Patent Publication Number: US-2021193894-A1

Title: Method of repairing light emitting device, apparatus for repairing light emitting device, and display panel having repaired light emitting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/953,399 filed on Dec. 24, 2019, and U.S. Provisional Patent Application No. 62/964,440, filed on Jan. 22, 2020, each of which is hereby incorporated by reference for all purposes as if fully set forth herein 
    
    
     BACKGROUND 
     Field 
     Exemplary embodiments of the invention relate generally to a method of repairing a light emitting device, an apparatus for repairing a light emitting device, a display panel having the repaired light emitting device, and a display apparatus having the same. More particularly, exemplary embodiments of the invention relate generally to a method of repairing micro LEDs, an apparatus for repairing micro LEDs, a display panel having the repaired micro LEDs, and a display apparatus having the same. 
     Discussion of the Background 
     As an inorganic light source, light emitting diodes have been used in various fields including displays, vehicular lamps, general lighting, and the like. With various advantages such as long lifespan, low power consumption, and rapid response, light emitting diodes have been replacing existing light sources in the art. 
     Meanwhile, conventional light emitting diodes have been mainly used as backlight light sources in display apparatuses. However, recently, small-sized light emitting diodes, that is, LED display apparatuses that directly implement an image using micro LEDs, have been developed. 
     In general, a display apparatus realizes various colors through mixture of blue, green and red light. In order to realize various images, the display apparatus includes a plurality of pixels, each of which includes sub-pixels corresponding to blue, green and red light, respectively, in which a color of a certain pixel is determined based on the colors of the sub-pixels so that images can be realized through combination of such pixels. 
     LEDs can emit light of various colors depending on their materials, and a display apparatus in which individual micro LEDs emitting blue, green, and red are arranged on a two-dimensional plane, or a display apparatus in which micro LEDs having a stacked structure in which a blue LED, a green LED, and a red LED are stacked one above another are arranged on a two-dimensional plane may be provided. 
     Micro LEDs used in one display apparatus usually require more than one million even for a small-sized display. Due to the small size of micro LEDs and the enormous number required, mass production of micro LED display apparatus according to a conventional technology is almost impossible because of the conventional die bonding technology in which LED chips are individually mounted. As such, a technology for transferring a plurality of micro LEDs onto a circuit board in a group has been recently developed. 
     Meanwhile, some of the micro LEDs transferred in a group may exhibit bonding failure or poor luminescence characteristics. These defective micro LEDs need to be repaired. Generally, repairment of micro LEDs is to replace defective micro LEDs with favorable micro LEDs, and repairment of micro LEDs is quite difficult due to the small size of the micro LEDs. 
     The above information disclosed in this Background section is only for understanding of the background of the inventive concepts, and, therefore, it may contain information that does not constitute prior art. 
     SUMMARY 
     Methods according to exemplary embodiments of the invention are capable of repairing a light emitting device for a display, particularly micro LEDs. 
     Exemplary embodiments provide an apparatus for repairing a light emitting device for a display, particularly micro LEDs. 
     Additional features of the inventive concepts will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the inventive concepts. 
     A display panel according to an exemplary embodiment includes a circuit board including first pads, first light emitting devices disposed on the circuit board and including pads, at least one second light emitting device disposed on the circuit board and including pads, metal bonding layers disposed between the pads of the first light emitting devices and the first pads on the circuit board, and a conductive material layer electrically connecting the pads of the second light emitting device to the first pads on the circuit board, in which the conductive material layer includes a conductive portion and a non-conductive portion. 
     The conductive material layer may include at least one of an anisotropic conductive film, an anisotropic conductive paste, and an anisotropic conductive adhesive. 
     The conductive portion of the conductive material layer may include conductive balls disposed between the pads of the second light emitting device and the pads of the circuit board. 
     The metal bonding layer may include at least one of AuSn, CuSn, and In. 
     An upper surface of the second light emitting device may be disposed higher than those of the first light emitting devices. 
     Each of the first and second light emitting devices may be configured to emit each of blue light, green light, and red light. 
     The conductive material layer may contact the first light emitting device adjacent to the second light emitting device. 
     The conductive material layer may be spaced apart from adjacent first light emitting devices. 
     The conductive material layer may have a wider width than that of the corresponding second light emitting device. 
     A method of repairing a light emitting device according to another exemplary embodiment includes removing at least one defective light emitting device among a plurality of light emitting devices transferred onto a circuit board, and mounting a second light emitting device at a location of the circuit board where the defective light emitting device is removed using a conductive material layer, in which the conductive material layer includes a conductive portion and a non-conductive portion. 
     Mounting the second light emitting device may include disposing the conductive material layer at the location of the circuit board where the defective light emitting device is removed, disposing the second light emitting device on the conductive material layer, and curing the conductive material layer. 
     Disposing the second light emitting device may include forming the second light emitting device on a substrate, and transferring the second light emitting device disposed on the substrate to the conductive material layer, and the substrate may be removed from the second light emitting device after the conductive material layer is cured. 
     The substrate may include a single second light emitting device. 
     A plurality of defective light emitting devices on the circuit board may be repaired using a plurality of substrates each including the single second light emitting devices, respectively. 
     The method may further include forming bonding material layers on first pads of the circuit board, respectively, disposing the first light emitting devices on the bonding material layers, and forming metal bonding layers by applying heat to the bonding material layers. 
     The defective light emitting device may be removed by applying gas to the first light emitting device using a gas blower. 
     The gas blower may apply the gas to the first light emitting device at a predetermined pressure. 
     The gas may be applied to each of the first light emitting devices transferred onto the circuit board using the gas blower. 
     The defective light emitting device may be detected in advance, and the gas may be applied only to the defective light emitting device using the gas blower. 
     An apparatus for repairing a light emitting device according to yet another exemplary embodiment includes a first table to support a circuit board on which first light emitting devices are mounted, a second table to support a temporary substrate to which second light emitting devices are adhered, a third table to support a bath including a conductive adhesive material, and a pickup unit configured to pick up at least one of the second light emitting devices from the temporary substrate and place the at least one of the second light emitting devices on the circuit board. 
     The pickup unit may include a needle to pick up the second light emitting device from the temporary substrate. 
     The needle may have a passage to vacuum-adsorb the second light emitting device. 
     The apparatus may further include a moving device to move the needle in the vertical direction. 
     The first, second, and third tables may be configured to move laterally with respect to the pickup unit. 
     The apparatus may further include at least one vision device. 
     The at least one vision device may include a first vision device configured to be placed over the first, second, and third tables, and a second vision device configured to be placed under the first, second, and third tables. 
     The apparatus may further include a display configured to display an image photographed using the vision device. 
     At least one of the first table and the pickup unit may be configured to vibrate in the lateral direction to separate at least one of the light emitting devices from the circuit board. 
     The conductive adhesive material may include at least one of an anisotropic conductive paste and an anisotropic conductive adhesive. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the inventive concepts. 
         FIG. 1  shows schematic perspective views of display apparatuses according to exemplary embodiments. 
         FIG. 2  is a schematic plan view of a display panel according to an exemplary embodiment. 
         FIG. 3  is a schematic enlarged partial cross-sectional view taken along line A-A′ of  FIG. 2  according to an exemplary embodiment. 
         FIGS. 4A, 4B, 4C, 4D, and 4E  are schematic cross-sectional views illustrating a process of repairing a light emitting device according to exemplary embodiments. 
