Method for transferring an optoelectronic device

Abstract

The invention relates to a method for transferring an optoelectronic device from a donor substrate to a receiver substrate (2, 2a, 2b, 2c) comprising protruding copper patterns (21). The device (100a, 100b) is joined to the receiver substrate (2, 2a, 2b, 2c) by means of the protruding copper patterns (21) having a polished upper surface (212). The device (100a, 100b) is then detached from the donor substrate, for example by laser ablation. The protruding copper patterns (21) are advantageously formed on a seed layer (20) which can be used for restoring contact with the device (100a, 100b).

Description

[0001] "Method for transferring an optoelectronic device"

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of optoelectronic technologies. Its particularly advantageous application is the mass transfer of optoelectronic devices, for example GaN-based light-emitting diodes.

[0004] STATE OF THE ART

[0005] To create a self-emissive display screen comprising a plurality of RGB (Red Green Blue) pixels emitting their own light, various LEDs (Light Emitting Diodes) are typically assembled on a display substrate, which may include control electronics. The LEDs are generally formed on a donor or growth substrate and then possibly individualized—that is, separated from one another—before being transferred to the display substrate or a receiving substrate. Not all LEDs from the donor substrate are necessarily transferred to the receiving substrate.

[0006] One solution for transferring these LEDs involves assembling the LEDs from the donor substrate with a copper layer from the recipient substrate using direct Cu-Cu bonding. Each LED typically includes a copper pad that is brought into contact with the copper layer of the recipient substrate. A bond is formed between the copper pad and the copper layer, for example, by a thermocompression process. The LED is then detached from the donor substrate, for example, by laser ablation.

[0007] The paper "Wafer-level hybrid bonding technology with copper / polymer co-planarization, M. Aoki et al., 2010 IEEE International 3D Systems Integration Conference (3DIC)" describes a solution using hybrid copper-polymer bonding between two substrates. In this solution, each substrate has juxtaposed copper-based and polymer-based regions. The polymer-based regions of both substrates are aligned with each other, and the copper-based regions of both substrates are aligned with each other. The bonding is then achieved through polymer-to-polymer and copper-to-copper bonding at the corresponding regions. This type of bonding, involving materials of different natures, is called hybrid bonding. In practice, this solution requires a very clean surface with very low roughness. This makes the process more complex and expensive, and poorly suited, if at all, for localized device transfer.

[0008] The present invention aims to at least partially overcome the drawbacks of the solutions mentioned above.

[0009] In particular, one object of the present invention is to provide an industrial method for the localized transfer of an optoelectronic device. Another object is to provide a method for multiple transfers, that is, from a single donor substrate to several recipient substrates.

[0010] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated.

[0011] SUMMARY

[0012] To achieve the objectives mentioned above, one object of the invention relates to a method of transferring at least one optoelectronic device from a first substrate called donor to a second substrate called receiver.

[0013] The process includes at least the following steps:

[0014] • provide the donor substrate bearing at least one optoelectronic device, at least one optoelectronic device comprising at least one copper pad,

[0015] • provide the receiving substrate having a so-called receiving face,

[0016] • to form a germination layer on the receiving face of the substrate, the germination layer being copper-based,

[0017] • form on the germination layer a mask defining openings exposing the germination layer, the openings having a height hsi along a so-called vertical direction,

[0018] • fill the openings with a copper deposit,

[0019] • Remove the mask to reveal copper patterns protruding from the germination layer,

[0020] • Preferably, but optionally, perform a mechano-chemical polishing on the copper motifs so that the copper motifs have a polished upper surface, then

[0021] • assemble at least one optoelectronic device with the receiving substrate by bonding at least one copper pad to the upper surface – preferably polished – of at least one copper motif,

[0022] • Detach at least one optoelectronic device from the donor substrate. Advantageously, copper patterns protruding from the nucleation layer are formed. This facilitates the localized transfer of devices. The copper pad of a device to be transferred can be brought into contact with a copper pattern of the receiving substrate without the copper pad of the neighboring device touching the receiving substrate. Only the device to be transferred is then effectively assembled to the receiving substrate via the protruding copper pattern. The donor substrate typically carries a multitude of protruding devices, separated from one another, and having distal faces substantially contained in the same plane. The method according to the invention makes it possible to transfer a small number of these devices without the other, non-transferred devices touching the receiving substrate.The process according to the invention also allows for multiple transfers, for example by repeating the transfer operation to deposit other devices from the donor substrate to other areas of the receiving substrate or to other receiving substrates.

[0023] Furthermore, the process advantageously allows for the upper surface of the protruding copper motif to be polished after the mask used to form the motif is removed. The polishing of the copper motifs and the assembly of the device(s) are thus performed consecutively, without any intermediate step that could contaminate the upper surfaces of the copper motifs. This results in a clean surface finish with perfectly controlled roughness on the upper surfaces of the copper motifs. The height of the protruding copper motifs is also precisely controlled. Such conditions facilitate assembly, particularly during multiple transfers. Various industrial assembly processes, such as thermocompression bonding, can therefore be advantageously considered.Advantageously, polishing is performed on a surface free of material heterogeneity, unlike the copper / resin or copper / dielectric surfaces used in hybrid bonding processes. This facilitates polishing, and roughness is better controlled. Furthermore, it prevents contamination of the polishing equipment and / or the surface of the copper patterns. Additionally, polishing avoids the "dishing" phenomenon, where the copper patterns are recessed relative to the adjacent resin or dielectric surface, which is particularly detrimental to a subsequent bonding step involving a small number of devices among the multitude of devices on the donor substrate.

