PATENT DOCUMENT

Publication Number: US-10734269-B1
Application Number: US-201815914595-A
Country: US
Kind Code: B1

Title: Micro device metal joint process

Abstract:
Metal-to-metal adhesion joints are described as a manner to hold down micro devices to a carrier substrate within the context of a micro device transfer manufacturing process. In accordance with embodiments, the metal-to-metal adhesion joints must be broken in order to pick up the micro devices from a carrier substrate, resulting in micro devices with nubs protruding from bottom contacts of the micro devices. Once integrated, the micro devices are bonded to a receiving substrate, the nubs may be embedded in a metallic joint, or alternatively be diffused within the metallic joint as interstitial metallic material that is embedded within the metallic joint.

Claims:
What is claimed is: 
     
       1. A light emitting structure comprising:
 a landing pad; 
 a metallic joint on the landing pad; 
 a light emitting diode that includes a bottom contact bonded with the metallic joint on the landing pad, and a nub protruding from the bottom contact; 
 wherein the nub is embedded within the metallic joint; 
 wherein the nub comprises a bulk layer and an adhesion layer lining a top surface and sidewalls of the bulk layer, the adhesion layer in direct contact with the bottom contact between the bulk layer and the bottom contact. 
 
     
     
       2. The light emitting structure of  claim 1 , wherein the bottom contact comprises an interface layer that is bonded to the metallic joint, and the adhesion layer is in direct contact with the interface layer. 
     
     
       3. The light emitting structure of  claim 2 , wherein the nub and the interface layer formed of materials sharing a same metallic element. 
     
     
       4. The light emitting structure of  claim 3 , wherein the metallic element is selected from the group consisting of gold and aluminum. 
     
     
       5. The light emitting structure of  claim 3 , wherein the interface layer is formed of gold, and the nub is formed of a gold alloy. 
     
     
       6. The light emitting structure of  claim 2  comprising a plurality of nubs protruding from the bottom contact, wherein the plurality of nubs are embedded within the metallic joint, the bottom contact comprises an interface layer that is bonded to the metallic joint, and the plurality of nubs are in direct contact with the interface layer. 
     
     
       7. The light emitting structure of  claim 2 , wherein the metallic joint comprises a bonding layer and a compound region, wherein the compound region connects the bonding layer and the interface layer. 
     
