Die transfer method, loaded die transfer carrier and use thereof

Abstract

The invention provides a method (100) of redistributing singulated grains (1), the method comprising: providing (110) a donor substrate (10) comprising a split foil (11) supporting an array (A) of said grains and providing (111) an acceptor substrate (20) comprising a carrier substrate (21) having a cover layer (25) of a photocurable adhesive composition (26); assembling (120) the split foil onto the acceptor substrate to form a stack (30) with the single granulated grains sandwiched between the split foil and the cover layer of the photocurable adhesive composition; photocuring (130) the photocurable adhesive composition at the singulation lanes (2) between adjacent ones of the singulated grains by providing photon exposure (PE) from the stack of singulated foil sides (31); developing (140) the cover layer of the photocurable adhesive composition by thermal exposure; and separating the foil from the stack release (150).

Description

[0001] Technical Field and Background

[0002] This disclosure relates to a method for transferring a monolithic grain array. Specifically, it involves redistributing a donor grain to a target substrate. This disclosure also relates to a grain transfer carrier loaded with grains for redistribution.

[0003] In the semiconductor industry, wafers with monolithic (divided) die arrays are typically received on UV or thermally released foils. These components are usually transferred according to circuit design, for example, by pick-and-place methods.

[0004] Achieving high spatial density and precision in batch transfer methods is highly relevant to the manufacture of microelectronic devices, such as the manufacture of displays based on micro-LEDs. Furthermore, selective transfer is required to improve yield, for example, to accommodate lost components and allow for repair.

[0005] Although it is possible to transfer directly from epitaxial (also known as epi) wafers using specific laser sources, these processes often require improvements in reducing the release of unwanted debris and / or residues during the transfer and / or in transfer accuracy.

[0006] It is known to transfer dies by means of an intermediate step of transferring the die array to an intermediate carrier. For example, dicing tape or a specific transfer carrier. Undesirable drift of regularly placed micro-components can be replicated during the final laser-transfer of the die to the target substrate.

[0007] Depending on the specific laser die transfer strategy and release method used, the die redistribution steps may vary, but the process typically begins with transferring the die (e.g., a µLED grown on an epitaxial wafer) to a laser-transparent carrier with a sacrificial layer (dynamic release layer, DRL) on its surface. This transfer is usually performed using intermediate transfer tapes to ensure that the die is ultimately oriented on the DRL carrier with its active side away from the glass substrate, ready for flip-chip assembly. Alternatively, for face-up integration (chip-first approach), the intermediate steps can be skipped.

[0008] WO2022 / 186689 discloses the release of laser grains from an intermediate carrier loaded with grains. The intermediate carrier comprises a multilayer stack consisting of three functional layers: a light-absorbing metal layer with a high melting temperature; a molten layer with a melting temperature lower than that of the light-absorbing metal layer; and a polymeric binder having a decomposition temperature closely matched to the melting temperature of the molten metal layer.

[0009] The accuracy of die placement using intermediate transfer solutions is limited by the accuracy of the die being positioned on these transfer carriers. Summary of the Invention

[0010] While the process of using intermediate transfer tape / carriers taught in WO2022 / 186689 offers specific benefits, there is a need to improve overall transfer performance while retaining those benefits. Specifically, this disclosure aims to mitigate even minor issues with positioning accuracy caused by the loading and / or heat treatment of intermediate carriers.

[0011] This disclosure relates to a grain transfer method. Specifically, the method provides the transfer of grains from a source comprising a plurality of monolithic grains to a target. The source may be a dicing foil supporting an array of said grains, or other carriers, such as carriers containing grown grains (e.g., epitaxial wafers), received, for example, from a manufacturing plant. In some embodiments, the target, once loaded with grains, can serve as an intermediate transfer substrate from which the grains in the array can be redistributed, for example, individually, as a subset, or as part of the array, or even as part of the array. Alternatively, the target substrate may be part of a final product.

[0012] The methods disclosed herein comprise at least the following steps: i) providing a donor substrate and a acceptor substrate, the donor substrate comprising or consisting of a donor carrier (e.g., a segmented foil) supporting an array of monolithic grains, the acceptor substrate comprising a carrier substrate having a cover layer of a photocurable adhesive composition. The photocurable adhesive composition may advantageously be a commercially available composition.

[0013] Advantageously, the methods disclosed herein enable the rapid, reliable and accurate transfer of grain arrays to a target substrate, so that the relative positioning of the grains, such as spacing and relative orientation, can remain unchanged.

[0014] The donor substrate can advantageously be a segmented or transfer foil that is generally available, for example, a segmented foil on which an array of individual grains (segmented grains, such as sawn grains) are mounted. Alternatively or additionally, the source can be a carrier that supports an array of components formed or grown thereon. For example, a so-called EPI wafer contains multiple microelectronic components or grains formed thereon.

