Micro LED element

Abstract

To provide a micro LED element capable of reducing or avoiding cracking of a micro LED element (a die) of which one side in which an AlGaInP system light emission element structure and two electrodes of which a polarity is different are provided on the same surface is less than 100 μm.SOLUTION: In a micro LED element structure, there is a step between an upper part electrode 17 and a lower part electrode 18, and a stress concentration point is easily generated. By having a light emission element structure 8 so as to surround the circumference of the lower part electrode 18, the step of the circumference of the upper part electrode 17 and the lower part electrode 18 can be reduced. A part which has to be the stress concentration point is the light emission element structure 8, a strength degradation is hardly generated. Therefore, the frequency of cracking in a die can be reduced.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a micro LED element, and more particularly to a structure of a micro LED element that can reduce or avoid cracks. [Background technology]

[0002] Patent Document 1 discloses a technology for realizing a micro LED display, in which an LED is peeled off from a starting substrate using laser lift-off (LLO), transferred to a mounting substrate, and then transferred to a drive substrate. However, this technology is only applicable to GaN-based LEDs, and there are few technical disclosures regarding micro LED elements using AlGaInP-based LEDs.

[0003] To realize a micro LED element using the LLO process with an AlGaInP LED, it is necessary to transfer the LED to a sapphire substrate. Prior art techniques for transferring an AlGaInP LED to a sapphire substrate are disclosed in, for example, Patent Document 7.

[0004] However, AlGaInP-based LEDs are mechanically more fragile than GaN-based LEDs, and die cracking is more likely to occur during the LLO process depending on the appropriateness of the die design. There is no technical disclosure regarding how to prevent micro LED die cracking during the LLO process. In particular, there is no prior disclosure of technology regarding die design and cracking.

[0005] Patent Document 2 discloses a design in which a rectangular ohmic electrode is placed at the long edge of a chip with long and short sides. While this is a typical chip design, it does not take into consideration die cracking. The bottom and top electrodes are formed separately (in separate batches), making it difficult to achieve an absolute height match. Due to the difference in height, stress is applied to the region between the top and bottom electrodes during LLO. If the mechanical strength of the base connecting the top and bottom electrode regions is weak, it can lead to die cracking. In AlGaInP-based LEDs, the base is typically made of GaP, which has a high density of crystal dislocations and has extremely low mechanical strength.

[0006] Patent Document 3 discloses a structure in which the lower electrode is surrounded on three sides by a DH layer (light-emitting layer). In this structure, the lower electrode and upper electrode are formed separately (in separate batches), making it difficult to ensure that their heights are identical. Therefore, as in the case of Patent Document 2, the technology disclosed in Patent Document 3 is prone to die cracking. Therefore, the technology disclosed in Patent Document 3 is not a technology for increasing the mechanical strength of the die.

[0007] As a technology similar to Patent Document 3, Patent Document 4 discloses a design in which the bottom electrode has long sides and the top electrode surrounds three sides of the bottom electrode. However, one side of the bottom electrode is not surrounded, and the bottom electrode is extended in the direction that is not surrounded. Furthermore, the top is open, and the element is partially thin in the opening part. Therefore, the mechanical strength of the bottom electrode in the opening part is low. Usually, the side of the die is in the cleavage direction. <100> Therefore, the structure of Patent Document 4, in which one side is not enclosed, is not a suitable technique for avoiding die cracking.

[0008] Patent Document 5 discloses a design for multiple circular bottom electrodes surrounded by a periphery for GaN-based LEDs. In contrast, in micro LED devices, the side of a die is typically less than 100 μm, and the long side of the bottom electrode is often around 50 μm or less, with the short side being approximately half that. Applying Patent Document 5 to AlGaInP-based LEDs requires removing the AlGaInP-based light-emitting layer, which is approximately 2–3 μm thick, to provide multiple electrodes. Because the active layer is exposed during the removal of the AlGaInP-based light-emitting layer, a passivation film must be formed on the processed surface to prevent short circuits. As a result, the area available for ohmic contact is smaller than the diameter of the opening. While the smaller area of ​​the contact electrode compared to the opening area is not a major issue for larger dice (not micro LED devices), it results in poor space efficiency for tiny dice such as micro LED devices. Furthermore, prior art technology requires that the electrode portions that contact multiple bottom electrodes be located in separate spaces, which also reduces space efficiency. Although Patent Document 5 does not specify the die size, it is clear that the technology is not suitable for designing small dies such as micro LED elements.