[0024] The method according to the present invention is particularly suited to the localized transfer of optoelectronic devices onto a receiving substrate comprising metallic contacts and tracks, for example, a screen substrate including pixel control electronics. Another aspect of the invention relates to a device comprising a receiving substrate, a copper-based germination layer on the surface of said receiving substrate, and copper motifs projecting from said germination layer, said copper motifs preferably having a polished upper surface, said germination layer being exposed to air between said copper motifs.

[0025] BRIEF DESCRIPTION OF THE FIGURES The aims, objects, features, and advantages of the invention will become clearer from the detailed description of embodiments thereof, which are illustrated by the following accompanying drawings in which:

[0026] Figures 1 to 15 schematically illustrate steps in a transfer process according to an embodiment of the present invention. In particular, Figures 1 to 7 schematically illustrate steps in the formation of copper patterns protruding from a receiving substrate, with or without structuring of the receiving substrate. Figures 8 to 11 schematically illustrate a first transfer of optoelectronic devices onto the receiving substrate. Figures 12 to 14 schematically illustrate a second transfer of optoelectronic devices onto the receiving substrate. Figure 15 schematically illustrates structuring of the receiving substrate after the transfer of the optoelectronic devices onto the receiving substrate.

[0027] Figures 16 to 29 schematically illustrate steps in a transfer process according to another embodiment of the present invention. In particular, Figures 16 to 22 schematically illustrate steps of transfer and re-establishment of contact on a receiving substrate comprising buried metallic tracks, according to a first embodiment. Figures 23 to 29 schematically illustrate steps of transfer and re-establishment of contact on a receiving substrate comprising buried metallic tracks, according to a second embodiment. The drawings are given by way of example and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions of the various layers and parts of the transfer structures and LEDs are not necessarily representative of reality.

[0028] DETAILED DESCRIPTION

[0029] Before undertaking a detailed review of embodiments of the invention, it is recalled that the invention, according to its first aspect, includes in particular the following optional features which may be used in combination or alternatively:

[0030] According to one example, the process further comprises, after removal of the mask and before assembly of said at least one optoelectronic device with said receiving substrate, a mechano-chemical polishing of said copper motifs such that the upper surface of said copper motifs is polished. The roughness of the polished upper surface is typically less than 5 nm, preferably less than 1 nm.

[0031] In one example, the process further includes structuring the germination layer after detaching at least one optoelectronic device. Structuring the germination layer typically allows for the electrical isolation of the optoelectronic devices from each other. In one example, the germination layer is structured to form conductive metallic tracks using this layer. These metallic tracks can connect separate copper patterns and / or copper patterns and electrical contacts of the receiving substrate. The electrical contacts of the receiving substrate can be embedded within the substrate or placed on its surface. This structuring step is performed after the optoelectronic devices have been transferred. This prevents the copper patterns from being contaminated before the optoelectronic devices are bonded.This helps maintain the integrity of the germination layer during bonding. The mechanical strength of the copper patterns held by the germination layer is thus optimized for bonding.

[0032] In one example, the process further includes structuring the nucleation layer after mask removal and preferably before chemical polishing. As before, structuring the nucleation layer electrically isolates the optoelectronic devices from each other. It also allows for the formation of metallic tracks and / or contacts on the surface of the receiving substrate. This structuring step is performed before assembling the optoelectronic device(s) onto the receiving substrate and typically before polishing the copper patterns. This eliminates any potential contamination, related to the structuring process, on the surface of the copper patterns for bonding the optoelectronic devices. Furthermore, it avoids exposing the optoelectronic devices during the structuring step. This eliminates the need for a separate protection step for the optoelectronic devices prior to structuring the nucleation layer.

[0033] In one example, the openings are filled by electrochemical copper deposition. In another example, the bonding is achieved by thermocompression at a temperature between 200 and 400°C. This bonding process is compatible with mass transfer on industrial transfer equipment.

[0034] In one example, the donor substrate carries a plurality of optoelectronic devices, and only some of these devices are assembled onto the receiving substrate and detached from the donor substrate. This process is thus implemented for the localized transfer of optoelectronic devices onto the receiving substrate. The donor substrate can be reused to transfer other optoelectronic devices, for example, to another area of ​​the same receiving substrate or to a different receiving substrate. The optoelectronic devices to be transferred are typically located between optoelectronic devices intended to remain on the donor substrate. This results in a lower density of optoelectronic devices on the receiving substrate than the initial density of optoelectronic devices on the donor substrate.

[0035] In one example, the receiving face of the receiving substrate includes at least one metallic track. In another example, the germination layer forms a connection with said at least one metallic track. The germination layer can be used as a contact to connect the optoelectronic device to the metallic track of the receiving substrate.

