Patent Publication Number: US-10325928-B2

Title: Method of manufacturing thin film transistor, dehydrogenating apparatus for performing the same, and organic light emitting display device including thin film transistor manufactured by the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Republic of Korea Patent Application No. 10-2016-0068618 filed on Jun. 2, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field 
     The present disclosure relates to a method of manufacturing a thin film transistor, a dehydrogenating apparatus for performing the method, and an organic light emitting display device including a thin film transistor manufactured by the same, and more particularly, to a method of manufacturing a thin film transistor, a dehydrogenating apparatus for performing the method, and an organic light emitting display device including a thin film transistor manufactured by the same with an improved film characteristic. 
     Description of the Related Art 
     A flat panel display device such as a liquid crystal display device, a plasma display panel device, and an organic light emitting display device is getting spotlight as a next generation display device due to a small thickness and low power consumption. 
     Specifically, the organic light emitting display device is a self-light emitting display device and does not need a separate light source unlike a liquid crystal display device. Thus, the organic light emitting display device can be manufactured into a lightweight and thin form. Further, the organic light emitting diode display device is advantageous in terms of power consumption since it is driven with a low voltage. Also, the organic light emitting diode display device has a high response speed, a wide viewing angle, and a high contrast ratio (CR). Therefore, the organic light emitting diode display device has been researched as a next-generation display device. 
     The organic light emitting display device includes an organic light emitting diode (OLED) and a thin film transistor connected to the organic light emitting diode. The organic light emitting display device emits light having a specific wavelength based on a driving current transmitted through the thin film transistor. 
     Since the intensity of light generated in the organic light emitting diode is proportional to an intensity of a driving current which is transmitted through the thin film transistor, brightness of a sub pixel including the organic light emitting diode may be adjusted by controlling an amount of the driving current transmitted through the thin film transistor. 
     However, during the process of manufacturing the thin film transistor, a film characteristic of an active layer of the thin film transistor may deteriorate and thus a device characteristic of the thin film transistor in the organic light emitting display device may not be uniform. 
     Specifically, the thin film transistor includes a polysilicon layer, a gate insulating layer on the polysilicon layer, a gate electrode which overlaps the polysilicon layer on the gate insulating layer, and a source electrode and a drain electrode which are connected to the polysilicon layer. The polysilicon layer may be formed of low temperature polycrystalline silicon (LTPS). The LTPS is formed by forming the amorphous silicon layer on the substrate and then crystallizing an amorphous silicon layer using a high energy laser. 
     The amorphous silicon layer may be formed by a plasma enhanced chemical vapor deposition (PECVD) method. The PECVD method is advantageous to enhance a processing speed and lower the cost of a thin film transistor manufacturing process since it has a low processing temperature and a fast deposition speed. However, when the amorphous silicon layer is formed using the PECVD, a silane gas (SiH 4 ) is used as a source gas. In this case, during the process of forming the amorphous silicon layer, a large amount of hydrogen may be contained in the amorphous silicon layer. Hydrogen has a high vapor pressure, so that the hydrogen may easily evaporate. 
     Specifically, when a high energy laser is irradiated onto the amorphous silicon layer during a process of forming the polysilicon layer by crystalizing the amorphous silicon layer, the amorphous silicon layer may be melted and the hydrogen may evaporate through a surface of the melted amorphous silicon layer. In this case, the hydrogen penetrates the surface of the melted amorphous silicon layer to make the surface rough and the melted amorphous silicon layer is crystallized to be hardened as it is, so that the polysilicon layer has a rough surface. The rough surface of the polysilicon layer interrupts the movement of charges through the polysilicon layer, which may deteriorate the device characteristics of the thin film transistor. In order to solve the above-described problem, a dehydrogenation process which removes hydrogen in the amorphous silicon layer is performed before crystalizing the amorphous silicon layer. 
     The dehydrogenation process is performed such that hydrogen from the amorphous silicon layer is escaped by applying heat of approximately 400° C. to the amorphous silicon layer. The hydrogen is removed through the dehydrogenation process so that the problem of degradation of the film characteristic due to hydrogen during the process of crystalizing the amorphous silicon layer may be solved. However, the film characteristic of the polysilicon layer may be degraded due to various elements being entered during the dehydrogenation process. 
     Specifically, the dehydrogenation process is performed by applying heat to the amorphous silicon layer in a chamber under a normal pressure environment (1 atm). However, the environment in the chamber cannot be controlled so that various hetero elements present in the chamber under the high temperature environment may react with the surface of the amorphous silicon layer and may be adsorbed thereon. After completing the dehydrogenation process, during the process of crystalizing the amorphous silicon layer, the hetero elements partially absorbs laser which crystallizes the amorphous silicon layer. Thus, the laser energy may not be uniformly transmitted into the amorphous silicon layer. In this case, when a phase of the amorphous silicon which is melted by the laser energy is transformed from a liquid phase to a solid phase, non-uniform nucleation and non-uniform crystal grain growth may be generated in the amorphous silicon layer. When the crystallization of the amorphous silicon layer is not uniformly performed, the film characteristic of the polysilicon layer is degraded and thus the device characteristic of the thin film transistor may also be degraded. 
     Specifically, a laser which crystallizes the amorphous silicon layer is irradiated onto the substrate in the form of lines with a constant interval so that the polycrystalline layer may have a line shaped rough surface. As a result, the device characteristic of the thin film transistors formed on the lines onto which the laser is irradiated may be degraded. Further, brightness of the organic light emitting diodes connected to the thin film transistors having the degraded device characteristic may be lower than that of the organic light emitting diode in other part. Accordingly, a striped stain may be generated in the organic light emitting display device and the quality of the organic light emitting display device may be degraded. 
     SUMMARY 
     The inventors of the present disclosure recognized that hetero elements in the chamber are adsorbed onto a surface of the amorphous silicon layer during the process of performing the dehydrogenation process to interrupt the crystallization of the amorphous silicon layer and degrade the film characteristic of the polysilicon layer. Accordingly, the inventors of the present disclosure invented a method of manufacturing a thin film transistor which controls an atmosphere in the chamber for performing the dehydrogenation process before performing the dehydrogenation process to minimize adsorption of hetero elements onto the surface of the amorphous silicon layer. 
     An object to be achieved by the present disclosure is to provide a method of manufacturing a thin film transistor, so that the uniformity and roughness of surface of the polysilicon layer is improved and enhanced by reducing an oxygen content in a chamber for performing a dehydrogenation process to a predetermined content, a dehydrogenating apparatus for performing the method, and an organic light emitting display device including a thin film transistor manufactured by the method. Further, another object to be achieved by the present disclosure is to provide a method of manufacturing a thin film transistor, having an enhanced device characteristic through improving a surface roughness of the polysilicon layer and forming substantially uniform a silicon crystal grain of the polysilicon layer, a dehydrogenating apparatus for performing the method, and an organic light emitting display device including a thin film transistor manufactured by the method. 
     Objects of the present disclosure are not limited to the above-mentioned objects, and other objects, which are not mentioned above, can be clearly understood by those skilled in the art from the following descriptions. 
     According to an aspect of the present disclosure, there is provided a method of manufacturing a thin film transistor. The method of manufacturing a thin film transistor includes reducing a content of oxygen in a chamber for performing a dehydrogenation process of an amorphous silicon layer to a predetermined content, inserting a substrate on which the amorphous silicon layer is formed into the chamber, heating the inside of the chamber to perform the dehydrogenation process on the amorphous silicon layer, and forming a polysilicon layer by crystallizing the amorphous silicon layer using a laser. The method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure reduces the content of oxygen in the chamber for performing a dehydrogenation process to a predetermined content. Therefore, adsorption of oxygen and hetero elements onto the surface of the amorphous silicon layer during the dehydrogenation process may be minimized. Therefore, the polysilicon layer formed by crystallizing the amorphous silicon layer has a low surface roughness value (Rq) and has substantially uniform silicon grains. As a result, the thin film transistor formed of a polysilicon layer has an enhanced device characteristic. 
     According to another aspect of the present disclosure, there is provided a dehydrogenating apparatus for manufacturing a thin film transistor. The dehydrogenating apparatus includes a chamber, a substrate support, a gas supplying unit, and a gas exhausting unit. The chamber is a chamber for performing a dehydrogenation process which removes hydrogen of the amorphous silicon layer on the substrate. The substrate support is configured to support the substrate. The gas supplying unit is configured to inject an oxygen content control gas to control a content of oxygen in the chamber during the dehydrogenation process to a predetermined content. The gas exhausting unit is configured to exhaust oxygen in the chamber and the oxygen content control gas together. The dehydrogenating apparatus for manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure incudes a gas supplying unit configured to inject an oxygen content control gas and a gas exhausting unit configured to exhaust oxygen in the chamber and the oxygen content control gas together. Therefore, the content of oxygen in the chamber for a dehydrogenation process is reduced to a predetermined content. Accordingly, adsorption of oxygen and hetero elements onto the surface of the amorphous silicon layer during the dehydrogenation process may be minimized and the surface roughness of the polysilicon layer formed by crystallization of the amorphous silicon layer may be improved. 
