Patent Publication Number: US-2022216383-A1

Title: Light emitting device and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Chinese application serial no. 202110004695.0, filed on Jan. 4, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a light emitting device and a manufacturing method thereof, and in particular to a light emitting device and a manufacturing method thereof that may reduce the problem of short-circuit during bonding or may improve the bonding yield. 
     Description of Related Art 
     With the miniaturization of light emitting devices and the development of light emitting elements towards integration and miniaturization, the spacing between the contacts of the light emitting elements is also shortened, making the bonding between the light emitting elements and the carrier board more and more difficult. Therefore, how to improve the bonding yield is now the goal of the industry. 
     SUMMARY 
     The disclosure provides a light emitting device and a manufacturing method thereof, capable of reducing a problem of short-circuit during bonding or improving bonding yield. 
     According to an embodiment of the disclosure, a light emitting device includes a substrate, a light emitting element, and a bonding structure. The light emitting element is disposed on the substrate. The light emitting element is disposed on the substrate through the bonding structure. The bonding structure includes at least three bonding layers and at least two passivation layers, and the at least three bonding layers and the at least two passivation layers are in a staggered arrangement. 
     According to an embodiment of the disclosure, a method for manufacturing a light emitting device includes the following steps. A substrate is provided. A first bonding layer is formed on the substrate. A first passivation layer is formed on the first bonding layer. A light emitting element is provided. A second bonding layer is formed on the light emitting element. A second passivation layer is formed on the second bonding layer. The second passivation layer on the light emitting element is contacted with the first passivation layer to form a third bonding layer and bond the light emitting element to the substrate. 
     To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1A  to  FIG. 1D  are schematic cross-sectional views of a method of manufacturing a light emitting device according to an embodiment of the disclosure. 
         FIG. 2  is a schematic cross-sectional view of a light emitting device according to another embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The disclosure can be understood by referring to the following detailed description and also in conjunction with the accompanying drawings. It should be noted that, for the reader&#39;s ease of understanding and for the sake of brevity of the accompanying drawings, only a portion of the light emitting device is illustrated in a number of the accompanying drawings in the disclosure, and that particular elements in the accompanying drawings are not drawn to actual scale. In addition, the number and dimensions of the components in the drawings are for illustrative purposes only and are not intended to limit the scope of the disclosure. 
     In the following description and the claims, terms such as “include” and “comprise” are open-ended, and therefore should be interpreted as “include but not limited to”. 
     It should be understood that when a component or membrane layer is said to be “on” or “connected to” another component or membrane layer, it may be directly on or directly connected to such other component or membrane layer, or there may be an inserted component or membrane layer between the two (the non-direct case). Conversely, when the component is said to be “directly” on or “directly connected to” another component or membrane layer, there is no inserted component or membrane layer between the two. 
     It should be understood that while the terms first, second, third . . . may be used to describe a variety of constituent components, the constituent components are not limited to this terminology. 
     This term is used only to distinguish a single component from other components in the specification. Instead of using the same terminology in the claims, the terms first, second, third . . . are substituted in the order in which the components are declared in the claims. Therefore, in the following description, the first constituent component may be the second constituent component in the claims. 
     In some embodiments of the disclosure, terms such as “joint”, “interconnection”, etc., unless specifically defined, may refer to two structures in direct contact, or may refer to two structures that are not in direct contact and in which other structures are provided between the two structures. The terms about connecting and joint may also include the case where both structures are movable, or where both structures are fixed. In addition, the term “coupling” includes any direct and indirect means of electrical connection. 
     In the disclosure, the length and width can be measured by using an optical microscope, and the thickness can be measured by a profile image in an electron microscope, but not limited thereto. In addition, any two values or directions used for comparison may have a certain amount of error. 
     The types of light emitting devices disclosed in the disclosure may include display device, lighting device, etc., or other devices that contain light source, such as sensing device, touch device, and curved device, free shape display, bendable device, flexible device, tiled device, or a combination of the foregoing, but not limited thereto. The light emitting device may include a light emitting diode (LED), liquid crystal, fluorescence, phosphor, quantum dot (QD), other suitable materials, or a combination of the foregoing, but not limited thereto. The light emitting diode may include an organic light emitting diode (OLED), inorganic light emitting diode, sub-millimeter light emitting diode (mini LED), micro LED or quantum dot light emitting diode (QLED, QDLED), other suitable LED types or any combination of the above, but not limited thereto. The display device may also include, for example, a tiled display device, but is not limited thereto. The antenna device may be, for example, a liquid crystal antenna, but is not limited thereto. The antenna device may include, for example, a tiled antenna device, but is not limited thereto. It should be noted that the light emitting device can be any combination described above, but is not limited thereto. The light emitting device may have peripheral systems such as a driving system, a control system, a shelf system, etc. to support the display device, the lighting device, or the tiled device, etc., but the disclosure is not limited thereto. 
