Abstract:
A thin film transistor liquid crystal display (TFT-LCD) pixel structure comprising: a gate line and a gate electrode formed on a substrate; a first insulating layer, a semiconductor layer, and a doped semiconductor layer formed sequentially on the gate electrode and the gate line, wherein an isolating groove is formed above the gate line which disconnects the semiconductor layer on the gate line; a second insulating layer covering the isolating groove and a portion of the substrate where the gate line and the gate are not formed; a pixel electrode formed on the second insulating layer, wherein the pixel electrode is integral with a drain electrode and is connected with the doped semiconductor layer on the gate electrode at a place where the drain electrode is formed; a source electrode, which is a portion of a data line, formed on the doped semiconductor layer; and a channel formed between the source electrode and the drain electrode.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of manufacturing a thin film transistor liquid crystal display (TFT-LCD) and the TFT-LCD thus manufactured. 
       BACKGROUND OF THE INVENTION 
       [0002]    At present, a liquid crystal displays (LCD) exemplified by a TFT-LCD has become one very important type of flat panel displays and has attracted extensive attention. During manufacture of a TFT-LCD, efforts have been made to adopt a more advanced manufacturing method, simplify producing process, and reduce production cost. Among the others, simplification of process and the reduction of production cost for each device of a TFT-LCD directly lead to the simplification of manufacturing process and the reduction of production cost of the whole TFT-LCD. 
         [0003]    A LCD generally comprises an upper substrate and a lower substrate which are joined together by a seal agent. Electrodes are formed on the upper and lower substrates, and liquid crystal material is filled between the two substrates. Particles of a certain diameter are distributed between the two substrates to maintain a constant gap between the two substrates. A thin film transistor (TFT) is formed on the surface of the lower substrate as a switching element. The TFT can comprise a gate electrode connected with a gate line, a source electrode connected with a signal line, and a drain electrode connected with a pixel electrode. Specifically, the TFTs used for a TFT-LCD commonly comprise a gate electrode which may be a portion of the gate line, an active layer (comprising a semiconductor layer and a doped semiconductor layer) which forms a channel, a source electrode which may be a portion of the data line, and a drain electrode which opposes the source on the active layer and is electrically connected with the pixel electrode. The TFT, as a switching element, controls, under the electrical signal transmitted to the gate electrode through the gate line, the transmission of the data signal transmitted through the data line to the pixel electrode. 
         [0004]    In recent years, in a conventional method of manufacturing a TFT-LCD, an array forming process is widely used, in which patterning processes by photolithography with a mask are performed for several times on a glass base substrate to form a TFT array. Since the mask for exposing is very expensive, it is an efficient method to decrease production cost by reducing the times of photolithography with a mask. However, decrease of the times of photolithography with a mask may render other processes in manufacturing a TFT-LCD complicated and may even make impossible to carry out such processes. 
         [0005]    One currently popular method of manufacturing a TFT-LCD is a four-mask method, in which photolithography processes are carried out for four times, for which four masks are needed. In addition, processes such as deposition, etching, and/or stripping are necessary for forming a pattern. In the four-mask manufacturing method, a gray tone mask technology can be used for etching to form the source/drain metal electrodes and the channel portion of the active layer of the TFT. The fabrication of these portions is the key for manufacturing a TFT-LCD, which, in practice, imposes rigorous requirements on etching selectivity and the photolithography process and further brings complication to the manufacturing process. 
         [0006]    Therefore, there is a need for a method of manufacturing a TFT-LCD which uses less masks and which is also simple in procedure and easy to carry out. 