     According to still another aspect of the present disclosure, there is provided an organic light emitting display device. The organic light emitting display device includes a polysilicon layer on a substrate, a gate insulating layer which covers the polysilicon layer, a gate electrode which overlaps the polysilicon layer on the gate insulating layer, an interlayer insulating layer which covers the gate insulating layer and the gate electrode, a source electrode and a drain electrode which are connected to the polysilicon layer on the interlayer insulating layer, a planarizing layer which covers the source electrode and the drain electrode, and a thin film transistor which includes an organic light emitting diode (OLED) connected to the source electrode or the drain electrode on the planarizing layer. A surface roughness value (Rq) of the polysilicon layer is 10 nm or less and the surface roughness value (Rq) of the polysilicon layer is defined by a root mean square (rms) value of height values of a curved surface of the polysilicon layer which is measured with respect to the reference plane. The organic light emitting display device according to an exemplary embodiment of the present disclosure includes a thin film transistor including a polysilicon layer which has a low surface roughness value (Rq), substantially uniform polysilicon grains, and slight defect and thus has an enhanced display quality. All the plurality of thin film transistors formed by a polysilicon layer having an enhanced film characteristic has an enhanced device characteristic, so that a precise driving current is supplied to the organic light emitting diode connected to the thin film transistor and organic light emitting diodes emit light at the same gray level. Accordingly, a striped stain caused due to degraded film characteristic of the polysilicon layer may be significantly reduced. 
     Embodiments also relate to a method of manufacturing a polysilicon layer. At least a portion of oxygen is reduced in a chamber to change an amount of oxygen in the chamber from a first value to a second value of 100 ppm or lower. A substrate on which an amorphous silicon layer is formed is inserted into the chamber. A dehydrogenation process is performed in the chamber for the amorphous silicon layer. The amorphous silicon layer is crystallized to form the polysilicon layer. 
     Embodiments also relate to an electroluminescence (EL) display device. The EL device includes a substrate, a thin film transistor (TFT) on the substrate, and an EL device coupled to the TFT. The TFT includes a polysilicon active layer. A surface roughness of the polysilicon active layer is 10 nm or lower, where the surface roughness of the polysilicon active layer is defined as the root mean square (RMS) of deviations of surfaces of the polysilicon active layer from a reference plane. 
     Embodiments also relate to a method of forming a TFT including a gate electrode, a polysilicon layer, a gate insulation layer, a source electrode, and a drain electrode. For forming the polysilicon layer, an amorphous silicon layer is formed on a substrate. An oxygen content control gas is injected into a chamber. A portion of oxygen is exhausted from the chamber together with at least a portion of the injected oxygen content control gas. The substrate with the amorphous silicon layer is inserted into the chamber. A dehydrogenation process is performed in the chamber for the amorphous silicon layer. The amorphous silicon layer is crystallized to form the polysilicon layer. 
     Other detailed matters of the exemplary embodiments are included in the detailed description and the drawings. 
     According to the present disclosure, it is possible to minimize adsorption of oxygen and hetero elements onto the surface of the amorphous silicon layer, reduce a surface roughness of the polysilicon layer formed from the amorphous silicon layer, and uniformly form silicon crystal grains of the polysilicon layer. 
     Further, it is possible to improve the device characteristic of the thin film transistor, provide precise driving current to the organic light emitting diode connected to the thin film transistor, and significantly reduce a striped stain caused by the degraded film characteristic of the polysilicon layer. 
     The effects according to the present disclosure are not limited to the contents exemplified above, and more various effects are included in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic plan view illustrating an organic light emitting display device according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is a flowchart explaining a method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIGS. 3A to 3D  are cross-sectional views explaining a method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIGS. 4A to 4C  are cross-sectional views explaining a comparative method of manufacturing a thin film transistor. 
         FIG. 5  is a graph explaining an improved surface roughness of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIGS. 6A and 6B  are atomic-force microscopy (AFM) images explaining an improved surface roughness of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIGS. 7A and 7B  are scanning electron microscope (SEM) images explaining an improved crystallization uniformity of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIG. 8  is a schematic perspective view explaining a dehydrogenating apparatus for manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure. 
         FIG. 9A  is a schematic cross-sectional view taken along the line XI-XI′ of  FIG. 8 . 
         FIG. 9B  is a partial enlarged cross-sectional view of a region A of  FIG. 9A . 
         FIG. 10  is a schematic cross-sectional view taken along the line X-X′ of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Advantages and characteristics of the present disclosure and a method of achieving the advantages and characteristics will be clear by referring to exemplary embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to exemplary embodiment disclosed herein but will be implemented in various forms. The exemplary embodiments are provided by way of example so that a person of ordinary skilled in the art can fully understand the disclosures of the present disclosure and the scope of the present disclosure. 
     The shapes, sizes, ratios, angles, numbers, and the like illustrated in the accompanying drawings for describing the exemplary embodiments of the present disclosure are merely examples, and the present disclosure is not limited thereto. Like reference numerals generally denote like elements throughout the specification. Further, in the following description of the present disclosure, a detailed explanation of known related technologies may be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. The terms such as “including,” and “having” used herein are generally intended to allow other components to be added unless the terms are used with the term “only”. Any references to singular may include plural unless expressly stated otherwise. 
     Components are interpreted to include an ordinary error range even if not expressly stated. 
     When the position relation between two parts is described using the terms such as “on”, “above”, “below”, and “next”, one or more parts may be positioned between the two parts unless the terms are used with the term “immediately” or “directly” is used. 
     When an element or layer is disposed “on” other element or layer, another layer or another element may be interposed directly on the other element or therebetween. 
     Although the terms “first”, “second”, and the like are used for describing various components, these components are not confined by these terms. These terms are merely used for distinguishing one component from the other components. Therefore, a first component to be mentioned below may be a second component in a technical concept of the present disclosure. 
     Like reference numerals generally denote like elements throughout the specification. 
     A size and a thickness of each component illustrated in the drawing are illustrated for convenience of description, and the present disclosure is not limited to the size and the thickness of the component illustrated. 
     The features of various embodiments of the present disclosure can be partially or entirely coupled to or combined with each other and can be interlocked and operated in technically various ways, and the embodiments can be carried out independently of or in association with each other. 
     Hereinafter, various exemplary embodiments of the present disclosure will be described in detail with reference to accompanying drawings. 
       FIG. 1  is a schematic plan view illustrating an organic light emitting display device according to an exemplary embodiment of the present disclosure. An organic light emitting display device  100  according to an exemplary embodiment of the present disclosure includes a substrate  111 , a thin film transistor  120 , and an organic light emitting diode  140 . Even though one thin film transistor  120  and one organic light emitting diode  140  are illustrated in  FIG. 1 , the organic light emitting display device  100  according to the exemplary embodiment of the present disclosure includes a plurality of thin film transistors  120  disposed on the substrate  111  in a matrix and a plurality of organic light emitting diodes  140 . The organic light emitting diodes  140  configure one sub pixel and adjacent sub pixels form a group to be configured as a pixel. 
     The substrate  111  supports and protects several components of the organic light emitting display device  100 . The substrate  111  may be formed of an insulating material, for example, may be formed of glass or a plastic material. 
     The thin film transistor  120  is disposed on a buffer layer  112  on the substrate  111 . The buffer layer  112  may suppress moisture or impurities from permeating through the substrate  111  and planarize an upper portion of the substrate  111 . However, the buffer layer  112  is not an essential component and whether to form the buffer layer  112  is determined depending on a type of substrate  111  or a type of thin film transistor (TFT). 
     The thin film transistor  120  is disposed on the buffer layer  112  and supplies a signal to the organic light emitting diode  140 . The thin film transistor  120  includes a polysilicon layer  122 , a gate electrode  124 , a source electrode  125 , and a drain electrode  126 . Specifically, the polysilicon layer  122  is formed on the buffer layer  112  and the gate insulating layer  113  which covers the polysilicon layer  122  and insulates the gate electrode  124  from the polysilicon layer  122  is formed on the polysilicon layer  122 . Further, the gate electrode  124  is formed on the gate insulating layer  113  to overlap the polysilicon layer  122  and an interlayer insulating layer  114  is formed to cover the gate electrode  124  and the gate insulating layer  113 . The source electrode  125  and the drain electrode  126  which are connected to the polysilicon layer  122  are formed on the interlayer insulating layer  114 . 
     The polysilicon layer  122  is formed of low temperature polycrystalline silicon (LTPS). The polysilicon layer  122  is formed by crystallizing an amorphous silicon layer using a high energy laser after forming the amorphous silicon layer on the buffer layer  112 . Detailed description thereof will be provided with reference to  FIGS. 2 to 3D . 
     The polysilicon layer  122  has a flat top surface. Specifically, the polysilicon layer  122  has a low surface roughness and for example, has a surface roughness of 10 nm or lower. Here, the surface roughness is a physical quantity representing a degree of roughness of a specific surface. In one embodiment, the surface roughness value (R q ) is defined as a root mean square (RMS) value of deviation values of curved surfaces of an actual polysilicon layer  122  with respect to an ideally flat reference plane. When the surface of the polysilicon layer  122  is ideally flat, the reference plane refers to the same plane as the surface and becomes a referential point for measuring a height. Specifically, the surface roughness value (R q ) is defined by the following Equation 1. 
     