[0036] In one example, the method further comprises structuring the germination layer, said structuring being configured such that at least one metallic track of the receiving substrate is connected to at least two optoelectronic devices via at least two copper motifs protruding from the structured germination layer. The germination layer is typically structured as a track on the surface of the receiving substrate, said track connecting two protruding copper motifs. The at least one metallic track of the receiving substrate is typically at least partially embedded in the receiving substrate. For example, it may be flush with the surface of the receiving substrate. The at least one metallic track of the receiving substrate can typically control two devices identically. This allows for device redundancy, for example, redundancy of LEDs at the pixel level of a display screen.

[0037] As an example, the at least one copper motif, after polishing, has a height h2if greater than 200 nm in the vertical direction. This prevents a device near the device to be transferred onto the at least one copper motif from touching the germination layer or the surface of the receiving substrate.

[0038] As an example, at least one copper motif has a characteristic dimension I21 less than or equal to 10 pm along a so-called horizontal direction, perpendicular to the vertical direction. Such copper motifs are suitable for transferring micro-devices, such as micro-LEDs or LEDs in the form of microwires or nanowires.

[0039] As an example, at least one optoelectronic device is a light-emitting diode (LED) having on one face a first contact formed by at least one copper pad, and a second contact on a second face. The second face is typically opposite the first face in the vertical direction.

[0040] According to one example, the process further comprises, after decoupling of at least one optoelectronic device, the formation of a transparent conductive layer on the second contact, said transparent conductive layer being electrically isolated from the nucleation layer bearing at least one copper motif connected to the first contact.

[0041] In one example, the receiving face of the receiving substrate comprises a first metallic track connected to the first contact via the germination layer, and a second metallic track connected to the second contact via the transparent conductive layer. All contacts typically occur at the receiving face of the receiving substrate, i.e., the "front face".

[0042] According to one example, the first metallic track is connected to the first contact via a first portion of the germination layer.

[0043] In one example, the transparent conductive layer is in direct contact with the second metallic track.

[0044] In another example, the second metal track is connected to the second contact via a second portion of the germination layer. This second portion of the germination layer is typically sandwiched between the transparent conductive layer and the second metal track.

[0045] According to one example, the separation of at least one optoelectronic device from the donor substrate is done by localized laser ablation.

[0046] According to one example, the germination layer includes at least a copper-based surface layer as well as an anchoring layer and / or a barrier layer.

[0047] In one example, the germination layer is structured as conductive metallic tracks connecting at least two distinct copper motifs and / or connecting copper motifs and electrical contacts of the receiving substrate. In another example, the receiving substrate includes at least one metallic track, and the germination layer forms a connection with said at least one metallic track.

[0048] According to one example, the device further includes optoelectronic devices arranged on and in electrical contact with the copper patterns.

[0049] Unless otherwise required, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and without limitation, so as to form another embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0050] In the present invention, the method is particularly dedicated to the transfer of devices with micrometer dimensions such as light-emitting diodes (LEDs). Individual LEDs typically have dimensions, when projected onto an xy basis plane, ranging from a few hundred nanometers to a few micrometers or a few tens of micrometers.

[0051] The invention can be implemented more broadly for various optoelectronic devices. For example, the invention can be implemented in laser devices, photovoltaic devices, or detection devices, such as photodiodes.

[0052] Unless explicitly stated otherwise, it is specified that, within the framework of the present invention, the relative arrangement of a third layer interposed between a first layer and a second layer does not necessarily mean that the layers are directly in contact with each other, but rather means that the third layer is either directly in contact with the first and second layers, or separated from them by at least one other layer or element. Thus, the terms and phrases "to rest upon" and "to cover" or "to re-cover" do not necessarily mean "in contact with".

[0053] The steps of the process as claimed are understood in a broad sense and may possibly be carried out in several sub-steps.

[0054] In this patent application, the terms "light-emitting diode," "LED," or simply "diode" are used synonymously. An "LED" may also refer to a "micro-LED" or even a smart LED, where applicable.

[0055] A substrate, layer, or device "based" on a material M is understood to be a substrate, layer, or device comprising only that material M, or that material M and possibly other materials, for example, alloying elements or dopant elements. Thus, a GaN-based diode typically comprises GaN and alloys of AIGaN or InGaN.

[0056] A coordinate system, preferably orthonormal, comprising the x, y, and z axes is shown in the attached figures. The vertical direction is taken along the z-axis. The horizontal direction is taken in the xy-plane.

[0057] In this patent application, the terms thickness for a layer and height for a structure or device will be preferred. Thickness is measured along a direction normal to the principal plane of extension of the layer, and height is measured perpendicular to the xy basis plane. Thus, a layer typically has a thickness along the z-axis when it extends primarily along an xy plane, and a projecting element, such as a motif or device, has a height along the z-axis. The relative terms "on," "under," and "below" preferentially refer to positions measured along the z-direction.

[0058] Dimensional values ​​are understood to be within manufacturing and measurement tolerances. Roughness values ​​typically correspond to the root mean square roughness of the surface (Rq) or the arithmetic roughness (Ra).

