Abstract:
A method for forming a pattern of a liquid crystal display device is provided. The method includes providing a substrate having a layer to be patterned, providing a master substrate having an intaglio portion corresponding to a desired pattern, filling an organic material into the intaglio portion of the master substrate, placing the master substrate in contact with the substrate, hardening the organic material to produce a hardened organic film pattern, transferring the hardened organic film pattern onto a surface of the layer to be patterned by separating the master substrate from the substrate, and etching the layer to be patterned by using the organic film pattern as a mask.

Description:
[0001]     The present application claims the benefit of Korean Patent Application No. 2003-62748 filed Sep. 8, 2003, the entire contents of which are herein fully incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for forming a pattern of a liquid crystal display device, and more particularly, to a method for forming a pattern of a liquid crystal display device using a microtransfer method, a non-photolithography method, and a method for fabricating a thin film transistor array substrate of a liquid crystal display device using the same.  
         [0004]     2. Description of the Related Art  
         [0005]     As the interest in an information display and the demand for a portable information media increase, researches on a light flat panel display (FPD) substituting for a cathode ray tube (CRT) are preponderantly ongoing. Particularly, a liquid crystal display device of such flat panel displays is a device for displaying an image using optical anisotropy of a liquid crystal and is being actively used for a notebook computer or a desktop monitor because of its excellent resolution, color display and image quality.  
         [0006]     A general liquid crystal display device displays an image by controlling the light transmittance of a liquid crystal by using an electric field. To this end, a liquid crystal display device largely includes a color filter substrate, an array substrate and a liquid crystal layer formed between the color filter substrate and the array substrate.  
         [0007]      FIG. 1  is a partial plan view of one pixel region of an array substrate for a liquid crystal display device according to a related art. It is known that the array substrate has a plurality of such pixel regions.  
         [0008]     In  FIG. 1 , the array substrate  10  includes a pixel electrode  18  formed on a pixel region, a gate line  16  and a data line  17  arranged horizontally and vertically on the substrate  10 , and a thin film transistor (TFT)  20  (a switching element) formed at an intersection of the gate line  16  and the data line  17 .  
         [0009]     The thin film transistor  20  includes a gate electrode  21  connected to the gate line  16 , a source electrode  22  connected to the data line  17  and a drain electrode  23  connected to the pixel electrode  18 . The thin film transistor  20  includes a first insulating film (not shown) for insulating the source/drain electrode  22 ,  23  and an active layer  24  forming a conductive channel between the source electrode  22  and the drain electrode  23  by a gate voltage supplied to the gate electrode  21 . In addition, a second insulating film (not shown) having a contact hole  26  is formed on the drain electrode  23 , so that the drain electrode  23  and the pixel electrode  18  are electrically connected through the contact hole  26 .  
         [0010]     Here, the pixel region means an image-displayed region defined by the intersection of the gate line  16  and the data line  17 . The pixel electrode  18  formed on the pixel region is made of a transparent conductive material having excellent light transmittance, such as Indium Tin Oxide (ITO).  
         [0011]     The array substrate constructed as above constitutes a liquid crystal display panel by being attached to the color filter substrate by a sealant, and the attachment of these two substrates is made through an attachment key formed at the array substrate or the color filter substrate.  
         [0012]     Meanwhile, in fabricating a liquid crystal display, a plurality of mask processes (i.e., photolithography process) are needed to fabricate an array substrate including thin film transistors. Therefore, in order to improve productivity, a method for reducing the number of mask processes is required.  
         [0013]     Hereinafter, a process for fabricating a general liquid crystal display device will now be described in detail with reference to  FIGS. 2A  to  2 G.  
         [0014]      FIGS. 2A  to  2 G are flow charts showing a fabrication process of a liquid crystal display device shown in  FIG. 1 , and particularly, a fabrication process of an array substrate including a thin film transistor is shown.  
         [0015]     First, as shown in  FIG. 2A , a gate electrode  21  is formed on a substrate  10  made of a transparent insulating material such as glass. The gate electrode  21  is formed such that gate metal is deposited at the entire surface of the substrate  10 , which then passes through a photolithography process.  