[0015] The method further includes ii) assembling an array of donors onto a acceptor substrate to form a stack, whereby monolithic grains are sandwiched between the donor substrate and a cover layer of the photocurable adhesive composition. Because the grains adhere to the donor (e.g., a split foil) during contact, relative directional displacement or loss can be mitigated. In some embodiments, contact can be performed in a lamination apparatus, for example, under applied contact pressure. Alternatively or additionally, heat can be applied before and / or during contact to increase the tackiness of the adhesive cover layer. Furthermore, in some embodiments, the method may include measures to reduce the initial adhesive force between the donor and the grains (e.g., to about 10% of the initial adhesive force). For example, depending on the type of donor (e.g., a heat-release foil or a UV-release foil), this measure may include exposure to appropriate heat and / or light. Similarly, the acceptor substrate may be treated to increase the initial tackiness of the photocurable adhesive composition, such as through a soft baking process. Reducing the initial adhesive force between the donor and the grain and / or increasing the initial tack of the photocurable adhesive composition (especially when combined) can increase the accuracy (fidelity) of the transfer array. It should be understood that measures to reduce initial adhesive force and / or increase tack can be performed as separate steps prior to assembly. Alternatively or additionally, one or more of these measures can be performed during assembly.

[0016] The method further includes iii) photocuring the photocurable adhesive composition at the intervals (e.g., cleavage channels) between adjacent monolithic grains in the monolithic grains by providing photon exposure from the donor side of the stack. Depending on the type of photocurable adhesive composition, and particularly according to the photoinitiator contained therein, the exposure typically involves UV exposure. It should be understood that the donor matrix is ​​transparent or at least translucent to light within the frequency range of the activation energy of the photoinitiator contained in the photocurable adhesive. Preferably, the donor transmits at least 10% of the light at the relevant frequency, preferably more, such as at least 20%, preferably at least 50%, even more preferably 50% or even more, such as 60%, 70%, 80%, or even 90% or more.

[0017] Advantageously, many commercially available segmented foils are at least partially transparent within the relevant photocuring bandwidth. By exposing the overlay through the segmented foil, the grains advantageously act as a mask, preventing the photocurable adhesive composition beneath the grains from being exposed. Thus, photocuring can be limited to the region of the overlay corresponding to the spacing between the grains.

[0018] In some embodiments, the method includes one or more chip transfer stages. These steps can be performed when it is desired to perform one or more pre-flipping operations on the component or when the component is placed or received on a substrate with insufficient transparency in the relevant UV range for photocuring the photocurable adhesive. As will be detailed below, these transfer steps can be performed using one or more commercially available transfer substrates / tapes (e.g., UV transfer carriers and / or thermal transfer carriers). Regardless of whether intermediate transfer stages are used, the method typically also includes the following process referred to as iv): developing (140) the overlay layer of the photocurable adhesive composition by applying heat. This development leads to the progression of the thermally initiated curing and / or crosslinking process of the photocurable adhesive initiated by photon exposure of the composition, which also occurs in portions not directly exposed to light. To maximize crosslinking efficiency, this development is preferably applied after photocuring, preferably immediately after photocuring, or even partially during photocuring. To minimize the heat load on the grains, heat is preferably provided preferentially or even specifically via the bottom surface of the stack, for example, from the bottom side of the carrier substrate 21 opposite to the cover layer 25. For example, via a heated bottom plate of a laminator.

[0019] Following development, the process also includes: v) releasing the segment foil from the stack. This release may involve peeling, such as manual peeling or automated release, for example, using a clamp (e.g., a vacuum clamp). If desired, the adhesion between the grain and the donor (e.g., the segment foil or transfer carrier) may be reduced beforehand (e.g., reduced to approximately zero) by one or more of the measures mentioned above (e.g., heat / UV).

[0020] Alternatively, the thermal crosslinking and / or foil release processes can be delayed (e.g., performed externally). Thus, for example, in the manufacture of micro-LED displays, the stack can be considered an intermediate product for later use, as disclosed herein.

[0021] As will be further elaborated in the following description, the methods disclosed herein advantageously mitigate positional accuracy and / or heat treatment problems during heat treatment, while being compatible with industry standards such as heat-release / splitting tapes and UV-release / splitting tapes. Specifically, the inventors have found that the initial photocuring of the adhesive overlay, confined to the area corresponding to the spacers / splitting channels between grains, mitigates grain displacement / drift in subsequent stages, particularly during development. The inventors have found that the photocurable spacers (e.g., splitting channels) between grains act as rigid barriers that substantially restrict or eliminate grain flow / drift on softened or even melted unexposed areas of the photocurable adhesive composition during heat curing (e.g., hard baking).

