Abstract:
A method of fabricating a liquid crystal display device is provided. An aluminum alloy layer and a copper metal layer are sequentially formed on a substrate. A photoresist pattern is formed on the copper metal layer and the copper metal layer and the underlying aluminum alloy layer are etched to form a gate line. A gate insulating layer, an amorphous silicon layer and an impurity-doped amorphous silicon layer are deposited and then etched to form a semiconductor layer. An aluminum alloy layer and a copper metal layer are sequentially formed and etched on the structure to form a data line, a source electrode and a drain electrode. A passivation layer is formed and a contact hole and a pad opening are formed in the passivation layer. A transparent conductive thin film is deposited on this structure.

Description:
[0001]     This application claims the benefit of the Korean Patent Application No. P2003-42074 filed in Korea on Jun. 26, 2003, which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method of fabricating a liquid crystal display device and a wiring structure of the LCD, and more particularly, to a method of fabricating a liquid crystal display device and a wiring structure of the LCD in which a gate line and a data line are formed of a low resistance metal.  
         [0004]     2. Description of the Related Art  
         [0005]     Recently, as modern society is rapidly changing to an information-oriented society, display techniques for processing a large amount of information and displaying images are actively advancing. In particular, flat panel liquid crystal displays (LCD) have been gaining in popularity due to advantageous characteristics such as slimness, lightweight, low power consumption requirements and the like. Of these, a thin film transistor liquid crystal display device (TFT-LCD) having superior color reproduction and slimming has been developed.  
         [0006]     Generally, the LCD uses optical anisotropy and polarization of liquid crystal for its operation. Liquid crystal molecules with a thin and long structure have directionality in their configuration. Hence, by applying an electric field to the liquid crystal molecules, it is possible to control the alignment direction of the liquid crystal molecules.  
         [0007]     To this end, by arbitrarily controlling the alignment direction of the liquid crystal molecules, the alignment of the liquid crystal molecules is varied and a polarized light is modulated by the optical anisotropy of the liquid crystal, thereby displaying image information.  
         [0008]     Recently, an active matrix LCD (AM-LCD) in which the aforementioned thin film transistors and pixel electrodes connected to the thin film transistors are arranged in a matrix configuration is gaining popularity due to its high resolution and superior moving picture reproducing capability.  
         [0009]      FIG. 1  is a plane view illustrating a pixel structure of a related art LCD.  
         [0010]     Referring to  FIG. 1 , a plurality of gate lines  10  for applying a driving signal are arranged on a thin film transistor substrate  1  of an LCD. A plurality of data lines  30  are arranged on the thin film transistor substrate and cross the gate lines perpendicularly. A plurality of pixel regions are defined by the gate lines  10  and the data lines  30 .  
         [0011]     In a unit pixel region defined by the pair of gate lines  10  and the pair of data lines  30 , a thin film transistor (TFT) serving as a switching element is arranged.  
         [0012]     The TFT has a structure in which a gate insulating layer, a semiconductor layer  50  consisting of an amorphous silicon (a-Si) layer and an impurity-doped amorphous silicon (n+a-Si) layer, a source electrode  60   a  and a drain electrode  60   b  are formed on a gate electrode  10   a  branched from the gate line  10 .  
         [0013]     The drain electrode  60   b  of the TFT is electrically connected with a pixel electrode  100  through a contact hole  70  within the unit pixel region defined by the gate line  10  and the data line  30 .  
         [0014]     Recently, as the resolution and screen sizes of the LCD have increased, the use of a metal with decreased resistance as the gate line and the data line has become more desirable. To enable use of the resistance metal, methods of fabricating the LCD using such a metal are being developed.  
         [0015]      FIGS. 2A and 2B  are sectional views illustrating a stack structure of a gate electrode in a fabrication method of an LCD according to a related art. Specifically,  FIG. 2A  shows a metal line on a substrate is formed of a single metal layer such as molybdenum (Mo) or chromium (Cr). The metal line formed of Mo or Cr is able to be chemically etched in a simple manner.  
