Flexible substrate for manufacturing Micro-LED and preparation method and application thereof

Abstract

The invention discloses a flexible substrate for manufacturing a Micro-LED and a preparation method and application thereof. The flexible substrate comprises a base and a plurality of flexible structures on the base. The flexible structure is a hollow hexahedron of which the upper top surface is a plane, and the height of the flexible structure is greater than the thickness of the Micro-LED epitaxial layer grown on the surface of the flexible structure. The bonding layer with small growth defects and small strain can be prepared on the flexible substrate. Compared with a plane layer, the flexible substrate provided by the invention can be used for growing to obtain a Micro-LED epitaxial layer of which the screw dislocation density is obviously reduced, and the growth quality of a Micro-LED chip is improved. According to the Micro-LED chip manufactured based on the flexible substrate, chemical corrosion and laser lift-off do not need to be carried out on the chip in the preparation and lift-off processes of the Micro-LED chip, damage to the chip is avoided, and the optical and electrical properties of the chip can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor light-emitting devices, and particularly relates to a flexible substrate for manufacturing Micro-LEDs, a preparation method and an application thereof. Background Art

[0002] Micro-light emitting diode (Micro-LED) display technology is a technology that microstructures, miniaturizes, and arrays LED structures, and the size of a single device is less than 100 μm. As a micron-level LED light-emitting unit, Micro-LED has advantages such as high pixels and high contrast, and is considered to be the most promising next-generation display technology. The combination of technologies such as augmented reality (AR) and virtual reality (VR) with the currently commercial 5G communication technology has further promoted the development of Micro-LED.

[0003] Currently, there are still technical bottlenecks in the epitaxial growth technology and transfer technology of Micro-LED. Traditional Micro-LED epitaxial growth technology usually grows GaN on a c-plane sapphire substrate. Due to the lattice mismatch generated during the thermal expansion process of GaN and the sapphire substrate, a high defect density and high compressive stress are caused in the GaN layer, thereby affecting the LED performance. Traditional chip transfer methods mainly include the pick-and-place method and the laser lift-off method. The pick-and-place method uses different types of forces to pick up the Micro-LED chip onto the transfer head, and releases the Micro-LED chip onto the substrate by precisely controlling the movement of the transfer head. Its efficiency decreases with the increase in the number of chips, and at the same time, its high cost also seriously hinders the commercialization of Micro-LED. The laser lift-off method avoids the process of picking up the Micro-LED chip. First, the Micro-LED chip is bonded to a temporary transfer substrate, and then a laser is irradiated onto the GaN / sapphire interface. The GaN near the interface is thermally decomposed, and the Micro-LED chip is peeled off from the original substrate. Subsequently, the bonding material of the temporary transfer substrate is decomposed by the laser, and finally the transfer of the Micro-LED chip is achieved. However, the chip may be thermally damaged during the laser irradiation process, affecting the optoelectronic performance of the chip.

[0004] Growing the Micro-LED epitaxial layer on a flexible substrate and peeling off the Micro-LED epitaxial layer from the flexible substrate by applying stress and dry etching can avoid chemical corrosion and laser lift-off, and improve the optical and electrical properties of Micro-LED. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a flexible substrate for manufacturing Micro-LEDs, including a substrate and a plurality of flexible structures on the substrate; The flexible structure is a hollow hexahedron with a flat upper top surface, and the height of the flexible structure is greater than the total thickness of the bonding layer and the Micro-LED epitaxial layer grown on its surface.

[0006] Further, the thickness of the flexible structure is 80 - 150 nm.

[0007] Further, the pitch of the flexible structure is 3 - 10 μm.

[0008] Further, the material of the flexible structure is α-phase Al2O3.

[0009] The present invention also provides a preparation method for a flexible substrate for manufacturing Micro-LEDs, including: Designing lithography parameters according to the Micro-LED epitaxial layer to be manufactured; Etching and depositing a first sacrificial material in a first direction on a substrate to obtain a substrate with a first pattern formed by the first sacrificial material; Growing a flexible material and a sacrificial material in sequence on the first pattern of the substrate to obtain a first product; Etching the intermediate product in a second direction to obtain a predetermined structure, thereby obtaining a second product, wherein the first direction is perpendicular to the second direction; Removing the first sacrificial material and the second sacrificial material in the second product to obtain a substrate and a plurality of flexible structures on the substrate, the flexible structures being hollow hexahedrons with flat upper top surfaces, and the height of the flexible structures being greater than the thickness of the Micro-LED epitaxial layer grown on their surfaces.

