Patent Publication Number: US-7906781-B2

Title: Liquid crystal display device and fabricating method thereof

Description:
This application is a divisional of 11/907,945, filed Oct. 18, 2007 now U.S. Pat. No. 7,488,612, which is a divisional application of U.S. patent application Ser. No. 11/015,019 filed on Dec. 20, 2004, now U.S. Pat. No. 7,298,431 B1, issued Nov. 20, 2007, which claims the benefit of Korean Patent Application No. 2003-0099291 filed Dec. 29, 2003, all of which are hereby incorporated by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device and its fabricating method, and more particularly, to a liquid crystal display device and its fabricating method that reduces the number of mask processes in forming a thin film transistor. 
     2. Description of the Related Art 
     As demands for the information display device and the portable information display media is growing, research on a light-weight thin film type flat panel display (FPD) is becoming a trend of industry threatening the related art cathode ray tube (CRT) display device. One type of FPDs is a liquid crystal display (LCD), which displays an image using the optical anisotropy of liquid crystal material, is actively employed in notebook computers and a desktop monitors because of its high quality resolution, color display, and picture quality. 
     The LCD includes a color filter substrate (a first substrate), an array substrate (a second substrate), and a liquid crystal layer formed between the color filter substrate and the array substrate. A thin film transistor (TFT) is generally used as a switching device of the LCD and an amorphous silicon thin film or a polycrystalline silicon thin film is used as a channel layer of the TFT. 
     A fabrication process of the LCD generally requires a plurality of masking processes (namely, a photolithography process) for fabrication of the array substrate including the TFT. Accordingly, reducing the number of masking processes is necessary to increase a productivity. 
     The structure of a general LCD will now be described with reference to  FIG. 1 .  FIG. 1  is a plan view showing a portion of the array substrate of the related art LCD. An actual LCD has N×M pixels with N gate lines intersecting M data lines. In  FIG. 1 , only one pixel is shown in the drawing to simplify the explanation. 
     As shown, in  FIG. 1 , the array substrate  10  includes a pixel electrode  18  formed on a pixel region, gate lines  16  and data lines  17  arranged vertically and horizontally on the substrate  10  to define a pixel electrode, and a TFT (the switching device) formed at the intersection of the gate line  16  and the data line  17 . 
     The TFT 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 TFT further includes a first insulation film (not shown) and a second insulation film (not shown) for insulating the gate electrode  21  and the source/drain electrodes  22  and  23 , and an active pattern  24  for forming a conductive channel between the source electrode  22  and the drain electrode  23 . The gate electrode  21  supplies a gate voltage at the conductive channel. 
     The source electrode  22  is electrically connected to a source region of the active pattern  24  and the drain electrode  23  is electrically connected to a drain region of the active pattern  24  through a plurality of first contact holes  40 A defined through the first insulation film and the second insulation film. A third insulation film (not shown) having a second contact hole  40 B is formed on the drain electrode  23  so that the drain electrode  23  and the pixel electrode  18  are electrically connected. 
     A process for fabricating the LCD as described above will now be explained with reference to  FIGS. 2A to 2F .  FIGS. 2A to 2F  are sequential cross-sectional views showing a fabrication process of the LCD taken along line I-I of  FIG. 1 . The TFT in the related art uses polycrystalline silicon as a channel layer. With reference to  FIG. 2A , an active pattern  24  made of a polycrystalline silicon thin film is formed on a substrate  10  using photolithography. 
     Next, as shown in  FIG. 2B , a first insulation film  15 A and a conductive metal material are disposed on the entire surface of the substrate  10  already provided with the active pattern  24 . Thereafter, the conductive metal material is selectively patterned using photolithography, thereby forming a gate electrode  21  over the active pattern  24 . The gate electrode  21  is insulated from the active pattern  24  by the gate insulation film  15 A interposed therebetween. 