         [0016]     The process of forming the gate line is performed like in the process of forming the gate line of a general LCD. In other words, a metal layer of Mo or Cr is deposited on a cleaned substrate  200 . A photoresist film is coated on the metal layer, and is exposed and developed using a mask, thereby forming a photoresist pattern. The metal film is etched by using the photoresist pattern as an etch mask, thereby forming a gate line and a gate electrode  201  at the same time.  
         [0017]      FIG. 2B  shows a gate line has a double layered structure consisting of an Mo metal layer and an Al alloy layer. Referring to  FIG. 2B , an Al alloy layer  301  is deposited on a substrate  300 , and then an Mo metal layer  301   a  is deposited on the Al alloy layer  301 .  
         [0018]     Since the Al alloy layer  301  has superior adhesion to the substrate and low resistance characteristics compared with the Mo metal layer  301   a,  the double layered structure is superior in resistance characteristic to the single layer structure of Mo or Cr shown in  FIG. 2A .  
         [0019]     The Mo metal layer  301   a  continuously deposited on the Al alloy layer  301  prevents an aluminum oxide (Al 2 O 3 ) layer from being formed on the Al alloy layer  301 , thereby decreasing a contact resistance between gate pad and pixel electrode to be formed later.  
         [0020]     Also, the Mo metal layer  301   a  prevents the Al alloy layer  301  from being damaged while a photolithography process of the semiconductor layer and the metal layer is performed.  
         [0021]      FIGS. 3A and 3B  are sectional views illustrating a fabrication method of an LCD, and structures of source and drain electrodes the array substrate according to a related art. Specifically,  FIG. 3A  shows that a source electrode  205   a  and a drain electrode  205   b  are formed above the gate electrode  201  shown in  FIG. 2A , thereby forming a TFT.  
         [0022]     The fabrication method of the TFT will now be described in more detail.  
         [0023]     A gate insulating layer  202  is formed on the gate electrode  201  formed of a single metal layer and a transparent substrate  200 . Thereafter, a semiconductor layer  203 ,  204  is formed on a resultant structure of the transparent substrate  200  by depositing an amorphous silicon (a-Si) layer  203  and an impurity-doped amorphous silicon (n+a-Si) layer  204 .  
         [0024]     Next, a single metal layer of Mo or Cr is deposited on the semiconductor layer  204  and is then etched, thereby forming a source electrode  205   a  and a drain electrode  205   b.  By the above processes, a thin film transistor having electrodes made of the aforementioned signal metal layer can be formed.  
         [0025]     Unlike in the above,  FIG. 3B  shows that a source electrode and a drain electrode are formed above the gate electrode shown in  FIG. 2B . That is,  FIG. 3B  shows that each of the electrodes of a TFT is formed in a double layered structure consisting of an Mo metal layer and an Al alloy layer.  
         [0026]     The fabrication method of the TFT will now be described in more detail.  
         [0027]     A gate insulating layer  302  and a semiconductor layer  303 ,  304  are sequentially formed on a substrate  300  and a gate electrode  301 ,  301   a  having a double layered structure consisting of an Mo metal layer  301   a  and an Al alloy layer  301 . Next, an Mo metal layer  306 ,  307  and an Al alloy layer are sequentially formed on the semiconductor layer  303 ,  304  and are then etched, thereby forming a source electrode  305   a  and a drain electrode  305   b,  each having a triple layered structure consisting of the Mo metal layer  306 ,  307  and the Al alloy layer.  
         [0028]     In the above method, the Mo metal layer  301   a,    306 ,  307  may replaced by a Cr metal layer.  
         [0029]     The Al alloy is generally used as a material of the gate line, and has a relatively low resistance, thereby enabling a rapid signal transmission.  
         [0030]     The Mo (or Cr) metal layer formed on the source electrode  305   a  and the drain electrode  305   b  prevents an aluminum oxide (Al 2 O 3 ) layer from being formed on the Al alloy layer  307 , thereby decreasing a contact resistance between the source/drain electrode and the pixel electrode connected to a data pad later.  
         [0031]     Also, the Mo (or Cr) metal layer functions as a buffer layer for preventing the Al alloy layer  301  from being damaged while a photolithography process of the semiconductor layer and the metal layer is performed.  
         [0032]     However, since the single Mo or Cr layer, and the double layers of the Mo or Cr layer and the Al alloy layer are have a high resistance, it is difficult to use them in an LCD with a high resolution of greater than UXGA (1600×1200) level.  
