Apparatus and method for transferring light-emitting diodes

Abstract

An apparatus for transferring light emitting diodes (LEDs) includes a backing board for supporting a backplane, a sealing member formed on the backing board around a periphery of the backplane, a transparent panel formed on the sealing member such that a space is formed between the backing board and the transparent panel, and a vacuum source for drawing a vacuum in the space.

Description

【Technical Field】 【0004】 【0001】 Related Applications This application claims the benefit of priority from U.S. Provisional Patent Application No. 63 / 214,445, filed Jun. 24, 2021, the entire contents of which are incorporated herein by reference. 【0002】 Embodiments of the present invention generally relate to an apparatus for transferring light-emitting diodes (LEDs), and a method of transferring LEDs, including evacuating a space such that a transparent panel presses a plurality of LED coupons against a backplane. 【Background Art】 【0003】 Light-emitting diodes (LEDs) are used in electronic displays such as the liquid crystal display of a laptop or an LED television. However, it is difficult to attach LEDs to a backplane (e.g., a display backplane) with a high yield. 【Summary of the Invention】 <​​​​​​According to yet another aspect of the present disclosure, a method for transferring light-emitting diodes (LEDs) includes arranging a backplane on a backing board, wherein a sealing member is arranged around the backplane; arranging a plurality of first LED coupons on the backplane; arranging a transparent panel on the sealing member over the plurality of first LED coupons such that a space is formed between the backing board and the transparent panel; evacuating the space such that the transparent panel presses the plurality of first LED coupons toward the backplane; and directing laser radiation through the transparent panel to illuminate the plurality of first LED coupons arranged on the backplane. [Brief explanation of the drawing] 【0006】 [Figure 1] Figure 1 shows a top view of an LED coupon (e.g., a first source coupon) 1 including a growth substrate 8 containing the die of an LED 10, according to several embodiments. 【0007】 [Figure 2] Figure 2 shows side cross-sectional views of the LED coupon 1 according to several embodiments. 【0008】 [Figure 3] Figure 3 shows a side cross-sectional view of the arrangement of the LED coupon 1 in preparation for transferring the LEDs 10A, 10B, and 10C from the LED coupon 1 to the backplane 32, according to several embodiments. 【0009】 [Figure 4A] Figure 4A shows a side cross-sectional view of a device 400 that may be used to transfer LEDs 10A, 10B, and 10C from LED coupon 1 to backplane 32 according to several embodiments. 【0010】 [Figure 4B] Figure 4B shows a side cross-sectional view of the apparatus 400 after the space S has been evacuated by the vacuum source 440, according to several embodiments. 【0011】 [Figure 5] Figure 5 shows a side cross-sectional view of an LED transfer device 450 according to several embodiments. 【0012】 [Figure 6A] Figure 6A shows a side cross-sectional view of a backplane 32 placed on a backing board 410, an LED coupon 1 placed on the backplane 32, and a transparent panel 430 placed on the LED coupon 1, according to several embodiments. 【0013】 [Figure 6B] Figure 6B shows a side cross-sectional view of a sequential laser irradiation process performed to irradiate the buffer layer 11 of the LED 10A, which is transferred to the backplane 32, with a separated laser beam LD, according to several embodiments. 【0014】 [Figure 6C] Figure 6C shows a side cross-sectional view of a liquid gallium-rich drop 111 that solidifies into a solid gallium-rich material portion (e.g., pure gallium or gallium-rich alloy particles or regions) 211 after irradiation, according to several embodiments. 【0015】 [Figure 6D] Figure 6D shows a side cross-sectional view of the backplane 32 and LED coupon 1 pressed against each other to cause deformation of the joint material portions (17, 37) according to several embodiments. 【0016】 [Figure 6E] Figure 6E shows a side cross-sectional view of a localized laser irradiation process performed to cause reflow and bonding of the mating pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 located beneath the LED 10A, according to several embodiments. 【0017】 [Figure 6F]FIG. 6F shows a cross-sectional view of a vacuum source 440 that stops evacuating the space S between the backplane 32 and the LED coupon 1 so that the transparent panel 430 stops applying a downward pressure to the LED coupon 1, according to some embodiments. 【0018】 [Figure 7] FIG. 7 shows a flowchart of a method for transferring LEDs, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION 【0019】 Embodiments of the present disclosure are directed to an apparatus and method for transferring LEDs, and various aspects thereof will be described below. Throughout the drawings, like elements are described by like reference numerals. Unless otherwise specified, elements having the same reference numerals are assumed to have the same material composition. The drawings are not drawn to scale. Multiple instances of an element may overlap if not explicitly stated that there is no overlap of the element or otherwise clearly shown as a single instance of the element. Ordinal numbers such as "first", "second", and "third" are used merely to identify like elements, and different ordinal numbers may be used throughout the specification and claims of the present disclosure. 【0020】 The LED may be a vertical structure (e.g., vertical LED) in which the p-side contact and the n-side contact are located on opposite sides of the structure, or may be a horizontal structure in which the p-side contact and the n-side contact are located on the same side of the structure. In embodiments of the present disclosure, a method for transferring LEDs (e.g., an array of LEDs) from a growth substrate to a target substrate such as a backplane is provided. In an exemplary example, the target substrate may be a backplane such as an active or passive matrix backplane substrate for driving the LEDs. As used herein, "backplane" refers to any substrate configured to mount a plurality of LEDs thereon. 