[0059] The terms "approximately," "about," and "on the order of" mean, when referring to a value, "within 10%" of that value, or, when referring to an angular orientation, "within 10°" of that orientation. Thus, a direction approximately normal to a plane means a direction at an angle of 90±10° to the plane.

[0060] One object of the invention is to transfer an optoelectronic device onto a receiving substrate, for example a screen support, via protruding copper patterns. One principle of the invention consists of combining the polishing of the protruding copper patterns with the bonding of the devices.

[0061] Figures 1 to 7 illustrate more specifically the formation of copper patterns on the receiving substrate 2, 2a, 2b, 2c.

[0062] As illustrated in Figure 1, a receiving substrate 2, 2a, 2b, 2c is provided. The receiving substrate 2, 2a, 2b, 2c can be glass-based or silicon-based. It can be solid. Alternatively, it can include embedded metallic traces, for example, interconnects formed by a so-called "back-end" stack comprising a succession of dielectric and conductive layers. The receiving substrate 2, 2a, 2b, 2c can also include control electronics, for example, transistor-based electronics.

[0063] As illustrated in Figure 2, a copper-based germination layer 20 is formed on the surface 201 of the receiving substrate 2, 2a, 2b, 2c. This germination layer 20 comprises at least one surface copper-based layer 20c. The germination layer 20 can comprise different layers, for example, an adhesion layer 20a and a barrier layer 20b. Various adhesion layer / barrier layer pairs 20a / 20b are known to be possible, for example, Ti / TiN or TiN / Ti or Ta / TaN or TaN / Ta. The individual layers 20a, 20b, 20c of the germination layer 20 can be formed by physical vapor deposition (PVD).

[0064] As illustrated in Figure 3, a mask 30 is formed, typically by photolithography, on the surface of the seed layer 20. This mask 30 can be made of a photosensitive resin. The mask 30 includes apertures 31 defining the copper patterns to be formed. The surface of the seed layer 20 is exposed through the apertures 31. The apertures 31 have a height hsi on the order of a few tens to a few hundred nanometers or a few micrometers, which typically corresponds to the thickness of the mask layer 30. As illustrated in Figure 4, the apertures are then filled with a copper deposit to form the copper patterns 21. The copper deposit is preferably an electrochemical deposit, allowing the copper to be deposited in a localized manner only within the apertures, on the exposed surfaces of the copper-based seed layer.During electrochemical deposition, the seed layer 20 is maintained at a specific electrical potential, enabling copper deposition. This makes the copper deposition selective, as the copper is actually deposited within the openings 31 and not on the surface of the electrically non-conductive mask 30. This copper deposition is configured so that the height h2i of the copper motifs 21 is less than the height hsi of the openings. This allows the formation of copper motifs 21 whose lateral dimensions, in the xy plane, correspond to the lateral dimensions of the openings. As illustrated in Figure 5, after the copper has been deposited in the openings, the mask 30 is removed, for example, by reducing plasma, oxygen-based plasma, or with a solvent. This allows the formation of copper motifs 21 that protrude from the seed layer 20. At this stage, the copper motifs 21 have a height h2i along the z-axis and a characteristic lateral dimension I21 along the y-axis.The characteristic lateral dimension I21 is typically less than or equal to 10 pm, for example 8 pm, or even on the order of a micrometer.

[0065] As illustrated in Figure 6, as an optional step, structuring 200a of the germination layer 20 can be performed after mask removal. This structuring 200a typically isolates the copper motifs 21 from each other. The structuring 200a can be carried out by photolithography and etching of the germination layer 20. This creates areas exposing the surface 201 of the receiving substrate 2, 2a, 2b, 2c between the copper motifs 21. Structuring 200a of the germination layer 20 before transferring the devices prevents damage or contamination of the devices during structuring. A protective layer for the devices prior to structuring is not required. This optimizes the number of process steps.

[0066] The following steps, illustrated in Figures 7 to 14, are nevertheless described without structuring the germination layer 20. The integrity of the germination layer 20 is preserved during these steps. This improves the mechanical strength of the copper motifs 21 on the receiving substrate 2, 2a, 2b, 2c. The anchoring of the copper motifs 21 in the continuous germination layer 20 is optimized.