         FIGS. 5A, 5B, 5C, and 5D  are schematic cross-sectional views illustrating a method of repairing a light emitting device according to an exemplary embodiment. 
         FIG. 6  is a schematic plan view illustrating light emitting devices for repairing according to an exemplary embodiment. 
         FIG. 7  is a schematic plan view of an apparatus for repairing a light emitting device according to an exemplary embodiment. 
         FIG. 8  is a schematic cross-sectional view taken along line B-B′ of  FIG. 7 . 
         FIG. 9  is a schematic cross-sectional view illustrating a process of removing a defective device according to an exemplary embodiment. 
         FIGS. 10A and 10B  are schematic cross-sectional views illustrating a process of transferring a light emitting device according to an exemplary embodiment. 
         FIG. 11  is a schematic cross-sectional view illustrating a process of removing a defective device according to another exemplary embodiment. 
         FIG. 12  is a schematic cross-sectional view illustrating a process of transferring a light emitting device for repairing onto a temporary substrate. 
         FIGS. 13A and 13B  are schematic cross-sectional views illustrating a process of mounting a light emitting device for repairing on a circuit board. 
         FIG. 14  is a schematic plan view illustrating a display panel having a light emitting device for repairing according to an exemplary embodiment. 
         FIG. 15  is an enlarged schematic partial cross-sectional view taken along line C-C′ of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments or implementations of the invention. As used herein “embodiments” and “implementations” are interchangeable words that are non-limiting examples of devices or methods employing one or more of the inventive concepts disclosed herein. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments. Further, various exemplary embodiments may be different, but do not have to be exclusive. For example, specific shapes, configurations, and characteristics of an exemplary embodiment may be used or implemented in another exemplary embodiment without departing from the inventive concepts. 
     Unless otherwise specified, the illustrated exemplary embodiments are to be understood as providing exemplary features of varying detail of some ways in which the inventive concepts may be implemented in practice. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions, and/or aspects, etc. (hereinafter individually or collectively referred to as “elements”), of the various embodiments may be otherwise combined, separated, interchanged, and/or rearranged without departing from the inventive concepts. 
     The use of cross-hatching and/or shading in the accompanying drawings is generally provided to clarify boundaries between adjacent elements. As such, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, dimensions, proportions, commonalities between illustrated elements, and/or any other characteristic, attribute, property, etc., of the elements, unless specified. Further, in the accompanying drawings, the size and relative sizes of elements may be exaggerated for clarity and/or descriptive purposes. When an exemplary embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. Also, like reference numerals denote like elements. 
     When an element, such as a layer, is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. To this end, the term “connected” may refer to physical, electrical, and/or fluid connection, with or without intervening elements. Further, the D1-axis, the D2-axis, and the D3-axis are not limited to three axes of a rectangular coordinate system, such as the x, y, and z-axes, and may be interpreted in a broader sense. For example, the D1-axis, the D2-axis, and the D3-axis may be perpendicular to one another, or may represent different directions that are not perpendicular to one another. For the purposes of this disclosure, “at least one of X, Y, and Z” and “at least one selected from the group consisting of X, Y, and Z” may be construed as X only, Y only, Z only, or any combination of two or more of X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms “first,” “second,” etc. may be used herein to describe various types of elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the teachings of the disclosure. 
     Spatially relative terms, such as “beneath,” “below,” “under,” “lower,” “above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), and the like, may be used herein for descriptive purposes, and, thereby, to describe one elements relationship to another element(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and/or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms, “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It is also noted that, as used herein, the terms “substantially,” “about,” and other similar terms, are used as terms of approximation and not as terms of degree, and, as such, are utilized to account for inherent deviations in measured, calculated, and/or provided values that would be recognized by one of ordinary skill in the art. 
     Various exemplary embodiments are described herein with reference to sectional and/or exploded illustrations that are schematic illustrations of idealized exemplary embodiments and/or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not necessarily be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. In this manner, regions illustrated in the drawings may be schematic in nature and the shapes of these regions may not reflect actual shapes of regions of a device and, as such, are not necessarily intended to be limiting. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
     Hereinafter, exemplary embodiments of the inventive concepts will be described in detail with reference to the accompanying drawings. 
       FIG. 1  shows schematic perspective views of display apparatuses according to exemplary embodiments. 
     The light emitting device according to an exemplary embodiments may be used in a VR display apparatus such as a smart watch  1000   a  or a VR headset  1000   b , or an AR display apparatus such as augmented reality glasses  1000   c , without being limited thereto. 
     A display panel for displaying an image is mounted on a display apparatus.  FIG. 2  is a schematic plan view of a display panel  1000  according to an exemplary embodiment, and  FIG. 3  is a schematic enlarged partial cross-sectional view taken along line A-A′ of  FIG. 2 . 
     Referring to  FIGS. 2 and 3 , the display panel  1000  includes a circuit board  110  and light emitting devices  100  and  100   a . The light emitting devices  100  and  100   a  may be small-sized LEDs, commonly referred to as micro LEDs. For example, the light emitting device  100  may have a size smaller than 500 μm×500 μm, and further, smaller than 100 μm×100 μm. However, the inventive concepts are not limited to a particular size of the light emitting device  100 . 
     The circuit board  110  may include a circuit for passive matrix driving or active matrix driving. In an exemplary embodiment, the circuit board  110  may include interconnection lines and resistors therein. In another exemplary embodiment, the circuit board  110  may include interconnection lines, transistors, and capacitors. The circuit board  110  may also have pads disposed on an upper surface thereof to allow electrical connection to the circuit therein. 
     A plurality of light emitting devices  100  and  100   a  is arranged on the circuit board  110 . The light emitting device  100  represents a light emitting device of good performance mounted on the circuit board  110  by group transfer, and the light emitting device  100   a  represents a repaired light emitting device. A structure of the light emitting device  100   a  may be substantially the same as that of the light emitting device  100 , but the inventive concepts are not limited thereto. An interval between the light emitting devices  100  and  100   a  may be at least wider than a width of the light emitting device  100  or  100   a.    
     In an exemplary embodiment, the light emitting devices  100  and  100   a  may be sub-pixels that emit light of a specific color, and the sub-pixels may form one pixel. For example, a blue LED, a green LED, and a red LED may be adjacent to one another to form one pixel. However, the inventive concepts are not limited thereto, and each of the light emitting devices  100  and  100   a  may have a stacked structure emitting light of various colors. For example, each of the light emitting devices  100  and  100   a  may have a structure in which a blue LED, a green LED, and a red LED are stacked to overlap one another, and thus, one light emitting device  100  and  100   a  may form one pixel. 
     The light emitting device  100  may have pads  105 , and the pads  105  may be adhered to corresponding pads  115  of the circuit board  110  through a bonding layer  120 . The bonding layer  120  may be formed by solder bonding, and may include, for example, a metallic bonding material such as AuSn, CuSn, In, or the like. 
     The light emitting device  100   a  may have pads  105 , and the pads  105  may be adhered to the corresponding pads  115  of the circuit board  110  through a conductive material layer  120   a . The conductive material layer  120   a  includes a conductive portion and a non-conductive portion. The conductive material layer  120   a  may be formed using, for example, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or an anisotropic conductive adhesive (ACA). The light emitting device  100   a  may be electrically connected to the circuit board  110  by conductive balls  125  in the conductive material layer  120   a.    
     The conductive material layer  120   a  may be in contact with an adjacent light emitting device  100  as shows, but the inventive concepts are not limited thereto. In some exemplary embodiments, the conductive material layer  120   a  may be spaced apart from the light emitting device  100 . 
