Abstract:
Disclosed is a method for forming a bonding pad in a TFT array process for a reflective LCD and the bonding pad formed by the method, in which an ITO is formed on the first or second metal layer directly during the fabrication of the TFT structure for the reflective LCD to thereby obtain the bonding pad directly after etching the contact window for the scan bonding pad or data bonding pad, and thus an ITO mask process for bonding pad is saved and the LCD process is simplified.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a method for manufacture of liquid crystal display (LCD), and more particularly to a method for forming a bonding pad in a thin film transistor (TFT) array process for a reflective LCD and the bonding pad formed by the method.  
         BACKGROUND OF THE INVENTION  
         [0002]    Indium tin oxide (ITO) has been widely used in manufacture of TFT-LCDs for their transparent pixel electrodes and the contact layers of the TFT plate to be attached with external driver integrated circuits (ICs). Due to its low contact resistance and good reliability of life test, ITO is almost the best material for bonding pads. However, it is not a must be to use ITO for pixel electrodes in reflective LCDs, since the reflective metal layer already replaces it. Even though, it still needs an additional ITO photo mask procedure to make the bonding pads in the fabrication process for reflective LCDs.  
           [0003]    In a typical process for manufacture of a reflective LCD, as shown in FIG. 1, there are included first metal layer step  11 , amorphous silicon (a-Si) step  12  and second metal layer step  13  to fabricate TFTs structure, and the following steps comprise bumping  14  for scattering film to increase light efficiency, etching  15  for contact windows, ITO deposition  16  for bonding pads, and reflector formation  17 . Obviously, even though ITO is not used for pixel electrodes in a reflective LCDs, it is still necessary an additional ITO photo mask procedure to form bonding pads in the TFT array process, resulting in complicated and time consuming process and low throughput production. Moreover, during the contact windows etching process, the surfaces of the first and second metal layers connected to the gate and source/drain respectively are easily to be contaminated by residual chemicals and, as a result, the ITO subsequently deposited on the surfaces of the metal layers has poor adhesion, low conductivity and large contact resistance, such that the signal transmission efficiency thereof is reduced and the LCD has poor performance.  
         SUMMARY OF THE INVENTION  
         [0004]    An object of the present invention is to provide a simplified method for LCD manufacture. According to the present invention, a TFT array process for a reflective LCD comprises deposition of an ITO following the first and/or second metal layers to form a TFT array structure. Therefore, after contact windows etching, scan bonding pads and/or data bonding pads are obtained directly, and no more photo mask procedure is needed for ITO bonding pads, such that the LCD process is simplified. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The above and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:  
         [0006]    [0006]FIG. 1 shows a conventional process for manufacturing a reflective LCD;  
         [0007]    [0007]FIG. 2 shows the first embodiment process according to the present invention;  
         [0008]    FIGS.  3 A- 3 C are schematic illustration of the structures for a TFT structure, scan bonding pad and data bonding pad, respectively, manufactured by the process shown in FIG. 2;  
         [0009]    [0009]FIG. 4 shows the second embodiment process according to the present invention;  
         [0010]    FIGS.  5 A- 5 C are schematic illustration of the structures for a TFT structure, scan bonding pad and data bonding pad, respectively, manufactured by the process shown in FIG. 4;  
         [0011]    [0011]FIG. 6 shows the third embodiment process according to the present invention; and  
         [0012]    FIGS.  7 A- 7 C are schematic illustration of the structures for a TFT structure, scan bonding pad and data bonding pad, respectively, manufactured by the process shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    According to the present invention, a first embodiment process for manufacture of an LCD is shown in FIG. 2, in which step  11 ′ includes deposition of an ITO on a first metal later after the metal layer is formed. The first metal layer comprises a gate for a TFT structure and a scan bonding pad and a data bonding pad that will be formed in future. The following steps  12  to  17  are the same as the prior art process shown in FIG. 1, only without the ITO deposition  16  of FIG. 1 and thus saving one photo mask procedure and improving the adhesion between the ITO and the first metal layer. The ITO formed on the first metal layer can be used as the contact layer of bonding pad directly after the contact window etching. FIGS.  3 A- 3 C are cross-sectional views of structures manufactured by the process shown in FIG. 2, in which FIG. 3A is the schematic illustration of a TFT structure, FIG. 3B is the schematic illustration of a scan bonding pad structure, and FIG. 3C is the schematic illustration of a data bonding pad structure. In FIG. 3A, the TFT structure is similar to that in prior art, of which a gate  20   a  is provided by a first metal layer  20  on which an ITO  21  is deposited, a gate insulator  22  covered on the gate  20   a  with an a-Si island  23  formed thereon, and N+ regions  24  formed on the surface of the a-Si island  23  for contacts of source/drain that are provided by a second metal layer  25 . The structure is further covered by an insulator  26  and a passivation  27  that can be used for scattering film, and a reflector  28  is formed thereon with a connection to the second metal layer  25  in a contact window  29 . In FIG. 3B, a scan bonding pad  20   b  is provided by the first metal layer  20 , and there is already an ITO  21  on the scan bonding pad  20   b  after a contact window  30  is formed. In FIG. 3C, a data bonding pad  20   c  is also provided by the first metal layer  20 , which is different from the traditional LCD, and a data line  25   d  is still provided by the second metal layer  25  with the reflector  28  to connect it to the data bonding pad  20   c . The reflector  28  is connected to the data line  25   d  in the contact window  31  and to the data bonding pad  20   c  in the contact window  32 .  