【0021】 LEDs can include different "types," such as red LEDs that emit red light, green LEDs that emit green light, and blue LEDs that emit blue light. LEDs of the same type can be manufactured on their respective growth substrates (e.g., initial growth substrates). In particular, LEDs can be manufactured as arrays on growth substrates that are processed to form various electronic devices, including LEDs and sensor devices (e.g., photodetectors), on or within them. LEDs may be, for example, vertical LEDs, horizontal LEDs, or any combination thereof. 【0022】 Referring to Figure 1, an LED coupon (e.g., a first source coupon) 1 is shown, which includes a growth substrate 8 containing the die of the LED 10. The growth substrate 8 may include an edge exclusion region 300 on which the LED 10 is not formed. The growth substrate 8 may include LEDs of the same type (e.g., red LEDs, green LEDs, blue LEDs, etc.) arranged in the first array 100. That is, the LED 10 may include multiple instances of the same type of LED, which may be light-emitting diodes emitting light at the same peak wavelength, for example. 【0023】 The first array 100 has a primary pitch Px1 along each primary direction (i.e., the primary direction of the first array 100) and a secondary pitch Py1 along each secondary direction (i.e., the secondary direction of the first array 100). As used herein, the primary and secondary directions of an array refer to the two directions in which the unit cells of the array are repeated. In a rectangular array, the primary and secondary directions may be perpendicular to each other and are referred to as the x and y directions. 【0024】 The LEDs 10 on the growth substrate 8 can be transferred to one or more backplanes having bonding sites configured in a second array. A predetermined transfer pattern and transfer sequence may be used for transferring the LEDs 10. Different types of LEDs (e.g., green LEDs and blue LEDs) transferred from different growth substrates can be used in combination with the LEDs 10 (e.g., red LEDs) to provide a functional direct-view LED assembly. 【0025】 Figure 2 shows a cross-sectional view of an LED coupon 1 according to several embodiments. As shown in Figure 2, the LED coupon 1 includes a growth substrate 8 and a plurality of LEDs 10A, 10B, 10C arranged on the growth substrate 8. The growth substrate 8 can be any suitable substrate on which an LED layer can be grown, such as a single crystal substrate on which an LED semiconductor layer can be grown. For example, the growth substrate 8 may include a sapphire substrate. 【0026】 LEDs 10A, 10B, and 10C may include a buffer layer 11 and a first conductivity type semiconductor layer 12. The buffer layer 11 may include an amorphous III-V compound semiconductor layer containing gallium and nitrogen. The first conductivity type semiconductor layer 12 may include a crystalline III-V compound semiconductor material layer containing gallium and nitrogen. For example, the buffer layer 11 may include amorphous gallium nitride (GaN), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), or aluminum indium gallium nitride (AlInGaN), and the first conductivity type semiconductor layer 12 may include single crystal or polycrystalline GaN, InGaN, AlGaN, or AlInGaN. The first conductivity type semiconductor layer 12 has a first conductivity type, which may be n-type or p-type. For example, the first conductivity type semiconductor layer 12 may include an n-type semiconductor layer. The buffer layer 11 may be undoped or may have a first conductivity type. 【0027】 The buffer layer 11 is located between the first conductivity type semiconductor layer 12 and the growth substrate 8. The buffer layer 11 may have the same material composition as the first conductivity type semiconductor layer 12. 【0028】 For example, in one embodiment, both the buffer layer 11 and the first conductivity semiconductor layer 12 may contain gallium nitride. In this embodiment, the buffer layer 11 may be formed during the initial deposition of the crystalline gallium nitride first conductivity semiconductor layer 12 onto a growth substrate 8, which may be a patterned sapphire substrate (PSS). That is, the buffer layer 11 may be formed to transition the growth conditions of the gallium nitride from amorphous to crystalline gallium nitride layer. The thickness of the buffer layer 11 can be in the range of 100 nm to 400 nm, for example, 150 nm to 300 nm, but thinner or thicker thicknesses can also be used. The thickness of the first conductivity semiconductor layer 12 can be 500 nm to 5 microns, for example, 1 to 3 microns, but thinner or thicker thicknesses can also be used. 【0029】 The active layer 13 may be formed 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 13 may have a stack of one or more InGaN quantum well layers between each GaN barrier layer and / or AlGaN barrier layer. In general, any light-emitting layer stack known in the art can be used for the active layer 13. 【0030】 A second conductivity type semiconductor layer 14 may be formed on the active layer 13. The second conductivity type semiconductor layer 14 may have doping of the 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 positioned between the first conductivity type semiconductor layer 12 and the second conductivity type semiconductor layer 14. 【0031】 The contact-level material layer 15 may be formed on the second conductivity type semiconductor layer 14. The contact-level material layer 15 may include 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 layer stack from bottom to top, comprising a transparent conductive oxide layer, a reflector layer, and / or a bonding pad material layer. The transparent conductive oxide layer may include a transparent conductive oxide material such as indium tin oxide or aluminum-doped zinc oxide. The reflector layer may include gold, silver, and / or aluminum. The bonding pad material layer may include a metallic material that can function as a bonding pad, such as gold, copper, nickel, titanium, titanium nitride, tungsten, tungsten nitride, another metal having a higher melting point than the solder material used later, an alloy of those metals, and / or a layer stack of those metals. 