Abstract:
The present invention relates to a method for manufacturing an oxide semiconductor thin film transistor and to an actively operating display device and actively operating sensor display device using the same. A method for manufacturing an oxide semiconductor thin film transistor includes: forming a gate electrode by depositing and patterning a gate layer over a substrate; sequentially depositing a gate insulation film, an oxide semiconductor, and an etch stopper over the gate electrode and patterning the etch stopper; patterning the oxide semiconductor; forming a source electrode and a drain electrode over the patterned oxide semiconductor; and depositing a protective layer over the source electrode and the drain electrode and forming a contact hole in the protective layer, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/KR2013/000378 filed on Jan. 17, 2013, which claims priority to Korean Patent Application No. 10-2012-0006730 filed on Jan. 20, 2012, which applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a method for manufacturing an oxide semiconductor thin film transistor and an actively operating display device and actively operating sensor display device using the same, more particularly to a method for manufacturing an oxide semiconductor thin film transistor and an actively operating display device and actively operating sensor display device using the same that increase reliability by supplementing and improving instability against photoelectric fields. 
       RELATED ART 
       [0003]    In recent times, there have been much research and development effort directed towards the thin film transistor that uses an oxide semiconductor as an active layer. The oxide semiconductor thin film transistor is applied to flat panel displays such as those using TFT-LCD and AMOLED, various sensors, operating and logic circuits, etc., due to the advantages it provides, including high electric field mobility, a low threshold voltage near 0V, low current leakage, etc. 
         [0004]    In spite of the above advantages, however, the oxide semiconductor thin film transistor may also entail problems regarding reliability against electric fields and reliability against photoelectric fields. 
         [0005]    Research focused on improving reliability against electric fields have provided stabilization techniques based on improving the material used for the insulation film or the protective layer and improving the structure of the thin film transistor. However, the research efforts conducted worldwide on improving reliability against photoelectric fields have not been much fruitful. 
         [0006]    Specifically, when a negative electric field and light are provided simultaneously, the threshold voltage of the oxide semiconductor thin film transistor may move considerably in the negative direction with the passage of time. 
         [0007]    An oxide semiconductor thin film transistor that uses an oxide semiconductor for the active layer is an electrical element that provides benefits such as high electric field mobility, of 10 cm 2 /Vs or higher, and low current leakage, etc. These can be applied to displays and sensors, etc., which use a switching property, as well as to operating and logic circuits, etc. 
         [0008]      FIG. 1  is a graph illustrating changes in the transition curve properties and electric field mobility of an oxide semiconductor thin film transistor according to the related art under a photoelectric field for a 0.1V drain voltage. 
         [0009]      FIG. 1  shows changes in transition curve properties according to time when an electric field of −20V is applied together with light of 10,000 lux to a thin film transistor using an oxide active layer according to the related art. The graph shows the result that the instability pertaining to the movement of the threshold voltage of the transition curve when photoelectric stress is applied is not improved. 
         [0010]    As such, there is much research being conducted on mechanisms relating to the movement of the threshold voltage, but the problem has not yet been fundamentally resolved. 
       SUMMARY 
       [0011]    An aspect of the present invention is to supplement and improve instability against photoelectric fields and thereby improve reliability by having the oxide semiconductor of the oxide semiconductor thin film transistor deposited with a small thickness. 
         [0012]    Also, an aspect of the present invention is to improve reliability against photoelectric fields without changing or adding to the processing by adjusting the thickness of the oxide semiconductor, and thus enable application to actively operating displays, actively operating sensors, and the like. 
         [0013]    To resolve the problems above, an embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of forming a gate electrode by depositing and patterning a gate layer over a substrate; a second step of sequentially depositing a gate insulation film, an oxide semiconductor, and an etch stopper over the gate electrode and patterning the etch stopper; a third step of patterning the oxide semiconductor; a fourth step of forming a source electrode and a drain electrode over the patterned oxide semiconductor; and a fifth step of depositing a protective layer over the source electrode and the drain electrode and forming a contact hole in the protective layer, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm. 
         [0014]    Another embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of sequentially depositing a buffer layer, an oxide semiconductor, a gate insulation film, and a gate layer over a substrate; a second step of forming a gate electrode by patterning the gate layer; a third step of patterning the oxide semiconductor; a fourth step of depositing a protective layer over the oxide semiconductor and forming a contact hole in the protective layer; and a fifth step of forming a source electrode and a drain electrode over the contact hole, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm. 
