Light emitting diode die transfer method using partial laser lift-off - Patents.com

Abstract

The transfer method includes providing a first light emitting diode on a first substrate, performing a partial laser lift-off of the first light emitting diode from the first substrate, laser bonding the first light emitting diode to a backplane after performing the partial laser lift-off, and separating the first substrate from the first light emitting diode after the laser bonding.

Description

[Technical field]

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 946,557, filed December 11, 2019, which is incorporated by reference herein in its entirety.

[0002] SUMMARY OF THE DISCLOSURE FIELD OF THE DISCLOSURE

[0002] Embodiments of the present invention relate generally to methods of manufacturing semiconductor light emitting diodes, and more particularly, to methods of light emitting diode die transfer using partial laser lift-off and structures formed thereby. [Background technology]

[0003] Light emitting diodes (LEDs) are used, for example, in liquid crystal displays in laptops or LED televisions. However, it is difficult to mount LEDs of different colors on the same backplane of a display device with high yield. Summary of the Invention

[0004] According to one aspect of the present disclosure, a transfer method includes providing a first light emitting diode on a first substrate, performing a partial laser lift-off of the first light emitting diode from the first substrate, laser bonding the first light emitting diode to a backplane after performing the partial laser lift-off, and separating the first substrate from the first light emitting diode after the laser bonding.

[0005] According to yet another aspect of the present disclosure, a light emitting device assembly includes a backplane including bonding pads and first light emitting diodes attached to a first subset of the bonding pads via respective bonding material portions, each of the first light emitting diodes including a first conductivity type semiconductor layer and a gallium-rich material portion overlying a surface of the first conductivity type semiconductor layer, the gallium-rich material portion including gallium at an atomic concentration greater than 55%. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 illustrates a schematic diagram of a substrate including a light emitting device die according to an embodiment of the present disclosure.

[0007] [Diagram 2] FIG. 2 shows an example transfer pattern and an example transfer sequence for transferring four different types of devices from four transfer boards to four backplanes.

[0008] [Figure 3A] , [Figure 3B] , [Figure 3C] , [Figure 3D] , [Figure 3E] 3A-3E are a schematic sequence for transferring light-emitting devices according to the exemplary transfer pattern shown in FIG.

[0009] [Figure 4] FIG. 4 is a side cross-sectional view of a source coupon including a light emitting diode located above a source substrate according to an embodiment of the present disclosure.

[0010] [Figure 5A] FIG. 5A is a side cross-sectional view of a first exemplary structure including a backplane and a first source coupon including a first light emitting diode located over a first substrate according to a first embodiment of the present disclosure.

[0011] [Figure 5B] FIG. 5B is a vertical cross-sectional view of the first exemplary structure after aligning and clamping the backplane and the first source coupon according to the first embodiment of the present disclosure.

[0012] [Figure 5C] FIG. 5C is a vertical cross-sectional view of the first exemplary structure after isolation laser irradiation in accordance with the first embodiment of the present disclosure.

[0013] [Figure 5D]FIG. 5D is a vertical cross-sectional view of the first exemplary structure after a cooling step in accordance with the first embodiment of the present disclosure.

[0014] [Figure 5E] FIG. 5E is a side cross-sectional view of the first exemplary structure after the backplane and the first source coupon are pressed together in accordance with the first embodiment of the present disclosure.

[0015] [Figure 5F] FIG. 5F is a vertical cross-sectional view of the first exemplary structure after bonding laser irradiation in accordance with the first embodiment of the present disclosure.

[0016] [Figure 5G] FIG. 5G is a vertical cross-sectional view of the first exemplary structure after separating the first assembly of the backplane and the first subset of the first light-emitting diodes from the second assembly of the first substrate and the second subset of the first light-emitting diodes according to the first embodiment of the present disclosure.

[0017] [Figure 6A] FIG. 6A is a vertical cross-sectional view of a first exemplary structure after aligning a second source coupon including a second light emitting diode located on a second substrate to the first assembly according to a first embodiment of the present disclosure.

[0018] [Figure 6B] FIG. 6B is a side cross-sectional view of the first exemplary structure after aligning and clamping the second source coupon to the first assembly according to the first embodiment of the present disclosure.

[0019] [Figure 6C] FIG. 6C is a vertical cross-sectional view of the first exemplary structure after separating the third assembly of the backplane, the first subset of the first light-emitting diodes, and the first subset of the second light-emitting diodes from the fourth assembly of the second substrate according to the first embodiment of the present disclosure.

[0020] [Figure 7] FIG. 7 is a vertical cross-sectional view of the first exemplary structure after transferring the third light-emitting diode to the backplane according to the first embodiment of the present disclosure.

[0021] [Figure 8A] FIG. 8A is a vertical cross-sectional view of a second exemplary structure after stamping a diode-side bonding material portion over a first light-emitting diode to a dummy substrate according to a second embodiment of the present disclosure.

[0022] [Figure 8B] , [Figure 8C] 8B and 8C are vertical cross-sectional views of a second exemplary structure after successive separation laser and partial adhesion laser irradiation steps according to a second embodiment of the present disclosure.

[0023] [Figure 8D] FIG. 8D is a vertical cross-sectional view of the second exemplary structure after separation of the first source coupon from the dummy substrate in accordance with the second embodiment of the present disclosure.

[0024] [Figure 8E] FIG. 8E is a vertical cross-sectional view of the second exemplary structure after aligning and clamping the backplane and the first source coupon according to a second embodiment of the present disclosure.

[0025] [Figure 8F] FIG. 8F is a vertical cross-sectional view of the second exemplary structure after bonding laser irradiation in accordance with the second embodiment of the present disclosure.

[0026] [Figure 8G] FIG. 8G is a vertical cross-sectional view of a second exemplary structure after separating the first assembly of the backplane and the first subset of the first light-emitting diodes from the second assembly of the first substrate and the second subset of the first light-emitting diodes according to a second embodiment of the present disclosure.

[0027] [Figure 9A] FIG. 9A is a vertical cross-sectional view of a second exemplary structure after aligning a second source coupon including a second light emitting diode located on a second substrate to the first assembly according to a second embodiment of the present disclosure.

[0028] [Figure 9B] FIG. 9B is a vertical cross-sectional view of the second exemplary structure after separating the third assembly of the backplane, the first subset of the first light-emitting diodes, and the first subset of the second light-emitting diodes from the fourth assembly of the second substrate according to the second embodiment of the present disclosure.

[0029] [Figure 10] FIG. 10 is a vertical cross-sectional view of the second exemplary structure after transferring the third light emitting diode to the backplane according to the second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Embodiments of the present disclosure relate to a method for manufacturing light emitting diodes, in particular a method for LED die transfer using partial laser lift-off, and structures formed thereby, various aspects of which are described below. Throughout the drawings, like elements are indicated by the same reference numbers. Unless otherwise noted, elements having the same reference numbers are presumed to have the same material composition. The drawings are not drawn to scale. Although a single instance of an element may be written, multiple instances of an element may be duplicated unless the lack of element redundancy is clearly stated or explicitly indicated otherwise. Ordinal numbers, such as "first", "second" and "third", are used merely to distinguish similar elements, and different ordinal numbers may be used throughout the specification and claims of the present disclosure.