【0032】 The stack of the second conductivity semiconductor layer 14, the active layer 13, and optionally the first conductivity semiconductor layer 12 within each LED 10A, 10B, 10C can be patterned using various patterning methods to form grooves 19 between adjacent LEDs 10A, 10B, 10C. A dielectric matrix layer 16 can be formed between the first LEDs 10A, 10B, 10C. The grooves 19 define the region of each LED 10A, 10B, 10C. Specifically, each continuous set of patterned material layers on the growth substrate 8 and laterally surrounded by a set of grooves 19 can constitute LEDs 10A, 10B, 10C. In one embodiment, the grooves 19 may be formed in a grid pattern to provide an array of LEDs, which may be a periodic array of LEDs. LEDs 10A, 10B, 10C can emit light at a first peak wavelength, such as blue light having a first peak wavelength within the blue spectral range. 【0033】 Figure 2 shows a specific embodiment of the LED coupon 1 including LEDs 10A, 10B, and 10C, but any configuration of LEDs 10A, 10B, and 10C can be used in the embodiments of the present disclosure, provided that the structure for attaching the bonding material portion is provided on the side of LEDs 10A, 10B, and 10C that faces away from the growth substrate 8. 【0034】 Figure 3 shows the arrangement of the LED coupon 1 in preparation for transferring LEDs 10A, 10B, and 10C from the LED coupon 1 to the backplane 32, according to several embodiments. As shown in Figure 3, the diode-side junction material portion 17 may be formed on the contact-level material layer 15 for each of the LEDs 10A, 10B, and 10C. In one embodiment, the diode-side junction material portion 17 may be a solder material portion such as pure tin or an alloy of tin and indium. 【0035】 The backplane 32 may be a single large panel version of a substrate 38, or several substrates 38 arranged to mate within the space of a large panel, and a metal interconnect layer 325 formed on the front surface of the substrates 38. In one embodiment, the substrates 38 may include plastic (e.g., polymer) substrates, glass substrates, or silicon substrates. The backplane 32 may also have a large size (e.g., Gen8 or larger). In one embodiment, the metal interconnect layer 325 may include a plurality of metal interconnect structures that are arranged on the surface of the substrates 38 and / or embedded in at least one insulating material, providing electrical connections between LEDs bonded to the backplane 32 and the input / output pins of the backplane 32. 【0036】 The bonding pads 34 may be formed on the surface of the backplane 32 (for example, the surface of the substrate 38) above the metal interconnection layer 325. In one embodiment, the bonding pads 34 may be arranged as a two-dimensional periodic array or as a one-dimensional periodic array. The bonding pad materials for the bonding pads 34 may include gold, copper, nickel, titanium, titanium nitride, tungsten, tungsten nitride, another metal having a higher melting point than the solder material to be used later, alloys thereof, and / or stacks thereof. 【0037】 The backplane-side bonding material portion 37 may be formed on the bonding pad 34. In one embodiment, the backplane-side bonding material portion 37 may be a solder material portion such as pure tin or an alloy of tin and indium. The LED coupon 1 and the backplane 32 may be aligned such that a pair of diode-side bonding material portions 17 and backplane-side bonding material portions 37 face each other at each grid point of the periodic arrangement of the bonding pad 34. 【0038】 Figure 4A shows a device 400 that can be used to transfer LEDs 10A, 10B, and 10C from LED coupon 1 to backplane 32 according to several embodiments. The method will be described in detail below for LED 10A, but LEDs 10B and 10C can be transferred sequentially to the same backplane 32 according to the same method. 【0039】 The apparatus 400 may include a backing board 410 for supporting the backplane 32, a sealing member 420 formed on the backing board 410 around the backplane 32, a transparent panel 430 positioned on the sealing member 420 such that a space S is formed between the backing board 410 and the transparent panel 430, and a vacuum source 440 for vacuuming the space S. 【0040】 The apparatus 400 may also include a laser radiation source (i.e., a laser) 450 that directs laser radiation L through a transparent panel 430 to irradiate an LED coupon 1 formed on a backplane 32 in space S. In one embodiment, the laser radiation source 450 can emit laser radiation L to irradiate the buffer layer 11 of the LED 10A to perform a partial laser lift-off process on the LED 10A. 【0041】 The process of transferring LEDs to the backplane 32 can be initiated, for example, at room temperature by placing the backplane 32 on a backing board 410 (e.g., a non-compliant, rigid backing board) in a vacuum laminator 445, and then placing a plurality of LED coupons 1 onto the backplane 32. The LED coupons 1 can include, for example, a microLED coupon, each containing a substrate (e.g., a growth substrate) and a plurality of microLEDs formed on the substrate and transferred from the substrate to the backplane 32. MicroLEDs can be much smaller than, for example, about 100 microns, and can be as small as 1 to 20 microns, or for example, 2 to 10 microns. However, larger LEDs or monolithic arrays of LEDs can also be transferred. 【0042】 Multiple LED coupons 1 may be arranged in an array on the backplane 32, for example, as shown in Figure 3, such that the diode-side bonding material portion 17 formed on the LEDs 10A, 10B, and 10C is aligned with the backplane-side bonding material portion 37 on bonding pads 34 arranged in an array on the backplane 32. Specifically, the LED coupons 1 may be "tiled" on the backplane 32 so as to cover substantially the entire backplane 32. Alignment of the LED coupons 1 may be performed, for example, by an optical sensor (not shown) that determines the precise position of the LED coupons 1 and a robotic arm (not shown) that positions the LED coupons 1 in the precise position. 