[0067] As illustrated in Figure 7, a chemical-mechanical polishing (CMP) process is performed on the surface of the copper motifs. This results in a polished upper surface with controlled roughness. The roughness of the upper surface is preferably less than or equal to 3 nm after CMP polishing. This allows for bonding processes requiring a low surface roughness, such as thermocompression bonding. The height h2if of the copper motifs is preferably greater than or equal to 200 nm after CMP polishing. The angles of the copper motifs may be more or less rounded after CMP polishing, as illustrated in Figure 7. This does not affect the function of the copper motifs, which are intended to receive devices from a donor substrate. More or less rounded angles of the copper motifs may indicate implementation of the process according to the invention.After CMP polishing, a receiving substrate 2, 2a, 2b, 2c comprising protruding copper motifs 21, suitable for receiving devices from a donor substrate, is advantageously formed. Figures 8 to 11 illustrate in particular a first transfer of optoelectronic devices 100 from a donor substrate 1 to a receiving substrate 2, 2a. In this example, the receiving substrate 2, 2a is bulky. The density of copper motifs 21 in the receiving substrate 2, 2a is lower than the density of optoelectronic devices 100 in the donor substrate 1. The pitch r1 between two optoelectronic devices 100 in the donor substrate 1 can be on the order of a few micrometers, for example, on the order of 5 pm. The pitch r2 between two motifs 21 of copper of the receiving substrate 2, 2a can be on the order of a few tens of micrometers, for example on the order of 40 pm.Therefore, only some optoelectronic devices 100a from the donor substrate 1 are actually transferred to the recipient substrate 2, 2a after this first transfer. Some optoelectronic devices 100b remain on the donor substrate 1 after the transfer. These optoelectronic devices 100b are typically located between the positions of the optoelectronic devices 100a that were transferred.

[0068] As illustrated in Figure 8, a donor substrate 1 bearing optoelectronic devices 100 is brought into contact with the recipient substrate 2, 2a. The donor substrate 1 is typically the substrate on which the optoelectronic devices 100 are formed, for example, by epitaxy. It may be silicon-based or sapphire-based. It may have been partially trimmed to reduce its thickness, for example, to facilitate the alignment and transfer of the optoelectronic devices 100 onto the copper motifs 21 of the recipient substrate 2, 2a. A sacrificial layer 10 is preferably intercalated between the donor substrate 1 and the optoelectronic devices 100. This facilitates the release of the optoelectronic devices 100 after they have been bonded to the copper motifs 21 of the recipient substrate 2, 2a. Each of the optoelectronic devices 100 includes a copper pad 12 at its end.The donor substrate 1 is rotated so that the copper pads 12 are opposite the copper patterns 21 of the receiving substrate 2, 2a.

[0069] As illustrated in Figure 9, after alignment of the pads 12 and the motifs 21, a Cu-Cu bond is performed, for example by thermocompression, between certain pads 12 and the motifs 21. The Cu-Cu bond by thermocompression can be carried out at a relatively low temperature, typically between 200°C and 400°C. This helps to limit the thermal load experienced by the optoelectronic devices 100.

[0070] As illustrated in Figure 10, after bonding, the optoelectronic devices 100a assembled to the motifs 21 are detached from the donor substrate 1. This can be achieved by localized laser ablation, for example, through the transparent donor substrate 1. This technique allows for the local removal of the sacrificial layer 10 carrying the optoelectronic devices 100a. The optoelectronic devices 100a, which are attached to the recipient substrate 2, 2a, are then freed from the donor substrate 1.

[0071] As illustrated in Figure 11, the donor substrate 1, still carrying optoelectronic devices 100b, is then moved away from the recipient substrate 2, 2a, which carries the optoelectronic devices 100a. The optoelectronic devices 100a were transferred from the donor substrate 1 to the recipient substrate 2, 2a via Cu-Cu bonding between the pads 12 of the optoelectronic devices 100a and the motifs 21 of the recipient substrate 2, 2a. Figures 12 to 14 illustrate a second transfer of devices 100b from the previously used donor substrate 1 to a recipient substrate 2, 2b. In this example, the recipient substrate 2, 2b is solid. The recipient substrate 2 may be the one onto which the optoelectronic devices 100a were transferred during the first transfer. Alternatively, the recipient substrate 2b may be different from the recipient substrate 2a used previously.The density of copper motifs 21 of the receiving substrate 2, 2b may be less than or equal to the density of optoelectronic devices 100b of the donor substrate 1. In this example, only some optoelectronic devices 100b of the donor substrate 1 are actually transferred to the receiving substrate 2, 2b as a result of this second transfer.

[0072] As illustrated in Figure 12, after the first transfer described above, the donor substrate 1, still carrying the optoelectronic devices 100b, is moved to another location on the recipient substrate 2, 2a or above another recipient substrate 2, 2b. The donor substrate 1 is thus reused either to populate another area of ​​the recipient substrate 2, 2a, for example with the same density as the area onto which the optoelectronic devices 100a were transferred, or to populate another recipient substrate 2, 2b. In the case of manufacturing large displays, the effective surface area of ​​the donor substrate 1 is much smaller than the surface area of ​​the recipient substrate 2.

[0073] As illustrated in Figure 13, after alignment of the studs 12 and the patterns 21, a Cu-Cu bonding is carried out, for example by thermocompression, as before.

[0074] As illustrated in Figure 14, after bonding, the optoelectronic devices 100b assembled to the motifs 21 are detached from the donor substrate 1. This can be achieved by localized laser ablation, as before. This technique allows for the local removal of the sacrificial layer 10 bearing the optoelectronic devices 100b. The optoelectronic devices 100b, which are attached to the recipient substrate 2, 2b, are then freed from the donor substrate 1. The donor substrate 1, still bearing optoelectronic devices 100c, is then moved away from the recipient substrate 2, 2b, which carries the optoelectronic devices 100b.

