Abstract:
A method for forming a pattern is provided that includes: providing a cliché having a plurality of convex patterns; applying an adhesive force reinforcing agent onto each surface of the convex patterns; forming an etching object layer on a substrate and then applying ink onto an upper portion of the etching object layer; attaching the cliché and the substrate to each other such that the convex patterns onto which the adhesive force reinforcing agent is applied can come in contact with the ink applied onto the etching object layer; and forming ink patterns which selectively remain on the etching object layer by separating the substrate and the cliché from each other.

Description:
This application claims the benefit of Korean Patent Application No. 30772, filed on Apr. 30, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing method for forming a pattern in a liquid crystal display panel, and more particularly, to a method for forming a pattern with uniform thickness on a substrate. 
     2. Description of the Related Art 
     A display device, especially, a flat panel display such as a liquid crystal display (LCD) device is driven by an active device such as a thin film transistor provided at each pixel. The driving method is referred as an active matrix driving method. According to the active matrix driving method, the active device is arranged at each pixel to drive the corresponding pixel. 
       FIG. 1  is a view illustrating an active matrix type LCD device. The LCD device is a TFT LCD device in which a thin film transistor is used as the active device. As illustrated, at each pixel of the TFT LCD device, wherein N×M pixels are arranged horizontally and vertically, a TFT formed at a gate line  4  to which a scan signal is applied from an external driving circuit and a data line  6  to which an image signal is applied is provided. The TFT includes a gate electrode  3  connected to the gate line  4 , a semiconductor layer  8  formed on the gate electrode  3  and activated as a scan signal is applied to the gate electrode  3 , and a source/drain electrode  5  formed on the semiconductor layer  8 . A pixel electrode  10  is formed in a display region of the pixel  1 . The pixel electrode  10  is connected to the source/drain electrode  5  and operates liquid crystal (not illustrated) by receiving an image signal through the source/drain electrode  5  as the semiconductor layer  8  is activated. 
       FIG. 2  is a view illustrating the structure of the TFT arranged at each pixel. As illustrated, the TFT includes a substrate  20  formed of a transparent insulating material such as glass, a gate electrode  3  formed on the substrate  20 , a gate insulating layer  22  formed on the entire surface of the substrate  20 , a semiconductor layer  8  formed on the gate insulating layer  22  and activated as a signal is applied to the gate electrode  3 , a source/drain electrode  5  formed on the semiconductor layer, and a passivation layer  25  formed on the source/drain electrode  5  for protecting the device. 
     The source/drain electrode  5  of the TFT is electrically connected to a pixel electrode formed in the pixel region, and displays an image by driving liquid crystal as a signal is applied to the pixel electrode through the source/drain electrode  5 . 
     In the active matrix type LCD device, each pixel has a size corresponding to several tens of μm. Accordingly, the active device such as the TFT arranged in the pixel has to be formed to have a minute size corresponding to several μm. Moreover, as the consumer&#39;s demand for a display device of a high image quality such as an HDTV is being increased, more pixels have to be arranged on a screen of the same area. Accordingly, an active device pattern arranged in each pixel (including a gate line pattern and a data line pattern) has to be also formed to have a minute size. 
     In order to fabricate an active device such as a TFT according to the related art, a pattern, a line, and the like of the active device are formed using a photolithographic process using an exposing device. However, the photolithographic process includes a series of processes such as a photoresist deposition, an alignment process, an exposure process, a developing process, a cleaning process, and the like. 
     Also, the photolithographic process must be repeated several times to form patterns of the liquid crystal display device, thereby lowering productivity. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a printing method for forming a pattern that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     Therefore, an advantage of the present invention is to provide a printing method for forming a pattern capable of improving productivity by forming patterns using a single process. 
     Another advantage of the present invention is to provide a method for forming a pattern uniform thickness. 
     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 my 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 herein, there is provided A method for forming a pattern in a display device, comprising: providing a cliché having a plurality of convex patterns; applying an adhesive force reinforcing agent onto each surface of the plurality of convex patterns; forming an etching object layer on a substrate and then applying ink onto the etching object layer; attaching the cliché and the substrate to each other such that the convex patterns onto which the adhesive force reinforcing agent is applied contact the ink applied to the etching object layer; and forming ink patterns which selectively remain on the etching object layer by separating the substrate and the cliché from each other. 
     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: 
         FIG. 1  is a plane view illustrating a structure of a typical liquid crystal display device; 
         FIG. 2  is a cross-sectional diagram illustrating a structure of a thin film transistor of the liquid crystal display device illustrated in  FIG. 1 ; 
         FIGS. 3A to 3C  are views illustrating a gravure offset printing method for forming a pattern; 
         FIGS. 4A to 4G  are views illustrating a method for forming a pattern in accordance with an embodiment of the present invention; and 
         FIGS. 5A to 5G  are views illustrating a method for forming a pattern in accordance with the another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     The present invention provides a printing method for forming a pattern for an active device of a display device like a liquid crystal display device. In particular, the present invention provides a gravure offset printing method in which ink is put on a concave plate, redundant ink is removed by scraping, and then printing is performed. 