     
       8. The light emitting structure of  claim 2 , wherein the nub has a maximum width of less than 0.5 μm.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Application No. 62/516,559 filed Jun. 7, 2017 which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein relate to micro devices. More particularly embodiments relate to the stabilization of micro device on a carrier substrate and transfer to a receiving substrate. 
     Background Information 
     State of the art displays for phones, tablets, computers, and televisions utilize glass substrates with thin film transistor (TFTs) to control transmission of backlight though pixels based on liquid crystals. More recently emissive displays such as those based on organic light emitting diodes (OLEDs) have been introduced as being more power efficient, and allowing each pixel to be turned off completely when displaying black. Even more recently, it has been proposed to incorporate emissive inorganic semiconductor-based micro LEDs into high resolution displays. 
     In one implementation, it has been proposed to transfer an array of inorganic semiconductor-based micro LEDs from a carrier substrate to a receiving (e.g. display) substrate using an array electrostatic transfer heads. For example, it has been proposed in U.S. Pat. No. 8,835,940 to stage an array of micro LEDs on an array of stabilization posts formed of an adhesive bonding material, such as a thermoset material. During the transfer process, it is described that the array of electrostatic transfer heads generate a sufficient pressure to overcome the adhesion strength between the adhesive bonding material and the micro LEDs. 
     SUMMARY 
     Embodiments describe metal-to-metal adhesion joints to hold down micro devices to a carrier substrate within the context of a micro device transfer manufacturing process. In accordance with embodiments the micro devices may include residual nubs protruding from their bottom contacts at the conclusion of the micro device transfer process. For example, the nubs may be embedded within metallic joint used to join the micro devices to a receiving substrate. Alternatively, the nubs may at least partially diffuse within the metallic joint and form volumes of interstitial metallic material embedded within the metallic joint. In an embodiment, the nubs are formed as the result of a pick up operation, in which portions of metal posts used to form metal-to-metal adhesion joints with the micro devices are picked up along with the micro devices. In another embodiment, the nubs are formed as part of the bottom contacts of the micro devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional side view illustration of a micro device poised for pick upon on a plurality of stabilization posts in accordance with an embodiment. 
         FIG. 1B  is a cross-sectional side view illustration of a micro device with a nano-pillar within a bottom contact in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view illustration of a bulk LED substrate in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view illustration of an array of bottom contacts formed on a bulk LED substrate in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view illustration of the formation of a patterned sacrificial release layer in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view illustration of the formation of a metallic stabilization layer in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view illustration of the metallic stabilization layer bonded to a carrier substrate in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view illustration of a thinned p-n diode layer in accordance with an embodiment. 
         FIG. 8  is a cross-section side view illustration of a plurality of mesa structures formed in an LED device layer in accordance with an embodiment. 
         FIG. 9  is a cross-section side view illustration of the removal of the sacrificial release layer in accordance with an embodiment. 
         FIG. 10A  is a cross-sectional side view illustration of an array of electrostatic transfer heads positioned over an array of micro devices on a carrier substrate in accordance with an embodiment. 
         FIG. 10B  is a cross-sectional side view illustration of an array of electrostatic transfer heads in contact with an array of micro devices in accordance with an embodiment. 
         FIG. 10C  is a cross-sectional side view illustration of an array of electrostatic transfer heads picking up an array of micro devices in accordance with an embodiment. 
         FIG. 10D  is a cross-sectional side view illustration of an array of micro devices positioned over a receiving substrate in accordance with an embodiment. 
         FIG. 10E  is a cross-sectional side view illustration of an array of micro devices released onto a receiving substrate in accordance with an embodiment. 
         FIG. 11A  is a cross-sectional side view illustration of a micro device including a nub protruding from a bottom contact bonded to a receiving substrate in accordance with an embodiment. 
         FIG. 11B  is a cross-sectional side view illustration of a micro device including a partially diffused nub bonded to a receiving substrate in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view illustration of a micro device including a nano-pillar bonded to a receiving substrate in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe structures and methods of forming metal-to-metal adhesion joints to hold down micro devices to a carrier substrate within the context of a micro device transfer manufacturing process. 
     It has been observed that micro device transfer processes utilizing implementations of a stabilization layer that retains micro devices on the carrier substrate by way of surface adhesion may be unreliable, with an observed wide distribution of adhesion force among micro devices. For example, U.S. Pat. No. 8,835,940 describes an implementation which utilizes surface chemistry interaction of polymers such as benzocyclobutene (BCB) to a gold surface achieved during spin coating. It has been observed that such a process may be sensitive to pre-spin coat processing, as well as the fluidic interaction in and around the openings within the sacrificial release layer used to define adhesion of the stabilization posts. This variation of adhesion may in turn translate to a measurable micro device pick up yield within a volume manufacturing process. 