         [0016]     Then, as shown in  FIG. 2B , a first insulating film  15   a  which is a gate insulating film, an amorphous silicon thin film  24   a  and an n+ amorphous silicon thin film  25  are deposited at the entire surface of the substrate on which the gate electrode  21  is formed in turn. The amorphous silicon thin film  24   a  is patterned to be used as an active layer of the thin film transistor, and the n+ amorphous silicon thin film  25  is formed for ohmic-contact between the source/drain electrodes and source/drain regions of the active layer.  
         [0017]     Then, as shown in  FIG. 2C , the first insulating film  15   a , the amorphous silicon thin film  24   a  and the n+ amorphous silicon thin film  25  are patterned through a photolithography process, thereby forming a gate insulating film  15  pattern, an active pattern  24 , and a patterned film  25 .  
         [0018]     Thereafter, as shown in  FIG. 2D , a conductive metal  30  for forming source/drain electrodes is deposited at the entire surface of the substrate  10 .  
         [0019]     Next, as shown in  FIG. 2E , the conductive metal  30  is patterned through a photolithography process, thereby forming a source electrode  22  and a drain electrode  23 . Here, the conductive metal  30  and the n+ amorphous silicon thin film  25  are completely removed except for their portions corresponding to the source/drain electrodes  22 ,  23  patterns.  
         [0020]     Next, as shown in  FIG. 2F , a second insulating film  15   b  is deposited at the entire surface of the substrate  10 , and then a contact hole  26  exposing a part of the drain electrode  23  is formed through a photolithography process.  
         [0021]     Lastly, as shown in  FIG. 2G , a transparent conductive material such as Indium Tin Oxide (ITO) is deposited at the entire surface of the substrate  10  on which the second insulating film  15   b  is formed, and then a pixel electrode  18  connected to the drain electrode  23  through the contact hole  26  is formed through a photolithography process.  
         [0022]     As discussed above, in order to fabricate such a liquid crystal display device, several deposition processes and photolithography processes have to be performed. Particularly, in fabricating an array substrate including a thin film transistor array as described above, a plurality of photolithography processes are required to form a gate electrode, an active pattern, a source/drain electrodes, a contact hole and a pixel electrode.  
         [0023]     The photolithography technology includes a plurality of complex processes, such as the application of photosensitive material, alignment, exposure, development or the like as a series of processes for forming a desired pattern by transcribing a pattern drawn on a mask onto a substrate where a thin film is deposited.  
         [0024]     In the exposure process, a mask is disposed at a proper position, align keys of the mask and the substrate are aligned, and then a light source is radiated. Here, however, because of the limitation of the exposure equipment, it is difficult to make the accurate alignment. Accordingly, there is a limit to forming a fine pattern which requires high precision, and productivity is deteriorated since a plurality of photolithography process need to be repeated.  
         [0025]     In addition, since a mask designed to form a pattern is very expensive, as the number of masks used during the process is increased, the fabrication cost of a liquid crystal display device is increased in proportion to the increased number of masks.  
       SUMMARY OF THE INVENTION  
       [0026]     Accordingly, the present invention is directed to a method for forming a pattern of a liquid crystal display device that substantially obviates one or more the problems due to limitations and disadvantages of the related art.  
         [0027]     An object of the present invention is to provide a method for forming a pattern of a liquid crystal display device capable of forming a pattern through one process by a microtransfer method, which is a non-photolithography method.  
         [0028]     Another object of the present invention is to provide a method for forming a pattern for forming a gate electrode and an active pattern of a thin film transistor by the microtransfer method, and to provide a method for fabricating a TFT array substrate of a liquid crystal display device using this pattern forming method.  
         [0029]     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for forming a pattern of a liquid crystal display device, includes providing a substrate having a layer to be patterned; providing a master substrate having an intaglio portion corresponding to a desired pattern; filling an organic material into the intaglio portion of the master substrate; placing the master substrate in contact with the substrate; hardening the organic material to produce a hardened organic film pattern; transferring the hardened organic film pattern onto a surface of the layer to be patterned by separating the master substrate from the substrate; and etching the layer to be patterned by using the organic film pattern as a mask.  