     It should be noted that the following embodiments can be used in a number of different embodiments by replacing, recombining, or mixing features to complete other embodiments without departing from the spirit of the disclosure. The features of each embodiment can be mixed and matched as long as they do not contradict the spirit of the disclosure or conflict with each other. 
     Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1A  to  FIG. 1D  are schematic cross-sectional views of a method of manufacturing a light emitting device according to an embodiment of the disclosure. Referring to  FIG. 1A , a substrate  100  is provided. The substrate  100  may have an upper surface  102  and a lower surface  104  opposite to each other. According to this embodiment, the substrate  100  may include a rigid substrate, a flexible substrate, or a combination of the foregoing. For example, a material of the substrate  100  may include glass, quartz, sapphire, ceramic, polycarbonate (PC), polyimide (PI), polyethylene terephthalate (PET), other suitable substrate materials, or a combination of the foregoing, but not limited thereto. 
     Next, a first bonding layer  110   a  and a first bonding layer  110   b  are formed on the substrate  100 . In detail, the first bonding layer  110   a  and the first bonding layer  110   b  may be disposed on the upper surface  102  of the substrate  100  and electrically connected to the substrate  100 . The first bonding layer  110   a  and the first bonding layer  110   b  may include a first portion  110   a   1  and a first portion  110   b   1  and a second portion  110   a   2  a second portion  110   b   2 . The second portion  110   a   2  and the second portion  110   b   2  are located between the first portion  110   a   1 , the first portion  110   b   1 , and the substrate  100 . According to this embodiment, a material of the first bonding layer  110   a  and the first bonding layer  110   b  may be copper (Cu), but not limited thereto. According to other embodiment, a material of the first bonding layer may be gold (Au), indium (In), tin (Sn) or other solid metal with electrical conductivity. According to this embodiment, the first bonding layer  110   a  and the first bonding layer  110   b  may be, for example, bumps, pads, pillars, connectors, or other electrically conductive connection member, but not limited thereto. 
     Next, referring to  FIG. 1A , a first passivation layer  120   a  and a first passivation layer  120   b  are formed on the first bonding layer  110   a  and the first bonding layer  110   b . In detail, the first passivation layer  120   a  and the first passivation layer  120   b  may have a top surface  122   a  and a top surface  122   b  and a bottom surface  124   a  and a bottom surface  124   b  opposite to each other. The bottom surface  124   a  and the bottom surface  124   b  may directly contact a surface  112   a  and a surface  112   b  of the first bonding layer  110   a  and the first bonding layer  110   b  away from the substrate  100 . That is, the first passivation layer  120   a  and the substrate  100  are respectively located at opposite sides of the first bonding layer  110   a , and the first passivation layer  120   b  and the substrate  100  are respectively located at opposite sides of the first bonding layer  110   b . Areas of the bottom surface  124   a  and the bottom surface  124   b  of the first passivation layer  120   a  and the first passivation layer  120   b  may be substantially greater than or equal to areas of the surface  112   a  and the surface  112   b  of the first bonding layer  110   a  and the first bonding layer  110   b . In a case of the same area, orthographic projections of the first passivation layer  120   a  and the first passivation layer  120   b  on the first bonding layer  110   a  and the first bonding layer  110   b  may substantially completely overlap the surface  112   a  and the surface  112   b  of the first bonding layer  110   a  and the first bonding layer  110   b . When the bottom surface  124   a  and the bottom surface  124   b  of the first passivation layer  120   a  and the first passivation layer  120   b  are greater than the areas of the surface  112   