     In accordance with embodiments, a sputtered, evaporated or electroplated metal-to-metal joint is described to hold down micro devices to their respective carrier substrate. In an embodiment, a metal contact pad is fabricated for the bottom contact of a corresponding micro device. A sacrificial release layer is then deposited and patterned, followed by the deposition of a blanket metal layer over the entire surface of the wafer. This blanket metal layer may include multiple layers, such as an adhesion layer and a bulk layer. This blanket metal layer becomes the stabilization layer including the stabilization posts which form the metal joint in the contact openings within the sacrificial release layer. The substrate may then be bonded to a carrier substrate using a variety of methods, including blanket polymer, eutectic, or thermocompression bonding techniques. In another embodiment, one or more nano-pillars are formed within the bottom contact to define the area of the metal-to-metal joints. In such an embodiment, the stabilization posts in effect have been created within the bottom contact. 
     In one aspect, the metal-to-metal joints in accordance with embodiments may provide alternative approaches for adhering micro devices to a carrier substrate that eliminate variable fluidic and surface chemistry effects. In place, adhesion strength may be determined by metal properties and geometries. 
     In various embodiments, description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions and processes, etc., in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the embodiments. Reference throughout this specification to “one embodiment” means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “over”, “to”, “between”, and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over”, or “on” another layer or bonded “to” or in “contact” with another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     While embodiments are described with specific regard to micro LED devices comprising p-n diodes, it is to be appreciated that embodiments of the invention are not so limited and that certain embodiments may also be applicable to other micro devices which are designed in such a way so as to perform in a controlled fashion a predetermined electronic function (e.g. diode, transistor, integrated circuit, display circuitry, sensor) or photonic function (LED, laser). Embodiments are also applicable to micro chips. 
     The terms “micro” device, “micro” mesa, “micro” chip, or “micro” LED device as used herein may refer to the descriptive size of certain devices, chips, or structures in accordance with embodiments of the invention. As used herein the term “micro device” specifically includes “micro LED device” and “micro chip”. As used herein, the terms “micro” devices or structures are meant to refer to the scale of 1 to 300 μm. In an embodiment, a single micro device or structure has a maximum dimension, for example length or width, of 1 to 300 μm, or 1 to 100 μm. In an embodiment, the top contact surface of each micro device, micro structure, or electrostatic transfer head has a maximum dimension of 1 to 300 μm, 1 to 100 μm, or more specifically 3 to 20 μm. 
       FIG. 1A  is a cross-sectional side view illustration of a micro device poised for pick upon on a plurality of stabilization posts in accordance with an embodiment. As shown, the stabilization structure  100  includes a metallic stabilization layer  106  including one or more stabilization posts  108 . A micro device  200  is on the one or more stabilization posts  108 . The micro device  200  includes a bottom contact  210  that is in direct contact with and wider than a corresponding stabilization post  108  directly underneath the bottom contact  210 . In a particular embodiment, the micro device is a micro LED device including a micro p-n diode  250 . 
     As shown in the close up illustration, the bottom contact  210  may be a multiple layer stack. In an accordance with embodiments, the multiple layer stack may include a number of combinations of layers such as a contact layer, mirror layer, barrier layer, and interface layer, though not all layers are required, and different layers may be included. For example, a bottom contact  210  may include a contact layer  212  for ohmic contact, a mirror layer  214 , a barrier layer  216 , and an interface layer  218 . Various adhesion layers may be formed between any of the layers within the layer stack. In an embodiment, contact layer  212  is formed of a high work-function metal such as nickel. In an embodiment, a mirror layer  214  such as silver or aluminum is formed over the contact layer  212  to reflect the transmission of the visible wavelength emitted from the micro p-n diode  250 . In an embodiment, platinum is used as a diffusion barrier layer  216  to interface layer  218 . Interface layer  218  may be formed of a variety of materials that can be chosen for bonding to the receiving substrate and/or to achieve the requisite tensile strength or adhesion or surface tension with the stabilization posts. 
     In an embodiment, interface layer  218  is formed of a conductive material (both pure metals and alloys) that can diffuse with a bonding layer (e.g. gold, indium, or tin) on a receiving substrate and is also amenable to forming a metal-to-metal joint on the carrier substrate  102 . While embodiments are not limited to specific metals, exemplary materials for interface layer  218  include gold and aluminum, as well as their alloys. 
     In accordance with an embodiment, a sputtered or evaporated metal-to-metal joint is described to hold down micro devices to their respective carrier substrate. In this manner, adhesion strength is determined by metal properties of the materials and geometries forming the metal-to-metal joints. In an embodiment, total adhesion may be within a workable range so that the pick up can be achieved with an applied pick up pressure on the transfer head of 20 atmospheres or less, or more particularly 5-10 atmospheres. 