[0075] As illustrated in Figure 15, the process allows the transfer of optoelectronic devices 100a, 100b from the donor substrate 1 to the recipient substrate 2, 2a, 2b via Cu-Cu bonding between the pads 12 of the optoelectronic devices 100a, 100b and the motifs 21 of the recipient substrate 2, 2a, 2b. Optionally, a structuring 200b of the seed layer 20 can be performed after the transfer of the optoelectronic devices 100a, 100b. This structuring 200b typically allows the optoelectronic devices 100a, 100b to be electrically isolated from each other. The 200b structuring can be carried out by photolithography and etching of the germination layer 20. A protective layer of the optoelectronic devices 100a, 100b, for example based on photosensitive resin, can be provided during the 200b structuring (not shown).Areas exposing the surface 201 of the receiving substrate 2, 2a, 2b are thus formed between the optoelectronic devices 100a, 100b. A structuring 200b of the germination layer 20 after device transfer allows the integrity of the germination layer 20 to be maintained during the transfer. This optimizes the mechanical strength of the patterns 21 on the receiving substrate 2, 2a, 2b, particularly during the bonding and debonding steps of the optoelectronic devices 100 from the donor substrate 1, and the polishing step.

[0076] Figures 16 to 22 illustrate the transfer of devices 100a, 100b onto a receiving substrate 2, 2c. In this example, the receiving substrate 2, 2c typically includes buried metallic tracks 22, 22a, 22b. These metallic tracks 22, 22a, 22b can be part of an interconnection network designed to link the devices 100a, 100b to control electronics, for example, transistor-based electronics. The receiving substrate 2, 2c is thus functionalized.

[0077] As illustrated in Figure 16, a receiving substrate 2, 2c comprising metallic tracks 22, 22a, 22b is provided. An insulating layer 40 based on a dielectric material is deposited on the receiving substrate 2, 2c. It is structured so as to expose some metallic tracks 22a and mask some metallic tracks 22b.

[0078] As illustrated in Figure 17, the germination layer 20, comprising, for example, as before, the sublayers 20a, 20b, and 20c, is formed on the insulation layer 40 and on the exposed metal tracks 22a. The germination layer 20 thus forms a connection 221 with the metal track 22a. The germination layer 20 can be formed, as before, by PVD. The copper motifs 21 are formed, as before, projecting from the germination layer 20. They have a polished upper surface 212, obtained by CMP. In the following figures, the copper motifs 21 are shown with right angles for simplification. The copper motifs 21 may have more or less rounded angles after CMP polishing, as illustrated in Figure 7.

[0079] As illustrated in Figure 18, optoelectronic devices 100a, 100b are transferred as before onto the copper motifs 21. Each optoelectronic device 100a, 100b typically includes an active area 101 for emitting or receiving light radiation. The top and / or sides of the active area 101 may be covered by an encapsulation layer 102. The copper pads 12 of the optoelectronic devices 100a, 100b form, on a first side 121 of the active area 101, a first contact C1 electrically connected to the metal track 22a via the motifs 21, the seed layer 20, and the connection 221. The seed layer 20 is advantageously functionalized. It allows the contact C1 to be re-established to connect the metal track 22a.

[0080] As illustrated in Figure 19, a dielectric layer 41, for example based on SiN, is conformally deposited on the optoelectronic devices 100a, 100b and on the seed layer 20. This dielectric layer 41 typically allows the optoelectronic devices 100a, 100b to be passivated and the seed layer 20 to be electrically isolated.

[0081] As illustrated in Figure 20, a structuring 200b of the germination layer 20 is then performed. The structuring 200b is configured so that two optoelectronic devices 100a, 100b are electrically connected to the metal track 22a via the patterns 21 of the germination layer 20 and the connection 221. The germination layer 20 advantageously allows the electrical connection of a plurality of optoelectronic devices 100a, 100b to a metal track 22, 22a of the receiving substrate 2, 2c. During the structuring 200b, the etching of the germination layer 20 can be stopped at the insulating layer 40. This protects the metal track 22b. Following structuring 200b, flanks 20f of the germination layer 20 are exposed.

[0082] As illustrated in Figure 21, a second dielectric layer 42, for example based on SiN, is conformally deposited on the optoelectronic devices 100a, 100b and on the seed layer 20. This dielectric layer 42 typically allows the flanks 20f to be electrically isolated from the seed layer 20.

[0083] As illustrated in Figure 22, the dielectric layers 40, 42 are etched to expose the metal track 22b and the encapsulation layer 102 at the top of the optoelectronic devices 100a, 100b. The encapsulation layer 102 is partially removed to expose the top of the active area 101 of the optoelectronic devices 100a, 100b. A transparent conductive layer 50, for example based on a transparent conductive oxide (TCO), is conformally deposited on the optoelectronic devices 100a, 100b and on the exposed metal track 22b. The transparent conductive layer 50 forms a second contact C2 on a second side 122 of the active area 101, which is electrically connected to the metal track 22b. Functional optoelectronic devices 100a, 100b, whose contacts C1, C2 are connected on the "front face" of the receiving substrate 2, 2c respectively to the metallic tracks 22a, 22b, are thus advantageously obtained.