[0022] In some embodiments, the release of the segmenting foil can be performed at least partially during the development process of the photocurable adhesive composition. The inventors have found that the heat provided during thermal curing can advantageously reduce the adhesive force between the grains and the donor foil. Depending on the type of donor foil, the added heat can at least partially reduce grain adhesion relative to the donor foil, particularly for heat-release-based donors (e.g., heat-release segmenting foils / heat-release tapes).

[0023] To maximize the spatial stability of the grains in the array during transfer, the donor substrate (e.g., a segmented foil) is preferably removed from the stack (e.g., peeled off) after the photocurable adhesive layer has been fully developed (hard baked).

[0024] In some preferred embodiments, the method includes: soft baking a cover layer of the photocurable adhesive composition prior to assembly. Soft baking can increase the viscosity and / or initial tack of the photocurable adhesive composition, for example, by removing a significant portion, most or even substantially all of the volatiles (e.g., solvents) initially contained in the provided cover layer.

[0025] In other or additional preferred embodiments, the method further includes reducing the adhesive force between the monolithized grain and the donor. For example, by providing photonic exposure from the rear side of the donor matrix opposite the grain before and / or during assembly.

[0026] In some preferred embodiments, the receptor includes a release stack disposed on a carrier substrate, the release stack being configured to release one or more grains transferred on the release stack to the target substrate after the release stack is irradiated by a beam (L) passing through the carrier substrate, wherein the release stack comprises:

[0027] - The molten layer, which has a melting temperature,

[0028] - A light-absorbing layer disposed between a carrier substrate and a molten layer, wherein the light-absorbing layer has an absorption coefficient for absorbing light beams, thereby heating the light-absorbing layer, wherein the heated light-absorbing layer is in thermal contact with the molten layer to conduct its heat to the molten layer, thereby raising the temperature of the molten layer above its melting temperature, wherein the melting temperature of the light-absorbing layer is higher than the melting temperature of the molten layer, so that the light-absorbing layer can remain solid while the molten layer is melted by the heat conducted from the light-absorbing layer.

[0029] - A coating layer of a photocurable adhesive composition, which covers the molten layer, wherein

[0030] The temperature during the transfer of the array of monolithic grains from the donor to the acceptor will be kept below the melting temperature of the molten layer. For details regarding the dynamic release stack, including but not limited to the composition and characteristics of the molten layer, the light-absorbing layer, its geometric modifications, and its application in redistribution to a target substrate (e.g., a circuit board), refer to WO2022 / 186689, which is incorporated herein by reference.

[0031] According to another aspect, a loaded grain transfer carrier is provided. In some variations, the grain transfer carrier can be understood as a acceptor substrate as disclosed herein, which is loaded with an array of grains according to the method disclosed herein. The grain transfer carrier includes a carrier substrate having a capping layer formed of a photocurable adhesive composition and an array of monolithic grains, wherein a first portion of the photocurable adhesive composition corresponding to a region below the spacing between adjacent monolithic grains in the monolithic grains is photocured.

[0032] In a preferred variant, the grain transfer carrier comprises a release stack (melt layer / light-absorbing layer / capping layer) as disclosed herein.

[0033] Depending on the application, the portion of the capping layer beneath the grains may not be cured. Typically, for example, in grain redistribution, the capping layer is cured before use (e.g., by development). The use involves at least the following process: redistributing one or more grains transferred to the acceptor substrate to a target location on a product carrier (e.g., a circuit board). For example, by locally triggering the release stack, such as by using a laser or masked irradiation. Attached Figure Description

[0034] These and other features, aspects, and advantages of the apparatus, systems, and methods disclosed herein will be better understood from the following description, the appended claims, and the accompanying drawings, wherein:

[0035] Figure 1 A method 100 for redistributing monolithic grains 1 is schematically illustrated;

[0036] Figures 2A to 2I The various aspects and characteristics of this method at different stages of its development are illustrated;

[0037] Figure 3 The loaded grain transfer carrier 200 is schematically shown;

[0038] Figure 4A The loaded grain transfer carrier 200 is shown;

[0039] Figure 4B The loaded transfer vehicle 200 during use is shown;

[0040] Figure 4C A variant of the loaded grain transfer carrier 200 is shown;

[0041] Figure 5 A to Figure 5 E illustrates various aspects of the method;

[0042] Figure 6A and Figure 6B The experiment details were provided; and

[0043] Figure 7 Further experimental details were provided. Detailed Implementation