         [0030]     In another aspect of the present invention, there is provided a method for fabricating a thin film transistor (TFT) array substrate for a liquid crystal display device, comprising providing a first substrate; forming a gate metal on the first substrate; transferring a first organic film pattern onto the gate metal; forming a gate electrode by etching the gate metal by using the first organic film pattern as a mask; depositing a first insulating film, an amorphous silicon thin film and an n+ amorphous silicon thin film on the first substrate on which the gate electrode is formed; forming an active pattern by patterning the n+ amorphous silicon thin film and the amorphous silicon thin film; forming a source electrode and a drain electrode on the active pattern; forming a second insulating film having a contact hole exposing a part of the drain electrode; and forming a pixel electrode electrically connected to the drain electrode through the contact hole.  
         [0031]     In another aspect of the present invention, there is provided a method for fabricating a thin film transistor (TFT) array substrate of liquid crystal display device, comprising providing a first substrate; forming a gate electrode on the first substrate; depositing a first insulating film, an amorphous silicon thin film and an n+ amorphous silicon thin film on the first substrate on which the gate electrode is formed; transferring an organic film pattern onto the first substrate; forming an active pattern by etching the n+ amorphous silicon thin film and the amorphous silicon thin film by using the organic film pattern as a mask; forming a source electrode and a drain electrode on the active pattern; forming a second insulating film having a contact hole exposing a part of the drain electrode; and forming a pixel electrode electrically connected to the drain electrode through the contact hole.  
         [0032]     In another aspect of the present invention, there is provided a method of forming a pattern of a display device, comprising providing a mold layer having a groove filled with a photosensitive material; hardening the photosensitive material; transferring the hardened photosensitive material onto a surface of a layer to be patterned; and patterning the layer to be patterned by using the transferred photosensitive material as a mask.  
         [0033]     It is to be understand that both the foregoing general description and the following detailed description are exemplary and explanation and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]     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.  
         [0035]     In the drawings:  
         [0036]      FIG. 1  is a partial plan view of an array substrate for a liquid crystal display device according to a related art;  
         [0037]      FIGS. 2A  to  2 G are flow charts showing a process for fabricating a liquid crystal display device shown in  FIG. 1 ;  
         [0038]      FIGS. 3A  to  3 M are flow charts showing a process for fabricating a liquid crystal display device by a microtransfer method in accordance with a first embodiment of the present invention; and  
         [0039]      FIGS. 4A  to  4 C are flow charts showing a process for forming an active pattern in accordance with a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0041]     In general, a pattern of a liquid crystal display device is formed by using a photolithography technology. However, as the size of a substrate becomes large and the size of a pattern becomes small, the photolithography method requires expensive equipment, precision and the like, which makes the application thereof difficult and expensive.  
         [0042]     In order to solve such a problem, a non-photolithography technology substituting for the photolithography technology has been proposed. As the non-photolithography technology, there are a microcontact printing (μCP), a replica molding (REM), a microtransfer molding (μTM), a micromolding in capillaries, and a solvent-assisted micromolding.  
         [0043]     Such technologies are methods wherein a desired pattern is transcribed onto a substrate by using an elastic rubber stamp for printing, a mold or the like, and have high resolutions of 30 nm˜1 μm. The stamp or the mold is made of an elastomer, which is an elastic polymer of natural rubber or synthetic rubber. Especially, these technologies are advantageous in that a large pattern can be easily formed at a low cost compared to the related art photolithography method.  
         [0044]     Accordingly, the present invention provides a method for forming a pattern of a liquid crystal display by using a microtransfer method, which is a non-photolithography technology.  
         [0045]     As for the microtransfer method, organic material such as photosensitive material is injected into a pattern formed at a mold, and then the photosensitive film pattern is transferred to a substrate on which a predetermined layer to be patterned is formed, so that a desired pattern can be formed. Here, the transfer of the photosensitive film pattern is made in such a manner that the mold having a pattern filled with the photosensitive material and the substrate contact each other. Then the photosensitive material is hardened by radiating light such as ultraviolet (UV) light thereto and is absorbed onto the substrate.  
         [0046]      FIGS. 3A  to  3 M are flow charts showing a process of fabricating a liquid crystal display device in accordance with a first embodiment of the present invention, and particularly, show a process for fabricating an array substrate including a thin film transistor by a microtransfer method.  
         [0047]     First, as shown in  FIG. 3A , a master substrate  100  having a first mold  150   a  including an intaglio portion at its upper portion is provided. The master substrate  100  may be made of a transparent insulating material such as glass, and the first mold  150   a  has a concave intaglio portion  170  corresponding to a gate electrode pattern.  