     In an exemplary embodiment, an upper surface of the light emitting device  100   a  may be placed higher than that of the light emitting device  100 . In particular, the conductive material layer  120   a  located under the pads  105  of the light emitting device  100   a  may be thicker than the bonding layer  120 . 
     The display panel  1000  may include at least one light emitting device  100   a , and the light emitting device  100   a  bonded to the circuit board  110  by the conductive material layer  120   a  may be distinguished from the light emitting device  100  bonded to the circuit board  110  by the bonding layer  120 , which may include a metallic material. 
       FIGS. 4A, 4B, 4C, 4D, and 4E  are schematic cross-sectional views illustrating a process of repairing a micro LED according to exemplary embodiments. 
     Referring to  FIG. 4A , a circuit board  110  includes pads  115 . The pads  115  are connected to circuits in the circuit board  110  and provide contact points for connecting a light emitting device  100  to the circuits. The pads  115  are disposed in each region of the circuit board  110  where the light emitting devices  100  are to be mounted to mount a plurality of light emitting devices  100 . The pads  115  may be formed of a metal layer including Au. For example, the pads  115  may have a multilayer structure of Cu/Ni/Au. 
     Barrier layers  121  are provided on the pads  115 , and bonding material layer  123  is provided on the barrier layer  121 . The barrier layers  121  may prevent the bonding material layers  123  from diffusing into the pads  115 , thereby preventing damage to the pads  115 . The barrier layer  121  may be a metal layer mixed with the bonding material layer  123 , or a metal layer for blocking diffusion of the bonding material layer  123 . For example, the barrier layer  121  may include at least one of Ni, Cr, Ti, Ta, Mo, and W. For example, the barrier layer  121  may have a multilayer structure of Cr/Ni or Ti/Ni. 
     The bonding material layer  123  may include AuSn, CuSn, or In. In general, the bonding material layers  123  are provided on the pads  115  for group transfer using micro LED technology. The bonding material layer  123  may be formed using, for example, a solder paste including flux and a metallic material. The bonding material layer  123  may be formed on the pads  115  using, for example, a screen printing technique. 
     In some exemplary embodiments, a metal layer mixed with the bonding material layer  123  such as an Au layer may be interposed between the barrier layer  121  and the bonding material layer  123 . 
     The light emitting device  100  has pads  105 . The pads  105  correspond to the pads  115  of the circuit board  110 . As shown in the drawing, the pads  105  may be bump pads protruding from the light emitting device  100 , but in some exemplary embodiments, the pads  105  may not necessarily have a protruding shape. The plurality of light emitting devices  100  may be transported to correspond to the pads  115  of the circuit board  110 . 
     Referring to  FIG. 4B , after the pads  105  of the light emitting device  100  are arranged on the bonding material layers  123  as shown in  FIG. 4A , a metal bonding layer  120  is formed by applying heat at a bonding temperature. In particular, the barrier layer  121  and the bonding material layer  123  may be mixed with each other by heat, and at least a portion of the pads  105  may be mixed with the bonding material layer  123 . In this manner, the light emitting device  100  may be stably attached to the circuit board  110  by the metal bonding layer  120 . 
     Referring to  FIG. 4C , as described with reference to  FIG. 4B , once the light emitting devices  100  are bonded to the circuit board  110 , some of the light emitting devices  100  having defects may be detected. Such defects in the light emitting device  100  may be caused by, for example, bonding failure or by a failure in performance of the light emitting device  100 . 
     In this case, a defective light emitting device  100  is removed from the circuit board  110 . The light emitting device  100  having defective bonding may be removed using a gas blower  300 , which will be described in more detail later with reference to  FIG. 5A . 
     The bonding layer  120  may be removed together with the defective light emitting device  100 , or the remaining bonding layer  120  may be separately removed using a laser or the like after the defective light emitting device  100  is removed. As such, the pads  115  may be retained on the circuit board  110  after the defective light emitting device  100  is removed. The remaining pads  115  may be substantially the same as the pads  115  before the light emitting device  100  is bonded, but may be deformed in some cases from the pads  115 . 
     Referring to  FIG. 4D , after the defective light emitting device  100  is removed, a conductive material layer  120   a  is formed on the exposed pads  115 . The conductive material layer  120   a  may include conductive balls  125 . The conductive material layer  120   a  may be, for example, an anisotropic conductive film, an anisotropic conductive paste, or an anisotropic conductive adhesive. For example, the conductive material layer  120   a  may be formed to cover the pads  115  by dispensing the anisotropic conductive paste or the anisotropic conductive adhesive. 
     Referring to  FIG. 4E , a light emitting device  100   a  for repairing is disposed on the conductive material layer  120   a . The light emitting device  100   a  for repairing is disposed on the conductive material layer  120   a  so that the pads  105  of the light emitting device  100   a  for repairing match the pads  115  of the circuit board  110 . The light emitting device  100   a  for repairing replaces the defective light emitting device  100 , and may have performance required as the light emitting device  100 . Further, the light emitting device  100   a  may have substantially the same structure as the light emitting device  100 , but the inventive concepts are not limited thereto. 
     The pads  105  of the light emitting device  100   a  are electrically connected to the pads  115  of the circuit board  110  by the conductive balls  125 . The light emitting device  100   a  may be pressed towards the circuit board  110 , and thus, the conductive balls  125  may electrically connect the pads  105  and  115  to each other. The conductive material layer  120   a  may then be cured. 
     In general, handling of the light emitting device  100   a  is difficult due to its small size. As such, the light emitting device  100   a  may be formed on a substrate  20   a  which will be described in more detail later, and then be bonded to the circuit board  110  by handling the substrate  20   a . The substrate  20   a  may be separated from the light emitting device  100   a  through a technique, such as laser lift-off, which will also be described in more detail later. 
     Hereinafter, a method of repairing a micro LED according to exemplary embodiments will be described in detail. 
       FIGS. 5A, 5B, 5C, and 5D  are schematic cross-sectional views illustrating a method of repairing a micro LED according to an exemplary embodiment. 
     Referring to  FIG. 5A , a display panel  1000   a  in which light emitting devices  100  are transferred onto a circuit board  110  is prepared. The light emitting devices  100  may be formed on a wafer and transferred to the circuit board  110  in a group. The light emitting devices  100  may be transferred to the circuit board  110  using a laser lift-off technique, but the inventive concepts are not limited thereto. Various known methods of transferring the light emitting devices  100  onto the circuit board  110  may be used in other exemplary embodiments. 
     The display panel  1000   a  may be transported to a light emitting device removing apparatus to remove a defective light emitting device. In an exemplary embodiment, the removing apparatus may include a stage  210 , a gas blower  300 , and a camera  400 . However, the inventive concepts are not limited to a particular removing apparatus. 
     The display panel  1000   a  may be placed on the stage  210  and may be clamped to be fixed on the stage  210 . The stage  210  may be movable in the X and Y directions, and may also be movable in the Z direction. For example, when the display panel  1000   a  is transferred, the stage  210  may move downwardly in the Z direction to receive the display panel  1000   a , and then move upwardly to remove the defective light emitting device  100 . 
     The gas blower  300  may include a needle  310  having a gas outlet, a pressure control device  320 , and a gas supply pipe  330 . The needle  310  may have a gas outlet having a small inner diameter so as to blow gas toward the light emitting device  100 . For example, the gas outlet may have an inner diameter of about 10 μm to about 50 μm. 