[0044] The terminology used to describe particular embodiments is not intended to limit the invention. As used herein, unless the context clearly indicates otherwise, the singular forms “a / an” and “the” are intended to include the plural forms as well. The term “and / or” includes any and all combinations of one or more of the associated listed items. It should be understood that the term “comprises and / or comprising” specifies the presence of the stated feature but does not exclude the presence or addition of one or more other features. It should be further understood that, unless otherwise specified, when a particular step of a method is referred to as following another step, that step may be performed directly after that other step or before performing that particular step, and one or more intermediate steps may be performed. Similarly, it should be understood that, unless otherwise specified, when describing a connection between structures or components, such connection may be established directly or via intermediate structures or components. It should be further understood that the term “consisting essentially of and essentially consists of” as used in the reference materials (e.g., metals, semiconductors, polymers) herein means that other components may be present, provided that such components do not substantially affect the essential properties of the compound or composition. Alternatively or additionally, these terms may be used to indicate the main components, such as where the mass percentage is >90%, >95%, >99%, >99.9%, or 100% (or simply "composed of").

[0045] The invention will be described more fully below with reference to the accompanying drawings, in which embodiments of the invention are illustrated. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments can be described with reference to schematic diagrams and / or cross-sectional views of possible idealized embodiments and intermediate structures of the invention. Throughout the description and drawings, similar numbers refer to similar components. Relative terms and their derivatives should be considered as referring to orientations shown in the figures described subsequently or discussed below. These relative terms are for ease of description and, unless otherwise stated, do not require the system to be constructed or operated in a specific orientation.

[0046] Figure 1 A schematic diagram of an embodiment of a method 100 for republishing monolithic grains as disclosed herein is provided. The method includes at least the following process steps: 110, providing a donor substrate and a acceptor substrate, the donor substrate supporting an array of grains, the acceptor substrate including a carrier substrate having a cover layer of a photocurable adhesive composition; 120, assembling a donor onto the acceptor substrate to form a stack such that monolithic grains are sandwiched between the donor and the cover layer of the photocurable adhesive composition; 130, photocuring the photocurable adhesive composition at intervals between adjacent monolithic grains by providing photon exposure from a rear side of the donor; 140, developing the cover layer of the photocurable adhesive composition by thermal exposure; and 150, releasing the donor substrate from the stack. In some embodiments, such as those shown, the method further includes one or more of the following:

[0047] - 115, Soft bake the overlay of the photocurable adhesive composition prior to assembly, and

[0048] - 112, reducing the adhesion between monolithic grains and the donor.

[0049] The soft baking and / or reduction of 112 adhesive force are provided prior to and / or in combination with the assembly process of 120.

[0050] Figure 2A A cross-sectional side view of the donor substrate 10, as provided in 110 for further processing in this method, is provided. The donor substrate 10 includes a substrate 12 that supports a plurality of monolithic grains 1. The donor is transparent to UV light. From this point onward, an example will be described in detail, such as when the donor is a diced foil. The grains are arranged in an array A (e.g., a 2D array) 10. The substrate can be a diced foil obtained from a factory. The spacing between the grains in the array (w2, see...) Figure 2 F) can be ≤100 μm, for example about 50 μm, 60 μm, or 70 μm or smaller, and this spacing is generally referred to as the slit track and depends, for example, on the width of the saw blade used for slitting. To facilitate adhesion / release of the grains to the slit foil, a dynamic release layer 13 (DRL) is typically included. As is known in the art, the slit foil can be a thermally released foil or a UV-release foil.

[0051] Figure 2BA cross-sectional side view of the acceptor substrate 20 is provided. The acceptor substrate 20 includes at least a carrier substrate 21 and a capping layer 25. The dimensions of the acceptor substrate 20 may depend on the number or size of the grains to be transferred to the acceptor substrate. Typically, the acceptor substrate 20 is configured to receive an entire row A of grains from a slit foil. The capping layer 25 may advantageously be composed of an adhesive composition 26, for example, without an additional layer as shown. The photocurable adhesive composition 26 may be a commercial composition and may be a negative photoresist composition, such as an epoxy-based negative photoresist, such as a SU8-based resist. To allow photocuring of the resist, the carrier substrate is at least partially transparent within a bandwidth encompassing the activation of the photoresist.

[0052] Figure 2C A schematic cross-sectional side view is provided of the donor substrate 10 and acceptor substrate 20 assembled on top of each other to form a stack 30. The stack includes (as illustrated, in top-to-bottom order): the donor substrate 10 (carrier 21 and DRL 13), an array of monolithic grains 1, a capping layer 25, and the carrier substrate 21.

[0053] To improve the contact between the top surface of the cover layer 25 opposite to the carrier substrate 21 and the top surface of the grain opposite to the segmented foil, contact pressure can be applied as indicated by the dashed arrow. For example, by placing the stack in a laminator. To prevent grain displacement, contact force can be maintained during subsequent stages of photocuring 130, which will be referenced to... Figure 2 E and Figure 2 F explains in more detail.