         [0015]    Still another embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of depositing and patterning a source electrode and a drain electrode over a substrate; a second step of depositing an oxide semiconductor, a gate insulation film, and a gate layer over the source electrode and the drain electrode; a third step of patterning the gate insulation film and the gate layer; a fourth step of patterning the oxide semiconductor; and a fifth step of depositing a protective layer over the patterned gate insulation film and the oxide semiconductor and forming a contact hole, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm. 
         [0016]    Yet another embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of depositing and patterning a buffer layer and an oxide semiconductor over a substrate; a second step of depositing and patterning a source electrode and a drain electrode over the oxide semiconductor; a third step of forming a gate pattern by depositing a gate insulation film and a gate layer over the source electrode and the drain electrode and patterning the gate layer; and a fourth step of forming and patterning a protective layer over the gate pattern, where the oxide semiconductor is formed to a thickness of 4 nm or smaller. 
         [0017]    Another embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of forming a gate electrode by depositing and patterning a gate layer over a substrate; a second step of depositing a gate insulation film and an oxide semiconductor over the gate electrode; a third step of patterning the oxide semiconductor; a fourth step of forming a source electrode and a drain electrode over the patterned oxide semiconductor; and a fifth step of depositing a protective layer over the source electrode and the drain electrode and forming a contact hole in the protective layer, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm. 
         [0018]    Still another embodiment of the invention provides a method for manufacturing an oxide semiconductor thin film transistor that includes: a first step of forming a gate electrode by depositing and patterning a gate layer over a substrate; a second step of depositing a gate insulation film, a source electrode, and a drain electrode over the gate electrode; a third step of patterning the source electrode and the drain electrode; a fourth step of depositing and patterning an oxide semiconductor over the patterned source electrode and drain electrode; and a fifth step of depositing a protective layer over the patterned oxide semiconductor and forming a contact hole in the protective layer, where the oxide semiconductor is formed to a thickness that is smaller than or equal to 4 nm. 
         [0019]    An actively operating display device including an oxide semiconductor thin film transistor based on an embodiment of the invention may be manufactured according to one of the methods set forth above. 
         [0020]    Also, an actively operating sensor device including an oxide semiconductor thin film transistor based on an embodiment of the invention may be manufactured according to one of the methods set forth above. 
         [0021]    According to an embodiment of the invention, the oxide semiconductor in an oxide semiconductor thin film transistor can be deposited with a small thickness, whereby the instability against photoelectric fields can be supplemented and improved for greater reliability. 
         [0022]    Also, according to an embodiment of the invention, the reliability against photoelectric fields can be improved, without changing or adding to the processing, by adjusting the thickness of the oxide semiconductor, enabling applications to actively operating displays, actively operating sensors, and the like. 
         [0023]    Additional aspects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a graph illustrating changes in the transition curve properties and electric field mobility of an oxide semiconductor thin film transistor according to the related art under a photoelectric field for a 0.1V drain voltage. 
           [0025]      FIG. 2A ,  FIG. 2B ,  FIG. 2C ,  FIG. 2D , and  FIG. 2E  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to an embodiment of the invention. 
           [0026]      FIG. 3A  and  FIG. 3B  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to another embodiment of the invention. 
           [0027]      FIG. 4A ,  FIG. 4B ,  FIG. 4C ,  FIG. 4D , and  FIG. 4E  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to still an embodiment of the invention. 
           [0028]      FIG. 5 ,  FIG. 6 ,  FIG. 7 , and  FIG. 8  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to yet another embodiment of the invention. 
           [0029]      FIG. 9A  is a graph illustrating the current and voltage properties of an oxide semiconductor thin film transistor according to an embodiment of the invention. 
           [0030]      FIG. 9B  is a graph illustrating the output properties of an oxide semiconductor thin film transistor according to an embodiment of the invention. 
           [0031]      FIG. 10A  is a graph illustrating changes in the transition curve properties and electric field mobility of an oxide semiconductor thin film transistor according to an embodiment of the invention under a photoelectric field for a 0.1V drain voltage. 