       SUMMARY OF THE INVENTION 
       [0007]    An embodiment of the invention provides a thin film transistor liquid crystal display (TFT-LCD) pixel structure comprising: a gate line and a gate electrode formed on a substrate; a first insulating layer, a semiconductor layer, and a doped semiconductor layer formed sequentially on the gate electrode and the gate line, wherein an isolating groove is formed above the gate line which disconnects the semiconductor layer on the gate line; a second insulating layer covering the isolating groove and a portion of the substrate where the gate line and the gate are not formed; a pixel electrode formed on the second insulating layer, wherein the pixel electrode is integral with a drain electrode and is connected with the doped semiconductor layer on the gate electrode at a place where the drain electrode is formed; a source electrode, which is a portion of a data line, formed on the doped semiconductor layer; and a channel formed between the source electrode and the drain electrode. 
         [0008]    Another embodiment of the invention provides a method for manufacturing a thin film transistor liquid crystal display (TFT-LCD) pixel structure comprising the following steps: 
         [0009]    (I) depositing sequentially a gate conductive layer, a first insulating layer, a semiconductor layer and a doped semiconductor layer on a substrate, forming a first photoresist pattern with a first gray tone mask to comprise a first non-photoresist region, a first partially retained photoresist region and a first fully retained photoresist region on the substrate; etching the first non-photoresist region to form a gate line and a gate electrode; ashing the first photoresist pattern to remove the photoresist in the first partially retained photoresist region to expose a portion of the doped semiconductor layer on the gate line and thin the photoresist in the first fully retained photoresist region, and then etching the exposed portion of the doped semiconductor layer and the underlying semiconductor layer to form an isolating groove above the gate line; depositing a second insulating layer, and lifting off the remained first photoresist pattern along with the second insulating layer deposited thereon on the gate line and the gate electrode; and 
         [0010]    (II) depositing sequentially a pixel electrode layer and a source/drain electrode layer on the substrate after step I, forming a second photoresist pattern with a second gray tone mask to comprise a second non-photoresist region, a second partially retained photoresist region and a second fully retained photoresist region; etching the second non-photoresist region to form a channel of a TFT, a pixel electrode and a drain electrode which is integral with the pixel electrode, and a data line and a source electrode which is integral with the data line; ashing the second photoresist pattern to remove the photoresist in the second partially retained photoresist region to expose the source electrode and the data line and thin the photoresist in the second fully retained photoresist region; depositing a passivation layer, lifting off the remained second photoresist pattern along with the passivation layer deposited thereon on the pixel electrode, and etching the source/drain electrode layer in the region on the substrate corresponding to the pixel electrode and the drain electrode to expose the pixel electrode. 
         [0011]    The TFT-LCD pixel structure and the manufacturing method thereof according to the embodiments of the present invention can reach the following advantages. 
         [0012]    A second insulating layer is deposited during the first photolithography process so that the pixel structure can be planarized, which provides process tolerance for subsequent processes. In addition, a portion of the transparent pixel electrode is also used as the drain electrode of the TFT, which can avoid the problem about contact resistance. 
         [0013]    As compared with the conventional method, two masks can be used to manufacture a TFT-LCD pixel structure, the number of masks can be decreased, the cost for the array process and the seizing time can be reduced, and the production volume and yield can be improved. In addition, since the number of the masks and also exposure processes is decreased, the complication of the process can be reduced, the process tolerance can be increased, and the production volume and yield can be improved. 