         [0048]     In addition, the first mold  170  may be made of an elastic resin such as polydiethylsiloxane (PDMS), polyurethane or polyimide. Especially, the PDMS is a transparent elastomer, an elastic polymer such as natural rubber, synthetic rubber or the like, and a surface of the PDMS has small interfacial free energy and is not chemically activated, easily. In addition, the PDMS can maintain elasticity for a long time, so it is proper to form a high quality pattern.  
         [0049]     Here, the master substrate  100  is for preventing the first mold  150   a  from being bent, and it may be fabricated together with the first mold  150   a  or may be attached to the first mold  150   a  after being fabricated in a process separate from the first mold  150   a.    
         [0050]     Thereafter, as shown in  FIG. 3B , the intaglio portion  170  of the first mold  150   a  is filled with a photosensitive material  140  such as photoresist. Here, as a method for injecting the photosensitive material  140  into the intaglio portion  170 , spin coating, ink-jet printing, knife jetting, etc., can be used.  
         [0051]     Next, as shown in  FIG. 3C , a surface of a substrate  110  on which a layer to be patterned is formed contacts a surface of the first mold  150   a . Here, a gate metal  121   a  for forming a gate electrode pattern has already been deposited on the entire surface of the substrate  110 .  
         [0052]     Thereafter, as shown in  FIG. 3D , light such as ultraviolet light is radiated onto the resultant structure to thereby harden the photosensitive material  140 . Here, the light should be radiated from a lower side of the master substrate  100  since the opaque gate metal  121   a  is deposited on the array substrate which is in contact with an upper portion of the master substrate  100 .  
         [0053]     A light source which can harden the photosensitive material  140  (a photosensitive resin) is enough for the radiated light, and the radiation can be made by a scan method.  
         [0054]     Next, as shown in  FIG. 3E , when the master substrate  100  is detached from the array substrate  110 , the photosensitive film pattern  140   a  having a good adherence property to metal is adhered onto the surface of the gate metal  121   a  of the array substrate  110  so as to be transferred thereto.  
         [0055]     And, as shown in  FIG. 3F , the gate metal  121   a  is etched by using the transferred photosensitive film pattern  140   a  as a mask to thereby form a gate electrode  121  pattern on the substrate  110 .  
         [0056]     Next, as shown in  FIG. 3G , a first insulating film  115   a  which is a gate insulating film, an amorphous silicon thin film  124   a  and an n+ amorphous silicon thin film  125  are deposited at the entire surface of the substrate  110  on which the gate electrode  121  is formed in turn. The amorphous silicon thin film  124   a  is patterned to be used as an active layer of the thin film transistor, and the n+ amorphous silicon thin film  125  is formed for ohmic-contact between the source/drain electrodes and the source/drain regions of the active layer.  
         [0057]     Next, as shown in  FIG. 3H , in order to form an active pattern, the master substrate  100  having a second mold  150   b  and the photosensitive material  140  as in  FIG. 3B , is used. The substrate  110  and the master substrate  100  having the second mold  150   b  contact each other, and then light is radiated from a lower side of the master substrate  100 . Here, the second mold  150   b  has a concave groove corresponding to an active pattern, and the photosensitive material  140  is injected into the groove.  
         [0058]     Again, the photosensitive material  140  injected into the second mold  150   b  is hardened by the radiated light and transferred to the surface of the n+ amorphous silicon thin film  125  of the substrate  110 .  
         [0059]     Next, as shown in  FIG. 31 , the n+ amorphous silicon thin film  125  and the amorphous silicon thin film  124   a  are etched by using the transferred photosensitive film pattern  140  as a mask, thereby forming an active pattern  124  and an ohmic contact layer  125 .  
         [0060]     And, as shown in  FIGS. 3J and 3K , a conductive metal  130  for source/drain electrodes is deposited at the entire surface of the resultant substrate  110 , and then the conductive metal  130  is patterned through a photolithography process, thereby forming a source electrode  122  and a drain electrode  123 .  
         [0061]     The conductive metal  130  and the n+ amorphous silicon thin film  125  are completely removed except for their portions corresponding to the source/drain electrodes  122 ,  123  patterns.  
