Micro LED preparation method

Abstract

The invention discloses a Micro LED preparation method, and the method comprises the following steps: S1, enabling a Micro LED epitaxial layer to be bonded to a drive substrate through a metal bonding technology; s2, forming a Mesa mask through a photoetching process, and forming a Mesa structure on the bonded epitaxial layer by adopting an etching process; s3, forming a double-layer or multi-layer photoresist structure on the surface of the Mesa structure through a two-time or multi-time gluing process; a lower layer'undercut 'structure is formed after exposure and development; s4, etching the bonding metal layer by taking the mask with the undercut structure as a template; s5, removing the photoresist through a developing solution or a photoresist removing solution, and synchronously stripping the discontinuous metal layer on the side wall to obtain a Micro LED with an independent pixel structure; through the innovative process steps, especially the design and application of the mask with the undercut structure, the problem that a metal fence is abnormal in the existing Micro LED preparation technology is successfully solved, and the yield of Micro LEDs is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of Micro LED display, and particularly relates to a method for preparing Micro LED. Background Art

[0002] In the current technical field of Micro LED preparation, with the continuous development of display technology, the requirements for the preparation process of Micro LED are also getting higher and higher; in the existing microdisplay Micro LED preparation technology, the common method is to first integrate the CMOS wafer (driver substrate) and the LED epitaxial layer through full-surface metal bonding, and then use processes such as photolithography and etching to prepare independent Micro LEDs, so as to realize a Micro LED screen body with a high pixel density (ppi).

[0003] To achieve electrical isolation between anodes or cathodes of each pixel, methods of photolithographic patterning and IBE (ion beam etching) are used to perform IBE etching on the full-surface bonding metal, so that the lower electrodes (cathodes or anodes) of each Micro LED pixel are separated from each other. However, during the process of etching the metal using IBE, the phenomenon of metal redeposition will inevitably occur. These deposited metals will adhere to the photoresist on the side of the LED. When the photoresist is removed, this part of the metal will still remain in its original position and is difficult to remove, thus forming the so-called "metal fence", as shown in the attachment. Figure 2 as shown.

[0004] The existence of the "metal fence" will seriously affect the performance and manufacturing yield of Micro LED. It will cause the subsequent film layers to be unable to effectively cover, resulting in short circuits or open circuits in the LED, and ultimately leading to the failure of Micro LED, which brings great obstacles to the large-scale production and application of Micro LED. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing Micro LED, so as to solve the abnormal problem of "metal fence" occurring during the etching of the metal in the pixel bonding layer in the prior art, improve the LED short circuit / open circuit situation caused thereby, and greatly improve the manufacturing yield of Micro LED.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: A method for preparing Micro LED, comprising the following steps: S1, through a metal bonding process, bond the Micro LED epitaxial layer to the driver substrate, the thickness of the epitaxial layer is 0.5 - 10 μm, and the thickness of the bonding metal layer is 0.1 - 5 μm; S2. Form a Mesa mask through a lithography process, and use an etching process to form a Mesa structure on the epitaxial layer after bonding. S3. Through two or more spin-coating processes, form a double-layer or multi-layer photoresist structure on the surface of the Mesa structure; wherein, the thickness of the first photoresist is 0.1 - 1 μm, and the chain scission or crosslinking effects of the first photoresist and the second photoresist under the same exposure and development conditions are different, so that an underlying "undercut" structure is formed after exposure and development, that is, the photoresist mask forms a stepped structure that is wider at the top and narrower at the bottom on the sidewalls. S4. Using the "undercut" structure mask as a template, etch the bonded metal layer. During the etching process, the metal deposited on the sidewalls cannot form a continuous layer due to the existence of the "undercut" structure, and only discontinuously adheres to the top and bottom of the mask. S5. Remove the photoresist through a developer or a stripping solution, and simultaneously strip the discontinuous metal layer on the sidewalls to obtain a Micro LED with an independent pixel structure.

[0007] Preferably, in step S1, the metal bonding process adopts one of the methods of thermocompression bonding, eutectic bonding or flip-chip bonding. Among them, the thermocompression bonding temperature is 150 - 300 °C, the pressure is 5 - 20 MPa, and the bonding time is 30 - 1200 s; the eutectic bonding temperature is 200 - 350 °C, and the bonding time is 10 - 60 s; when performing flip-chip bonding, the solder used is indium, tin or gold-tin alloy, the bonding temperature is 180 - 300 °C, and the pressure is 3 - 15 MPa.