           [0032]      FIG. 10B  is a graph comparing the output properties of an oxide semiconductor thin film transistor according to an embodiment of the invention before and after photoelectric stress. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    In the following, a detailed description is provided, with reference to the accompanying drawings, for a lighting member based on a preferred mode of practice. In describing the mode of practice, certain descriptions may be omitted for well-known functions or components if they are deemed to unnecessarily obscure the essence of the present invention. Also, the components shown in the drawings may be exaggerated in size for the sake of easier description and understanding; their relative sizes may differ in actual application. 
         [0034]      FIG. 2A  through  FIG. 2E  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to an embodiment of the invention. 
         [0035]    A method for manufacturing an oxide semiconductor thin film transistor according to an embodiment of the invention is described below with reference to  FIGS. 2A to 2   e.    
         [0036]    After depositing a gate electrode  12  over a substrate  11  as illustrated in  FIG. 2A , a gate insulation film  13  may be formed over the gate electrode  12  as illustrated in  FIG. 2B . 
         [0037]    Here, the substrate  11  can be formed as a glass substrate, a plastic substrate, a silicon substrate, or a polymer material formed over the glass substrate, and can also be formed to have an oxidation protection layer deposited over the substrate  11 . 
         [0038]    Also, the gate insulation film  13  can be formed as a silicon oxide film or a silicon nitride film. 
         [0039]    Then, an oxide semiconductor  14  may be formed over the gate insulation film  13 , an etch stopper  15  may be formed deposited over the oxide semiconductor  14 , and the oxide semiconductor  14  may be patterned as illustrated in  FIG. 2C . 
         [0040]    Here, it may be desirable to form the oxide semiconductor  14  to a thickness that is smaller than or equal to 4 nm. 
         [0041]    Thus, according to an embodiment of the invention, the oxide semiconductor  14  may be formed to a thickness of 4 nm or smaller, and as the oxide semiconductor is deposited with a small thickness, the instability to photoelectric fields can be supplemented and improved, for increased reliability. 
         [0042]    An oxide semiconductor  14  in an embodiment of the invention can include any one of indium gallium zinc oxide (Amorphous-InGaZnO4), zinc oxide (ZnO), indium zinc oxide (IZO), indium tin oxide (ITO), zinc tin oxide (ZTO), gallium zinc oxide (GZO), hafnium indium zinc oxide (HIZO), zinc indium tin oxide (ZITO) and aluminum zinc tin oxide (AZTO) in an amorphous or a polycrystalline form. 
         [0043]    Then, a source electrode  18  and a drain electrode  19  may be formed over the patterned oxide semiconductor, as illustrated in  FIG. 2D , a protective layer  20  may be deposited over the source electrode  18  and drain electrode  19 , and a contact hole  21  may be formed in the protective layer  20 . 
         [0044]    Here, the source electrode  18  and the drain electrode  19  can include molybdenum (Mo) or indium tin oxide (ITO), and the protective layer  20  can be formed as a silicon oxide film or a silicon nitride film. 
         [0045]      FIG. 3A  and  FIG. 3B  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to another embodiment of the invention. 
         [0046]    As illustrated in  FIG. 3A , a gate electrode  12  may be deposited over a substrate  11 , and a gate insulation film  13  may be formed over the gate electrode  12 . Here, the substrate  11  can be formed as a glass substrate, a plastic substrate, a silicon substrate, or a polymer material formed over the glass substrate, and can also be formed to have an oxidation protection layer deposited over the substrate  11 . The gate insulation film  13  can be formed as a silicon oxide film or a silicon nitride film. 
         [0047]    Then, an oxide semiconductor  14  may be formed over the gate insulation film  13 , an etch stopper  15  may be deposited over the oxide semiconductor  14 , and the oxide semiconductor  14  may be patterned. Here, it may be desirable to have the oxide semiconductor  14  deposited to a thickness of two or three layers of the molecules of which the oxide semiconductor is composed, with the oxide semiconductor formed to a thickness of 4 nm or smaller. 
         [0048]    Similarly to the embodiment illustrated in  FIGS. 2A to 2E , the embodiment illustrated in  FIGS. 3A and 3B  can also have the oxide semiconductor deposited with a small thickness, so that the instability to photoelectric fields can be supplemented and improved, for increased reliability. 
         [0049]    An oxide semiconductor  14  in an embodiment of the invention can include any one of indium gallium zinc oxide (Amorphous-InGaZnO4), zinc oxide (ZnO), indium zinc oxide (IZO), indium tin oxide (ITO), zinc tin oxide (ZTO), gallium zinc oxide (GZO), hafnium indium zinc oxide (HIZO), zinc indium tin oxide (ZITO) and aluminum zinc tin oxide (AZTO) in an amorphous or a polycrystalline form. 