[0054] In example Figure 2D In some embodiments shown, the stacking can occur prior to the soft baking 115 stage of the cover layer 25. As is known in the art, soft baking, such as SU8, can be understood as a heat treatment configured to remove (evaporate) most of the volatile content, such as solvent, in the layer without causing curing of the layer, for example, below the heat curing temperature of the photocurable adhesive composition 26. Soft baking can increase the tackiness of the cover layer 25 and / or structural rigidity, for example, reducing compression of the cover layer 25 due to contact forces. As indicated, the temperature used to achieve the soft baking temperature (T...) SB The heat can be conveniently supplied by a heating plate (HP) (e.g., the heated base plate of a laminator).

[0055] Figure 2 E provides a cross-sectional side view of the stack during photocuring 130 of a photocurable adhesive composition at a slit channel 2 between adjacent monogranules 1 by providing photon exposure of PE from the slit foil side 31 of the stack. As shown, light L can pass through the slit foils 12, 13. See further reference. Figure 2The partial detail view in F best shows that only those areas of the overlay 25 that are not masked by the grains are exposed to light, thus producing the locally photocured portion 26c (see [reference]). Figure 3 C). The light used for initial photocuring can be readily provided using known methods (e.g., a UV source). Advantageously, the PE can be provided, for example, via a transparent window or pore provided in the top plate of the laminator, during the application of contact pressure to the stack.

[0056] Figure 2G A cross-sectional side view of the stack is provided during the development 140 process of the cover layer 25. In some embodiments, such as those shown, the heat for thermal curing can be provided via the bottom side of the stack. For example, as per [reference to...] Figure 2D The same heating plate mentioned. Providing heat for curing from the bottom side (e.g., the base plate of a laminator) reduces the heat load / exposure of the monolithic grains 1.

[0057] Figure 2H A cross-sectional side view of the stack is provided during the release of 150 segments of foil. In one embodiment, for example, the foil may be peeled off as indicated by the dashed arrow.

[0058] Figure 2I This demonstrates how providing UV exposure from the rear side of the segmented foil opposite to the grains can reduce the adhesion between the monolithic grain 10 and the segmented foils 12 and 13.

[0059] Figure 3 A cross-sectional side view of an intermediate grain transfer carrier 200 is provided. This grain transfer carrier can be a product of a method that follows the stage of photocuring 130 on the split track but before hard baking / full curing.

[0060] In some embodiments, the donors (segmented foils) 11, 12 can be removed, for example, by peeling off the reduced adhesive force induced by thermo-optical forces. In other variations, the intermediate grain transfer carrier 200 can be manufactured while the donors are still in place, for example, for later development 140, such as at different locations. Of course, the cover layer 25 of the intermediate grain transfer carrier 200 can be cured.

[0061] It should be noted that, due to the photocuring of the segmentation layer, the adhesive force is shifted from the segmentation foil to the cover layer 25 through thermal curing, and optionally the adhesive force between the 112 monolithic grains and the segmentation foil is reduced, the grains can remain in the proper position throughout the transfer process.

[0062] Figure 4AA modified cross-sectional side view is provided, in which the intermediate grain transfer carrier 200 includes the release stack S. The capping layer 25 is always cured by subsequent photocuring of the trenches between the grains and hard baking during / after removal of the donor substrate.

[0063] The release stack includes: a molten layer 23 having a melting temperature; a light-absorbing layer 24 disposed between the carrier substrate and the molten layer, wherein the light-absorbing layer has an absorption coefficient for absorbing light beams, thereby heating the light-absorbing layer, wherein the heated light-absorbing layer is in thermal contact with the molten layer to conduct its heat to the molten layer, thereby raising the temperature of the molten layer above its melting temperature, wherein the melting temperature of the light-absorbing layer is higher than the melting temperature of the molten layer, so that the light-absorbing layer can remain solid when the molten layer is melted by the heat conducted from the light-absorbing layer; and a cover layer 25 of a photocurable adhesive composition 26 covering the molten layer 23.

[0064] like Figure 4B As indicated, during release, light L passes through the carrier substrate 21 and heats the light-absorbing layer 24. Heat is transferred from the light-absorbing layer 24 to the underlying molten layer 23. After layer 23 melts, the adhesion between the capping layer 25 and the associated grain decreases, for example, due to dewetting between the capping layer 25 and the molten layer 23 via molten droplets 23'. Therefore, for example, under the influence of gravity, the grain 1 can be released onto the bonding area 1001 of the circuit board 1000. Residues associated with the transferred grain on the capping layer 25 can be removed using standard methods.

[0065] In the variant, the molten layer comprises a first metal layer.

[0066] In another or additional variant, the light-absorbing layer comprises a second metal layer.