[0008] Preferably, in step S2, the photoresist used in the lithography process is a positive photoresist or a negative photoresist, the exposure light source is one of deep ultraviolet light (DUV), extreme ultraviolet light (EUV) or electron beam exposure, the exposure dose is 10 - 500 mJ / cm², and the development time is 30 - 120 s.

[0009] Preferably, in step S2, the etching process adopts dry etching or wet etching. The gas used for dry etching is , , , , , Ar and other mixed gases, the etching power is 100 - 500 W, and the etching time is 5 - 20 min; the etching solution used for wet etching is , , HCl solution or KOH, NaOH alkaline solution, the etching temperature is 20 - 50 °C, and the etching time is 2 - 10 min.

[0010] In a preferred embodiment, in step S3, the first photoresist is a chemically amplified photoresist, and the second photoresist is a phenolic resin-based photoresist.

[0011] In a preferred embodiment, in step S3, the first photoresist is a photoresist based on polymethyl methacrylate (PMMA), and the second photoresist is a cyclized rubber-based photoresist.

[0012] In a preferred embodiment, in step S3, in the bilayer photoresist structure, the thickness of the second photoresist layer is 0.5 - 2 μm; in the multilayer photoresist structure, except for the first photoresist layer, the thickness of each other photoresist layer is 0.3 - 1.5 μm, and adjacent photoresist layers cooperate with each other in terms of chain unwinding or crosslinking characteristics to enhance the "undercut" structure.

[0013] In a preferred embodiment, in step S4, when etching the bonding metal layer, ion beam etching (IBE) is used, the ion beam energy is 500 - 2000 eV, the beam current density is 1 - 5 mA / cm², and the etching time is 10 - 30 min.

[0014] In a preferred embodiment, in step S5, the developer or the photoresist remover is an organic solvent, the photoresist removal temperature is 40 - 80 °C, and the photoresist removal time is 10 - 30 min.

[0015] In a preferred embodiment, in step S5, the developer or the photoresist remover is an organic alkaline solution with a concentration of 2 - 5 wt%, the photoresist removal temperature is 40 - 80 °C, and the photoresist removal time is 10 - 30 min.

[0016] Due to the application of the above technical solutions, the beneficial effects of this application compared with the prior art are as follows: A method for preparing Micro LEDs provided by this application, through innovative process steps, especially the design and application of the "undercut" structure mask, successfully solves the problem of the "metal fence" anomaly in the existing Micro LED preparation technology, effectively avoids the LED short circuit / open circuit problem caused by the "metal fence", significantly improves the yield of Micro LEDs, and provides strong support for the large-scale production and application of Micro LEDs.

[0017] During the entire preparation process, the parameters of each process step have a certain degree of flexibility and can be adjusted according to different material characteristics, production equipment, and actual production requirements. For example, there are various options for metal bonding methods, photoresist types, etching processes and parameters, etc. This enables the preparation method of the present invention to better adapt to diverse production scenarios and has a wide range of application prospects.

[0018] Due to the elimination of the adverse effects of the "metal fence", the Micro LEDs prepared by the method of the present invention have been significantly improved in performance, with better film layer coverage and more reliable electrical isolation between electrodes, thus improving the luminous efficiency, stability and service life of Micro LEDs, which helps to promote the further development of Micro LED display technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a flowchart of a method for preparing a Micro LED according to the present invention; Figure 2 It is a schematic diagram of the "metal fence" abnormality existing in the Micro LED process in the prior art; Figure 3 It is a schematic diagram of step S1 in the preparation method of Embodiment 1 of the present invention; Figure 4 It is a schematic diagram of step S2 in the preparation method of Embodiment 1 of the present invention; Figure 5 、 Figure 6 It is a schematic diagram of step S3 in the preparation method of Embodiment 1 of the present invention; Figure 7 It is a structural schematic diagram of step S4 in the preparation method of Embodiment 1 of the present invention; Figure 8 It is a structural schematic diagram of step S5 in the preparation method of Embodiment 1 of the present invention; Among them, 1, driving substrate; 2, bonding metal layer; 3, epitaxial layer; 4, Mesa structure; 5, first photoresist; 6, second photoresist; 7, metal layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to enable those skilled in the art to better understand the solution of the present application, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0022] It should be noted that in the description and claims of this application and the above-mentioned drawings, terms such as "first" and "second" are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so as to implement the embodiments of the present application described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0023] In this application, the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation or be constructed and operated in a specific orientation.

[0024] Moreover, in addition to being able to represent an orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0025] In addition, the terms "installed", "set", "provided with", "connected", "connected to", "socketed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there is an internal connection between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail this application.