[0031] The light emitting diodes may be in a vertical configuration (e.g., a vertical LED) with the p-side and n-side contacts on opposite sides of the structure, or in a horizontal configuration with the p-side and n-side contacts on the same side of the structure. As used herein, a "light emitting device assembly" refers to an assembly in which at least one light emitting diode is structurally secured to a carrier structure, which may include, for example, a backplane or any other structure configured to provide stable mechanical support for the at least one light emitting diode.

[0032] In an embodiment of the present disclosure, a method is provided for transferring an array of light emitting diodes from a growth substrate to a target substrate, such as, for example, a backplane. In an illustrative example, the target substrate can be a backplane substrate, such as, for example, an active or passive matrix backplane substrate, for driving the light emitting diodes. As used herein, a "backplane" or "backplane substrate" refers to any substrate configured to have a plurality of diodes attached thereon. In one embodiment, the center-to-center distance of adjacent light emitting diodes on the backplane substrate can be an integer multiple of the center-to-center distance of adjacent light emitting diodes on the growth substrate. The light emitting diodes may include a plurality of light emitting diodes, such as, for example, a group of two light emitting diodes, one configured to emit blue light and one configured to emit green light. The light emitting diodes may include a group of three light emitting diodes, one configured to emit blue light, one configured to emit green light, and one configured to emit red light. As used herein, "adjacent light emitting diodes" refers to a plurality of two or more light emitting diodes that are located closer together than at least one other light emitting diode. The methods of the present disclosure can provide for selective transfer of a portion of light emitting diodes from an array of light emitting diodes on a growth substrate to a backplane substrate.

[0033] The same type of diodes may be fabricated on the individual initial growth substrates. As used herein, "initial growth substrate" refers to a substrate that is processed to form devices thereon or therein. The devices may include light emitting diodes, and / or sensor devices (e.g., photodetectors), and / or any other electronic devices. The light emitting diodes may be any type of light emitting diode, i.e., vertical light emitting diodes, horizontal light emitting diodes, or any combination thereof. The same type of diodes may be formed on each initial growth substrate, with the type differing from one initial growth substrate to another. The diodes may be formed as an array on the individual initial growth substrates.

[0034] Referring to FIG. 1, a first source coupon 1 is shown that includes a growth substrate that includes a die of a light emitting diode 10. The substrate may include an edge exclusion region 300 where no diodes are formed at the outer edge. The substrate may include light emitting diodes of the same type (referred to herein as a first type) arranged in a first array configuration. The first type of light emitting diodes are multiple instances of the same diode, which may be, for example, light emitting diodes that emit light at the same peak wavelength. For example, the first type of light emitting diodes may be red light emitting diodes, green light emitting diodes, or blue light emitting diodes.

[0035] The first array configurations have a first direction pitch Px1 along a first direction (i.e., the first direction of the first array configuration) and a second direction pitch Py1 along a second direction (i.e., the second direction of the first array configuration). As used herein, the first and second directions of the array configuration refer to the two directions along which the unit cells of the array configuration are repeated. In a rectangular array configuration, the first and second directions may be perpendicular to each other and are referred to as the x and y directions.

[0036] The light emitting diodes 10 on the substrate can be transferred to a plurality of backplanes having bonding sites in a second array configuration. A predetermined transfer pattern and a predetermined transfer sequence can be used for the transfer of the light emitting diodes 10. Different types of light emitting diodes provided from different substrates can be used together with the light emitting diodes 10 from the substrate to provide a functional direct view light emitting diode assembly.

[0037] Referring to FIG. 2, an exemplary transfer pattern and an exemplary transfer sequence for transferring four different types of devices (10B, 10G, 10R, 10S) (e.g., blue, green and red light emitting LEDs, respectively, and an optional sensor) to four backplanes (BP1, BP2, BP3, BP4) are shown. The four different types of devices (10B, 10G, 10R, 10S) may be provided on four source substrates (B, G, R, S), which may include four transfer substrates, or four growth substrates, or a combination thereof. The first light emitting diode 10B may be provided on the first source substrate B, the second light emitting diode 10G may be provided on the second source substrate G, the third light emitting diode 10R may be provided on the third source substrate R, and the sensor 10S may be provided on the fourth source substrate S.

[0038] A subset of the first light emitting diodes 10B labeled "1" may be transferred from the first source substrate B to the first backplane BP1 at locations marked "1". Then, a subset of the second diodes 10G labeled "2" may be transferred from the second source substrate G to the second substrate BP2 at locations marked "2" on the second backplane BP2. Successive transfers continue with each set of diodes labeled with increasing numerical indexes up to the set of diodes labeled with numerical index "16".

[0039] Although the exemplary transfer pattern and exemplary transfer sequence are shown for the case where four source substrates (B, G, R, S) and four backplanes (BP1, BP2, BP3, BP4) are used, the method of the present disclosure may be applied to any case where m transfer assemblies and n backplanes are used, where m is an integer greater than 1, n is an integer greater than 1, and n is equal to or greater than m. The n backplanes bond with diodes from the m transfer assemblies to form n integrated light emitting diode assemblies. In one embodiment, n may be the same as m or may be greater than m.

[0040] A plurality of transfer assemblies, for example m transfer assemblies, are provided. Each of the m transfer assemblies includes a respective source substrate (B, G, R, S) and a respective device (10B, 10G, 10R, 10S) in a two-dimensional array having the same two-dimensional periodicity. As used herein, the same two-dimensional periodicity for the plurality of structures refers to a configuration in which each of the plurality of structures has an individual unit structure, and instances of the individual unit structure are repeated along two independent directions of periodicity (e.g., a first periodicity direction and a second periodicity direction), where the unit structure is repeated along each of the first periodicity directions with the same first pitch and along each of the second periodicity directions with the same second pitch for all of the plurality of structures, and the angle between the first periodicity direction and the second periodicity direction is the same for all of the plurality of structures. Each of the n backplanes has a periodic repetition of an individual unit bonding material portion pattern configured to implement m types of diodes.

[0041] Each of the m types of devices may be one of the devices in a separate transfer assembly between the m transfer assemblies. The pitch of each unit bonding material portion pattern along two independent directions in each of the n backplanes may be a multiple of the separate pitch of the two-dimensional periodicity of the devices in each of the m transfer assemblies. In an illustrative example, each of the devices (10B, 10G, 10R, 10S) may be periodic in the respective transfer assembly with a first period a along a first direction and a second period b along a second direction (which may be perpendicular to the first direction). The unit conductive bonding pad pattern in each of the backplanes may have a first periodicity 2a (which is an integer multiple of a) along the first direction and a second periodicity 2b (which is an integer multiple of b) along the second direction (which may be perpendicular to the first direction).

[0042] By positioning each transport assembly on its respective backplane (BP1, BP2, BP3, BP4) in a position that prevents collision of existing devices on each transport assembly with any of the devices (10B, 10G, 10R, 10S) previously bonded to the respective backplane (BP1, BP2, BP3, BP4), a subset of devices (10B, 10G, 10R, 10S) from each of the m transport assemblies can be sequentially transferred to a respective one of the n backplanes (BP1, BP2, BP3, BP4).

