Laser-induced forward transfer method and receiving substrate

Abstract

The present invention is a laser-induced forward transfer method in which a microstructure formed on a supply substrate is transferred to a reception substrate by laser lift-off, the surface of the microstructure facing the reception substrate having a recess in which the outer region of the surface is higher than the inner region thereof, the surface of the receiving substrate on which the microstructure is transferred has a resin layer, and laser lift-off is performed in a state in which the resin layer is in contact with or close to the bottom surface of the recess of the microstructure. As a result, it is possible to provide a laser-induced forward transfer method in which a microstructure having a recessed portion can be transferred to a receiving substrate by laser lift-off without damaging the microstructure.

Description

Technical Field

[0001] The present invention relates to a laser-induced forward transfer (LIFT) method for transferring relatively easily damaged microstructures such as mini light-emitting diodes (hereinafter also referred to as mini LEDs) or microscopic light-emitting diodes with concave-convex parts such as solder particles (hereinafter also referred to as micro LEDs) from a supply substrate to a receiving substrate without causing damage by laser lift-off (hereinafter also referred to as LLO), and a receiving substrate that can receive the microstructure by laser lift-off without causing damage to the microstructure. Background Art

[0002] In recent years, as semiconductor elements have become smaller, microstructure transfer technology using adhesive resins has attracted attention as a means of assembling electrical / electronic application products using semiconductor elements. In particular, the development of technology to manufacture LED displays for signage, televisions, medical, automotive, and smartphones by transferring tens of thousands of mini light emitting diodes (LEDs) (LED elements with short sides of 100 μm to hundreds of μm) or micro LEDs (LED elements with short sides of 100 μm or less, and even less than 50 μm) at a time has become active.

[0003] Conventionally, a method of transferring a microstructure such as a micro LED using a silicone adhesive hardened material as a donor substrate or a transfer stamp material, and a method of mounting the microstructure on a circuit board have been developed (Patent Document 1).

[0004] On the other hand, semiconductor elements generally have electrodes formed at both ends of a mesa region, and thus have a shape having minute irregularities. Fig. 9 Schematically shows a supply substrate including an example of a general semiconductor element. Fig. 9 In the supply substrate 20 shown, the semiconductor element 100 is bonded to the sapphire wafer 21 via a benzocyclobutene (BCB) adhesive layer 22. The surface 100A of the semiconductor element 100 opposite to the surface in contact with the BCB adhesive layer 22 has a recess 110 such that the outer region 102 of the surface 100A is higher than the inner region 101.

[0005] Therefore, for mini LED components that are larger than micro LED components, the problem of component cracking is observed during the laser lift-off (LLO) process when the components are transferred from the supply substrate to the receiving substrate. In addition, the constituent element group of red LED components is different from that of blue or green LED components, so they are relatively fragile and easy to crack. Therefore, cracking also occurs in the LLO process.

[0006] In addition, it is known that there is a method of using a conductive adhesive when electrically connecting a microstructure such as a transferred LED element to a circuit substrate. However, in this connection method, it is difficult to follow the further miniaturization of semiconductor elements in terms of the requirement of high position accuracy when carrying a microstructure and the limitation of the miniaturization of conductive fillers. In addition, since microstructures such as semiconductor elements generate heat or emit light, the adhesive resin component deteriorates and it is difficult to obtain long-term reliability. In this context, the solder process is currently attracting much attention. It is a method of using a semiconductor element with a bump in which solder particles (hereinafter also referred to as bumps) are pre-mounted on the electrodes of the element, and it is a technology of melting the solder particles by reflowing after being mounted on the circuit substrate to be installed on the circuit. By adjusting the amount of solder, the flow of miniaturization can be coped with, and a self-alignment effect of positional offset correction can be obtained when the solder particles are melted, thereby having a margin for the mounting position accuracy. In addition, the molten solder itself acts as an adhesive, so it is relatively easy to suppress degradation over time.

[0007] However, since the bump portion has a convex shape due to the formation of the bump, when transferring such a device, the convex device surface needs to be received by the resin layer of the donor substrate, which may cause the device to break due to the impact of LLO.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2021-34610 Summary of the invention

[0011] Problems to be solved by the invention

[0012] A method is required for transferring microstructures having step differences such as bumps or fragile and easily damaged microstructures such as red LEDs from a supply substrate to a receiving substrate by LLO without damaging the microstructures, in addition to the microstructures such as blue LEDs and green LEDs studied in the past.

[0013] The present invention is made to solve the above-mentioned problem, and its purpose is to provide a laser induced forward transfer method that can transfer a microstructure with a recessed portion to a receiving substrate by laser peeling without damaging the microstructure, and a receiving substrate that can receive the microstructure by laser peeling without damaging the microstructure.

[0014] Technical means of solving problems

[0015] In order to solve the above-mentioned problem, the present invention provides a laser induced forward transfer method, in which a microstructure formed on a supply substrate is transferred to a receiving substrate by laser lift-off. In the laser induced forward transfer method,

[0016] The surface of the microstructure facing the receiving substrate has a concave portion such that the outer area of ​​the surface is higher than the inner area.