     Then, a high density impurity ion is injected into a desired portion of the active pattern  24 . The gate electrode  21  is used as a mask to form p+ or n+ source/drain regions  24 A and  24 B. The source/drain regions  24 A and  24 B make an ohmic contact with source/drain electrodes. Subsequently, as shown in  FIG. 2C , the second insulation film  15 B is disposed on the entire surface of the substrate  10  already provided with the gate electrode  21 , thereafter, a portion of the first and second insulation films  15 A and  15 B are removed to form a first contact hole  40 A exposing a portion of the source/drain regions  24 A and  24 B. 
     Furthermore, as shown in  FIG. 2D , a conductive metal material is disposed on the entire surface of the substrate  10  and then patterned by using photolithography process to form a source electrode  22  connected to the source region  24 A and a drain electrode  23  connected to the drain region  24 B through plurality of the first contact hole  40 A. In this case, a portion of the conductive metal layer forming the source electrode  22  extends in a first direction to be connected with the data line  17 . 
     As shown in  FIG. 2E , after a third insulation film  15 C is disposed on the entire surface of the substrate  10 , a second contact hole  40 B is formed to expose a portion of the drain electrode  23  by photolithography. Finally, as shown in  FIG. 2F , a transparent conductive metal material is disposed on the entire surface of the substrate  10  already provided with the third insulation film  15 C, and patterned by photolithography, thereby forming the pixel electrode  18  connected with the drain electrode  23  within the second contact hole  40 B. 
     As described above, when fabricating the LCD, including the polycrystalline silicon TFT, a total of six photolithography processes are required to pattern the active pattern, the gate electrode, the first contact hole, the source/drain electrode, the second contact hole and the pixel electrode. The photolithography process is a series of processes to form a desired pattern on a thin film-deposited substrate, consisting of a plurality of processes including coating a photosensitive material, exposing the photosensitive material, and developing the photosensitive material. Accordingly, the plurality of photolithography processes contribute to a reduction in production yield and increase in TFT defects. Since a mask designed to form a pattern is costly, an, increase in the number of masks significantly increases the LCD fabrication cost. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a LCD device and fabricating method thereof that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an LCD device and its fabrication method capable of reducing the number of masks by simultaneously patterning an active pattern and a data line to fabricate a thin film transistor. 
     Another object of the present invention is to form an active pattern and a gate electrode simultaneously in single mask process using a diffraction exposure and ashing technique. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or 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 hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for fabricating a liquid crystal display (LCD) device comprises forming an active pattern and a data line on a substrate, the active pattern including a source region, a drain region, and a channel region; disposing a first insulation film on a portion of the substrate; forming a gate electrode in a portion of the active pattern where the first insulation film is formed; disposing a second insulation film on the substrate; forming a plurality of first contact holes to expose a portion of the source and drain regions and a second contact hole to expose a portion of the data line; forming a source electrode from a transparent conductive material connected to a source region within one of the plurality of first contact holes and a data line within the second contact hole; and forming a pixel electrode and a drain electrode from the transparent conductive material connected to a drain region within the other one of the plurality of first contact holes. 
     In another aspect, a method for fabricating an liquid crystal display (LCD) device comprises disposing a silicon layer on a substrate; disposing a conductive metal layer on the silicon layer; patterning the conductive metal layer and the silicon layer to form an active pattern and a data line, the active pattern includes a source region, a drain region and a channel region; disposing a first insulation film on a portion of the substrate; removing the first insulation film and the conductive metal layer disposed in a portion of the active pattern; disposing a second insulation film on the substrate; forming a gate electrode in a portion of the active pattern where the second insulation film has been disposed; disposing a third insulation film on a portion of the substrate; forming a plurality of first contact holes defined through the second and third insulation films to expose a portion of the source and drain regions; forming a second contact hole defined through the first, second, and third insulation films to expose a portion of the data line; forming a source electrode connected to the source region within one of the plurality of first contact holes and a data line within the second contact hole; and forming a pixel electrode and a drain electrode connected to the drain region within the other one of the plurality of first contact holes. 