a  and the surface  112   b  of the first bonding layer  110   a  and the first bonding layer  110   b , at least a portion of the first passivation layer  120   a  and the first passivation layer  120   b  may cover sides of the first bonding layer  110   a  and the first bonding layer  110   b . In  FIG. 1A , side surfaces of the first bonding layer  110   a  and the first bonding layer  110   b  are perpendicular to a bottom surface  114   a  and a bottom surface  114   b  of the first bonding layer  110   a  and the first bonding layer  110   b , but the disclosure is not limited thereto. According to some embodiments, an angle between the side surfaces of the first bonding layer  110   a  and the first bonding layer  110   b  and the bottom surface  114   a  and the bottom surface  114   b  may be between 15 degrees and 90 degrees (15 degrees≤the angle≤90 degrees). According to this embodiment, a material of the first passivation layer  120   a  and the first passivation layer  120   b  may include silver (Ag), gold (Au), chromium (Cr), hafnium (HO, iridium (Ir), molybdenum (Mo), niobium (Nb), osmium (Os), palladium (Pd), platinum (Pt), Rhenium (Re), rhodium (Rh), ruthenium (Ru), tantalum (Ta), titanium (Ti), vanadium (V), tungsten (W) or zirconium (Zr) or other relatively stable pure metal materials that are less prone to oxidation, low activity, high melting point, etc., but not limited thereto. Here, the first passivation layer  120   a  and the first passivation layer  120   b  may be formed by, for example, chemical coating or other suitable processes, but the disclosure is not limited in this regard. According to this embodiment, the first passivation layer  120   a  and the first passivation layer  120   b  have a thickness T 1  between the top surface  122   a  and the top surface  122   b  and the bottom surface  124   a  and the bottom surface  124   b , and the thickness T 1  may range, for example, from 20 Å to 250 Å (20 Å≤T 1 ≤250 Å), but is not limited thereto. According to some embodiments, the thickness T 1  of the first passivation layer  120   a  and the first passivation layer  120   b  may also range, for example, from 50 Å to 150 Å (50 Å≤T 1 ≤150 Å). According to this embodiment, the thickness T 1  may be, for example, a maximum thickness of the first passivation layer  120   a  and the first passivation layer  120   b  measured along a normal direction Z of the substrate  100 . 
     Then, referring to  FIG. 1B , a light emitting element  200  is provided. The light emitting element  200  may have an active surface  202  and a back surface  204 , and the active surface  202  and the back surface  204  are opposite to each other. 
     Next, a second bonding layer  210   a  and a second bonding layer  210   b  are formed on the light emitting element  200 . In detail, the second bonding layer  210   a  and the second bonding layer  210   b  may be disposed on the active surface  202  of the light emitting element  200  and electrically connected to the light emitting element  200 . The second bonding layer  210   a  and the second bonding layer  210   b  may include a third portion  210   a   1  and a third portion  210   b   1  and a fourth portion  210   a   2  and a fourth portion  210   b   2 . The fourth portion  210   a   2  and the fourth portion  210   b   2  are located between the third portion  210   a   1  and the third portion  210   b   1  and the light emitting element  200 . According to the disclosure, a material of the second bonding layer  210   a  and the second bonding layer  210   b  may be same as or different from the material of the first bonding layer  110   a  and the first bonding layer  110   b . According to this embodiment, the material of the second bonding layer  210   a  and the second bonding layer  210   b  may be copper (Cu), but not limited thereto. According to other embodiment, a material of the second bonding layer may be gold (Au), indium (In), Tin (Sn) or other solid metal with electrical conductivity. According to this embodiment, the second bonding layer  210   a  and the second bonding layer  210   b  may be, for example, bumps, pads, pillars, connectors, or other electrically conductive connection member, but not limited thereto. 