[0043] 4, a first source coupon 1 is shown including a first substrate 8A (also referred to as a first growth substrate or a first source substrate) and a first light emitting diode 10B located on the first substrate 8A. The first substrate 8A may be any suitable substrate on which an LED layer may be grown, such as, for example, a single crystal substrate on which an LED semiconductor layer may be grown. For example, the first substrate 8A may be a sapphire substrate.

[0044] Each of the first light-emitting diodes 10B includes a buffer layer 11 and a first conductive type semiconductor layer 12. Each of the buffer layers 11 is an amorphous III-V compound semiconductor layer containing gallium and nitrogen. Each of the first conductive type semiconductor layers 12 is a crystalline III-V compound semiconductor material layer containing gallium and nitrogen. For example, the buffer layer may include amorphous gallium nitride (GaN), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), or aluminum indium gallium nitride (AlInGaN), and the first conductive type semiconductor layer 12 may include monocrystalline or polycrystalline GaN, InGaN, AlGaN, or AlInGaN. The first conductive type semiconductor layer 12 has a first type of conductivity, which may be n-type or p-type. For example, the first conductive type semiconductor layer 12 includes an n-type semiconductor layer. The buffer layer 11 may be undoped or may be of the first conductive type.

[0045] The buffer layer 11 is located between the first conductivity type semiconductor layer 12 and the first substrate 8A. The buffer layer 11 may have the same material composition as the first conductivity type semiconductor layer 12. For example, the buffer layer 11 and the first conductivity type semiconductor layer 12 may both include gallium nitride. The amorphous gallium nitride buffer layer 11 may be formed during the initial deposition of the crystalline gallium nitride first conductivity type semiconductor layer 12 on the patterned sapphire substrate (PSS) 8A, where the gallium nitride growth conditions transition from amorphous to crystalline gallium nitride layer growth. The thickness of the buffer layer 11 may range from 100 nm to 400 nm, such as from 150 nm to 300 nm, although smaller and larger thicknesses may also be used. The thickness of the first conductivity type semiconductor layer 12 may range from 500 nm to 5 microns, such as from 1 to 3 microns, although smaller and larger thicknesses may also be used.

[0046] An active layer 13 is located on the first conductivity type semiconductor layer 12. In one embodiment, the active layer 13 may include at least one bulk, quasi-bulk or quantum well layer selected from GaN, InGaN, AlGaN and / or AlInGaN. For example, the active layer may include a stack of one or more InGaN quantum well layers between respective GaN and / or AlGaN barrier layers. In general, any light emitting layer stack known in the art may be used for the active layer 13.

[0047] A second conductivity type semiconductor layer 14 is located above the active layer. The second conductivity type semiconductor layer 14 has a doping of a second conductivity type. The second conductivity type is opposite to the first conductivity type. If the first conductivity type is n-type, the second conductivity type is p-type, and vice versa. In one embodiment, the first conductivity type is n-type and the second conductivity type is p-type. Each second conductivity type semiconductor layer 14 may include a crystalline (e.g., single crystal or polycrystalline) GaN, InGaN, AlGaN and / or AlInGaN layer. Thus, the active layer 13 is located between the first and second conductivity type layers.

[0048] A contact level material layer 15 is located on the second conductivity type layer 14. The contact level material layer 15 includes at least one conductive layer that functions as an electrode (e.g., a p-type side electrode). The contact level material layer 15 may include a stack including, from bottom to top, a transparent conductive oxide layer, a reflector layer and / or a bonding pad material layer. The transparent conductive oxide layer includes a transparent conductive oxide material, such as, for example, indium tin oxide or aluminum doped zinc oxide. The reflector layer includes gold, silver and / or aluminum. The bonding pad material layer includes a metallic material that can function as a bonding pad, such as, for example, gold, copper, nickel, titanium, titanium nitride, tungsten, tungsten nitride, other metals with a higher melting point than the solder material used later, their alloys and / or layer stacks thereof.

[0049] The stack of the second conductivity type semiconductor layer 14, the active layer 13, and optionally the first conductivity type semiconductor layer 12 in each first light emitting diode 10B can be patterned to form grooves 19 between adjacent LEDs 10B using various patterning methods. A dielectric matrix layer 16 can be formed between the first LEDs 10B. The grooves 19 define the area of ​​each first LED 10B. Specifically, each successive set of patterned material layers covering the first substrate 8A and laterally bounded by a set of grooves 19 constitutes a first light emitting diode 10B. In one embodiment, the grooves 19 can be formed in a grid pattern to provide an array of first light emitting diodes 10B, which can be a periodic array of first light emitting diodes 10B. The first light emitting diodes 10B can emit light of a first peak wavelength, such as blue light having a first peak wavelength in the range of the blue spectrum.

[0050] Although FIG. 4 illustrates a particular embodiment of the first light-emitting diodes 10B, embodiments of the present disclosure may be utilized using any configuration for the first light-emitting diodes 10B, provided that a structure is provided for attaching a bonding material portion to the side of each first light-emitting diode 10B facing away from the first substrate 8A.

[0051] 5A, in each of the first light emitting diodes 10B, a diode side bonding material 17 may be attached to the contact level material layer 15. In one embodiment, the diode side bonding material 17 may be a solder material such as, for example, pure tin or an alloy of tin and indium.

[0052] A backplane 32 is provided. The backplane 32 includes a substrate and a metal interconnect layer 325 formed on a front surface of the substrate. In one embodiment, the substrate may include a plastic (e.g., polymer) substrate. In one embodiment, the metal interconnect layer 325 may include a plurality of metal interconnect structures located on a surface of the substrate and / or embedded in at least one insulating material, and provides electrical connections between light emitting diodes bonded onto the backplane 32 and input / output pins of the backplane 32.

[0053] Bond pads 34 may be provided on a surface of the backplane 32 overlying the metal interconnect layer 325. In one embodiment, the bond pads 34 may be arranged as a two-dimensional periodic array or as a one-dimensional periodic array. The bond pads 34 may include a bond pad material such as, for example, gold, copper, nickel, titanium, titanium nitride, tungsten, tungsten nitride, other metals having a higher melting point than the subsequently used solder material, alloys thereof, and / or layer stacks thereof.

[0054] A backplane bonding material 37 may be attached to the bond pad 34. In one embodiment, the backplane bonding material 37 may be a solder material such as, for example, pure tin or an alloy of tin and indium.

[0055] The first source coupon 1 and backplane 32 may be aligned such that pairs of diode-side bonding material portions 17 and backplane-side bonding material portions 37 face each other at each grid point of the periodic array of bonding pads 34 .