[0009] Patent Document 6 discloses a structure in which a lower electrode is surrounded on two sides by a DH layer (light-emitting layer). The processed structure of the DH layer in Patent Document 6 is for improving brightness and interconnection, and is an example of a size of more than 100 μm on a side, and does not disclose a technology that takes into account cracks in micro LED elements with long sides of less than 100 μm.

[0010] As described above, there is no disclosure of a technique for avoiding die cracking during the LLO process in micro LED elements having an active layer made of AlGaInP-based material. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Special Publication No. 2020-521181 [Patent Document 2] Japanese Patent Application Publication No. 2019-129299 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-179590 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-124248 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-117796 [Patent Document 6] WO2010 / 074288 [Patent Document 7] Japanese Patent Publication No. 2022-013203 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above-mentioned problems, and aims to provide a micro LED element (dice) that has an AlGaInP-based light-emitting element structure and two electrodes of different polarities on the same surface, and that has a side length of less than 100 μm, and that can reduce or avoid cracking. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides a method for producing a fluororesin comprising the steps of: y Ga 1-y ) x In 1-x The present invention provides a micro LED element having a side length of less than 100 μm, the micro LED element having a light emitting element structure in which an active layer made of P (0.4≦x≦0.6, 0≦y≦0.5) is sandwiched between a first clad and a second clad, an upper electrode, and a lower electrode having a polarity different from that of the upper electrode, the light emitting element structure, the upper electrode, and the lower electrode being disposed on a first surface of the micro LED element, the upper electrode being disposed on the top surface of the light emitting element structure, and the lower electrode being disposed in a position where the light emitting element structure is not present, and the micro LED element having the light emitting element structure surrounding the periphery of the lower electrode.

[0014] In conventional micro LED element structures, there is a step between the upper and lower electrodes, which makes it easy for stress concentration points to occur, but with the micro LED element of the present invention, by having a light emitting element structure surrounding the periphery of the lower electrode, it is possible to reduce the step around the upper and lower electrodes, and the light emitting element structure is located in the area that would otherwise become a stress concentration point, making it less likely to cause a decrease in strength, thereby reducing the frequency of die cracking.

[0015] Furthermore, it is preferable that the light-emitting element structure surrounding the lower electrode either surrounds the lower electrode continuously and seamlessly or has a partial cutout, and that the boundary between the cutout and the outer edge of the light-emitting element structure is located outside the edge of the lower electrode. If the light-emitting element structure surrounds the lower electrode continuously and seamlessly, there will be no steps around the lower electrode, and strength reduction will be minimized. Even if the light-emitting element structure has a partial cutout, strength reduction can be sufficiently prevented as long as the boundary between the cutout and the outer edge of the light-emitting element structure is located outside the edge of the lower electrode. By preventing strength reduction in this way, the frequency of die cracking can be reduced.

[0016] It is also preferable that a wafer that is transparent to the emission wavelength is bonded to the second surface of the micro LED element with an adhesive or bonding material. When such a bonded wafer is subjected to an LLO (Laser Lift-Off) process, LLO has traditionally been a process that frequently results in cracks, but the present invention can reduce the frequency of die cracks.

[0017] The adhesive or bonding material is preferably BCB. Such adhesives or bonding materials can be suitably applied to micro LED elements.

[0018] The transparent wafer is preferably sapphire or quartz. Such a transparent wafer can be suitably applied to micro LED elements. [Effects of the Invention]