     Referring to  FIG. 1B , a second passivation layer  220   a  and a second passivation layer  220   b  are formed on the second bonding layer  210   a  and the second bonding layer  210   b . In detail, the second passivation layer  220   a  and the second passivation layer  220   b  may have a top surface  222   a  and a top surface  222   b  and a bottom surface  224   a  and a bottom surface  224   b  opposite to each other. The bottom surface  224   a  and the bottom surface  224   b  may directly contact a surface  212   a  and a surface  212   b  of the second bonding layer  210   a  and the second bonding layer  210   b  away from the light emitting element  200 . That is, the second passivation layer  220   a  and the light emitting element  200  are respectively located at opposite sides of the second bonding layer  210   a , and the second passivation layer  220   b  and the light emitting element  200  are respectively located at opposite sides of the second bonding layer  210   b . Areas of the bottom surface  224   a  and the bottom surface  224   b  of the second passivation layer  220   a  and the second passivation layer  220   b  may be substantially equal to or greater than areas of the surface  212   a  and the surface  212   b  of the second bonding layer  210   a  and the second bonding layer  210   b . In a case of the same area, orthographic projections of the second passivation layer  220   a  and the second passivation layer  220   b  on the second bonding layer  210   a  and the second bonding layer  210   b  may substantially completely overlap the surface  212   a  and the surface  212   b  of the second bonding layer  210   a  and the second bonding layer  210   b . When the bottom surface  224   a  and the bottom surface  224   b  of the second passivation layer  220   a  and the second passivation layer  220   b  are greater than the areas of the surface  212   a  and the surface  212   b  of the second bonding layer  210   a  and the second bonding layer  210   b , at least a portion of the second passivation layer  220   a  and the second passivation layer  220   b  may cover sides of the second bonding layer  210   a  and the second bonding layer  210   b . In  FIG. 1B , side surfaces of the second bonding layer  210   a  and the second bonding layer  210   b  are perpendicular to a bottom surface  214   a  and a bottom surface  214   b  of the second bonding layer  210   a  and the second bonding layer  210   b , but the disclosure is not limited thereto. According to some embodiments, an angle between the side surfaces of the second bonding layer  210   a  and the second bonding layer  210   b  and the bottom surface  214   a  and the bottom surface  214   b  may be between 15 degrees and 90 degrees (15 degrees≤the angle≤90 degrees). According to this embodiment, a material of the second passivation layer  220   a  and the second passivation layer  220   b  may include silver, gold, chromium, hafnium, iridium, molybdenum, niobium, osmium, palladium, platinum, Rhenium, rhodium, ruthenium, tantalum, titanium, vanadium, tungsten or zirconium, or other relatively stable pure metal materials that are less prone to oxidation, low activity, high melting point, etc., but not limited thereto. 
     Here, the material of the first passivation layer  120   a  and the first passivation layer  120   b  may be, for example, same as the material of the second passivation layer  220   a  and the second passivation layer  220   b , and the second passivation layer  220   a  and the second passivation layer  220   b  may be formed by, for example, chemical coating or other suitable processes, but the disclosure is not limited in this regard. According to this embodiment, the second passivation layer  220   a  and the second passivation layer  220   b  have a thickness T 2  between the top surface  222   a  and the top surface  222   b  and the bottom surface  224   a  and the bottom surface  224   b , and the thickness T 2  may range, for example, from 20 Å to 250 Å (20 Å≤T 2 ≤250 Å), but is not limited thereto. According to some embodiments, the thickness T 2  of the second passivation layer  220   a  and the second passivation layer  220   b  may also range, for example, from 50 Å to 150 Å (50 Å≤T 2 ≤150 Å). According to this embodiment, the thickness T 2  may be, for example, a maximum thickness of the second passivation layer  220   a  and the second passivation layer  220   b  measured along a normal direction Z′ of the light emitting element  200 . 
     Referring  FIG. 1A  and  FIG. 1B  at the same time, a first spacing D 1  exists between the first bonding layer  110   a  and the first bonding layer  110   b , in which the first bonding layer  110   a  and the first bonding layer  110   b  are adjacent to each other, and a second spacing D 2  exists between the second bonding layer  210   a  and the second bonding layer  210   a , in which the second bonding layer  210   a  and the second bonding layer  210   a  are adjacent to each other. A size of the first spacing D 1  is approximately the same as a size of the second spacing D 2 . The size of the first spacing D 1  may be, for example, less than or equal to 100 μm (0 μm&lt;D 1 ≤100 μm). Similarly, the size of the second spacing D 2  may be, for example, less than or equal to 100 μm (0 μm&lt;D 2 ≤100 μm), but not limited thereto. 
     Then, referring to  FIG. 1C , the second passivation layer  220   a  and the second passivation layer  220   b  on the light emitting element  200  are contacted with the first passivation layer  120   a  and the first passivation layer  120   b . Specifically, the light emitting element  200  of  FIG. 1B  is flipped upside down, so that the light emitting element  200  is bonded to the substrate  100  in a flip chip manner. The top surface  122   a  of the first passivation layer  120   a  may directly contact the top surface  222   a  of the second passivation layer  220   a , and the top surface  122   b  of the first passivation layer  120   b  may directly contact the top surface  222   b  of the second passivation layer  220   b.    
