Abstract:
A method for fabricating a clich{acute over (e,)} including: providing a transparent glass substrate; depositing a metal layer on the substrate; patterning the metal layer and thereby forming a first metal pattern; etching the glass substrate by using the first metal pattern as a mask and thereby forming a first convex pattern; patterning the first metal pattern and thereby forming a second metal pattern; and etching the first convex pattern by using the second metal pattern as a mask and thereby forming a second convex pattern.

Description:
[0001]     This application claims the benefit of Korean Patent Application No. 30768, filed on Apr. 30, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     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 fabricating a cliché used to form a pattern with uniform thickness on the entire surface of a substrate and a method for forming a pattern using the same.  
         [0004]     2. Description of the Related Art  
         [0005]     A display device, especially, a flat panel display such as a liquid crystal display (LCD) device is driven by being provided with an active device such as a thin film transistor at each pixel. The driving method is called as an active matrix driving method. According to the active matrix driving method, the active device is arranged at each pixel arranged as a matrix form to drive a corresponding pixel.  
         [0006]      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 an active device. As illustrated, at each pixel of the TFT LCD device that N×M pixels are arranged horizontally and vertically, provided is 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. 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 at 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.  
         [0007]      FIG. 2  is a view illustrating a 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.  
         [0008]     The source/drain electrode  5  of the TFT is electrically connected to a pixel electrode formed in a pixel, and displays an image by driving liquid crystal as a signal is applied to the pixel electrode through the source/drain electrode  5 .  
         [0009]     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.  
         [0010]     In order to fabricate an active device such as a TFT according to the related art, a pattern, a line, etc. of the active device is formed by a photolithographic process using an exposing device. However, the photolithographic process is composed of a series of processes such as a photoresist deposition, an alignment process, an exposure process, a developing process, a cleaning process, and the like.  
         [0011]     Also, the photolithographic process has to be repeated many times in order to form a pattern of the LCD device thereby lowering productivity.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, the present invention is directed to a method for fabricating a cliché and method for forming a pattern using the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
         [0013]     Therefore, an advantage of the present invention is to provide a printing method for forming a pattern which enhances productivity by forming the pattern with a single process.  
         [0014]     Another advantage of the present invention is to provide a printing method for forming a pattern with a uniform thickness.  
         [0015]     Still another advantage of the present invention is to provide a method for fabricating a cliché with an increased an adhesion force to ink.  
         [0016]     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent form 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 thereof as well as the appended drawings.  
         [0017]     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 fabricating a cliché comprising: providing a transparent glass substrate; depositing a metal layer on the substrate; patterning the metal layer to form a first metal pattern; etching the glass substrate using the first metal pattern as a mask, thereby forming a first convex pattern; patterning the first metal pattern to form a second metal pattern; and etching the first convex pattern using the second metal pattern as a mask, thereby forming a second convex pattern.  
         [0018]     In another aspect of the present invention, there is provided a method for fabricating a cliché comprising: providing a transparent glass substrate; depositing a photoresist on the substrate; forming a first photoresist pattern having a first thickness and a second photoresist pattern having a second thickness, the first and second photoresist patterns alternating with each other; etching the glass substrate using the first photoresist pattern as a mask, thereby forming a first convex pattern; and removing the first photoresist pattern, then etching the first convex pattern using the second photoresist pattern as a mask, thereby forming a second convex pattern.  
         [0019]     In another aspect of the present invention, there is provided A method for forming a pattern comprising: providing a cliché having a plurality of convex patterns and a plurality of convexo concavo patterns on surfaces of the convex patterns; forming an etching object layer on a substrate; applying ink on the etching object layer; attaching the cliché and the substrate to each other so that the surfaces of the convex patterns are in contact with the ink applied onto the etching object layer; and separating the substrate and the cliché from each other, thereby forming an ink pattern that partially remains on the etching object layer.  
         [0020]     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     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.  