[0017] The surface of the receiving substrate on which the microstructure is transferred has a resin layer,

[0018] Laser lift-off is performed in a state where the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0019] If this is the laser induced forward transfer method, laser stripping is performed while the resin layer is in contact with or close to the bottom surface of the concave portion of the microstructure, and the impact applied to the microstructure during laser stripping is dispersed and absorbed into the resin layer to be mitigated. Thus, the microstructure can be transferred from the supply substrate to the receiving substrate without damaging it. Therefore, if the laser induced forward transfer method of the present invention is used, even for microstructures that are fragile and easily broken, such as red LED elements, or LED elements with bumps and other concave and convex surfaces, which are easily damaged, they can be transferred by laser stripping without damaging them.

[0020] The outer region of the microstructure may have an electrode or a bump.

[0021] According to the laser induced forward transfer method of the present invention, even a microstructure having, for example, an electrode or a bump in the outer region can be transferred without damaging the microstructure.

[0022] The inner region of the microstructure may be a mesa region.

[0023] The inner region of the microstructure is not particularly limited, and may be a mesa region.

[0024] For example, the microstructure may be one or more LED elements selected from a red LED, a blue LED, or a green LED.

[0025] The transfer target in the present invention, that is, the microstructure, is not limited as long as it has a recessed portion, and may be, for example, an LED element such as a red LED, a blue LED, or a green LED.

[0026] The resin layer may be prepared by forming at least one curing reaction selected from the group consisting of a radical curing reaction, a cationic curing reaction, an anionic curing reaction, an addition curing reaction, and a condensation curing reaction.

[0027] The resin layer may be formed, for example, by at least one curing reaction selected from the group consisting of a free radical curing reaction, a cationic curing reaction, an anionic curing reaction, an addition curing reaction, and a condensation curing reaction.

[0028] For example, the supply substrate and the receiving substrate may be attached to each other and pressurized to deform the resin layer so that the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0029] For example, by applying pressure, the resin layer can be brought into a state of being in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0030] As the resin layer, it is preferable to use a resin layer having flexibility or fluidity.

[0031] When such a resin layer is used, it is easy to be in contact with or close to the bottom surface of the concave portion of the microstructure.

[0032] In such a case, it is more preferable to use a resin layer having a storage elastic modulus at 25° C. of 1 kPa to 300 kPa as the resin layer.

[0033] When such a resin layer is used, it is easier to achieve a state of being in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0034] In addition, the present invention provides a receiving substrate for transferring and receiving a microstructure formed on a supply substrate by laser lift-off, wherein the receiving substrate

[0035] A resin layer is provided on the surface on which the microstructure is transferred,

[0036] The surface of the microstructure facing the receiving substrate has a concave portion in a manner such that the outer region of the surface is higher than the inner region.

[0037] The resin layer is deformed by attaching and pressurizing the supply substrate and the receiving substrate.

[0038] If it is such a receiving substrate, the resin layer is deformed by bonding the supply substrate and the receiving substrate and pressurizing them, so that the impact applied to the microstructure during laser stripping is dispersed and absorbed into the resin layer and mitigated. As a result, the microstructure can be received from the supply substrate without damaging the microstructure. Therefore, if it is the receiving substrate of the present invention, even if the microstructure is a fragile and easily broken red LED element, or an LED element with a bump or other concave-convex surface, which is easily damaged, it can be received by transfer based on laser stripping without damaging it.

[0039] The resin layer is preferably deformed by an amount sufficient to be in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0040] If the receiving substrate has such a resin layer, it is possible to more reliably prevent the microstructure from being damaged.

[0041] In this case, the resin layer is more preferably a resin layer having a storage elastic modulus at 25° C. of 1 kPa to 300 kPa.

[0042] If the receiving substrate has such a resin layer, it is possible to more reliably prevent the microstructure from being damaged.

[0043] Effects of the Invention

[0044] As described above, according to the laser-induced forward transfer method of the present invention, a microstructure having a concave portion can be transferred to a receiving substrate by laser lift-off without damaging it. This method can be particularly applied to the manufacturing process of LED displays for use in signage, TV, medical, automotive, smart phones, etc.

[0045] In addition, according to the receiving substrate of the present invention, a microstructure having a recessed portion can be received by transfer by laser lift-off without damaging the microstructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] [ Figure 1 ] is a schematic diagram showing an example of a receiving substrate of the present invention.

[0047] [ Figure 2 ] is a schematic diagram of another side of an example of a receiving substrate of the present invention.

[0048] [ Figure 3 ] is a schematic diagram showing an example of the laser induced forward transfer method of the present invention.

[0049] [ Figure 4 ] is a schematic diagram showing an example of a supply substrate that can be used in the laser induced forward transfer method of the present invention.

[0050] [ Figure 5 ] is a schematic diagram showing another example of a supply substrate that can be used in the laser induced forward transfer method of the present invention.

[0051] [ Figure 6 ] is a schematic diagram showing a process of one embodiment of the laser induced forward transfer method of the present invention.

[0052] [ Figure 7 ] is a schematic diagram showing another process of one embodiment of the laser induced forward transfer method of the present invention.

[0053] [ Figure 8 ] is a schematic diagram showing a laser-induced forward transfer method of a comparative example.

[0054] [ Fig. 9 ] is a schematic diagram showing an example of a supply substrate including a general semiconductor element. DETAILED DESCRIPTION

[0055] As described above, it is required to develop a laser induced forward transfer method that can transfer a microstructure having a recessed portion to a receiving substrate by laser lift-off without damaging the microstructure, and a receiving substrate that can receive the microstructure by laser lift-off without damaging the microstructure.