[0056] 5B, the backplane 32 and the first source coupon 1 are brought into contact with each other such that opposing pairs of diode-side bonding material portions 17 and backplane-side bonding material portions 37 are in contact with each other. Each of the diode-side bonding material portions 17 can have an overlap in area with the respective underlying backplane-side bonding material portion 37. In one embodiment, the overlapping area can be at least 70%, such as, for example, more than 80% and / or more than 90% of the area of ​​the diode-side bonding material portion 17. In one embodiment, the geometric center of each diode-side bonding material portion 17 can cover the geometric center of the underlying backplane-side bonding material portion 37.

[0057] In general, at least one bonding material portion (17, 37) may be disposed between each vertically adjacent pair of respective bonding pads 34 and first light emitting diodes 10B. In one embodiment, one pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 may be provided between each vertically adjacent pair of respective bonding pads 34 and first light emitting diodes 10B. In one embodiment, the diode-side bonding material portion 17 may be omitted. In another embodiment, the backplane-side bonding material portion 37 may be omitted.

[0058] In one embodiment, solder flux 35 may be applied between the backplane 32 and the first light emitting diode 10B such that the solder flux 35 laterally surrounds each of the bonding material portions (17, 37). The solder flux 35 may be any suitable liquid flux that reacts with the tin oxide to leave behind the metallic bonding material portions (17, 37). In one embodiment, a fixture such as, for example, a clamp 400 may be used to hold the assembly of the backplane 32 and the first source coupon 1 in place without lateral shifting. In an illustrative example, the clamp 400 may include an upper plate 400U that presses against one of the backsides of the backplane 32 or the first source coupon 1, a lower plate 400L that presses against the other of the backplane 32 or the first source coupon 1, a frame 400F that includes mechanical support elements that hold the upper plate 400U and the lower plate 400L in place, and an adjustment unit 400A that adjusts the force applied to the upper plate 400U and / or the lower plate 400L or adjusts the distance between the upper plate 400U and the lower plate 400L. For example, the plate that contacts the first source coupon 1, such as the upper plate 400U, may include a material that is transparent to UV, visible, or IR laser radiation and / or the upper plate 400U may clamp only the edges of the first source coupon 1 and include a central opening to allow, for example, a laser beam to pass through it.

[0059] In an illustrative example, the backplane 32 and the first source coupon 1 may be held in place while a compressive force is applied along a direction perpendicular to the assembly of the backplane 32, the bonding material portions (17, 37), and the first source coupon 1. The magnitude of the compressive force may be selected such that the bonding material portions (17, 37) do not significantly deform, i.e., the bonding material portions (17, 37) maintain the shape provided prior to clamping and do not bond the respective bonding material portions 17 and 37 to one another. In an illustrative example, if 100,000 pairs of diode-side bonding material portions 17 and backplane-side bonding material portions 37 are present between the backplane 32 and the first source coupon 1, the magnitude of the compressive force applied by the clamp 400 may range from 250 N to 400 N.

[0060] Referring to FIG. 5C, a sequential laser irradiation process may then be performed to selectively irradiate each buffer layer 11 on the first light emitting diodes 10B to be transferred to the backplane 32 with a separation laser beam LD. The set of all the first light emitting diodes 10B then transferred to the backplane 32 is referred to herein as a first subset of the first light emitting diodes 10B. The separation laser beam LD performs a partial laser lift-off process used to partially lift off the first subset of the first light emitting diodes 10B, referred to herein as a separation laser irradiation process. Each buffer layer 11 of the first subset of the first light emitting diodes 10B is sequentially irradiated with the separation laser beam LD. The lateral dimensions (e.g., diameter, etc.) of the separation laser beam LD may be approximately the same as the lateral dimensions of the first light emitting diodes 10B. Thus, each buffer layer 11 may be individually irradiated without significantly changing the composition of the adjacent buffer layers 11.

[0061] The isolating laser beam LD may have an ultraviolet wavelength or a wavelength in the visible light range and may be absorbed by the gallium and nitrogen-containing III-V compound semiconductor material of the irradiated buffer layer 11. Without wishing to be bound by a particular theory, it is believed that the irradiation of the isolating laser beam LD onto the buffer layer 11 evaporates nitrogen atoms without evaporating gallium atoms or with minimal evaporation of gallium atoms. Thus, the irradiation reduces the atomic percentage of nitrogen in the remaining material. The first source coupon 1 and backplane 32 may be mechanically held in place by clamps 400 during and after this step.

[0062] In one embodiment, without being bound by any particular theory, it is believed that the irradiated subset of the buffer layers 11 in the first subset of first light emitting diodes 10B may be converted into gallium-rich droplets 111. The gallium-rich droplets 111 may consist of pure liquid gallium-rich droplets or may comprise an alloy of gallium and nitrogen containing an atomic concentration of gallium greater than 55%, e.g., between 60% and 99%.

[0063] As shown in FIG. 5D, if the temperature of the first source coupon 1 is maintained below the melting temperature of gallium (e.g., 29.76° C.) or its alloys, the liquid gallium-rich droplets 111 may solidify into solid gallium-rich material portions (e.g., pure gallium or gallium-rich alloy particles or regions) 211 after irradiation. In one embodiment, each remaining portion of the laser-irradiated buffer layer 11 (which is a subset of the buffer layer 11 in the first subset of first light-emitting diodes 10B) may include gallium-rich material portions 211 (i.e., solid pure gallium or gallium-rich alloy particles or regions). In one embodiment, the gallium-rich material portions 211 may include an atomic concentration of gallium atoms of more than 55%, such as, for example, 60% to 100%. The gallium-rich material portions 211 may have an average thickness ranging from 5 nm to 100 nm, such as, for example, 10 nm to 50 nm, although smaller and larger thicknesses may also be used. Each gallium-rich material portion 211 may include a continuous material layer or may include a cluster of ball-shaped material portions. A subset of the buffer layer 11 located within the second subset of first light-emitting diodes 10B that are not subsequently transferred to the backplane 32 is not irradiated with the laser beam LD and thus remains as a buffer layer 11, such as, for example, a gallium nitride buffer layer having about 50 atomic percent gallium and thus a higher melting point than the gallium-rich material portions 211.

[0064] Because the backplane-side bonding material portion 37 and the diode-side bonding material portion 17 in each adjacent pair merely contact each other during laser irradiation and are not bonded to each other, mechanical shock from the laser irradiation is not transferred to the backplane 32, which may include a relatively fragile polymer. Thus, the partial laser lift-off described above with respect to Figures 5C and 5D to form the gallium-rich material portion 211 may cause little or no damage to the backplane 32 and the conductive elements (34, 325) thereon. Furthermore, the partial laser lift-off process limits damage to the resolidified bonding material portion in subsequent process steps, such as the process step of Figure 5F, because bonding reflow occurs after the partial laser lift-off.

[0065] 5E, the backplane 32 and the first source coupon 1 can be pressed together with a greater force to induce deformation of the bonding material portions (17, 37) (i.e., to coin the bonding material portions and smooth any rough bonding surfaces). Thus, each mating pair of the respective diode-side bonding material portion 17 and the respective backplane-side bonding material portion 37 can be pressed together with a second pressure that exceeds the first pressure after converting a subset of the buffer layer 11 to the gallium-rich material portion 211. The second pressure is sufficient to form deformations of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37. In an illustrative example, when 100,000 pairs of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 are present between the backplane 32 and the first source coupon 1, the magnitude of the compressive force applied by the clamp 400 can range from 500 N to 1,000 N.