         [0022]     In the drawings:  
         [0023]      FIG. 1  is a plane view illustrating a structure of a general LCD device;  
         [0024]      FIG. 2  is a sectional view illustrating a structure of a thin film transistor of the LCD device in  FIG. 1 ;  
         [0025]      FIGS. 3A  to  3 C are views illustrating a method for forming a pattern using a gravure offset printing method;  
         [0026]      FIGS. 4A  to  4 G are views illustrating a method for forming a pattern according to the present invention;  
         [0027]      FIGS. 5A  to  5 G are views illustrating a method for forming a pattern according to another embodiment of the present invention;  
         [0028]      FIGS. 6A  to  6 E are views illustrating a method for fabricating a cliché according to the present invention;  
         [0029]      FIG. 7  is a view illustrating a shape of a second convex pattern of the cliché formed by the processes illustrated in  FIGS. 6A  to  6 E;  
         [0030]      FIG. 8  is a view illustrating another shape of the second convex pattern of the cliché formed by the processes illustrated in  FIGS. 6A  to  6 E;  
         [0031]      FIG. 9  is a view illustrating still another shape of the second convex pattern of the cliché formed by the processes illustrated in  FIGS. 6A  to  6 E; and  
         [0032]      FIGS. 10A  to  10 F are views illustrating a method for fabricating a cliché according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0034]     According to the present invention, a printing method is used to form an active device pattern of a display device such as an LCD device. As the printing method, a gravure offset printing method is used in each field such as for publishing, packaging, cellophane, vinyl, polyethylene, etc. by applying ink on a concave plate and then scratching the redundant ink. For example, a gravure offset printing method is used to fabricate an active device or a circuit pattern for a display device.  
         [0035]     The gravure offset printing method transfers ink onto a substrate using a transfer roller. Furthermore, if a transfer roller corresponding to an area of a desired display device is used, a pattern can be formed on the substrate of the display device with a single transfer even if the display device has a large area.  
         [0036]     The gravure offset printing method can be used to form various kinds of patterns for a display device, for example, TFT patterns, gate lines, data lines, pixel electrodes, and a metal pattern for a capacitor in case of an LCD device.  
         [0037]      FIGS. 3A  to  3 C are views illustrating a gravure offset printing method for forming a pattern according to an embodiment of the present invention. As illustrated in  FIG. 3A , a plurality of grooves  132  are formed at specific positions to form a concave plate or cliché  130 , and then filled with ink  134 . The grooves  132  are formed in the cliché  130  using a general photolithographic process. The grooves are filled with ink  134  by applying the ink  134  on the surface of the cliché  130  and then pushing a blade  138  across the surface of the cliché  130 . As the blade  138  is moved on the cliché  130 , the ink  134  is filled in the groove  132  and at the same time the ink  134  remaining on the surface of the cliché  130  is removed.  
         [0038]     The ink  134  remaining in the grooves  132  of the cliché  130  is then transferred onto a surface of a printing roller  131  as the printing roller is rotated across the surface of the cliché  130  as illustrated in  FIG. 3B . The printing roller  131  has the same width as that of the display panel to be fabricated, and has a circumference that is the same length as that of the panel to be fabricated. Accordingly, the ink  134  of the cliché  130  is transferred onto the surface of the printing roller  131  with a single rotation of the printing roller  131 .  
         [0039]     As illustrated in  FIG. 3C , the printing roller  131  is then rotated across the surface of an etching object layer  140  formed on a substrate  130 ′, thereby transferring the ink  134  onto the etching object layer  140 . The ink  134  is thereafter dried by irradiating ultraviolet rays or by heat to form an ink pattern  133 . The ink pattern  133  is also formed on the entire surface of the substrate  130 ′ with a single rotation of the printing roller  131 . The etching object layer  140  is etched using the ink pattern  133  as a mask to form a desired pattern.  
         [0040]     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 a pattern can be formed on the substrate  130 ′ with a single transfer of the printing roller  131 . Accordingly, a pattern of a display device of a large area can be formed by a single process.  
         [0041]     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.  
         [0042]     In case of forming a pattern of a display device, 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 layer is etched using a general etching process, thereby forming a layer with the desired pattern, for example, an electrode structure, a contact hole, and the like.  
         [0043]     The printing method of the present invention has many advantages. The most representative advantage is that an ink pattern is formed on a display device with a large area with a single process which is simpler than the conventional photolithographic process.  