         [0050]    Then, in the embodiment of  FIG. 3A , a second oxide semiconductor  16  may be deposited over the oxide semiconductor  14  and the etch stopper  15 . In order to improve the current and voltage properties of the oxide semiconductor thin film transistor, the second oxide semiconductor  16  may be deposited with a large thickness of 20 nm over the very thin oxide semiconductor  14  in the ohmic region. 
         [0051]    Then, as illustrated in  FIG. 3B , a source electrode  18  and a drain electrode  19  may be formed over the second oxide semiconductor  16 , a protective layer  20  may be deposited over the source electrode  18  and drain electrode  19 , and a contact hole  21  may be formed in the protective layer  20 . 
         [0052]    Here, the source electrode and the drain electrode can include molybdenum (Mo) or indium tin oxide (ITO), and the protective layer  20  can be formed as a silicon oxide film or a silicon nitride film. 
         [0053]      FIG. 4A  through  FIG. 4E  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to still an embodiment of the invention. 
         [0054]    First, a buffer layer  22 , an oxide semiconductor  14 , a gate insulation film  13 , and a gate layer  12  may be deposited sequentially over a substrate  11 , as illustrated in  FIG. 4A . 
         [0055]    Here, the oxide semiconductor  14  can be deposited to a thickness of two or three layers of the molecules of which the oxide semiconductor is composed, to form a thickness smaller than or equal to 3 nm or 4 nm, and as the oxide semiconductor is thus deposited with a small thickness, the instability to photoelectric fields can be supplemented and improved, for increased reliability. 
         [0056]    Then, as illustrated in  FIG. 4B , a gate electrode  12  may be formed by patterning the gate layer, and as illustrated in  FIG. 4C , the oxide semiconductor  14  may be patterned. 
         [0057]    Then, as illustrated in  FIG. 4D , a protective layer  20  may be deposited, and contact holes  21  may be formed in the protective layer  20 , and as illustrated in  FIG. 4E , a source electrode  16  and a drain electrode  17  may be formed over the contact holes  21  of the protective layer  20 . 
         [0058]      FIG. 5  through  FIG. 8  illustrate a method of manufacturing an oxide semiconductor thin film transistor according to yet another embodiment of the invention. 
         [0059]    To be more specific,  FIG. 5  shows an embodiment for an oxide semiconductor thin film transistor that has an active layer having a thickness of 3 nm or smaller and has a top gate, bottom contact configuration. 
         [0060]    Looking at the embodiment in more detail, a source electrode  18  and a drain electrode  19  may be deposited and patterned over a substrate  11 , and an oxide semiconductor  14 , a gate insulation film  13 , and a gate layer may be deposited over the source electrode  18  and the drain electrode  19 . Then, the gate layer  12  may be patterned, and the gate insulation film  13  may be patterned. Then, a protective layer  20  may be deposited over the patterned gate insulation film  13  and the oxide semiconductor  14 , and a contact hole  21  may be formed. 
         [0061]      FIG. 6  shows an embodiment for an oxide semiconductor thin film transistor that has an active layer having a thickness of 3 nm or smaller and has a top gate, top contact configuration. 
         [0062]    Looking at the embodiment in more detail, a buffer layer and an oxide semiconductor  14  may be deposited and patterned over a substrate  11 , and a source electrode  18  and a drain electrode  19  may be deposited and patterned over the oxide semiconductor  14 . A gate insulation film  13  and a gate layer may be deposited over the source electrode  18  and the drain electrode  19 , and the gate layer may be patterned to form a gate pattern  12 . Then, a protective layer  20  may be formed and patterned over the gate pattern  12 . 
         [0063]      FIG. 7  shows an embodiment for an oxide semiconductor thin film transistor that has an active layer having a thickness of 3 nm or smaller and has a bottom gate, top contact configuration. 
         [0064]    Looking at the embodiment in more detail, a gate electrode  12  may be formed by depositing and patterning a gate layer over a substrate  11 , and a gate insulation film  13  and an oxide semiconductor  14  may be deposited over the gate electrode  12 . Then, the oxide semiconductor  14  may be patterned, and a source electrode  18  and a drain electrode  19  may be formed over the patterned oxide semiconductor  14 . A protective layer  20  may be deposited over the source electrode  18  and the drain electrode  19 , and a contact hole  21  may be formed in the protective layer  20 . 