[0010] Further, before removing the first sacrificial material and the second sacrificial material in the second product, a protection plate is also used to protect the predetermined structure.

[0011] Further, the flexible material is Al2O3; After removing the first sacrificial material and the second sacrificial material in the second product, annealing is performed to obtain flexible structures of α-phase Al2O3.

[0012] Further, the thickness of the flexible structure is also thinned.

[0013] The present invention also provides an application of the above flexible substrate in the preparation of Micro-LED chips.

[0014] Further, the application includes: Preparing a bonding layer and a Micro-LED epitaxial layer on the flexible structures of the flexible substrate for manufacturing Micro-LEDs; Peeling the Micro-LED epitaxial layer from the bonding layer and the flexible structures; Prepare the lead electrode of the Micro-LED epitaxial layer to obtain a Micro-LED chip.

[0015] It should be noted that the types and compositions of the bonding layer and the Micro-LED epitaxial layer in the present invention do not need to be strictly limited and can be selected according to the conventional understanding in the art. The Micro-LED epitaxial layer is successively composed of an n-type material layer, a multi-quantum well active layer, a p-type material layer, etc. Exemplarily, if the Micro-LED epitaxial layer is a GaN-based material, the bonding layer is selected as undoped GaN.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) A bonding layer with smaller growth defects and smaller strain can be prepared on the flexible substrate of the present invention. Compared with the planar layer, using the flexible substrate of the present invention can grow a Micro-LED epitaxial layer with a significantly reduced screw dislocation density, improving the growth quality of the Micro-LED chip.

[0017] (2) The flexible substrate of the present invention can generate greater bending and torque, and the fracture threshold is significantly reduced. Compared with the bonding layer grown on a traditional planar substrate, the efficiency of mechanical peeling can be greatly improved.

[0018] (3) The flexible substrate of the present invention has a height greater than the total thickness of the bonding layer and the Micro-LED epitaxial layer grown on its surface, and can avoid the adhesion between the bonding layer and the Micro-LED epitaxial layer when growing the Micro-LED epitaxial layer, improving the peeling efficiency.

[0019] (4) For the Micro-LED chip manufactured based on the flexible substrate of the present invention, there is no need to chemically etch and laser peel the chip during the preparation and peeling of the Micro-LED chip, avoiding damage to the chip and effectively improving the optical and electrical properties of the chip. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 Shows the structural schematic diagram of the product obtained in step S102 of Embodiment 1; Figure 2 Shows the structural schematic diagram of the product obtained in step S103 of Embodiment 1; Figure 3Shows the structural schematic diagram of the product obtained in step S104 of Embodiment 1; Figure 4 Shows the structural schematic diagram of the product obtained in step S105 of Embodiment 1; Figure 5 Shows the structural schematic diagram of the product obtained in step S106 of Embodiment 1; Figure 6 Shows the structural schematic diagram of the flexible substrate for manufacturing Micro-LED prepared in Embodiment 1; Figure 7 Shows the structural schematic diagram of the product obtained in step T101 of Embodiment 2; Figure 8 Shows the structural schematic diagram of the product obtained in step T102 of Embodiment 2; Figure 9 Shows the structural schematic diagram of the product obtained in step T103 of Embodiment 2; Figure 10 Shows the structural schematic diagram of the product obtained in step T104 of Embodiment 2; Figure 11 Shows the structural schematic diagram of the product obtained in step T105 of Embodiment 2; Figure 12 Shows the structural schematic diagram of the fracture of the flexible structure and the bonding layer under force in step T106 of Embodiment 2; Figure 13 Shows the structural schematic diagram of the product obtained in step T107 of Embodiment 2; Figure 14 Shows the structural schematic diagram of the Micro-LED chip prepared in Embodiment 2; Explanation of reference numerals: 1. Substrate; 2. First pattern; 3. Amorphous Al2O3 atomic layer; 4. SiO2 layer; 5. Second pattern; 6. Flexible structure; 7. Undoped GaN layer; 8. n-GaN layer; 9. InGaN / GaN multi-quantum well active layer; 10. p-GaN layer; 11. Ag / TiW microstructure; 12. p-type conductive substrate; 13. n electrode; 14. p electrode; 15. SiO2 insulating layer. Detailed implementation manners

