Abstract:
An embodiment of the invention provides a manufacturing method of a thin film transistor substrate including: sequentially forming a gate electrode, a gate insulating layer covering the gate electrode, an active material layer, and a photo-sensitive material layer on a first substrate; performing a photolithography process by using a half tone mask to form a photo-sensitive protective layer which is above the gate electrode and has a first recess and a second recess; etching the active material layer by using the photo-sensitive protective layer as a mask to form an active layer; removing a portion of the photo-sensitive protective layer at bottoms of the first recess and the second recess to expose a first portion and a second portion of the active layer respectively; forming a first electrode connecting to the first portion; and forming a second electrode connecting to the second portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 100147908, filed on Dec. 22, 2011, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field 
     The present invention relates to a thin film transistor substrate, and in particular relates to a bottom gate thin film transistor substrate. 
     2. Description of the Related Art 
     As display technology progressively develops, everyday life conveniences for people increase, due to the multitude of displays available. Light and thin features are desired for displays. Thus, flat panel displays (FPD) are now the most popular type of displays desired. There are many kinds of FPDs provided, among which liquid crystal displays (LCD) are popular among consumers because of the advantages such as efficient space utilization, low power consumption, no radiance, and low electromagnetic interference (EMI). 
     Liquid crystal displays are mainly formed by a thin film transistor substrate, a color filter substrate and a liquid crystal layer therebetween. The thin film transistor substrate has a plurality of bottom gate thin film transistors. 
     In the related art, the manufacturing process of the bottom gate thin film transistor easily suffers from some problems. For example, the forming of a source electrode and a drain electrode may easily damage an active layer therebelow, which results in back channel damage. 
     BRIEF SUMMARY 
     An embodiment of the invention provides a manufacturing method of a thin film transistor substrate, which includes: providing a first substrate; forming a gate electrode on the first substrate; forming a gate insulating layer covering the gate electrode on the first substrate; forming an active material layer on the gate insulating layer; forming a photo-sensitive material layer on the active material layer; performing a photolithography process on the photo-sensitive material layer by using a half tone mask to pattern the photo-sensitive material layer so as to form a photo-sensitive protective layer, wherein the photo-sensitive protective layer is above the gate electrode and has a first recess and a second recess which do not pass through the photo-sensitive protective layer; etching the active material layer by using the photo-sensitive protective layer as a mask to form an active layer; removing the photo-sensitive protective layer under the first recess and the second recess to expose a first portion and a second portion of the active layer respectively; forming a first electrode connecting to the first portion; and forming a second electrode connecting to the second portion, wherein the first electrode is one of a source electrode and a drain electrode, and the second electrode is another one of the source electrode and the drain electrode. 
     An embodiment of the invention provides a thin film transistor substrate, which includes: a first substrate; a gate electrode disposed on the first substrate; a gate insulating layer disposed on the first substrate and covering the gate electrode; an active layer disposed on the gate insulating layer and located above the gate electrode; a photo-sensitive protective layer disposed on the active layer and exposing a first portion and a second portion of the active layer; a first electrode connecting to the first portion; and a second electrode connecting to the second portion. 
     An embodiment of the invention provides a display, which includes: the thin film transistor substrate described above; a second substrate opposite to the thin film transistor substrate; and a display medium disposed between the thin film transistor substrate and the second substrate. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1A  to  FIG. 1F  are cross-sectional views of a manufacturing process of a thin film transistor substrate according to an embodiment of the present invention; 
         FIGS. 2A to 2D  are top views of  FIGS. 1B to 1E , and  FIGS. 1B to 1E  are cross-sectional views of the structure along a sectional line I-I in  FIGS. 2A to 2D ; 
         FIG. 3A  to  FIG. 3F  are cross-sectional views of a manufacturing process of a thin film transistor substrate according to another embodiment of the present invention; 
         FIGS. 4A to 4D  are top views of  FIGS. 3B to 3E , and  FIGS. 3B to 3E  are cross-sectional views of the structure along a sectional line I-I in  FIGS. 4A to 4D ; and 
         FIG. 5  is a cross-sectional view of a display according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     It is understood, that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numbers and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Furthermore, descriptions of a first layer “on,” “overlying,” (and like descriptions) a second layer, include embodiments where the first and second layers are in direct contact and those where one or more layers are interposing the first and second layers. 