     In another aspect, an liquid crystal display (LCD) device comprises an active pattern formed of a silicon layer on a substrate, and having a source region, a drain region and a channel region; a data line formed as a double layer of the silicon layer and a conductive metal layer; a first insulation film formed on a portion of the substrate; a gate electrode formed in a portion of the active pattern on the first insulation film; a second insulation film formed on the substrate; and a source electrode connected to the source region and a drain electrode connected to the drain region within a plurality of first contact holes defined though the first and second insulation films. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a plan view showing a portion of an array substrate of the related art LCD; 
         FIGS. 2A to 2F  are cross-sectional views showing step-by-step fabrication process of the LCD taken along line I-I′ of  FIG. 1 ; 
         FIG. 3  is a plan view showing a portion of an array substrate of an LCD in accordance with a first exemplary embodiment of the present invention; 
         FIGS. 4A to 4E  are sequential cross-sectional views taken along line III-III′ of the LCD of  FIG. 3 ; 
         FIGS. 5A to 5E  are plan views showing step-by-step fabrication process of an LCD in accordance with the first embodiment of the present invention; 
         FIGS. 6A to 6E  are cross-sectional view showing a process of simultaneously forming an active pattern and a data line of  FIGS. 4A and 4B  in accordance with the first embodiment of the present invention; 
         FIGS. 7A to 7D  are cross-sectional views showing step-by-step fabrication process of an LCD in accordance with a second exemplary embodiment of the present invention; and 
         FIGS. 8A to 8D  are cross-sectional views showing a process of simultaneously forming an active pattern and a data line using a diffraction exposure in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE 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. 
     An active matrix (AM) structure includes a driving mechanism to drive liquid crystal material of a pixel unit using a thin film transistor (TFT) as a switching device. In such active matrix structure, amorphous silicon or polycrystalline silicon is used as a channel layer of the TFT. A concept of an amorphous silicon thin film transistor technique was established by LeComber et al. of England in 1979 and then was put to practical use as a 3-inch liquid crystal portable TV in 1986. Recently, a TFT LCD having a size greater than 50 inches has been developed. 
     However, an electric mobility (˜1 cm 2 /Vsec) of the amorphous silicon thin film transistor is limited in its application to a peripheral circuit which requires a fast clock operation of 1 MHz or higher. Thus, integrating a pixel unit and a driving circuit unit on a glass substrate simultaneously by the polycrystalline silicon TFT is taking attention from researchers because the polycrystalline silicon TFT has greater field effect mobility than the amorphous silicon TFT. 
     The polycrystalline silicon thin film transistor technique has been applied to a compact module such as a camcorder since liquid crystal color TV was developed in 1982. Due to a low photo sensitivity and high field effect mobility, the polycrystalline silicon thin film transistor includes the driving circuit that can be directly fabricated on a substrate. In particular, increased mobility enhances an operation frequency of a driving circuit unit which determines the number of driving pixels. In addition, reduction of time taken to change a signal voltage of the pixel unit reduces a distortion of a transmission signal, thereby improving picture. Moreover, the polycrystalline silicon TFT can be driven with a voltage smaller than 10V compared to the amorphous silicon thin film transistor which requires a high driving voltage (˜25V), thereby saving a power consumption. 
     However, due to an increased number of photolithography processes required to fabricate an LCD including the polycrystalline silicon TFT, the fabrication cost increases. To solve this problem, the number of photolithography processes, specifically, the number of masks used, needs to be reduced. Accordingly, the present invention provides a LCD device and its fabrication method in which first and second contact holes are formed masking process at the same time by simultaneously pattering the active pattern and the data line, thereby reducing the number of masks. 
     The LCD device and its fabrication method in accordance with a preferred embodiment of the present invention will now be described with reference to the accompanying drawings. 
       FIG. 3  is a plan view showing a portion of an array substrate of a LCD device in accordance with a first exemplary embodiment of the present invention. A LCD device of the first embodiment includes N×M pixels formed by N gate lines and M data lines intersecting each other. For convenience, only a single pixel is shown in  FIG. 3 . 
     The first embodiment of the present invention implements a polycrystalline silicon TFT using a polycrystalline silicon thin film as a channel layer. However, choice of channel layer is not limited thereto, and an amorphous silicon thin film can be also used as the channel layer. As shown in  FIG. 3 , gate line  116  and data line  117  are formed on an array substrate  110 . The gate line  116  intersects data line  117 , thereby defining pixel regions. 