[0066] Referring to FIG. 5F, a sequential localized laser irradiation process can be performed to induce reflow and subsequent bonding of the respective mating pairs of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 located under the first subset of the first light-emitting diodes 10B transferred to the backplane 32. The laser irradiation induces bonding of the first subset of the first light-emitting diodes 10B to the backplane 32, and is referred to herein as a bonding laser irradiation process. The laser beam LB used during the bonding laser irradiation process has a photon energy smaller than the band gap of the III-V compound semiconductor material (e.g., gallium and nitrogen-containing material) in the first light-emitting diodes 10B, and thus passes through the first light-emitting diodes 10B. For example, the laser beam LB used in the bonding laser irradiation process can be an infrared laser beam, such as a carbon dioxide laser beam having a wavelength of 9.4 microns or 10.6 microns.

[0067] The laser beam LB may sequentially irradiate each mating pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37. Each irradiated pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 is heated to a reflow temperature at which the bonding material (which may be a solder material) of the pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 reflows. Upon completion of irradiation of the mating pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 with the laser beam, the reflowed material resolidifies to provide a resolidified bonding material portion 47. Each resolidified bonding material portion 47 is bonded to the bonding pad 34 and the contact level material layer 15 of the first light emitting diode 10B.

[0068] In general, the first subset of first light emitting diodes 10B may be bonded to a respective underlying one of the bonding pads 34 by localized laser irradiation onto a respective underlying set of at least one bonding material portion (17, 37), which are reflowed and resolidified to form a resolidified bonding material portion 47. In one embodiment, the respective mating pairs of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 may be pressed together with a second pressure during the localized laser irradiation. Each first light emitting diode 10B in the first subset of first light emitting diodes 10B may be bonded to the backplane 32, and each first light emitting diode 10B in the second subset of first light emitting diodes 10B may remain unbonded to the backplane 32. The gallium-rich material portion 211 provides a weak adhesion between the first substrate 8A and the first conductivity type semiconductor layer 12. Because the first light emitting diode 10B is held in place by the gallium rich material portion 211, a lower power laser beam LB can be used than in prior art bonding processes, further minimizing damage to the backplane 32. The solder flux 35 may be evaporated during irradiation with the laser beam LB or allowed to flow out after this step.

[0069] 5G, the first source coupon 1 and the backplane 32 are removed from the clamps 400 and heated to a temperature higher than the melting temperature of the gallium-rich material portion 211 but lower than the melting point of the amorphous buffer layer 11 (e.g., lower than the melting temperature of gallium nitride). For example, if the gallium-rich material portion 211 comprises pure gallium, the temperature is raised to at least 30° C., such as 35 to 50° C., to melt the gallium-rich material portion 211 into gallium-rich droplets 111. This separates the backplane 32 and the first subset of first light-emitting diodes 10B from the second assembly of the first substrate 8A and the second subset of first light-emitting diodes 10B with or without the application of mechanical force. For example, the second assembly can be pulled away from the first assembly with a force of less than 100 N. Optionally, gallium-rich material portion 311 (e.g., remnants of resolidified gallium-rich droplets 111 or portions 211) may be located on the surface of first conductivity type semiconductor layer 12. Gallium-rich material portion 311 includes an atomic concentration of gallium greater than 55%, which may be greater than 95%. In one embodiment, gallium-rich material portion 311 may consist essentially of gallium and may have a thickness in the range of 5 nm to 100 nm, such as 10 nm to 50 nm.

[0070] If a single color LED device is desired, the manufacturing process ends with the step shown in Figure 5G. Alternatively, the steps shown in Figures 5A-5G may be repeated so that LEDs of different colors are bonded to backplane 32 to form a multi-color display.

[0071] Referring to FIG. 6A, a second source coupon 2 may be provided that includes second light emitting diodes 10G located on a second substrate 8B. Each of the second light emitting diodes 10G may include a respective additional buffer layer 11 at an interface with the second substrate 8B. The second light emitting diodes 10G may be arranged in a pattern that includes voids that include a mirror image pattern of a first subset of the first light emitting diodes 10B in the first assembly. In one embodiment, the second light emitting diodes 10G may emit light at a second peak wavelength that is different from the first peak wavelength. The second source coupon and the first assembly may be aligned with each other such that each of the first light emitting diodes 10B on the backplane 32 is located under a respective one of the voids in the second source coupon.

[0072] Referring to Figure 6B, the second light emitting diodes 10G may be disposed on the first assembly such that at least one additional bonding material portion (17, 37) is disposed between each vertically adjacent pair of respective bonding pads 34 and each of the second light emitting diodes 10G. The second source coupon 2 may be aligned and clamped to the first assembly using clamp 400 using the process steps described above with respect to Figure 5B. Solder flux 35 (not shown for clarity) may be used during these steps as well.

[0073] A subset of the additional buffer layers 11 may be converted into additional gallium-rich material portions 211 by performing the process steps of Figures 5C and 5D on each additional buffer layer 11 in the first subset of second light-emitting diodes 10G that are subsequently transferred to the backplane 32.

[0074] 5E and 5F may then be performed to bond the first subset of second light emitting diodes 10G to the underlying one of the bonding pads 34 by localized laser irradiation on the respective underlying set of at least one additional bonding material portion (17, 37). Each irradiated pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 is heated to a reflow temperature at which the bonding material (which may be a solder material) of the pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 reflows. When irradiation of the mating pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 with the laser beam is completed, the reflowed material resolidifies to provide a resolidified bonding material portion 47. Each resolidified bonding material portion 47 is bonded to a bonding pad 34 and a contact level material layer 15 of the second light emitting diode 10G.

[0075] 6C , the third assembly on the backplane 32, the first subset of the first light emitting diodes 10B, and the first subset of the second light emitting diodes 10G may be separated (i.e., isolated) from the fourth assembly on the second substrate 8B and the second subset of the second light emitting diodes 10G that are not bonded to the backplane 32 by separating them with an additional gallium-rich material portion 211. The gallium-rich material portion 311 (e.g., a resolidified gallium-rich layer, etc.) may be located on a surface of the first conductivity type semiconductor layer 12 of the second light emitting diodes 10G.

[0076] Referring to FIG. 7, a third source coupon may be provided that includes third light emitting diodes 10R located on a third substrate. Each of the third light emitting diodes 10R may include a respective additional buffer layer at an interface with the third substrate. The third light emitting diodes 10R may be arranged in a pattern that includes voids that include a mirror image pattern of a first subset of the first light emitting diodes 10B and a first subset of the second light emitting diodes 10G in the third assembly. In one embodiment, the third light emitting diodes 10R may emit light at a third peak wavelength that is different from the first peak wavelength and the second peak wavelength.