[0019] As described above, the micro LED element of the present invention has a light emitting element structure surrounding the lower electrode, which reduces the step between the upper and lower electrodes, and the light emitting element structure is located in the area where stress would otherwise be concentrated, making it less likely to cause a decrease in strength, thereby reducing the frequency of die cracking. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 2] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 3] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 4] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 5] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 6] 1 is a schematic cross-sectional view showing one step of a method for manufacturing a micro LED element according to a first embodiment of the present invention. FIG. [Figure 7] 1 is a schematic cross-sectional view showing an example of a method for transferring the micro LED element according to the first embodiment of the present invention. FIG. [Figure 8] 1 is a top view of a micro LED element according to a first embodiment of the present invention; [Figure 9] 1 is a cross-sectional view of a micro LED element according to a first embodiment of the present invention. [Figure 10] FIG. 2 is a top view of a micro LED device according to a second embodiment of the present invention. [Figure 11]FIG. 2 is a cross-sectional view of a micro LED element according to a second embodiment of the present invention. [Figure 12] FIG. 2 is a cross-sectional view of a micro LED element according to a second embodiment of the present invention. [Figure 13] FIG. 2 is a cross-sectional view of a micro LED element according to a second embodiment of the present invention. [Figure 14] FIG. 10 is a top view of another example of a micro LED device according to the second embodiment of the present invention. [Figure 15] FIG. 1 is a top view of a conventional micro LED device. [Figure 16] FIG. 1 is a cross-sectional view of a conventional micro LED device. DETAILED DESCRIPTION OF THE INVENTION

[0021] As mentioned above, it was found that there is no disclosure of technology to prevent die cracking during the LLO process in micro LED elements with a side length of less than 100 μm that have an AlGaInP-based light-emitting element structure and two electrodes of different polarities on the same surface.

[0022] After further investigation, the inventors found that in the above-mentioned micro LED element, by having a light-emitting element structure surrounding the lower electrode, the step between the upper and lower electrodes can be reduced, making it less likely that a decrease in strength will occur and reducing the frequency of die cracking, and thus completed the present invention.

[0023] That is, the present invention provides (Al y Ga 1-y ) x In 1-x The micro LED element has a side length of less than 100 μm and comprises a light emitting element structure in which an active layer made of P (0.4≦x≦0.6, 0≦y≦0.5) is sandwiched between a first clad and a second clad, an upper electrode, and a lower electrode having a polarity different from that of the upper electrode, wherein the light emitting element structure, the upper electrode, and the lower electrode are disposed on a first surface of the micro LED element, the upper electrode is disposed on the top surface of the light emitting element structure, and the lower electrode is disposed in a position where there is no light emitting element structure, and the light emitting element structure surrounds the periphery of the lower electrode.

[0024] The present invention will be described in detail below, but the present invention is not limited thereto.

[0025] (First embodiment) First, as shown in FIG. 1, a first conductivity type GaAs buffer layer is laminated on a first conductivity type GaAs starting substrate 1, and then a first conductivity type GaAs layer having a thickness of, for example, 0.1 μm is formed as an etch stop layer 2. x In 1-x A P(0.4≦x≦0.6) first etch stop layer, e.g., a 0.1 μm thick GaAs second etch stop layer of the first conductivity type, and further, e.g., a 1.0 μm thick (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0.6≦y≦1.0) first clad layer (first clad 3), undoped (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0≦y≦0.5) active layer 4, for example, a 1.0 μm thick second conductivity type (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0.6≦y≦1.0) second cladding layer (second cladding layer 5), for example, 0.1 μm thick second conductivity type Ga x In 1-x An epitaxial wafer 7 is prepared, which has a light-emitting device structure as an epitaxial functional layer formed by sequentially growing a P(0.5≦x≦1.0) intermediate layer and a second-conductivity type GaP window layer 6. Here, the layers from the first cladding layer 3 to the second cladding layer 5 are referred to as a double hetero (DH) structure portion (DH layer 8, or light-emitting device structure 8).

[0026] The thicknesses mentioned above are merely examples, and are merely parameters that should be changed depending on the device's operating specifications, and are not limited to the thicknesses described here. Furthermore, while the first and second cladding layers are both 1.0 μm thick, the rated current density of a micro LED device is smaller than that of a large-sized discrete LED device, and the cladding layer function is not impaired even if the thickness is thinner than this.

[0027] As will be described later, since an electrode is formed in contact with the first cladding layer 3, it is preferable that the first cladding layer 3 has a thickness of 0.6 μm or more, taking into consideration metal diffusion during ohmic contact formation. Any thickness greater than this can be selected. However, if the thickness is too thick, it will increase costs, reduce the light emission efficiency during constant current operation, or increase wafer warpage, which can lead to reduced yields. Therefore, it is preferable to design the thickness within the range of 10 μm or less.