     In gravure offset printing, since ink is transferred to a substrate using a transfer roller, the pattern can be formed with a single transfer even in display devices having large display areas because the transfer roller used corresponds to the area of the desired display device. Gravure offset printing can be used to form various patterns for the display device such as a gate line and a data line connecting with a TFT, a pixel electrode, a metal pattern for a capacitor as well as the TFT, which constitute a liquid crystal display device. 
       FIGS. 3A to 3C  are views illustrating a printing method for forming ink patterns on a substrate. As illustrated in  FIG. 3A , after grooves  132  are formed at specific positions on a concave plate or a cliché  130 , the grooves  132  are filled ink  134 . The grooves  132  formed on the cliché  130  are formed by a photolithographic method. The ink  134  is filled in the grooves  132  by applying the ink  134  onto the cliché  130  and then pushing a blade  138  across the surface of the cliché  130 . Thus, as the blade  138  is pushed, the ink  134  is filled in the grooves  132  and at the same time the ink  130  remaining at the surface of the cliché  130  is removed. 
     As illustrated in  FIG. 3B , the ink  134  filled in the grooves  132  is transferred onto a surface of a printing roller  131  as the roller is rotated across the surface of the cliché  130 . The printing roller  131  is formed to have the same width as a the desired display panel to be fabricated, and has a circumference equal to a length of the panel. Accordingly, the ink  134  is transferred onto the printing roller  33  in a single pass across the cliché. 
     Thereafter, as illustrated in  FIG. 3C , the ink  134  transferred to the printing roller  131  is transferred onto an etching object layer  140  as the printing roller  131  is rotated across the surface of the etching object layer  140  formed on a substrate  130 ′. The transferred ink  134  is dried by UV-irradiation or heat to form ink patterns  133 . The desired patterns  133  are formed on the etching object layer  140  of the display device in a single rotation of the printing roller  131 . Subsequently, the etching object layer  140  is etched using the ink patterns  133  as a mask to form the desired patterns. 
     In the aforementioned printing method, the cliché  130  and the printing roller  131  are fabricated according to the size of a desired display device, such that the desired pattern can be transferred to the substrate  130 ′ in a single pass of the printing roller  131 . 
     The etching object layer  140  may be a metal layer for forming a gate electrode, a source/drain electrode, a gate line, a data line of a TFT, or a pixel electrode, a semiconductor layer for forming an active layer, or an insulating layer such as SiOx or SiNx. 
     The ink pattern  133  serves as a resist in the conventional photolithographic process. Accordingly, the ink pattern  133  is formed on a metal layer or an insulating layer, and then the metal layer or the insulating layer is etched by a general etching process, thereby forming a metal layer of a desired pattern (for example, an electrode structure) or an insulating layer of a desired pattern (for example, a contact hole, etc.). 
     The above described printing method has many advantages. In particular, the printing method has a typical advantage that ink patterns are formed on a large area display unit with a single process or processes which are very simple in comparison to the photolithographic processes of the related art. 
     As the size of the printing roller increases, the likelihood of a non-uniform pressure being applied to the substrate when the ink pattern is transferred from the surface of the printing roller increases. Accordingly, the ink pattern formed on the substrate may have a non-uniform thickness. 
     To solve the problem, a method for forming a pattern on a substrate without using a printing roller is provided. Accordingly, to this embodiment of the invention ink is applied directly on the substrate and then partially removed using a cliché, such the remaining ink provides the desired pattern, as illustrated in  FIGS. 4A to 4G  and  FIGS. 5A to 5G . 
     According to this embodiment of the invention, a ink  250  is applied to the entire surface of a substrate  240 , as illustrated in  FIG. 4A  and  FIG. 5A . The substrate  240  includes an etching object layer, and the ink  250  is applied onto the etching object layer. 
     A cliché  230  having a plurality of convex patterns  230   a  is formed, for example, from a transparent glass substrate. The cliché may be formed by depositing a metal layer on a glass substrate, and patterning the metal layer to form a metal pattern. Then, the glass substrate is etched using the metal pattern as a mask to form convex patterns as illustrated in  FIG. 4B  and  FIG. 5B . The cliché  230 , having a plurality of convex patterns  230   a  is prepared, and then an adhesion force intensifier  220 , for example, Hexa Methyl Disilazane (HMDS), is applied to the surface of the convex pattern  230   a  using an adhesion force intensifying applicator  220 ′. 
