Patent Publication Number: US-7713799-B2

Title: Method of forming pattern having step difference and method of making thin film transistor and liquid crystal display using the same

Description:
RELATED APPLICATIONS 
   The present patent document is a divisional of U.S. application Ser. No. 11/207,668, filed Aug. 18, 2005, U.S. Pat. No, 7,494,695, which claims the benefit of Korean Application No. P2004-107723, filed on Dec. 17, 2004, which is hereby incorporated by reference as if fully set forth herein. 

   TECHNICAL FIELD 
   The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method of forming a pattern of an LCD device. 
   BACKGROUND 
   An ultra thin flat panel display device has a display screen with a thickness of several centimeters. Especially, a liquid crystal display (LCD) device among the flat panel display device is widely used for monitors of notebook computers, spacecrafts, and aircrafts, owing to features and advantages of low driving voltage, low power consumption, and portable size. 
   The LCD device includes a lower substrate, an upper substrate, and a liquid crystal layer formed between the substrates. Generally, a thin film transistor and a pixel electrode are formed on the lower substrate, and a light-shielding layer, a color filter layer and a common electrode are formed on the upper substrate. 
   As mentioned above, the LCD device includes various elements, and a number of processes are repeatedly required to form the elements. Therefore, to improve productivity under the mass production system, various efforts are required in the process of forming the elements constituting the LCD device. Examples of efforts include reducing the process time, improving process devices to reduce the manufacturing cost, and developing a new process. Therefore, various improvements have been suggested. 
   As an example of such improvements, there is an improvement in the process of making a thin film transistor formed on a lower substrate of an LCD device. Hereinafter, the process of making a thin film transistor will be described in more detail with reference to the accompanying drawings. 
     FIG. 1  is a sectional view illustrating a thin film transistor formed on a lower substrate for a general LCD device. 
   As shown in  FIG. 1 , a gate electrode  12  is formed on a substrate  10 , and a gate insulating film  14  is formed on a gate electrode. A semiconductor layer  16  is formed on the gate insulating film  14 , and a source electrode  18   a  and a drain electrode  18   b  are formed separated from each other on the semiconductor layer  16 . 
   To form such a thin film transistor in the related art, a mask for patterning the gate electrode  12 , a mask for patterning the semiconductor layer  16 , and a mask for patterning the source and drain electrodes  18   a  and  18   b  were required. In other words, in the related art, three masks were required to form the thin film transistor, and three pattern formation processes were required because the elements were separately patterned. 
   In this respect, studies for reducing the number of pattern formation processes have been performed. As a result, a method for patterning the semiconductor layer  16  and the source and drain electrodes  18   a  and  18   b  using one mask through diffraction exposure has been recently developed. 
     FIG. 2A  to  FIG. 2D  are sectional views illustrating a process of forming a thin film transistor to reduce the number of masks and pattern formation processes. 
   As shown in  FIG. 2A , a gate electrode  12  is formed on a substrate  10 , and a gate insulating film  14 , a semiconductor layer  16  and a metal layer  18  for source and drain electrodes are sequentially formed on the gate electrode  12 . 
   Afterwards, as shown in  FIG. 2B , a mask pattern  20  having a step difference is formed on the metal layer  18  using diffraction exposure. A method of forming the mask pattern  20  having a step difference using the diffraction exposure is shown in  FIG. 3A  to  FIG. 3C . 
   First, as shown in  FIG. 3A , a resist layer  20  to be a mask pattern is formed on the substrate  10 . Then, as shown in  FIG. 3B , a diffraction mask  30  is disposed on the substrate  10  where the resist layer  20  is formed, and then light is irradiated thereon. The diffraction mask  30  includes a light-transmitting region  30   a , a light-shielding region  30   b , and a partially light-transmitting region  30   c . Thereafter, the mask pattern  20  having a step difference is completed by a developing process as shown in  FIG. 3C . During the developing process, the resist layer corresponding to the light-transmitting region is removed, the resist layer corresponding to the light-shielding region remains, and the resist layer corresponding to the partially light-transmitting region is partially removed. Thus, the mask pattern  20  is formed with a step difference. 