         [0044]     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.  
         [0045]     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  4 G and  FIGS. 5A  to  5 G.  
         [0046]     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.  
         [0047]     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 ′.  
         [0048]     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 .  
         [0049]     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 .  
         [0050]     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 .  
         [0051]      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, heat is applied or ultraviolet rays are irradiated onto the ink pattern  250   a  to harden the pattern.  
         [0052]     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).  
         [0053]     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.  
         [0054]     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.  
         [0055]     According to the aforementioned embodiment of the present invention, ink is applied onto the substrate where a pattern is to be formed, then a cliché having convex patterns is applied onto the ink with a certain pressure. Accordingly, ink that is in contact with the convex patterns is detached from the substrate, and an ink pattern is formed at the rest region that is not in contact with the convex patterns. Since ink is applied onto the substrate and then the ink in unnecessary regions is removed using a cliché, an ink pattern with a uniform thickness is formed on the entire surface of the substrate.  
         [0056]     According to another embodiment of the present invention, a method for fabricating a cliché capable of intensifying an adhesion force between the cliché and ink by forming a convexo-concavo pattern on the surfaces of the convex patterns is provided. In case of forming a convexo-concavo pattern on the surfaces of the convex patterns, a contact area between the cliché and the substrate is increased. Accordingly, an adhesion force between the cliché and the ink is increased than in the previous case ( FIGS. 4A  to  4 G and  FIGS. 5A  to  5 G), thereby decreasing pattern inferiority.  
         [0057]      FIGS. 6A  to  6 E are sectional views illustrating a method for fabricating a cliché according to the present invention. As illustrated in  FIG. 6A , a transparent substrate  330  is provided, and a metal layer  340  is deposited on the substrate  330 . Then, a photoresist  350  is applied on the metal layer  340 . Then, the photoresist  350  is patterned to form photoresist patterns  350   a  as illustrated in  FIG. 6B . Using the photoresist patterns  350   a  as a mask, the metal layer is etched to form first metal patterns  340   a  that remain on specific regions. Then, the photoresist patterns  350   a  are removed, and the glass substrate  330  is etched using the first metal patterns  340   a  as a mask, thereby forming first convex patterns  330   a  on the surface of the glass substrate  330  as illustrated in  FIG. 6C . The first convex patterns  330   a  are formed by etching the glass substrate  330 , which are formed by using a part of the substrate.  
         [0058]     Then, the first metal patterns  340   a  applied to the surfaces of the first convex patterns  330   a  are patterned, thereby forming second metal patterns  340   b  on the first convex patterns  330   a . The second metal pattern  340   b , for example, has a bar or dot shape, but is not limited to these shapes.  
         [0059]     The first convex patterns  330   a  are etched using the second metal pattern  340   b  as a mask, thereby forming second convex patterns  330   b  on the first convex patterns  330   a  as illustrated in  FIG. 6D . The second convex patterns  330   b  are formed by etching the first convex patterns  330   a , which are formed by using a part of the substrate like the first convex patterns  330   a . Then, the second metal patterns  340   b  that remain on the second convex patterns  330   a  are removed, thereby forming the second convex patterns  330   b  of a convexo-concavo pattern on the surfaces of the first convex patterns  330   a  as illustrated in  FIG. 6E .  
         [0060]      FIG. 7  illustrates a surface of the first convex pattern  330   a  on which the second convex pattern  330   b  is formed. As illustrated, on the surface of the first convex pattern  330   a , the second convex pattern  330   b  is formed. The shape of the second convex pattern  330   b  is determined by the shape of the second metal pattern. If the second metal pattern has a bar shape, then the second convex pattern  330   b  also has a bar shape. Since the shape of the second convex pattern  330   b  is varied according to the shape of the second metal pattern, the second convex pattern  330   b  can have a dot shape  430   a , as illustrated in  FIG. 8  or an embossing shape  530   b  as illustrated in  FIG. 9 . However, the shape of the second convex pattern  330   b  is not limited to the above shapes. The second convex pattern is formed on the surface of the first convex pattern in order to increase a surface area of the first convex pattern, and the second convex pattern can have any shape.  