[0027] Embodiment 1 Please refer to Figure 1 、 Figure 3-8 , a method for preparing Micro LED, including the following steps: S1. Bond the Micro LED epitaxial layer 3 to the driving substrate 1 through a metal bonding process. The thickness of the epitaxial layer 3 is 0.5 - 10 μm, and the thickness of the bonding metal layer 2 is 0.1 - 5 μm. The metal bonding process adopts one of the methods of thermocompression bonding, eutectic bonding or flip-chip bonding. Among them, the thermocompression bonding temperature is 150 - 300 °C, the pressure is 5 - 20 MPa, and the bonding time is 30 - 1200 s; the eutectic bonding temperature is 200 - 350 °C, and the bonding time is 10 - 60 s; when performing flip-chip bonding, the solder used is indium, tin or gold-tin alloy, the bonding temperature is 180 - 300 °C, and the pressure is 3 - 15 MPa. Different bonding methods and parameter selections can be flexibly adjusted according to actual production requirements and material characteristics to ensure a stable and reliable bonding connection between the epitaxial layer 3 and the driving substrate 1; S2. Form a Mesa mask through a photolithography process, and use an etching process to form a Mesa structure 4 on the bonded epitaxial layer 3. The photoresist used in the photolithography process is a positive photoresist or a negative photoresist, and the exposure light source is one of deep ultraviolet light (DUV), extreme ultraviolet light (EUV) or electron beam exposure. The exposure dose is 10 - 500 mJ / cm², and the development time is 30 - 120 s. The etching process adopts dry etching or wet etching. The gas used in dry etching is , , , , , Ar and other mixed gases, the etching power is 100 - 500 W, and the etching time is 5 - 20 min; the etching solution used in wet etching is , , HCl solution or KOH, NaOH alkaline solution, the etching temperature is 20 - 50 °C, and the etching time is 2 - 10 min. By precisely controlling the parameters of photolithography and etching, a Mesa structure that meets the requirements can be prepared, laying a foundation for subsequent process steps; S3. Form a double-layer or multi-layer photoresist structure on the surface of the Mesa structure 4 through two or more coating processes. Among them, the thickness of the first photoresist 5 is 0.1 - 1 μm, and the de-linking or cross-linking effects of the first photoresist 5 and the second photoresist 6 under the same exposure and development conditions are different, resulting in a "undercut" structure in the lower layer after exposure and development, that is, the photoresist mask forms a stepped structure with a wider upper part and a narrower lower part on the side wall; For example, the first photoresist 5 can be a chemically amplified photoresist, and the second photoresist 6 can be a phenolic resin-based photoresist; or the first photoresist 5 is a photoresist based on polymethyl methacrylate (PMMA), and the second photoresist 6 is a cyclized rubber-based photoresist. After exposure and development, a stepped "undercut" structure with a wider top and a narrower bottom will be formed at the sidewalls of the photoresist mask; in the double-layer photoresist structure, the thickness of the second photoresist 6 layer is generally 0.5 - 2 μm; in the multi-layer photoresist structure, except for the first photoresist 5 layer, the thickness of each other photoresist layer is 0.3 - 1.5 μm, and adjacent photoresist layers cooperate with each other in terms of depolymerization or cross-linking characteristics to enhance the effect of the "undercut" structure. This "undercut" structure mask is one of the key innovations of the present invention, which provides an important guarantee for subsequent solving the "metal fence" problem; S4, using the "undercut" structure mask as a template, etching the bonding metal layer 2. During the etching process, the metal deposited on the sidewalls cannot form a continuous layer due to the existence of the "undercut" structure, and is only discontinuously attached to the top and bottom of the mask, thus effectively avoiding the formation of the "metal fence"; the etching method can adopt ion beam etching (IBE). If ion beam etching (IBE) is adopted, the ion beam energy is 500 - 2000 eV, the beam current density is 1 - 5 mA / cm², and the etching time is 10 - 30 min; S5, removing the photoresist through a developer or a stripping solution, and simultaneously stripping the discontinuous metal layer 7 on the sidewalls. The developer or the stripping solution can be an organic alkaline solution, such as a tetramethylammonium hydroxide (TMAH) solution with a concentration of 2 - 5 wt%; or it can be an organic solvent, such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), etc. The stripping temperature is 40 - 80 °C, and the stripping time is 10 - 30 min. After this step, a Micro LED with an independent pixel structure can be obtained, and it will not be affected by the "metal fence", greatly improving the performance and manufacturing yield of the product.