       
         
           
             
               
                 
                   
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                                 z 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
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                   [ 
                   
                     Equation 
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                     1 
                   
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     Here, R q  is a surface roughness value, 1 means a measurement area where the height of the surface is measured, and z(x) means a height value at a point which is spaced apart from a referential point for measuring the height of the surface by x on the plane. 
     Therefore, when the polysilicon layer  122  has a surface roughness valued (R q ) of 10 nm or less, it means that the RMS value of the surface height values of the polysilicon layer  122  measured with reference to the reference plane is 10 nm or less. That is, the surface roughness value (R q ) indicates flatness of the surface and the lower the surface roughness value (R q ) value, the flatter the surface. The organic light emitting display device according to the exemplary embodiment of the present disclosure includes the thin film transistor  120  equipped with the polysilicon layer  122  having an enhanced surface roughness value (R q ) of 10 nm or less. The polysilicon layer can have a uniform thickness by improving the roughness of the surface where the polysilicon layer is formed. Therefore, the thin film transistor  120  may transmit a precise driving current corresponding to a data voltage to the organic light emitting diode  140  and the organic light emitting diode  140  may emit light at a gray level corresponding to the data voltage. Detailed description thereof will be provided with reference to  FIGS. 4A to 4C . 
     Further, the polysilicon layer  122  has a silicon crystal grain which is uniformly grown and the silicon crystal grain has slight defects. In other words, the polysilicon layer  122  has an enhanced film characteristic. Specifically, the polysilicon layer  122  may include substantially uniform silicon crystal grains having a size of 0.13 μm to 0.75 μm and the silicon crystal grains may be uniformly disposed. Detailed description thereof will be provided with reference to  FIGS. 6A to 7B . 
     In  FIG. 1 , for the convenience of description, among various thin film transistors  120  which may be included in the organic light emitting display device  100 , a driving thin film transistor  120  which is connected to the organic light emitting diode  140  is illustrated. However, the organic light emitting display device  100  may further include a switching thin film transistor or a capacitor which drives the organic light emitting diode  140 . Further, even though in the present disclosure, it is described that the thin film transistor  120  has a coplanar structure, an inverted staggered thin film transistor  120  may also be used. 
     A planarizing layer  115  which covers the source electrode  125  and the drain electrode  126  is disposed on the thin film transistor  120 . The planarizing layer  115  is a layer which planarizes an upper portion of the substrate  111  and may be formed of an organic insulating layer to cover a step portion of the upper portion of the substrate  111 . The planarizing layer  115  includes a contact hole which electrically connects the thin film transistor  120  to the anode  141  of the organic light emitting diode  140 . 
     The organic light emitting diode  140  is disposed on the planarizing layer  115  and includes an anode  141 , an organic layer  142 , and a cathode  143 . 
     The anode  141  is an electrode which supplies holes to the organic layer  142  and may be configured by a transparent conductive material having a high work function. The transparent conductive material may include ITO, IZO, or ITZO, but is not limited thereto. Here, the anode  141  may also be referred to as a pixel electrode. 
     The cathode  143  is an electrode which supplies electrons to the organic layer  142 . The cathode  143  may be configured by a metal having a relatively low work function, for example, silver, titanium (Ti), aluminum, molybdenum (Mo), and an alloy (Ag:Mg) of silver and magnesium. Here, the cathode  143  may also be referred to as a common electrode. 
     The organic layer  142  is disposed between the anode  141  and the cathode  143 . The organic layer  142  includes an organic light emitting layer. As illustrated in  FIG. 1 , the organic layer  142  may be commonly formed for all sub pixels on the substrate  111 . In this case, the organic light emitting layer of the organic layer  142  may be formed of a material which emits white light and a color filter may be disposed to correspond to an area where the organic light emitting layer emits light. 
     In addition to the organic light emitting layer, the organic layer  142  may further includes an injecting layer or a transporting layer which improve an emission efficiency of the organic light emitting diode  140 . For example, in addition to the organic light emitting layer, a hole injecting layer or a hole transporting layer is further disposed between the anode  141  and the cathode  143  to smoothly move the holes. The hole injecting layer or the hole transporting layer may have a common structure to be commonly disposed in the plurality of sub pixels. 
     A bank layer  116  may define a sub pixel and exposes a part of a top surface of the anode  141 . Specifically, the bank layer  116  may be disposed to cover an edge of the anode  141 . The bank layer  116  is formed of an insulating material which insulates anodes  141  of the adjacent sub pixels from each other. 
       FIG. 2  is a flowchart explaining a method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure.  FIGS. 3A to 3D  are cross-sectional views explaining a method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure. The method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure is characterized by a method of forming a polysilicon layer  122  of a thin film transistor. Therefore, in  FIGS. 2 to 3D , the method of forming a polysilicon layer  122  is illustrated, but the remaining of the method of manufacturing a thin film transistor is not illustrated. For the convenience of description, when  FIGS. 2 to 3D  are described,  FIG. 1  may also be referred to. 
     First, the buffer layer  112  is formed on the substrate  111 . The buffer layer  112  may be formed of silicon oxide (SiOx) and/or silicon nitride SiNx and may be formed on the substrate by a chemical vapor deposition (CVD) method or a PECVD method. 
     The amorphous semiconductor layer  121  is formed on the buffer layer  112 . The amorphous silicon layer  121  may be deposited by the PECVD method using silane (SiH 4 ) as a source gas. The PECVD method has a low deposition temperature of 400° C. and a high deposition speed, so that it is advantageous in that a cost and a time for the manufacturing process of the thin film transistor  120  are saved. The amorphous silicon layer  121  formed on the buffer layer  112  is formed to be a polysilicon layer  122  through a dehydrogenation process and a laser annealing process. This will be described in detail with reference to  FIGS. 2 to 3D . 
     Referring to  FIGS. 2 and 3A , in the method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure, a content of oxygen  131  in the chamber for performing the dehydrogenation process of the amorphous silicon layer  121  is reduced to a predetermined content (S 210 ). A content of oxygen  131  in the chamber may refer to an amount of oxygen gas (e.g., in units of moles, g) and/or a concentration of oxygen gas (e.g., in units of moles/volume, ppm). For example, an amount of oxygen in the chamber may be reduced from a first value to a second value smaller than the first value. 
     As illustrated in  FIG. 3A , there may be various hetero elements  130  in the chamber for performing the dehydrogenation process. For example, in the chamber for performing the dehydrogenation process, various hetero elements  130  such as oxygen  131 , sulfur  132 , boron  133 , and ammonia  134  may be present. The hetero elements  130  do not react with the amorphous silicon layer  121 , but may be adsorbed onto a surface of the amorphous silicon layer  121 . Various hetero elements  130  are present in the chamber and a content of oxygen  131  may be particularly high. Specifically, 200,000 ppm or higher of oxygen  131  may be contained in the chamber. Oxygen  131  may be adsorbed onto the surface of the amorphous silicon layer  121  to interrupt crystallization of the amorphous silicon layer  121 , so that it is necessary to reduce the content of oxygen  131  in the chamber to a predetermined content before inputting the substrate  111  in the chamber. 
     Specifically, the content of oxygen  131  in the chamber may be reduced to a value below a threshold. In one embodiment, the content of oxygen  131  is reduced to 100 ppm or less. In order to reduce the content of oxygen  131  in the chamber to 100 ppm or less, an oxygen content control gas may be injected. The oxygen content control gas is a gas having a low reactivity and may use a gas which is formed of an element which is hardly adsorbed onto the surface of the amorphous silicon layer  121 . For example, as illustrated in  FIG. 3A , a nitrogen gas N 2  may be used as the oxygen content control gas. However, the oxygen content control gas is not limited to the nitrogen gas (N 2 ), but inert gas which has a low reactivity and is hardly adsorbed onto the surface of the amorphous silicon layer  121  may be used as the oxygen content control gas. For example, argon gas Ar may also be used as the oxygen content control gas. 
     The nitrogen gas (N 2 ) is injected through a gas supplying unit disposed on one side of the chamber and is discharged through a gas exhausting unit disposed on the other side of the chamber. The hetero elements  130  including the oxygen  131  in the chamber are discharged to the gas exhausting unit in accordance with floating of the nitrogen gas (N 2 ) so that the content of oxygen  131  in the chamber may be reduced. Thus, oxygen content in the chamber may be reduced by injecting the oxygen content control gas into the chamber and exhausting at least a portion of the injected oxygen content control gas from the chamber together with at least a portion of oxygen in the chamber. 
     Nitrogen gas N 2  is consistently supplied at an appropriate flow rate to sufficiently purge oxygen  131  in the chamber. The oxygen content control gas may be injected at a first flow rate before the hydrogenation process. For example, Nitrogen gas N 2  may be consistently supplied at a flow rate of 150 slm (standard liter per minute) for 10 minutes or more. 
     As described above, the oxygen content in the chamber may be reduced before inserting the substrate  111 . Therefore, the substrate  111  is not disposed on a substrate support  361  in  FIG. 3A . The substrate support  361  is configured to support the substrate  111  below the substrate  111  during the dehydrogenation process. 
     In some exemplary embodiments, the atmosphere in the chamber is formed to be vacuous so that the content of oxygen  131  may be reduced. In this case, a pressure in the chamber is reduced to be an atmospheric pressure (1 atm) or less and the atmosphere in the chamber becomes vacuous, so that the content of oxygen  131  is reduced. 
     Referring to  FIGS. 2 and 3B , the substrate  111  on which the amorphous silicon layer  121  is formed is inputted into the chamber (S 220 ). 
     The substrate  111  is inputted through a substrate insertion slot of the chamber and is located on the substrate support  361  in the chamber. Even though one substrate  111  is located on the substrate support  361  in  FIG. 3B , a plurality of substrates  111  may be inputted into the chamber in a batch type. In this case, a plurality of substrate supports  361  may be disposed in the chamber. 
     When the substrate  111  is inputted into the chamber, the content of oxygen  131  in the chamber is continuously maintained to be 100 ppm or less. To this end, the oxygen content control gas may consistently flow therein. For example, the nitrogen gas (N 2 ) may consistently flow therein through a gas inlet. In this case, the nitrogen gas (N 2 ) flows to float above the amorphous silicon layer  121  as illustrated in  FIG. 3B  so that the nitrogen gas (N 2 ) injected through the gas inlet does not affect the surface of the amorphous silicon layer  121 . 