     The pressure control device  320  adjusts a pressure of gas to release gas at a pressure suitable for removing the light emitting device  100  having failed bonding. 
     In an exemplary embodiment, the defective light emitting device may be detected in advance before being placed in the light emitting device removing apparatus, and the removing apparatus may remove the light emitting devices  100  determined to have failed bonding. In another exemplary embodiment, the light emitting device  100  may be evaluated for a failure in bonding by releasing a gas pressure from the gas blower  300 . For example, a gas pressure suitable for evaluating the bonding characteristics of the light emitting device  100  may be predetermined, and the pressure control device  320  may release gas at a predetermined pressure through the gas outlet. When gas is released at the predetermined pressure, the light emitting device  100  having failed bonding is removed while normal light emitting devices  100  are retained. In this manner, a separate process for determining defective light emitting devices  100  may be obviated. 
     The gas supply pipe  330  supplies gas to the pressure control device  320  from a storage tank storing gas. The gas supply pipe  330  may be a flexible tube to freely move a location of the needle  310 , without being limited thereto. 
     In the illustrated exemplary embodiment, gas may be air or an inert gas, and in particular, may be an inert gas, such as He or N 2 . The inert gas may not cause oxidation of a metal bonding layer. 
     The camera  400  may be disposed to observe the light emitting device  100  to which gas is applied from the needle  310 . The camera  400  may be disposed above the light emitting device  100  to capture an image of the light emitting device  100  on the circuit board  110 , but the inventive concepts are not limited thereto. 
     In the illustrated exemplary embodiment, although the stage  210  is exemplarily illustrated and described as being disposed under the gas blower  300  and the camera  400 , but the inventive concepts are not limited thereto. In some exemplary embodiments, the stage  210  may be disposed above the camera  400  and the gas blower  300   
     The gas blower  300  applies gas to the light emitting device  100  through the needle  310 . The gas blower  300  releases gas at a predetermined pressure using the pressure control device  320  to remove the light emitting device having failed bonding. In an exemplary embodiment, the gas blower  300  may apply gas only to light emitting devices  100  that are determined as defective light emitting devices among the light emitting devices  100  on the circuit board  110  for the removal. In another exemplary embodiment, the gas blower  300  may apply gas to all of the light emitting devices  100  on the circuit board  110  at a predetermined pressure and remove the light emitting devices having failed bonding. 
     The camera  400  observes whether the light emitting device  100  to which gas is applied by the gas blower  300  is attached or detached from the circuit board  110 . A location where the light emitting device  100  is removed may be specified using the camera  400 . When gas is applied to one light emitting device  100  and removes that light emitting device  100 , the stage  210  may move in the lateral direction to apply gas to another light emitting device  100 . In this manner, each of the light emitting devices having failed bonding among the light emitting devices  100  on the circuit board  110  may be removed using the gas blower  300 . 
       FIG. 5B  shows the circuit board  110  from which the light emitting devices having failed bonding are removed. When the defective light emitting devices  100  are removed, a metal bonding layer  120  corresponding thereto may also be removed while the corresponding pads  115  may be retained on the circuit board  110  at locations where the light emitting devices  100  have been removed. 
     Referring to  FIG. 5C , a conductive material layer  120   a  is disposed at the location where the light emitting device  100  is removed, and a light emitting device  100   a  for repairing is disposed thereon. The light emitting device  100   a  for repairing may be formed on a substrate  20   a , and the light emitting device  100   a  may be disposed at a desired location by handling the substrate  20   a . The substrate  20   a  may be a growth substrate for growing an epitaxial layer. For example, the substrate  20   a  may be a sapphire substrate, a silicon substrate, a GaAs substrate, or the like. The light emitting devices  100   a  may be manufactured using epitaxial layers grown on the substrate  20   a , and may include a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. Furthermore, the light emitting devices  100   a  may have a structure in which a plurality of LEDs is stacked. 
     A plurality of light emitting devices  100  may be removed from the circuit board  110 , the conductive material layer  120   a  may be disposed at each of the locations where the light emitting devices  100  are removed, and the substrates  20   a  on which the light emitting devices  100   a  are formed may be disposed thereon, respectively. According to an exemplary embodiment, one light emitting device  100   a  may be formed on one substrate  20   a , and thus, the substrates  20   a  are spaced apart from each other. 
     The light emitting device  100   a  for repairing may be pressed against the circuit board  110 , and thus, pads  105  of the light emitting devices  100   a  and pads  115  on the circuit board  110  may be electrically connected. 
     The conductive material layer  120   a  may be cured by heat, and thus, the light emitting devices  100   a  may be adhered to the circuit board  110 . 
     After the conductive material layer  120   a  is cured, the substrate  20   a  may be separated from the light emitting device  100   a  using the laser lift-off technique or the like. The display panel  1000  is completed as shown in  FIG. 5D  by separating each of the substrates  20   a  from the light emitting devices  100   a.    
     In the illustrated exemplary embodiment, although the conductive material layers  120   a  disposed on the circuit board  110  to correspond to the light emitting devices  100   a  are exemplarily described as being simultaneously cured, the inventive concepts are not necessarily limited thereto. For example, in some exemplary embodiments, each of the defective light emitting devices  100  on the circuit board  110  may be individually repaired by repeatedly performing a process of mounting the light emitting device  100   a  to the location where the defective light emitting device  100  is removed using each substrate  20   a  having the light emitting device  100   a  for repairing. 
     In the illustrated exemplary embodiment, an upper surface of the light emitting device  100   a  for repairing mounted on the circuit board  110  may be placed higher than that of the light emitting device  100 . As such, damage to the light emitting devices  100  that have already been mounted on the circuit board  110  by the substrate  20   a  may be prevented. However, the inventive concepts are not limited thereto, and in some exemplary embodiments, elevations of upper surfaces of the light emitting devices  100  and  100   a  may be substantially the same. 
     A region between the light emitting devices  100  and  100   a  may be filled with a light reflecting material or a light blocking material such, as a black matrix, to prevent light interference between the light emitting devices  100  and  100   a . In this case, the conductive material layer  120   a  may be disposed under the light blocking material. 
       FIG. 6  is a schematic plan view of light emitting devices  100   a  for repairing according to an exemplary embodiment. 
     Referring to  FIG. 6 , a plurality of light emitting devices  100   a  for repairing may be formed on a wafer  20 . The light emitting device  100   a  for repairing may be formed by forming epitaxial layers on a substrate  20   a  and patterning the epitaxial layers. A process of forming the light emitting device  100   a  for repairing is generally similar to that of forming the light emitting device  100 , and thus, the light emitting devices  100   a  may have substantially the same or similar structure as that of the light emitting device  100 . In an exemplary embodiment, the light emitting device  100   a  may have a structure including a single active layer to form one sub-pixel. In another exemplary embodiment, the light emitting device  100   a  may have an LED stacked structure having multiple active layers, and thus, may form one pixel. 
     The wafer  20  may be divided into a plurality of sections, and each section may include a single light emitting device  100   a . The light emitting device  100   a  has a smaller size than the corresponding section, and thus, the substrate  20   a  of each section has a relatively large width compared to the light emitting device  100   a.    
     The substrate  20   a  may have a size suitable for handling, and thus, the light emitting device  100   a  may be easily attached to the circuit board  110  using the substrate  20   a . In addition, the light emitting device  100   a  may be easily transferred from the substrate  20   a  onto the circuit board  110  without damaging normal light emitting devices  100  mounted on the circuit board  110 . As described above, the substrate  20   a  is separated from the light emitting device  100   a  during mounting process using a technique such as laser lift-off. 
