Transfer method

Abstract

The present invention is a transfer method for transferring a plurality of microstructures provided on a substrate from the substrate by laser irradiation, wherein at least the spaces between adjacent microstructures are filled with a polymer material, the method comprising: a first laser irradiation step for emitting a laser beam through the substrate toward the microstructures; and a second laser irradiation step for emitting a laser beam through the substrate toward the polymer material. In the first laser irradiation step, the laser directed toward the microstructures irradiates regions corresponding to the microstructures. As a result, it is possible to suppress the occurrence of chipping or cracking in the microstructures when transferring the microstructures from the substrate.

Description

Transfer method

[0001] The present invention relates to a transfer method.

[0002] In recent years, with the miniaturization of semiconductor elements, microstructure transfer technology using adhesive resins has attracted attention as a means of assembling electrical and electronic products using semiconductor elements. In particular, there has been active development of technology for manufacturing LED displays for applications such as signage, TVs, medical devices, in-vehicle displays, and smartphones by transferring tens of thousands of mini-LEDs (LED elements with short sides of 100 μm to several hundred μm) or micro-LEDs (LED elements with short sides of 100 μm or less, or even 50 μm or less) at once.

[0003] To date, methods have been developed for transferring microstructures such as microLEDs and mounting them on circuit boards using silicone adhesive cured materials as donor substrates or transfer stamp materials (see, for example, Patent Document 1).

[0004] Furthermore, a technique has been proposed that can transfer semiconductor chips with high precision by mitigating the impact during transfer (for example, Patent Document 2).

[0005] JP 2021-34610 A JP 2019-67892 A

[0006] To improve the yield of transfer, it is important to prevent chipping or cracking of the structure when the microstructure is peeled off from the base material such as a substrate.

[0007] The present invention has been made to solve the above problems, and aims to provide a transfer method that can prevent chips and cracks from occurring in microstructures when transferring them from a substrate.

[0008] In order to solve the above problems, the present invention provides a transfer method for transferring a plurality of microstructures provided on a substrate from the substrate by laser irradiation, wherein at least the space between adjacent microstructures is filled with a polymer material, and the transfer method includes a first laser irradiation step of irradiating a laser through the substrate toward the microstructures, and a second laser irradiation step of irradiating a laser through the substrate toward the polymer material, wherein in the first laser irradiation step, the laser directed toward the microstructures is irradiated onto an area corresponding to the microstructures.

[0009] With this transfer method, the spaces between the microstructures are filled with polymeric material, and two-stage irradiation is performed: a first laser irradiation process in which the laser is irradiated onto the microstructure, and a second laser irradiation process in which the laser is irradiated onto the polymeric material, thereby making it possible to transfer the microstructure from the substrate while preventing chips and cracks from occurring in the microstructure.

[0010] For example, it is preferable that the second laser irradiation step is performed after the first laser irradiation step.

[0011] By performing the second laser irradiation step after the first laser irradiation step, for example, the polymer material can be peeled off in the second laser irradiation step without being peeled off in the first laser irradiation step, which makes it possible to transfer the microstructure from the substrate while more reliably suppressing chipping or cracking in the microstructure.

[0012] In the second laser irradiation step, the polymer material and the microstructure may be irradiated with a laser.

[0013] In the second laser irradiation step, the polymer material may be irradiated with the laser, but the microstructure may also be irradiated with the laser. In the second laser irradiation step, the entire surface of the substrate may also be irradiated with the laser.

[0014] For example, the first laser irradiation step can be performed with an energy density that sufficiently ablates the polymer material.

[0015] For example, the laser irradiation in the first laser irradiation step can be performed at a high energy density that is sufficient to ablate the polymer material.

[0016] For example, the plurality of microstructures may be provided on the substrate via GaN, and the first laser irradiation step may be performed with an energy density that thermally decomposes GaN.

[0017] In such a first laser irradiation step, the microstructure provided on the substrate via GaN can be reliably peeled off from the substrate.

[0018] Furthermore, for example, the second laser irradiation step can be performed at an energy density lower than that at which the polymer material is sufficiently ablated.

[0019] The second laser irradiation step may be performed with laser irradiation at an energy density lower than that at which the polymer material is sufficiently ablated.

[0020] For example, the second laser irradiation step can be performed with an energy density that vaporizes the polymer material.

[0021] By carrying out the second laser irradiation step, the polymer material can be vaporized.

[0022] The second laser irradiation step is preferably carried out at an energy density that can suppress the generation of carbon-based debris derived from the polymer material.

[0023] It is preferable that the second laser irradiation step be carried out while suppressing the generation of carbon-based debris in this manner.

[0024] For example, the laser irradiation in the first laser irradiation step and the second laser irradiation step may be performed by an excimer laser having a wavelength of 248 nm, and the energy density of the laser irradiation in the first laser irradiation step may be 700 mJ / cm. ２ or more, and the energy density of the laser irradiation in the second laser irradiation step is 30 to 500 mJ / cm ２ It can be said that:

[0025] The wavelength and energy density of the laser can be set, for example, as described above.