[0028] Embodiment 2 A method for preparing a Micro LED includes the following steps: S1, epitaxial layer bonding: Preparing materials and equipment: Select a Micro LED epitaxial layer with a thickness of 2 μm, which has good crystal structure and optical properties and is suitable for high-resolution Micro LED displays; the driving substrate is a pre-treated CMOS wafer with a flat surface and good electrical conductivity and thermal stability; the bonding metal layer material is a gold-tin alloy, which has good welding performance and reliability and can ensure a stable connection between the epitaxial layer and the driving substrate; use a high-precision thermocompression bonding device, which can precisely control parameters such as temperature, pressure, and time.

[0029] Bonding process: Place the epitaxial layer and the driving substrate on the workbench of the thermocompression bonding equipment, and adjust the positions to accurately align the two; Set the thermocompression bonding parameters, with the temperature at 200 °C, the pressure at 10 MPa, and the bonding time at 60 s; During the bonding process, the AuSn alloy gradually melts and diffuses under the action of high temperature and high pressure to achieve a firm bond between the epitaxial layer and the driving substrate; After bonding, detect the bonding interface, and use a scanning electron microscope (SEM) to observe the microstructure of the bonding interface to ensure that the bonding interface is uniform and free of defects such as voids and cracks.

[0030] S2, Form the Mesa structure: Lithography process: Select a positive photoresist, which has advantages such as high resolution and steep line edges and is suitable for preparing a high-precision Mesa mask. Use a deep ultraviolet light (DUV) exposure machine for exposure, and set the exposure dose to 30 mJ / cm²; Before exposure, first evenly coat the photoresist on the surface of the bonded epitaxial layer, and control the thickness of the photoresist through a spin coater to make its thickness uniform and meet the process requirements; After exposure, put the sample into the developer for development, and the development time is 60 s. During the development process, the exposed part of the photoresist will be dissolved and removed, thus forming an accurate Mesa mask pattern.

[0031] Etching process: Adopt a dry etching process, and the etching gas is , , mixed gas, and are mainly used to etch the epitaxial layer material, is used to remove by-products such as polymers generated during the etching process to ensure the smooth progress of the etching process; Set the power of the etching equipment to 200 W and the etching time to 10 min; During the etching process, accurately control the etching depth and the perpendicularity of the sidewalls by controlling parameters such as gas flow rate, pressure, and etching time. Finally, successfully form a Mesa structure on the bonded epitaxial layer, and use an atomic force microscope (AFM) to measure the surface morphology and size of the Mesa structure to ensure that parameters such as the height, width, and sidewall angle of the Mesa structure meet the design requirements.

[0032] S3, Prepare the mask for the "undercut" structure: Glue Coating Process: First, a chemically amplified photoresist with a thickness of 0.5 μm is coated as the first photoresist layer. The chemically amplified photoresist features high sensitivity and high resolution, capable of generating obvious chemical changes during the exposure process. A spin coater is used to evenly coat the photoresist on the surface of the Mesa structure. The thickness of the photoresist is controlled by adjusting the rotation speed and time of the coater. Then, a phenolic resin-based photoresist with a thickness of 1 μm is coated as the second photoresist layer. The phenolic resin photoresist has good etching resistance and thermal stability, enabling it to maintain the integrity of the mask during subsequent processes. Similarly, a spin coater is used for coating to ensure the uniformity of the thickness of the second photoresist layer.

[0033] Exposure and Development: The sample coated with photoresist is placed in an exposure machine for exposure. The exposure light source is the same as that when forming the Mesa mask, which is deep ultraviolet light (DUV). Since the chemically amplified photoresist and the phenolic resin-based photoresist have different depolymerization or crosslinking effects under the same exposure conditions, after exposure, development is carried out. During the development process, the exposed part of the chemically amplified photoresist will quickly depolymerize and dissolve in the developer, while the phenolic resin-based photoresist will undergo a crosslinking reaction and its solubility in the developer decreases. By precisely controlling the development time and developer concentration, a "undercut" structure mask with a wider upper sidewall and a narrower lower sidewall is finally formed. A scanning electron microscope (SEM) is used to observe the sidewall morphology of the "undercut" structure mask and measure parameters such as the depth and angle of the "undercut" structure to ensure that the "undercut" structure meets the design requirements.

[0034] S4, Metal Layer Etching: Etching Equipment and Parameters: An ion beam etching (IBE) equipment is used to etch the bonding metal layer. IBE has the advantages of high etching accuracy and good anisotropy, capable of precisely controlling the etching position and depth. The sample is placed in the vacuum chamber of the IBE equipment, and the energy of the ion beam is adjusted to 1000 eV, the beam current density is 3 mA / cm², and the etching time is 20 min. During the etching process, the ion beam bombards the surface of the bonding metal layer, causing metal atoms to sputter out from the surface to achieve the etching of the metal layer. Due to the existence of the "undercut" structure mask, the metal deposited on the sidewalls cannot form a continuous layer and only adheres discontinuously at the top and bottom of the mask.