[0028] When the second conductivity type is P-type, the effective mass of holes is large, so even if the second cladding layer 5 is approximately 0.2 μm thick, it functions as if it were 1.0 μm thick. Therefore, any thickness greater than 0.2 μm can be selected. However, if the thickness is too thick, it can increase costs, reduce light emission efficiency during constant current operation, or increase wafer warpage, resulting in reduced yield. Therefore, it is preferable to design the thickness within the range of 10 μm or less.

[0029] Furthermore, each layer may not be a single composition layer, but may have multiple composition layers within the composition ranges exemplified.

[0030] Furthermore, the level of the carrier concentration may not be uniform in each layer, but may have a plurality of levels within each layer.

[0031] The active layer 4 may be composed of a single composition, or may have a superlattice structure in which multiple barrier layers and active layers are alternately stacked, and both have similar functions, so either can be selected. Regardless of which structure is selected, the effects of the present technology are the same.

[0032] The thickness of the GaP window layer 6 must be more than 5 μm, and can be, for example, about 6 μm, but is not limited to this thickness. Any thickness can be selected as long as it is thinner than the short side length of the isolation layer described later.

[0033] 2, benzocyclobutene (BCB) is spin-coated onto the epitaxial wafer 7 as a thermosetting bonding material (hereinafter referred to as bonding material 9), and then the epitaxial wafer 7 is placed face-to-face with a sapphire wafer 10 (transparent wafer 10) to be bonded, and the two wafers are thermocompression bonded in a vacuum atmosphere. When applying BCB by spin coating, the designed film thickness can be, for example, 0.6 μm.

[0034] Furthermore, the atmosphere is not limited to a vacuum atmosphere, and any atmosphere can be used as long as it can produce an atmosphere with an oxygen concentration of 100 ppm or less. Similar effects can be obtained with a nitrogen atmosphere or an argon atmosphere.

[0035] Furthermore, the substrate to be bonded is not limited to sapphire, and any material can be selected as long as it is transparent to the LLO laser light and has flatness. In addition to sapphire, quartz can also be selected.

[0036] Furthermore, BCB is not limited to being applied in a layered form. Similar results can be obtained by patterning the photosensitive BCB into isolated islands, lines, or other shapes and then performing the bonding process.

[0037] Furthermore, the thickness of the BCB is not limited to 0.6 μm, and the same effect can be obtained even if the thickness is thinner than this.

[0038] Next, as shown in FIG. 3, the GaAs starting substrate is removed by wet etching to expose the first etch stop layer, and the first and second etch stop layers are then removed using appropriate etchants to expose the first cladding layer 3, thereby producing an epitaxial junction substrate 11 that retains only the DH layer 8 and the GaP window layer 6.

[0039] Next, as shown in FIG. 4, a SiO2 film is formed on the epitaxial layer of the epitaxial bonded substrate 11 using a P-CVD method using TEOS and O2 as raw materials, to a thickness of, for example, 1 μm. Next, a resist pattern is formed using photolithography (hereinafter referred to as photolithography), and a SiO2 pattern shape is created using a hydrofluoric acid solution. Note that this SiO2 pattern shape should have a side length of less than 100 μm. Next, using the SiO2 pattern as a hard mask, an ICP process is performed in an ICP apparatus introducing chlorine-based gas. The DH layer 8 and GaP window layer 6 are dry-etched, exposing the BCB layer (bonding material 9). The etching gas is then switched and the exposed BCB layer (bonding material 9) is further dry-etched to expose the sapphire wafer (transparent wafer 10), forming an isolation pattern consisting of the DH layer 8 and GaP window layer 6. After the element isolation pattern is formed, an SiO2 pattern is formed so that a part of the element isolation pattern is opened, and a part of the DH layer 8 is etched by the ICP method as described above to expose the second cladding layer 5, the intermediate layer, or the GaP window layer 6 and process it so that it has a bathtub-shaped processed portion 12.

[0040] Although the bathtub-shaped processed portion 12 in FIG. 4 has vertical walls, the walls are not limited to being vertical. Depending on the ICP processing conditions, it is easy to form a slope of about 10 to 15 degrees, and a sloped shape is also acceptable.