     A TFT, working as a switching device, is formed at the intersection of the gate line  116  and the data line  117 . A pixel electrode  118  connected to the TFT is formed in the pixel region to drive liquid crystal material (not shown). A common electrode of a color filter substrate (not shown) also is formed in the pixel region and connected to the TFT. 
     The TFT includes a gate electrode  121  connected to the gate line  116 , a source electrode  122  connected to the data line  117 , and a drain electrode  123  connected to the pixel electrode  118 . The TFT further includes the second and third insulation films (not shown) to insulate the gate electrode  121 , the source/drain electrodes  122 ,  123 , and an active pattern  120 B. An active pattern  120 B forms a conductive channel between the source electrode  122  and the drain electrode  123  where a gate voltage is supplied to the gate electrode  121 . 
     The source electrode  122  is electrically connected to the source region of the active pattern  120 B within one of the plurality of first contact holes  140 A defined through the second and third insulation films, and the drain electrode  123  is electrically connected to the drain region of the active pattern  120 B within the other one of the plurality of first contact holes  140 A. A portion of the source electrode  122  is electrically connected to the data line  117  within the second contact hole  140 B defined through the first, second and third insulation films, and a portion of the drain electrode  123  is extended into the pixel region to form the pixel electrode  118 . 
     By patterning the active pattern  120 B and the data line  117  in the same masking process, and furthermore forming the pixel electrode  118 , the source/drain electrodes  122  and  123  from the same material, the number of masks can be reduced while fabricating the TFT. A fabrication process of the TFT will be described in detail next. 
       FIGS. 4A to 4E  are sequential cross-sectional views taken along line III-III′ of the LCD of  FIG. 3 , and  FIGS. 5A to 5E  are plan views showing a step-by-step fabrication process of an LCD according to the first embodiment of the present invention. 
     As shown in  FIGS. 4A and 5A , the active pattern  120 B and the data line  117  are simultaneously patterned by a photolithography process (the first masking process) on the substrate  110 . The substrate  110  is made of a transparent insulation material such as glass. 
     The data line  117  includes a first data line pattern  120 A formed of a silicon layer  120  which also forms the active pattern  120 B and a second data line pattern  130 A formed of a conductive metal material. The conductive metal material pattern  130 B remains on the upper portion of the active pattern  120 B. As shown in  FIGS. 4B and 5B , the first insulation film  115 A is disposed on the entire surface of the substrate  110 . Thereafter, the first insulation film  115 A and the conductive metal material pattern  130 B are removed by the photolithography process (the second masking process), thereby exposing the surface of the active pattern  120 B. 
     The first and second masking processes, namely, the process of simultaneously forming the data line and the active pattern will be described in detail as follows. 
       FIGS. 6A to 6E  are cross-sectional view showing a process of simultaneously forming an active pattern  120 B and a data line  117  of  FIGS. 4A and 4B  in accordance with the first embodiment of the present invention. 
     As shown in  FIG. 6A , a silicon layer  120  is disposed on the substrate  110 . The silicon layer  120  can be formed of an amorphous silicon thin film or a crystallized silicon thin film. In the first embodiment of the present invention, the TFT is formed by a crystallized polycrystalline silicon thin film. The polycrystalline silicon thin film is formed through several crystallization methods after the amorphous silicon thin film is deposited on the substrate  110 . The method of forming the polycrystalline silicon thin film will be described next. 
     First, the amorphous silicon thin film is deposited by a low pressure chemical vapor deposition (LPCVD) or a plasma enhanced chemical vapor deposition (PECVD). Thereafter, a dehydrogenation process is performed to remove hydrogen atom existing in the amorphous silicon thin film, and then, crystallization is performed. The methods for crystallizing the amorphous silicon thin film include a solid phase crystallization (SPC) for heat-treating the amorphous silicon thin film at a high temperature in a furnace and an eximer laser annealing (ELA) method using laser. Laser crystallization, such as ELA, commonly uses a pulse form laser. Recently, a sequential lateral solidification (SLS) which improves the crystallization characteristics by growing crystal grains in a horizontal direction has been proposed. 