【0043】 Next, the transparent panel 430 may be positioned over the multiple LED coupons 1 and sealing members 420 such that a space S is formed between the backing board 410 and the transparent panel 430. Then, the vacuum source 440 evacuates the space S, and the evacuation of the space may pull the transparent panel 430 toward the backplane 32, causing the transparent panel 430 to press the LED coupons 1 toward the backplane 32. Specifically, the pressure exerted by the transparent panel on the multiple LED coupons may be substantially uniform across the multiple LED coupons. 【0044】 In some embodiments, the backing board 410 may include a rigid backing board made from, for example, a metal or a rigid polymer material. The backing board 410 may also include a vacuum laminator backing board which may include one or more slits 411 (e.g., through holes, channels, etc.) to allow a vacuum source 440 to access the space S and to allow the vacuum source 440 to vacuum the space S through the slits 411. Alternatively, in addition to or instead of passing through the slits 411, vacuuming may be performed through or adjacent to the sides of the backing board 410. The backing board 410 must also be large in size (e.g., area) to accommodate a large backplane 32 (e.g., Gen8 or larger) and to accommodate a sealing member 420 that may be formed around the backplane 32. 【0045】 The sealing member 420 may be a perimeter shim frame that can eliminate edge effects and provide good sealing with the transparent panel 430. In some embodiments, the sealing member 420 may include an O-ring type or gasket type sealing member that can be configured in a rectangular shape that approximates the shape of the backplane 32. The sealing member 420 may be formed continuously around the perimeter of the backplane 32 such that the gap between the sealing member 420 and the perimeter of the backplane 32 (e.g., in the X direction in Figure 4A) is about 2 centimeters or less. The sealing member 420 may be formed from a polymer material such as polyurethane, silicone, neoprene, nitrile rubber, fluorocarbon, polytetrafluoroethylene (PTFE), or ethylene propylene diene monomer (EPDM) rubber. The thickness of the sealing member 420 (e.g., in the Z direction in Figure 4A) should be substantially the same as the sum of the thicknesses of the backplane 32 and the LED coupon 1. If the thickness of the sealing member 420 is too small, the transparent panel 430 will not be able to rest on the LED coupon 1 and will not come into contact with the sealing member 420, and as a result, a seal cannot be formed around the space S. However, if the thickness of the sealing member 430 is too large, the distance between the transparent panel 430 and the backplane 32 may be too large, and the transparent panel 430 may not be able to push the LED coupon 1 toward the backplane 32 under vacuum. Therefore, if the sum of the thicknesses of the backplane and the LED coupon is Tb, the thickness Ts of the sealing member 420 should be in the range of 0.9Tb ≤ Ts ≤ 1.1Tb. 【0046】 The transparent panel 430 can be a compliant (e.g., flexible or pliable) transparent panel that is large enough (e.g., has a sufficiently large area) to cover the sealing member 420 around the entire perimeter of the backplane 32. In other words, the transparent panel 430 can have lower rigidity (i.e., lower stiffness and lower Young's modulus) than the backing board 410. The transparent panel 430 may be sufficiently transparent so as not to interfere with the laser radiation L guided through the transparent panel 430 to the LED coupon 1 in space S. In one embodiment, the transparent panel 430 can have a thickness of a few millimeters or less (e.g., less than about 5 millimeters, e.g., 0.1 to 2 mm, e.g., 0.5 to 1 mm). If the thickness is too large, the focal point of the laser radiation from the radiation source 450 may be too far from the working surface on the LED coupon 1 during the subsequent laser irradiation process. The transparent panel 430 may be made of glass such as borosilicate glass, but other types of glass may be used as long as they are transparent to the laser radiation emitted by the laser radiation source 450. 【0047】 The vacuum source 440 may include a vacuum laminator 445, a vacuum pump 442 for vacuuming, and piping 444 connecting the vacuum pump 442 to one or more vacuum ports on the vacuum laminator 445. The vacuum pump 442 can sufficiently vacuum the space S so that the pressure at which the transparent panel 430 presses the LED coupon 1 can be easily and very precisely controlled to any pressure range up to atmospheric pressure of 14.7 psi, and can be applied substantially uniformly throughout the transparent panel 430. 【0048】 The laser source 450 may include one or more types of lasers for generating laser radiation L at different wavelengths and power levels. The laser source 450 may be configured to perform in-situ laser lift-off (LLO) and laser scanning (LS) rasters (e.g., in the Y direction in Figure 4A), while the backing board 410 is indexed in the vertical direction (e.g., in the X direction in Figure 4A). Specifically, the laser source 450 may generate a separation laser beam LD for separating LED 10 from LED coupon 1 in a partial laser lift-off process. The separation laser beam LD may have ultraviolet wavelengths or wavelengths in the visible light region. In some embodiments, the laser source 450 may include an excimer (UV) laser having a wavelength of 248 nm or 193 nm for generating the separation laser beam LD. The laser source 450 may also generate a laser beam LB (e.g., an infrared laser beam) during a bonding laser irradiation process. In some embodiments, the laser radiation source 450 may include a CO2 laser for generating a laser beam LB (e.g., an infrared laser beam) having a wavelength of 9.4 microns or 10.6 microns. In other words, the laser radiation source 450 may include two or more different lasers. 