[0026] The second laser irradiation step may be performed multiple times.

[0027] The second laser irradiation step may be performed at least once, or may be performed multiple times.

[0028] For example, the substrate on which the plurality of microstructures are provided may be coated with a polymer material so as to cover the plurality of microstructures.

[0029] A polymeric material coating may be formed to cover the plurality of microstructures.

[0030] As described above, the transfer method of the present invention makes it possible to transfer a microstructure from a substrate while suppressing the occurrence of chipping or cracks in the microstructure.

[0031] Fig. 1 is a schematic cross-sectional view showing a composite to be irradiated with laser in an example of the transfer method of the present invention. Fig. 2 is a schematic plan view of the composite of Fig. 1 as seen from the substrate side. Fig. 3 is a schematic cross-sectional view illustrating a first laser irradiation step in an example of the transfer method of the present invention. Fig. 4 is a schematic cross-sectional view illustrating a second laser irradiation step in an example of the transfer method of the present invention. Fig. 5 is an optical microscope photograph in Example 1. Fig. 6 is an optical microscope photograph in a comparative example.

[0032] As described above, there has been a demand for the development of a transfer method that can prevent chipping and cracking of the microstructure when transferring the microstructure from the substrate.

[0033] As a result of extensive research into the above-mentioned problems, the inventors discovered that by performing a two-stage irradiation process, consisting of a first laser irradiation process in which a laser is irradiated onto the microstructure and a second laser irradiation process in which a laser is irradiated onto the polymeric material while the spaces between the microstructures are filled with a polymeric material, it is possible to transfer the microstructure from the substrate while suppressing the occurrence of chips or cracks in the microstructure, and thus completed the present invention.

[0034] In other words, the present invention is a transfer method for transferring a plurality of microstructures provided on a substrate from the substrate by laser irradiation, wherein at least the space between adjacent microstructures is filled with a polymer material, and the transfer method comprises: a first laser irradiation step of irradiating a laser through the substrate toward the microstructures; and a second laser irradiation step of irradiating a laser through the substrate toward the polymer material, wherein in the first laser irradiation step, the laser directed toward the microstructures is irradiated onto an area corresponding to the microstructures.

[0035] The present invention will be described in detail below, but the present invention is not limited thereto.

[0036] [Laser Irradiation Target] First, the laser irradiation target in an example of the transfer method of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing a composite to be laser irradiated in an example of the transfer method of the present invention. Figure 2 is a schematic plan view of the composite of Figure 1 as seen from the substrate side. However, the laser irradiation target in the transfer method of the present invention is not limited to the composite shown in Figures 1 and 2.

[0037] 1 and 2 includes a substrate 1 and a plurality of (four in this example) microstructures 2 provided on the substrate 1. The composite 10 also includes a polymer material 3. The polymer material 3 includes a portion 31 that fills at least the spaces between adjacent microstructures 2. In other words, at least the spaces 2 between adjacent microstructures are filled with the polymer material 3.

[0038] Such a composite 10 can be obtained, for example, by a step of forming a plurality of minute structures 2 on a substrate 1 and a step of filling at least the spaces between adjacent minute structures 2 with a polymer material 3 .

[0039] As shown in FIGS. 1 and 2 , the polymer material 3 may further include a portion 32 covering the microstructure 2 and / or a portion 33 covering the outside of the microstructure 2. That is, the substrate 1 on which a plurality of microstructures 2 are provided may be coated with the polymer material 3 so as to cover the plurality of microstructures 2. However, in the laser irradiation target in the transfer method of the present invention, the polymer material 3 need only include at least the portion 31 filling the space between adjacent microstructures 2, and may not include the portion 32 covering the microstructure 2 or the portion 33 covering the outside of the microstructure 2. From the viewpoint of reducing impact on the microstructure 2, it is preferable to provide the polymer material 3 not only on the portion 31 filling the space between adjacent microstructures 2 but also on the portion 33 covering the outside of the microstructure 2. Furthermore, providing the polymer material 3 on the portion 32 covering the microstructure 2 can further reduce impact on the microstructure 2. If the polymer material 3 provided on the portion 32 covering the microstructure 2 is not necessary for the final product, it can be removed, for example, by cleaning or polishing in a process subsequent to the transfer process.

[0040] When the microstructure 2 is rectangular, it is preferable that the polymer material 3 be disposed on all of its outer peripheries, i.e., on the outside of all four sides. However, even when the polymer material 3 is disposed on only a part of the outer periphery of the microstructure 2, for example, on only the outside of one side of the rectangular microstructure 2, it is possible to expect better impact mitigation on the microstructure 2 than when no polymer material is disposed at all. Furthermore, when the polymer material 3 is disposed on the outside of two opposing sides, it is possible to expect better impact mitigation on the microstructure 2 than when the polymer material 3 is disposed only on the outside of one side.

[0041] The material of the substrate 1 is not particularly limited as long as it can be used to irradiate the microstructure 2 and / or the polymer material 3 with a laser in the first laser irradiation step and the second laser irradiation step described below. For example, an inorganic transparent substrate such as a sapphire substrate, a GaAs substrate (gallium arsenide substrate), a Si substrate, a SiC substrate, or a quartz substrate can be suitably used as the substrate 1. Alternatively, an organic transparent substrate that is resistant to laser irradiation can be used.