[0041] Furthermore, the bathtub-shaped processed portion 12 is not limited to a substantially rectangular shape as shown in Fig. 8, but may be an ellipse, a circle, a polygon, or other shape. By forming the bathtub-shaped processed portion 12 in this manner, the outer periphery of the element (die 13) is surrounded by the light-emitting element structure 8, and the light-emitting element structure 8 is located in the area that would become a stress concentration point, making it less likely to cause a decrease in strength. As a result, the frequency of die 13 cracking is reduced.

[0042] 5, the entire surface is covered with a SiO2 layer having a thickness of, for example, 0.1 μm by P-CVD using TEOS and O2 as raw materials to form an insulating film 14. Note that the method is not limited to P-CVD, and other film formation methods such as sputtering, photo-CVD, EB deposition, and PLD may also be used.

[0043] Next, a resist pattern is formed by photolithography so as to expose both the bottom of bathtub-shaped processed portion 12, i.e., second contact portion 15 (opening 15), and a part of first cladding layer 3, i.e., first contact portion 16 (opening 16), and openings are then formed by wet etching using a hydrofluoric acid etchant. Openings 15 and 16 are the bottom of bathtub-shaped processed portion, i.e., the second contact portion, and the first contact portion where a part of the first cladding layer is exposed.

[0044] Next, after opening processing, a first contact electrode (first ohmic electrode 17) is formed on the first contact portion 16, and a second contact electrode (second ohmic electrode 18) is formed on the second contact portion 15 (see FIG. 8). When the first conductivity type is P-type, the first contact electrode is made of a metal containing AuZn or AuBe, and the second contact electrode is made of a metal containing AuGe or AuSi. When the first conductivity type is N-type, the first contact electrode is made of a metal containing AuGe or AuSi, and the second contact electrode is made of a metal containing AuZn or AuBe. The thickness of each electrode can be approximately the same as that of the SiO2 insulating film 14, for example, 0.1 μm.

[0045] The thickness of each contact electrode is not limited to 0.1 μm. Similar effects can be achieved whether the thickness is thicker or thinner than this thickness. However, if the thickness is too thin, ohmic contact properties may be reduced. To prevent this, a thickness of 0.05 μm or greater is preferable. In this technology, it is important to make the thickness of the contact electrode and the SiO2 insulating film 14 approximately the same. Therefore, if the SiO2 insulating film 14 is too thin, the coverage rate on the processed side surface will decrease, potentially resulting in electrical leakage on the processed side surface. Therefore, a SiO2 insulating film 14 that is too thin is not desirable. Therefore, a thickness of 0.05 μm or greater is preferable. Furthermore, if the contact electrode is too thick, the effect of this technology will be reduced during the formation of the pad electrode, as described below. Therefore, the thickness of the contact electrode is preferably 1 / 5 or less of the pad electrode, as described below. Pad electrodes generally do not exceed 3 μm in thickness. Therefore, the contact electrode is preferably 0.6 μm or less.

[0046] Next, as shown in FIG. 6, after the contact electrodes are formed, pad electrodes 19 and 20 are formed so as to contact at least a portion of each contact electrode and electrically separate the electrodes. The thickness of the pad electrodes is preferably at least five times the thickness of the contact electrodes, particularly the contact electrodes in contact with the first cladding layer 3. The pad electrodes can be formed, for example, by vacuum deposition. Furthermore, by making the pad electrodes at least five times thicker than the contact electrodes, i.e., at least 0.25 μm thick, the unevenness (height difference) between the SiO2 insulating film and the contact electrode surfaces, which are made approximately uniform, is reduced, thereby reducing or avoiding stress concentration during the LLO process. Note that FIG. 8 shows a top view of the pad electrodes 19 and 20 after their formation, illustrating their relationship to the first contact electrode (first ohmic electrode 17) and the second contact electrode (second ohmic electrode 18). Also, FIG. 9 shows a cross-sectional view of line AA′ in FIG. 8.

[0047] Next, as shown in Figure 7, the micro LED element pattern is pressed against a quartz substrate (transfer substrate 22) that has a silicone convex pattern (silicone layer 21) similar to the micro LED element pattern and pitch, and an excimer laser is irradiated from the sapphire substrate side to sublimate the BCB. As the BCB sublimes, an LLO process is performed to separate the micro LED elements from the sapphire, and they are then transferred from the sapphire substrate to a quartz substrate.