     Then, referring to  FIG. 1C  and  FIG. 1D  at the same time, after the light emitting device  200  is bonded to the substrate  100 , a third bonding layer  310   a  and a third bonding layer  310   b  are gradually formed and the light emitting device  200  is bonded to the substrate  100 . Specifically, when the second passivation layer  220   a  and the second passivation layer  220   b  on the light emitting element  200  contact the first passivation layer  120   a  and the first passivation layer  120   b  on the substrate  100 , a diffusion step is performed, and by applying suitable conditions such as time, temperature, and/or pressure, metal atoms of the first portion  110   a   1  and the first portion  110   b   1  of the first bonding layer  110   a  and the first bonding layer  110   b  may be diffused in the diffusion step in a direction toward the light emitting element  200  and pass through the first passivation layer  120   a  and the first passivation layer  120   b , and/or metal atoms of the first passivation layer  120   a  and the first passivation layer  120   b  may be diffused in a direction toward the substrate  100  and pass through the first portion  110   a   1  and the first portion  110   b   1  of the first bonding layer  110   a  and the first bonding layer  110   b . Similarly, in the diffusion step, metal atoms of the third portion  210   a   1  and the third portion  210   b   1  of the second bonding layer  210   a  and second bonding layer  210   b  may be diffused in the direction toward the substrate  100  and pass through the second passivation layer  220   a  and the second passivation layer  220   b , and/or metal atoms of the second passivation layer  220   a  and the second passivation layer  220   b  may be diffused in the direction toward the light emitting element  200  and pass through the third portion  210   a   1  and the third portion  210   b   1  of the second bonding layer  210   a  and the second bonding layer  210   b . Thereby, the metal atoms of the first bonding layer  110   a  and the first bonding layer  110   b  and the first passivation layer  120   a  and the first passivation layer  120   b  may be diffused with each other, and the metal atoms of the second bonding layer  210   a  and the second bonding layer  210   b  and the second passivation layer  220   a  and the second passivation layer  220   b  may be diffused with each other, thereby forming the third bonding layer  310   a  and the third bonding layer  310   b . The third bonding layer  310   a  and the third bonding layer  310   b  are located between the first passivation layer  120   a  and the first passivation layer  120   b  and the second passivation layer  220   a  and the second passivation layer  220   b . The third bonding layer  310   a  and the third bonding layer  310   b  may include the metal atoms from the first portion  110   a   1  and the first portion  110   b   1  of the first bonding layer  110   a  and the first bonding layer  110   b  and the metal atoms from the third portion  210   a   1  and the third portion  210   b   1  of the second bonding layer  210   a  and the second bonding layer  210   b . According to this embodiment, the third bonding layer  310   a  and the third bonding layer  310   b  have a thickness T 3  (that is, a distance between the first passivation layer  120   a  and the second passivation layer  220   a , in which the first passivation layer  120   a  and the second passivation layer  220   a  are adjacent to each other), which may be, for example, 10 Å to 200 Å (10↑≤T 2 ≤200 Å), but not limited thereto. According to some embodiments, a range of the thickness T 3  may be greater than 200 Å. And with the increase of diffusion time, temperature and pressure, the thickness T 3  will increase. The thickness T 3  may be, for example, a maximum thickness of the third bonding layer  310   a  and the third bonding layer  310   b  measured along the normal direction Z of the substrate  100 . 
     As shown in  FIG. 1D , the light emitting element  200  may be bonded to the substrate  100  through a bonding structure  300   a  and a bonding structure  300   b  (including, for example, at least the fourth portion  210   a   2  and the fourth portion  210   b   2  of the second bonding layer  210   a  and the second bonding layer  210   b , the second passivation layer  220   a  and the second passivation layer  220   b , the third bonding layer  310   a  and the third bonding layer  310   b , the first passivation layer  120   a  and the first passivation layer  120   b , and the second portion  110   a   2  and the second portion  110   b   2  of the first bonding layer  110   a  and the first bonding layer  110   b ), and a light emitting device  10  of this embodiment is manufactured. In other words, the light emitting device  10  of this embodiment may include the substrate  100 , the light emitting element  200 , and the bonding structure  300   a  and the bonding structure  300   b . The light emitting element  200  may be disposed on the substrate  100  through the bonding structure  300   a  and the bonding structure  300   b.    