         [0014]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
           [0016]      FIG. 1  is a top view showing a pattern after a first photolithography is carried out with the first gray tone mask; 
           [0017]      FIG. 1A  is a cross-sectional view along line A-A′ in  FIG. 1 ; 
           [0018]    FIG.  1 A′ is a cross-sectional view along line B-B′ in  FIG. 1 ; 
           [0019]      FIG. 1B  is a cross-sectional view along line A-A′ in  FIG. 1  after etching on the non-photoresist region during the first photolithography process; 
           [0020]      FIG. 1C  is a cross-sectional view along line A-A′ in  FIG. 1  after ashing of the photoresist during the first photolithography process; 
           [0021]    FIG.  1 B′ is a cross-sectional view along line B-B′ in  FIG. 1  after ashing of the photoresist during the first photolithography process; 
           [0022]    FIG.  1 C′ is a cross-sectional view along line B-B′ in  FIG. 1  after etching of the semiconductor layer during the first photolithography process; 
           [0023]      FIG. 1D  is a cross-sectional view along line A-A′ in  FIG. 1  after deposition of the second insulating layer during the first photolithography process; 
           [0024]      FIG. 1E  is a cross-sectional view along line A-A′ in  FIG. 1  after the lifting-off process during the first photolithography process; 
           [0025]    FIG.  1 D′ is a cross-sectional view along line B-B′ in  FIG. 1  after deposition of the second insulating layer during the first photolithography process; 
           [0026]    FIG.  1 E′ is a cross-sectional view along line B-B′ in  FIG. 1  after the lifting-off process during the first photolithography process; 
           [0027]    FIG.  1 ′ is a plan view showing the pixel structure in which the first photolithography process is completed; 
           [0028]      FIG. 2  is a view showing the pattern after a second photolithography is carried out with a second gray tone mask; 
           [0029]      FIG. 2A  is a cross-sectional view along line A-A′ in  FIG. 2 ; 
           [0030]      FIG. 2B  is a cross-sectional view along line A-A′ in  FIG. 2 ; 
           [0031]      FIG. 2C  is a cross-sectional view along line A-A′ in  FIG. 2  after ashing of the photoresist during the second photolithography process; 
           [0032]      FIG. 2D  is a cross-sectional view along line A-A′ in  FIG. 2  after deposition of the passivation layer during the second photolithography process; 
           [0033]      FIG. 2E  is a cross-sectional view along line A-A′ in  FIG. 2  after the lift-off process during the second photolithography process; and 
           [0034]      FIG. 2F  is a cross-sectional view along line A-A′ in  FIG. 2  after etching of the source/drain metal layer during the second photolithography process. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Embodiments of the present invention are described below in detail with reference to the accompanying drawings. In this disclosure, a gray tone mask may be a mask with a transparence region, a translucence region and a blocked region, and the translucence region can be obtained with slits that can diffract light, a translucent material of low transmissivity and the like, thus a gray tone mask also comprises a half tone mask. 
         [0036]      FIG. 1  is a top view showing a pattern after a first photolithography is carried out with a first gray tone mask,  FIG. 1A  is a cross-sectional view along line A-A′ in  FIG. 1 , and FIG.  1 A′ is a cross-sectional view along line B-B′ in  FIG. 1 . As shown in  FIGS. 1 ,  1 A, and  1 A′, a gate conductive layer  11 , a first insulating layer  12 , a semiconductor layer  13 , and a doped semiconductor layer  14  are deposited in sequence on a substrate  100 , a photoresist film is applied on the resultant layer structure, and an exposure process with the first gray tone mask and development process are carried out to form a photoresist pattern corresponding to a gate line and gate island pattern, as shown in  FIG. 1 . As can be seen from  FIGS. 1 ,  1 A, and  1 A′, there is no photoresist in the region other than a gate line  101  and a gate electrode  102  that are to be formed, an isolating groove  103  is to be formed on the gate line and corresponds to the partially retained photoresist region  15  in the first photolithography process, and the portions other than the isolating groove  103  on the gate line corresponds to the fully retained photoresist region  15 ′ in the first photolithography. Then, etching is carried out by using the photoresist pattern as an etching mask so that the region which is not protected by the photoresist pattern is removed, i.e., the doped semiconductor layer  14 , the semiconductor layer  13 , the first insulating layer  12 , and the gate conductive layer  11  in the non-photoresist region that is not covered by the photoresist is etched away.  FIG. 1B  shows a cross-sectional view along line A-A′ in  FIG. 1  after etching on the non-photoresist region. Then, an ashing process on photoresist is carried out. The cross-sectional view along line A-A′ in  FIG. 1  after ashing is shown in  FIG. 1C , and the cross-sectional view along line B-B′ in  FIG. 1  after ashing is shown in FIG.  1 B′. As shown in FIG.  1 B′, a portion of the doped semiconductor layer  14  corresponding to the isolating groove  103  on the gate line is exposed, and the fully retained photoresist region  15 ′ is thinned in thickness. The exposed portion of the doped semiconductor layer  14  and the semiconductor layer  13  under the doped semiconductor layer  14  are etched to form the isolating groove  103 ′ on the gate line, as shown in FIG.  1 C′. 