[0056] The inventors of the present invention have repeatedly conducted diligent research on the above-mentioned subject and found that by providing a resin layer on the surface of the receiving substrate on which the microstructure is to be transferred and performing laser peeling while the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure, the microstructure with the recessed portion can be transferred to the receiving substrate without being damaged, thereby completing the present invention.

[0057] That is, the present invention is a laser induced forward transfer method, in which a microstructure formed on a supply substrate is transferred to a receiving substrate by laser lift-off, wherein:

[0058] The surface of the microstructure facing the receiving substrate has a concave portion such that the outer area of ​​the surface is higher than the inner area.

[0059] The surface of the receiving substrate on which the microstructure is transferred has a resin layer,

[0060] Laser lift-off is performed in a state where the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0061] In addition, the present invention is a receiving substrate for transferring and receiving a microstructure formed on a supply substrate by laser lift-off, wherein the receiving substrate

[0062] A resin layer is provided on the surface on which the microstructure is transferred,

[0063] The surface of the microstructure facing the receiving substrate has a concave portion in a manner such that the outer region of the surface is higher than the inner region.

[0064] The resin layer is deformed by attaching and pressurizing the substrate and the receiving substrate.

[0065] Hereinafter, the present invention will be described in detail, but the present invention is not limited to these descriptions.

[0066] [Receiving substrate]

[0067] Figure 1 An example of a receiving substrate of the present invention is schematically shown in FIG. However, the receiving substrate of the present invention is not limited to Figure 1 Example shown.

[0068] Figure 1 The receiving substrate 10 shown includes a resin layer 12 on a supporting substrate 11. A surface 10A of the receiving substrate 10 on which the resin layer 12 is provided is a surface on which a microstructure described below is transferred.

[0069] like Figure 2 As shown, the resin layer 12 is deformed by attaching and pressing the supply substrate 20 and the receiving substrate 10 .

[0070] also, Figure 2 The supply substrate 20 shown is similar to the reference Fig. 9 The supply substrate 20 is the same as that described above. Specifically, the supply substrate 20 includes a support substrate 21 and a microstructure 100 supported by the support substrate 21. The surface 100A of the microstructure 100 opposite to the surface facing the support substrate 21 has a concave portion 110 such that the outer region 102 of the surface 100A is higher than the inner region 101. The shape of the supply substrate 20 will be described later.

[0071] If this is the receiving substrate 10, the resin layer 12 is deformed by attaching the supply substrate 20 and the receiving substrate 10 and applying pressure, so that the impact applied to the microstructure 100 during laser stripping is dispersed and absorbed into the resin layer 12 to be mitigated. As a result, the microstructure 100 can be received from the supply substrate 20 without damaging the microstructure 100. Therefore, if it is the receiving substrate 10 of the present invention, even if the microstructure 100 is a fragile and easily broken red LED element, or an LED element with a bump or other concave-convex surface, which is a microstructure that is easily damaged, it can be received by transfer based on laser stripping without damaging it.

[0072] For example Figure 2As shown in (B), the resin layer 12 of the receiving substrate 10 is preferably deformed to an amount sufficient to be in contact with or close to the bottom surface 110A of the recess 110 of the microstructure 100 .

[0073] If the receiving substrate 10 includes such a resin layer 12 , it is possible to more reliably prevent the microstructure 100 from being damaged.

[0074] The receiving substrate 10 can be formed, for example, by applying a precursor of the resin layer 12 (eg, a silicone-based gel composition) on the supporting substrate 11 and curing the precursor.

[0075] As the supporting substrate 11 used in the receiving substrate 10, for example, a synthetic quartz glass substrate, float glass, etc. can be listed. In particular, from the viewpoint of flatness and the viewpoint of transferring the microstructure 100 having a bump or other concave-convex portion (concave portion 110), in order to confirm whether the resin layer 12 is in contact with or close to the bottom surface 110A of the concave portion 110 after the bonding process described later, the supporting substrate 11 is required to have transparency. In this respect, a synthetic quartz glass substrate is preferably used.

[0076] In addition, the size of the support substrate 11 used in the receiving substrate 10 is preferably the same as or larger than the diameter of the supply substrate 20 used. Specifically, when a sapphire substrate with an outer diameter of 10.16 cm (4 inches) is used as the supply substrate 20, a receiving substrate 10 with an outer diameter of 10.16 cm to 20.32 cm (4 inches to 8 inches) can be used.

[0077] In order to reliably transfer part or all of the multiple microstructures 100 from the supply substrate 20 to the receiving substrate 10, in the bonding of the multiple microstructures 100 formed on one surface of the supply substrate 20 and the receiving substrate 10 provided with a resin layer 12 on the supporting substrate 11, it is preferred that each microstructure 100 is temporarily and identically fixed to the resin layer 12 of the receiving substrate 10.

[0078] In order to temporarily fix the microstructure 100 with good accuracy, the support substrate 11 used in the receiving substrate 10 is preferably: for an area of ​​6.01 mm×6.01 mm, the spatial frequency is 1 mm as measured by a white interferometer with a pixel number of 1240×1240. -1 The power spectral density above is 10 12 nm 4 In particular, when the microstructure 100 is a micro LED, considering the distance between the microstructures 100, it is preferred that the spatial frequency 10 mm is measured by a white interferometer with a pixel number of 1240×1240 for an area of ​​6.01 mm×6.01 mm. -1 Above and 50mm -1The power spectral density of the following is 10 9 nm 4 the following.