     Since the bonding structure  300   a  and the bonding structure  300   b  have approximately the same structure, the following is a further description of the bonding structure  300   a  as an example. Referring to  FIG. 1D , according to this embodiment, the bonding structure  300   a  may include at least three bonding layers (i.e., the fourth portion  210   a   2  of the second bonding layer  210   a , the third bonding layer  310   a , and the second portion  110   a   2  of the first bonding layer  110   a ) and at least two passivation layers (i.e., the second passivation layer  220   a  and first passivation layer  120   a ) in a staggered arrangement. More specifically, according to this embodiment, the first passivation layer  120   a  may be located between the second portion  110   a   2  of the first bonding layer  110   a  and the third bonding layer  310   a , the third bonding layer  310   a  may be located between the second passivation layer  220   a  and the first passivation layer  120   a , and the second passivation layer  220   a  may be located between the fourth portion  210   a   2  of the second bonding layer  210   a  and the third bonding layer  310   a.    
     According to this embodiment, the time, temperature, and pressure applied during the metal atom diffusion step do not cause the first bonding layer  110   a , the first passivation layer  120   a , the second bonding layer  210   a , and the second passivation layer  220   a  to melt, but allow the first bonding layer  110   a , the first passivation layer  120   a , the second bonding layer  210   a , and the second passivation layer  220   a  to form the third bonding layer  310   a  by diffusion in a solid state, and to bond the first bonding layer  110   a  to the second bonding layer  210   a.    
     According to this embodiment, the conditions of time, temperature, and pressure applied during the diffusion step may be, for example, 1 minute of diffusion at a pressure of 50 MPa and a temperature of 200° C., but is not limited thereto. According to some embodiments, the conditions under which the diffusion step is performed may also be 1 minute of diffusion at a pressure of 10 MPa and a temperature of 400° C. According to some embodiments, the conditions under which the diffusion step is performed may also be 10 minutes of diffusion at a pressure of 50 MPa and a temperature of 150° C. According to other embodiments, the conditions of time, temperature, and pressure applied during the diffusion step may also be adjusted, for example, in the following manner. For example, when the value of one or both of time, temperature, and pressure is increased, the value of the remaining one or both may be decreased. In addition, according to some other embodiments, diffusion reaction may continue after the diffusion step has been completed (i.e., the original process conditions of time, temperature, and pressure are no longer supplied). 
     According to this embodiment, bonding between solid metal and solid metal (e.g. between the first bonding layer  110   a  and the second bonding layer  210   a , and more specifically between metal atoms passing from the first bonding layer  110   a  through the first passivation layer  120   a  and metal atoms passing from the second bonding layer  210   a  through the second passivation layer  220   a ) may be, for example, bonding between gold and gold, bonding between copper and copper, or bonding between indium and tin, but not limited thereto. That is, the material of the first bonding layer  110   a  may be the same as or different from the material of the second bonding layer  210   a , but a material of each bonding layer may not be limited to the materials. 
     According to this embodiment, when bonding between solid metal and solid metal, metallic bonds between the solid metal and the solid metal have a large number of shared electron orbit, and it is easier to diffuse and move between solid metal atoms than electronic structure of metal oxide, which requires the formation of an octet structure. Therefore, presence of oxidized metal at a bonding interface may prevent the diffusion of the solid metal and lead to the failure of the bonding between the solid metal and the solid metal. Therefore, in the manufacturing method according to this embodiment, oxidation of the first bonding layer  110   a  and the second bonding layer  210   a  due to contact with air may be reduced by providing metal materials (e.g., the first passivation layer  120   a  and the second passivation layer  220   a ) that are not easily oxidized, and thus the first bonding layer  110   a  and the second bonding layer  210   a  may be bonded by diffusion. 
     However, according to some embodiments, the first bonding layer  110   a  (or the second bonding layer  210   a ), which is not easily oxidized, may also optionally be provided without an additional first passivation layer  120   a  (or the second passivation layer  220   a ). For example, when the first bonding layer  110   a  and the second bonding layer  210   a  are made of gold that is not easily oxidized, the first bonding layer and the second bonding layer may be directly contacted by the first bonding layer without the need for an additional first passivation layer and second passivation layer. When the gold that is not easily oxidized is used as the first bonding layer  110   a  and a solid metal that is easily oxidized (for example, copper) is used as the second bonding layer  210   a , a second passivation layer must be additionally provided on the second bonding layer, so that the first bonding layer may be directly contact the second passivation layer  220   a.    