     SLS takes advantage of the fact that crystal grains grow in a vertical direction to a boundary face between liquid phase silicon and solid phase silicon (Robert S. Sposilli, M. A. Crowder, and James S. Im, Mat. Res. Soc. Symp. Proc. Vol. 452, 956˜957, 1997). In the SLS, the size of the silicon grains can be enhanced by growing grains laterally up to a certain length. Proper control of laser energy size and an irradiation range of laser beam are required to achieve this result. 
     A conductive metal material  130  such as aluminum, an aluminum alloy, tungsten (W), copper (Cu), chromium (Cr) or molybdenum (Mo) is deposited on the entire surface of the substrate  110 . The conductive metal material  130  forms the data line  117 . 
     Thereafter, the first photosensitive film  170 A made of a photosensitive material, such as photoresist, is disposed on the entire surface of the substrate  110 . As shown in  FIGS. 6B and 6C , after light is selectively irradiated and developed on the first photosensitive film  170 A, the conductive metal material  130  and the silicon layer  120  are patterned simultaneously to form the active pattern  120 B and the data line  117  through one-time masking process. At this time, the data line  117  includes the first data line pattern  120 A formed of the silicon layer which also forms the active pattern  120 B and the second data line pattern  130 A formed of the conductive metal material. The conductive metal material pattern  130 B having the same pattern as the active pattern  120 B remains on the upper portion of the active pattern  120 B. 
     Then, as shown in  FIG. 6D , the first insulation film  115 A and the second photosensitive film  170 B are disposed on the entire surface of the substrate  110 . Thereafter, as shown in  FIG. 6E , the second photosensitive film  170 B is exposed and developed using a mask whose size is as large as or larger than the active pattern  120 B to form the second photosensitive pattern  170 B′. Then, when the first insulation film  115 A and the conductive metal material pattern  130 B are removed using the second photosensitive film pattern  170 B′ as a mask, the active pattern  120 B is exposed. Next, as shown in  FIGS. 4C and 5C , the second insulation film  115 B are disposed on the entire surface of the substrate  110 . The second insulation film  115 B can be formed relatively thinner than the first insulation film  115 A. 
     After the gate electrode  121  is formed at an upper portion of the active pattern  120 B where the second insulation film  115 B has been disposed (the third masking process), an impurity ion is injected to a certain region of the active pattern  120 B using the gate electrode  121  as a mask, thereby forming the source region  124 A, and drain regions  124 B, and channel region  124 C. In this case, the gate electrode  121  serves as an ion stopper which prevents an infiltration of a dopant into the channel region  124 C of the active pattern  120 B. The electrical characteristics of the active pattern  120 B vary according to a type of an injected dopant. If the injected dopant corresponds to a group III element such as boron, the active pattern  120 B operates as a P-type TFT, and if the injected dopant corresponds to a group V element, the active pattern  120 B operates as an N-type TFT. A process for activating the injected dopant can be performed after the ion injection process. 
     As shown in  FIG. 5C , when the gate electrode  121  is formed, the gate line  116  is formed substantially vertical to the data line  117 . In the first embodiment of the present invention, when the first insulation film  115 A is formed relatively thick on the upper portion of the data line  117 , a signal interference can be prevented at an intersection of the data line  117  and the gate line  116 . 
     Next, as shown in  FIGS. 4D and 5D , the third insulation film  115 C is disposed on the entire surface of the substrate  110  where the gate electrode  121  has been formed. Then, a portion of the second insulation film  115 B and the third insulation film  115 C are removed through photolithography to define a plurality of first contact holes  140 A to expose a portion of the source/drain regions  124 A and  124 B. A portion of the first, second and third insulation films  115 A,  115 B and  115 C are removed to define the second contact hole  140 B, thereby connecting the source region  124 A and the data line  117  electrically. The third insulation film  115 C is formed of a transparent organic insulation material such as benzocyclobutene (BCB) or an acrylic resin for a high aperture ratio. 