[0079] In addition, the receiving substrate 10 preferably has a small thickness deviation in order to temporarily fix the microstructure 100 with good precision. For example, the thickness deviation (total thickness variation (TTV)) measured by a wavelength conversion Fizeau flatness tester of Mizojiri Optical Industry Co., Ltd. is preferably 2 μm or less, more preferably 1 μm or less, and further preferably 0.5 μm or less.

[0080] The resin layer 12 is preferably a flexible or fluid resin layer, and more preferably a resin layer having a storage elastic modulus of 1 kPa to 300 kPa at 25° C. Such a resin layer 12 may be, for example, a silicone gel layer, but is not limited thereto.

[0081] The silicone gel layer is provided, for example, by curing a silicone gel composition, and the curing form is preferably at least one curing reaction selected from addition curing reaction, free radical curing reaction such as photo radical polymerization reaction or thermal radical polymerization reaction, cation curing reaction, anion curing reaction, and condensation curing reaction, wherein addition curing reaction, photo radical polymerization reaction, and thermal radical polymerization reaction are preferably used in terms of ease of resin design or ease of curing. The silicone gel layer may also be, for example, a curable resin layer that can be further cured, in which case the silicone gel composition may be a two-stage curing silicone gel composition.

[0082] The silicone gel composition can be applied to the support substrate 11, for example, by the following method: the silicone gel composition is applied to the support substrate 11 by spin coating in a manner such that the thickness is preferably 1 μm to 500 μm, more preferably 5 μm to 200 μm, and further preferably 10 μm to 10 μm. The thickness can be arbitrarily determined in consideration of the shape or thickness of the transferred microstructure 100. At this time, the entire surface of the support substrate 11 can be coated, and the excess silicone gel composition can be washed away by edge washing or the like for reasons such as ensuring operability, so that the support substrate 11 is exposed at a portion of the periphery. In addition, it can be coated in any thickness and shape by slit coating or screen printing.

[0083] In order to improve the adhesion or tackiness at the interface between the support substrate 11 and the resin layer 12 , the support substrate 11 may be primed in advance.

[0084] After the coating step, for example, when curing is performed by addition curing reaction, it is preferably placed in a heating furnace at 20°C to 200°C for 5 minutes to 90 minutes, or when curing is performed by photo-radical polymerization reaction, it is preferably heated at 50 mW / cm2 in a nitrogen atmosphere with 365 nm light as an index. 2 ~3000mW / cm 2 The illumination is 100mJ / cm 2 ~20000mJ / cm 2 By irradiating the composition with ultraviolet rays or the like with a cumulative light amount equal to or greater than 10%, the resin layer 12 can be formed under curing conditions suitable for the silicone composition used.

[0085] [Laser-induced forward transfer method]

[0086] Next, refer to Figure 3 , and refer again Figure 1 and Figure 2 The laser-induced forward transfer method of the present invention will be described below. However, the present invention is not limited to the illustrated embodiment.

[0087] Figure 3 An example of the laser induced forward transfer method of the present invention is schematically shown in FIG.

[0088] The laser induced forward transfer method of the present invention is a laser induced forward transfer method for transferring the microstructure 100 formed on the supply substrate 20 to the receiving substrate 10 by laser lift-off.

[0089] and Figure 2 As shown in FIG. 1 , the surface 100A of the microstructure 100 formed on the supply substrate 20 facing the receiving substrate 10 has a concave portion 110 such that the outer region 102 of the surface 100A is higher than the inner region 101. Figure 1 As shown, the surface 10A of the receiving substrate 10 on which the microstructure is transferred has a resin layer 12 .

[0090] In the laser induced forward transfer method of the present invention, Figure 3 As shown, the laser light L is irradiated to the back surface of the support substrate 21 of the supply substrate 20 to perform laser lift-off while the resin layer 12 is in contact with or close to the bottom surface 110A of the recess 110 of the microstructure 100. The laser lift-off will be described in detail later.

[0091] The state in which the resin layer 12 is in contact with the bottom surface 110A of the concave portion 110 of the microstructure 100 is not limited to the state in which the bottom surface 110A is in contact with the resin layer 12 in its entirety. Figure 3As shown, a portion of the bottom surface 110A may be in contact with the resin layer 12. When the resin layer 12 is in contact with the bottom surface 110A of the recess 110 of the microstructure 100, the interval (shortest distance) between the bottom surface 110A of the recess 110 of the microstructure 100 and the resin layer 12 is 0 μm.

[0092] The state in which the resin layer 12 is close to the bottom surface 110A of the recess 110 of the microstructure 100 refers to the presence of a small gap between the bottom surface 110A and the resin layer 12 that can mitigate the impact applied to the microstructure 100 during laser peeling. Specifically, the so-called close state may refer to, for example, a state in which the gap between the bottom surface 110A and the resin layer 12 exceeds 0 μm and is less than 1 μm, preferably a state in which the gap between the bottom surface 110A and the resin layer 12 exceeds 0 μm and is less than 0.5 μm. On the other hand, when the depth of the recess 110 of the microstructure 100 is set to "1", it may refer to a state in which the gap between the bottom surface 110A and the resin layer 12 exceeds "0" and is less than "0.1", preferably a state in which the gap between the bottom surface 110A and the resin layer 12 exceeds "0" and is less than "0.05".