   Afterwards, as shown in  FIG. 2C , the semiconductor layer  16  and the metal layer  18  at left and right sides of the mask pattern are removed by an etching process. 
   Subsequently, as shown in  FIG. 2D , the metal layer  18  at a middle portion of the mask pattern is removed to form the source and drain electrodes  18   a  and  18   b . The mask pattern  20  is finally removed to complete the thin film transistor. 
   As described above, the semiconductor layer and the source and drain electrodes are formed by one process using the mask pattern  20  manufactured with a step difference by the diffraction exposure, thereby improving productivity. 
   The above method based on one mask has advantages in that the process steps were simplified and the process time was reduced in comparison with the related art method for forming a semiconductor layer and source and drain electrodes using two masks. However, in the method based on one mask, there exists a problem in that the process time is still long because exposure and developing processes are required. Moreover, a problem occurs in that the manufacturing cost increases because a diffraction mask of high cost is required. 
   BRIEF SUMMARY 
   Accordingly, the present invention is directed to a method of forming a pattern having a step difference and a method of making a thin film transistor and an LCD device, which substantially obviate one or more problems due to limitations and disadvantages of the related art. 
   Additional advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may 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 invention, as embodied and broadly described herein, a method of forming a pattern having a step difference includes the steps of a) forming a first pattern having a predetermined shape on a first printing roll, b) rotating the first printing roll on a substrate to transfer the first pattern onto the substrate, c) forming a second pattern having a predetermined shape on a second printing roll, and d) rotating the second printing roll on the substrate, to transfer the second pattern onto the substrate. 
   In the present invention, since the pattern having a step difference is formed using the printing rolls, exposure and developing processes are not required unlike the related art diffraction exposure. Therefore, the manufacturing cost is reduced and the manufacturing processes are reduced. 
   In another aspect of the present invention, a method of making a thin film transistor includes the steps of preparing a mask having a step difference using the method of forming a pattern and forming a semiconductor layer, a source electrode and a drain electrode using the mask having a step difference. 
   In other aspect of the present invention, a method of making an LCD device is provided using the method of making a thin film transistor through the mask having a step difference. 
   In yet another aspect, a method of forming a pattern having a step difference includes forming a first pattern having a predetermined shape on a first printing roll and forming a second pattern having a predetermined shape on a second printing roll and sequentially rotating the first printing roll on a substrate to transfer the first pattern onto the substrate and rotating the second printing roll on the substrate, to transfer the second pattern onto the substrate. 
   In still another aspect, a method of making a thin film transistor includes forming a gate electrode on a substrate; forming a gate insulating film on the substrate including the gate electrode; sequentially forming a semiconductor layer and a metal layer on the gate insulating film; sequentially rotating a first printing roll on a the metal layer to transfer a first pattern onto the metal layer and rotating a second printing roll on the first pattern to transfer a second pattern onto the onto the first pattern to form a masking pattern having a step difference on the metal layer; etching the semiconductor layer and the metal layer using the masking pattern as a etch mask; and removing the pattern. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention 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 application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG. 1  is a sectional view illustrating a thin film transistor formed on a lower substrate of a related art LCD device; 
       FIG. 2A  to  FIG. 2D  are sectional views illustrating a related art process of forming a thin film transistor; 
       FIG. 3A  to  FIG. 3C  illustrate a method of forming a mask pattern having a step difference using a related art diffraction exposure; 
       FIG. 4A  to  FIG. 4F  are sectional views illustrating a method of forming a pattern having a step difference according to the first embodiment of the present invention; 
       FIG. 5A  is a perspective view illustrating a printing nozzle according to the present invention; 
       FIG. 5B  is a sectional view taken along line A-A of  FIG. 5A ; 
       FIG. 5C  is a sectional view taken along line B-B of  FIG. 5A ; 
       FIG. 6  is a layout of a method of forming a pattern having a step difference according to the first embodiment of the present invention; 
       FIG. 7A  to  FIG. 7F  are sectional views illustrating a method of forming a pattern having a step difference according to the second embodiment of the present invention; 
       FIG. 8A  to  FIG. 8D  are sectional views illustrating a method of forming a pattern having a step difference according to the third embodiment of the present invention; 
       FIG. 9A  to  FIG. 9D  are sectional views illustrating a method of making a thin film transistor according to the embodiment of the present invention; and 
       FIG. 10A  to  FIG. 10C  are sectional views illustrating a method of making an LCD device according to the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY 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. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   In the first to third embodiments, although one pattern is formed on a substrate, a plurality of patterns may be formed thereon. 
