Patent Publication Number: US-2003222310-A1

Title: [method of fabricating thin film transistor array substrate of reflective liquid crystal display]

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001] This application claims the priority benefit of Taiwan application serial no. 91111522, filed on May 30, 2002.  
       BACKGROUND OF INVENTION  
       [0002] 1. Field of Invention  
       [0003] This invention relates to a method of fabricating a thin film transistor array substrate of a reflective liquid crystal display. More particularly, this invention relates to a fabrication method for forming a thin film transistor array substrate in which the source/drain electrode and data line can be fabricated at the same time.  
       [0004] 2. Description of Related Art  
       [0005] The fast growing on the multi-media industry is greatly benefiting from the great functional improvements on semiconductor devices or displaying devices. Among the displaying devices, the cathode ray tube (CRT) had been occupying the market because of its advantages of fine displaying quality and low cost. However, CRT has the problems in space occupation and power consumption. Since the demand has been increasing for displays with fine displaying quality, light weight, thin, short, and small size, and low power consumption, the thin film transistor liquid crystal display (TFT-LCD) has gradually become the dominant product in the market due to its fine displaying quality, light weight, thin, short and more compact size, as well as its low power consumption. However, the price of the liquid crystal displayers is usually high. Therefore, if its fabrication cost can be reduced, the liquid crystal displayers can be much more competitive over other products in the market.  
       [0006] Referring to FIG. 1 to FIG. 5, a group of fabrication process flow diagrams are shown for forming a conventional thin film transistor array substrate of a reflective liquid crystal displayer. In FIG. 1, a substrate  100  is provided. A gate electrode  102  and a scan line (not shown) connected with the gate electrode  102  are formed over the substrate  100 .  
       [0007] Followed with FIG. 2, a gate-insulating layer  104  is formed in blanket over the substrate  100  and the gate electrode  102 . A channel layer  106 , which includes amorphous silicon material, is then formed over the gate insulating-layer  104 .  
       [0008] Next, referring to FIG. 3 and FIG. 4, after the formation of the channel layer  106 , a source/drain electrode region  108  and a data line (not shown) connected with one of the source/drain electrode  108  are formed at each side of the channel layer  106 . Following that, a protection layer  1   10  is then formed over the substrate  100 , covering the thin film transistor, which includes the gate electrode  102 , the insulating layer  104 , the channel layer  106 , and the source/drain electrode region  108 , as well as covering other regions of the substrate  100 .  
       [0009] Finally, referring, to FIG. 5, a bumpy layer  112  is first formed over the protection layer  110  on the substrate  100 . Then a reflection electrode  114  is formed on the bumpy layer  112 . Since the bumpy layer  112  is made of organic material, from the micro point of view, its upper surface has many concave and convex areas, which form many bumps. This bumpy surface  111  of the bumpy layer  112 , due to its concave and convex regions, can reflect the light which is incident to the reflection electrode  114  and scatter the light into multiple directions, providing a good reflection quality for the reflection electrode  114 .  
       [0010] The conventional method of fabricating a thin film transistor array substrate for the liquid crystal display includes first making the source/drain electrode region and the data line, and followed by forming the reflective electrode. Therefore, two photo masks are needed to accomplish the processes for forming the source/drain electrode, the data line, and the reflective electrode, resulting in a higher fabrication cost.  
       SUMMARY OF INVENTION  
       [0011] Therefore, the present invention provides a method of fabricating the thin film transistor array substrate for the liquid crystal display, in which the source/drain electrode, the data line and the reflective electrode are fabricated together using one photolithography step, improving from the prior art where two photo steps must be needed, so as to reduce the fabrication cost.  
       [0012] To realize at least the advantages mentioned above and avoid the drawbacks from the prior art process, the present invention provides a method of fabricating the thin film transistor array substrate of the reflective liquid crystal display. The method includes providing a substrate, forming a first conductive layer having a gate electrode and a scan line connected with the gate, forming a gate insulating layer covering over the substrate. A channel layer is formed over the gate. The method further includes forming a source/drain electrode region over the substrate, a data line connected with the source/drain electrode region and a second conductive layer serving as a reflective electrode. The characteristic is that the source/drain electrode region, the data line connected with the source/drain electrode region, and the reflective electrode are fabricated with one photolithography step. After that, a protection layer is formed over the substrate. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0013] The invention can be more fully understood by reading the following detailed description of the preferred embodiments with reference made to the accompanying drawings.  
     [0014] FIGS.  1  to  5  are schematic diagrams showing the conventional process flow of fabricating thin film transistor array substrate of reflective liquid crystal display.  
     [0015] FIGS.  6  to  10  are schematic diagrams showing the process flow of fabricating thin film transistor array substrate of reflective liquid crystal display according to one preferred embodiment of the present invention.  
     [0016] FIGS.  11  to  12  are schematic diagrams showing a method of fabricating thin film transistor array substrate of reflective liquid crystal display according to another preferred embodiment of the current invention. 
    