[0093] The state in which the resin layer 12 is in contact with or close to the bottom surface 110A of the recess 110 of the microstructure 100 may also be referred to as a "substantially contacting state". The substantially contacting state may refer to a state in which the interval between the bottom surface 110A and the resin layer 12 is greater than 0 μm and less than 1 μm. On the other hand, when the depth of the recess 110 of the microstructure 100 is set to "1", it may also refer to a state in which the interval between the bottom surface 110A and the resin layer 12 is greater than "0" and less than "0.1".

[0094] In the case of such a laser-induced forward transfer method, laser lift-off is performed while the resin layer 12 is in contact with or close to the bottom surface 110A of the recess 110 of the microstructure 100, and the impact applied to the microstructure 100 during laser lift-off is dispersed and absorbed into the resin layer 12 to be mitigated. Thus, the microstructure 100 can be transferred from the supply substrate 20 to the receiving substrate 10 without damaging it. Therefore, in the case of the laser-induced forward transfer method of the present invention, even if the microstructure 100 is a fragile and easily broken red LED element, or an LED element with a bump or other concave-convex surface, which is a microstructure that is easily damaged, it can be transferred by laser lift-off without damaging it.

[0095] Hereinafter, a receiving substrate and a supply substrate used in the laser induced forward transfer method of the present invention will be described.

[0096] [Receiving substrate]

[0097] As the receiving substrate 10 , for example, the receiving substrate 10 of the present invention described above can be used.

[0098] When preparing the receiving substrate 10 , for example, the resin layer 12 may be formed by at least one curing reaction selected from the group consisting of a radical curing reaction, a cationic curing reaction, an anionic curing reaction, an addition curing reaction, and a condensation curing reaction.

[0099] As the resin layer 12 , it is preferable to use a resin layer having flexibility or fluidity, and it is more preferable to use a resin layer having a storage elastic modulus at 25° C. of 1 kPa to 300 kPa.

[0100] For other details of the receiving substrate 10 , please refer to the previous description of the receiving substrate 10 of the present invention.

[0101] [Supply substrate and microstructure]

[0102] As reference Figure 2 As described above, the supply substrate 20 used in the laser induced forward transfer method of the present invention has a microstructure 100 formed thereon. The surface 100A of the microstructure 100 facing the receiving substrate 10 has a recess 110 in which the outer region 102 of the surface 100A is higher than the inner region 101 .

[0103] For example, the substrate 20 is provided as Figure 4 As shown, a plurality of microstructures 100 are formed on one surface of the support substrate 21, and the microstructure 100 may be a device body 120 having electrodes 130 formed thereon. The region corresponding to the electrode 130 is the outer region 102, which is higher than the inner region 101. Thus, recesses 110 are formed between the electrodes 130.

[0104] In the case of a bump, Figure 5 As shown, a bump 140 is further formed on the electrode 130 .

[0105] The inner region 101 of the microstructure 100 may also be a mesa region.

[0106] Examples of the support substrate 21 used for the supply substrate 20 include a sapphire substrate, a GaAs substrate (gallium arsenide substrate), a Si substrate, and a SiC substrate, and the diameter thereof is arbitrary.

[0107] In addition, as the microstructure 100, for example, there can be listed elements obtained in the following manner: after being provided with a basic structure as a device on a supply substrate 20 through processes performed in common semiconductor pre-processes such as epitaxial growth, ion implantation, wet etching, dry etching, evaporation, electrode formation, etc., separation is carried out by conventional methods such as blade dicing, dry etching, laser cutting, etc. until the depth of separation of the elements is reached.

[0108] For example, in the case where the microstructure 100 is an LED element, the supply substrate 20 can be prepared according to the following process. Prepare an LED epitaxial substrate, which is provided with a buffer layer on a 4-inch sapphire substrate as a supporting substrate 21, and after forming a 3μm N-type GaN layer, a known light-emitting layer structure is provided, and the total epitaxial thickness of the P-type GaN stacked is 4μm. Then, after partially exposing the N layer by dry etching, a P-type electrode is formed on the P layer by a known process, and an N-type electrode is formed in contact with the exposed N layer, and a bump is formed on the electrode by plating, evaporation or sputtering. Then, in order to separate LED elements of a specified size, laser cutting is performed in a manner that at least reaches the sapphire substrate and makes the elements completely separated. Thus, a supply substrate 20 on which LED elements serving as a microstructure 100 are formed is obtained.

[0109] The size of the microstructure 100 used in the present invention is arbitrary, for example, in the case of a power LED, it is about 1 mm square. In addition, in the case of an LED element, it is about 300 μm square, in the case of a mini LED, it is about 100 μm square, in the case of a micro LED, it is about 60 μm square or less, and in the case of an extremely small-sized micro LED, it is about 30 μm square or less.

[0110] In addition, the shape of the microstructure 100 described above is an example of a substantially square shape, but the present invention is not limited thereto. For example, in the case of a micro LED, it may be a rectangular shape with one side being 30 μm to 60 μm and the other side being 10 μm to 30 μm.

[0111] In addition, the thickness of the main body of the microstructure 100 depends on the thickness of the epitaxial growth on the support substrate 21 of the supply substrate 20, and is not particularly limited, preferably about 3μm to 10μm. The thickness of the electrode is not particularly limited, preferably less than 2μm, and the thickness of the bump is not particularly limited, preferably about 1μm to 10μm.