       FIG. 7  is a schematic plan view of an apparatus  10  for repairing a light emitting device according to an exemplary embodiment, and  FIG. 8  is a schematic cross-sectional view taken along line B-B′ of  FIG. 7 . 
     Referring to  FIGS. 7 and 8 , the apparatus  10  may include a first table  11 , a second table  13 , a third table  17 , a bath  19 , and a first vision device  23   a , a second vision device  23   b   23   b , first and second displays  33   a  and  33   b , a work station  51 , a circuit board  110 , a temporary substrate  130 , and a pickup unit  150 . The pickup unit  150  may include a moving device  21 , a header  23 , a needle  25 , and an absorption pipe  27 . 
     The work station  51  provides a space for carrying out a repairing operation of a light emitting device. The first, second, and third tables  11 ,  13 , and  17  may be laterally and/or vertically movable on the work station  51 . The first, second, and third tables  11 ,  13 , and  17 , for example, may be movable in the lateral direction (x, y direction) using a lateral direction moving part, and movable in the vertical direction (z direction) using a vertical direction moving part. 
     The first table  11  may move back and forth in the lateral direction, for example, in the x direction. The circuit board  110  on which the light emitting devices  100  are mounted may be disposed on the first table  11 . The first table  11  may be movable so that the circuit board  110  can be placed under a lower portion of the needle  25  of the pickup unit  150 , or the circuit board  110  can be spaced far apart from the lower portion of the needle  25  of the pickup unit  150 . 
     The first table  11  may also be movable in the vertical direction, that is, in the z direction, so that an elevation of the first table  11  may be adjusted. 
     The second table  13  may move back and forth in the lateral direction, for example, in the x direction. The temporary substrate  130  on which light emitting devices  100   a  for repairing are mounted may be disposed on the second table  13 . The second table  13  may be movable so that the temporary substrate  130  can be placed under the lower portion of the needle  25  of the pickup unit  150 , or the temporary substrate  130  can be spaced far apart from the lower portion of the needle  25  of the pickup unit  150 . 
     The second table  13  may also be movable in the vertical direction, that is, in the z direction, and thus, an elevation of the second table  13  may be adjusted. 
     The third table  17  may move back and forth in the lateral direction, for example, in the y direction. The bath  19  containing a conductive adhesive material may be disposed on the third table  17 . The third table  17  may be movable so that the bath  19  can be placed under the lower portion of the needle, or the bath  19  can be spaced far apart from the lower portion of the needle  25 . 
     The third table  17  may also be movable in the vertical direction, that is, in the z direction, and thus, an elevation of the third table  17  may be adjusted. 
     The circuit board  110  is disposed on the first table  11 . The light emitting devices  100  are disposed on the circuit board  110 . The light emitting devices  100  are mounted on the circuit board  110  by group transfer, and the circuit board  110  is disposed on the first table  11  with the light emitting devices  100  mounted thereon. 
     Some of the light emitting devices  100  mounted on the circuit board  110  are removed from the circuit board  110  due to failures in bonding, electrical, and/or optical properties. As such, some regions of the circuit board  110  may have empty space by removing the defective light emitting device  100 . 
     The apparatus  10  is operated to place the light emitting device  100   a  for repairing at a location where the defective light emitting device  100  has been removed. When all of the defective light emitting devices  100  are replaced with the light emitting devices  100   a  for repairing, the circuit board  110  is transported from the first table  11  and a new circuit board  110  may be disposed on the first table  11 . 
     The temporary substrate  130  is disposed on the second table  13 . The light emitting devices  100   a  for repairing are disposed on the temporary substrate  130 . The light emitting devices  100   a  for repairing may be transferred from a growth substrate onto the temporary substrate  130  using a technique such as laser lift-off. The temporary substrate  130  may include an adhesive material layer. The adhesive material layer may be, for example, an ultraviolet (UV) tape that may be cured by UV irradiation. The adhesiveness of the adhesive material layer may be reduced to, for example, about 1/100 or less when cured. After the light emitting devices  100   a  for repairing are transferred onto the temporary substrate  130 , the adhesive material layer may be cured to facilitate separation of the light emitting devices  100   a  for repairing from the temporary substrate  130  by reduced adhesiveness of the adhesive material layer. 
     The bath  19  is disposed on the third table  17 . The bath  19  may contain a conductive adhesive material for bonding the light emitting device  100   a  for repairing to the circuit board  110 . The conductive adhesive material may be, for example, an anisotropic conductive paste (ACP) or an anisotropic conductive adhesive (ACA). 
     The first vision device  23   a  may be disposed over the work station  51 . The first vision device  23   a  observes a location where the needle  25  is operated, and whether the circuit board  110 , the temporary substrate  130 , or the bath  19  is accurately disposed under the needle  25 . The location of the light emitting device  100  on the circuit board  110  or the location of the light emitting device  100   a  on the temporary substrate  130  may be confirmed through the first vision device  23   a.    
     The first vision device  23   a  may include a camera to photograph an object to be observed, and a photographed image may be checked through the first display  33   a.    
     The second vision device  23   b  may be disposed to face the needle  25 . The second vision device  23   b  may be disposed under the work station  51 , and the work station  51  may include a groove for placing the second vision device  23   b.    
     The second vision device  23   b  is disposed under the needle  25 , and observes whether the needle  25  and the circuit board  110 , or the needle  25  and the temporary substrate  130  are accurately arranged. The needle  25  may be arranged with the light emitting device  100   a  on the temporary substrate  130  to pick up the light emitting device  100   a , and may also be arranged in a recovery space on the circuit board  110  to place the picked-up light emitting device  100   a  in an empty space on the circuit board  110 . To this end, the second vision device  23   b  may provide a visual assistance to ensure proper placement of the needle  25 . 
     For example, the second vision device  23   b  may include a camera to photograph an object to be observed, and a photographed image may be checked through the second display  33   b.    
     The first and second displays  33   a  and  33   b  display the images photographed by the first and second vision devices  23   a  and  31   b . In this manner, a user may visually check an operation state of the needle  25  using the displays  33   a  and  33   b.    
     The circuit board  110  is disposed on the first table  11 . The circuit board  110  may be laterally transported relative to the pickup unit  150  by lateral movement of the first table  11 . In another exemplary embodiment, the pickup unit  150  may be laterally movable rather than the first table  11 . 
     The circuit board  110  may include the light emitting devices  100  mounted by group transfer. In this case, some of the light emitting devices  100  mounted on the circuit board  110  may have mounting failure or defective electrical and optical properties. As such, the circuit board  110  may be transported to the apparatus  10  to replace the defective light emitting devices  100  with light emitting devices  100   a  for repairing. 
     When each of the defective light emitting devices  100  is replaced with the light emitting devices  100   a  for repairing, a display panel ( 2000  in  FIG. 14 ) including the light emitting devices  100   a  for repairing and the light emitting devices  100  is provided. 
     The temporary substrate  130  is disposed on the second table  13 . The temporary substrate  130  may be laterally transported relative to the pickup unit  150  by lateral movement of the second table  13 . In another exemplary embodiment, the pickup unit  150  may be laterally movable rather than the second table  13 . 