     The nitrogen gas (N 2 ) flows therein at an appropriate flow rate so as not to affect the surface of the amorphous silicon layer  121  while maintaining the content of oxygen to be 100 ppm or lower. The oxygen content control gas may be injected after the substrate  111  is inputted in the chamber at a second flow rate smaller than the first flow rate. For example, the nitrogen gas (N 2 ) may flow at a flow rate of 10 slm. 
     Since the content of oxygen  131  in the chamber is 100 ppm or less, oxygen  131  may be hardly adsorbed onto the surface of the amorphous silicon layer  121 . Therefore, during the subsequent dehydrogenation process, the amorphous silicon layer  121  may be uniformly crystallized. 
     Referring to  FIGS. 2 and 3C , the chamber is heated to perform the dehydrogenation process on the amorphous silicon layer  121  (S 230 ). 
     As described above, the amorphous silicon layer  121  may be formed by the PECVD method and in the PECVD method, silane is used as a source gas. Therefore, a large amount of hydrogen may be included in the amorphous silicon layer  121 . For example, hydrogen may be contained in the amorphous silicon layer  121  at a ratio of 13% or higher as compared with a content of amorphous silicon. When the amorphous silicon  121  is crystallized without removing hydrogen in the amorphous silicon layer  121 , hydrogen may cause the surface of the polysilicon layer  122  to be rough. 
     Specifically, a high energy laser may be irradiated onto the amorphous silicon layer  121  to crystallize the amorphous silicon layer  121 . Hydrogen has a high vapor pressure, so that the hydrogen may quickly evaporate. When the laser is irradiated onto the amorphous silicon layer  121  so that the amorphous silicon layer is melted, the hydrogen may evaporate through the surface of the melted amorphous silicon layer  121 . When the hydrogen penetrates the surface of the melted amorphous silicon layer  121 , the surface of the amorphous silicon layer  121  may become uneven. Further, the melted amorphous silicon layer is crystallized so that the uneven surface may be hardened as it is. In this case, the polysilicon layer  122  has an uneven surface and the surface roughness of the polysilicon layer  122  may be increased. The uneven surface of the polysilicon layer  122  interrupts movement of charges, so that the thin film transistor  120  including the polysilicon layer  122  having a high surface roughness may have a degraded device characteristic. 
     In order to prevent the above-described problem, hydrogen in the amorphous silicon layer  121  may be removed before irradiating a laser onto the amorphous silicon layer  121 . To this end, the chamber may be heated at a predetermined temperature. For example, the chamber may be heated at a temperature of 400° C. to 500° C. In this case, hydrogen in the amorphous silicon layer  121  evaporates by breaking a silicon-hydrogen bond in the amorphous silicon layer  121  at a high temperature environment and a content of hydrogen in the amorphous silicon layer  121  may be reduced. 
     The dehydrogenation process may be performed until the content of hydrogen in the amorphous silicon layer  121  is sufficiently reduced. For example, the dehydrogenation process may be performed to reduce the content of hydrogen in the amorphous silicon layer  121  to 1% or less as compared with amorphous silicon before performing the dehydrogenation process. To this end, the chamber may be heated at a temperature of 400° C. to 500° C. for approximately 15 minutes. 
     In the meantime, the content of oxygen  131  in the chamber may be maintained to be 100 ppm or less during at least a part of the dehydrogenation process, or throughout the entire dehydrogenation process. To this end, the oxygen content control gas may consistently flow in the chamber. The oxygen content control gas may be injected during the dehydrogenation process in the chamber at a third flow rate smaller than the first flow rate. For example, the oxygen content control gas may consistently flow thereon at a flow rate of 10 slm during the dehydrogenation process. 
     Since the content of oxygen  131  in the chamber is 100 ppm or less, a small amount of oxygen  131  is present in the chamber and the number of oxygen  131  which is adsorbed onto the surface of the amorphous silicon layer  121  may be correspondingly reduced during the dehydrogenation process. Therefore, the increase of the surface roughness value (Rq) of the polysilicon layer  122  due to the adsorption of oxygen  131  may be sufficiently reduced. In order to completely suppress the adsorption of oxygen, an environment where no oxygen  131  is present in the chamber needs to be ideally provided. However, it is difficult to actually provide such an environment and it may increase the processing cost and time. However, in the method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure, the oxygen content control gas is sprayed for 10 minutes to reduce the content of oxygen  131  to 100 ppm or less and then the dehydrogenation process is performed. Therefore, the oxygen  131  which is adsorbed onto the amorphous silicon layer  121  is sufficiently reduced until the dehydrogenation process ends from the beginning of the dehydrogenation process and the increase of the processing cost and time may be minimized. 
     Referring to  FIGS. 2 and 3D , the amorphous silicon layer  121  is crystallized using a laser, to form the polysilicon layer  122  (S 240 ). 
     A laser annealing process for forming the polysilicon layer  122  may be performed in a separate annealing chamber which is different from a chamber for performing the dehydrogenation process. 
     The laser annealing process may be performed using a high energy laser. For example, the amorphous silicon layer  121  may be crystallized using an excimer laser. Specifically, the excimer laser is irradiated onto the amorphous silicon layer  121  in the form of lines with a constant interval and the amorphous silicon layer  121  may be melted by energy of the laser. A nucleation site may be formed in the melted amorphous silicon layer  121  and the silicon is crystallized with respect to the nucleation site to form crystal grains of polysilicon. By the laser annealing process, the polysilicon layer  122  is formed. 
     Thereafter, the polysilicon layer  122  may be patterned. For example, the polysilicon layer  122  may be patterned by a photolithograph process and the thin film transistor  120  is formed in a region where the patterned polysilicon layer  122  is disposed. 
     In the meantime, the gate insulating layer  112  is formed to cover the patterned polysilicon layer  122  and the gate electrode  124  is formed to overlap the polysilicon layer  122 . Further, impurities are doped on the polysilicon layer  122  using the gate electrode  124  as a mask and the interlayer insulating layer  113  is formed to cover the gate electrode  124  and the gate insulating layer  112 . Thereafter, a hole is formed in the interlayer insulating layer  113  and the gate insulating layer  112  to expose the polysilicon layer  122  through the interlayer insulating layer  113  and the gate insulating layer  112  and the source electrode  125  and the drain electrode  126  which are in contact with the polysilicon layer  122  through a hole are formed. The gate insulating layer  112 , the gate electrode  124 , the interlayer insulating layer  113 , the source electrode  125 , and the drain electrode  126  may be formed by a known method. 
     A feature in that the content of oxygen in the chamber for performing the dehydrogenation process is controlled to a predetermined content to improve the film characteristic of the polysilicon layer  122  has been described in the present disclosure. However, the oxygen content control gas may be configured not only to control the content of oxygen in the chamber but also to purge hetero elements  130  in the chamber. 
     The method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure controls the atmosphere in the chamber for the dehydrogenation process before performing the dehydrogenation process on the amorphous silicon layer  121 . Specifically, according to the method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure, the content of oxygen  131  in the chamber is reduced to a predetermined content. In order to adjust the content of oxygen  131  in the chamber, the oxygen content adjusting gas flow into the chamber or a pressure in the chamber is lowered to 1 atm or less to form the status in the chamber to be a vacuous state. The content of oxygen  131  in the chamber may be reduced to 100 ppm or less. During the dehydrogenation process, the content of oxygen  131  in the chamber may be maintained to be 100 ppm or less. In this case, adsorption of the oxygen  131  onto the surface of the amorphous silicon layer  121  during the dehydrogenation process may be minimized and the polysilicon layer  122  formed by the laser annealing process may have low surface roughness value (Rq) and have polysilicon grains which are grown with a substantially uniform size. In contrast, when the dehydrogenation process is performed in a chamber where the content of oxygen  131  is not controlled, a large quantity of oxygen  131  may be adopted onto the surface of the amorphous silicon layer  121  during the dehydrogenation process. Therefore, the surface roughness value (Rq) of the polysilicon layer  122  is increased, the silicon crystal grains have non-uniform sizes and defect may be generated in the silicon crystal grains. Detailed description thereof will be provided with reference to  FIGS. 4A to 4C . 
       FIGS. 4A to 4C  are cross-sectional views explaining a method of manufacturing a thin film transistor. 
     Referring to  FIGS. 4A to 4C , when the content of oxygen  131  is not controlled during the dehydrogenation process, the polysilicon layer  122  may have a high surface roughness and also have silicon crystal grains with non-uniform sizes and arrangements. 
     Specifically, as illustrated in  FIG. 4A , in the chamber where the content of oxygen  131  is not controlled, 200,000 ppm or higher of oxygen may be contained. When the dehydrogenation process is performed in the chamber where a large amount of oxygen  131  is contained, oxygen  131  actively moves under a high temperature chamber atmosphere to be easily adsorbed onto the surface of the amorphous silicon layer  121 . 
     After completing the dehydrogenation process, as illustrated in  FIG. 4B , a laser may be irradiated onto the amorphous silicon layer  121  onto which oxygen  131  has been adsorbed. In this case, the oxygen  131  adsorbed onto the surface of the amorphous silicon layer  121  may partially absorb an energy of the laser or scatter the laser during the laser annealing process. In this case, due to the oxygen  131 , the laser energy may not be properly transferred to the amorphous silicon layer  121  and the amorphous silicon layer  121  may not be uniformly melted. Therefore, the nucleation site NS in the melted amorphous silicon layer  121  may be non-uniformly formed. 
     Silicon in the amorphous silicon layer  121  is crystallized with respect to the nucleation site which is non-uniformly formed to form silicon crystal grains. Therefore, as illustrated in  FIG. 4C , the silicon crystal grains may be formed to have non-uniform sizes. Further, the silicon is crystallized with respect to the nucleation site which is non-uniformly formed, so that arrangement of the silicon crystal grains may be non-uniform and various defects may be generated in the silicon crystal grains. 
     In the meantime, the oxygen  131  adsorbed onto the surface of the amorphous silicon layer  121  absorbs the energy of the laser during the laser annealing process, so that a melting degree of the amorphous silicon layer in a portion where the oxygen  131  is adsorbed may be different from a melting degree of the amorphous silicon layer in a portion where the oxygen  131  is not adsorbed. A phase of the amorphous silicon which is melted to a liquid phase is transformed to a solid phase and volume thereof may expand. Further, a degree of volume expansion of the amorphous silicon in a portion where the oxygen  131  is adsorbed may be different from a degree of volume expansion of the amorphous silicon in a portion where the oxygen  131  is not adsorbed. Due to the difference of expansion, as illustrated in  FIG. 4C , the polysilicon layer  122  may have uneven surface and include silicon crystal grains G with non-uniform sizes, non-uniform arrangement, and defects D. Therefore, the film characteristic of the polysilicon layer  122  may be degraded. 
     The movement of charges of the polysilicon layer  122  may be interrupted due to the above-described degraded film characteristic of the polysilicon layer  122  and an amount of current flowing through the polysilicon layer  122  may be reduced. Accordingly, the thin film transistor  120  including a polysilicon layer  122  with a degraded film characteristic may not smoothly transfer the charges as compared with the thin film transistor  120  including a polysilicon layer  122  with an enhanced film characteristic. Further, a device characteristic thereof may be degraded. 