         [0065]      FIG. 8  shows an embodiment for an oxide semiconductor thin film transistor that has an active layer having a thickness of 3 nm or smaller and has a bottom gate, bottom contact configuration. 
         [0066]    Looking at the embodiment in more detail, a gate electrode  12  may be formed by depositing and patterning a gate layer over a substrate  11 ; a gate insulation film  13 , a source electrode  18 , and a drain electrode  19  may be deposited over the gate electrode  12 ; and the source electrode  18  and the drain electrode may be patterned. Then, an oxide semiconductor  14  may be deposited and patterned over the patterned source electrode  18  and drain electrode  19 ; a protective layer  20  may be deposited over the patterned oxide semiconductor  14 ; and a contact hole  21  may be formed in the protective layer  20 . 
         [0067]    An oxide semiconductor thin film transistor according to an embodiment of the invention as illustrated in  FIGS. 5 to 8  above may have the structure of a regular thin film transistor, but the oxide semiconductor  14  may be formed to a thickness of two or three layers of the molecules of which the oxide semiconductor is composed, such that the oxide semiconductor is formed to a thickness smaller than or equal to 3 nm or 4 nm. 
         [0068]    Thus, similarly to the embodiments described above, the oxide semiconductor can be deposited with a small thickness, so that the instability to photoelectric fields can be supplemented and improved, for increased reliability. 
         [0069]      FIG. 9A  is a graph illustrating the current and voltage properties of an oxide semiconductor thin film transistor according to an embodiment of the invention, and  FIG. 9B  is a graph illustrating the output properties of an oxide semiconductor thin film transistor according to an embodiment of the invention. 
         [0070]    More specifically,  FIG. 9A  shows the current and voltage properties of an oxide semiconductor thin film transistor having a 3 nm thick active layer, and  FIG. 9B  shows the output properties of an oxide semiconductor thin film transistor having a 3 nm thick active layer. 
         [0071]      FIG. 9A  shows the current and voltage properties of an oxide semiconductor thin film transistor having an active layer when the drain voltage is 0.1V and 1V. From the graphs of  FIGS. 9A and 9B , it can be seen that the functions of a thin film transistor is implemented to a sufficient degree, even though a very thin oxide semiconductor active layer of 3 nm is being used. 
         [0072]    That is, as the thin film transistor using a very thin oxide semiconductor active layer of 3 nm allows the flow of a current amounting to several μA, it can sufficiently implement the properties of a switching element. 
         [0073]      FIG. 10A  is a graph illustrating changes in the transition curve properties and electric field mobility of an oxide semiconductor thin film transistor according to an embodiment of the invention under a photoelectric field for a 0.1V drain voltage, and  FIG. 10B  is a graph comparing the output properties of an oxide semiconductor thin film transistor according to an embodiment of the invention before and after photoelectric stress. 
         [0074]    More specifically,  FIG. 10A  shows the changes in the transition curve properties and electric field mobility of an oxide semiconductor thin film transistor having a 3 nm thick active layer under a photoelectric field for a drain voltage of 0.1V, and  FIG. 10B  compares the output properties of an oxide semiconductor thin film transistor having a 3 nm thick active layer before and after photoelectric stress. 
         [0075]      FIG. 10A  shows changes in the transition curves according to time when an electric field of −20V was applied in white light having a luminous intensity of 10,000 lux. With a regular oxide semiconductor thin film transistor, the photoelectric field conditions above would result in a change in threshold voltage of −5V or −10V or more with the passage of time. In contrast, the oxide semiconductor thin film transistor having an active layer thickness of 3 nm according to an embodiment of the invention shows no change in threshold voltage even with photoelectric stress. 
         [0076]    Also,  FIG. 10B  shows the output properties of an oxide semiconductor thin film transistor having an active layer of 3 nm, before and after photoelectric stress is applied. Not only is there no movement of the threshold voltage after photoelectric stress is applied, but also there is no change in current, meaning that there is high stability in the photoelectric properties. 
         [0077]    Particular embodiments of the invention are described above. However, numerous variations can be derived without departing from the scope of the present invention. The technical spirit of the present invention is not to be limited to the embodiments of the invention described above, but is to be defined by the scope of claims as well as the equivalents of the claims.