     The temporary substrate  130  supports the light emitting devices  100   a  for repairing. The temporary substrate  130  may include an adhesive material layer, such as a UV tape, and the light emitting devices  100   a  for repairing are attached to the adhesive material layer and supported by the temporary substrate  130 . 
     The pickup unit  150  picks up the light emitting device  100   a  for repairing from the temporary substrate  130  and mounts the light emitting device  100   a  for repairing on the circuit board  110 . The moving device  21  causes the needle  25  to move upward and downward, and to this end, the moving device  21  a step motor, for example. In an exemplary embodiment, the moving device  21  may move the needle  25  in the lateral direction. 
     The header  23  may be used to mount the needle  25 , and is attached to the moving device  21  to move upward and downward by the moving device  21 . 
     The needle  25  is operated to pick up the light emitting device  100   a  on the temporary substrate  130  and place the light emitting device  100   a  at a predetermined location on the circuit board  110 . In an exemplary embodiment, the needle  25  may vacuum-adsorb the light emitting device  100   a , and may detach the light emitting device  100   a  from the temporary substrate  130  using a vacuum-absorption force. To this end, the needle  25  may include a passage for vacuum-absorption. 
     The light emitting device  100   a  adsorbed by the needle  25  is at least partially immersed in the conductive adhesive material in the bath  19 , and is thereafter bonded to pads of the circuit board  110 . When the light emitting device  100   a  is bonded onto the circuit board  110 , the needle  25  is separated from the light emitting device  100   a . The needle  25  may be easily separated from the light emitting device  100   a  by injecting gas into the passage for vacuum-absorption. 
     The absorption pipe  27  is used to vacuum-exhaust the passage in the needle  25 . The absorption pipe  27  may be connected to the moving device  21  or may be connected to the header  23 . An absorption passage of the absorption pipe  27  is connected to the passage of the needle  25 , and thus, when the needle  25  is disposed on an upper surface of the light emitting device  100   a , the passage of the needle  25  may be vacuum-exhausted and the light emitting device  100   a  may be vacuum-adsorbed. 
     In the illustrated exemplary embodiment, although the needle  25  is exemplarily described as adsorbing the light emitting device  100   a  using vacuum-absorption, the inventive concepts are not limited thereto. In some exemplary embodiments, in addition to vacuum-absorption, the needle  25  may pick up the light emitting device  100   a  and detach the light emitting device  100   a  from the temporary substrate  130  using various known techniques. 
     Hereinafter, an operation of the apparatus  10  according to an exemplary embodiment will be described in more detail. In particular, a process for forming a display panel  2000   a , and a process for removing the defective light emitting device from the display panel  2000   a  will be described. Subsequently, a process of providing the light emitting devices  100   a  for repairing on the temporary substrate  130 , and a process for replacing the defective light emitting devices with the light emitting devices  100   a  for repairing replace using a conductive adhesive material will be described. 
       FIG. 9  is a schematic cross-sectional view illustrating a process of removing a defective device according to an exemplary embodiment. 
     Referring to  FIG. 9 , the display panel  2000   a  including a circuit board  110  on which light emitting devices  100  are mounted is prepared. The light emitting devices  100  may be formed on a wafer and transferred to the circuit board  110  in a group. The light emitting devices  100  may be transferred to the circuit board  110  using a laser lift-off technique, but the inventive concepts are not limited thereto. In other exemplary embodiments, various known methods for transferring the light emitting devices  100  onto the circuit board  110  may be used. The process of bonding the light emitting device  100  to pads of the circuit board  110  will be described in more detail later with reference to  FIGS. 10A and 10B . 
     The display panel  2000   a  may be placed in a light emitting device removing apparatus to remove a defective light emitting device. The removing apparatus is not particularly limited, and various known apparatuses to remove the defective light emitting device may be used. In an exemplary embodiment, the removing apparatus may include a stage  210 , a gas blower  300 , and a camera  400 . 
     The display panel  2000   a  may be placed on the stage  210  and may be clamped to be fixed on the stage  210 . The stage  210  may be movable in the X and Y directions, and may also be movable in the Z direction. For example, when the display panel  2000   a  is transported, the stage  210  may move downwardly in the Z direction to receive the display panel  2000   a , and thereafter, move upwardly to remove the defective light emitting device  100 . 
     The gas blower  300  may include a needle  310  having a gas outlet, a pressure control device  320 , and a gas supply pipe  330 . The needle  310  may have a gas outlet having a small inner diameter so as to blow gas toward the light emitting device  100 . For example, the gas outlet may have an inner diameter of about 10 μm to about 50 μm. 
     The pressure control device  320  adjusts a pressure of gas to release gas at a pressure suitable for removing the defective light emitting device  100 . 
     In an exemplary embodiment, whether the light emitting device  100  is defective may be detected in advance before being placed in the light emitting device removing apparatus, and the removing apparatus may remove the light emitting devices  100  determined to have failed bonding. In another exemplary embodiment, the light emitting device  100  may be evaluated for a failure in bonding by releasing a gas pressure from the gas blower  300 . For example, a gas pressure suitable for evaluating the bonding characteristics of the light emitting device  100  may be predetermined, and the pressure control device  320  may release gas at a predetermined pressure through the gas outlet. When gas is released at the predetermined pressure, the light emitting device  100  having failed bonding is removed while normal light emitting device  100  are retained. 
     The gas supply pipe  330  supplies gas to the pressure control device  320  from a storage tank storing gas. The gas supply pipe  330  may be a flexible tube to freely move a location of the needle  310 , without being limited thereto. 
     In the illustrated exemplary embodiment, gas may be air or an inert gas, and in particular, may be an inert gas, such as He or N 2 . The inert gas may not cause oxidation of a metal bonding layer. 
     The camera  400  may be disposed to observe the light emitting device  100  to which gas is applied from the needle  310 . The camera  400  may be disposed above the light emitting device  100  to capture an image of the light emitting device  100  on the circuit board  110 , but the inventive concepts are not limited thereto. 
     In the illustrated exemplary embodiment, although the stage  210  is exemplarily illustrated and described as being disposed under the gas blower  300  and the camera  400 , but the inventive concepts are not limited thereto. In some exemplary embodiments, the stage  210  may be disposed above the camera  400  and the gas blower  300 . 
     The gas blower  300  applies gas to the light emitting device  100  through the needle  310 . The gas blower  300  releases gas at a predetermined pressure using the pressure control device  320  to remove the light emitting device having failed bonding. In an exemplary embodiment, the gas blower  300  may apply gas only to light emitting devices  100  that are determined as defective light emitting devices among the light emitting devices  100  on the circuit board  110  for the removal. In this manner, since gas is not applied to each of the light emitting devices  100 , a process time may be shortened. In another exemplary embodiment, the gas blower  300  may apply gas to all of the light emitting devices  100  on the circuit board  110  at a predetermined pressure and remove the light emitting devices having failed bonding. 
     The camera  400  observes whether the light emitting device  100  to which gas is applied by the gas blower  300  is attached or detached from the circuit board  110 . A location where the light emitting device  100  is removed may be specified using the camera  400 . When gas is applied to one light emitting device  100  and removes that light emitting device  100 , the stage  210  may move in the lateral direction to apply gas to another light emitting device  100 . In this manner, each of the light emitting devices having failed bonding among the light emitting devices  100  on the circuit board  110  may be removed using the gas blower  300 . 
     Once each of the defective light emitting devices  100  are removed, the circuit board  110  may be placed on the first table  11  of the apparatus  10  described above. 