[0067] It should be understood that one or more grains to be released can be selected and transferred individually (or by subset or by the entire set) by selective irradiation, for example by sequentially irradiating individual grains or a series of grains with a focused beam. Multiple grains can be released simultaneously by using wide-area irradiation.

[0068] In another or yet another variation, the capping layer 25 comprises a polymer-based adhesive, such as a negative photoresist.

[0069] In other variations, the capping layer and the light-absorbing layer have a higher surface energy per unit area than the adhesive layer, wherein, after the molten layer in the release stack of the selected die / module melts, the molten layer mainly adheres to the light-absorbing layer of the release stack, while the adhesive capping layer 25 mainly adheres to the selected die / module 1, wherein the adhesive layer can be transferred to the target 1000 together with the selected die, while the molten layer mainly remains together with a portion of the release stack.

[0070] In other or additional variations, the beam L2 irradiating the release stack is configured to raise the temperature of the molten layer above its melting temperature, but below its evaporation temperature.

[0071] Preferably, the disintegration temperature of the covering layer is higher than the melting temperature of the molten layer, or higher than 300 Kelvin below the melting temperature of the molten layer.

[0072] Preferably, the melting temperature of the molten layer is less than 600 Kelvin, wherein the melting temperature of the light-absorbing layer is at least 100 Kelvin higher than the melting temperature of the molten layer.

[0073] For examples of suitable compositions of the molten layer 23 and the light-absorbing layer 24, refer to WO2022 / 186689.

[0074] Preferably, one or more layers in the release stack are patterned prior to the photoinduced release of one or more grains to separate the grains. Grain separation advantageously reduces lateral adhesion between grains, particularly via a cured adhesive overlay.

[0075] Figure 4C A loaded grain transfer carrier 200 is shown, wherein the grains have been separated by removing portions 27 between adjacent grains of layer 25 (e.g., by etching). The removed portions may coincide with previously photocured areas, but do not necessarily need to. Removal of additional material (under partial etching) or less material (e.g., by a focused ion beam) is also anticipated. Of course, corresponding areas of one or more of the molten layer 23 and the light-absorbing layer 24 can also be removed to further separate the grains. The inventors have found that localized removal of layer 25 is sufficient to mitigate the adverse effects of lateral adhesion on transfer fidelity.

[0076] In a variant, the method includes a prior transfer process to transfer grains / assemblies from the source to form a suitable donor matrix.

[0077] In another or additional variation, the method includes two (or more) prior transfer processes to transfer grains / assemblies from a source to form a suitable donor matrix.

[0078] A single prior transfer process may be particularly relevant if the component / die is supplied on a carrier whose transparency is insufficient to allow for photopolymerization processes as disclosed herein. For example, when the die / component is supplied on a so-called epitaxial wafer. Alternatively or additionally, a single prior transfer process may be particularly relevant if die flipping is anticipated (e.g., in the case where a die on the original source is formed or set with the wrong side facing up).

[0079] When the grains are correctly oriented (and when the transfer carrier is selected to have sufficient UV transparency), the resulting stack can be used directly as a donor matrix (see [link to documentation]). Figure 1 Phase 110 in the middle.

[0080] Figure 5 A method comprising one or more intermediate transition stages is shown. Figure 4A Multiple grains 1 formed on an epitaxial (EPI) wafer are shown. For illustrative purposes, the grains on the original substrate 5 (epithelial wafer) are held in place by a common release layer 5r. To track grain orientation, the top side 5t of the grain is marked. In the next step, a first intermediate transfer carrier 90 (e.g., thermal release tape) is positioned on top of the grain. The carrier 90c with the transfer tape, the adhesive 90a of the transfer tape, and the grain are stacked (in top-to-bottom order), such that the adhesive 90a contacts the top of the grain ( Figure 2B After removing the original carrier, the die was transferred 102 to the tape ( Figure 5 C). From this point onward, the transfer tape can be used as a donor in a method for redistributing monolithic grains. Alternatively, for example, if another transfer is desired (e.g., to reorient the assembly), the process can continue via a subsequent transfer 104 of the grains from the first intermediate transfer carrier 90 to the second intermediate transfer carrier 92, thereby flipping the grains and forming a donor matrix. For the transfer of the assembly, the second intermediate transfer carrier 92 is positioned over the source to form a stack, wherein the top of the assembly contacts the adhesive layer (see [link to documentation]). Figure 5 D and Figure 5 E). When the adhesive force (z) of the second intermediate carrier exceeds the adhesive force (y), removing the first substrate 90 will cause the grain to be transferred 104 to the second intermediate carrier. It should be noted that the grain orientation is hereby reversed (e.g., Figure 5 (As indicated in E). It should be understood that the prior transfer process may include another stage in the transfer / flip phases as discussed herein.