[0048] As described above, the micro LED element in this embodiment is y Ga 1-y ) x In 1-x In a micro LED element having a side length of less than 100 μm, the micro LED element has a light-emitting element structure 8 in which an active layer 4 made of P (0.4≦x≦0.6, 0≦y≦0.5) is sandwiched between a first clad 3 and a second clad 5, an upper electrode 17 (first contact electrode, first ohmic electrode), and a lower electrode 18 (second contact electrode, second ohmic electrode) having a polarity different from that of the upper electrode, the light-emitting element structure 8, the upper electrode 17, and the lower electrode 18 are arranged on a first surface of the micro LED element, the upper electrode 17 is arranged on the top surface of the light-emitting element structure 8, and the lower electrode 18 is arranged in a position where the light-emitting element structure 8 is not present, and the light-emitting element structure 8 surrounds the periphery of the lower electrode 18.

[0049] In conventional micro LED element structures, there is a step between the upper electrode and the lower electrode, which is likely to create a stress concentration point, but in the micro LED element of the present invention, as is clear from the configurations in Figures 8 and 9, the light emitting element structure 8 is located in the area that would otherwise become a stress concentration point, making it less likely to cause a decrease in strength. This reduces the frequency of die cracking.

[0050] In the first embodiment, the light emitting element structure 8 surrounding the periphery of the lower electrode 18 surrounds the periphery of the lower electrode 18 continuously and seamlessly. If the light-emitting element structure 8 surrounds the lower electrode 18 continuously and seamlessly, there will be no steps in the area surrounding the upper electrode 17 and the lower electrode 18, which will be least likely to cause a decrease in strength. Preventing a decrease in strength in this way can reduce the frequency of die cracking.

[0051] Furthermore, a wafer (sapphire wafer 10) that is transparent to the emission wavelength and the laser light for LLO transfer is bonded to the second surface of the micro LED element with BCB (bonding material 9) that is transparent to the emission wavelength and absorbs the laser light for LLO transfer. When performing the LLO (laser lift-off) process on such bonded wafers, LLO has traditionally been a process that frequently results in cracking, but the present invention can reduce the frequency of die cracking.

[0052] Furthermore, although the bonding material 9 is BCB, it is not limited to BCB, and a similar adhesive or bonding material may be used.

[0053] Furthermore, although the transparent wafer 10 is made of sapphire, it is not limited to sapphire and may be made of quartz, or any material may be selected as long as it ensures transparency to the LLO laser light and flatness.

[0054] (Second embodiment) In the second embodiment, the process of processing to have a bathtub-shaped processed portion where a second conductivity type layer such as a second cladding layer, a GaInP intermediate layer, or a GaP window layer is exposed is the same as in the first embodiment, but it differs from the first embodiment in that a notch is provided in the corner direction of the element isolation pattern.

[0055] As shown in Fig. 10, there are two notches 23 at the corners, and as shown in Fig. 14, there is one. Fig. 11 shows a cross-sectional view taken along line AA' in Fig. 10. The cross-sectional view in Fig. 14 is omitted because it is the same as Fig. 11.

[0056] In FIG. 10, the notch 23 at the corner and the outer boundary 24 of the light-emitting element structure 8 are arranged so as not to be inside the edge 25 of the lower electrode (the edge of the second contact electrode (second ohmic electrode 18)). In other words, the length D in FIG. 10 is set to D≧0. With this structure, the light-emitting element structure 8 is located in a portion that would become a stress concentration point, preventing stress from being applied to the lower electrode (second contact electrode (second ohmic electrode 18)), which is a thin portion of the element (die), and making it less likely to cause a decrease in strength. As a result, the frequency of die cracking is reduced.

[0057] 12 shows a cross-sectional view taken along line BB' in FIG. 10, and FIG. 13 shows a cross-sectional view taken along line CC' in FIG. 10. It can be seen that by arranging the light-emitting element structures 8 at both ends in FIG. 12 and at the center in FIG. 13, stress is less likely to be applied to the lower electrode (second contact electrode (second ohmic electrode 18)).