         [0033]     Thus, if the resistance of the electrodes or signal lines is not sufficiently low, a signal transmission delay and a signal transmission loss may be caused.  
       SUMMARY OF THE INVENTION  
       [0034]     A method of fabricating a liquid crystal display device and a wiring structure of the LCD are presented that employ a low resistance wiring structure and permit high resolution and large-sized screen to be fabricated.  
         [0035]     A liquid crystal display device and fabrication method are presented that can minimize loss of the semiconductor layer by reducing a height difference in a stepped portion of the semiconductor layer.  
         [0036]     As embodied and broadly described herein, there is provided a method of fabricating a liquid crystal display device is provided. The method includes: sequentially forming an aluminum alloy layer and a copper metal layer on a substrate; forming a photoresist pattern on the copper metal layer and etching the copper metal layer and the underlying aluminum alloy layer to form a gate line; depositing and etching a gate insulating layer, an amorphous silicon layer and an impurity-doped amorphous silicon layer to form a semiconductor layer; sequentially forming and etching an aluminum alloy layer and a copper metal layer on a resultant structure of the substrate including the semiconductor layer to form a data line, a source electrode and a drain electrode; forming a passivation layer on a resultant structure of the substrate including the data line, the source electrode and the drain electrode, and forming a contact hole and a pad opening in the passivation layer; and depositing a transparent conductive thin film on a resultant structure of the substrate including the passivation layer having the contact hole and the pad opening.  
         [0037]     According to another aspect of the present invention, there is provided a wiring structure of an LCD including a gate line, a data line, and a thin film transistor, the thin film transistor having a gate electrode, a source electrode and a drain electrode, wherein each of the gate line, the data line, the gate electrode, the source electrode, and the drain electrode is formed in a double layers of an aluminum alloy layer and a copper metal layer.  
         [0038]     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  
       [0039]     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:  
         [0040]      FIG. 1  is a plane view illustrating a pixel structure of a related art LCD;  
         [0041]      FIGS. 2A and 2B  are sectional views illustrating a stack structure of a gate electrode in a fabrication method of an LCD according to a related art;  
         [0042]      FIGS. 3A and 3B  are sectional views illustrating a fabrication method of an LCD, and structures of source and drain electrodes the array substrate according to a related art;  
         [0043]      FIG. 4  is a sectional view illustrating a structure of a gate line in an LCD according to the present invention;  
         [0044]      FIG. 5  is a sectional view illustrating a fabrication method of an LCD and a source/drain structure of the LCD according to the present invention;  
         [0045]      FIGS. 6A through 6C  are sectional views illustrating a fabrication method of an LCD according to the present invention;  
         [0046]      FIG. 7A  is a schematic view illustrating a sectional structure of electrodes of an LCD formed by a continuous deposition;  
         [0047]      FIG. 7B  is a schematic view illustrating a sectional structure of electrodes of an LCD formed by a non-continuous deposition;  
         [0048]      FIG. 8  is a graph illustrating variation in specific resistance when thermally annealing the electrodes fabricated as in  FIGS. 7A and 7B ; and  
         [0049]      FIG. 9  is a graph illustrating variation in specific resistance with respect to the thickness of the electrodes fabricated as in  FIGS. 7A and 7B . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]     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.  
         [0051]      FIG. 4  is a sectional view illustrating a structure of a gate line in an LCD according to an embodiment of the present invention.  
         [0052]     Referring to  FIG. 4 , an inventive LCD includes a gate line having a double layered structure consisting of a copper metal layer  501   a  and an aluminum alloy layer  501 .  
         [0053]     To form the gate line, an aluminum alloy layer  501  is deposited on a transparent substrate  300  and a copper metal layer  501   a  is deposited on the aluminum alloy layer  501  in an identical chamber. Alternatively, the aluminum alloy layer  501  is first deposited, is exposed to air, and then the copper metal layer  501   a  is deposited in a copper film deposition chamber.  
         [0054]     The aluminum alloy layer  501  is formed thinner than the copper metal layer  501   a  because the resistance of the double gate line is dependent on the thickness of the copper metal layer  501   a  and the thickness of the aluminum alloy layer  501 . Detailed description relating to the resistance will be described later with reference to  FIGS. 8 and 9 .  