[0022] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the specific embodiments of the present invention and the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1 A preparation method for a flexible substrate for manufacturing Micro-LED is as follows. S101. Design lithography parameters according to the Micro-LED epitaxial layer to be manufactured. The lithography parameters mainly control the height of the finally obtained flexible structure. The length and width of the flexible structure can be adjusted adaptively according to the lateral cross-sectional size of the manufactured Micro-LED epitaxial layer, but the height of the flexible structure should be greater than the total thickness of the bonding layer and the Micro-LED epitaxial layer grown on its surface. S102. Use lithography technology to etch longitudinally on a sapphire substrate, as Figure 1 shown, to obtain a substrate 1 and a first pattern 2 on the substrate 1. Among them, the cross-section of the substrate 1 is rectangular, and the first pattern 2 is a plurality of cuboid structures made of photoresist. The width and height of the cuboid are 5 μm and 3.5 μm respectively, and the spacing between adjacent cuboids is 4 μm. S103. As Figure 2 shown, using trimethylaluminum and deionized water as the precursors of Al and O, deposit an amorphous Al2O3 atomic layer 3 with a thickness of 120 nm on the lithography pattern at 115 °C by atomic layer deposition. S104. As Figure 3 shown, deposit a SiO2 layer 4 with a thickness of 100 nm on the amorphous Al2O3 atomic layer 3 by plasma-enhanced chemical vapor deposition. S105. As Figure 4 shown, use lithography technology to etch longitudinally on the substrate 1 to obtain a second pattern 5, and leave the required predetermined structure using a photomask. S106. As Figure 5 shown, use a buffered oxide etch wet etching process to etch the SiO2 layer 4. S107. Use acetone to remove the residual photoresist on the substrate, and anneal in an air atmosphere at 1200 °C for 120 min to convert the amorphous Al2O3 atomic layer into α-phase Al2O3; subsequently, crystallize along the sapphire substrate by solid-phase epitaxy technology to reduce the thickness of the α-phase Al2O3 to 100 nm. As Figure 6 shown, form a flexible structure 6 on the substrate 1. The length, width, height, and spacing of the flexible structure 6 are 10 μm, 5 μm, 3.5 μm, and 4 μm respectively.

[0025] Example 2 Prepare a Micro-LED chip using the flexible substrate prepared in Example 1, and the steps are as follows. T101. As Figure 7 shown, use metal-organic chemical vapor deposition to grow an undoped GaN layer 7 with a thickness of about 1.4 μm as a bonding layer on the flexible structure 6 of the flexible substrate for manufacturing Micro-LED. T102. As Figure 8 shown, grow an n-GaN layer 8 with a thickness of about 0.8 μm on the undoped GaN layer 7. T103. As Figure 9 shown, grow an InGaN / GaN multi-quantum well active layer 9 with 5 periods and a thickness of about 100 - 130 nm on the n-GaN layer 8. T104. As Figure 10 shown, continue to grow a p-GaN layer 10 with a thickness of about 0.5 μm on the InGaN / GaN multi-quantum well active layer 9. After this step, a complete Micro-LED epitaxial layer is obtained, which includes an n-GaN layer 8, an nGaN / GaN multi-quantum well active layer 9, and a p-GaN layer 10 from bottom to top. T105. As Figure 11 shown, sputter an Ag / TiW microstructure 11 on the p-GaN layer 10 by ion beam sputtering. The thicknesses of Ag and TiW in the Ag / TiW microstructure 11 are 120 nm and 70 nm respectively. T106. Deposit an In layer on the Ag / TiW microstructure 11 by electron beam evaporation, deposit a Ti layer, a Pt layer, and an Au layer on the p-type conductive substrate 12. After flipping the flexible substrate, use the Au-In eutectic bonding method to flip-bond the Micro-LED epitaxial layer and the p-type conductive substrate 12 together. At the same time, apply a uniform force of 2500 - 3000 N at one end of the flexible structure 6 for 15 min to break the flexible structure 6 and the undoped GaN layer 7. As Figure 12 shown, the upper arrow in the figure indicates the application of force at one end of the flexible structure 6, and the lower arrow indicates that no additional force is applied during the bonding process. T107. Through ICP dry etching technology, use a BCl3 / Ar mixed gas to etch the remaining α-phase Al2O3 and the undoped GaN layer 7 to expose the n-GaN layer 8. As Figure 13 shown; T108. Using photolithography technology, with photoresist as a mask, deposit a Cr / Pt / Au metal stack layer with thicknesses of 20 nm / 20 nm / 1.5 μm respectively on the exposed surface of the n-GaN layer 8 by electron beam evaporation technology; deposit a Ti / Au metal stack layer with thicknesses of 7 nm / 5 nm respectively on the back of the p-type conductive substrate 12, and remove the excess metal by lift-off to form electrode patterns, thus preparing the n-electrode 13 and the p-electrode 14; T109. Using plasma enhanced chemical vapor deposition process, with N2O and 10% SiH4 as reaction gases, deposit the SiO2 insulating layer 15 on the side of the product obtained in step T108, to obtain the Figure 14 Micro-LED chip as shown.