[0112] [Implementation Method]

[0113] Next, refer to Figure 6 and Figure 7 An embodiment of the laser induced forward transfer method of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[0114] The laser induced forward transfer method of the embodiment described here includes a lamination step, a transfer step by laser lift-off, and a peeling step.

[0115] [Lamination process]

[0116] The bonding of the plurality of microstructures 100 formed on one surface of the supply substrate 20 to the resin layer 12 of the receiving substrate 10 can be performed, for example, as follows: Figure 6 Specifically, as described below. In the embodiment described below, a silicone gel layer is used as the resin layer 12 of the receiving substrate 10, and a silicone gel layer is used as the supply substrate 20. Figure 4 The microstructure 100 is provided on a substrate 20 .

[0117] First, if Figure 6 As shown in (A), the supply substrate 20 and the receiving substrate 10 are aligned. Then, the silicone gel layer 12 of the receiving substrate 10 is attached to the electrode 130 and the element body 120 of the microstructure 100. Figure 6 As shown in (B), the receiving substrate 10 is pressed against the supply substrate 20 to deform the silicone gel layer 12. Figure 2 (B) is the same as that shown in FIG. 1 , where the silicone gel layer 12 is in contact with or close to the bottom surface 110A of the concave portion 110 of the microstructure 100. Figure 6 In (B), the microstructure 100 is covered with the gel of the silicone gel layer 12. Figure 5 When the supply substrate 20 on which the microstructure 100 with the bumps 140 is formed is provided, the bonding is also performed through the same process.

[0118] There is no particular limitation on the pressure load during lamination as long as the plurality of microstructures 100 can be transferred to the silicone gel layer 12. For example, it is preferred to apply a load of preferably 0.05 MPa to 1.0 MPa, more preferably 0.10 MPa to 0.5 MPa for lamination. In addition, at this time, in order to easily follow the shape of the microstructure 100, vacuum decompression or heat can also be applied while mechanically pressurizing.

[0119] By such a laminating process including pressurization, a substrate including a supply substrate 20 and a receiving substrate 10 attached to the supply substrate 20 can be obtained. Figure 6 (B) shows a laminated substrate 30.

[0120] After the laminating process, the silicone gel layer 12 deforms to follow the shape of the concave and convex parts caused by the presence of the electrodes 130 or the bumps 140 on the microstructure 100, thereby being substantially in contact with the bottom surface 110A of the concave part 110 of the microstructure 100, and it can also be confirmed through the substrate using a laser microscope or the like that there is no gap greater than 1 μm between the silicone gel layer 12 and the microstructure 100. Since gel cured products are generally soft and adhesive, as long as the silicone gel layer 12 is in contact with or close to the bottom surface 110A of the concave part 110 of the microstructure 100 through the laminating process, the state can be maintained in the LLO process described later, and as a result, damage to the microstructure 100 can be prevented.

[0121] [Transfer process and peeling process by laser lift-off]

[0122] The transfer process based on LLO (laser lift-off) is shown in Figure 7 middle.

[0123] like Figure 7 As shown in (A), the laminated substrate 30 obtained by the lamination process is irradiated with a laser light L formed by pulse oscillation from the surface of the supply substrate 20 opposite to the surface on which the microstructure 100 is formed, so that the microstructure 100 is peeled off from the supporting substrate 21. After all the microstructures 100 to be transferred are irradiated with the same laser, the supporting substrate 11 of the receiving substrate 10 and the supporting substrate 21 of the supply substrate 20 are torn apart using a clamp, thereby forming Figure 7 (B) shows the state, whereby the microstructure 100 can be transferred to the silicone gel layer 12 on the receiving substrate 10 .

[0124] In the LLO process, for example, when the gallium nitride microstructure 100 fixed to the support substrate 21 such as a sapphire substrate is peeled off, the gallium nitride in the irradiated part is melted by irradiation with laser light such as an excimer laser or a yttrium aluminum garnet (YAG) laser, and the gallium nitride microstructure 100 can be peeled off from the supply substrate 20. In such a case, especially in micro-LEDs, KrF excimer laser light is preferably used from the viewpoint of reliability of the microstructure 100.

[0125] Specifically, laser light is selectively irradiated to generate laser ablation at the interface between the microstructure 100 as the selected object and the support substrate 21 of the supply substrate 20. Thus, between the microstructure 100 as the selected object and the support substrate 21 of the supply substrate 20, for example, in the case of a gallium nitride microstructure 100, gallium nitride is decomposed into metal gallium and nitrogen and generates gas, and the microstructure 100 can be peeled off relatively easily.

[0126] On the other hand, since the gel material is generally soft and viscous, it can easily absorb and receive the microstructure 100 peeled from the supply substrate 20 , and as a result, the microstructure 100 can be transferred.

[0127] This transfer method can be used even for easily damaged microstructures 100 such as fragile and easily cracked red LED elements, or LED elements with bumps and other concave-convex surfaces. By pressurizing and bonding the silicone gel layer 12 on the receiving substrate 10, the gel deforms to follow the shape of the microstructure 100, and the silicone gel layer 12 is in contact with or close to the bottom surface 110A of the recess 110 of the microstructure 100. By performing LLO in the above state, the silicone gel disperses and absorbs the impact applied to the microstructure 100 during LLO, so that the microstructure 100 can be transferred to the receiving substrate 10 without being damaged.