     It should be noted that, according to this embodiment, the thickness T 1  of the first passivation layer  120   a  and/or the thickness T 2  of the second passivation layer  220   a  may range from 20 Å to 250 Å (20 Å≤the thickness T 2 ≤250 Å) or from 50 Å to 150 Å (50 Å≤the thickness T 2 ≤150 Å), but not limited thereto. It should be noted that a passivation layer that is too thin tends to reduce the ability to protect the bonding layer due to poor thickness uniformity, and a passivation layer that is too thick requires higher process time, temperature or pressure to allow the bonding layer to diffuse. An appropriate range of the thickness of the passivation layer may allow the solid metal (e.g., copper) in the first bonding layer  110   a  to diffuse relatively quickly through the first passivation layer  120   a , and allows the solid metal (e.g., copper) in the second bonding layer  210   a  to diffuse relatively quickly through the second passivation layer  220   a  and be less susceptible to metal oxides. 
     In addition, since the third bonding layer  310   a  is formed by the diffusion of metal atoms of the first bonding layer  110   a  and the second bonding layer  210   a , the material of the third bonding layer  310   a  may include the material of the first bonding layer  110   a  and the material of the second bonding layer  210   a . For example, according to this embodiment, when the material of the first bonding layer  110   a  is copper and the material of the second bonding layer  210   a  is copper, the material of the third bonding layer  310   a  may be copper, for example. According to some embodiments, when the material of the first bonding layer is gold and the material of the second bonding layer is gold, the material of the third bonding layer may be gold, for example. According to some embodiments, when the material of the first bonding layer is tin and the material of the second bonding layer is indium, the material of the third bonding layer may, for example, include indium and tin. 
     Since the third bonding layer  310   a  is formed by the diffusion of metal atoms from the first bonding layer  110   a  and the second bonding layer  210   a , concentration distribution of metal atoms may not be uniform throughout the third bonding layer  310   a . However, according to this embodiment, when using an elemental analyzer to analyze composition of the third bonding layer  310   a , analysis results may be interfered by signals of the first passivation layer  120   a  and the second passivation layer  220   a  at opposite sides of the third bonding layer  310   a  due to measurement capability of the instrument itself. For example, according to this embodiment, when the material of the first bonding layer  110   a  is copper and the material of the second bonding layer  210   a  is also copper, the material of the third bonding layer  310   a  measured using the element analyzer may, for example, include more than 50% copper, but not limited thereto. According to other embodiments, the material of the third bonding layer  310   a , which may also be measured, may for example include 80% to 100% copper. Therefore, according to this embodiment, the third bonding layer  310   a  and the third bonding layer  310   b  are defined as a region where “the concentration of the same metal atoms as in the first bonding layer  110   a  and the first bonding layer  110   b  and/or the second bonding layer  210   a  and the second bonding layer  210   b  is greater than or equal to 50% in the two passivation layers”. 
     In short, in the light emitting device  10  and the manufacturing method thereof according to the embodiment of the disclosure, the third bonding layer  310   a  and the third bonding layer  310   b  may be formed between the first passivation layer  120   a  and the first passivation layer  120   b  and the second passivation layer  220   a  and the second passivation layer  220   b  without melting the solid metal by means of mutual diffusion between the solid metal and the solid metal. In this way, the light emitting device  200  may be bonded to the substrate  100  through the bonding structure  300   a  and the bonding structure  300   b . In addition, since the first spacing D 1  (or the second spacing D 2 ) before bonding may be substantially the same as a first spacing D 1 ′ (or a second spacing D 2 ′) after bonding, the light emitting device  10  of the disclosure and the manufacturing method thereof may reduce the problem of short-circuit during bonding or may improve the bonding yield compared to a case where a first spacing (or a second spacing) may be shortened due to overflow of solder after bonding using molten solder. 
     Other embodiments are set forth below for illustrative purposes. It should be noted here that the following embodiments follow the numeral references and parts of the previous embodiments, where the same numeral references are used to indicate the same or similar components, and the description of the same technical content is omitted. The description of the omitted parts can be found in the preceding embodiments, and will not be repeated in the following embodiments. 