[0042] The thickness of the substrate 1 can be, for example, 0.001 mm or more and 3 mm or less, but is not particularly limited. The substrate may be either rigid or flexible. The shape of the substrate 1 is typically rectangular or circular, but may also be elliptical, polygonal other than rectangular, or polygonal with some of the sides replaced with curves, or may be in the form of a long tape. If necessary, providing an orientation flat or notch on the outer edge of the substrate makes it easier to handle and adjust the position.

[0043] The microstructure 2 is not particularly limited, and may be, for example, an LED chip such as a micro LED or a mini LED, or may be a semiconductor chip or other electronic component.

[0044] Generally, the planar shape of the minute structure 2 is a rectangle, but there is no particular limitation, and it may be a circle, an ellipse, a polygon other than a rectangle, or a shape in which some of the sides of a polygon are replaced by curves.

[0045] When the microstructure 2 has a rectangular shape, the upper limit of one side can be, for example, 2.5 mm. According to the transfer method of the present invention, even a microstructure 2 measuring, for example, 1 mm square can be transferred without chipping or cracking, as will be explained in detail below. The lower limit of one side of the microstructure 2 is not particularly limited, but can be, for example, 0.001 mm. The side of the microstructure 2 is preferably 0.005 mm or more and 2 mm or less. Of course, the present invention can also be applied to microstructures with sides greater than 2.5 mm or less than 0.001 mm. The thickness of the microstructure is not particularly limited, but is generally 200 μm or less, and may be 100 μm or less, or 50 μm or less. In particular, when the thickness is 50 μm or less, even a small chip occurring in the microstructure increases the possibility of fatal damage in a subsequent process, making the transfer method of the present invention effective. This is particularly noticeable when the thickness is 30 μm or less. The lower limit of thickness has been decreasing with technological advances, but is still around 1 μm.

[0046] The constituent material of the microstructure 2 is not particularly limited, but for example, the surface of the microstructure 2 on the substrate 1 side may contain, for example, gallium nitride (GaN), gallium phosphide (GaP), or indium phosphide (InP). Typically, the multiple microstructures 2 are provided on the substrate 1 via an inorganic material such as GaN 21. More specifically, they may be LED chips manufactured on an epitaxial substrate such as a sapphire substrate. Of course, they may also be microstructures provided on the various inorganic transparent substrates or organic transparent substrates described above via an adhesive or the like.

[0047] Depending on the size of the microstructures and substrate, tens of thousands to hundreds of thousands of microstructures are typically arranged in a matrix on the substrate. Adjacent microstructures are spaced apart. These spaces are free of microstructures and expose the substrate, sometimes called streets. The width of the streets is often determined by the size of the LED chip and the type of dicing. For micro LED chips and chemical dicing, the street width is often small, typically on the order of a few micrometers (1 to 10 μm). For mini LEDs and mechanical dicing, the street width is often slightly larger, typically on the order of tens of micrometers (10 to 100 μm).

[0048] The polymer material 3 is not particularly limited, but may be, for example, a resin selected from the group consisting of polyimide, silicone, polystyrene, and acrylic resin, a composition containing such a resin, or a cured product thereof. From the viewpoint of absorbing impact on the microstructure 2, a material having a certain degree of elasticity, such as a rubber-like substance, is preferable. Examples of silicones include straight silicones such as dimethyl silicone and methylphenyl silicone, modified silicones such as acrylic-modified silicone and methacrylic-modified silicone, and combinations thereof. These may be of the side chain type, single-end type, or double-end type.

[0049] The polymer material can be filled by applying, for example, a liquid resin. These application methods can be performed using a spin coater, a dispenser, or the like. Materials that have sufficient fluidity to fill the gaps between adjacent microstructures during application and, if necessary, can reduce their fluidity after application are easy to apply. Therefore, thermoplastic materials, thermosetting materials, photocurable materials, and solutions of these materials dissolved in a solvent are useful. In particular, resins such as solvent-soluble thermoplastic resins and solutions of these materials dissolved in a solvent allow the polymer compound to be easily removed by the solvent after transfer. The polymer material may be filled between adjacent microstructures in a manner that prevents the formation of bubbles or voids, or may be filled in a manner that leaves voids on the substrate side. From the perspective of mitigating impact on the microstructures, more than half of the thickness of the microstructure may be filled. Even when filling to prevent the formation of bubbles, the inclusion of bubbles, which is difficult to avoid in the manufacturing process, is acceptable.

[0050] In addition, when a thermosetting material or a photocurable material is used as the polymer material 3 and the thermosetting material or the photocurable material is in a state where it is firmly cured after transfer, it may be difficult to remove the polymer material 3 from the microstructure 2 after transfer. In such cases, it is possible to use a curable material that becomes a rubber-like material after curing, to cure the curable material so that the reaction rate is low, for example, to cure it to a B-stage state, or to increase the flexibility of the cured product by including a rubber component in the composition of the curable material.