[0077] 5B-5G may be performed to transfer the first subset of the third light emitting diodes 10R to the backplane 32. The backplane 32 may include an array of pixels to provide a direct-view display device. Each pixel may include one or more LEDs (10B, 10G, 10R). In one embodiment, the backplane 32 may be a display frame for a direct-view display device, and each pixel of the direct-view display device may include at least one red light emitting diode (e.g., third light emitting diode 10R, etc.) configured to emit light with a peak wavelength in the range of 620 nm to 750 nm, at least one green light emitting diode (e.g., second light emitting diode 10G, etc.) configured to emit light with a peak wavelength in the range of 495 nm to 570 nm, and at least one blue light emitting diode (e.g., first light emitting diode 10B, etc.) configured to emit light with a peak wavelength in the range of 450 to 495 nm.

[0078] 8A, the second exemplary structure may be derived from the first exemplary structure of FIG. 5B by replacing the combination of the backplane 32, the bonding pads 34, and the backplane-side bonding material portion 37 with a flat surface (i.e., a plane). The flat surface may include a flat surface of a dummy substrate 932 or a flat surface of a support, such as, for example, a stage, a chuck, or a clamp. Thus, prior to clamping the first source coupon 1 with the clamp 400, the diode-side bonding material portion 17 may be formed on each of the first light-emitting diodes 10B on a flat surface, such as, for example, the plane of the dummy substrate.

[0079] In an illustrative example, the dummy substrate 932 and the first source coupon 1 may be lightly pressed against each other to avoid deformation of the diode-side bonding material portions 17. When 100,000 diode-side bonding material portions 17 are provided on the first source coupon 1, the magnitude of the compressive force applied by the clamp 400 may range from 100 N to 200 N.

[0080] Referring to FIG. 8B, a first laser irradiation process is performed while the diode-side bonding material portion 17 is disposed on the plane of the dummy substrate 932. Each buffer layer 11 of the first light-emitting diode 10B to be separated is irradiated with a laser beam, which is referred to herein as a separation laser beam LD. The set of all the first light-emitting diodes 10B to be subsequently separated is referred to herein as a first subset of the first light-emitting diodes 10B. Each buffer layer 11 can be sequentially irradiated with a separation laser beam LD. The lateral dimensions (e.g., diameter, etc.) of the separation laser beam LD can be approximately the same as the lateral dimensions of the first light-emitting diodes 10B. Thus, each buffer layer 11 can be irradiated individually without significantly changing the composition of the adjacent buffer layers 11.

[0081] The separation laser beam LD may have an ultraviolet wavelength or a wavelength in the visible light range and may be absorbed by the III-V compound semiconductor material of the buffer layer 11. Irradiation of the buffer layer 11 with the separation laser beam LD is believed to evaporate nitrogen atoms without or with minimal evaporation of gallium atoms, thus reducing the atomic percentage of nitrogen in the remaining material. In one embodiment, the irradiated subset of the buffer layer in the first subset of first light emitting diodes 10B may be converted into gallium rich droplets 111. The gallium rich droplets 111 may include an atomic concentration of gallium greater than 55%, as described above. Additionally, the thermal shock of the laser irradiation is believed to coin (e.g., planarize) the diode-side bonding material portion 17 against the relatively hard flat surface of the dummy substrate 932.

[0082] Referring to FIG. 8C, a second laser irradiation process is performed on the first subset of the first light emitting diodes 10B while the diode-side bonding material portion 17 is disposed on the plane of the dummy substrate 932. The second laser beam is referred to herein as the attachment laser beam LA. Without wishing to be bound by a particular theory, it is believed that the attachment laser beam LA causes the gallium-rich droplets 111 and / or the gallium-rich material portion 211 (if the gallium-rich droplets 111 solidify after being irradiated with the detachment laser beam LD) to reflow and become more tacky to form a gallium-rich adhesive portion 411 that weakly attaches (i.e., partially connects) the irradiated first light emitting diodes 10B to the first substrate 8A. The attachment laser beam LA may have the same parameters (i.e., wavelength and power) as the detachment laser beam LD. The gallium-rich adhesive portion 411 may have a greater adhesive strength than the gallium-rich material portion 211.

[0083] In one embodiment, the gallium-rich bonds 411 may include an atomic concentration of gallium atoms greater than 55%, including greater than 90%, such as, for example, 60% to 100%. The gallium-rich bonds 411 may have an average thickness ranging from 5 nm to 100 nm, such as, for example, 10 nm to 50 nm, although smaller and larger thicknesses may also be used. Each gallium-rich bond 411 may include a continuous material layer or may include a cluster of ball-shaped material portions. A subset of the buffer layer 11 located within the second subset of first light-emitting diodes 10B that are not irradiated with the laser beams LD and LA remains as the buffer layer 11.

[0084] Referring to FIG. 8D, the first source coupon 1 is separated from the dummy substrate 932 by unclamping the clamp 400 and removing the assembly of the first substrate 8A and all the first light emitting diodes 10B from the clamp 400. The gallium-rich adhesive 411 provides less adhesion (i.e., a lower adhesion magnitude) between the first substrate 8A and each of the first light emitting diodes 10B underlying the first subset than the adhesion provided by the buffer layer 11 between the first substrate 8A and each of the first light emitting diodes 10B underlying the second subset. However, the adhesion force provided by the gallium-rich adhesive 411 is sufficient to bond the first light emitting diodes 10B underlying the first subset to the first substrate 8A during transfer of the first source coupon 1. The first source coupon 1 may be stored for future use (e.g., for future attachment of the first light emitting diodes 10B of the first subset to a backplane). In an alternative embodiment, all of the first light emitting diodes 10B on the first substrate 8A are irradiated with the laser beams LD and LA, and all of the buffer layers 11 are converted into gallium-rich adhesives 411. In this alternative embodiment, the second set of first light emitting diodes 10B does not exist, and all of the first light emitting diodes 10B of the first source coupon 1 may be transferred to the same backplane 32.

[0085] 8E, the first source coupon 1 is placed on top of a backplane 32 having bonding pads 34 and backplane-side bonding material portions 37 thereon. Optional solder flux 35 may be applied around the bonding material portions (17, 37). The first source coupon 1 and backplane 32 may be aligned such that a mating pair of diode-side bonding material portions 17 and backplane-side bonding material portions 37 is located between an opposing pair of first light emitting diodes 10B and bonding pads 34. A clamp 400 may be used to hold the first source coupon 1 and backplane 32 assembly in place.

[0086] In general, the first light emitting diodes 10B may be disposed on the array of bonding pads 34 on the backplane 32 such that at least one bonding material portion (17, 37) is disposed between each vertically adjacent pair of respective bonding pads 34 and each of the first light emitting diodes 10B. As in the first embodiment, after disposing the first light emitting diodes 10B on the array of bonding pads 34, the backplane side bonding material portions 37 may be stamped (e.g., coined) by pressing the diode side bonding material portion 17 against a respective one of the backplane side bonding material portions 37. In an illustrative example, when 100,000 pairs of the diode side bonding material portions 17 and the backplane side bonding material portions 37 are present between the backplane 32 and the first source coupon 1, the magnitude of the compressive force applied by the clamp 400 may range from 500N to 1,000N. In one embodiment, each of the at least one bonding material portion (17, 37) may include a stack of a respective one of the diode side bonding material portions 17 and a respective one of the backplane side bonding material portions 37.