       FIG. 2  is a schematic cross-sectional view of a light emitting device according to another embodiment of the disclosure. Referring  FIG. 2  and  FIG. 1D  at the same time, a light emitting device  20  according to this embodiment is substantially similar to the light emitting device  10  of  FIG. 1D , so the same and similar components of the two embodiments are not repeated here. The light emitting device  20  according to this embodiment differs from the light emitting device  10  mainly in that in the light emitting device  20  according to this embodiment, a material of a first passivation layer  120   a ′ and a first passivation layer  120   b ′ and a material of a second passivation layer  220   a ′ and a second passivation layer  220   b ′ may be different. 
     Specifically, referring to  FIG. 2 , according to this embodiment, the light emitting device  20  may include the substrate  100 , the light emitting element  200 , and a bonding structure  300   a ′ and a bonding structure  300   b ′. The light emitting element  200  may be disposed on the substrate  100  through the bonding structure  300   a ′ and the bonding structure  300   b′.    
     The following is a description of the bonding structure  300   a ′ as an example. Similar to the bonding structure  300   a  in the previous embodiment, the bonding structure  300   a ′ may include at least three bonding layers (i.e., the fourth portion  210   a   2  of the second bonding layer  210   a , the third bonding layer  310   a , and the second portion  110   a   2  of the first bonding layer  110   a ) and at least two passivation layers (i.e., the second passivation layer  220   a ′ and the first passivation layer  120   a ′) in a staggered arrangement. More specifically, according to this embodiment, the first passivation layer  120   a ′ may be located between the second portion  110   a   2  of the first bonding layer and the third bonding layer  310   a , and the third bonding layer  310   a  may be located between the second passivation layer  220   a ′ and the first passivation layer  120   a ′, and the second passivation layer  220   a ′ may be located between the fourth portion  210   a   2  of the second bonding layer  210   a  and the third bonding layer  310   a.    
     The following are examples of possible combinations of a material of the first passivation layer  120   a ′ and a material of the second passivation layer  220   a ′ according to this embodiment, but the disclosure is not limited thereto. According to this embodiment, the material of the first passivation layer  120   a ′ (or the second passivation layer  220   a ′) may be silver or titanium, for example, and the material of the second passivation layer  220   a ′ (or the first passivation layer  120   a ′) may be gold, for example. Since silver, titanium, and gold are commonly used metals in the manufacturing process of light emitting devices, the manufacturing method using silver or titanium as the material for the first passivation layer  120   a ′ (or the second passivation layer  220   a ′) and gold as the material for the second passivation layer  220   a ′ (or the first passivation layer  120   a ′) is compatible with the manufacturing process of various types of light emitting devices. 
     According to some embodiments, the material of the first passivation layer  120   a ′ may be, for example, palladium, and the material of the second passivation layer  220   a ′ may be, for example, gold. Since palladium can be grown on a surface of the first bonding layer  110   a  by chemical coating, and the chemical coating process is highly compatible with the process of the light emitting device and easy to perform, the manufacturing method using palladium as the material of the first passivation layer  120   a ′ and gold as the material of the second passivation layer  220   a ′ is also compatible with the manufacturing process of various types of light emitting devices. 
     In summary, in the light emitting device and the manufacturing method thereof according to the embodiment of the disclosure, the third bonding layer may be formed between the first passivation layer and the second passivation layer without melting the solid metal by means of mutual diffusion between the solid metal and the solid metal (i.e., between the second bonding layer and the second passivation layer, or between the first bonding layer and the first passivation layer, but not limited thereto). In this way, the second bonding layer may be bonded to the first bonding layer through the second passivation layer, the third bonding layer, and the first passivation layer, and the light emitting element may be bonded to the substrate through the bonding structure (i.e., including the second bonding layer, the second passivation layer, the third bonding layer, the first passivation layer, and the first bonding layer). In addition, since a first spacing (or a second spacing) before bonding may be substantially the same as a first spacing (or a second spacing) after bonding, the light emitting device of the disclosure and the manufacturing method thereof may reduce the problem of short-circuit during bonding or may improve the bonding yield compared to a case using molten solder, which causes short-circuit of two adjacent first bonding layers (or two adjacent second bonding layers) due to shortening of the first spacing (or the second spacing) after bonding. 
     A number of contacts of the light emitting element according to each embodiment of the disclosure is two, but is not limited thereto. There may be more contacts on one element among different elements, or a light emitting element with a special structure may only have a single contact, and the light emitting device may be completed by the bonding method shown in this disclosure. 
     Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the disclosure and not to limit them. Although the disclosure is described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.