       FIG. 1A  to  FIG. 1F  are cross-sectional views of a manufacturing process of a thin film transistor substrate according to an embodiment of the present invention. Firstly, referring to  FIG. 1A , a first substrate  110  is provided, such as a glass substrate. Then, a gate electrode  120  and a gate insulating layer  130  covering the gate electrode  120  are formed on the first substrate  110 . In one embodiment, the gate  120  may include aluminum (Al), molybdenum (Mo), or other suitable conductive materials. The gate insulating layer  130  includes, for example, silicon dioxide or other dielectric materials with high dielectric constants. 
     Then, an active material layer  140   a  is formed on the gate insulating layer  130 . The active material layer  140   a  includes, for example, indium-gallium-zinc-oxide (IGZO) or other semiconductor materials suitable for serving as an active layer. Then, a photo-sensitive material layer  150   a  is formed on the active material layer  140   a . The photo-sensitive material layer  150   a  includes, for example, a photo-sensitive organic-inorganic hybrid material, wherein the photo-sensitive organic-inorganic hybrid material may include siloxane and acrylic resin. As such, the photo-sensitive material layer  150   a  has photosensitive properties as well as improved chemical resistance because of the silicon content. 
     Then, referring to  FIGS. 1A and 1B , a photolithography process is performed on the photo-sensitive material layer  150   a  by using a half tone mask M to pattern the photo-sensitive material layer  150   a  to form a photo-sensitive protective layer  150 . The half tone mask M has an opaque region A 1 , a semitransparent region A 2  (the light transmittance may be 1% to 99%), and a transparent region A 3 . The photo-sensitive protective layer  150  formed by the photolithography process is formed directly on the gate electrode  120  and has a first recess R 1  and a second recess R 2 , wherein the first recess R 1  and the second recess R 2  both do not penetrate through the photo-sensitive protective layer  150 . The first recess R 1  and the second recess R 2  correspond to the semitransparent region A 2 . 
       FIGS. 2A to 2D  are top views of  FIGS. 1B to 1E , and  FIGS. 1B to 1E  are cross-sectional views of the structure along a sectional line I-I in  FIGS. 2A to 2D . Referring to  FIGS. 1B and 2A , in one embodiment, the first recess R 1  and the second recess R 2  are adjacent to two opposite edges  152  and  154  of the photo-sensitive protective layer  150  respectively. 
     Then, referring to  FIGS. 1C and 2B , the active material layer  140   a  is etched by using the photo-sensitive protective layer  150  as a mask to form an active layer  140 . The etching of the active material layer  140   a  includes, for example, wet etching. In one embodiment, a side wall  142  of the active layer  140  is recessed from a side wall  156  of the photo-sensitive protective layer  150 . Namely, an undercut structure is formed by the etch process. 
     Then, referring to  FIGS. 1D and 2C , a plasma ashing process may be optionally performed on the photo-sensitive protective layer  150  to remove the photo-sensitive protective layer  150  under the first recess R 1  and the second recess R 2  so as to expose a first portion  144  and a second portion  146  of the active layer  140  respectively. In this case, the side wall  142  of the active layer  140  extends beyond the side wall  156  of the photo-sensitive protective layer  150 . 
     It should be noted that, when the active layer  140  includes an oxide semiconductor, an oxygen content of the active layer  140  is inversely proportional to an electrical conductivity of the active layer  140 . Because the plasma ashing process may reduce the oxygen content of the first portion  144  and the second portion  146 , the electrical conductivity of the first portion  144  and the second portion  146  is improved. Therefore, the electrical conductivity of the first portion  144  and the second portion  146  may be higher than that of a third portion  148  of the active layer  140  under the photo-sensitive protective layer  150 . 