[0051] Photocurable materials whose adhesive strength decreases upon exposure to light can also be used. Photocurable materials whose adhesive strength (tackiness) decreases upon exposure to UV light are widely used as dicing tapes, and typically contain a base resin such as a (meth)acrylic copolymer, a photocurable component such as a polyfunctional (meth)acrylate, and a photoinitiator such as a photoradical generator. In this case, it is preferable to use a photoinitiator that has sufficiently low absorption of the wavelength of the laser used in the transfer method.

[0052] The receiving substrate to which the microstructure 2 is transferred is not particularly limited, but inorganic transparent substrates such as sapphire substrates, GaAs (gallium arsenide) substrates, Si substrates, SiC substrates, and quartz substrates are suitable. In subsequent steps of the transfer method of the present invention, an opaque substrate may be used if laser irradiation through the receiving substrate is not performed. Similarly, organic substrates may also be used as long as the receiving substrate is not exposed to excessive heat or chemical treatment in subsequent steps. The shape of the receiving substrate is typically rectangular or circular, but it may also be elliptical, polygonal, or polygonal, with some of the sides replaced by curves, or it may be a long tape. If necessary, providing an orientation flat or notch on the outer edge of the substrate facilitates handling and positioning.

[0053] Furthermore, the surface (transfer surface) of the receiving substrate onto which the microstructure 2 is transferred can have, for example, an adhesive layer partially or entirely thereon to temporarily or permanently hold the transferred microstructure 2. Here, when the microstructure 2 and the polymer material 3 are transferred together, the polymer material 3 can hold the microstructure 2 on the receiving substrate.

[0054] In the present invention, for example, a laminate obtained by applying a polymer material to a substrate provided with a plurality of microstructures and contacting a receiving substrate with the side on which the polymer material is provided can be used for laser irradiation. If necessary, a solvent drying step can be provided after application. Similarly, if necessary, a curing step can be provided before or after contacting the receiving substrate. Furthermore, the laser may be irradiated in a spaced state, i.e., in a non-contact state, rather than in a contacting state, state with the receiving substrate. When using a laminate in contact with the receiving substrate, it is preferable that the substrate and the receiving substrate have the same shape.

[0055] Alternatively, the polymer material can be applied to a receiving substrate and pressed against a plurality of microstructures on the substrate to fill the spaces between adjacent microstructures. In this case, the flowability of the polymer material can be reduced after filling rather than after application, if necessary.

[0056] [First Laser Irradiation Step] In the first laser irradiation step in the transfer method of the present invention, for example, as shown in FIG. 3, a laser L1 is irradiated onto the microstructure 2 through the substrate 1.

[0057] In the first laser irradiation step in the transfer method of the present invention, the laser L1 directed toward the minute structure 2 is irradiated onto the region 12 corresponding to the minute structure 2 .

[0058] Here, the region 12 corresponding to the microstructure 2 may include only the microstructure 2, or may include the microstructure 2 and a portion 34 of the polymer material 3 adjacent to the microstructure 2, as shown in Figure 3. Furthermore, it may be a region inside the outer edge of the microstructure 2, as long as it is within a range that allows peeling from the substrate 1 by the second laser irradiation step. Therefore, the area of ​​the region corresponding to the microstructure 2 is preferably about 90 to 120% of the area of ​​the microstructure 2, more preferably about 95 to 110%, and particularly preferably 98 to 105%.

[0059] In the first laser irradiation step, irradiation of the region 12 corresponding to the microstructure 2 does not necessarily have to be performed in one irradiation. For example, by performing irradiation multiple times with different irradiation regions, the impact on the microstructure 2 can be alleviated. Furthermore, by performing irradiation multiple times so that the irradiation regions overlap with an energy density that is insufficiently weak to peel the microstructure 2 from the substrate 1, the impact on the microstructure 2 can be alleviated and the generation of foreign matter can also be reduced. Furthermore, the region inside the outer edge of the microstructure 2 may be irradiated, and then the entire microstructure may be irradiated.

[0060] In this example, the irradiation of the laser L1 in the first laser irradiation step allows the microstructure 2 to be peeled off from the substrate 1 while the portion 31 of the polymer material 3 that fills the spaces between adjacent microstructures 2 remains on the substrate 1 (is not peeled off). Due to the presence of the portion 31 of the polymer material 3, the microstructure 2 can be maintained in an unseparated state from the substrate 1.

[0061] The irradiation conditions of the laser L1 in the first laser irradiation step will be described later.

[0062] [Second Laser Irradiation Step] In the second laser irradiation step, for example, as shown in FIG. 4, a laser beam L2 is irradiated onto the polymer material 3 through the substrate 1.

[0063] In the second laser irradiation step, the laser L2 may be irradiated toward the polymer material 3, but the laser L2 may also be irradiated toward the microstructure 2 as shown in Fig. 4. Furthermore, the laser L2 may be irradiated toward a plurality of microstructures 2, or the entire surface of the composite 10 may be irradiated with the laser L2. Note that when the area of ​​the composite is large, a high-power laser oscillator is required, and therefore it is preferable to form the laser into a line or rectangle so that the irradiation area does not become too large.