       FIGS. 10A and 10B  are schematic cross-sectional views illustrating a process of transferring a light emitting device according to an exemplary embodiment. 
     Referring to  FIG. 10A , a circuit board  110  includes pads  115 . The pads  115  are connected to circuits in the circuit board  110 , and provide contact points for connecting the light emitting device  100  to the circuits. The pads  115  are disposed in each region of the circuit board  110  where the light emitting devices  100  are to be mounted. The pads  115  may be formed of a metal layer including Au. For example, the pads  115  may have a multilayer structure of Cu/Ni/Au. 
     Barrier layers  121  are provided on the pads  115 , and a bonding material layer  123  is provided on the barrier layer  121 . The barrier layers  121  may prevent the bonding material layers  123  from diffusing into the pads  115 , thereby preventing damage to the pads  115 . The barrier layer  121  may be a metal layer mixed with the bonding material layer  123 , or a metal layer for blocking diffusion of the bonding material layer  123 . For example, the barrier layer  121  may include at least one of Ni, Cr, Ti, Ta, Mo, and W. For example, the barrier layer  121  may have a multilayer structure of Cr/Ni or Ti/Ni. 
     The bonding material layer  123  may include AuSn, CuSn, or In. In general, the bonding material layers  123  are provided on the pads  115  for group transfer using micro LED technology. The bonding material layer  123  may be formed using, for example, a solder paste including flux and a metallic material. The bonding material layer  123  may be formed on the pads  115  using, for example, a screen printing technique. 
     In some exemplary embodiments, a metal layer mixed with the bonding material layer  123  such as an Au layer may be interposed between the barrier layer  121  and the bonding material layer  123 . 
     The light emitting device  100  has pads  105 . The pads  105  correspond to the pads  115  of the circuit board  110 . As shown in the drawing, the pads  105  may be bump pads protruding from the light emitting device  100 , but in some exemplary embodiments, the pads  105  may not necessarily have a protruding shape. By group transfer, the plurality of light emitting devices  100  may be transported to correspond to the pads  115  of the circuit board  110 . 
     Referring to  FIG. 10B , after the pads  105  of the light emitting device  100  are arranged on the bonding material layers  123  as shown in  FIG. 10A , a metal bonding layer  120  is formed by applying heat at a bonding temperature. In particular, the barrier layer  121  and the bonding material layer  123  may be mixed with each other by heat, and at least a portion of the pads  105  may be mixed with the bonding material layer  123 . In this manner, the light emitting device  100  may be stably attached to the circuit board  110  by the metal bonding layer  120 . In this case, a support substrate used to transfer the light emitting devices  100  to the circuit board  110  is removed from the light emitting devices  100 , and thus, the display panel  2000   a  described in  FIG. 9  may be provided. 
       FIG. 11  is a schematic cross-sectional view illustrating a process of removing a defective device according to another exemplary embodiment. In the illustrated exemplary embodiment, a pickup unit  150  of an apparatus  10  is used to remove the defective light emitting device. 
     Referring to  FIG. 11 , a display panel  2000   a  having the defective light emitting device  100  may be directly disposed on a first table  11 . Whether the light emitting device  100  is defective or not may be determined in advance, and the defective light emitting device  100  may be placed under a needle  25  by lateral movement of the first table  11 . The needle  25  may be placed above the defective light emitting device  100  by the movement of the moving device  21 , and vacuum-adsorb the defective light emitting device  100 . 
     Once the needle  25  is in close contact with the defective light emitting device  100 , the defective light emitting device  100  may be separated from the circuit board  110  by vibrating the first table  11  or the needle  25  in the lateral direction. Subsequently, the needle  25  may discard the defective light emitting device  100  by lifting the defective light emitting device  100  in a vacuum-adsorbed state. 
     According to the illustrated exemplary embodiment, since the apparatus  10  removes the defective light emitting device  100  and mount the light emitting device  100   a  for repairing, a process of repairing the light emitting device may be further simplified. 
       FIG. 12  is a schematic cross-sectional view illustrating a process of transferring a light emitting device  100   a  for repairing onto a temporary substrate  130 . 
     Referring to  FIG. 12 , the light emitting devices  100   a  may be formed on a substrate  101 . The substrate  101  may be a growth substrate for growing an epitaxial layer, for example, a sapphire substrate, a GaAs substrate, a silicon substrate, a GaN substrate, or a SiC substrate, but the inventive concepts are not limited thereto. The substrate  101  may be divided into a plurality of sections having a predetermined size, and the light emitting devices  100  on each section may be transferred together to the temporary substrate  130 . 
     The light emitting device  100   a  according to the illustrated exemplary embodiment may have the same size and structure as those of the light emitting device  100  described above. The light emitting devices  100  and  100   a  may have, for example, sizes smaller than 500 μm×500 μm, and further, smaller than 100 μm×100 μm, which are known in the art as mini-LEDs or micro-LEDs according to their sizes. In an exemplary embodiment, the light emitting devices  100  and  100   a  may be sub-pixels that emit light of a specific color, and the sub-pixels may form one pixel. For example, a blue micro LED, a green micro LED, and a red micro LED may be disposed adjacent to one another to form one pixel. In this case, the substrate  101  is used to form micro LEDs for emitting light of a specific color. In another exemplary embodiment, each of the light emitting devices  100  and  100   a  may have a stacked structure that emits light of various colors. For example, each of the light emitting devices  100  and  100   a  may have a structure in which a blue LED, a green LED, and a red LED are stacked to overlap one another, and thus, each one of the light emitting devices  100  and  100   a  may form one pixel. 
     The temporary substrate  130  according to an exemplary embodiment may be a light-transmitting substrate. The temporary substrate  130  may include an adhesive material layer on a surface thereof. The adhesive material layer may be a material layer that may have varying adhesiveness upon curing. For example, the adhesiveness of the adhesive material layer may be reduced when cured. According to an exemplary embodiment, the adhesive material layer may be an ultraviolet tape (UV) tape. When the ultraviolet tape is cured by UV irradiation, the adhesiveness thereof may be reduced to about 1/100 or less, further to about 1/200 or less. For example, the adhesiveness of the adhesive material layer may be about 100 gf/mm before curing, and may be about 0.5 gf/mm after curing. 
     The light emitting devices  100   a  on the substrate  101  are attached to the temporary substrate  130  having an uncured adhesive material layer. Each of the light emitting devices  100   a  on the substrate  101  may be attached to the temporary substrate  130  by the adhesive material layer. 
     Subsequently, the substrate  101  is removed from the light emitting devices  100   a  using a technique, such as laser lift off (LLO) or the like. The adhesive material layer may prevent locations of the light emitting devices  100   a  from being changed while the substrate  101  is separated using laser lift-off. After the substrate  101  is removed, the temporary substrate  130  is placed on a second table  13  of the apparatus  10  with the light emitting devices  100   a  attached thereon. 
     Referring back to  FIGS. 7 and 8 , the temporary substrate  130  disposed on the second table  13  may be transported to the lower portion of the needle  25  by lateral movement of the second table  13 . The needle  25  picks up the light emitting device  100   a  from the temporary substrate  130 . When the needle  25  picks up the light emitting device  100   a , the second table  13  moves in the lateral direction and returns back to an original location. 
     Subsequently, the third table  17  moves laterally to the lower portion of the needle  25 . The needle  25  moves downward to cause at least a portion of the light emitting device  100   a  contact the conductive adhesive material in the bath  19  on the third table  17 . As such, the conductive adhesive material is attached to a lower surface of the light emitting device  100   a.    