     As illustrated in  FIG. 4C , an ink layer  250  applied onto the substrate  240  is arranged to face the convex patterns  230   a  of the cliché  230 . The substrate  240  is positioned at a lower side and the cliché  230  is positioned at an upper side. Then, the cliché  230  is moved downward and applied with uniform pressure so that the convex patterns  230   a  of the cliché  230  come into contact with the ink layer  250 . 
     As illustrated in  FIG. 5C , it is also possible to position the substrate  240  at an upper side and to position the cliché  230  at a lower side. In this case, the substrate  240  is moved downward to contact the ink layer  250  of the substrate  240  to the convex patterns  230   a  of the cliché  230 . 
     As illustrated in  FIG. 4E , when the cliché  230  is detached from the substrate  240 , or the substrate  240  is detached from the cliché, as illustrated in  FIG. 5E , the ink  250 ′ in the regions that are in contact with the convex patterns  230   a  is attached to the surfaces of the convex patterns  230   a  and therefore removed from the substrate  240 . Accordingly, an ink pattern  250   a  is formed on the substrate  240 , and the ink pattern  250   a  remains at a region that is not in contact with the convex patterns  230   a  of the cliché  230 . The adhesion force intensifier  220  applied to the surfaces of the convex patterns  230   a  enhances the adhesion force between the cliché and the ink such that it is greater than the is adhesion force between the ink and the substrate  240 . As a result, the ink  250 ′ contacting the cliché  230  is easily removed from the substrate  240 . Accordingly, ink in a region that is in contact with the convex patterns  230   a  of the cliché  230  is removed, and the ink pattern  250   a  is formed at a region that is not in contact with the convex patterns  230   a . Accordingly, the convex patterns  230   a  of the cliché  230  have the same shape as the rest region except pattern regions to be formed on the substrate  240 . 
       FIG. 4F  and  FIG. 5F  illustrates the ink pattern  250   a  formed on the substrate  240 . An etching object layer of the substrate is etched by using the ink pattern  250   a  as a mask to form a desired device pattern. Before using the ink pattern  250   a  as a mask, the pattern is harden by applying heat or irradiating with ultraviolet rays. 
     The etching object layer may be a metal layer for forming a gate electrode, a source/drain electrode, a gate line, a data line of a TFT, or a pixel electrode, a semiconductor layer for forming an active layer, or an insulating layer such as SiOx or SiNx. When forming a pattern of a display device, the ink pattern  250   a  serves as a resist in the conventional photolithographic process. Accordingly, the ink pattern  250   a  is formed on a metal layer or an insulating layer, and then the metal layer or the insulating layer is etched by a general etching process using the ink pattern  250   a  as a mask, thereby forming a metal layer of a desired pattern (fore example, an electrode structure) or an insulating layer of a desired pattern (for example, a contact hole). 
     M As illustrated in  FIG. 4G  and  FIG. 5G , the ink  250 ′ and the adhesion force intensifier  220  applied to the surfaces of the convex patterns  230   a  of the cliché  230  can be removed from the cliché with a cleaning device  270 . Cleaning solution injected from the cleaning device  270  removes the ink  250 ′ and the adhesion force intensifier  220  applied to the surfaces of the convex patterns  230   a . For example, the cleaning solution can be acetone, N-Methyle Pyrolidone (NMP) and the like. 
     The cleaning device can be a nozzle type which removes ink by spraying a cleaning solution from a nozzle. In addition, though not illustrated in the drawings, a roller type cleaner may be used. With the roller type cleaning device, a material capable of improving an adhesive force with respect to ink is applied onto the surface of a cleaning roller and the cleaning roller is rotated across the cliché thereby transferring the ink from the cliché to the surface of the cleaning roller. Accordingly, the ink applied onto the cliché can be removed. 
     According to the aforementioned embodiment of the present invention, after ink is applied onto a substrate on which a pattern is formed, the ink in contact with convex patterns is separated from the substrate by contacting a cliché having convex patterns with a surface of the ink with uniform pressure applied thereto, so that ink patterns are formed at regions where they do not contact with the convex patterns. 
     After ink is pre-applied onto a substrate, a cliché having convex patterns comes in contact with the ink to form printing patterns. In such a case, printing equipment can be simplified because a printing roller is not used, processes are simplified compared to the case where the printing roller is used, and accuracy of patterns can be improved. By simplifying printing equipment and printing processes, production efficiency can be improved. 
     As described so far, the present invention provides a method for forming a pattern by a printing method, and more particularly, a method for forming a pattern, capable of forming ink patterns having a uniform thickness by using a cliché having convex patterns. 
     In addition, the method for forming a pattern by a printing method may be used to form a device in a semiconductor substrate as well as an active device or a circuit of a display device such as a liquid crystal display device. 
     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.