     Then, as shown in  FIGS. 4E and 5E , after a transparent conductive material having an excellent transmittance such as ITO (Indium Tin Oxide) or an IZO (Indium Zinc Oxide) is disposed on the entire surface of the substrate  110 . At this time, a portion of the source electrode  122  is electrically connected to the data line  117  within the second contact hole  140 B, and a portion of the drain electrode  123  is extended into the pixel region to form the pixel electrode  118 . Furthermore, the source electrode  122  is electrically connected to the source region  124 A within the one of the plurality of first contact holes  140 A and the drain electrode  123  is electrically connected to the drain region  124 B within the other one of the plurality of first contact holes  140 A. 
     As mentioned above, in the fabrication process of the LCD in accordance with the first embodiment of the present invention, the active pattern  120 B and the data line  117  are simultaneously patterned to define the first and second contact holes in one masking process, thus number of masking process is reduced compared to the fabrication process of the related art. Accordingly, increased production yield and a reduction of fabrication cost are achieved. 
     Meanwhile, a one-time masking process for patterning the active pattern  120 B and the data line  117  simultaneously can be further reduced using a diffraction exposure and ashing technique. Diffraction exposure and ashing technique will now be described in a second embodiment of the present invention. 
       FIGS. 7A to 7D  are cross-sectional views sequentially showing a fabrication process of an LCD in accordance with the second embodiment of the present invention. 
     As shown in  FIG. 7A , the active pattern  220 B and the data line  217  are simultaneously formed on a substrate  210  using photolithography (the first masking process). The substrate  210  is made of a transparent insulation material such as glass. In the second embodiment of the present invention, the one-time masking process including the diffraction exposure and ashing process is implemented to form the active pattern  220 B and the data line  217 . In the one-time masking process of the second embodiment, a conductive metal material is absent from the upper portion of the active pattern  220 B, while the data line  217  and the active pattern  220 B are formed. 
     The details of the one-time masking process in the second embodiment will be described with reference in  FIGS. 8A and 8D .  FIGS. 8A to 8D  are cross-sectional views showing a process of simultaneously forming an active pattern and a data line by using a diffraction exposure. 
     As shown in  FIG. 8A , a conductive metal material  230  forming a data line is disposed on the entire surface of the substrate  210  where a silicon layer  220  has already been disposed. Next, as shown in  FIG. 8B , a photosensitive film  270  formed of a photosensitive material such as photoresist is disposed on the entire surface of the substrate  210  already provided with the conductive metal material  230 . 
     The photoresist includes a positive photoresist and a negative photo resist. The positive photoresist comprises a group of a Novolak based resin, wherein a region exposed to light source is dissolved in reaction with a developer. The negative photoresist comprises an acryl based monomer wherein an exposed region is not reacted with the developer. The photoresist further comprises a solvent serving to adjust viscosity, a photo active-based compound causing photo-sensing and a resin, and a chemically coupled material. 
     Thereafter, a diffraction mask  280  is positioned on the substrate  210  which is already provided with the photosensitive film  270  and photo-sensing is performed by light such as ultraviolet rays. In the second embodiment of the present invention, the positive photoresist is used as a photosensitive film  270 . However, a choice of photoresist for a photosensitive film is not limited to the positive photoresist only. The negative photoresist can be also used as a photosensitive film, and other suitable photosensitive material other than the photoresist can be also used. 
     While using the positive photoresist, the first region (A) is completely covered to leave the photoresist as it is (leaving the relatively thick photosensitive film), the second region (B) has a slit pattern to form a relatively thin photoresist, and the third region (C) is removed, thereby forming a diffraction mask  280  including a slit pattern. The slit pattern serves to reduce strength of light incident on the substrate  210  by making the incident light diffracted. The slit pattern has a slit interval suitable for diffraction exposure. A slit interval narrower than resolution of an optical source is used for photo-sensing. In the second embodiment of the present invention, the slit pattern is used for the second region (B), but a semi-transmission film can be also used. 