         [0061]     The second convex patterns  330   b ,  430   b , and  530   b  increase a contact area between the cliché and the ink applied onto the substrate during the processes of  FIGS. 4A  to  4 G and  FIGS. 5A  to  5 G thereby to increase an adhesion force between the cliché and the ink. Accordingly, when using the cliché having the second convex patterns, an adhesion force intensifier can be omitted. However, if the adhesion force intensifier is applied onto the surfaces of the second convex patterns, the adhesion force between the cliché and the ink is increased.  
         [0062]     As aforementioned, in case of forming the first and second convex patterns by using the metal pattern as a mask, mask processes have to be performed two times. That is, a single mask process has to be performed in order to form the first metal pattern for forming the first convex patterns, and a single mask process has to be performed in order to form the second metal pattern for forming the second convex patterns. However, as aforementioned, the mask process (a photolithography process) is composed of complicated processes such as a photoresist deposition, an exposure process, a development process, etc., the increase of the number of the mask processes causes the production cost to be increased and the production efficiency to be lowered.  
         [0063]      FIGS. 10A  to  10 F are views illustrating a method for fabricating a cliché according to another embodiment of the present invention. As illustrated in  FIG. 10A , a transparent glass substrate  630  is provided, and then a photoresist  650  is applied on an entire surface of the substrate  630 . The photoresist  650  is then diffraction-exposed or halftone-exposed, forming a photoresist pattern  650 ′ having a first photoresist pattern  650   a  with a first thickness and a second photoresist pattern  650   b  with a second thickness that alternate with each other as illustrated in  FIG. 10B . The diffraction exposure or halftone exposure is performed using a diffraction or halftone mask wherein an optical transmittance rate is differently set according to position. An exposed degree of the photoresist to light becomes different by an optical transmittance rate, and thereby a thickness of the photoresist pattern becomes different.  
         [0064]     As illustrated in  FIG. 10C , the glass substrate  630  is etched using the photoresist pattern  650 ′ as a mask, thereby forming first convex patterns  630   a . That is, the first convex patterns  630   a  are formed at regions that the photoresist patterns  650 ′ are positioned. The first convex patterns  630   a  are formed by using a part of the glass substrate  630 . As illustrated in  FIG. 10D , the first photoresist patterns  650   a  are removed leaving only the second photoresist patterns  650   b  on the first convex patterns  630   a . In the process that the first photoresist patterns  650   a  are removed, the thickness of the second photoresist patterns  650   b  becomes thin. The first photoresist patterns  650   a  can be removed using an ashing process, and can be formed on the first convex patterns  630   a  with a regular shape or with an irregular shape.  
         [0065]     Then, the second photoresist patterns  650   b  are used as a mask to etch the first convex patterns  630   a , thereby forming the second convex patterns  630   b  on the first convex patterns  630   a . The second convex patterns  630   b  are formed by etching the first convex patterns  630   a , which are formed by using a part of the glass substrate. The shape of the second convex patterns  630   b  is determined by the shape of the second photoresist patterns  650   b , and the second convex patterns  650   b  can have various shapes as illustrated in FIGS.  7  to  9 .  
         [0066]     Finally, the second photoresist patterns  650   b  that remain on the second convex patterns  630   b  are removed, thereby forming the second convex patterns  630   b  of a convexo-concave shape on the first convex patterns  630   a  as illustrated in  FIG. 10F .  
         [0067]     In the method for fabricating a cliché according to the present invention, the first convex patterns and the second convex patterns are formed by a diffraction or halftone exposure to reduce the number of the mask processes by a single time.  
         [0068]     As aforementioned, the present invention provides a method for forming a pattern capable of uniformly forming a thickness of an ink pattern using a cliché having convex patterns. Furthermore, the present invention provides a method for fabricating a cliché capable of enhancing an adhesion force between the cliché and ink, by increasing the contact area between the convex patterns of the cliché and the ink.  
         [0069]     The method for forming a pattern by a printing method according to the present invention can be applied not only to an active device or a circuit of a display device such as an LCD device but also to a method for forming a device on a semiconductor substrater.  
         [0070]     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.