     The metallic stabilization layer  106  in accordance with embodiments may be formed of one or more layers and materials. For example, the stabilization layer may include a bulk layer  110  and optional adhesion layer  112  to promote adhesion with the bulk layer  110  and the bottom contact  210 . As shown, the optional adhesion layer  112  may line the sidewalls  113  and top surface  115  of the bulk layer  110  for a stabilization post  108 . While embodiments are not limited to specific metals, exemplary materials for bulk layer  110  include gold and aluminum, as well as alloys in which elemental impurities can be added to tailor mechanical properties (e.g. yield strength, hardness, ductility) of the metal-to-metal joint. Exemplary elemental impurities that may be included are Co, Ni, Be, Al, Ca, Mo, Au. In an embodiment, a gold alloy material includes 0 to 5% by weight of impurity. The interface layer  218  may additionally be formed of any of these materials. While embodiments are not limited to specific metallic materials, exemplary materials for adhesion layer  112  include Ti, TiW, and Ni. Adhesion layer  112  may also be selected to control joint adhesion, and additionally the break point during the transfer process. Geometry of the stabilization posts  108  may also be varied to control adhesion. For example, the stabilization posts  108  and resultant metal-to-metal joints may be in the form of solid posts, annular rings, etc. The number of stabilization posts  108  and location can also be adjusted to control the pull force required for transfer. 
     In an embodiment, a stabilization structure includes a metallic stabilization layer  106  with an array of stabilization posts  108 , and an array of micro devices  200  on the array of stabilization posts  108 . Each micro device  200  includes a bottom contact  210  that is in direct contact with and wider than a corresponding stabilization post  108  directly underneath the bottom contact  210 . Specifically, the bottom contact  210  includes an interface layer  218 , and the stabilization post  108  is in direct contact with the interface layer  218 . In an embodiment, the stabilization post  108  and the interface layer  218  formed of materials sharing a same metallic element, such as gold or aluminum. In an embodiment, the interface layer is formed of gold, while the stabilization layer includes a gold alloy. The stabilization layer  106  may additionally include an adhesion layer  112  and a bulk layer  110 , with the adhesion layer  112  being in direct contact with the interface layer  218 . In an embodiment, each stabilization post has a maximum width of less than 0.5 μm. In an embodiment, plurality of stabilization posts  108  in direct contact with each interface layer  218 . 
       FIG. 1B  is a cross-sectional side view illustration of a stabilization structure  100  including a micro device with a nano-pillar within a bottom contact in accordance with an embodiment. In particular, the embodiment illustrated in  FIG. 1B  is designed to create one or more protrusions within the bottom contact  210  rather than separately forming stabilization posts. Specifically, the micro device  200  structure may include a micro p-n diode  250  and a bottom contact  210 . In addition to including any of a contact layer  212 , mirror layer  214 , barrier layer  216 , and interface layer  218  as previously described with regard to  FIG. 1A , the bottom contact  210  includes one or more nano-mesas  260 . The nano-mesas  260  may be formed on the micro p-n diode  250  prior to forming the other layers of the bottom contact  210 , between any layers within the bottom contact  210 , or formed on and after the interface layer  218 . In the specific embodiment illustrated in  FIG. 1B , the nano-mesas are formed just prior to the interface layers  218 , so as to create a protruding profile within the bottom contact  210 . 
     In accordance with embodiments, the nano-mesas  260  may be of similar size and shape as the stabilization posts  108  described herein, such as between 100 nm and 1,000 nm wide, or more specifically approximately 200 nm to 500 nm wide, and between approximately 0.25 and 3 microns thick, or more specifically approximately 0.5 to 1 microns thick. In this manner, the interface layer  218  formed over a corresponding nano-mesa  260  protrudes from the surrounding areas of the bottom contact  210 /interface layer  218 . The protruding portion of the interface layer  218  may be bonded, for example, using thermocompression bonding, to a joining layer  104  on the carrier substrate  102 . In an embodiment, the joining layer  104  and interface layer  218  are formed of the same or different materials to facilitate thermocompression bonding and create the metal-to-metal joint, control adhesion, and break point. The joining layer  104  illustrated in  FIG. 1B  may be formed of any of the materials described with regard to the stabilization layer  106  of  FIG. 1A . The joining layer  104  may also including multiple layers. 
     Referring now to  FIGS. 2-9  cross-sectional side view illustrations are provided of a method of forming an array of micro devices supported by an array of stabilization posts such as that illustrated in  FIG. 1A  in accordance with embodiments.  FIG. 2  is a cross-sectional side view illustration of a bulk LED substrate in accordance with an embodiment. As shown, the process sequence may start with a bulk LED substrate  201  including a p-n diode layer  221  including a first doped layer  226  doped with a first dopant type (e.g. n-type), a second doped layer  222  doped with a second dopant type (e.g. p-type) opposite the first dopant type, and an active layer  224  between the doped layers  226 ,  222 . The active layer  224  may include one or more quantum well layers separated by barrier layers. In accordance with embodiments, the p-n diode layer  221  may be formed of III-V or II-VI inorganic semiconductor-based materials, and be designed for emission at a variety of primary wavelengths, such as red, green, blue, etc. 