[0064] By irradiating the laser beam L2 in the second laser irradiation step in this example, the portion 31 of the polymer material 3 that fills the spaces between the adjacent minute structures 2 can be peeled off from the substrate 1.

[0065] Typically, the first laser irradiation step is followed by the second laser irradiation step. As described above, after the first laser irradiation step, the microstructure 2 is peeled off from the substrate 1 but can maintain a state in which it is not separated from the substrate 1.

[0066] The present invention is particularly effective when the minimum energy density A required to peel the microstructure 2 from the substrate 1 is greater than the minimum energy density B required to peel the polymer material 3 from the substrate 1. In this case, if the transfer process is performed uniformly at the minimum energy density A, the energy density is likely to increase the impact on the microstructure 2, which can easily cause chipping or cracking in the microstructure 2. Even if the microstructure 2 is irradiated with a laser at the minimum energy density A, which is likely to increase the impact on the microstructure 2, or at an energy density higher than that, the present invention can prevent chipping or cracking in the microstructure 2 because the presence of the polymer material 3 mitigates the impact. Therefore, it is possible to increase the energy density and improve the transfer success rate.

[0067] Furthermore, even if the microstructure 2 is irradiated with a laser having an energy density less than the minimum energy density A in the first laser irradiation step, the laser can be irradiated in the second laser irradiation step so as to include the microstructure, thereby enabling transfer. Therefore, the impact of laser irradiation on the microstructure can be alleviated. In this way, even if the microstructure 2 is not completely peeled off from the substrate 1 in the first laser irradiation step, or if the peeled microstructure 2 re-adheres to the substrate 1 due to a subsequent temperature drop, transfer is possible by the second laser irradiation step.

[0068] The second laser irradiation step may be performed multiple times as necessary. Alternatively, the second laser irradiation step may be performed once to separate one microstructure 2 from the substrate 1, and then the first laser irradiation step may be performed on another microstructure 2.

[0069] Hereinafter, preferred aspects and specific examples of the irradiation conditions of the lasers L1 and L2 in the first laser irradiation step and the second laser irradiation step will be described.

[0070] The wavelengths of the lasers L1 and L2 in the first laser irradiation step and the second laser irradiation step can be set appropriately in consideration of the material constituting the microstructure 2 and the polymer material 3. For example, an excimer laser with a wavelength of 248 nm, an excimer laser with a wavelength of 266 nm, an excimer laser with a wavelength of 193 nm, or an excimer laser with a wavelength of 351 nm can be used, but are not particularly limited thereto.

[0071] For example, the first laser irradiation step is performed at an energy density (e.g., 700 mJ / cm) that sufficiently ablates the polymer material 3. ２ More than 2000mJ / cm ２ This can be done using the following method:

[0072] Here, ablation generally refers to a phenomenon in which, when a laser beam is irradiated onto a solid or liquid surface, plasma is generated and the constituent materials of the surface are explosively released. Generally, when a polymeric material is ablated, the polymeric material is thermally decomposed and photodecomposed. Furthermore, when a polymeric material 3 is ablated, a portion of the polymeric material may become soot-like carbon-based debris.

[0073] When the polymer material 3 is polyimide, for example, the energy density in the first laser irradiation step is set to 40 mJ / cm at a wavelength of 248 nm and a pulse width of 20 ns. ２ More than 400mJ / cm ２ It is preferable to set it to 80 mJ / cm or less. ２ More than 300mJ / cm ２ When the polymer material 3 is silicone, for example, the energy density in the first laser irradiation step is set to 100 mJ / cm at a wavelength of 248 nm and a pulse width of 20 ns. ２ More than 500mJ / cm ２ It is preferable to set the dose to 200 mJ / cm or less. ２ More than 400mJ / cm ２ When the polymer material 3 is an acrylic resin, for example, the energy density in the first laser irradiation step is set to 40 mJ / cm at a wavelength of 248 nm and a pulse width of 20 ns. ２ More than 700mJ / cm ２ It is preferable to set it to 80 mJ / cm or less. ２ More than 400mJ / cm ２ It is more preferable to do the following:

[0074] In the case where a plurality of microstructures 2 are provided on the substrate 1 via GaN 21, for example, the first laser irradiation step is performed at an energy density sufficient to thermally decompose GaN (for example, 0.8 J / cm at a wavelength of 248 nm and a pulse width of 20 ns). ２ 2J / cm or more ２ This can be done using the following method:

[0075] In such a first laser irradiation step, the microstructure 2 provided on the base material 1 via the GaN 21 can be reliably peeled off from the base material 1 .