[0035] Etching Monitoring: During the etching process, in-situ monitoring equipment is used to monitor the progress and quality of the etching in real-time. By monitoring parameters such as the current and voltage of the ion beam and the composition of the etching products, the etching process parameters are adjusted in a timely manner to ensure the stability and consistency of the etching process. After etching is completed, the scanning electron microscope (SEM) is used again to observe the etching effect of the bonding metal layer, measure the thickness of the etched metal layer and the deposition of the sidewall metal, and verify the effectiveness of the "undercut" structure mask in preventing continuous metal deposition.

[0036] S5, Remove the photoresist and sidewall metal: Photoresist removal solution and conditions: Use an organic alkaline solution with a concentration of 3 wt% as the developer and photoresist removal solution. The organic alkaline solution can effectively dissolve the photoresist and has less corrosion to the Micro LED structure. Place the etched sample into the photoresist removal solution, control the temperature at 60 °C, and the photoresist removal time is 20 min. During the photoresist removal process, the alkaline components in the solution will chemically react with the photoresist, causing the photoresist to gradually dissolve. At the same time, due to the discontinuous attachment of the sidewall metal, the sidewall metal will also be stripped synchronously during the dissolution of the photoresist.

[0037] Cleaning and detection: After photoresist removal is completed, use deionized water to wash the sample multiple times to remove impurities such as the residual photoresist removal solution and metal debris on the sample surface. Then use an optical microscope and a scanning electron microscope (SEM) to detect the sample, and observe the surface morphology and structural integrity of the Micro LED; through detection, it is found that the photoresist and sidewall metal are completely removed, the Micro LED forms an independent pixel structure, and there is no "metal fence" phenomenon. Conduct electrical performance tests on this batch of Micro LEDs, including measuring parameters such as the current-voltage characteristics and luminous intensity of each pixel. The results show that the yield rate of this batch of Micro LEDs reaches more than 95%, which has been significantly improved compared with the traditional preparation method.

[0038] Example Three A method for preparing Micro LEDs, comprising the following steps: S1, Epitaxial layer bonding: Material selection and preparation: Select a high-quality Micro LED epitaxial layer with a thickness of 5 μm, which has excellent luminous efficiency and uniformity; the driving substrate uses a specially treated glass substrate, which has good insulation performance and optical transmittance and is suitable for Micro LED displays; the solder used for flip-chip bonding is indium, which has a low melting point and good wettability and can achieve reliable electrical and mechanical connections; use a high-precision flip-chip bonding device, which can accurately control the bonding position and pressure.

[0039] Bonding operation: Fix the epitaxial layer and the driving substrate on the two workbenches of the flip-chip bonding device respectively, and achieve precise alignment of the two through the optical alignment system; set the bonding parameters, the bonding temperature is 250 °C, and the pressure is 8 MPa; during the bonding process, the indium solder melts at high temperature and fills the gap between the epitaxial layer and the driving substrate to achieve the connection between the two; after bonding is completed, use an X-ray detection device to detect the bonding points to ensure that the quality and quantity of the bonding points meet the requirements and there are no defects such as virtual soldering and short circuits.

[0040] S2, form a Mesa structure: Lithography step: Select a negative photoresist. The negative photoresist has high contrast and etching resistance, and is suitable for preparing a mask for a complex Mesa structure. Electron beam lithography technology is used for exposure. Electron beam lithography has extremely high resolution and can achieve high-precision patterning. Before exposure, the negative photoresist is evenly coated on the surface of the bonded epitaxial layer. The thickness of the photoresist is controlled by adjusting the coating process. The exposure dose is set at 40 mJ / cm². After exposure, the sample is placed in a developer for development. The development time is 90 s. During development, the unexposed part of the photoresist will be dissolved and removed, thus forming the required Mesa mask pattern.

[0041] Etching process: Use a wet etching process. The etching solution is , , a mixed solution of HCl or an alkaline solution of KOH and NaOH, which is mainly used to etch the epitaxial layer material, plays an oxidation role to promote the etching reaction, and HCl is used to adjust the acidity and etching rate of the etching solution; the etching temperature is controlled at 30 °C, and the etching time is 5 min. During etching, the uniformity of etching is ensured by stirring the etching solution and controlling the etching time. After etching, a profiler is used to measure size parameters such as the height and width of the Mesa structure to ensure that the Mesa structure meets the design requirements.