[0081] Similar to the description above, the prior transfer processes 102, 104 may include the following steps: reducing the adhesion between the monolithic grain and the current carrier before peeling off the current carrier (e.g., by UV exposure in the case of UV transfer tape, or by heat treatment in the case of thermal transfer tape).

[0082] The inventors have discovered that a practical working configuration for a dual prior transfer process can involve using a UV transfer tape as a first intermediate carrier substrate and a thermal transfer tape as a second intermediate carrier substrate.

[0083] It should be understood that the release temperature of the last intermediate transfer matrix is ​​preferably below the soft baking temperature of the photocurable adhesive and above the hard baking temperature of the photocurable adhesive. Preferably, the release temperature of the donor matrix overlaps with the hard baking temperature (most preferably ±°C). In this way, the relative positions of the grains during the redistribution from the donor to the acceptor are fixed by at least one adhesive.

[0084] Figure 6 and Figure 7 Experimental details were provided.

[0085] Figure 6A and Figure 6B The experimental details are shown, in which Figure 6A Micrographs (scale bar 500 μm) are provided, showing a portion of a grain array transferred from the donor to the acceptor according to the method disclosed herein, i.e., with photocurable intervals between adjacent grains 1, and... Figure 6B A comparative example is provided where there is no photocuring interval between adjacent grains. As can be seen, the grains transferred according to the disclosed method maintain a regular column, while the transfer accuracy is lower in the absence of photocuring.

[0086] Figure 7 A series of loaded grain transfer carriers are shown. For each carrier, the source (epitaxy wafer) contains >50,000 grains arranged in a regular array. The carriers have been manufactured in a variation of the process involving a two-stage intermediate grain transfer (source-intermediate 1-intermediate 2-target). Intermediate carrier 1 is a commercial UV transfer tape, and intermediate carrier 2 is a commercial thermal transfer tape, both of which have high adhesion. For each carrier, the overlay and photocurable adhesive composition have been photocured prior to the final transfer from the second intermediate carrier.

[0087] The differences between the depicted carriers lie in the degree to which the initial adhesive strength of the UV transfer tape and thermal transfer tape decreases before transfer. For the sample in the upper left, the adhesive strength of both the UV and thermal tapes decreases below the initial tack of the receiving substrate. For the remaining samples, the degree of decrease gradually diminishes. The amount of effectively transferred grains correlates with the level of adhesive strength reduction: from only one grain lost (from >50,000) to approximately half the grains lost without prior adhesive strength reduction.

[0088] For clarity and conciseness, features are described herein as part of the same or separate embodiments; however, it should be understood that the scope of the invention can include embodiments having all or some of the described features. For example, while an embodiment for loading an intermediate die transfer carrier 200 is shown, those skilled in the art who benefit from this disclosure will envision alternative methods to achieve similar functionality and results. Of course, it should be understood that any of the above embodiments or processes can be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages. It should be understood that this disclosure benefits from providing high fidelity in the transfer of individual dies, such as in micro-LED displays, offering specific advantages for device fabrication and can generally be applied to any application with high-density microelectronic components (dies).

[0089] In interpreting the appended claims, it should be understood that, unless specifically stated otherwise, the word "comprising" does not exclude the presence of other components or actions besides those listed in a given claim; the word "a" preceding a component does not exclude the presence of a plurality of such components; any reference numerals in the claims do not limit their scope; several "means" may be represented by the same or different items or implementations of structure or function; any of the disclosed means or portions thereof may be combined together or divided into other parts. Where one claim refers to another, this may indicate synergistic advantages achieved by combining their features. However, the mere fact that certain measures are recited in mutually different claims does not indicate, nor can such a combination of measures be used advantageously. Therefore, embodiments of the invention may include all working combinations of the claims, wherein, in principle, each claim may refer to any preceding claim unless the context explicitly excludes it.

Claims

1. A method (100) for redistributing monolithic grains (1) from a donor matrix, the method comprising: i) Provide (110) a donor substrate (10) and provide (111) a acceptor substrate (20), the donor substrate (10) supporting the array (A) of the grains, the acceptor substrate (20) comprising a carrier substrate (21) having a cover layer (25) of a photocurable adhesive composition (26). ii) Assemble (120) the donor substrate (10) onto the acceptor substrate to form a stack (30) such that the monolithic grains are sandwiched between the donor substrate and the cover layer of the photocurable adhesive composition; iii) Photocurable adhesive composition is photocured at the interval (2) between adjacent monogranules in the monogranules by providing photon exposure (PE) from the rear side (31) of the donor matrix opposite to the grain (130). iv) Developing the coating layer of the photocurable adhesive composition by heat exposure (140); and v) Release (150) the donor substrate from the stack.