【0049】 Figure 4B shows a side view of the apparatus 400 after the space S has been evacuated by the vacuum source 440, according to some embodiments. As shown in Figure 4B, the transparent panel 430 may be flexible enough to flex downward (for example, in the Z direction in Figure 4B) under the vacuum of the vacuum source 440 within the space S sealed by the sealing member 420. The amount of downward pressure applied to the LED coupon 1 by the transparent panel 430 can be adjusted by adjusting the amount of vacuum applied by the vacuum source 440, and therefore by adjusting the amount of current supplied to the vacuum pump 442. That is, the downward pressure can be increased by increasing the vacuum applied by the vacuum source 440, and decreased by decreasing the vacuum applied by the vacuum source 440. In some embodiments, the downward pressure applied to the LED coupon 1 by the transparent panel 430 may be 10 to 15 psi and may be applied substantially uniformly throughout the transparent panel 430. 【0050】 Figure 5 shows a side view of an apparatus 450 for transferring LEDs according to several embodiments. As shown in Figure 5, the apparatus 450 may include the features of the apparatus 400 of Figures 4A-4B, except that the vacuum source 440 may be different. In the apparatus 450, the vacuum source 440 may include a vacuum bag 446 which may be formed over the backing board 410, sealing member 420 and transparent panel 430. The vacuum bag 446 may be made of plastic or another material which is transparent to and unaffected by the laser radiation L emitted from the laser radiation source 450. The vacuum bag 446 may also include one or more ports 446a to which vacuum piping 444 may be connected. During operation, the vacuum source 440 can vacuum the space S by vacuuming the vacuum bag 446 with substantially the same results as provided by the apparatus 400 shown in Figure 4B. In other words, the vacuum results in a downward pressure applied to the LED coupon 1 by the transparent panel 430, which is 10-15 psi and can be applied substantially uniformly throughout the transparent panel 430. 【0051】 In some embodiments, apparatus 400 and apparatus 450 can provide uniform clamping pressure over very large area panels, such as Gen8 size or larger (e.g., 20 inches diagonally or larger), for the purpose of micro-LED material transfer, and can perform similarly well with multi-transfer coupon designs (e.g., LED coupons of different colors). Specifically, apparatus 400 and apparatus 450 can reduce height distribution differences and shift the neutral stress point upward so that gaps and stress distributions remain within acceptable limits across the entire micro-LED array and from one processing step to the next. Thus, inherent micron-size range waviness in the backplane and / or LED coupons (e.g., due to surface roughness or warpage) can be reduced or eliminated by the uniform pressure applied by the apparatus across the entire backplane area. This improves the quality and accuracy of the bonding and increases the yield of the display device, because non-uniform coupon height relative to the backplane will hinder the transfer of mass LEDs and reduce the yield of the display device. 【0052】 In apparatus 400, the method of transferring the LEDs begins by placing a backplane 32 (e.g., a display backplane) on a backing board 410 (e.g., a rigid backing board) in a vacuum laminator 445, whereas in apparatus 450, the method may begin by placing a backplane 32 (e.g., a display backplane) on a backing board 410 (e.g., a rigid backing board) in a vacuum bag 446. The LED coupon may be placed (e.g., tiled) on the backplane 32 (e.g., a display panel, TV panel, etc.) until it covers the entire backplane 32. A sealing member 420 (e.g., a shim frame) may be placed around the backplane 32 to eliminate edge effects and provide good sealing. A transparent panel 430 (e.g., a cover glass) may then be placed on top of the LED coupon 1 to form a space S that is sealed by the sealing member 420. A vacuum source 440 may then be used to vacuum the space S until a desired level of vacuum (e.g., pressure) is reached. These processing steps can be repeated for LED coupon 1, which contains LEDs of different colors. 【0053】 Referring again to the drawings, Figures 6A to 6F show a method for transferring LED 10A from LED coupon 1 to backplane 32 according to several embodiments. As described above, the same method can also be used to transfer LEDs 10B and 10C to backplane 32. This method can be implemented by using either the apparatus 400 or apparatus 450 described above. As shown in Figure 6A, according to some embodiments, the backplane 32 may be placed on the backing board 410, the LED coupon 1 may be placed on the backplane 32, and the transparent panel 430 may be placed on the LED coupon 1. LEDs 10A, 10B, and 10C of LED coupon 1 may be in contact with the backplane 32 such that opposing pairs of diode-side junction material portions 17 and backplane-side junction material portions 37 are in contact with each other. Each of the diode-side junction material portions 17 may have an area overlap with the backplane-side junction material portion 37 below it. In one embodiment, the overlapping area may be at least 70%, for example 80%, and / or greater than 90% of the area of ​​the diode-side junction material portion 17. In one embodiment, the geometric center of each diode-side junction material portion 17 may overlap the geometric center of the underlying backplane-side junction material portion 37. 【0054】 Generally, at least one bonding material portion (17, 37) may be positioned between each longitudinally adjacent pair of bonding pads 34 and each of the LEDs 10A, 10B, and 10C. In one embodiment, the pair of diode-side bonding material portion 17 and backplane-side bonding material portion 37 may be provided between each longitudinally adjacent pair of bonding pads 34 and each of the LEDs 10A, 10B, and 10C. 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. 【0055】 In one embodiment, the solder flux 35 may be applied between the backplane 32 and the LEDs 10A, 10B, and 10C such that the solder flux 35 laterally surrounds each joint material portion (17, 37). The solder flux 35 may be any suitable liquid flux that reacts with tin oxide to leave behind metallic tin joint material portions (17, 37). 