   First Embodiment 
     FIG. 4A  to  FIG. 4F  are sectional views illustrating a method of forming a pattern having a step difference according to the first embodiment of the present invention. 
   As shown in  FIG. 4A , a pattern material  150  is coated on a first printing roll  100  using a first printing device  130 . 
   Afterwards, as shown in  FIG. 4B , the first printing roll  100  is rotated on a first printing plate  170  provided with a projection  170   a  having a predetermined shape. In such case, a pattern material  150   a  is partially transferred onto the projection  170   a  of the first printing plate  170  to form a first pattern  150   b  having a predetermined shape on the first printing roll  100 . 
   Subsequently, as shown in  FIG. 4C , the first printing roll  100  is rotated on a substrate  200  so that the first pattern  150   b  is formed on the substrate  200 . 
   As shown in  FIG. 4D , a pattern material  350  is coated on a second printing roll  300  using a second printing device  330 . 
   As shown in  FIG. 4E , the second printing roll  300  is rotated on a second printing plate  370  where a projection  370   a  having a predetermined shape is formed. In such case, a pattern material  350   a  is partially transferred onto the projection  370   a  of the second printing plate  370  to form a second pattern  350   b  having a predetermined shape on the second printing roll  300 . 
   Thereafter, as shown in  FIG. 4F , the second printing roll  300  is rotated on the substrate  200  where the first pattern  150   b  is formed, so that the second pattern  350   b  is formed on the substrate  200 . 
   As described above, the pattern having a step difference is formed as the first pattern  150   b  and the second pattern  350   b  are formed in combination. A pattern having various shapes can be formed if the first pattern  150   b  and the second pattern  350   b  are formed in proper combination. 
   Meanwhile, to form a pattern having a U-shape in cross-section, the second pattern  350   b  may be formed on the first pattern  150   b  as shown in step ( 1 ) of  FIG. 4F  while the second pattern  350   b  may be formed at a side of the first pattern  150   b  as shown in step ( 2 ) of  FIG. 4F . 
   In step ( 2 ) of  FIG. 4F , the height of the second pattern  350   b  should be higher than that of the first pattern  150   b . In step ( 1 ) of  FIG. 4F , it is noted that the second pattern  350   b  and the first pattern  150   b  may not have the same height as each other and their heights may be modified properly if necessary. The height difference between the first pattern  150   b  and the second pattern  350   b  can be obtained by controlling either the amount of the pattern materials  150  and  350  discharged from the first printing device  130  and the second printing device  330  or rotational speed of the first printing roll  100  and the second printing roll  300 . 
   If the height difference between the first pattern  150   b  and the second pattern  350   b  is obtained by controlling the amount of the pattern materials  150  and  350  discharged from the printing nozzles, a printing nozzle shown in  FIG. 5  is preferably used. 
     FIG. 5A  is a perspective view illustrating a printing device according to the present invention,  FIG. 5B  is a sectional view taken along line A-A of  FIG. 5A , and  FIG. 5C  is a sectional view taken along line B-B of  FIG. 5A . Since the printing device of  FIG. 5  includes a plurality of nozzle portions that can separately control the amount of the pattern materials, it is possible to easily control the amount of the pattern materials coated on the printing roll, thereby easily controlling the thickness of the pattern. Hereinafter, the printing nozzle according to the present invention will be described in more detail with reference to  FIG. 5A  to  FIG. 5C . 