[0084] Figures 23 to 29 illustrate a variant of the transfer process of devices 100a, 100b onto a receiving substrate 2, 2c, illustrated in Figures 16 to 22. Only the different characteristics of this variant are described below, the other characteristics being assumed to be identical to the characteristics of the transfer process illustrated in Figures 16 to 22.

[0085] As illustrated in Figure 23, the receiving substrate 2, 2c, comprising metallic tracks 22, 22a, 22b, is provided. An insulating layer 40 based on a dielectric material is deposited on the receiving substrate 2, 2c. It is structured so as to expose all the metallic tracks 22a, 22b.

[0086] As illustrated in Figure 24, the nucleation layer 20 is formed, typically by PVD, on the insulation layer 40 and on the exposed metal tracks 22a, 22b. The nucleation layer 20 thus forms a connection 221 with the metal track 22a and a connection 222 with the metal track 22b. The copper patterns 21 are formed as before. They may have more or less rounded corners after CMP polishing, as illustrated in Figure 7.

[0087] As illustrated in Figure 25, optoelectronic devices 100a, 100b are transferred as before onto the copper motifs 21. The copper pads 12 of the optoelectronic devices 100a, 100b form on a first side 121 of the active area 101 a first contact C1 electrically connected to the metallic tracks 22a, 22b via the motifs 21, the seed layer 20 and the connections 221, 222.

[0088] As illustrated in Figure 26, a dielectric layer 41, for example based on SiN, is conformally deposited on the optoelectronic devices 100a, 100b and on the seed layer 20. As illustrated in Figure 27, a structuring 200b of the seed layer 20 is then performed. The structuring 200b is configured so that two optoelectronic devices 100a, 100b are electrically connected to the metal track 22a via a first portion P1 of the seed layer 20 and the connection 221. The structuring 200b is configured so that a second portion P2 of the seed layer 20 is electrically connected via the connection 222 to the metal track 22b. The second portion P2 of the germination layer 20 is separated from the first portion P1.

[0089] As illustrated in Figure 28, a second dielectric layer 42, for example based on SiN, is conformally deposited on the optoelectronic devices 100a, 100b and on the portions P1, P2 of the germination layer 20. This dielectric layer 42 typically allows the sides of the portions P1, P2 of the germination layer 20 to be electrically isolated.

[0090] As illustrated in Figure 29, the dielectric layers 42, 41 are etched here to expose the second portion P2 of the seed layer 20 connected to the metal track 22b and the encapsulation layer 102 at the top of the optoelectronic devices 100a, 100b. The top of the active area 101 of the optoelectronic devices 100a, 100b is also exposed as before by removing the encapsulation layer 102. A transparent conductive layer 50, for example based on TCO, is conformally deposited on the optoelectronic devices 100a, 100b and on the second exposed portion P2. The transparent conductive layer 50 forms a second contact C2 on a second side 122 of the active area 101, electrically connected to the metal track 22b via the second portion P2. The second portion P2 typically forms a contact pad for the resumption of contact C2 on the front face of the receiving substrate 2, 2c.

[0091] As illustrated by the preceding examples, the transfer method according to the invention advantageously allows the localized transfer of optoelectronic devices from a donor substrate to a recipient substrate. However, the invention is not limited to the embodiments described above. In particular, the number, shape, and arrangement of the protruding motifs on the recipient substrate can be adapted to suit the intended applications.

Claims

Demands 1. A method for transferring at least one optoelectronic device (100) from a first substrate (1), called the donor, to a second substrate (2a, 2b), called the recipient, said method comprising at least the following steps: • provide said donor substrate (1) bearing at least one optoelectronic device (100, 100a, 100b, 100c), said at least one optoelectronic device (100, 100a, 100b, 100c) comprising at least one copper pad (12), • provide said receiving substrate (2, 2a, 2b, 2c) having a so-called receiving face (201), • to form a germination layer (20) on said receiving face (201) of said receiving substrate (2, 2a, 2b, 2c), said germination layer (20) being copper-based, • to form on said germination layer (20) a mask (30) defining openings (31) exposing said germination layer (20), said openings (31) having a height hsi along a direction (z) called vertical, • fill said openings (31) with a copper deposit, • remove said mask (30) so as to obtain copper patterns (21) protruding from said germination layer (20), • assemble said at least one optoelectronic device (100, 100a, 100b) with said receiving substrate (2, 2a, 2b, 2c), by bonding said at least one copper pad (12) onto an upper surface (212) of said at least one copper motif (21), • decouple said at least one optoelectronic device (100, 100a, 100b) from said donor substrate (1).

2. Method according to the preceding claim further comprising, after removal of the mask (30) and before assembly of said at least one optoelectronic device (100, 100a, 100b) with said receiving substrate (2, 2a, 2b, 2c), a mechano-chemical polishing (210) on said copper motifs (21) so that the upper surface (212) of said copper motifs (21) is polished.

3. A method according to any one of the preceding claims further comprising a structuring (200a, 200b) of the germination layer (20) after removal of the mask (30).