         [0062]     Next, as shown in  FIG. 3L , a second insulating film  115   b  is deposited at the entire surface of the substrate  110 , and then a contact hole  126  exposing a part of the drain electrode  123  is formed through a photolithography process.  
         [0063]     And, as shown in  FIG. 3M , a transparent conductive material such as Indium Tin Oxide (ITO) is deposited at the entire surface of the substrate  110  on which the second insulating film  115   b  is formed, and then a pixel electrode  118  electrically connected to the drain electrode  123  through the contact hole  126  is formed through a photolithography process.  
         [0064]     As so far described, in the method for forming a pattern by the microtransfer method, a surface of a thin film to be patterned contacts a surface of a mold having an intaglio portion corresponding to the pattern so as to transfer the photosensitive material injected in the intaglio portion to the surface of the thin film, and then the thin film is etched by a general etching process, whereby a desired pattern is formed. Thus, unlike the related art photolithography method, an alignment process, an exposure process and a development process due to a use of a mask are not required. Accordingly, the fabrication cost and process of a liquid crystal display device can be reduced greatly.  
         [0065]     In addition, in the method for forming a pattern in accordance with the present embodiment, a master substrate having a mold can be fabricated, corresponding to a desired size of a display device, and a desired pattern can be formed at a substrate by one transfer, so that a pattern can be simply formed even for a large-sized liquid crystal display device.  
         [0066]     In addition, the method for forming a pattern by the microtransfer method according to the present invention is used to form a gate electrode and an active pattern. However, the method can be used to form a different pattern for a thin film transistor, to form a color filter pattern for a color filter substrate of a liquid crystal display device, or to form a pattern for a display device.  
         [0067]     Meanwhile, in the present embodiment, an intaglio portion of a mold for molding an active pattern is formed in a concave groove shape having a width similar to that of a gate electrode because layers on a gate electrode are stepped at a higher height compared to their other portions.  
         [0068]     However, since the photosensitive material injected into the groove of the mold is in a jell state having a certain fluidity until the photosensitive material is hardened by the light radiation, an intaglio portion having a width enough for stepped portions to completely sink to the photosensitive material, that is, an active pattern, may be formed. An embodiment thereabout will now be described.  
         [0069]      FIGS. 4A  to  4 C are flow charts showing a process for forming an active pattern in accordance with a second embodiment of the present invention.  
         [0070]     First, a gate electrode  221  is formed on a substrate  210  in the same manner as the first embodiment, and then, as shown in  FIG. 4A , a first insulating film  215   a , an amorphous silicon thin film  224   a  and an n+ amorphous silicon thin film  225  are deposited at the entire surface of the resultant substrate  210  in turn.  
         [0071]     Next, as shown in  FIG. 4B , a master substrate  200  including a mold  250  contacts the substrate  210 , and then light is radiated from a lower side of the master substrate  200 . The mold  250  has a concave intaglio portion corresponding to an active pattern, and the groove is filled with a photosensitive material  240 .  
         [0072]     Here, the groove formed at the mold  250  in accordance with the present embodiment has such a width so as to cover stepped portions  270  of layers on the gate electrode  221  of the substrate  210  in order to form an active pattern having a sufficiently wide width compared to the active pattern according to the first embodiment.  
         [0073]     Thereafter, the photosensitive material  240  injected into the mold  250  is hardened by the radiated light and transferred to a surface of the n+ amorphous silicon thin film  225  on the substrate  210 .  
         [0074]     Next, as shown in  FIG. 4C , by using the transcribed photosensitive film pattern  240  as a mask, the n+ amorphous silicon thin film  225  and the amorphous silicon thin film  224   a  are etched, to thereby form the active pattern  224  and the ohmic contact layer  225 .  
         [0075]     Thereafter, the same process described in  FIGS. 3J  to  3 M of the first embodiment is performed.  
         [0076]     Although  FIGS. 3A-4C  show one TFT and pixel region, the present invention encompasses the process of forming an array of TFTs and pixel regions of a liquid crystal display device.  
         [0077]     It will be apparent to those skilled in the art that various modifications and variation can be made in the method for forming pattern of liquid crystal display device and method for fabricating liquid crystal display device of the present inventions without departing from the spirit or scope of the invention. Thus, it is intended that the present cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.