[0128] The microstructure 100 transferred to the receiving substrate 10 through this process can be installed on the circuit substrate through a desired process such as using the transfer stamp material described in patent document 1 or transferring the microstructure to a polyimide layer again, after the surface is cleaned using an acidic cleaning solution or an alkaline cleaning solution, or plasma treatment.

[0129] That is, the receiving substrate 10 that transfers the microstructures 100 and receives the microstructures 100 by the laser induced forward transfer method of the present invention can also be used as a supply substrate (donor substrate) in other steps.

[0130] Example

[0131] Hereinafter, the present invention will be specifically described using Examples and Comparative Examples, but the present invention is not limited thereto.

[0132] Supply substrates including the following microstructures were prepared respectively.

[0133] <Supplying substrate A and microstructure A>

[0134] A sapphire substrate cut into 1.5 cm squares and equipped with a blue mini LED element measuring 90 μm x 140 μm, with a total thickness of 19 μm and a bump height of 7 μm.

[0135] <Supplying substrate B and microstructure B>

[0136] A sapphire substrate cut into 1.5 cm squares and equipped with a 90 μm × 140 μm blue mini LED element with a total thickness of 12 μm.

[0137] <Supplying substrate C and microstructure C>

[0138] A sapphire substrate cut into 1.5 cm squares and equipped with 18 μm × 36 μm red micro LED elements with a total thickness of 5 μm

[0139] In addition, the following substrates were prepared as support substrates for receiving substrates.

[0140] <Support substrate for receiving substrate>

[0141] Synthetic quartz substrate with an outer diameter of 15.24 cm (6 inches), a thickness of 1 mm, and a thickness deviation (TTV) of 0.8 μm

[0142] <Examples 1 to 5>

[0143] [Production of receiving substrate]

[0144] 3 g of the heat-curable or light-curable silicone gel composition shown below was dripped onto the supporting substrate, and the coating was uniformly applied onto the supporting substrate using a spin coater so that the film thickness became 30 μm. The supporting substrate coated with silicone was subjected to the curing conditions described below to cure it into a gel state, thereby preparing a receiving substrate having a silicone gel layer as a resin layer.

[0145] [Fitting]

[0146] The supply substrate and the receiving substrate were bonded together while being pressurized at 0.5 MPa in such a manner that the microstructure on the supply substrate and the silicone gel on the receiving substrate were in contact as shown in Table 1 below. Then, using a laser microscope, it was confirmed that there was no gap greater than 1 μm between the bottom surface of the concave portion of the microstructure and the silicone gel layer.

[0147] [LLO]

[0148] The microstructures were irradiated with KrF excimer laser light from the back of the supply substrate to perform LLO. The supply substrate was then torn off from the receiving substrate, and the transfer rate and breakage rate of the microstructures from the supply substrate to the receiving substrate were evaluated. The results are summarized in Table 1.

[0149] [Determination of elastic modulus]

[0150] The dynamic viscoelastic properties of the cured silicone gel in the present invention are defined by the characteristic frequency and the storage elastic modulus G' at a specific temperature, and the measurement is performed using the viscoelasticity measuring device ARES G-II manufactured by TA Instrument. The silicone resin hardened and formed into a 3 cm square and 500 μm thick is clamped between the circular shape measuring part of the testing machine and the parallel plate with a diameter of 20 mm in a manner that does not contain bubbles, and the temperature is maintained at 25°C while setting the strain value to 4% and the frequency to 1 Hz for 10 minutes. The value read 10 minutes after the start of the measurement is used as the storage elastic modulus G'.

[0151] [Silicone gel composition and curing conditions]

[0152] Silicone 1: A silicone gel composition that is cured by heating at 120°C for 1 hour and has a storage elastic modulus of 0.2 kPa at 25°C

[0153] Silicone 2: by irradiation with 365nm ultraviolet (UV)-LED 3000mJ / cm under nitrogen 2 (Illuminance: 100mW / cm 2 ) and undergoes photo-radical curing, and a silicone gel composition having a storage elastic modulus of 0.2 kPa at 25°C

[0154] Silicone 3: by irradiation with 365nm UV-LED 3000mJ / cm under nitrogen 2 (Illuminance: 100mW / cm 2 ) and photo-radical cured, and the storage elastic modulus at 25° C. becomes 5.3 kPa of the silicone gel composition

[0155] <Comparative Examples 1 to 4>

[0156] In Comparative Examples 1 to 4, transfer was performed in the same manner as in the example, except that the silicone gel composition for the receiving substrate was changed to the following Silicone 4 or Silicone 5 and the supply substrates shown in the following Table 1 were used.

[0157] Silicone 4: A silicone rubber composition that is cured by heating at 120°C for 1 hour and has a storage elastic modulus of 500 kPa at 25°C

[0158] Silicone 5: A silicone rubber composition that is cured by heating at 120°C for 1 hour and has a storage elastic modulus of 3 MPa at 25°C

[0159] In the comparative example, Figure 8 As shown, LLO is performed in a state where silicone is not deformed and silicone is neither in contact with nor close to the surface of the recessed portion of the microstructure.