2. The method of claim 1, further comprising, prior to i): Provide (100) the original substrate (5) supporting the grains in the array. Position the first intermediate carrier (90) on top of the grain. After the original carrier (5) is removed, the grain is transferred (102) to the first intermediate transfer carrier (90), thereby flipping the grain and forming the donor matrix.

3. The method of claim 1, further comprising, prior to i): Provide (100) the original substrate (5) supporting the grains in the array. The grain is transferred (102) to a first intermediate transfer carrier (90), thereby flipping the grain. The grain is transferred (104) from the first intermediate transfer carrier (90) to the second intermediate transfer carrier (92), thereby flipping the grain and forming the donor matrix.

4. The method as claimed in any of the preceding claims, wherein the release (150) of the donor matrix is ​​performed during the development (140) of the photocurable adhesive composition.

5. The method of claim 1 or 2, further comprising: The cover layer of the photocurable adhesive composition is soft-baked (115) prior to the assembly (120).

6. The method as described in any of the preceding claims, further comprising: (112) The adhesion between the monolithic grains and the donor matrix is ​​reduced by exposing the donor to heat exposure and / or UV exposure before and / or during the assembly.

7. The method of any one of the preceding claims, wherein, The receptor (20) includes a release stack (S) disposed on the carrier substrate (21), the release stack being used to release one or more of the grains transferred to the release stack to the target substrate (90) after the release stack is irradiated by a beam (L) passing through the carrier substrate (21), wherein the release stack comprises: The molten layer (23) has a melting temperature (Tm23). A light-absorbing layer (24) is disposed between the carrier substrate and the molten layer, wherein the light-absorbing layer has an absorption coefficient for absorbing light beams, thereby heating the light-absorbing layer, wherein the heated light-absorbing layer is in thermal contact with the molten layer to conduct its heat to the molten layer, thereby raising the temperature of the molten layer above its melting temperature, wherein the melting temperature of the light-absorbing layer is higher than the melting temperature of the molten layer, such that the light-absorbing layer remains solid when the molten layer is melted by the heat conducted from the light-absorbing layer. The photocurable adhesive composition (26) has a cover layer (25) that covers the molten layer (23), wherein... The temperature during the transfer of the array of monolithic grains from the donor to the acceptor is kept below the melting temperature of the molten layer (23).

8. The method of any of the preceding claims, wherein the photocurable adhesive composition (26) comprises a negative photoresist.

9. The method of any of the preceding claims, wherein the photocurable adhesive composition (26) is an epoxy-negative photoresist.

10. The method of any of the preceding claims, wherein the photocurable adhesive composition (26) comprises SU8.

11. A loaded grain transfer carrier (200) comprising a carrier substrate (21) having a capping layer (25) formed of a photocurable adhesive composition (26) and an array (A) of monolithic grains (1), wherein, A first portion of the photocurable adhesive composition (26) is photocured (26c), the first portion corresponding to the gap below the dividing channel (2) between adjacent monogranules in the monogranules (1), wherein the photocured gap acts as a rigid barrier that can substantially resist the flow / drift of the grains during thermocuring.

12. The die transfer carrier of claim 11, wherein the carrier substrate (20) comprises a transparent carrier (21) and a release stack (S) disposed on the carrier, the release stack being configured to release one or more of the dies supported on the release stack to a target substrate (90) after the release stack has been irradiated by a light beam (L) passing through the transparent carrier, wherein the release stack comprises: The molten layer (23) has a melting temperature (Tm23). A light-absorbing layer (24) is disposed between the transparent carrier and the molten layer, wherein the light-absorbing layer has an absorption coefficient for absorbing light beams, thereby heating the light-absorbing layer, wherein the heated light-absorbing layer is in thermal contact with the molten layer to conduct its heat to the molten layer, thereby raising the temperature of the molten layer above its melting temperature (Tm13), wherein the melting temperature (Tm24) of the light-absorbing layer is higher than the melting temperature of the molten layer, such that the light-absorbing layer remains solid when the molten layer is melted by the heat conducted from the light-absorbing layer, and The covering layer (25) covers the molten layer (23).

13. The grain transfer carrier as described in any one of claims 11 to 12, wherein the photocurable adhesive composition (26) is an epoxy-negative photoresist, preferably wherein the photocurable adhesive composition (26) comprises SU8.

14. The die transfer carrier according to any one of claims 11 to 13, wherein the die is a micro LED semiconductor element.

15. Use of a die transfer carrier as claimed in any one of claims 11 to 14 in the manufacture of a microelectronic device, such as a micro LED display, the use comprising redistributing one or more of the dies transferred to a cover layer (25) of a carrier substrate (21) to a target location on a product carrier.

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