【0056】 As shown in Figure 6A, when the LED coupon 1 is formed on the backplane 32, the vacuum source 440 is linked to the transparent panel 430 to apply a first pressure (e.g., a first amount of downward pressure (e.g., a downward force)) to the LED coupon 1, thereby holding the LED coupon 1 in place on the backplane 32 without lateral slippage. Specifically, the backplane 32 and the LED coupon 1 can be held in place while the transparent panel 430 applies a downward force along the longitudinal direction to the LED coupon 1, the bonding material parts (17, 37), and the backplane 32. The magnitude of the downward force can be selected so as not to significantly deform the bonding material parts (17, 37) without bonding them to each other, i.e., so that the bonding material parts (17, 37) maintain the shape provided before clamping. In an exemplary example, if 2,000,000 pairs of diode-side junction material portions 17 and backplane-side junction material portions 37 are located between a 4-square-meter backplane 32 and a tiled LED coupon 1, the magnitude of the downward force applied by the transparent panel 430 may be in the range of 250N to 400N or approximately 0.1mN to 0.2mN per LED. 【0057】 Referring to Figure 6B, the sequential laser irradiation process can be performed by irradiating the buffer layer 11 of the LED 10A, which is transferred to the backplane 32, with a separated laser beam LD emitted from the laser radiation source 450. The separated laser beam LD may also perform a partial laser lift-off process used to partially lift off the LED 10A, which is referred to herein as the separated laser irradiation process. Each buffer layer 11 of LEDs 10A, 10B, and 10C may be sequentially irradiated with one separated laser beam LD at a time. The lateral dimension (e.g., diameter) of the separated laser beam LD may be approximately the same as the lateral dimension of LEDs 10A, 10B, and 10C. In other words, each buffer layer 11 can be irradiated individually without causing a large compositional change in adjacent buffer layers 11. 【0058】 The separation laser beam LD can have wavelengths in the ultraviolet or visible light region and can be absorbed by the gallium and nitrogen-containing III-V compound semiconductor material of the irradiated buffer layer 11. Although we do not wish to be constrained by any particular theory, it is thought that irradiation of the buffer layer 11 with the separation laser beam LD will evaporate nitrogen atoms without evaporating gallium atoms, or with minimal evaporation of gallium atoms. Thus, the irradiation will reduce the atomic percentage of nitrogen in the remaining material. The LED coupon 1 and backplane 32 can be held in place during and after this process by the pressure applied to the LED coupon 1 by the transparent panel 430. 【0059】 In one embodiment, without being constrained by any particular theory, the buffer layer 11 irradiated by the LED 10A can be converted into a gallium-rich drop 111. The gallium-rich drop 111 may consist of a pure liquid gallium-rich drop, or it may contain a gallium-nitrogen alloy containing gallium at an atomic concentration greater than 55%, such as 60% to 99%. 【0060】 As shown in Figure 6C, the liquid gallium-rich drop 111 may solidify into a solid gallium-rich material portion (e.g., pure gallium or gallium-rich alloy particles or regions) 211 after irradiation if the temperature of the LED coupon 1 is maintained below the melting temperature of gallium or its alloy (e.g., 29.76°C). In one embodiment, the gallium-rich material portion 211 may contain gallium atoms at an atomic concentration greater than 55%, such as 60% to 100%. The gallium-rich material portion 211 may have an average thickness in the range of 5 nm to 100 nm, such as 10 nm to 50 nm, but thinner and thicker thicknesses may be used. The gallium-rich material portion 211 may contain a continuous material layer or it may contain clusters of ball-shaped material portions. The buffer layers 11 of LEDs 10B and 10C on LED coupon 1 that are not irradiated by the laser beam LD remain as buffer layers 11 such as a gallium nitride buffer layer having about 50 atomic percent gallium, and therefore have a higher melting point than the gallium-rich material portion 211. 【0061】 Furthermore, since each adjacent pair of backplane-side bonding material portions 37 and diode-side bonding material portions 17 only come into contact with each other during laser irradiation and are not bonded to each other, the mechanical shock caused by laser irradiation is not transmitted to the backplane 32, which may contain relatively brittle polymers. Therefore, the partial laser lift-off described above with respect to Figures 6B and 6C, which form the gallium-rich material portion 211, causes little to no damage to the backplane 32 and the conductive elements (34, 325) on the backplane 32. In addition, the partial laser lift-off process prevents damage to the re-solidified bonding material portion in subsequent processing steps because the bonding reflow occurs after the partial laser lift-off. 【0062】 Referring to Figure 6D, the backplane 32 and LED coupons 1 can be pressed against each other with greater force to cause deformation of the bonding material portions (17, 37) (i.e., to press the bonding material portions and smooth any rough bonding surfaces). Thus, each diode-side bonding material portion 17 and each backplane-side bonding material portion 37 of each pair can be pressed against each other with a second pressure greater than the first pressure, after the buffer layer 11 of the LED 10A has been converted to a gallium-rich material portion 211. As shown in Figure 6D, the second pressure only needs to be sufficient to deform the diode-side bonding material portion 17 and the backplane-side bonding material portion 37. In an exemplary 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 LED coupons 1, the magnitude of the pressure applied by the transparent panel 430 can be in the range of 500N to 1,000N. 