[0076] The second laser irradiation step can be performed, for example, at an energy density lower than that at which the polymer material 3 is sufficiently ablated. That is, the energy density of the laser L2 in the second laser irradiation step can be lower than the energy density of the laser L1 in the first laser irradiation step. In order to reduce the influence on the region provided in the microstructure 2, it is preferable that the energy density in the second laser irradiation step is sufficiently lower than the energy density in the first laser irradiation step. At a wavelength of 248 nm and a pulse width of 20 ns, the energy density in the second laser irradiation step is 100 mJ / cm. ２ It is preferable that the difference is 300 mJ / cm or more. ２ It is more preferable that the difference is 500 mJ / cm or more. ２ The upper limit of the difference in energy density is not particularly limited, but is, for example, 1200 mJ / cm ２ It should be noted that "less than the energy density at which the polymer material is sufficiently ablated" means, in other words, that the energy density is lower than the energy density at which the microstructure can be transferred. By performing irradiation with such a sufficiently weak energy density multiple times, transfer can be performed while suppressing the generation of carbon-based debris. Although the generation of carbon-based debris can be suppressed by performing irradiation more times with a weaker energy density, from the viewpoint of improving throughput, it is preferable to set the number of irradiations to about 2 to 20 times, and more preferably to about 2 to 10 times.

[0077] On the other hand, when the generation of carbon-based debris is permitted or when a polymeric material that is less likely to generate carbon-based debris is used, irradiation may be performed at an energy density that sufficiently ablates the polymeric material, in other words, at an energy density equal to or greater than the minimum energy density B.

[0078] For example, the second laser irradiation step can be performed with an energy density that vaporizes the polymer material 3 .

[0079] By carrying out such a second laser irradiation step, the polymer material 3 can be vaporized.

[0080] The second laser irradiation step is preferably carried out at an energy density that can suppress the generation of carbon-based debris derived from the polymer material 3 .

[0081] The second laser irradiation step is preferably carried out while suppressing the generation of carbon-based debris in this manner. In the second laser irradiation step, the energy density (for example, 0.08 J / cm) is set so that the generation of debris is zero. ２ On the other hand, from the viewpoint of the transfer success rate, the energy density may be increased so that the amount of debris generated is 10% or less compared to the amount of debris generated when the polymer material 3 is fully ablated.

[0082] Specifically, the energy density of the laser irradiation in the second laser irradiation step is, for example, 30 to 500 mJ / cm ２ It can be said that:

[0083] Specifically, for example, when the polymer material 3 is polyimide and a laser L2 with a wavelength of 193 nm is used, the energy density is 20 mJ / cm ２ It is preferable that the concentration is about 20 to 200 mJ / cm or more. ２ Similarly, when a laser L2 with a wavelength of 248 nm is used, the energy density is about 30 mJ / cm ２ It is preferable that the concentration is about 30 to 500 mJ / cm or more. ２ When a laser L2 with a wavelength of 266 nm is used, the energy density is 40 mJ / cm ２ It is preferable that the concentration is about 40 to 400 mJ / cm or more. ２ When a laser L2 with a wavelength of 351 nm is used, the energy density is about 80 mJ / cm ２ It is preferable that the above amount is used.

[0084] Furthermore, when a laser L2 with a wavelength of 193 nm is used and the polymer material 3 is polystyrene, the energy density is 10 mJ / cm ２ When a laser L2 with a wavelength of 193 nm is used and the polymer material 3 is an acrylic resin, the energy density is 60 mJ / cm ２It is preferable that the above amount is used.

[0085] The transfer method of the present invention may be, for example, a type of laser lift-off (LLO) or laser induced forward transfer (LIFT). Specific device configurations and operation methods used in the transfer method of the present invention can be implemented with reference to, for example, International Publication No. 2019 / 244362.

[0086] The transfer process of the present invention can mitigate the impact on the microstructure 3 during the transfer process, making it effective for application to a brittle, easily cracked microstructure 3. Examples of brittle, easily cracked microstructures 3 include red LED chips and LED chips with uneven surfaces such as bumps. When a bump is mounted, the bump is further formed on the electrode, making the difference in unevenness large and therefore prone to breakage. Furthermore, microstructures with MESA regions generally have electrodes formed on both ends of the MESA region, resulting in a shape with slight unevenness and making them prone to breakage.

[0087] Furthermore, mini LED chips (LED elements with short sides of 100 μm or more to several hundred μm) are larger than micro LED chips (LED elements with short sides of 100 μm or less, or even 50 μm or less), and often suffer from chip cracking during transfer. Micro LED chips are also prone to breakage when they have an uneven surface, as mentioned above. Red LED chips are composed of a different group of elements than blue or green LED chips, making them relatively brittle and prone to cracking. Therefore, similar cracking has occurred during the transfer process.

[0088] The thickness of the main body of the microstructure 3 is not particularly limited, but is preferably about 3 to 10 μm. The thickness of the electrode is not particularly limited, but is preferably 2 μm or less. The thickness of the bump is not particularly limited, but is preferably about 1 to 10 μm.

[0089] Furthermore, the polymer material 3 in the present invention is useful as a protective material provided to protect the microstructures 2 from impact during transfer when a plurality of microstructures 2 provided on a substrate 1 are transferred from the substrate 1 by laser irradiation. This protective material is preferably removed after the microstructures 2 are transferred, because this makes it easier to use the microstructures 2 themselves.