     Further, a laser is irradiated in the form of lines with a constant interval during the laser annealing process, so that a striped curve may be formed on the surface of the polysilicon layer  122  along the line to which the laser is irradiated. Specifically, when the laser is irradiated in a region where the oxygen  131  is adsorbed in the form of lines, there may be a problem in that the oxygen  131  not only partially absorbs the laser energy but also scatters the laser. In this case, in a region where a relatively large amount of oxygen  131  is adsorbed, a large amount of laser may be scattered and the amorphous silicon on the line on which the laser is irradiated may be relatively less melted. As described above, the degree of volume expansion which is generated while the amorphous silicon is crystallized may vary depending on the melting degree of the amorphous silicon so that the surface of the polysilicon layer  122  may be formed to be curved along the line on where the laser is irradiated. The polysilicon layer  122  with a line shaped curved surface is patterned to be formed as a thin film transistor  120 . Specifically, the thin film transistors  120  are formed in a matrix to configure sub pixels in the form of a matrix, so that the thin film transistor  120  on a specific line may include a polysilicon layer  122  with a degraded film characteristic. Therefore, the thin film transistors  120  on a specific line may have a degraded device characteristic as compared with thin film transistor  120  in another region. As mentioned above, the thin film transistor  120  with the degraded device characteristic may not satisfactorily transfer the current as compared with the thin film transistor  120  with a normal characteristic. Therefore, an organic light emitting diode  140  which is connected to the thin film transistor  120  with the degraded device characteristic may emit light at a lower gray level than an organic light emitting diode  140  which is connected to a thin film transistor  120  with a normal characteristic. Therefore, a striped stain may be generated in the organic light emitting display device. 
     However, in the method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure, the content of oxygen  131  in the chamber is lowered to 100 ppm or lower before performing the dehydrogenation process, so that the amount of oxygen  131  which is adsorbed onto the surface of the amorphous silicon layer  121  may be reduced. Therefore, absorption of laser energy by the oxygen  131  which is adsorbed onto the surface of the amorphous silicon layer  121  during the laser annealing process may be minimized. Accordingly, the amorphous silicon layer  121  may receive substantially uniform energy and nucleation sites NS may be uniformly formed in the melted amorphous silicon layer  121 . As a result, the silicon may be uniformly crystallized, the crystallized silicon crystal grains G may be grown with a substantially uniform size, and arrangement of the silicon crystal grains G may become substantially uniform. Further, the silicon is crystallized with respect to the uniformly formed nucleation sites NS, so that the number of defects D in the silicon crystal grains G may be reduced. Further, the silicon on the amorphous silicon layer  121  is melted at uniform energy so that a degree of volume expansion may be substantially uniform and the surface roughness value (Rq) of the polysilicon layer  122  may be lowered. 
     In the meantime, a degree to which the amount of oxygen  131  adsorbed onto the surface of the amorphous silicon layer  121  is reduced may be understood by comparing the number of silicon-oxygen bonds present in the amorphous silicon layer  121  and the number of silicon-oxygen bonds present in the polysilicon layer  122 . Specifically, when the content of oxygen in the chamber for the dehydrogenation process is reduced to 100 ppm or less, the number of silicon-oxygen bonds present in the polysilicon layer  122  may be smaller than the number of silicon-oxygen bonds present in the amorphous silicon layer  121  before crystallization. For example, the number of silicon-oxygen bonds in the polysilicon layer  122  is reduced to 92% of the number of silicon-oxygen bonds present in the amorphous silicon layer  121  before crystallization. In contrast, when the content of oxygen in the chamber for the dehydrogenation process is not controlled, 200,000 ppm or more oxygen may be included in the chamber and a large amount of oxygen may be adsorbed onto the surface of the amorphous silicon layer  121 . Therefore, the polysilicon layer  122  may include a larger number of silicon-oxygen bonds than the number of silicon-oxygen bonds present in the amorphous silicon layer  121  before crystallization. For example, the number of silicon-oxygen bonds present in the polysilicon layer  122  may be increased to 145% of the number of silicon-oxygen bonds present in the amorphous silicon layer  121  before crystallization. That is, it is understood that when the content of oxygen in the chamber is not controlled, the oxygen  131  is adsorbed onto the amorphous silicon layer  121  during the dehydrogenation process to increase the number of silicon-oxygen bonds in the polysilicon layer  122 . In this case, the number of silicon-oxygen bonds in the amorphous silicon layer  121  and the polysilicon layer  122  may be measured by a dynamic secondary ion mass spectrometer (SIMS). 
     The surface roughness of the polysilicon layer  122  which is improved as the content of oxygen is controlled during the dehydrogenation process will be described with reference to  FIG. 5 . 
       FIG. 5  is a graph explaining an improved surface roughness of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. 
       FIG. 5  is a graph illustrating a surface roughness of a polysilicon layer which varies as the content of oxygen is controlled during the dehydrogenation process. The graph of  FIG. 5  is obtained by calculating the surface roughness value (Rq) of the polysilicon layer by Equation 1. Specifically, an amorphous silicon layer with a thickness of 500 Å is formed on a substrate with a width of 730 nm and a length of 920 nm and the dehydrogenation process is performed on the amorphous silicon layer in a chamber in which various contents of oxygen is contained, at 430° C. for 15 minutes and the amorphous silicon layer is crystallized using excimer laser. Therefore, after forming the polysilicon layer, the surface roughness value (Rq) of the polysilicon layer is measured. 
     Referring to  FIG. 5 , it is understood that the surface roughness value (Rq) of the polysilicon layer varies depending on the content of oxygen in the chamber for performing the dehydrogenation process. When the content of oxygen in the chamber is not controlled, 200,000 ppm or higher of oxygen is present in the chamber and the dehydrogenation process is performed in the chamber so that the formed polysilicon layer has a surface roughness value (Rq) of 17.095 nm. In contrast, the polysilicon layer which is formed by performing the dehydrogenation process after reducing the content of oxygen in the chamber to 100 ppm or less has a surface roughness value (Rq) of 3.2 nm. That is, when the content of oxygen in the chamber for performing the dehydrogenation process is reduced to 100 ppm or less, the amount of oxygen which is adsorbed onto the surface of the amorphous silicon layer is significantly reduced. Therefore, absorption of laser energy and scattering of laser due to the adsorbed oxygen may be minimized and the amorphous silicon layer may be uniformly crystallized. As a result, the surface roughness value (R q ) of the polysilicon layer may be reduced. The surface roughness of the polysilicon layer which is improved by controlling the atmosphere of the dehydrogenation process is controlled may be more clearly identified by referring to atomic-force microscopy (AFM) image of  FIGS. 6A and 6B . 
       FIGS. 6A and 6B  are AFM images explaining for an improved surface roughness of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. Specifically, the AFM image of  FIG. 6A  represents the surface roughness of the crystallized polysilicon layer after performing the dehydrogenation process in the chamber in which 200,000 ppm or higher of oxygen is included. The AFM image of  FIG. 6B  represents the surface roughness of the crystallized polysilicon layer after performing the dehydrogenation process in the chamber in which 100 ppm or less of oxygen is included. Referring to  FIGS. 6A and 6B , it is understood that the surface roughness of the polysilicon layer is improved by lowering the content of oxygen in the chamber to 100 ppm or less. 
     Further, when the content of oxygen in the chamber for the dehydrogenation process is lowered to 100 ppm or less, the amorphous silicon is uniformly crystallized. Therefore, the sizes and the arrangement of the silicon crystal grains become substantially uniform and thus the defect in the silicon crystal grain may be significantly reduced. The above-described effect may be clearly understood from the SEM images of  FIGS. 7A and 7B . 
       FIGS. 7A and 7B  are scanning electron microscope (SEM) images explaining an improved crystallization uniformity of a polysilicon layer included in a thin film transistor according to an exemplary embodiment of the present disclosure. Specifically, the SEM image of  FIG. 7A  represents the silicon crystal grain of the crystallized polysilicon layer after performing the dehydrogenation process in the chamber in which 200,000 ppm or higher of oxygen is included. The SEM image of  FIG. 7B  represents the silicon crystal grain of the crystallized polysilicon layer after performing the dehydrogenation process in the chamber in which 100 ppm or less of oxygen is included. Referring to  FIGS. 7A and 7B , it is understood that the sizes and arrangement of the silicon crystal grains of the polysilicon layer become substantially uniform by reducing the content of oxygen in the chamber to 100 ppm or less. It is further understood that the number of defects in the silicon crystal grain is reduced by reducing the content of oxygen in the chamber to 100 ppm or less. 
     In the meantime, as mentioned above, when the surface roughness of the polysilicon layer is 10 nm or less, the polysilicon layer may have a sufficiently enhanced film characteristic and the device characteristic of the thin film transistor may be improved. That is, as illustrated in  FIG. 5 , when the content of oxygen in the chamber is reduced to 300 ppm before the dehydrogenation process, the surface roughness value (R q ) of the polysilicon layer may be reduced to be 10 nm or less. However, after the laser annealing process on the amorphous silicon layer, in order to minimize the striped stain generated in the organic light emitting display device, it is desirable to reduce the content of oxygen in the chamber to 100 ppm. 
     Specifically, the oxygen adsorbed onto the surface of the amorphous silicon layer absorbs energy of the laser which is irradiated in the form of a line during the laser annealing process and scatters the laser, so that a wave-like shape is formed across the surface of the polysilicon layer. However, when the content of oxygen in the chamber for the dehydrogenation process is reduced, the number of oxygen which is adsorbed onto the surface of the amorphous silicon layer is reduced. Therefore, the absorption of laser energy and laser scattering may be significantly reduced and thus the striped curve may be minimized. The polysilicon layer in which the striped curves are minimized is patterned to form thin film transistors in the form of matrix, so that all the thin film transistors of the organic light emitting display device may have similar device characteristic. Accordingly, the thin film transistors may transfer the same driving current in response to the same data voltage and thus individual organic light emitting diodes which are connected to the thin film transistors may emit light at the same gray level. As a result, the striped stain which is generated in the organic light emitting display device may be minimized. Specifically, as represented in Table 1, the polysilicon layer manufactured by the method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure may have striped curves reduced as compared with a polysilicon layer manufactured by a method of manufacturing a thin film transistor according to a comparative embodiment. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Number of vertical 
                 Number of 
               