     An array of laterally separate bottom contacts  210  are then formed on the doped layer  222  as illustrated in  FIG. 3 . As previously described with regard to  FIG. 1A , the bottom contacts may include multiple layers, such as a contact layer  212  for ohmic contact, a mirror layer  214 , a barrier layer  216 , and an interface layer  218 . 
     Referring now to  FIG. 4  a sacrificial layer  232  is formed over the bottom contacts  210  on the bulk LED substrate  201  in accordance with an embodiment. In an embodiment, sacrificial layer  140  is between approximately 0.1 and 2 microns thick, or more specifically approximately 0.5 microns thick. In an embodiment, sacrificial layer is formed of an oxide (e.g. SiO 2 ) or nitride (e.g. SiN X ), though other materials may be used which can be selectively removed with respect to the other layers. The sacrificial layer  232  may then be patterned to form an array of contact openings  234  exposing the bottom contacts  210 . In accordance with embodiments, the thickness of the sacrificial layer  232  and shape of the contact openings  234  determine the shape and side of the stabilization posts to be formed, and the resultant area of the metal-to-metal joint. In an embodiment, the contact openings are between 100 nm and 1,000 nm wide, such as approximately 200 nm-500 nm wide. 
     Referring now to  FIG. 5  a metallic stabilization layer  106  is blanket deposited over the sacrificial layer  232  and within the array of contact openings  234  using a suitable technique such as sputtering, evaporation or electroplating. The portion of the metallic stabilization layer  106  within the contact openings  234  forms the stabilization posts  108  and metal-to-metal joints with the bottom contacts  210 . In an embodiment, the metallic stabilization layer  106  includes a total thickness of up to 3 microns, such as 1.5 microns, and may be sufficiently thick to fill the contact openings  234  as part of a continuous layer. The metallic stabilization layer  106  may include one or more adhesion layers  112  and a bulk layer  110  as described with regard to  FIG. 1A . 
     Referring now to  FIG. 6 , the substrate stack is then bonded to a carrier substrate  102 . For example, the metallic stabilization layer  106  may be bonded to the carrier substrate  102  using polymer or metal joining layer  104 , or with thermocompression bonding techniques. Following bonding to the carrier substrate  102 , the p-n diode layer  221  may be thinned and any growth substrates or buffer layers removed from the doped layer  226  as shown in  FIG. 7 . 
     Referring now to  FIG. 8 , the p-n diode layer  221  is etched to form an array of laterally separate micro p-n diode mesa structures  200  and expose the sacrificial layer  232 . In an embodiment, etching is performed using dry etching technique. The sacrificial layer  232  may then be removed as illustrated in  FIG. 9  using a suitable technique such as vapor-phase etching resulting in an array of micro devices  200  that are poised for pick up, and retained on the carrier substrate  102  by the array of stabilization posts  108 . As shown, a void  242  may surround the bottom and side surfaces of the micro devices  200  such that they are only retained on the carrier substrate  102  by the stabilization posts  108 . 
       FIGS. 10A-10E  are cross-sectional side view illustrations of a method of picking up and transferring an array of micro devices from a carrier substrate to a receiving substrate in accordance with an embodiment.  FIG. 10A  is a cross-sectional side view illustration of an array of micro device transfer heads  304  supported by substrate  300  and positioned over an array of micro devices  200  stabilized on stabilization posts  108  of stabilization layer  106  on a carrier substrate  102  in accordance with an embodiment. The array of micro devices  200  is then contacted with the array of transfer heads  304  as illustrated in  FIG. 10B . A voltage is applied to the array of transfer heads  304 . The voltage may be applied from the working circuitry within a transfer head assembly  306 . The array of micro devices  200  is then picked up with the array of transfer heads  304  as illustrated in  FIG. 10C . As shown, the pick up operation may result in nubs  109  of the stabilization posts  108  also being picked up, with the nubs  109  protruding from the bottom contacts  210 . 
     Referring now to  FIGS. 10D-10E , the array of micro devices  200  is positioned over an array of contact pads  402  on a receiving substrate  400 . The array of micro devices  200  is then bonded to the receiving substrate  400  and released form the array of micro device transfer heads  304 . In accordance with embodiments, bonding layers  404  are formed on the contact pads  402  to facilitate bonding with the interface layers  218  of the micro devices  200 . For example, bonding may be accomplished through reflow of the bonding layers  404  to form metallic joints. Reflow may additionally be accompanied by diffusion with the interface layers  218  to form compound regions  450  within the metallic joints. For example, the bonding layers  404  may be formed of a solder material such as indium, tin, etc. that can form an alloy or other compound with the interface layer  218 . 
     Referring now to  FIGS. 11A-11B  cross-sectional side view illustrations are provided of a micro device of  FIG. 1A  after being transferred and bonded to a receiving substrate in accordance with embodiments.  FIG. 12  is a cross-sectional side view illustration of a micro device of  FIG. 1B  after being transferred and bonded to a receiving substrate in accordance with an embodiment. As described with regard to  FIGS. 10A-10E , the transfer process in accordance with embodiments may include the use of a bonding layer  404  on the receiving substrate to facilitate bonding of the micro devices  200  to form metallic joints  460 . In particular, the bonding layer  404  may reflow during the transfer sequence. For example, this may be accomplished by the transfer of heat through the micro device transfer heads  304 . The transfer of heat and reflow, in turn, may cause diffusion across the interface layer  218  and bonding layer  404 , and possibly the nub  109 , resulting in a compound region  450 . In accordance with embodiments, the compound region  450  and any remaining bonding layer  404  material are referred to together as a metallic joint  460 . 