[0058] As described above, in the present embodiment, the light emitting element structure 8 surrounding the periphery of the lower electrode (second contact electrode (second ohmic electrode 18)) has a partial cutout portion 23, and the outer boundary portion 24 between the cutout portion 23 and the light emitting element structure 8 is located outside the end portion 25 of the lower electrode (second contact electrode (second ohmic electrode 18). In this way, even if the light-emitting element structure 8 has a partial cutout portion 23, as long as the boundary portion 24 between the cutout portion 23 and the outer surface of the light-emitting element structure 8 is positioned outside the end portion 25 of the lower electrode (second contact electrode (second ohmic electrode 18)), a decrease in strength can be sufficiently prevented. Preventing a decrease in strength in this way can reduce the frequency of die cracking. [Example]

[0059] The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to these examples.

[0060] Example 1 A first conductivity type GaAs buffer layer is laminated on a first conductivity type GaAs starting substrate, and then a 0.1 μm thick first conductivity type Ga x In 1-x P(0.4≦x≦0.6) first etch stop layer, a 0.1 μm thick GaAs second etch stop layer of the first conductivity type, and a 1.0 μm thick (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0.6≦y≦1.0) first cladding layer, undoped (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0≦y≦0.5) active layer, 1.0 μm thick second conductivity type (Al y Ga 1-y ) x In 1-x P(0.4≦x≦0.6, 0.6≦y≦1.0) second cladding layer, 0.1 μm thick second conductivity type Ga x In 1-x An epitaxial wafer having a light emitting device structure was prepared by successively growing a P(0.5≦x≦1.0) intermediate layer and a second conductivity type GaP window layer having a thickness of 6 μm as an epitaxial functional layer.

[0061] Next, benzocyclobutene (BCB) was spin-coated onto the epitaxial wafer as a thermosetting bonding material, and then placed face-to-face on a sapphire wafer, which was the wafer to be bonded, and then thermocompression bonded under a vacuum atmosphere. The designed film thickness for the BCB spin-coating was 0.6 μm.

[0062] Next, the GaAs starting substrate was removed by wet etching to expose the first etch-stop layer, and the first and second etch-stop layers were then removed using appropriate etchants to expose the first cladding layer, producing an epitaxial junction substrate that retains only the DH layer and window layer.

[0063] Next, a 1 μm-thick SiO2 film was formed on the EP bonded substrate using P-CVD with TEOS and O2 as raw materials. A resist pattern was formed using photolithography, and the SiO2 pattern was fabricated using a hydrofluoric acid solution. The SiO2 pattern was 35 × 55 μm square. Using the SiO2 pattern as a hard mask, an ICP process was performed using an ICP system with chlorine-based gas introduced. The DH layer and GaP layer were dry-etched, exposing the BCB layer. The BCB layer was then dry-etched using CF-based gas, forming an isolation pattern consisting of the DH layer and GaP layer. After the isolation pattern was formed, an SiO2 pattern was formed to open a portion of the isolation pattern. A portion of the DH layer was etched using the ICP process as described above, exposing the second cladding layer, intermediate layer, or GaP layer, resulting in a bathtub-shaped processing area.

[0064] After forming the bathtub-shaped processed portion, the entire surface was covered with a 0.1 μm thick SiO2 layer by the P-CVD method using TEOS and O2 as raw materials, forming an insulating film.

[0065] A resist pattern was formed by photolithography so that the bottom of the bathtub-shaped processed portion, i.e., the second contact portion, and both a part of the first cladding layer and the first contact portion were exposed, and an opening was then formed by wet etching using a hydrofluoric acid etchant. The opening is the first contact portion where the bottom of the bathtub-shaped processed portion, i.e., the second contact portion, and a part of the first cladding layer are exposed.

[0066] After the opening process, a first contact electrode was formed in the first contact portion, and a second contact electrode was formed in the second contact portion. The thickness of each electrode was 0.1 μm, which was approximately the same as that of the SiO2 insulating film.

[0067] After the contact electrodes were formed, pad electrodes were formed so as to be in contact with at least a portion of each contact electrode and to electrically separate the electrodes.