   As shown in  FIG. 5A , the printing device of the present invention includes a main body  210 , a plurality of nozzle units  220  formed below the main body  210 , a supply tube  240  for supplying the pattern materials to the main body  210 , and an exhaust tube  260  draining the pattern materials from the main body  210 . Although two nozzle units  220  are formed in the drawing, they are not limited to such case. 
   Referring to  FIG. 5B  and  FIG. 5C , a plurality of grooves  212  are formed inside the main body  210  to receive the pattern materials therein. 
   The nozzle units  220  are provided with slits  222  connected with the grooves  212 , so that the slits  222  can discharge the pattern materials to be coated on the printing roll. 
   Further, a spacer  214  is formed inside the main body  210 , and the size of each slit  222  is controlled by controlling the width of the spacer  214 . 
   Referring to  FIG. 5A , the supply tube  240  connected with the main body  210  includes a plurality of sub supply tubes  242  and a main supply tube  244 . The sub supply tubes  242  are respectively connected with the grooves  212  to supply the pattern materials to the grooves  212 . The main supply tube  244  connects the sub supply tubes  242  with each other. 
   Furthermore, the main supply tube  244  is provided with a main valve  245  to control a flow rate of the pattern materials supplied to the sub supply tubes  242 . The sub supply tubes  242  are provided with a sub valve  243  to control the flow rate of the pattern materials supplied to the grooves  212 . 
   As described above, after the pattern materials are received in the grooves  212  through the sub supply tubes  242 , they are coated on the printing roll through the slits  222 . At this time, the amount of the pattern materials discharged to the slits  222  is wholly controlled through the main valve  245 . In addition, the amount of the pattern materials discharged to the slits  222  is separately controlled through the sub valve  243 . Therefore, the discharge amount of the pattern materials can freely be controlled. This could easily control the pattern materials coated on the printing roll. 
   Meanwhile, the processes of  FIG. 4A  to  FIG. 4F  are performed more preferably in such a manner that a first pattern formation process (shown in  FIG. 4A  to  FIG. 4C ) and a second pattern formation process (shown in  FIG. 4D  to  FIG. 4F ) alternate for the unit of a predetermined time, than in such a manner that the processes of  FIG. 4A  to  FIG. 4F  are performed in serial order. 
   In other words, as shown in  FIG. 6 , the printing devices, the printing rolls, the printing plates, and the substrate are sequentially disposed on a moving rail. The first printing device  130  and the first printing roll  100  for the first pattern are disposed at the front while the second printing device  330  and the second printing roll  300  for the second pattern are disposed at the rear. The first printing plate  170  is disposed at the front while the second printing plate  370  is disposed at the rear. By doing so, the first pattern formation process and the second pattern formation process can be performed alternately for the unit of a predetermined time. 
   Second Embodiment 
     FIG. 7A  to  FIG. 7F  are sectional views illustrating a method of forming a pattern having a step difference according to the second embodiment of the present invention. 
   First, as shown in  FIG. 7A , the first printing plate  170  provided with a recess having a predetermined shape is prepared, and the pattern material  150  is formed in the recess. 
   Afterwards, as shown in  FIG. 7B , the first printing roll  100  is rotated on the first printing plate  170  so that the pattern material  150  formed in the recess of the first printing plate  170  is transferred onto the first printing roll  100  to form the first pattern  150   b  having a predetermined shape on the first printing roll  100 . 
   Subsequently, as shown in  FIG. 7C , the first printing roll  100  is rotated on the substrate  200  so that the first pattern  150   b  is formed on the substrate  200 . 
   As shown in  FIG. 7D , the second printing plate  370  provided with a recess having a predetermined shape is prepared, and the pattern material  350  is formed in the recess. 
   Then, as shown in  FIG. 7E , the second printing roll  300  is rotated on the second printing plate  370  so that the pattern material  350  formed in the recess is transferred onto the second printing roll  300  to form the second pattern  350   b  having a predetermined shape on the second printing roll  300 . 
   Thereafter, as shown in  FIG. 7F , the second printing roll  300  is rotated on the substrate  200  where the first pattern  150   b  is formed, so that the second pattern  350   b  is formed on the substrate  200 . 