         [0037]    Then, a second insulating layer  16  is deposited to protect the gate line and gate electrode. The cross-sectional view along line A-A′ in  FIG. 1  after deposition of the second insulating layer is shown in  FIG. 1D . A lift-off process is carried out to remove the fully retained photoresist region  15 ′ together with the second insulating layer  16  deposited thereon. The cross-sectional view along line A-A′ in  FIG. 1  after the lift-off process is shown in  FIG. 1E . The cross-sectional view along line B-B′ in  FIG. 1  after deposition of the second insulating layer  16  is shown in FIG.  1 D′. The semiconductor layer  13  corresponding to the isolating groove  103 ′ is covered by the second insulating layer  16 . 
         [0038]    The substrate  100  may be a glass substrate or a plastic substrate. The gate conductive layer  11  may be a single layer film of Al/Nd, Al, Cu, Mo, Mo/W or Cr, or a composite film of any combination of Al/Nd, Al, Cu, Mo, Mo/W and Cr. The first insulating layer  12  and second insulating layer  16  may be a single layer film of SiNx, SiOx or SiOxNy, or a composite film of any combination of SiNx, SiOx and SiOxNy. Both of the first insulating layer  12  and the second insulating layer  16  may be transparent so as to allow transmission of light. The semiconductor layer  13  may comprise amorphous silicon (a-Si), poly-silicon (p-Si) and the like. The doped semiconductor layer  14  may be doped with a dopant such as boron (B) or phosphor (P). 
         [0039]    Here, all the processes with the first gray tone mask have been described, and the plan view of the pixel structure after the processes are completed is shown in FIG.  1 ′. As can be seen from the above processes, in the present embodiment, a second insulating layer is deposited during the first photolithography process so that the pixel structure is planarized, which provides process tolerance for subsequent processes. In addition, the conventional gray tone mask and lift-off process for manufacturing a TFT-LCD can be used in the first photolithography process, which makes the first photolithography process easy to implement. 
         [0040]    Then, a transparent pixel electrode layer  21  and a source/drain electrode layer  22  are deposited in sequence over the pixel structure after the above processes. A photoresist film is applied on the resultant structure, and an exposure process with a second gray tone mask and a development process are carried out to form a second photoresist pattern having a photoresist pattern  201  corresponding to the data line to be formed and a photoresist pattern  202  corresponding to the pixel electrode to be formed, as shown in  FIG. 2 . The photoresist pattern  201  is relatively thin in thickness, i.e., it is a partially retained photoresist region  23  in the second photolithography process. The photoresist pattern  202  is relatively thick thickness, i.e., it is a fully retained photoresist region  23 ′ in the second photolithography process. Other region corresponds to the non-photoresist region, as shown in  FIG. 2A . Then, etching is carried out with the photoresist patterns as an etching mask on the non-photoresist region so that the source/drain electrode layer  22 , the transparent pixel electrode layer  21 , the doped semiconductor layer  14  and the semiconductor layer  13  which are not covered by the photoresist are removed. As a result, the source electrode  203  together with the data line, the drain electrode  204  together with the pixel electrode, and the channel of the semiconductor layer defined between the source electrode  203  and the drain electrode  204  are formed. Then, an ashing process on photoresist is carried out so that the source electrode  203  and the data line are exposed and the thick photoresist pattern  202  (i.e., the fully retained photoresist region  23 ′) is thinned in thickness, as shown in  FIG. 2C . 