     Also, because the photo-sensitive protective layer  150  of the present embodiment has the first recess R 1  and the second recess R 2  not penetrating through the photo-sensitive protective layer  150 , a portion of the active layer  140  may be exposed by removing the photo-sensitive protective layer  150  under the first recess R 1  and the second recess R 2 . After removing the photo-sensitive protective layer  150  under the first recess R 1  and the second recess R 2 , the side wall  142  of the active layer  140  may extend beyond the side wall  156  of the photo-sensitive protective layer  150  to eliminate the undercut structure (formed by etching the active material layer  140   a  by using the photo-sensitive protective layer  150  as a mask), which prevents poor contact between the active layer  140  and the source/drain regions subsequently formed thereon caused by the undercut. 
     Then, referring to  FIG. 1E  and  FIG. 2D , a conductive layer (not shown) is blanketly formed on the gate insulating layer  130  and is patterned by, for example, photolithography and etching to form a first electrode  160  and a second electrode  170  exposing a portion of the photo-sensitive protective layer  150 . The first electrode  160  connects to the first portion  144 , and the second electrode  170  connects to the second portion  146 . The first electrode  160  and the second electrode  170  may serve as a source electrode and a drain electrode. In one embodiment, the first electrode  160  extends from the photo-sensitive protective layer  150  to the gate insulating layer  130  through the first portion  144 , and the second electrode  170  extends from the photo-sensitive protective layer  150  to the gate insulating layer  130  through the second portion  146 . 
     It should be noted that, in the present embodiment, because the first portion  144  and the second portion  146  of the active layer  140  have higher conductivities, the contact resistance between the electrodes (i.e., the first electrode  160  and the second electrode  170 ) and the active layer  140  may be effectively reduced. 
     Also, during formation of the first electrode  160  and the second electrode  170  by etching, the photo-sensitive protective layer  150  of the present embodiment may be used as an etching stop layer to protect the active layer  140  therebelow from etching process damage. Furthermore, removal of the photo-sensitive protective layer  150  is not necessary, which prevents damage of the active layer  140  below the photo-sensitive protective layer  150  from the photoresist stripper. 
     Then, referring to  FIG. 1F , an insulating layer (not shown) is blanketly formed on the first substrate  110 , and then is patterned to form a patterned insulating layer  180  having an opening  182  exposing the second electrode  170 . Then, a conductive layer  190  is formed on the patterned insulating layer  180  and extends into the opening  182  to connect to the second electrode  170 . 
       FIG. 3A  to  FIG. 3F  are cross-sectional views of a manufacturing process of a thin film transistor substrate according to another embodiment of the present invention. It should be noted that, in the present embodiment, elements designed by the same reference numbers as those in  FIGS. 1A to 1F  have the structures and the materials similar thereto, and thus are not repeated herein. 
     Firstly, referring to  FIG. 3A , a first substrate  110  is provided. Then, a gate electrode  120  and a gate insulating layer  130  covering the gate electrode  120  are formed on the first substrate  110 . Then, an active material layer  140   a  is formed on the gate insulating layer  130 . Then, a photo-sensitive material layer  150   a  is formed on the active material layer  140   a.    
     Then, referring to  FIG. 3A  and  FIG. 3B , a photolithography process is performed on the photo-sensitive material layer  150   a  by using a half tone mask M to pattern the photo-sensitive material layer  150   a  to form a photo-sensitive protective layer  150 . The half tone mask M has an opaque region A 1 , a semitransparent region A 2  (the light transmittance may be 1% to 99%), and a transparent region A 3 . The photo-sensitive protective layer  150  formed by the photolithography process is directly on the gate electrode  120  and has a first recess R 1  and a second recess R 2 , wherein the first recess R 1  and the second recess R 2  both do not penetrate through the photo-sensitive protective layer  150 . The first recess R 1  and the second recess R 2  correspond to semitransparent regions A 4  and A 5  respectively. 