         [0014]    A second embodiment process for manufacture of an LCD according to the present invention is further shown in FIG. 4, which is similar to that shown in FIG. 2, only that step  11  for the first metal layer is the same as the conventional one as shown in FIG. 1 and step  13 ′ includes deposition of an ITO on a second metal later after the metal layer is formed. Moreover, the second metal layer comprises source/drain for a TFT structure and a scan bonding pad and a data bonding pad that will be formed in future. Likewise, this process needs not the step  16  for ITO deposition of FIG. 1 so as to save one photo mask procedure, and the adhesion between the ITO and second metal layer is improved. The ITO formed on the second metal layer can be used as the contact layer of bonding pad directly after the contact window etching. FIGS.  5 A- 5 C are cross-sectional views of structures manufactured by the process shown in FIG. 4, in which FIG. 5A is the schematic illustration of a TFT structure, FIG. 5B is the schematic illustration of a scan bonding pad structure, and FIG. 5C is the schematic illustration of a data bonding pad structure. In FIG. 5A, the TFT structure is similar to that shown in FIG. 3A, only that no ITO is deposited on the first metal layer  20 , and so the gate  20   a , instead, an ITO  21  is deposited on the second metal layer  25 . The remaining portion of the structure in FIG. 5A is same as that in FIG. 3A. In FIG. 5B, a scan bonding pad  20   b  is provided by the second metal layer  25 , which is different from the traditional LCD, and a scan line  20   d  is still provided by the first metal layer  20  with the reflector  28  to connect it to the scan bonding pad  25   b . The reflector  28  is connected to the scan line  20   d  in the contact window  34  and to the scan bonding pad  25   b  in the contact window  35 . In FIG. 5C, a data bonding pad  25   c  is also provided by the second metal layer  25 , and there is already an ITO  21  on the data bonding pad  25   c  after a contact window  33  is formed.  
         [0015]    [0015]FIG. 6 shows the third embodiment process for manufacture of an LCD according to the present invention, whose steps  11 ′ and  13 ′ include depositing an ITO on the first and second metal layers after these two metal layers are formed, respectively. The first metal layer comprises a gate for a TFT structure and a scan bonding pad that will be formed in future, and the second metal layer comprises source/drain for the TFT structure and a data bonding pad that will be formed in future. The other steps are same as those in conventional process. Likewise, this process needs not to deposite ITO for bonding pads after etching the contact windows, thereby saving a photo mask procedure and improving the adhesion of the deposited ITO to the first and second metal layers. The ITO formed on the first metal layer can be used as the contact layer of the scan bonding pad directly after the contact window etching, and the ITO formed on the second metal layer can be used as the contact layer of the data bonding pad directly after the contact window etching. FIGS.  7 A- 7 C are cross-sectional views of structures manufactured by the process shown in FIG. 6, in which FIG. 7A is the schematic illustration of a TFT structure, FIG. 7B is the schematic illustration of a scan bonding pad structure, and FIG. 7C is the schematic illustration of a data bonding pad structure. In FIG. 7A, the TFT structure is similar to a conventional one, only that on the gate  20   a  is deposited with an ITO  21   a , and on the second metal layer  25  is deposited with an ITO  21   b . Different from a conventional LCD, in FIG. 7B, a scan bonding pad  20   b  is provided by the first metal layer  20 , and there is already the ITO  21   a  on the scan bonding pad  20   b  after a contact window  30  is formed. Similarly, in FIG. 7C, a data bonding pad  25   c  is provided by the second metal layer  25 , and there is already the ITO  21   b  on the data bonding pad  25   c  after a contact window  33  is formed.  
         [0016]    While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.