               
                   
                 Classification 
                 lines 
                 horizontal lines 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Comparative 
                 29 
                 5 
               
               
                   
                 embodiment 
               
               
                   
                 Exemplary 
                 7 
                 4 
               
               
                   
                 embodiment 
               
               
                   
                   
               
            
           
         
       
     
     In Table 1, the polysilicon layer according to the exemplary embodiment of the present disclosure is formed by forming an amorphous silicon layer with a thickness of 500 Å on a substrate with a width of 730 nm and a length of 920 nm, performing the dehydrogenation process on the amorphous silicon layer in a chamber in which 100 ppm or less of oxygen is contained, at 430° C. for 15 minutes, and crystallizing the amorphous silicon layer using excimer laser. In contrast, the polysilicon layer according to the comparative embodiment is formed by forming an amorphous silicon layer with a thickness of 500 Å on a substrate with a width of 730 nm and a length of 920 nm, performing the dehydrogenation process on the amorphous silicon layer in a chamber in which 200,000 ppm or higher of oxygen is contained, at 430° C. for 15 minutes, and crystallizing the amorphous silicon layer using excimer laser. The stripes in Table 1 are derived by counting the number of stripes on the surface of the polysilicon layer with naked eye. 
     Referring to Table 1, it is understood that when the dehydrogenation process is performed in the chamber having 200,000 ppm or higher of oxygen content, the striped curves generated in the polysilicon layer include 29 vertical lines and 5 horizontal lines. In contrast, it is understood that when the dehydrogenation process is performed in the chamber having 100 ppm or less of oxygen content, the striped curves generated in the polysilicon layer include 7 vertical lines and 4 horizontal lines. That is, it is understood that the curves of the surface of the polysilicon layer may be reduced by controlling the atmosphere of the dehydrogenation process. 
     Further, when the content of oxygen in the chamber for the dehydrogenation process is lowered to be 100 ppm or less, the film characteristic of the polysilicon layer is improved, so that the thin film transistor including the polysilicon layer may have an enhanced device characteristic. Specifically, when the film characteristic of the polysilicon layer is improved, the surface roughness value (R q ) of the polysilicon layer is lowered, so that a breakdown voltage of the gate insulating layer which covers the polysilicon layer may be improved. 
     When the content of oxygen in the chamber for the dehydrogenation process is not controlled, a large number of oxygen is adsorbed onto the surface of the amorphous silicon layer during the dehydrogenation process, so that the film characteristic of the polysilicon layer may be degraded. In this case, the polysilicon layer has a high surface roughness value (R q ), so that a sharp portion may be formed on the surface of the polysilicon layer. In the meantime, the gate insulating layer is formed on the polysilicon layer and the gate electrode is formed on the gate insulating layer. When a predetermined voltage is applied to the gate electrode, arc may be generated between the gate electrode and a sharp protrusion of the polysilicon layer due to the predetermined voltage. In this case, charges are gathered on the gate insulating layer in a region where the arc is generated so that dielectric breakdown may be generated on the gate insulating layer. The more the sharp portions on the surface of the polysilicon layer, the more the above-mentioned arcs. Therefore, the dielectric breakdown of the gate insulating layer may be relatively easily generated. Therefore, the gate insulating layer on the polysilicon layer having a high surface roughness value (R q ) has a relatively low breakdown voltage. When the gate insulating layer has a low breakdown voltage due to the high surface roughness value (Rq) of the polysilicon layer, the thin film transistor may be easily broken due to a high gate voltage. Therefore, the reliability of the thin film transistor may be degraded. 
     In contrast, when the content of oxygen in the chamber for performing the dehydrogenation process is reduced to 100 ppm or less, the film characteristic of the polysilicon layer is improved and the number of sharp portions on the surface of the polysilicon layer may be reduced. Accordingly, the arc between the gate electrode and the polysilicon layer is generated less and the breakdown voltage of the gate insulating layer may be improved. 
     Specifically, the breakdown voltage of the gate insulating layer is improved as represented in Table 2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Exemplary 
               
               
                   
                   
                 embodiment 
                 embodiment 
               
               
                   
                   
               
             
            
               
                   
                 Breakdown voltage 
                 97.75 V 
                 104.5 V 
               
               
                   
                   
               
            
           
         
       