[0042] S3, prepare a mask for the "undercut" structure: Coating process: First, coat a photoresist based on polymethyl methacrylate (PMMA) with a thickness of 0.3 μm as the first photoresist layer; PMMA photoresist has good film-forming properties and lithography properties and can form precise patterns in subsequent processes; use a spin coater to evenly coat the PMMA photoresist on the surface of the Mesa structure, and control the thickness of the photoresist by adjusting the parameters of the spin coater. Then coat a cyclized rubber-based photoresist with a thickness of 0.8 μm as the second photoresist layer. The cyclized rubber-based photoresist has good antireflection properties and etching resistance and can enhance the stability of the "undercut" structure. Similarly, a spin coater is used for coating to ensure the uniformity of the thickness of the second photoresist layer.

[0043] Exposure and Development Optimization: The sample coated with photoresist is placed in an exposure machine for exposure. The exposure light source is an electron beam. Due to the different reaction characteristics of PMMA photoresist and cyclized rubber-based photoresist under electron beam exposure, development is carried out after exposure. During the development process, the exposed part of the PMMA photoresist will degrade and its solubility in the developer will increase, while the cyclized rubber-based photoresist will undergo a crosslinking reaction and its solubility will decrease. By precisely controlling the concentration, temperature, and development time of the developer, an ideal "undercut" structure mask is finally formed. The atomic force microscope (AFM) is used to measure the surface topography of the "undercut" structure mask and analyze parameters such as the flatness and roughness of the "undercut" structure to ensure that the "undercut" structure meets the process requirements.

[0044] S4, Metal Layer Etching: Ion Beam Etching Parameter Setting: The ion beam etching (IBE) process is used to etch the bonding metal layer; the ion beam energy is set to 1500 eV, the beam current density is 4 mA / cm², and the etching time is 15 min; during the etching process, the ion beam precisely bombards the bonding metal layer. Affected by the "undercut" structure mask, the metal deposited on the sidewalls cannot form a continuous layer and only discontinuously adheres to the top and bottom of the mask.

[0045] Etching Effect Monitoring: During the etching process, in-situ spectroscopic monitoring technology is used to monitor the etching depth and the etching rate of the metal in real time; after the etching is completed, the scanning electron microscope (SEM) is used again to observe the etching situation of the bonding metal layer, measure the thickness of the etched metal layer and the deposition state of the sidewall metal, and verify the effectiveness of the "undercut" structure in preventing continuous metal deposition.

[0046] S5, Removal of Photoresist and Sidewall Metal: Photoresist Removal and Cleaning: The organic solvent N-methylpyrrolidone (NMP) is used as the photoresist remover. N-methylpyrrolidone has good solubility and can quickly dissolve the photoresist. The etched sample is placed in the N-methylpyrrolidone solution, the temperature is controlled at 70 °C, and the photoresist removal time is 25 min; during the photoresist removal process, the photoresist gradually dissolves in the N-methylpyrrolidone solution, and at the same time, the discontinuous metal layer on the sidewalls will also be peeled off as the photoresist dissolves; after the photoresist removal is completed, the sample is washed multiple times with acetone and deionized water to remove impurities such as residual N-methylpyrrolidone and metal debris on the sample surface.

[0047] Performance detection and yield evaluation: The samples were detected using an optical microscope and a scanning electron microscope (SEM) to observe the surface morphology and structural integrity of the Micro LED; comprehensive performance tests were carried out on this batch of Micro LED, including electrical performance tests (such as current-voltage characteristics, resistance, etc.), optical performance tests (such as luminous intensity, wavelength, etc.) and reliability tests (such as high-temperature aging test, humidity test, etc.); through testing, it was found that the performance indicators of this batch of Micro LED met the design requirements, and there were no problems such as short circuits or open circuits caused by the "metal fence". The yield of this batch of products reached 96%, further verifying the effectiveness and stability of the method of the present invention.

[0048] Example 4 A method for preparing Micro LED, comprising the following steps: S1, epitaxial layer bonding: Material selection: Select a Micro LED epitaxial layer with a thickness of 3 μm, which shows excellent performance in terms of luminous efficiency and stability; the driving substrate is selected as a ceramic substrate with good heat dissipation performance to meet the heat dissipation requirements of Micro LED during operation; the bonding metal layer is made of silver-copper alloy, which has excellent electrical conductivity and high bonding strength.

[0049] Eutectic bonding operation: Adopt the eutectic bonding method, place the epitaxial layer and the ceramic substrate in the eutectic bonding equipment, set the bonding temperature to 280 °C, and the bonding time to 30 s; during the bonding process, the silver-copper alloy melts, and by precisely controlling the temperature and time, the alloy is evenly filled between the epitaxial layer and the ceramic substrate to achieve a firm bond between the two; after bonding, use an ultrasonic scanning microscope to detect the bonding interface to check for defects such as voids and poor soldering to ensure the bonding quality.