     As fabrication process proceeds using the diffraction mask  280 , a first photoresist pattern  270 A having a first thickness remains at the first region (A), a second photoresist pattern  270 B having a second thickness thinner than the first photoresist pattern  270 A remains at the second region (B), and the photoresist is completely removed at the third region (C). 
     As shown in  FIG. 8C , the conductive metal material  230  and the silicon layer  220  disposed at the third region (C) where photoresist pattern  270 A and  270 B are absent are removed to form the active pattern  220 B and the data line  217 . The data line  217  includes the first data line pattern  220 A formed of the silicon layer which also forms the active pattern  220 B, and the second data line pattern  230 A made of a conductive metal material. The conductive metal material pattern  230 B remains on the upper portion of the active pattern  220 B. 
     As a reference, the etching technique is a method for implementing a desired thin film pattern by selectively removing a portion of the thin film formed by photoresist using a physical or chemical reaction. In the etching process, a portion of the thin film where the photoresist pattern is absent is removed. The etching process includes dry etching using gas plasma and wet etching using a chemical solution. 
     As shown in  FIG. 8D , a process of removing a portion of the first photoresist pattern  270 A having the first thickness is performed. To remove a portion of the first photoresist pattern  270 A, the ashing technique is used. The ashing technique oxidizes the photosensitive film by a gas, for example, oxygen. At this time, the first photoresist pattern  270 A having the first thickness disposed on the upper portion of the data line  217  is precisely controlled by the ashing method. A portion of the first photoresist pattern  270 A is removed to form the third photoresist pattern  270 A′ having the third thickness while the second photoresist pattern  270 B disposed on the upper portion of the active pattern  220 B is completely removed, thereby exposing the conductive metal material pattern  230 B. Thereafter, the conductive metal material pattern  230 B is removed using the third photoresist pattern  270 A′ having the third thickness as a mask, to expose the surface of the active pattern  220 B. 
     Next, as shown in  FIG. 7B , the first insulation film  215 A is disposed on the entire surface of the substrate  210 . After a gate electrode  221  formed of a conductive metal material is disposed at an upper portion of the active pattern  220 B which is already provided with the gate insulation film  215 A (the second masking process), an impurity ion is injected to a certain region of the active pattern  220 B using the gate electrode  221  as a mask to form a source region  224 A and a drain region  224 B. 
     As shown in  FIG. 7C , the second insulation film  215 B is disposed at the entire surface of the substrate  210  where the gate electrode  221  is formed, then, a portion of the second and first insulation films  215 B and  215 A is removed through photolithography (the third masking process) to define a plurality of first contact holes  240 A and a second contact hole  240 B. The plurality of first contact holes  240 A exposes a portion of the source/drain regions  224 A and  224 B, and a second contact hole  240 B exposes the second data line pattern. Thereafter, as shown in  FIG. 7D , a transparent conductive metal material is disposed on the entire surface of the substrate  210 . 
     At this time, a portion of the source electrode  222  is electrically connected to the data line  217  within the second contact hole  240 B and a portion of the drain electrode  223  is extended into the pixel region to form the pixel electrode  218 . A source electrode  222  electrically connects with the source region  224 A within one of the plurality of first contact holes  240 A and a drain electrode  223  electrically connects with the drain region  224 B within another one of the plurality of first contact holes  240 A. 
     In this manner, the active pattern  220 B and the data line  217  are formed through one-time masking process using the diffraction exposure and ashing technique. Since process of forming a contact hole is eliminated, two masking processes required to form the contact hole can be reduced compared with the fabrication process of the related art. Accordingly, higher production yield and reduction of a fabrication cost are achieved by the simplified fabrication process. 
     As described, the method for fabricating an LCD in accordance with the present invention has the following advantages. Since the active pattern and the data line are simultaneously patterned, total number of mask process is reduced. Thus, the fabrication process and cost can be reduced. In addition, since the pixel electrode extends directly from a portion of the drain electrode and the pixel electrode does not need a contact hole to electrically connected with the drain electrode, the number of fabrication process and cost are further reduced. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the liquid crystal display device and its fabricatng method thereof 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.