[0090] The concept of the present invention can be effectively applied to a transfer method, but can also be applied to a peeling method. For example, a peeling method for peeling off multiple microstructures provided on a substrate from the substrate by laser irradiation, in which at least the spaces between adjacent microstructures are filled with a polymer material, includes a first laser irradiation step of irradiating the microstructures with a laser through the substrate, and a second laser irradiation step of irradiating the polymer material with a laser through the substrate, in which the laser directed to the microstructures in the first laser irradiation step is irradiated on the area corresponding to the microstructures. The components and conditions used in the peeling method can be the same as those used in the transfer method described above.

[0091] Furthermore, the polymer material 3 in the present invention is useful as a protective material provided to protect the microstructures 2 from impact during peeling when a plurality of microstructures 2 provided on a substrate 1 are peeled off from the substrate 1 by laser irradiation. This protective material is preferably removed after peeling of the microstructures 2, as this facilitates the use of the microstructures 2 themselves. On the other hand, the protective material may be used as a temporary or permanent support for the microstructures without being removed after peeling.

[0092] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0093] Example 1 [Preparation of Composite] First, a composite having a structure similar to that of the composite 10 described with reference to Figures 1 and 2 was prepared. In the prepared composite 10, the substrate 1 was a sapphire substrate with a thickness of 700 μm and a diameter of 4 inches. Each of the microstructures 2 was a 0.38 mm square LED chip, mounted on the substrate 1 via a GaN 21. Approximately 50,000 microstructures were arranged on the substrate in a matrix with 75 μm-wide streets sandwiched between them. The polymer material 3 was polyimide, and, as shown in Figures 1 and 2, included at least a portion 31 filling the spaces between adjacent microstructures 2, a portion 32 covering the tops of the microstructures 2, and a portion 32 covering the outside of the microstructures 2. Next, a quartz substrate with the same shape as the substrate was prepared as a receiving substrate. The composite was bonded to the side with the polymer material 3 in contact with it to obtain a laminate. The resulting laminate was fixed by suction to the stage of a laser irradiation device.

[0094] [First Laser Irradiation Step] In this state, a laser beam L1 was irradiated onto a region 12 corresponding to the microstructure 2 from the substrate 1 side of the composite 10, as shown in Fig. 3. The laser beam L1 was an excimer laser with a wavelength of 248 nm and a pulse width of 20 ns, and its energy density (irradiation density) was 1100 mJ / cm ２ By this first laser irradiation step, the minute structure 2 was peeled off from the substrate, but remained in a state where it was not separated from the substrate 1 due to the presence of the polymer material 3.

[0095] 4, the microstructure 2 and the polymer material 3 were irradiated with a laser beam L2. The laser beam L2 was an excimer laser with a wavelength of 248 nm, and its energy density (irradiation density) was 150 mJ / cm. ２ By this second laser irradiation step, the microstructure 1 was separated from the base material 1 and transferred to the receiving substrate.

[0096] After the transfer, the approximately 50,000 microstructures on the receiving substrate were inspected, and no noticeable cracks or chips were found in the microstructures 2 due to the transfer. Fig. 5 shows an optical microscope photograph.

[0097] Example 2 The polymer material 3 was silicone, the laser L2 in the second laser irradiation step was an excimer laser with a wavelength of 248 nm, and the energy density (irradiation density) was 300 mJ / cm ２ The microstructure 2 was transferred from the composite 10 in the same manner as in Example 1, except that the above-mentioned procedure was followed. After the transfer, approximately 50,000 microstructures on the receiving substrate were checked, and no noticeable cracks or chips in the microstructure 2 due to the transfer were found.

[0098] Example 3 The polymer material 3 was an acrylic resin, the laser L2 in the second laser irradiation step was an excimer laser with a wavelength of 248 nm, and the energy density (irradiation density) was 200 mJ / cm ２ The microstructure 2 was transferred from the composite 10 in the same manner as in Example 1, except that the above-mentioned procedure was followed. After the transfer, approximately 50,000 microstructures on the receiving substrate were checked, and no noticeable cracks or chips in the microstructure 2 due to the transfer were found.

[0099] Example 4 The laser L2 in the second laser irradiation step was an excimer laser with a wavelength of 193 nm, and its energy density (irradiation density) was 100 mJ / cm ２ The microstructure 2 was transferred from the composite 10 in the same manner as in Example 1, except that the above-mentioned procedure was followed. After the transfer, approximately 50,000 microstructures on the receiving substrate were checked, and no noticeable cracks or chips in the microstructure 2 due to the transfer were found.

[0100] (Example 5) The laser L2 in the second laser irradiation step was an excimer laser with a wavelength of 308 nm, and its energy density (irradiation density) was 200 mJ / cm ２ Except for this, the microstructure 2 was transferred from the composite 10 in the same manner as in Example 1. When the receiving substrate after the transfer was checked, no cracks or chips in the microstructure 2 due to the transfer were found.