[0068] The micro-LED element pattern was pressed against a quartz substrate having a silicone convex pattern similar to the micro-LED element pattern and pitch, and an excimer laser was irradiated from the sapphire substrate side to sublimate the BCB, thereby performing the LLO process to separate the micro-LED elements from the sapphire, and the micro-LED elements were transferred from the sapphire substrate to the quartz substrate.

[0069] Example 2 In Example 2, a micro LED element was manufactured under the same conditions as in Example 1, except that two cutouts were provided symmetrically at the corners of the element isolation pattern as shown in Figure 10. The length D of the cutouts at the corners was set to 2 μm as shown in Figure 10.

[0070] Example 3 In Example 3, a micro LED element was manufactured under the same conditions as in Example 2, except that the length D was set to 0 μm.

[0071] (Comparative Example 1) In Comparative Example 1, the second cladding layer was processed to expose the second conductivity type layer, as in Example 1. However, instead of a bathtub-shaped process, the second conductivity type layer was exposed all around the second contact electrode, as shown in Figures 15 and 16. A micro LED element was manufactured under the same conditions as in Example 1.

[0072] (Comparative Example 2) In Comparative Example 2, a micro LED element was manufactured under the same conditions as in Example 2, except that the length D was set to −2 μm.

[0073] (Cracks in Micro LED elements in Examples and Comparative Examples) Table 1 shows the cracking rates (%) of micro LED elements during the LLO process in Examples 1, 2, and 3 and Comparative Examples 1 and 2. As shown in Table 1, Example 1, which has a light-emitting element structure that continuously and seamlessly surrounds the lower electrode, and Examples 2 and 3, which have light-emitting element structures with cutouts at the corners and where the boundary between the cutouts and the light-emitting element structure is located outside the edge of the lower electrode (D≧0), have an average cracking rate of 0%. This is a significant improvement over the average cracking rates (30% and 27%) of Comparative Example 1, which has a conventional structure with no light-emitting element structure around the lower electrode, and Comparative Example 2, which has a light-emitting element structure with cutouts at the corners but where the boundary between the cutouts and the light-emitting element structure is located inside the edge of the lower electrode (D<0). [Table 1]

[0074] The present invention is not limited to the above-described examples, and any other configurations that are substantially identical to the technical ideas described in the claims of the present invention and that provide similar effects are included within the technical scope of the present invention. [Explanation of symbols]

[0075] 3...First clad layer (first clad) 4…Active layer 5...Second clad layer (second clad) 7...Epitaxial wafer 8...DH layer (light-emitting element structure) 9...Thermosetting joining material (joint material) 10...Sapphire wafer (transparent wafer) 11...Epitaxial junction substrate 12...Bathtub-shaped processed section 13...Element (dice) 14...Insulating film 15...Second contact part (opening) 16...First contact part (opening) 17...Upper electrode (first contact electrode, first ohmic electrode) 18... Lower electrode (second contact electrode, second ohmic electrode) 19, 20...Pad electrodes 22...Quartz substrate (transfer substrate) 23...Notch 24...Outer boundary 25...Edge of bottom electrode D...length.

Claims

1. (Al ｙ Ga １－ｙ ) ｘ In １－ｘ a light-emitting device structure in which an active layer made of P (0.4≦x≦0.6, 0≦y≦0.5) is sandwiched between a first clad and a second clad; an upper electrode; a lower electrode having a polarity different from that of the upper electrode; In a micro LED element having a side length of less than 100 μm, the light emitting device structure, the upper electrode, and the lower electrode are disposed on a first surface of the micro LED device; the upper electrode is disposed on an upper surface of the light-emitting element structure; the lower electrode is disposed at a position where the light emitting element structure is not present, A micro LED element having the light emitting element structure surrounding the lower electrode.

2. The light-emitting element structure surrounding the lower electrode is either continuous and seamless around the lower electrode or has a cutout portion, and the outer boundary between the cutout portion and the light-emitting element structure is located outside the edge of the lower electrode.

3. 3. The micro LED element according to claim 2, wherein a wafer transparent to the emission wavelength is bonded to the second surface of the micro LED element with an adhesive or a bonding material.

4. 4. The micro LED element according to claim 3, wherein the adhesive or bonding material is BCB.

5. 5. The micro LED device according to claim 3, wherein the transparent wafer is made of sapphire or quartz.

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