[0087] Referring to FIG. 8F, a third laser irradiation process may be performed, which is a localized laser irradiation process that induces reflow of each mating pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 under the first subset of the first light-emitting diodes 10B to be transferred to the backplane 32. The localized laser irradiation process induces bonding of the first subset of the first light-emitting diodes 10B to the backplane 32 and is referred to herein as a bonding laser irradiation process. The laser beam LB used during the bonding laser irradiation process has a photon energy smaller than the band gap of the III-V compound semiconductor material in the first light-emitting diodes 10B and therefore passes through the first light-emitting diodes 10B. For example, the laser beam LB used in the bonding laser irradiation process may be an infrared laser beam, such as a carbon dioxide laser beam having a wavelength of 9.4 microns or 10.6 microns.

[0088] The laser beam LB may sequentially irradiate each mating pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 under the first light-emitting diodes 10B of the first subset. Each irradiated pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 is heated to a reflow temperature at which the bonding material (which may be a solder material) of the pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 reflows. Upon completion of irradiation of the mating pair of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 by the laser beam, the reflowed material resolidifies to provide a resolidified bonding material portion 47. Each resolidified bonding material portion 47 is bonded to the bonding pad 34 and the contact level material layer 15 of the first light-emitting diodes 10B of the first subset.

[0089] In general, the first subset of first light emitting diodes 10B may be bonded to a respective underlying one of the bonding pads 34 by localized laser irradiation onto a respective underlying set of at least one bonding material portion (17, 37), which are reflowed and resolidified to form a resolidified bonding material portion 47. In one embodiment, the respective mating pairs of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 may be pressed together with a second pressure during the localized laser irradiation. Each first light emitting diode 10B in the first subset of first light emitting diodes 10B may be bonded to the backplane 32, and each first light emitting diode 10B in the second subset of first light emitting diodes 10B may remain unbonded from the backplane 32. The first source coupon 1 and the backplane 32 may be held in place by being pressed together via the array of first light emitting diodes 10B and the bonding material portion (17, 37, 47) during the localized laser irradiation.

[0090] Referring to FIG. 8G, the first assembly of the backplane 32 and the first subset of the first light-emitting diodes 10B can be separated from the second assembly of the first substrate 8A and the second subset of the first light-emitting diodes 10B by annealing the first assembly above the melting temperature of the gallium-rich bonding portion 411. For example, if the gallium-rich bonding portion 411 comprises pure gallium, the temperature is raised to at least 30° C., such as 35 to 50° C., to melt the gallium-rich bonding portion 411 into a gallium-rich droplet. This separates the backplane 32 and the first subset of the first light-emitting diodes 10B from the second assembly of the first substrate 8A and the second subset of the first light-emitting diodes 10B with or without the application of mechanical force. For example, the second assembly can be pulled away from the first assembly. The adhesion provided by the gallium-rich droplet is weak and separation can be induced by a force less than 100 N.

[0091] Optionally, gallium-rich material portion 311 (which may include remnants of gallium-rich adhesion portion 411) may be located on the surface of first conductivity type semiconductor layer 12. Gallium-rich material portion 311 includes an atomic concentration of gallium greater than 55%, which may be greater than 95%, such as 96% to 100%. In one embodiment, gallium-rich material portion 311 may consist essentially of gallium and may have a thickness in the range of, for example, 5 nm to 100 nm, such as 10 nm to 50 nm.

[0092] If a single color LED device is desired, the manufacturing process ends with the step shown in Figure 8G. Alternatively, the steps shown in Figures 8A-8G may be repeated so that LEDs of different colors are bonded to backplane 32 to form a multi-color display.

[0093] 9A, a second source coupon 2 may be provided that includes second light emitting diodes 10G located on a second substrate 8B. Each of the second light emitting diodes 10G may include a respective additional buffer layer 11 at an interface with the second substrate 8B. The second light emitting diodes 10G may be arranged in a pattern that includes voids that include a mirror image pattern of a first subset of the first light emitting diodes 10B in the first assembly. In one embodiment, the second light emitting diodes 10G may emit light at a second peak wavelength that is different from the first peak wavelength.

[0094] To partially laser lift-off and coin the diode side bonding material portion 17 on the second light-emitting diode 10G of the second source coupon 2, the process steps of Figures 8A to 8D can be performed using the second source coupon 2 instead of the first source coupon 1.

[0095] 9B, the second source coupon and the first assembly may be aligned with each other such that each first light emitting diode 10B on the backplane 32 is located under a respective one of the voids in the second source coupon. The steps of the process of FIGS. 8E-8G may then be performed to convert a subset of the additional buffer layer 11 into additional gallium rich bonding portions 411, bond a first subset of the second light emitting diodes 10G to a respective underlying one of the bonding pads 34 by localized laser irradiation on a respective underlying set of at least one additional bonding material portion (17, 37), and separate the third assembly on the backplane 32, the first subset of the first light emitting diodes 10B and the first subset of the second light emitting diodes 10G from the fourth assembly on the second substrate 8B and the second subset of the second light emitting diodes 10G that are not transferred to the backplane 32.

[0096] 10, a third source coupon may be provided that includes third light emitting diodes 10R disposed on a third substrate. Each of the third light emitting diodes 10R may include a respective additional buffer layer at an interface with the third substrate. In one embodiment, the third light emitting diodes 10R may emit light at a third peak wavelength that is different from the first peak wavelength and the second peak wavelength.

[0097] 8B-8G may be performed to transfer the first subset of third light emitting diodes 10R to the backplane 32. The third light emitting diodes 10R may be arranged in a pattern including voids that include a mirror image pattern of the first subset of first light emitting diodes 10B and the first subset of second light emitting diodes 10G in the third assembly. The backplane 32 may include an array of pixels to provide a direct-view display device, as described above with respect to the first embodiment.

[0098] With reference to all the drawings, in accordance with various embodiments of the present disclosure, a light emitting diode assembly is provided that includes a backplane 32 that includes bonding pads 34, and first light emitting diodes 10B attached to a first subset of the bonding pads 34 via respective bonding material portions 47. Each of the first light emitting diodes includes a first conductivity type semiconductor layer 12 and a gallium-rich material portion 311 located above a surface of the first conductivity type semiconductor layer 12 and including gallium at an atomic concentration greater than 55%.

[0099] In one embodiment, each of the gallium-rich material portions 311 includes an atomic concentration of gallium atoms greater than 55%, such as greater than 90%. In one embodiment, the gallium-rich material portions 311 include no nitrogen or include an atomic concentration of nitrogen atoms less than 5%. In one embodiment, the first conductivity type semiconductor layer 12 includes a crystalline gallium nitride layer.

[0100] In one embodiment, the assembly may also include second light emitting diodes 10G attached to a second subset of the bonding pads 34 on the backplane 32 via respective bonding material portions 47. Each of the second light emitting diodes 10G is configured to emit light at a different peak wavelength than each of the first light emitting diodes 10B. Each of the second light emitting diodes includes another first conductivity type semiconductor layer 12 and another gallium-rich material portion 311 overlying a surface of the first conductivity type semiconductor layer and including gallium at an atomic concentration greater than 55%.