       FIGS. 4A to 4D  are top views of  FIGS. 3B to 3E , and  FIGS. 3B to 3E  are cross-sectional views of the structure along a sectional line I-I in  FIGS. 4A to 4D . Referring to  FIG. 3B  and  FIG. 4A , in one embodiment, the first recess R 1  is adjacent to edges  152 ,  153 , and  155  of the photo-sensitive protective layer  150  and is substantially in a U-shape, and the second recess R 2  extends from an edge  154  of the photo-sensitive protective layer  150  inward to an inner of the photo-sensitive protective layer  150 , wherein the first recess R 1  surrounds the second recess R 2 . 
     Then, referring to  FIG. 3C  and  FIG. 4B , the active material layer  140   a  is etched by using the photo-sensitive protective layer  150  as a mask to form an active layer  140 . The etching of the active material layer  140   a  includes, for example, wet etching. In one embodiment, a side wall  142  of the active layer  140  is recessed from a side wall  156  of the photo-sensitive protective layer  150 . Namely, an undercut structure is formed by the etch process. 
     Then, referring to  FIG. 3D  and  FIG. 4C , a plasma ashing process may be optionally performed on the photo-sensitive protective layer  150  to remove the photo-sensitive protective layer  150  under the first recess R 1  and the second recess R 2  so as to expose a first portion  144  and a second portion  146  of the active layer  140  respectively. In this case, the side wall  142  of the active layer  140  extends beyond the side wall  156  of the photo-sensitive protective layer  150 . 
     Then, referring to  FIG. 3E  and  FIG. 4D , a conductive layer (not shown) is blanketly formed on the gate insulating layer  130  and is patterned to form a first electrode  160  and a second electrode  170  exposing a portion of the photo-sensitive protective layer  150 . The first electrode  160  connects to the first portion  144 , and the second electrode  170  connects to the second portion  146 . The first electrode  160  and the second electrode  170  may be used as a source electrode and a drain electrode. In one embodiment, the first electrode  160  extends from the photo-sensitive protective layer  150  to the gate insulating layer  130  through the first portion  144 , and the second electrode  170  extends from the photo-sensitive protective layer  150  to the gate insulating layer  130  through the second portion  146 . 
     Then, referring to  FIG. 3F , an insulating layer (not shown) is blanketly formed on the first substrate  110 , and then is patterned to form a patterned insulating layer  180  having an opening  182  exposing the second electrode  170 . Then, a conductive layer  190  is formed on the patterned insulating layer  180  and extends into the opening  182  to connect to the second electrode  170 . 
       FIG. 5  is a cross-sectional view of a display according to an embodiment of the present invention. Referring to  FIG. 5 , a display  500  of the present embodiment includes a thin film transistor substrate  510 , a second substrate  520 , and a display medium  530  disposed between the thin film transistor substrate  510  and the second substrate  520 . The thin film transistor substrate  510  may be the thin film transistor substrate shown in  FIG. 1F  or  FIG. 3F , and the display medium  530  may be a liquid crystal layer or an organic light emitting layer. The second substrate  520  may be, for example, a color filter substrate or a transparent substrate. 
     In light of the foregoing, the present invention employs a photosensitive material to form the photo-sensitive protective layer, so a half tone mask may be used to perform a photolithography process to form the photo-sensitive protective layer with recesses. The photo-sensitive protective layer of the present invention can serve as an etching mask during etching the active material layer, and also can serve as an etching stop layer during formation of the source electrode and the drain electrode to protect the active layer therebelow. Also, the present invention may optionally use the plasma ashing process to remove the photo-sensitive protective layer under the recesses to expose a portion of the active layer, wherein the plasma ashing process may reduce the oxygen content of the exposed portion of the active layer so as to improve the electrical conductivity of the exposed portion, which reduces the contact resistance between the source electrode, the drain electrode, and the exposed portion. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.