   As described above, the pattern having a step difference is formed as the first pattern and the second pattern are formed in combination. 
   Although the second pattern  350   b  is formed on the first pattern  150   b  in  FIG. 7F  to form a pattern having a U-shape in cross section, the second pattern  350   b  may be formed at a side of the first pattern  150   b  to form a pattern having U-shape in cross-section in the same manner as the first embodiment. 
   Further, the printing nozzle shown in  FIG. 5  is preferably used to control the height difference between the first pattern  150   b  and the second pattern  350   b  in the same manner as the first embodiment. 
   Still further, in the same manner as the first embodiment, the processes of  FIG. 7A  to  FIG. 7F  are performed more preferably in such a manner that a first pattern formation process (shown in  FIG. 7A  to  FIG. 7C ) and a second pattern formation process (shown in  FIG. 7D  to  FIG. 7F ) alternate for the unit of a predetermined time, than in such a manner that the processes of  FIG. 7A  to  FIG. 7F  are performed in serial order. 
   Third Embodiment 
     FIG. 8A  to  FIG. 8D  are sectional views illustrating a method of forming a pattern having a step difference according to the third embodiment of the present invention. 
   First, as shown in  FIG. 8A , the first printing roll  100  provided with a convex structure  120  having a predetermined shape is prepared, and the first printing roll  100  is rotated on the first printing plate  170  coated with the pattern material  150  so that the pattern material is transferred onto the convex structure  120  to form the first pattern  150   b  having a predetermined shape on the first printing roll  100 . 
   Afterwards, as shown in  FIG. 8B , the first printing roll  100  is rotated on the substrate  200  so that the first pattern  150   b  is formed on the substrate  200 . 
   Subsequently, as shown in  FIG. 8C , the second printing roll  300  provided with a convex  320  having a predetermined shape is prepared, and the second printing roll  300  is rotated on the second printing plate  370  so that the pattern material is transferred onto the convex  320  to form the second pattern  350   b  having a predetermined shape on the second printing roll  300 . 
   Thereafter, as shown in  FIG. 8D , the second printing roll  300  is rotated on the substrate  200  where the first pattern  150   b  is formed, so that the second pattern  350   b  is formed on the substrate  200 . 
   As described above, the pattern having a step difference is formed as the first pattern and the second pattern in combination are formed. 
   Although the second pattern  350   b  is formed on the first pattern  150   b  in  FIG. 8D  to form a pattern having a U-shape in cross-section, the second pattern  350   b  may be formed at a side of the first pattern  150   b  to form a pattern having a U-shape in cross-section in the same manner as the first embodiment. 
   Further, the printing nozzle shown in  FIG. 5  is preferably used to control the height difference between the first pattern  150   b  and the second pattern  350   b  in the same manner as the first embodiment. 
   Still further, in the same manner as the first embodiment, the processes of  FIG. 8A  to  FIG. 8D  are performed more preferably in such a manner that a first pattern formation process (shown in  FIG. 8A  and  FIG. 8B ) and a second pattern formation process (shown in  FIG. 8C  and  FIG. 8D ) alternate for the unit of a predetermined time, than in such a manner that the processes of  FIG. 8A  to  FIG. 8D  are performed in serial order. 
   Although the method of forming a pattern having a step difference has been described referring to the three embodiments, it is not limited to the three embodiments. 
   Further, although the first pattern formation process and the second pattern formation process have been performed in accordance with the same embodiment, the first pattern formation process may be performed in accordance with the first embodiment while the second pattern formation process may be performed in accordance with the second embodiment or the third embodiment. In other words, it does not matter whether the first pattern formation process and the second pattern formation process are performed in accordance with any one of the first embodiment to the third embodiment. 
   2. Method of Making a Thin Film Transistor 
     FIG. 9A  to  FIG. 9D  are sectional views illustrating a method of making a thin film transistor according to the embodiment of the present invention. 