[0050] S2, forming a Mesa structure: Lithography process: Select a negative photoresist for the lithography process, use an extreme ultraviolet light (EUV) exposure machine for exposure, and set the exposure dose to 25 mJ / cm²; before coating the photoresist, clean the surface of the bonded sample to enhance the adhesion of the photoresist; evenly coat the photoresist on the sample surface by spin coating to control the thickness of the photoresist; after exposure, put the sample into the developer for development, and the development time is 45 s to form a Mesa mask pattern.

[0051] Etching process: Use dry etching, and the etching gas is selected and The mixed gas, the etching power is adjusted to 300 W, and the etching time is set to 8 min; during the etching process, the etching rate and etching uniformity are monitored in real time, and by adjusting the gas flow rate and equipment parameters, ensure that a Mesa structure meeting the requirements is accurately etched on the epitaxial layer after bonding; after the etching is completed, a scanning electron microscope (SEM) is used to measure the key dimensions of the Mesa structure, such as height, width, and sidewall angle, etc., to ensure that it meets the design standards.

[0052] S3, prepare the mask for the "undercut" structure: Multi-layer photoresist coating: First, coat a chemically amplified photoresist with a thickness of 0.4 μm as the first photoresist layer, then coat a phenolic resin-based photoresist with a thickness of 1.2 μm as the second photoresist layer, and finally coat a special polymer photoresist with a thickness of 0.6 μm as the third photoresist layer; the special polymer photoresist can further optimize the "undercut" structure and enhance its stability.

[0053] Exposure and development to form the structure: Expose the sample coated with photoresist, and the exposure light source is extreme ultraviolet light (EUV); since the three-layer photoresist has different chain-breaking or cross-linking effects under the same exposure and development conditions, after exposure and development treatment, a complex and stable "undercut" structure mask is formed; use an atomic force microscope (AFM) to analyze the surface morphology of the "undercut" structure and measure its key parameters such as depth and slope to ensure that the "undercut" structure achieves the expected effect.

[0054] S4, metal layer etching: Ion beam etching parameter setting: Use the ion beam etching (IBE) process to etch the bonded metal layer; set the ion beam energy to 2000 eV, the beam current density to 5 mA / cm², and the etching time to 10 min; during the etching process, the ion beam precisely bombards the bonded metal layer. Affected by the "undercut" structure mask, the metal deposited on the sidewalls cannot form a continuous layer and only adheres discontinuously at the top and bottom of the mask.

[0055] Etching effect monitoring: During the etching process, use in-situ spectroscopy monitoring technology to monitor the etching depth and the etching rate of the metal in real time; after the etching is completed, use a scanning electron microscope (SEM) again to observe the etching situation of the bonded metal layer, measure the thickness of the etched metal layer and the deposition state of the sidewall metal, and verify the effectiveness of the "undercut" structure in preventing continuous metal deposition.

[0056] S5, remove the photoresist and sidewall metal: Desizing treatment: An organic alkaline solution with a concentration of 4 wt% is selected as the developer and desizing solution. The etched sample is immersed in the solution, with the temperature controlled at 75 °C and the desizing time being 20 min. During the desizing process, a chemical reaction occurs between the organic alkaline solution and the photoresist, causing the photoresist to gradually dissolve, and at the same time, the discontinuous metal layer on the sidewalls is also stripped off.

[0057] Cleaning and detection: After desizing, the sample is repeatedly cleaned with acetone, alcohol, and deionized water in sequence to remove the residual solution and impurities. Then, an optical microscope and a scanning electron microscope (SEM) are used to comprehensively detect the sample to observe the surface morphology and structural integrity of the Micro LED. Electrical performance tests are conducted on this batch of Micro LEDs, including measuring parameters such as the resistance of each pixel, current-voltage curve, etc., and luminescence performance tests are carried out to detect indicators such as luminous intensity and luminous uniformity. After testing, the yield rate of this batch of Micro LEDs reaches 97%, fully demonstrating the feasibility and superiority of the process in this embodiment.

[0058] A method for preparing Micro LEDs provided by this application, through innovative process steps, especially the design and application of the "undercut" structure mask, successfully solves the problem of the "metal fence" abnormality in the existing Micro LED preparation technology, effectively avoids the LED short circuit / open circuit problem caused by the "metal fence", significantly improves the yield rate of Micro LEDs, and provides strong support for the large-scale production and application of Micro LEDs.