     
     In Table 2, the thin film transistor according to the exemplary embodiment of the present disclosure is formed by forming an amorphous silicon layer with a thickness of 500 Å on a substrate with a width of 730 nm and a length of 920 nm, and performing the dehydrogenation process on the amorphous silicon layer in a chamber in which 100 ppm or less of oxygen is contained, at 430° C. for 15 minutes, and crystallizing the amorphous silicon layer using excimer laser. In contrast, the thin film transistor according to the comparative embodiment is formed by forming an amorphous silicon layer with a thickness of 500 Å on a substrate with a width of 730 nm and a length of 920 nm, performing the dehydrogenation process on the amorphous silicon layer in a chamber in which 200,000 ppm or higher of oxygen is contained, at 430° C. for 15 minutes, and crystallizing the amorphous silicon layer using excimer laser. The breakdown voltage of Table 2 is obtained by forming a gate insulating layer with a thickness of 1400 Å on the polysilicon layer formed by the above-described method using silicon oxide (SiO 2 ), forming a gate electrode with a thickness 500 Å using molybdenum (Mo), and then measuring a voltage value which is applied to the gate electrode at a moment when dielectric breakdown is generated on the gate insulating layer. 
     As seen from Table 2, it is understood that when the content of oxygen in the chamber for performing the dehydrogenation process is lowered to 100 ppm or less, the breakdown voltage of the gate insulating layer is 6.75 V increased as compared with the case when the content of oxygen in the chamber is not controlled. That is, when the content of oxygen in the chamber is lowered to 100 ppm or less, the breakdown voltage of the gate insulating layer is increased and the durability of the thin film transistor against the voltage may be improved. 
     The method of manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure may reduce the content of oxygen in the chamber for performing the dehydrogenation process to a predetermined content and the content of oxygen in the chamber may be adjusted by an oxygen content control gas. Therefore, the chamber for performing the dehydrogenation process has a specific structure to easily purge the oxygen in the chamber by the oxygen content control gas. Hereinafter, a structure of a chamber for a hydrogenation process will be described with reference to  FIGS. 8 to 10 . 
       FIG. 8  is a schematic perspective view explaining for a dehydrogenating apparatus for manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure.  FIG. 9A  is a schematic cross-sectional view taken along the line XI-XI′ of  FIG. 8  and  FIG. 9B  is a partial enlarged cross-sectional view of a region A of  FIG. 9A .  FIG. 10  is a schematic cross-sectional view taken along the line X-X′ of  FIG. 8 . 
     Referring to  FIGS. 8 to 10 , a dehydrogenating apparatus  800  for manufacturing a thin film transistor includes a chamber  810  for performing a dehydrogenation process on an amorphous silicon layer, a substrate support  861 , a gas supplying unit  850 , a gas exhausting unit  840 , a substrate insertion slot  805 , a shutter unit  820 , and a shutter open/close unit  861 . 
     As illustrated in  FIGS. 9A and 10 , the chamber  810  includes an outer wall  811 , an inner wall  814 , a heating member  812 , and a heat insulating member  813 . The outer wall  811  protects elements in the chamber  810 . The outer wall  811  encloses the heating member  812  and is configured by a material having an enhanced heat resistance so that heat generated in the heating member  812  is not leaked to the outside. 
     The heating member  812  is disposed inside the outer wall  811  and heats the inside of the chamber  810 . The heating member  812  includes an electric resistance heating body and is disposed to enclose a remaining region of the chamber  810  except a region where the substrate insertion slot  805  is disposed. 
     The heat insulating member  813  is disposed inside the heating member  812  and insulates inside the chamber  810  so that the heat in the chamber is not leaked to the outside. The heat insulating member  813  may be formed of quartz which has an enhanced heat resistance. However, the material which configures the heat insulating member  813  is not limited to quartz, but the heat insulating member  813  may be formed of various materials having an enhanced heat resistance. 
     The inner wall  814  defines an inner space of the chamber  810  and is disposed inside the heat insulating member  813 . The inner wall  814  may be configured by a material having a high heat conductivity so as to satisfactorily transfer heat generated in the heating member  812 . 
     The substrate support  861  supports the substrate  111  in the chamber  810 . The substrate support  861  is coupled to the inner wall  814  to support one surface of the substrate  111  and is disposed along a side of the inner wall  814  so that a plurality of substrates  111  is inputted in a batch type. 
     The gas supplying unit  850  is disposed on one side of the chamber  810 . For example, eight gas supplying units  850  are disposed on one side of the chamber  810 . However, the number of gas supplying units  850  may vary depending on the size of the chamber  810 . 
     As illustrated in  FIG. 9A , the gas supplying unit  850  is disposed to penetrate the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810 . The gas supplying unit  850  is configured to inject an oxygen content control gas so as to control the content of oxygen in the chamber  810  to a predetermined content in the dehydrogenation process. The gas supplying unit  850  is disposed to be spaced apart from one surface of the substrate  111  so that the oxygen content control gas is sprayed from one upper portion of the substrate  111  to flow to the other upper portion of the substrate  111 . For example, the gas supplying unit  850  is disposed in one side of the chamber  810  corresponding to one location between the substrates  111  so as to inject the oxygen content control gas into a space between the substrates  111  which are disposed in a batch type. 
     The gas supplying unit  850  supplies the oxygen content control gas at an appropriate flow rate to maintain the content of oxygen in the chamber  810  at a predetermined content. For example, the gas supplying unit  850  may provide nitrogen gas (N 2 ) at a flow rate of 150 slm as an oxygen content control gas to maintain the content of oxygen in the chamber  810  to be 100 ppm or lower. 
     As illustrated in  FIG. 9B , the gas supplying unit  850  includes an inlet  853 , a penetrating unit  851 , a nozzle housing  852 , and a first sealing member  854 . 
     The inlet  853  is a flange which is disposed outside of the outer wall  811  of the chamber  810  and is connected to a gas pipe which is configured to supply the oxygen content control gas. The oxygen content control gas flows into the penetrating unit  851  through the inlet  853 . 
     The penetrating unit  851  transfers the oxygen content control gas into the chamber  810  and penetrates the chamber  810 . For example, the penetrating unit  851  penetrates the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810 . Each of the inner wall  814 , the heat insulating member  813 , the heating member  812 , and the outer wall  811  of the chamber  810  includes a hole OP. Holes OP of the inner wall  814 , the heat insulating member  813 , the heating member  812 , and the outer wall  811  are connected to each other to form a space so that the penetrating unit  851  is continuous in the chamber  810 . 
     The nozzle housing  852  is disposed to enclose the penetrating unit  851  which is exposed through the outer surface of the outer wall  811  of the chamber  810  and is coupled to the outer wall  811  in the form of a ring. The inlet  853  is coupled to the nozzle housing  852  and the oxygen content control gas which flows through the inlet  853  flows to the penetrating unit  851  through the nozzle housing  852 . That is, the nozzle housing  852  is configured to connect the inlet  853  and the penetrating unit  851 . 
     The first sealing member  854  encloses the penetrating unit  851  and suppresses the gas in the chamber  810  from being carried out to the periphery of the penetrating unit  851 . The first sealing member  854  may be formed of a silicon material which may provide enhanced sealing and the first sealing member  854  may be disposed between the nozzle housing  852  and the outer wall  811  to enclose the side of the penetrating unit  851 . 
     As mentioned above, the penetrating unit  851  is connected to the inner space of the chamber through the holes OP equipped in the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810 . The holes OP are formed to be larger than a diameter of the penetrating unit  851  in consideration of an error in the process and thus a minute gap may be generated between the holes OP and the penetrating unit  851 . As mentioned above, the holes OP are formed to communicate from the inner wall  814  of the chamber to the outer wall  811 , so that the gas in the chamber  810  may be leaked through the minute gap between the holes OP and the penetrating unit  851 . When the first sealing member  854  is not provided, the gas in the chamber  810  may be leaked to the outside of the chamber  810  through the minute gap between the holes OP and the penetrating unit  851 . Further, the oxygen content control gas may backwardly flow to be leaked. In this case, the content of oxygen in the chamber  810  may not be controlled to a predetermined content and a large amount of oxygen may be adsorbed onto the surface of the amorphous silicon layer during the dehydrogenation process. However, the first sealing member  854  seals the gap between the penetrating unit  851  and the hole OP so that the backward flowing of the oxygen content control gas in the chamber  810  may be minimized and the oxygen in the chamber  810  may be reduced to a predetermined content. 
     As illustrated in  FIG. 9A , the gas exhausting unit  840  is disposed on one side of the chamber  810  which is opposite to the other side of the chamber  810  in which the gas supplying unit  850  is disposed. The gas exhausting unit  840  is disposed so as to correspond to the gas supplying unit  850  and eight gas exhausting units  840  are disposed on the one side of the chamber  810 . In this case, the oxygen content control gas which is injected from the gas supplying unit  850  flows from an upper portion of one side of the substrate  111  to flow to the other upper portion of the substrate and discharged through the gas exhausting unit  840 . The oxygen content control gas may flow above and across the substrate  111  from the one side of the chamber where the gas supplying unit  850  is located to the another side of the chamber where the gas exhausting unit  840  is located. However, the number of gas exhausting units  840  may vary depending on the size of the chamber  810 . The oxygen content control gas flows in the gas inlet  850  to purge the oxygen in the chamber  810  and is discharged to the gas exhausting unit  840  together with the oxygen. 
     The gas exhausting unit  840  has the same structure as the gas supplying unit  850 . That is, the gas exhausting unit  840  includes a penetrating unit which penetrates the inner wall  814 , the heat insulating member  813 , the heating member  812 , and the outer wall  811  of the chamber  810 , a nozzle housing which is disposed on the outer wall  811  of the chamber  810  to enclose the penetrating unit, and an inlet which is connected to the penetrating unit through the nozzle housing. The gas exhausting unit  840  is configured to exhaust at least a portion of oxygen in the chamber together with at least a portion of the injected oxygen content control gas from the chamber to control an amount of oxygen in the chamber during the dehydrogenation process. 
     As illustrated in  FIG. 10 , one sides of the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810  are formed with an opening. The substrate insertion slot  805  is disposed on portions of the chamber surrounding the opening. These may be portions of the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  surrounding the opening in the chamber  810 . 
     The substrate insertion slot  805  opens one side of the chamber  810  to connect the inside of the chamber  810  to the outside of the chamber  810 . The inside of the chamber  810  is open through the substrate insertion slot  805  and the substrate  111  may be disposed on the substrate support  861  in the chamber through the substrate insertion slot  805 . 
     The substrate insertion slot  805  is configured to enclose an exposed surface of an opening formed in the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810  and is curved to be L-shaped along the outer wall  811  on the exposed surface of the opening of the heating member  812  to enclose corners of the opening. 
     The shutter unit  820  is in contact with the substrate insertion slot  805  and is configured to vertically move to open and close the substrate insertion slot  805 . The shutter unit  820  has a plate which blocks the substrate insertion slot  805  and is connected to the shutter open/close unit  830 . The shutter unit  820  is in partially contact with a portion of the substrate insertion slot  805  which is curved to be L-shaped along the opening of the outer wall  811  of the chamber  810  and vertically moves along the outer wall  811  of the chamber  810 . Thus, the shutter unit  820  is configured to move in a first direction to cover the opening in the chamber and also expose the inside of the chamber through uncovering the opening in the chamber  810 . 
     The shutter open/close unit  830  is connected to one surface of the shutter unit  820  and vertically moves the shutter unit  820 . 
     A second sealing member  806  is disposed to seal the gap between the shutter unit  820  and the outer wall  811  of the chamber  810  and the substrate insertion slot  805  in a state that the shutter unit  820  closes the substrate insertion slot  805 . The second sealing member  806  seals a gap which may be generated between the substrate insertion slot  805  and the outer wall  811  of the chamber  810  and a gap which may be generated between the shutter unit  820  and the substrate insertion slot  805 . The second sealing member  806  may be formed of a silicon material which may provide enhanced sealing and the gap which may be generated between the shutter unit  820  and the outer wall  811  and the substrate insertion slot  805  may be closely sealed by the second sealing member  806 . 