   First, as shown in  FIG. 9A , a gate electrode  520  is formed on a substrate  500 , and a gate insulating film  540  is formed on the entire surface of the substrate  500  including the gate electrode  520 . A semiconductor layer  560  and a metal layer  580  for source and drain electrodes are sequentially formed on the gate insulating film  540 . 
   Afterwards, as shown in  FIG. 9B , a pattern  600  having a step difference is formed on the metal layer  580 . 
   The pattern  600  having a step difference is formed in accordance with the aforementioned embodiments. 
   Then, as shown in  FIG. 9C  and  FIG. 9D , the semiconductor layer  560  and the metal layer  580  are etched using the pattern  600  as a mask so that the semiconductor layer  560  and the source and drain electrodes  580   a  and  580   b  are completed. 
   In more detail, as shown in  FIG. 9C , an etching process is performed using the pattern  600  as a mask to remove the semiconductor layer  560  and the metal layer  580  at left and right sides of the mask pattern. Afterwards, as shown in  FIG. 9D , the metal layer  580  at a middle portion of the mask pattern  600  is removed to form the source and drain electrodes  580   a  and  580   b . The mask pattern  600  is finally removed so that the thin film transistor is completed. 
   It will be apparent to those skilled in the art that various modifications can be made in the material of the elements constituting the thin film transistor, such as the gate electrode and the gate insulating film, and the method of forming the elements without departing from the spirit or scope of the inventions. 
   3. Method of Making an LCD Device 
     FIG. 10A  to  FIG. 10C  are sectional views illustrating a method of making an LCD device according to the embodiment of the present invention. 
   As shown in  FIG. 10A , the thin film transistor is formed on the first substrate  500 , the thin film transistor being comprised of the gate electrode  520 , the gate insulating film  540 , the semiconductor substrate  560 , the source electrode  580   a  and the drain electrode  580   b . A passivation layer  590  is formed on the thin film transistor, and a pixel electrode  595  connected with the drain electrode  580   b  is formed on the passivation layer  590 . 
   At this time, the thin film transistor is formed in accordance with the method of  FIG. 9A  to  FIG. 9D . 
   Afterwards, as shown in  FIG. 10B , a light-shielding layer  720 , a color filter layer  740  and a common electrode  760  are sequentially formed on the second substrate  700 . 
   Then, as shown in  FIG. 10C , a liquid crystal layer  800  is formed between the substrates  500  and  700 . 
   In this case, the liquid crystal layer  800  can be formed by a vacuum injection method or a liquid crystal dropping method. In the vacuum injection method, the first substrate  500  and the second substrate  700  are bonded together through a sealant provided with an injection hole and then a liquid crystal layer is formed using a capillary phenomenon at the injection hole and pressure difference between bonded substrates. In the liquid crystal dropping method, a liquid crystal is dropped onto either the first substrate  500  or the second substrate  700  to form a liquid crystal layer and then both substrates are bonded together. 
   If the size of the substrates becomes great, the time required to form the liquid crystal layer  800  using the vacuum injection method becomes long, thereby reducing productivity. In this case, it is preferable that the liquid crystal dropping method is used. 
   Meanwhile, in an in-plane switching (IPS) mode LCD device, the common electrode  760  is formed on the first substrate  500  not the second substrate  700  in parallel with the pixel electrode  595  so that alignment of the liquid crystal layer  800  is controlled by a voltage applied in parallel between the common electrode  760  and the pixel electrode  595 . 
   It will be apparent to those skilled in the art that various modifications can be made in the material of the elements constituting the LCD device, and the method of forming the elements without departing from the spirit or scope of the inventions. 
   As aforementioned, the method of forming the pattern and the method of making the thin film transistor and the LCD device according to the present invention have the following advantages. 
   First, since the pattern having a step difference is formed using the printing rolls, exposure and developing processes are not required unlike the related art diffraction exposure. Therefore, the manufacturing cost is reduced and the manufacturing processes are reduced. 
   Second, since the first pattern formation process and the second pattern formation process alternate for the unit of a predetermined time, the manufacturing processes are reduced. 
   Finally, since the printing roll provided with a plurality of nozzle portions is used, it is possible to easily control the height of the pattern. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.