[0160]

[0161] As is clear from the results shown in Table 1, in Examples 1 to 5, by performing laser peeling while the silicone gel layer is in contact with or close to the bottom surface of the recessed portion of the microstructure, even if the transfer rate exceeds 99%, the damage during transfer due to laser peeling can be suppressed to less than 1%.

[0162] On the other hand, in Comparative Examples 1 to 4, laser lift-off was performed in a state where the silicone gel layer and the bottom surface of the recessed portion of the microstructure were neither in contact with nor close to each other, and therefore damage during transfer by laser lift-off was 5% or more.

[0163] This manual includes the following aspects.

[0164] [1] A laser induced forward transfer method, in which a microstructure formed on a supply substrate is transferred to a receiving substrate by laser stripping. In the laser induced forward transfer method, the surface of the microstructure facing the receiving substrate has a concave portion such that the outer area of ​​the surface is higher than the inner area, and the surface of the receiving substrate on which the microstructure is transferred has a resin layer, and laser stripping is performed in a state in which the resin layer is in contact with or close to the bottom surface of the concave portion of the microstructure.

[0165] [2] The laser induced forward transfer method according to [1], wherein the outer region of the microstructure has an electrode or a bump.

[0166] [3] The laser induced forward transfer method according to [1] or [2], wherein the inner region is a terrace region.

[0167] [4] The laser induced forward transfer method according to any one of [1] to [3], wherein the microstructure is one or more LED elements selected from a red LED, a blue LED or a green LED.

[0168] [5] A laser induced forward transfer method according to any one of [1] to [4], wherein the resin layer is prepared by forming at least one hardening reaction selected from the group consisting of a free radical hardening reaction, a cationic hardening reaction, an anionic hardening reaction, an addition hardening reaction and a condensation hardening reaction.

[0169] [6] A laser induced forward transfer method according to any one of [1] to [5], wherein the supply substrate and the receiving substrate are bonded together and pressurized to deform the resin layer so that the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure.

[0170] [7] The laser induced forward transfer method according to any one of [1] to [6], wherein a resin layer having flexibility or fluidity is used as the resin layer.

[0171] [8] The laser induced forward transfer method according to any one of [1] to [7], wherein the resin layer has a storage elastic modulus of 1 kPa to 300 kPa at 25° C.

[0172] [9] A receiving substrate for transferring and receiving a microstructure formed on a supply substrate by laser stripping, wherein the receiving substrate has a resin layer on the surface on which the microstructure is transferred, and the surface of the microstructure facing the receiving substrate has a recessed portion in a manner such that the outer region of the surface is higher than the inner region, and the resin layer is deformed by bonding and pressurizing the supply substrate and the receiving substrate.

[0173]

[10] The receiving substrate according to [9], wherein the amount of deformation of the resin layer is sufficient to come into contact with or approach a bottom surface of the recessed portion of the microstructure.

[0174]

[11] The receiving substrate according to [9] or

[10] , wherein the resin layer has a storage elastic modulus of 1 kPa to 300 kPa at 25°C.

[0175] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any form having substantially the same structure and achieving the same function and effect as the technical concept described in the claims of the present invention is included in the technical scope of the present invention.

Claims

1. A laser induced forward transfer method, wherein a microstructure formed on a supply substrate is transferred to a receiving substrate by laser lift-off, wherein: The surface of the microstructure facing the receiving substrate has a concave portion such that the outer area of ​​the surface is higher than the inner area. The surface of the receiving substrate on which the microstructure is transferred has a resin layer, Laser lift-off is performed in a state where the resin layer is in contact with or close to the bottom surface of the recessed portion of the microstructure.

2. The laser induced forward transfer method according to claim 1, in, The outer region of the microstructure has an electrode or a bump.

3. The laser induced forward transfer method according to claim 2, in, The inner area is a table area.

4. The laser induced forward transfer method according to claim 1, in, The microstructure is a light emitting diode element selected from a red light emitting diode, a blue light emitting diode or a green light emitting diode, or two or more light emitting diode elements.

5. The laser induced forward transfer method according to claim 1, in, The resin layer is prepared by forming at least one curing reaction selected from the group consisting of a radical curing reaction, a cationic curing reaction, an anionic curing reaction, an addition curing reaction, and a condensation curing reaction.

6. The laser induced forward transfer method according to any one of claims 1 to 5, in, The supply substrate and the receiving substrate are bonded together and pressurized to deform the resin layer so that the resin layer is in contact with or close to the bottom surface of the concave portion of the microstructure.

7. The laser induced forward transfer method according to any one of claims 1 to 5, in, As the resin layer, a resin layer having flexibility or fluidity is used.

8. The laser induced forward transfer method according to claim 7, in, As the resin layer, a resin layer having a storage elastic modulus at 25° C. of 1 kPa to 300 kPa is used.

9. A receiving substrate for transferring and receiving a microstructure formed on a supply substrate by laser lift-off, wherein: A resin layer is provided on the surface on which the microstructure is transferred, The surface of the microstructure facing the receiving substrate has a concave portion in a manner such that the outer region of the surface is higher than the inner region. The resin layer is deformed by attaching and pressurizing the supply substrate and the receiving substrate.

10. The receiving substrate according to claim 9, in, The resin layer is deformed by an amount sufficient to be in contact with or close to the bottom surface of the recessed portion of the microstructure.

11. The receiving substrate according to claim 9 or 10, in, The resin layer has a storage elastic modulus of 1 kPa to 300 kPa at 25°C.

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