[0101] Various embodiments of the present disclosure provide a partial laser lift-off process including a partial die separation method in which the gallium and nitrogen containing buffer layer 11 is converted to a gallium rich material portion 311 having a low melting point. A localized laser irradiation is used before bonding each mating pair of bonding pads 34 and contact level material layers in the subset of light emitting diodes (10B, 10G, 10R) transferred from the source coupon to the backplane 32. Thus, mechanical shock from the separation laser irradiation to the backplane 32 can be reduced or avoided. Separation of the bonded assembly of the backplane 32 and the remaining portion of the source coupon from the attached subset of light emitting diodes can be performed by heating the bonded assembly to a relatively low temperature that is higher than the melting temperature of the gallium rich material portion 211 of the first embodiment or the gallium rich material adhesive portion 411 of the second embodiment without applying mechanical force or while applying a small amount of mechanical force that does not damage the backplane 32.

[0102] Although the foregoing refers to certain preferred embodiments, it will be understood that the present invention is not limited thereto. Those skilled in the art may make various modifications to the disclosed embodiments, and such modifications are intended to be within the scope of the present invention. Where embodiments using specific structures and / or configurations are shown in this disclosure, it is understood that the present invention may be practiced with other compatible structures and / or configurations that are functionally equivalent, unless such substitutions are expressly prohibited or known to be impossible by those skilled in the art.

Claims

1. A method for transferring a light emitting diode die of a light emitting diode assembly, comprising the steps of: providing a first light emitting diode on a first substrate; providing a first source coupon including each of the first light emitting diodes including a buffer layer including gallium and nitrogen at an interface with the first substrate and an additional first light emitting diode located on the first substrate; providing a backplane including an array of bonding pads; forming a diode-side bonding material portion on each of the first light emitting diodes; forming a backplane side bonding material portion on each of said bonding pads; pressing each mating pair of the diode-side bonding material portions and the backplane-side bonding material portions together with a first force; pressing the first source coupon against the backplane and performing a partial laser lift-off of the first light emitting diode from the first substrate; coining the diode-side bonding material portions and the backplane-side bonding material portions by pressing each mating pair of the diode-side bonding material portions and the backplane-side bonding material portions together with a second force that exceeds the first force; laser bonding the first light emitting diode to the backplane; and separating the first substrate from the first light emitting diode.

2. The method described in claim 1, characterized in that the step of performing partial laser lift-off of the first light-emitting diode from the first substrate includes the step of irradiating the first light-emitting diode with an isolating laser beam through the first substrate.

3. The first light-emitting diode includes an amorphous buffer layer containing gallium and nitrogen between the first substrate and a crystalline semiconductor layer of a first conductivity type; 3. The method of claim 2, wherein the step of irradiating the first light emitting diode with a separating laser beam comprises converting the amorphous buffer layer into liquid gallium-rich droplets. [0010] 4. The liquid gallium-rich droplets solidify into a gallium-rich material portion comprising at least 55 atomic percent gallium connecting the first light emitting diode to the first substrate; 4. The method of claim 3, wherein separating the first substrate from the first light emitting diode comprises heating the first light emitting diode above a melting temperature of the gallium-rich material portion.

5. A method of manufacturing a semiconductor device comprising the steps of: arranging the first light emitting diodes over the array of bonding pads such that at least one bonding material portion is disposed between each vertically adjacent pair of a respective one of the bonding pads and a respective one of the first light emitting diodes; converting a subset of the buffer layer of a first subset of the first light emitting diodes into a gallium-rich material portion having gallium atoms in an atomic concentration of greater than 55% by performing the partial laser lift-off; laser bonding the first subset of the first light emitting diodes to respective underlying ones of the bonding pads by localized laser irradiation onto a respective underlying set of at least one bonding material portion; 2. The method of claim 1, further comprising: separating a first assembly of the backplane and the first subset of the first light emitting diodes from a second assembly of the first substrate and a second subset of the first light emitting diodes by melting the gallium rich material portion.

6. The method of claim 5, wherein each of the gallium-rich material portions contains gallium atoms at an atomic concentration of greater than 90%.

7. Each of the first light-emitting diodes includes a first conductivity type semiconductor layer including gallium and nitrogen spaced from the first substrate by each of the buffer layers; 7. The method of claim 6, wherein each of the buffer layers comprises gallium nitride.

8. Providing a second source coupon including a second light emitting diode located on a second substrate including an additional buffer layer at an interface with the second substrate; disposing the second light emitting diodes over the first assembly such that at least one additional bonding material portion is disposed between each vertically adjacent pair of the bonding pads and each of the second light emitting diodes; converting a subset of the additional buffer layer to an additional gallium-rich material portion that includes gallium atoms in an atomic concentration greater than 55% by another partial laser lift-off; laser bonding a first subset of the second light emitting diodes to an underlying one of each of the bonding pads by localized laser irradiation onto a respective underlying set of at least one additional bonding material portion; and separating a third assembly of the backplane, the first subset of the first light emitting diodes, and the first subset of the second light emitting diodes from a fourth assembly of the second substrate and the second subset of the first light emitting diodes by melting the additional gallium rich material portion; 6. The method of claim 5, wherein the second light emitting diodes are arranged in a pattern including voids that include a mirror image pattern of the first subset of the first light emitting diodes in the first assembly.

9. Pressing the first light-emitting diode against a flat surface; converting a first subset of the buffer layer in a first subset of the first light emitting diodes into gallium-rich droplets by a first laser irradiation; solidifying the gallium-rich droplet into a gallium-rich material portion having gallium atoms in an atomic concentration of greater than 55%; converting the gallium-rich material portion into a gallium-rich adhesive portion having a higher adhesive strength than the gallium-rich material portion by irradiating a second laser; removing the first light emitting diode from the planar surface; disposing the first light emitting diodes over the array of bonding pads such that at least one bonding material portion is disposed between each vertically adjacent pair of a respective one of the bonding pads and a respective one of the first light emitting diodes; laser bonding the first subset of the first light emitting diodes to respective underlying ones of the bonding pads by localized laser irradiation onto a respective underlying set of at least one bonding material portion; 2. The method of claim 1, further comprising: separating a first assembly of the backplane and the first subset of the first light emitting diodes from a second assembly of the first substrate and a second subset of the first light emitting diodes by melting the gallium-rich adhesive.

10. The method of claim 9, characterized in that the second subset of the first light-emitting diodes, after being separated from the first assembly, are attached to the first substrate of the second assembly by a second subset of the buffer layer.

11. The diode-side bonding material portion is pressed against the flat surface during the first laser irradiation step, 10. The method of claim 9, wherein the first laser irradiation coins the diode-side bonding material portion.

12. Each of the first light-emitting diodes includes a first conductivity type semiconductor layer including gallium and nitrogen spaced from the first substrate by each of the buffer layers; 10. The method of claim 9, wherein each of the buffer layers comprises gallium nitride.

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