of 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 that they come within the scope of the appended claims and their equivalents.

Technology Category: 4