     In accordance with embodiments such as those illustrated in  FIG. 11A  and  FIG. 12 , a light emitting structure may include a landing pad  402 , a metallic joint  460  on the landing pad, and an LED. The LED includes a bottom contact  210  bonded with metallic joint  460  on the landing pad  402 , and a nub  109  that protrudes from the bottom contact  210  and is embedded within the metallic joint  460 . Specifically, the nub  109  illustrated in  FIG. 11A  may be a portion of a stabilization post  108  that was pulled from a carrier substrate  102  during a transfer sequence. The nub  109  illustrated in  FIG. 12  may be a protrusion of the bottom contact  210 . For example, the nub  109  may include a nano-pillar  109  formed on or within the bottom contact  210 . 
     In accordance with embodiments, the nubs  109  may be at specific geometric locations of the bottom contact  210 . In an embodiment, the one or more nubs  109  may be arranged with a balanced center of gravity of the LED. For example, a light emitting structure may include a single nub  109  located at a center of the bottom contact. A light emitting structure including three or more nubs  109  may be arranged in a geometric pattern to have evenly supported weight of the LED when on the carrier substrate. A plurality of nubs  109  may also be arranged to have prevented tipping or tilting of the LED when on the carrier substrate. 
     In an embodiment the nub  109  includes an adhesion layer  112  and bulk layer  110 . The bottom contact  210  may include an interface layer  218  that is bonded to the metallic joint  460 . In an embodiment, the interface layer  218  is consumed by the metallic joint  460 . In the embodiment illustrated in  FIG. 11A , the nub  109  is in direct contact with the interface layer  218 . In the embodiment illustrated in  FIG. 11B , the interface layer  218  is a portion of the nub  109 . In an embodiment, the nub  109  has a maximum width of less than 0.5 μm. The nub  109  and the interface layer  218  may be formed of materials sharing a same metallic element, such as, but not limited to, gold and aluminum. In an embodiment, the interface layer is formed of gold, while the nub is formed of a gold alloy. The nub  109  may include multiple layers. For example, the nub  109  may include an adhesion layer  112  and a bulk layer  110 , with the adhesion layer  112  in direct contact with the interface layer  218 . Additionally, the LED may include a plurality of nubs  109  protruding from the bottom contact  210 , with the plurality of nubs  109  embedded within the metallic joint  460 . Similar to the embodiment illustrated in  FIG. 11A , the plurality of nubs  109  may be in direct contact with the interface layer  218 . The metallic joint  460  may be the result of reflow of a bonding layer  404 . In an embodiment, the metallic joint  460  includes a compound region  450 , where the compound region connects the bonding layer  404  and the interface layer  218 . 
     Up until this point, a high temperature bonding process has been described in which the transfer of heat may cause reflow of the bonding layer  404 , and diffusion across the interface layer  218  and the bonding layer  404  to form a compound region  450  within a metallic joint  460 . The compound region  450  may partially or completely consume either of the interface layer  218  or bonding layer  404 .  FIG. 11B  is an illustration of an embodiment in which the nub  109  diffuses with the bonding layer  404 , resulting a volume of interstitial metallic material  111  embedded in the metallic joint  460 . For example, this may be observed when the nub  109  had been formed of a material with a distinguishable chemical composition from the interface layer  218 . This may also potentially be observed by distance and location, even where the nub  109  and interface layer  218  are formed of a similar composition. In such an instance, the presence of the interstitial metallic material  111  composition may be detected using a suitable technique such as transmission electron microscope energy-dispersive X-ray spectroscopy (TEM-EDS) and Secondary Ion Mass Spectrometry (SIMS). 
     In an embodiment such as that illustrated in  FIG. 11B , a light emitting structure includes a landing pad  402 , a metallic joint  460  on the landing pad, and an LED that includes a bottom contact  210  bonded with the metallic joint  460  on the landing pad. One or more volumes of interstitial metallic material  111  are embedded within the metallic joint  460 . In an embodiment, a volume of interstitial metallic material  111  is confined to an area of less than 0.5 μm width. In an embodiment, a volume of interstitial metallic material  111  is beneath a center of the LED. In an embodiment, the metallic joint includes a bonding layer  404  and a compound region  450 , and the compound region  450  connects the bonding layer  404  and the interface layer  218 . In an embodiment, the volume of interstitial metallic material  111  includes a top volume of a first composition (e.g. of adhesion layer  112 ) and a bottom volume of a second composition (e.g. of bulk layer  110 ) different from the first composition. The first composition may substantially surround the second composition on top and lateral sides. 
     In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming metal-to-metal adhesion joints to hold down micro devices to a carrier substrate within the context of a micro device transfer manufacturing process. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.