4. Method according to the preceding claim in which the structuring (200b) of the germination layer (20) is carried out after decoupling of at least one optoelectronic device (100, 100a, 100b).

5. A method according to claim 3 wherein the structuring (200a) of the germination layer (20) is carried out before assembly of said at least one electronic device (100, 100a, 100b) with said receiving substrate (2, 2a, 2b, 2c), and preferably, when said method is carried out in combination with the method according to claim 2, before the mechano-chemical polishing (210).

6. A method according to any one of claims 3 to 5 wherein the structuring (200a, 200b) of the germination layer (20) is configured to form conductive metallic tracks connecting distinct copper patterns (21) and / or connecting copper patterns (21) and electrical contacts (22, 22a, 22b) of the receiving substrate (2, 2a, 2b, 2c).

7. A method according to any one of the preceding claims, wherein the bonding is carried out by thermocompression at a temperature between 200°C and 400°C.

8. A method according to any one of the preceding claims wherein the donor substrate (1) carries a plurality of optoelectronic devices (100a, 100b, 100c), and wherein only certain optoelectronic devices (100a, 100b) of said plurality are assembled to the receiving substrate (2, 2a, 2b, 2c) and decoupled from the donor substrate (1).

9. A method according to any one of the preceding claims wherein the receiving face (201) of the receiving substrate (2, 2c) comprises at least one metallic track (22, 22a, 22b) and wherein the germination layer (20) forms a connection (221) with said at least one metallic track (22, 22a).

10. Method according to the preceding claim further comprising a structuring (200a, 200b) of the germination layer (20), said structuring (200a, 200b) being configured such that at least one metallic track (22, 22a) of the receiving substrate (2, 2c) is connected to at least two optoelectronic devices (100a, 100b) via at least two copper motifs (21) protruding from the structured germination layer (20).

11. A method according to any one of the preceding claims wherein the filling of the openings (31) is configured so that the copper deposited in said openings (31) has a height h2i less than the height hsi of said openings (31), along the vertical direction (z).

12. A method according to any one of the preceding claims in which at least one copper motif (21) has, after polishing, a height h2if greater than 200 nm along the vertical direction (z).

13. A method according to any one of the preceding claims in which at least one copper motif has a characteristic dimension I21 less than or equal to 10 pm along a so-called horizontal direction (y), perpendicular to the vertical direction (z).

14. Method according to any one of the preceding claims wherein at least one optoelectronic device (100, 100a, 100b, 100c) is a light-emitting diode having on a first face (121) a first contact (C1) formed by at least one copper pad (12), and a second contact (C2) on a second face (122) opposite to the first face (121), along the vertical direction (z).

15. A method according to the preceding claim further comprising, after decoupling at least one optoelectronic device (100, 100a, 100b), the formation of a transparent conductive layer (50) on the second contact (C2), said transparent conductive layer (50) being electrically insulated from the layer of 17 germination (20) bearing at least one motif (21) of copper connected to the first contact (C1).

16. Method according to the preceding claim wherein the receiving face (201) of the receiving substrate (2, 2c) comprises a first metallic track (22a) connected to the first contact (C1) via the germination layer (20), and a second metallic track (22b) connected to the second contact (C2) via the transparent conductive layer (50).

17. Method according to the preceding claim in which the transparent conductive layer (50) is directly in contact with the second metallic track (22b).

18. Method according to claim 16 wherein the first metallic track (22a) is connected to the first contact (C1) via a first portion (P1) of the germination layer (20) and the second metallic track (22b) is connected to the second contact (C2) via a second portion (P2) of the germination layer (20).

19. A method according to any one of the preceding claims in which the decoupling of at least one optoelectronic device (100, 100a, 100b) from the donor substrate (1) is done by localized laser ablation.

20. Device intended to receive at least one optoelectronic device (100, 100a, 100b) comprising at least one copper pad (12), comprising a receiving substrate (2, 2a, 2b, 2c), a copper-based germination layer (20) on the surface of said receiving substrate (2, 2a, 2b, 2c), and copper motifs (21) projecting from said germination layer (20), said copper motifs (21) having a top surface (212) configured to be assembled with at least one copper pad (12) of at least one optoelectronic device (100, 100a, 100b), said germination layer (20) being exposed to air between said copper motifs (21).

21. Device according to the preceding claim in which the germination layer (20) comprises at least one surface layer (20c) based on copper as well as an adhesion layer (20a) and / or a barrier layer (20b).

22. Device according to any one of claims 20 to 21 in which the germination layer (20) is structured in the form of conductive metallic tracks connecting at least two distinct copper motifs (21) and / or connecting copper motifs (21) and electrical contacts (22, 22a, 22b) of the receiving substrate (2, 2a, 2b, 2c).

23. Device according to any one of claims 20 to 22 wherein the receiving substrate (2, 2a, 2b, 2c) comprises at least one metallic track (22, 22a, 22b) and wherein the germination layer (20) forms a connection (221, 222) with said at least one metallic track (22, 22a, 22b).

24. Device according to any one of claims 20 to 23 further comprising optoelectronic devices (100a, 100b) disposed on and in electrical contact with the copper motifs (21).

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