     In this case, the flowing of hetero elements such as oxygen through the minute gap between the substrate insertion slot  805  and the outer wall  811  and the minute gap between the shutter unit  820  and the substrate insertion slot  805  during the dehydrogenation process may be minimized. That is, the second sealing member  806  seals between the shutter unit  820  and the outer wall  811  and the substrate insertion slot  805  while the substrate insertion slot  805  is closed, so that the substrate insertion slot  805  may be completely closed from the outside and the inside of the chamber  810  may be sealed from the external environment. 
     In the meantime, as illustrated in  FIG. 10 , a part of the outer wall  811  of the chamber  810  may be configured to be separated. For example, the outer wall  811  may be configured by a first part  811   a  and a second part  811   b  and the second part  811   b  is configured to be separated or detached from the first part  811   a . When the second part  811   b  is separated from the first part  811   a , the heating member  812  may be exposed through a part from which the second part  811   b  is removed and a physical space for repairing elements of the chamber  810  may be secured. 
     In some exemplary embodiments, a third sealing member  815  may be inserted between the first part  811   a  and the second part  811   b  of the outer wall  811 . The third sealing member  815  seals a gap between the first part  811   a  and the second part  811   b  and minimizes the flowing of hetero elements such as oxygen between the first part  811   a  and the second part  811   b . Accordingly, the inside of the chamber  810  may be more closely sealed from the external environment. 
     Further, in some exemplary embodiments, the chamber  810  may further include a pressure controller to reduce the pressure in the chamber to 1 atm or less. In this case, the pressure controller may lower the environment in the chamber  810  to be 1 atm or less before the dehydrogenation process and the content of oxygen in the chamber  810  may be reduced to 100 ppm or less. The pressure controller may include a vacuum pipe and a vacuum pump which penetrates the outer wall  811 , the heating member  812 , the heat insulating member  813 , and the inner wall  814  of the chamber  810 . In this case, the oxygen in the chamber  810  may be removed by the vacuum pump and the pressure in the chamber  810  may be reduced to be 1 atm or less. 
     A dehydrogenating apparatus  800  for manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure includes a gas supplying unit  850  which is disposed on one surface of the chamber  810  to inject oxygen content control gas so as to control the content of oxygen in the chamber  810  to a predetermined content during the hydrogenation process and a gas exhausting unit  840  which is configured to exhaust the oxygen content control gas. Therefore, the content of oxygen in the chamber  810  may be maintained to a low content during the dehydrogenation process and a problem in that oxygen is adsorbed onto the surface of the silicon layer on the substrate  111  during the dehydrogenation process may be minimized. 
     Specifically, the gas supplying unit  850  and the gas exhausting unit  840  are spaced apart from one surface of the substrate  111  so that the oxygen content control gas flowing from the gas supplying unit  850  is sprayed from one upper portion of the substrate  111  to flow to the other upper portion of the substrate  111 . Therefore, the hitting of the surface of the amorphous silicon layer by the oxygen content control gas may be minimized. If the gas supplying unit  850  and the gas exhausting unit  840  are not spaced apart from one surface of the substrate  111 , the oxygen content control gas supplied from the gas supplying unit  850  may hit the surface of the amorphous silicon layer. Even though the oxygen content control gas has a low reactivity so that the oxygen content control gas is hardly adsorbed onto the surface of the amorphous silicon layer, when the oxygen content control gas consistently hits the surface of the amorphous silicon layer, it may affect the surface of the amorphous silicon layer. Further, the film characteristic of the polysilicon layer may be degraded after the laser annealing process. However, the dehydrogenating apparatus  800  according to the exemplary embodiment of the present disclosure includes the gas supplying unit  850  and the gas exhausting unit  840  which are spaced apart from one surface of the substrate  111  so that the content of oxygen in the chamber  810  may be efficiently reduced without affecting the surface of the amorphous silicon layer. 
     Further, the dehydrogenating apparatus  800  according to the exemplary embodiment of the present disclosure includes the first sealing member  854 , the second sealing member  806 , and the third sealing member  815 . The first sealing member  854  suppresses the gas in the chamber  810  from backwardly flowing through the gap between the penetrating unit  851  and the hole OP in the chamber around the penetrating unit  851  of the gas supplying unit  850 . The second sealing member  806  is disposed between the shutter unit  820 , the outer wall  811 , and the substrate insertion slot  805  to minimize the flowing of oxygen through a gap between the shutter unit  820  and the substrate insertion slot  805  or a gap between the substrate insertion slot  805  and the outer wall  811 . The third sealing member  815  is disposed between the second part  811   b  and the first part  811   a  of the outer wall which are separated for repairing the chamber  810  to minimize the flowing of oxygen between the first part  811   a  and the second part  811   b . Therefore, the content of oxygen in the chamber  810  in the dehydrogenating apparatus  800  may be efficiently reduced and the inside of the chamber  810  is disconnected from the external environment so that the dehydrogenation process may be more stably performed. 
     The exemplary embodiments of the present disclosure can also be described as follows: 
     According to an aspect of the present disclosure, a method of manufacturing a thin film transistor includes reducing a content of oxygen in a chamber for performing a dehydrogenation process of an amorphous silicon layer to a predetermined content; inputting a substrate on which the amorphous silicon layer is formed into the chamber; heating the inside of the chamber to perform the dehydrogenation process on the amorphous silicon layer; and forming a polysilicon layer by crystallizing the amorphous silicon layer using a laser. The method of manufacturing a thin film transistor according to the exemplary embodiment of the present disclosure reduces the content of oxygen in the chamber for performing a dehydrogenation process to a predetermined content. Therefore, adsorption of oxygen onto the surface of the amorphous silicon layer during the dehydrogenation process may be minimized. Therefore, the polysilicon layer formed by crystallizing the amorphous silicon layer has a low surface roughness value (Rq) and includes silicon grains with a substantially uniform size and arrangement. Accordingly, the thin film transistor formed by a polysilicon layer has an enhanced device characteristic. 
     The reducing of a content of oxygen in a chamber to a predetermined content includes may include injecting an oxygen content control gas in the chamber to maintain the content of oxygen in the chamber to be 100 ppm or less. 
     The oxygen content control gas may be nitrogen (N 2 ) gas. 
     The injecting of an oxygen content control gas in the chamber may include injecting the oxygen content control gas onto one upper portion of the substrate and exhausting the oxygen content control gas to the other upper portion of the substrate. 
     The reducing of a content of oxygen in a chamber to a predetermined content may include reducing a pressure in the chamber to 1 atm or less. 
     According to an aspect of the present disclosure, a dehydrogenating apparatus for manufacturing a thin film transistor includes a chamber, a substrate support, a gas supplying unit, and a gas exhausting unit. The chamber is a chamber for performing a dehydrogenation process which removes hydrogen of the amorphous silicon layer on the substrate. The substrate support is configured to support the substrate. The gas supplying unit is configured to inject an oxygen content control gas to control a content of oxygen in the chamber during the dehydrogenation process to a predetermined content. The gas exhausting unit is configured to exhaust oxygen in the chamber and the oxygen content control gas together. The dehydrogenating apparatus for manufacturing a thin film transistor according to an exemplary embodiment of the present disclosure incudes a gas supplying unit configured to inject an oxygen content control gas and a gas exhausting unit configured to exhaust oxygen with the oxygen content control gas together from the chamber. Therefore, the content of oxygen in the chamber for a dehydrogenation process is reduced to a predetermined content. Accordingly, adsorption of oxygen and hetero elements onto the surface of the amorphous silicon layer during the dehydrogenation process may be minimized and the surface roughness of the polysilicon layer formed by crystallization of the amorphous silicon layer may be improved. 
     The gas supplying unit may be configured to inject nitrogen gas and the gas supplying unit may be spaced apart from one surface of the substrate so that the nitrogen gas is sprayed from one upper portion of the substrate to flow to another upper portion of the substrate. 
     The gas supplying unit may inject the oxygen content control gas at a predetermined flow rate to maintain the content of oxygen in the chamber to be 100 ppm or less. 
     The hydrogenating apparatus for manufacturing a thin film transistor may further include a pressure controller configured to control a pressure in the chamber and the pressure controller may be configured to lower the pressure in the chamber to 1 atm or less so that the content of oxygen in the chamber is 100 ppm or less. 
     The gas supplying unit may include an inlet through which the oxygen content control gas is injected, a penetrating unit configured to transfer the oxygen content control gas to the chamber and penetrate the chamber, a nozzle housing configured to connect the penetrating unit and the inlet, and a first sealing member which seals a peripheral of the penetrating unit to suppress the gas in the chamber from backwardly flowing in the peripheral of the penetrating unit. 
     The hydrogenating apparatus for manufacturing a thin film transistor may further include a substrate insertion slot which opens one surface of the chamber to connect the inside of the chamber to the outside of the chamber and is in contact with the outer wall of the chamber, a shutter unit which is in contact with the substrate insertion slot and vertically moves to open/close the substrate insertion slot, and a second sealing member configured to seal a gap between the substrate insertion slot and the outer wall of the chamber and a gap between the shutter unit and the substrate insertion slot in a state where the substrate insertion slot is closed. 
     The hydrogenating apparatus for manufacturing a thin film transistor may further include a third sealing member. The outer wall of the chamber includes a first part and a second part which are separated from each other and the third sealing member may be disposed between the first part and the second part to seal a gap between the first part and the second part. 
     According to an aspect of the present disclosure, The organic light emitting display device includes: a polysilicon layer on a substrate; a gate insulating layer which covers the polysilicon layer; a gate electrode which overlaps the polysilicon layer on the gate insulating layer; an interlayer insulating layer which covers the gate insulating layer and the gate electrode; a source electrode and a drain electrode which are connected to the polysilicon layer on the interlayer insulating layer; a planarizing layer which covers the source electrode and the drain electrode; and a thin film transistor which includes an organic light emitting diode (OLED) connected to the source electrode or the drain electrode on the planarizing layer. A surface roughness value (Rq) of the polysilicon layer is 10 nm or less and the surface roughness value (Rq) of the polysilicon layer is defined by a root mean square (rms) value of height values of a curved surface of the polysilicon layer which is measured with respect to the reference plane. The organic light emitting display device according to the exemplary embodiment of the present disclosure includes a thin film transistor including a polysilicon layer with a low surface roughness value (Rq) so that a display quality may be enhanced. All the plurality of thin film transistors formed by a polysilicon layer having an enhanced film characteristic has a similar device characteristic, so that a similar driving current is supplied to the organic light emitting diode connected to the thin film transistor and organic light emitting diodes emit light at the same gray level. Accordingly, the striped stain caused by the degraded film characteristic of the polysilicon layer may be significantly reduced. 
     Although the exemplary embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited thereto and may be embodied in many different forms without departing from the technical concept of the present disclosure. Therefore, the exemplary embodiments of the present disclosure are provided for illustrative purposes only but not intended to limit the technical spirit of the present disclosure. The scope of the technical spirit of the present disclosure is not limited thereto. Therefore, it should be understood that the above-described exemplary embodiments are illustrative in all aspects and do not limit the present disclosure. The protective scope of the present disclosure should be construed based on the following claims, and all the technical concepts in the equivalent scope thereof should be construed as falling within the scope of the present disclosure.