【0063】 Referring to Figure 6E, localized laser irradiation may be performed to cause reflow and bonding of the mating pair between the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 located beneath the LED 10A. The laser irradiation causes bonding of the LED 10A to the backplane 32 and is referred to herein as bonding laser irradiation. The laser beam LB used during bonding laser irradiation can have a photon energy smaller than the band gap of the III-V compound semiconductor material (e.g., a material containing gallium and nitrogen) in the LED 10A, and therefore can pass through the LED 10A. For example, the laser beam LB used in bonding laser irradiation may be an infrared laser beam, such as a carbon dioxide laser beam having a wavelength of 9.4 microns or 10.6 microns. 【0064】 The pair of irradiated diode-side bonding material portions 17 and the backplane-side bonding material portion 37 connected to the LED 10A can be heated to a reflow temperature at which the bonding material (which may be solder) of the pair of diode-side bonding material portions 17 and backplane-side bonding material portions 37 reflows. When the irradiation of the laser beam LB to the bonding pair of diode-side bonding material portions 17 and backplane-side bonding material portions 37 ends, the reflowed material resolidifies to obtain a resolidated bonding material portion 47. In other words, the resolidated bonding material portion 47 is bonded to the bonding pad 34 and contact level material layer 15 of the LED 10A. 【0065】 Therefore, LED 10A can be bonded to one under each of the bonding pads 34 by localized laser irradiation to a set under each of at least one bonding material portion (17, 37) that is reflowed and resolidified to form a resolidating bonding material portion 47. During the localized laser irradiation for transferring LED 10A, the mating pairs of the diode-side bonding material portion 17 and the backplane-side bonding material portion 37 for LEDs 10B, 10C can be pressed against each other with a second pressure. Thus, LED 10A can be bonded to the backplane 32, while LEDs 10B, 10C on LED coupon 1 can remain unbonded to the backplane 32. The gallium-rich material portion 211 provides weak adhesion between the growth substrate 8 and the first conductivity type semiconductor layer 12. Since LED 10A is held in place by the gallium-rich material portion 211, a lower power laser beam LB can be used than in conventional bonding processes. This further reduces damage to the backplane 32. The solder flux 35 may be evaporated during irradiation with the laser beam LB, or it may be allowed to flow out after this process. 【0066】 Referring to Figure 6F, the vacuum source 440 stops evacuating the space S between the backplane 32 and the LED coupon 1, and the transparent panel 430 stops applying downward pressure to the LED coupon 1. The backplane 32 can then be heated to a temperature higher than the melting temperature of the gallium-rich material portion 211 but lower than the melting temperature 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 contains pure gallium, the temperature can be raised to at least 30 degrees Celsius (e.g., 35-50 degrees Celsius) to melt the gallium-rich material portion 211 into a gallium-rich drop 111. This makes it possible to separate LED 10A from the growth substrate 8 with or without mechanical force, while LEDs 10B and 10C remain fixed to the growth substrate 8 unaffected. Optionally, the gallium-rich material portion 311 (such as the re-solidified gallium-rich drop 111 or the remainder of portion 211) can be located on the surface of the first conductivity type semiconductor layer 12. 【0067】 The same method can be used sequentially to transfer LEDs 10B and 10C to the backplane 32. Specifically, the vacuum is released, and the remaining portion of the LED coupon 1, including the first color LED 10A, is removed from the apparatus 400 or 450 (i.e., the transparent panel 430 is lifted and then moved away from the backplane 32), while the bonded LED 10A remains bonded to the backplane. Then, a different LED coupon 1, including the different color LED 10B, is placed on the backplane 32. Vacuuming is performed again, and the processing steps in Figures 6A to 6F are repeated for LED 10B. Then, the same process is repeated for LED 10C. 【0068】 Figure 7 shows a flowchart of a method for transferring LEDs according to several embodiments. As shown in Figure 7, the method includes step 610 of placing a backplane on a backing board and placing a plurality of LED coupons on the backplane. The method also includes step 620 of providing a sealing member around the backplane. The sealing member 420 may be permanently attached to the backing board or may be placed in the apparatus before or after step 610. The method also includes step 630 of placing a flexible transparent panel on the sealing member over the plurality of LED coupons so that a space is formed between the backing board and the transparent panel. The method also includes step 640 of vacuuming the space so that the transparent panel presses the plurality of LED coupons toward the backplane. After vacuuming, the transparent panel flexes toward the backplane so that it presses the plurality of LED coupons toward the backplane. The method also includes step 650 of directing laser radiation through the transparent panel to illuminate the plurality of first LED coupons placed on the backplane. 【0069】 While the above refers to certain preferred embodiments, it should be understood that the present invention is not so limited. Those skilled in the art will see that various modifications can be made to the disclosed embodiments, and that such modifications are intended to be within the scope of the present invention. Where embodiments using certain structures and / or configurations are illustrated in this disclosure, it should be understood that the present invention may be carried out with any other compatible structures and / or configurations that are functionally equivalent, unless such substitutions are expressly prohibited or known to those skilled in the art as impossible otherwise.