         [0055]     Thus, since the gate line is formed of the double layered structure of the copper metal layer  501   a  and the aluminum alloy layer  501 , the gate line can be employed to create a high resolution LCD having low resistance line characteristics.  
         [0056]      FIG. 5  is a sectional view illustrating a fabrication method of an LCD and a source/drain structure of the LCD according to an embodiment of the present invention.  
         [0057]     Referring to  FIG. 5 , a gate electrode of a thin film transistor of an LCD has a double layered structure consisting of an aluminum alloy layer  501  and a copper metal layer  501   a.  A gate insulating layer  502  is formed on the gate electrode and a transparent substrate  500 . Thereafter, a semiconductor layer  503 ,  504 , a source electrode  505   a  and a drain electrode  505   b  each including an aluminum alloy layer  506  are formed on a resultant structure of the transparent substrate  500 .  
         [0058]     In the forming of the source and drain electrode layers  505   a  and  505   b  as the double layered structure including the aluminum alloy layer  506 , the aluminum alloy layer  506  and the copper metal layer  505   a,    505   b  are formed by a continuous deposition or a non-continuous deposition. At this time, to allow the double layers to have a low resistance, the source and drain electrode layer  505   a,    505   b  made of copper metal is formed thicker than the aluminum alloy layer  506 .  
         [0059]     The semiconductor layer  503 ,  504  includes an unintentionally doped amorphous silicon (a-Si) layer  503  and an impurity-doped amorphous silicon (n+a-Si), which are formed on the gate insulating layer  502 .  
         [0060]     Next, a fabrication method of an LCD according to the present invention will now be described with reference to  FIGS. 6A through 6C .  FIGS. 6A through 6C  are sectional views illustrating a fabrication method of an LCD according to an embodiment of the present invention.  
         [0061]     First, referring to  FIG. 6A , an aluminum alloy layer  501  is deposited on a transparent substrate  500  and then a copper metal layer  501   a  is deposited on the aluminum alloy layer  501 . At this time, the copper metal layer  501   a  and the aluminum alloy layer  501  can be continuously deposited in an identical chamber. Alternatively, the aluminum alloy layer  501  and the copper metal layer  501   a  can be deposited in a non-continuous deposition method. In other words, the aluminum alloy layer  501  is first deposited, is exposed to air, and then the copper metal layer  501   a  is deposited inside the chamber where the copper metal layer deposition has been deposited.  
         [0062]     The aluminum alloy layer  501  includes an aluminum layer, or an aluminum alloy layer containing a conductive metal element. The conductive metal element can be alloyed with aluminum.  
         [0063]     Next, a photoresist film is coated on an entire surface of a resultant structure of the substrate  500 , and is then patterned by a photolithography process including exposing, developing and etching, thereby forming a gate line  501 ,  501   a.    
         [0064]     Since the double layers of the copper layer  501   a  and the aluminum layer  501  are used as the gate line, an etchant used for patterning the gate line may be different, but other elements except for the etchant are the same as those of the related art fabrication method of the LCD.  
         [0065]     Next, referring to  FIG. 6B , after the gate pattern including the gate line and the gate electrode is formed, a gate insulating layer  502 , an unintentionally doped amorphous silicon (a-Si) layer  503 , an impurity-doped amorphous silicon (n+a-Si) layer  504  are sequentially deposited on a resultant structure of the substrate  500  including the gate pattern, and are patterned to form a semiconductor layer including an unintentionally doped amorphous silicon (a-Si) layer pattern  503  and an impurity-doped amorphous silicon (n+a-Si) layer pattern  504 .  
         [0066]     Next, referring to  FIG. 6C , after the semiconductor layer is formed, double layers consisting of an aluminum layer  506  and a copper metal layer are deposited by a continuous deposition or a non-continuous deposition like in the deposition of the gate pattern.  
         [0067]     The deposited double layers are patterned by a photolithography process including an exposing operation and an etching operation, thereby forming a source electrode  505   a  and a drain electrode  505   b.    