     Subsequently, the third table  17  returns back to an original location by lateral movement, and the first table  11  moves laterally to place the circuit board  110  under the lower portion of the needle  25 . In particular, a region of the circuit board  110  from which the defective light emitting device  100  has been removed is placed under the needle  25 . Subsequently, the needle  25  moves downward to place the light emitting device  100   a  on the circuit board  110 . The needle  25  may press the light emitting device  100   a  against the circuit board  110 , and thus, the light emitting device  100   a  may be attached to the circuit board  110  by a conductive adhesive material. Subsequently, the needle  25  releases the light emitting device  100   a , and thus, the light emitting device  100   a  is transferred onto the circuit board  110 . 
     A process of moving the light emitting devices  100   a  from the temporary substrate  130  to the circuit board  110  using the needle  25  may be continuously carried out, and thus, the light emitting devices  100   a  may replace each of the defective light emitting devices  100 . In this manner, the display panel  2000  in which the light emitting devices  100  and the defective light emitting devices  100   a  are arranged together is provided. 
       FIGS. 13A and 13B  are schematic cross-sectional views illustrating a process of mounting a light emitting device for repairing on a circuit board according to another exemplary embodiment. 
     Referring to  FIG. 13A , after the defective light emitting device  100  is removed, pads  115  may be retained on the circuit board  110 . The retained pads  115  may be substantially identical to the pads  115  before the light emitting device  100  is bonded, but may be deformed from the pads  115 . 
     The needle  25  adsorbs the light emitting device  100   a  for repairing, and dips the light emitting device  100   a  into the bath  19 , so that a portion of the conductive adhesive material, that is, a conductive material layer  120   a  is attached on the light emitting device  100   a . The conductive material layer  120   a  may have conductive balls  125  in an insulating matrix, and may be, for example, an anisotropic conductive paste or an anisotropic conductive adhesive (ACA). 
     Referring to  FIG. 13B , the needle  25  moves downward and presses the light emitting device  100   a  against the circuit board  110 , so that the light emitting device  100   a  is attached to the circuit board  110  by the conductive material layer  120   a . By pressing the light emitting device  100   a , a portion of the conductive material layer  120   a  may protrude to the outside of the light emitting device  100   a.    
     The conductive balls  125  may be disposed between the pad  105  of the light emitting device  100   a  and the pad  115  of the circuit board  110 , and the light emitting device  100   a  and the circuit board  110  may be electrically connected by the conductive balls  125 . The conductive material layer  120   a  may be cured by heat, and the apparatus  10  may include a heating unit for curing the conductive material layer  120   a.    
     After the conductive material layer  120   a  is cured, the needle  25  releases the light emitting device  100   a . By repeating this process, each of the defective light emitting devices  100  on the circuit board  110  may be replaced with the light emitting devices  100   a  for repairing, and thus, the display panel  2000  of  FIG. 14  may be provided. 
       FIG. 14  is a schematic plan view illustrating a display panel  2000  having a light emitting device for repairing according to an exemplary embodiment, and  FIG. 15  is an enlarged schematic partial cross-sectional view taken along line C-C′ of  FIG. 14 . 
     Referring to  FIGS. 14 and 15 , the display panel  2000  includes a circuit board  110  and light emitting devices  100  and  100   a . The light emitting devices  100  and  100   a  may be small-sized LEDs, commonly referred to as micro LEDs. For example, the light emitting device  100  may have a size smaller than 500 μm×500 μm, and further, smaller than 100 μm×100 μm. However, the inventive concepts are not limited to a particular size of the light emitting devices  100  and  100   a.    
     The circuit board  110  may include a circuit for passive matrix driving or active matrix driving. In an exemplary embodiment, the circuit board  110  may include interconnection lines and resistors therein. In another exemplary embodiment, the circuit board  110  may include interconnection lines, transistors, and capacitors. The circuit board  110  may also have pads disposed on an upper surface thereof to allow electrical connection to the circuit therein. 
     A plurality of light emitting devices  100  and  100   a  is arranged on the circuit board  110 . The light emitting device  100  represents a light emitting device of good performance mounted on the circuit board  110  by group transfer, and the light emitting device  100   a  represents a light emitting device for repairing. A structure of the light emitting device  100   a  may be substantially the same as that of the light emitting device  100 , but the inventive concepts are not limited thereto. An interval between the light emitting devices  100  and  100   a  may be at least wider than a width of the light emitting device  100  or  100   a.    
     In an exemplary embodiment, the light emitting devices  100  and  100   a  may be sub-pixels that emit light of a specific color, and the sub-pixels may form one pixel. For example, a blue LED, a green LED, and a red LED may be adjacent to one another to form one pixel. However, the inventive concepts are not limited thereto, and each of the light emitting devices  100  and  100   a  may have a stacked structure emitting light of various colors. For example, each of the light emitting devices  100  and  100   a  may have a structure in which a blue LED, a green LED, and a red LED are stacked to overlap one another, and thus, one light emitting device  100  and  100   a  may form one pixel. 
     The light emitting device  100  may have pads  105 , and the pads  105  may be adhered to corresponding pads  115  of the circuit board  110  through a bonding layer  120 . The bonding layer  120  may be formed by solder bonding, and may include, for example, a metallic bonding material such as AuSn, CuSn, In, or the like. 
     The light emitting device  100   a  may have pads  105 , and the pads  105  may be adhered to the corresponding pads  115  of the circuit board  110  through a conductive material layer  120   a . The conductive material layer  120   a  includes a conductive portion and a non-conductive portion. The conductive portion electrically connects the pads  105  to the pads  115 , and the non-conductive portion surrounds the conductive portion. The conductive material layer  120   a  may be formed using, for example, an anisotropic conductive paste (ACP) or an anisotropic conductive adhesive (ACA). The light emitting device  100   a  may be electrically connected to the circuit board  110  by conductive balls  125  in the conductive material layer  120   a . The conductive material layer  120   a  according to the illustrated exemplary embodiment may occupy a wider width than that of the light emitting device  100   a , as shown in the drawings. However, the conductive material layer  120   a  formed according to the illustrated exemplary embodiment does not significantly deviate from a region of the light emitting device  100   a , and thus, may be spaced apart from adjacent light emitting devices  100 . 
     In an exemplary embodiment, an upper surface of the light emitting device  100   a  may be placed higher than that of the light emitting device  100 . In particular, the conductive material layer  120   a  located under the pads  105  of the light emitting device  100   a  may be thicker than the bonding layer  120 . However, the inventive concepts are not limited thereto, and the upper surface of the light emitting device  100   a  may be placed at the same elevation as that of the upper surface of the light emitting device  100 , or may be placed lower than that of the upper surface of the light emitting device  100 . 
     The display panel  2000  may include at least one light emitting device  100   a , and the light emitting device  100   a  bonded to the circuit board  110  by the conductive material layer  120   a  may be distinguished from the light emitting device  100  bonded to the circuit board  110  by the metal bonding layer  120 . 
     The display panel  2000  may be mounted in various types of display apparatuses to display an image. The display panel  2000  may be used in a VR display apparatus such as a smart watch, a VR headset, or an AR display apparatus such augmented reality glasses, without being limited thereto. 
     Although certain exemplary embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. As such, the inventive concepts are not limited to such embodiments, but rather to the broader scope of the appended claims and various obvious modifications and equivalent arrangements as would be apparent to a person of ordinary skill in the art.