    
     DETAILED DESCRIPTION  
     [0017] Referring to FIG. 6 to FIG. 10, they are schematic diagrams showing the process flow of fabricating thin film transistor array substrate of reflective liquid crystal display according to one preferred embodiment of the present invention. Referring first to FIG. 6, a substrate  200  is provided, where the substrate  200  can include, for example, a transparent glass substrate. A first conductive layer is formed over the substrate  200 , wherein the first conductive layer includes a gate electrode  202  and a scan line (not shown) connected with the gate line  202 . The first conductive layer can include the materials of, for example, nickel (Cr), tantalum (Ta), or other metal materials.  
     [0018] Next, referring to FIG. 7, after forming the first conductive layer, a gate insulating layer  204  is deposited over the substrate  200  and the gate electrode  202 . The gate insulating layer  204  can include, for example, silicon nitride (SiNx) or silicon oxide (SiOx) having a proper dielectric constant ( ).  
     [0019] Referring to FIG. 7 again, after the formation of the gate insulating layer  204 , a channel layer  206  is then formed over the gate insulating layer  204 , which is above the gate electrode  202 . The above mentioned channel layer  206  can be formed by, for example, depositing a blanket amorphous silicon layer, and followed by a photolithographic and etching processes to remove a portion of the amorphous silicon layer other than the gate electrode  202 .  
     [0020] Further, referring to FIG. 8, a bumpy layer  212  is formed at the area where the reflective electrode is determined to locate, for example, at side region of the gate electrode  202  for the image pixel. This bumpy layer  212  can include, for example, an organic bump layer. Since the bumpy layer  212  includes, organic material, from the micro point of view, its upper surface has many concave and convex areas, forming many bumps, which thereby form a bumpy surface  211 . As a result, the reflective electrode (not shown), which is formed later, can have very high reflecting quality.  
     [0021] Next, referring to FIG. 9, a second conductive layer (not shown) is formed over the substrate  200 , where this second conductive layer includes a source/drain electrode  208   a,  a data line (now shown) connected with the source/drain  208   a,  and a reflective electrode  208   b.  The second conductive layer can include metal materials such as, aluminum, nickel, or titanium, which can be used to form the source/drain electrode  208   a  and the reflective electrode  208   b.  Also as shown in FIG. 8, since the bumpy layer  212  provides a bumpy upper surface  211 , which allows the reflective electrode  208   b  to reflect the incident light as well as scatter the incident light into different directions, resulting in a high reflecting quality of the reflective electrode  208   b.    
     [0022] Referring to FIG. 10, a protection layer  210  is formed over the source/drain electrode  208   a  as well as the channel layer  206 , in which the first part of fabricating the thin film transistor array substrate of the reflective liquid crystal display is accomplished.  
     [0023]FIG. 11 and FIG. 12 are schematic diagrams showing another, according to another preferred embodiment of the invention, of fabricating thin film transistor array substrate of reflective liquid crystal display. For a typical thin film transistor structure, since the source/drain electrode  208   a  includes metal material such as aluminum, nickel or titanium, thus when the source/drain electrode  208   a  is directly in contact with the underneath channel layer  206  and the gate insulating layer  204 , there are usually contact and electrical issues. Therefore, in the present invention, after the formation of the channel layer  206  and before the formation of the source/drain electrode  208   a,  a contact layer  214  including, for example, an n-type doped amorphous silicon material (n+a−Si) can be more advantageously formed in between the source/drain electrode layer  208   a,  and the channel layer  206  as well as the gate insulating layer  204 .  
     [0024] Additionally, since the formation of the source/drain electrode  208   a  involves a step of etching process, it often cause the damage of the channel layer  206  due to improper control of the etching process. Therefore, the present invention can further form, for example, an etch stop layer  216  over the channel layer  206  between the contact layer  214 , so as to prevent the channel layer  206  from being damaged.  
     [0025]FIG. 11 shows a schematic diagram of the process step of forming a contact layer  214  at both sides of the channel layer  206  after the channel layer  206  is formed and before the source/drain electrode  208   a  is formed. It also shows that an etch stop layer  216  is formed over the channel layer  206 .  
     [0026] Further, FIG. 2 shows a diagram of the process step where, after forming the bumpy layer  212  and before forming the source/drain electrode  208   a,  a contact layer  214  is formed on both sides of the channel layer  206 , and an etch stop layer  216  is further formed over the channel layer  206 .  
     [0027] From the above detailed descriptions, the present invention includes at least the advantages.  
     [0028] 1. In this invention, the method of fabricating the thin film transistor array substrate of reflective liquid crystal display includes forming the source/drain electrode, the data line and the reflective electrode together with one photolithography process, which greatly simplified the fabrication process.  
     [0029] 2. In this invention, the method of fabricating the thin film transistor array substrate of reflective liquid crystal display further includes forming the source/drain electrode, the data line and the reflective electrode all together with only one photolithography process. It reduces one time for forming the photomask, comparing with the conventional method, thus further reduced the fabrication cost.  
     [0030] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.