         [0068]     Thereafter, although not shown in the drawings, a passivation layer is formed on a resultant structure of the substrate including the source electrode  505   a  and the drain electrode  505   b,  and contact holes exposing the drain electrode  505   b  and the source electrode  505   a  are formed in the passivation layer. Then, an ITO thin film is deposited on a resultant structure of the substrate including the passivation layer, and is then patterned to form a pixel electrode, thereby completing a thin film transistor of an LCD.  
         [0069]     As described above, since the gate line, the gate electrode, the data line, the source electrode and the data electrode are all formed in double layers of aluminum layer and copper layer, the LCD has an effective low resistance wiring.  
         [0070]     Next, when the double layers of aluminum layer and copper layer are formed in an identical chamber by continuous deposition, and when the double layers of aluminum layer and copper layer are formed by the non-continuous deposition method including depositing the aluminum layer, exposing the deposited aluminum layer to air, and then depositing the copper layer, variation in resistance will now be described.  
         [0071]      FIG. 7A  is a schematic view illustrating a sectional structure of electrodes of an LCD formed by a continuous deposition.  
         [0072]     Referring to  FIG. 7A , an aluminum alloy layer  602  is deposited on a substrate  601  at a thickness of 200 Å. The deposited aluminum alloy layer  602  is exposed to air, and then a copper metal layer  604  is deposited thereon. An aluminum oxide layer  603  having a chemical formula of Al 2 O 3  is formed between the aluminum alloy layer  602  and the copper metal layer  604 .  
         [0073]     The aluminum oxide layer  603  has a thickness of a few Å. The non-continuous deposition method can maintain a low resistance without any variation in the total resistance, but has relatively low production yield due to processes being non-continuous.  
         [0074]      FIG. 7B  is a schematic view illustrating a sectional structure of electrodes of an LCD formed by a non-continuous deposition.  
         [0075]     Unlike in  FIG. 7A ,  FIG. 7B  corresponds to continuously deposition of an aluminum alloy layer  702  and a copper metal layer  704  without an exposure of the aluminum alloy layer  702 . Since the aluminum alloy layer  702  is not exposed to air, the aluminum oxide layer is not formed, but a CuAl layer  703  is formed at a thickness of a few of tens Å due to a chemical reaction between the copper metal layer  704  and the aluminum alloy layer  702 .  
         [0076]     Thus, if the aluminum alloy layer  702  and the copper metal layer  704  are deposited by the non-continuous deposition, resistivity increases due to thermal treatment and accordingly resistance may increase.  
         [0077]     However, if the aluminum alloy layer  702  and the copper metal layer  704  are deposited by the continuous deposition without a stop in the processes, production efficiency increases.  
         [0078]      FIG. 8  is a graph illustrating variation in specific resistance when thermally annealing the electrodes fabricated as in  FIGS. 7A and 7B , and  FIG. 9  is a graph illustrating variation in specific resistance with respect to the thickness of the electrodes fabricated as in  FIGS. 7A and 7B .  
         [0079]     Referring to  FIG. 8 , if the aluminum alloy layer  602  is deposited on a substrate  601 , exposed to air, and then the copper metal layer  604  deposited thereon, as shown in  FIG. 7A , the specific resistance does not vary appreciably and is essentially constant even after thermal annealing is performed. In other words, the low resistance of the copper layer is essentially maintained at a constant value.  
         [0080]     However, if the aluminum alloy layer  702  and the copper metal layer  704  are continuously deposited in the same chamber as shown in  FIG. 7B , specific resistance of the double layered electrode increases and accordingly the double layered electrode fails to maintain a low resistance.  
         [0081]     When considering the above facts, it is noted that the fabrication method presented herein can employ both the continuous deposition and the non-continuous deposition. However, if the lowest resistance is desired for a high resolution LCD, it is more desirable to use the continuous deposition process.  
         [0082]     Referring to  FIG. 9 , the resistance of the double layered electrode increases as the thickness of the aluminum alloy layer increases, or as the thickness of the copper metal layer decreases.  
         [0083]     Accordingly, when forming the wiring structure with a double layered electrode consisting of the aluminum alloy layer and the copper metal layer, the copper metal layer is made thick and the aluminum alloy layer is made thin.  
         [0084]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. 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.