[0026] In this embodiment, the height of the flexible structure is 3.5 μm, which is greater than the total thickness of the n-GaN layer and the Micro-LED epitaxial layer (about 3 μm).

[0027] Comparative Example 1 The Micro-LED chip prepared with a planar substrate has the same structure of the Micro-LED epitaxial layer as that in Example 2.

[0028] Similar to Comparative Example 1, in the current process, GaN-based LEDs are usually grown on planar substrates. However, the lattice mismatch and the difference in thermal expansion coefficients during the thermal expansion process between GaN and the substrate will cause a high defect density and high compressive stress in the GaN layer, thereby having a harmful impact on the LED performance. In Example 2 of the present invention, the strain related to the lattice mismatch between GaN and the substrate can be shared with the flexible structure on the flexible substrate. Since the flexible structure shares part of the strain in the epitaxial layer, the misfit dislocations at the GaN / flexible structure interface are effectively reduced, and the average distance between dislocations is increased, resulting in a further reduction in the threading dislocation density (TDD).

[0029] Comparative Example 2 Based on a flexible substrate similar to that obtained in the preparation method of Example 1, and referring to the method of Example 2 to prepare the Micro-LED chip, the difference is that: the height of the flexible structure is 2 μm, which is lower than the total thickness of the n-GaN layer and the Micro-LED epitaxial layer. During the growth of n-GaN, the n-GaN grown on the flexible substrate will adhere to the undoped GaN layer grown on the flexible structure, which will cause abnormal doping concentration distribution in the n-GaN layer, possibly affecting the ohmic contact characteristics between the electrode and n-GaN, aggravating Joule heat and voltage loss; the lattice mismatch or defects (such as dislocations, impurities) at the interface will become non-radiative recombination centers of carriers, reducing the internal quantum efficiency of the LED. At the same time, the adhesion may cause stress concentration of the lattice mismatch at the heterojunction interface, increasing the threading dislocation density and reducing the crystal quality and device life of the material.

[0030] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A flexible substrate for manufacturing Micro-LED, characterized in that: It includes a substrate and a plurality of flexible structures on the substrate; The flexible structure is a hollow hexahedron with a flat top surface, and the height of the flexible structure is greater than the total thickness of the bonding layer and the Micro-LED epitaxial layer grown on its surface.

2. The flexible substrate according to claim 1, characterized in that The thickness of the flexible structure is 80-150 nm.

3. The flexible substrate according to claim 1, characterized in that: The pitch of the flexible structure is 3-10 μm.

4. The flexible substrate according to claim 1, characterized in that: The material of the flexible structure is α-phase Al2O3.

5. A method for preparing a flexible substrate for manufacturing Micro-LED, characterized in that: include, Design lithography parameters according to the Micro-LED epitaxial layer to be manufactured; Etching and depositing a first sacrificial material in a first direction of the substrate to obtain a base, wherein the base has a first pattern formed by the first sacrificial material; sequentially growing a flexible material and a second sacrificial material on a first pattern of a substrate to obtain a first product; Etching the intermediate product along a second direction to obtain a predetermined structure to obtain a second product, wherein the first direction is perpendicular to the second direction; The first sacrificial material and the second sacrificial material in the second product are removed to obtain a substrate and several flexible structures on the substrate, wherein the flexible structure is a hollow hexahedron with a flat top surface, and the height of the flexible structure is greater than the thickness of the Micro-LED epitaxial layer grown on its surface.

6. The preparation method according to claim 5, characterized in that: Before removing the first sacrificial material and the second sacrificial material in the second product, a protective plate is also used to protect the predetermined structure.

7. The preparation method according to claim 5, characterized in that: The flexible material is Al2O3; After removing the first sacrificial material and the second sacrificial material in the second product, annealing is performed to obtain a flexible structure of α-phase Al2O3.

8. The preparation method according to claim 5, characterized in that: The thickness of the flexible structure is also reduced.

9. Use of the flexible substrate as described in any one of claims 1 to 4 in preparing a Micro-LED chip.

10. The use according to claim 9, characterized in that: include, Preparing a bonding layer and a Micro-LED epitaxial layer on a flexible structure of a flexible substrate for manufacturing Micro-LEDs; Peeling off the Micro-LED epitaxial layer from the bonding layer and the flexible structure; Prepare the lead-out electrode of the Micro-LED epitaxial layer to obtain a Micro-LED chip.

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