Claims

[Claim 1] A device for transferring light-emitting diodes (LEDs), A backing board configured to support the backplane, A sealing member disposed on the backing board around the position of the backplane, A transparent panel, wherein the transparent panel is placed on the sealing member such that a space is formed between the backing board and the transparent panel, A vacuum source configured to evacuate the aforementioned space, A laser radiation source configured to guide laser radiation through the transparent panel to illuminate an LED coupon, which includes a plurality of LEDs arranged on a growth substrate on the backing board within the space, A device equipped with the following features. [Claim 2] The backplane, which is placed on the backing board, The LED coupon arranged on the backplane, The apparatus according to claim 1, further comprising the following: [Claim 3] The apparatus according to claim 2, wherein the vacuuming of the space is performed by pulling the transparent panel toward the backplane and pressing the LED coupon toward the backplane against the transparent panel. [Claim 4] The apparatus according to claim 2, wherein the transparent panel presses the LED coupon with a pressure of 14.7 psi or less that is applied substantially uniformly over the entire transparent panel. [Claim 5] The apparatus according to claim 2, further comprising a plurality of LED coupons arranged in an array on the backplane, wherein the pressure exerted by the transparent panel on the plurality of LED coupons is substantially uniform across the plurality of LED coupons. [Claim 6] The apparatus according to claim 2, wherein the LED coupon includes a microLED coupon comprising a substrate and a plurality of microLEDs formed on the substrate and transferred from the substrate to the backplane. [Claim 7] The apparatus according to claim 1, wherein the backing board includes a through channel, and the vacuum source is connected to the backing board and configured to evacuate the space through the through channel. [Claim 8] The apparatus according to claim 1, wherein the vacuum source further includes a transparent vacuum bag formed around the backing board, the sealing member and the transparent panel, and the vacuum source is configured to evacuate the space by evacuating the transparent vacuum bag. [Claim 9] The apparatus according to claim 1, wherein the transparent panel includes a glass panel having a thickness of approximately 5 mm or less. [Claim 10] The apparatus according to claim 9, wherein the backing board includes a rigid backing board, and the transparent panel includes a flexible transparent panel having lower rigidity than the backing board. [Claim 11] A method for transferring light-emitting diodes (LEDs), The backplane is placed on the backing board, and the sealing member is arranged around the periphery of the backplane. The backplane is arranged to contain multiple first LED coupons, each containing multiple LEDs arranged on the growth substrate, The transparent panel is placed on the sealing member across the plurality of first LED coupons such that a space is formed between the backing board and the transparent panel, The transparent panel evacuates the space so that it presses the plurality of first LED coupons toward the backplane, Guide the laser radiation through the transparent panel so as to illuminate the plurality of first LED coupons arranged on the backplane, A method that includes this. [Claim 12] The method according to claim 11, wherein each of the plurality of first LED coupons includes a substrate and a plurality of LEDs formed on the substrate. [Claim 13] The method according to claim 12, wherein the step of guiding the laser radiation includes lifting off at least partially the LEDs from the substrate of each first LED coupon using laser lift-off, and bonding the at least partially lifted LEDs to the backplane using laser bonding. [Claim 14] The process of guiding the laser emission is followed by releasing the vacuum, The bonded LED remains bonded to the backplane, and the remaining portion of the plurality of first LED coupons is removed. On the backplane, a plurality of second LED coupons, each containing a plurality of LEDs arranged on the growth substrate, are arranged. The transparent panel is placed on the sealing member across the plurality of second LED coupons such that the space is formed between the backing board and the transparent panel, The transparent panel evacuates the space so that it presses the plurality of second LED coupons toward the backplane, Guide the laser radiation through the transparent panel so as to illuminate the plurality of second LED coupons arranged on the backplane, The method according to claim 13, further comprising: [Claim 15] The method according to claim 11, wherein the vacuuming step includes applying a pressure of 14.7 psi or less to the plurality of first LED coupons using the transparent panel, the pressure being substantially uniform throughout the transparent panel. [Claim 16] The method according to claim 11, wherein the backing board includes through channels, and the vacuuming step includes vacuuming the space through the through channels. [Claim 17] The method according to claim 11, wherein the vacuuming step includes arranging a transparent vacuum bag around the backing board, the sealing member and the transparent panel, and vacuuming the transparent vacuum bag. [Claim 18] The method according to claim 11, wherein the transparent panel includes a glass panel having a thickness of approximately 5 mm or less. [Claim 19] The backing board includes a rigid backing board, and the transparent panel includes a flexible transparent panel having lower rigidity than the backing board. The method according to claim 18, wherein the transparent panel flexes toward the backplane after the vacuum is applied, so as to press the plurality of first LED coupons toward the backplane. [Claim 20] The method according to claim 11, wherein the plurality of first LED coupons include a plurality of microLED coupons, and each of the plurality of microLED coupons includes a substrate and a plurality of microLEDs formed on the substrate.

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