[0101] Example 6 The laser L2 in the second laser irradiation step was an excimer laser with a wavelength of 351 nm, and its energy density (irradiation density) was 200 mJ / cm ２The microstructure 2 was transferred from the composite 10 in the same manner as in Example 1, except that the above-mentioned procedure was followed. After the transfer, approximately 50,000 microstructures on the receiving substrate were checked, and no noticeable cracks or chips in the microstructure 2 due to the transfer were found.

[0102] (Comparative Example) The microstructure 2 was transferred from the composite 10 in the same manner as in Example 1, except that in the first laser irradiation step, the laser L1 was irradiated onto all of the microstructure 2 and the polymer material 3, and the second laser irradiation step was not performed. When the approximately 50,000 microstructures on the receiving substrate after transfer were checked, it was found that cracks had occurred in most of the microstructures 2 due to the transfer. An optical microscope photograph is shown in Figure 6.

[0103] From the above results, it was confirmed that the transfer method of the present invention makes it possible to transfer the minute structure 2 while suppressing the occurrence of cracks and chips.

[0104] Furthermore, in Examples 1 to 6, no debris originating from the polymer material 3 remained on the substrate 1 after transfer.

[0105] This specification includes the following aspects. [1] A transfer method for transferring a plurality of microstructures provided on a substrate from the substrate by laser irradiation, wherein at least the spaces between adjacent microstructures are filled with a polymer material, the transfer method comprising: a first laser irradiation step of irradiating the microstructures with a laser through the substrate; and a second laser irradiation step of irradiating the polymer material with a laser through the substrate, wherein in the first laser irradiation step, the laser directed at the microstructures is directed at an area corresponding to the microstructures. [2] The transfer method according to [1], in which the second laser irradiation step is performed after the first laser irradiation step. [3] The transfer method according to [1] or [2], in which in the second laser irradiation step, a laser is irradiated toward the polymer material and the microstructures. [4] The transfer method according to any one of [1] to [3], in which the first laser irradiation step is performed with an energy density that sufficiently ablates the polymer material. [5] The transfer method according to any one of [1] to [4], wherein the plurality of microstructures are provided on the base material via GaN, and the first laser irradiation step is carried out at an energy density that thermally decomposes GaN. [6] The transfer method according to any one of [1] to [5], wherein the second laser irradiation step is carried out at an energy density that is lower than the energy density that sufficiently ablates the polymer material. [7] The transfer method according to [6], wherein the second laser irradiation step is carried out at an energy density that vaporizes the polymer material. [8] The transfer method according to [7], wherein the second laser irradiation step is carried out at an energy density that can suppress the generation of carbon-based debris derived from the polymer material. [9] The laser irradiation in the first laser irradiation step and the second laser irradiation step is irradiation with an excimer laser with a wavelength of 248 nm, and the energy density of the laser irradiation in the first laser irradiation step is 700 mJ / cm. ２ The energy density of the laser irradiation in the second laser irradiation step is 30 to 500 mJ / cm ２

[10] The transfer method according to any one of [1] to [9], wherein the second laser irradiation step is performed multiple times.

[11] The transfer method according to any one of [1] to

[10] , wherein the base material on which the plurality of microstructures are provided is coated with a polymer material so as to cover the plurality of microstructures.

[0106] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A transfer method for transferring a plurality of microstructures provided on a substrate from the substrate by laser irradiation, wherein at least the spaces between adjacent microstructures are filled with a polymer material, the transfer method comprising: a first laser irradiation step of irradiating the microstructures with a laser through the substrate; and a second laser irradiation step of irradiating the polymer material with a laser through the substrate, wherein in the first laser irradiation step, the laser directed at the microstructures is irradiated onto an area corresponding to the microstructures.

2. The transfer method according to claim 1, wherein the second laser irradiation step is carried out after the first laser irradiation step.

3. The transfer method according to claim 1, wherein in the second laser irradiation step, a laser is irradiated onto the polymer material and the minute structure.

4. A transfer method according to claim 1, wherein the first laser irradiation step is carried out with an energy density that is sufficient to ablate the polymer material.

5. A transfer method according to claim 1, wherein the plurality of microstructures are provided on the base material via GaN, and the first laser irradiation step is carried out with an energy density that thermally decomposes GaN.

6. A transfer method according to claim 1, wherein the second laser irradiation step is carried out at an energy density lower than that at which the polymer material is sufficiently ablated.

7. A transfer method according to claim 6, wherein the second laser irradiation step is carried out with an energy density that vaporizes the polymer material.

8. A transfer method according to claim 7, wherein the second laser irradiation step is carried out with an energy density capable of suppressing the generation of carbon-based debris derived from the polymer material.

9. The laser irradiation in the first laser irradiation step and the second laser irradiation step is irradiation with an excimer laser having a wavelength of 248 nm, and the energy density of the laser irradiation in the first laser irradiation step is 700 mJ / cm ２ The energy density of the laser irradiation in the second laser irradiation step is 30 to 500 mJ / cm ２ 2. The transfer method according to claim 1, wherein 10. The transfer method according to claim 1, wherein the second laser irradiation step is carried out a plurality of times.

11. A transfer method according to claim 1, wherein the substrate on which the plurality of minute structures are provided is coated with a polymer material so as to cover the plurality of minute structures.

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