Metadata:
Filing Date: 20180307
Publication Date: 20200804
Grant Date: 20200804
Priority Date: 20170607
Inventors: GOLDA, DARIUSZ
PERKINS, JAMES M.
BIBL, ANDREAS
Sood, Sumant
KIM, HYEUN-SU
Assignee: APPLE INC
CPC Classifications: [{"code": "H10H20/856", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/824", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/823", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/812", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/0364", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/857", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/857", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/0364", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/835", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/819", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/824", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/823", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/018", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/8381", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/83365", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/83005", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/7598", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/75725", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/75252", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/32503", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/3201", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29144", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29124", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29109", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05644", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05564", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05557", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05169", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05155", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05144", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05139", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05124", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/04026", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/03462", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/0345", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/03001", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/05", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/03", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/97", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/75", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/83815", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/97", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/12041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/32227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29111", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/291", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/83", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/29", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/83192", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05624", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68381", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68368", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68354", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/6834", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/68318", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/67144", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/12041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29076", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29144", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29124", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/67144", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/29019", "inventive": false, "first": false, "tree": "[]"}, {"code": "B65G47/92", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L24/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L33/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29076", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29124", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L33/62", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/29144", "inventive": false, "first": false, "tree": "[]"}, {"code": "B65G47/92", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/68363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L33/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L24/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L33/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/67144", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L33/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29019", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/12041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2933/0066", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 71838634