[0059] During the entire preparation process, the parameters of each process step have a certain degree of flexibility and can be adjusted according to different material properties, production equipment, and actual production requirements. For example, there are various options for metal bonding methods, photoresist types, etching processes and parameters, etc. This enables the preparation method of the present invention to better adapt to diverse production scenarios and has a broad application prospect.

[0060] Due to eliminating the adverse effects of the "metal fence", the Micro LEDs prepared according to the method of the present invention have been significantly improved in performance. Their film layer coverage effect is better, and the electrical isolation between electrodes is more reliable, thereby improving the luminous efficiency, stability, and service life of Micro LEDs, and contributing to the further development of Micro LED display technology.

[0061] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used 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 on 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 method for preparing Micro LED, characterized in that: The steps include: S1, bonding the Micro LED epitaxial layer to the driving substrate through a metal bonding process, wherein the epitaxial layer has a thickness of 0.5-10 μm and the bonding metal layer has a thickness of 0.1-5 μm; S2, forming a Mesa mask by a photolithography process, and forming a Mesa structure on the bonded epitaxial layer by an etching process; S3, forming a double-layer or multi-layer photoresist structure on the surface of the Mesa structure through two or more coating processes; wherein the thickness of the first photoresist is 0.1-1 μm, and the first photoresist and the second photoresist have different depolymerization or cross-linking effects under the same exposure and development conditions, so that a lower layer "undercut" structure is formed after exposure and development, that is, the photoresist mask forms a stepped structure with a wide top and a narrow bottom at the side wall; S4, using the "undercut" structure mask as a template, etching the bonding metal layer. During the etching process, the metal deposited on the sidewall cannot form a continuous layer due to the existence of the "undercut" structure, and is only discontinuously attached to the top and bottom of the mask; S5, removing the photoresist by using a developer or a degumming solution, and simultaneously peeling off the discontinuous metal layer on the side wall to obtain a Micro LED with an independent pixel structure.

2. A Micro LED preparation method according to claim 1, characterized in that: In step S1, the metal bonding process adopts one of hot compression bonding, eutectic bonding or flip chip bonding, wherein the hot compression bonding temperature is 150-300°C, the pressure is 5-20MPa, and the bonding time is 30-1200s; the eutectic bonding temperature is 200-350°C, and the bonding time is 10-60s; when flip chip bonding, the solder used is indium, tin or gold-tin alloy, the bonding temperature is 180-300°C, and the pressure is 3-15MPa.

3. The method for preparing Micro LED according to claim 1, characterized in that: In step S2, the photoresist used in the photolithography process is positive photoresist or negative photoresist, the exposure light source is one of deep ultraviolet (DUV), extreme ultraviolet (EUV) or electron beam exposure, the exposure dose is 10-500mJ / cm², and the development time is 30-120s.

4. The method for preparing Micro LED according to claim 1, characterized in that: In step S2, the etching process adopts dry etching or wet etching, and the gas used in dry etching is , , , , , a variety of mixed gases in Ar, the etching power is 100-500W, and the etching time is 5-20min; the etching solution used in wet etching is , , HCl solution or KOH, NaOH alkaline solution, the etching temperature is 20-50℃, and the etching time is 2-10min.

5. The method for preparing Micro LED according to claim 1, characterized in that: In step S3, the first photoresist is a chemically amplified photoresist, and the second photoresist is a phenolic resin-based photoresist.

6. The method for preparing Micro LED according to claim 1, characterized in that: In step S3 , the first photoresist is a photoresist based on polymethyl methacrylate (PMMA), and the second photoresist is a cyclized rubber-based photoresist.

7. The method for preparing Micro LED according to claim 1, characterized in that: In step S3, in the double-layer photoresist structure, the thickness of the second photoresist layer is 0.5-2 μm; In the multi-layer photoresist structure, except for the first photoresist layer, the thickness of other photoresist layers is 0.3-1.5μm, and the two adjacent photoresist layers cooperate with each other in terms of debonding or cross-linking characteristics to enhance the "undercut" structure.

8. The method for preparing Micro LED according to claim 1, characterized in that: In step S4, when etching the bonding metal layer, ion beam etching (IBE) is adopted, the ion beam energy is 500-2000eV, the beam current density is 1-5mA / cm², and the etching time is 10-30min.

9. The method for preparing Micro LED according to claim 1, characterized in that: In step S5, the developer or degumming solution is an organic solvent, the degumming temperature is 40-80°C, and the degumming time is 10-30 minutes.

10. The method for preparing Micro LED according to claim 1, characterized in that: In step S5, the developer or degumming solution is an organic alkaline solution with a concentration of 2-5 wt %, a degumming temperature of 40-80° C., and a degumming time of 10-30 min.

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