         [0041]    Then, a passivation layer  24  is deposited on the resultant structure, as shown in  FIG. 2D . A lift-off process is carried out to remove the photoresist  23 ′ together with the passivation layer deposited thereon. The cross-sectional view along line A-A′ in  FIG. 2  after the lift-off process is shown in  FIG. 2E . Since the region corresponding to the source electrode  203  and the data line is protected by the passivation layer, an etching process is carried out on the pixel electrode region to etch away the source/drain electrode layer  22  in the region corresponding to the pixel electrode to be formed and expose the transparent pixel electrode layer  21  as the pixel electrode, as shown in  FIG. 2F . In this way, the manufacturing process of the TFT-LCD pixel structure is completed here. 
         [0042]    The transparent pixel electrode layer  21  may be formed of indium tin oxides (ITO) which is superior in conductivity and transparency and can block ultraviolet and far-infrared radiation as well as electronic radiation which is harmful to a human being. Therefore, ITO can be applied in the pixel structure to enhance the conductivity and transparency and block the ultraviolet and far-infrared radiation as well as electronic radiation which is harmful to a human being. In addition, indium zinc oxide, tin oxide and other transparent conductive material can be used for the transparent pixel electrode layer  21 . The source/drain electrode layer  22  may be a single layer film of Mo, Mo/W or Cr, or a composite film of any combination of Mo, Mo/W and Cr. 
         [0043]    In addition, different materials in the drawings are differently indicated in the drawings. Since the substrate  100 , the source/drain electrode layer  22 , the second insulating layer  16 , and the transparent pixel electrode layer  21  are all transparent, these layers are illustrated with pure colors. One can refer to the indications in each drawing. 
         [0044]    Furthermore, during the second gray tone photolithography process in the above embodiment, a portion of the transparent pixel electrode is also formed as the drain electrode of the TFT, which can avoid the problem about contact resistance. 
         [0045]    Two masks can be used in the embodiment of the present invention to manufacture a TFT-LCD, thus the number of mask can be decreased, the cost for the array process and the occupation time can be reduced, and the production volume and yield can be improved compared with the conventional method. In addition, the conventional gray tone photolithography process and the lift-off process can be employed, which makes simple and convenient to implement the complete process. 
         [0046]    The TFT manufactured by the method described above comprises a substrate  100 , a gate line  101 , a first insulating layer  12 , a semiconductor layer  13 , a doped semiconductor layer  14 , a second insulating layer  16 , a source electrode  203  which is a portion of a data line, a drain electrode  204  which is a portion of a pixel electrode, and a passivation layer  24 . In the pixel structure of the embodiment of the present invention, the first insulating layer  12 , the semiconductor layer  13 , and the doped semiconductor layer  14  are disposed sequentially over the gate  102  and the gate line  101 , the isolating groove  103  is formed on the gate line  101  and disconnects the semiconductor layer on the gate line, the second insulating layer  16  covers the isolating groove  103  as well as the portion of the substrate where the gate line  101  and the gate  102  are not formed, the transparent pixel electrode layer  21  is retained under the source electrode  203  which is integral with the data line, the drain electrode  204  which is integral with the pixel electrode is formed over the second insulating layer  16 , that is, the pixel electrode is connected with the doped semiconductor layer  14  on the gate  102  at the place where the drain electrode  204  is formed, and the passivation layer  24  covers the portion of the substrate where the pixel electrode  204  is not formed, i.e., exposes the pixel electrode  204 . 
         [0047]    The surface of the second insulating layer  16  flushes with that of the doped semiconductor layer  14 . The transparent pixel electrode layer  21  for forming the drain electrode  204  which is a portion of the pixel electrode is also retained under the source electrode  203  which is a portion of the data line. 
         [0048]    In the embodiment described above, description is made by reference to the structure with one TFT and the manufacturing process thereof. There can be formed a plurality of TFTs on the substrate, and the TFTs can be manufactured simultaneously by the photolithography processes, in which case the isolating groove on the gate line can prevent the short circuit among the data lines. 
         [0049]    The embodiment of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to those skilled in the art are intended to be comprised within the scope of the following claims.