A method for preparing Micro LED

Abstract

The present application discloses a method for manufacturing Micro LEDs, comprising the following steps: S1, bonding a Micro LED epitaxial layer to a driving substrate through a metal bonding process; S2, forming a Mesa mask through a photolithography process, and forming a Mesa structure on the bonded epitaxial layer by using 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; so that a lower-layer "undercut" structure is formed after exposure and development; S4, etching the bonded metal layer by using the "undercut" structure mask as a template; S5, removing the photoresist by using a developer or a stripping solution, and simultaneously stripping the discontinuous metal layer on the sidewall to obtain Micro LEDs with an independent pixel structure; through the innovative process steps, especially the design and application of the "undercut" structure mask, the present application successfully solves the problem of the "metal fence" abnormality in the existing Micro LED manufacturing technology, and significantly improves the yield rate of Micro LEDs.

Description

Technical Field

[0001] The present invention relates to the technical field of Micro LED display, and particularly 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 micro-display 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 achieve 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 by 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 to solve the abnormal problem of "metal fence" that appears during the etching of the metal in the pixel bonding layer in the prior art, improve the short circuit / open circuit situation of the LED 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:

[0007] A method for preparing Micro LED includes the following steps:

[0008] 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;

[0009] S2, form a Mesa mask through a photolithography process, and form a Mesa structure on the epitaxial layer after bonding by using an etching process;

[0010] S3, form a double-layer or multi-layer photoresist structure on the surface of the Mesa structure through two or more photoresist coating processes; among them, the thickness of the first photoresist is 0.1 - 1 μm, and the unlinking or crosslinking effects of the first photoresist and the second photoresist under the same exposure and development conditions are different, so that a lower-layer "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;

[0011] 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;

[0012] S5, remove the photoresist through a developer or a photoresist remover, and simultaneously strip the discontinuous metal layer on the sidewalls to obtain a Micro LED with an independent pixel structure.

[0013] Preferably, in step S1, the metal bonding process adopts one of the hot pressing bonding, eutectic bonding or flip chip bonding methods, where the hot pressing 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 using 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.

[0014] Preferably, in step S2, the photoresist used in the photolithography 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 two photoresists cooperate with each other in the characteristics of unlinking or crosslinking to enhance the "undercut" structure.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] Due to the application of the above technical solutions, the beneficial effects of this application compared with the prior art are as follows:

[0023] A method for preparing Micro LED 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 LED, and provides strong support for the large-scale production and application of MicroLED.

[0024] During the whole 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 choices for the metal bonding method, photoresist type, etching process and parameters, etc. This makes the preparation method of the present invention better adapt to diverse production scenarios and has a wide application prospect.

[0025] 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. 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, which helps to promote the further development of Micro LED display technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 It is a flowchart of a method for preparing a Micro LED according to the present invention;

[0028] Figure 2 It is a schematic diagram of the "metal fence" abnormality existing in the Micro LED process in the prior art;

[0029] Figure 3 It is a schematic diagram of step S1 in the preparation method of Embodiment 1 of the present invention;

[0030] Figure 4 It is a schematic diagram of step S2 in the preparation method of Embodiment 1 of the present invention;

[0031] Figure 5 、 Figure 6 It is a schematic diagram of step S3 in the preparation method of Embodiment 1 of the present invention;

[0032] Figure 7 It is a schematic structural diagram of step S4 in the preparation method of Embodiment 1 of the present invention;

[0033] Figure 8 It is a schematic structural diagram of step S5 in the preparation method of Embodiment 1 of the present invention;

[0034] 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

[0035] To enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0036] It should be noted that the terms "first", "second", etc. in the specification, claims and above-mentioned drawings of this application are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances for the embodiments of this 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 comprising 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.

[0037] In this application, the orientation or positional relationship indicated by the terms "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 accompanying 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.

[0038] 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.

[0039] In addition, the terms "install", "set", "be provided with", "connect", "be connected", "be sleeved" 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 can be internal communication 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.

[0040] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] Embodiment 1

[0042] Please refer to Figure 1 、 Figures 3 - 8 , a method for manufacturing a Micro LED, comprising the following steps:

[0043] S1. Through a metal bonding process, bond the Micro LED epitaxial layer 3 to the driving substrate 1. 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 using 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;

[0044] 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, 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 for dry etching is 、 、 、 、 、 a variety of mixed gases of Ar, 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. 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;

[0045] S3. Form a double-layer or multi-layer photoresist structure on the surface of the Mesa structure 4 through two or more spin-coating processes. Among them, the thickness of the first photoresist 5 is 0.1 - 1 μm, and the chain scission or crosslinking 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 that is wider at the top and narrower at the bottom on the sidewalls.

[0046] For example, the first photoresist 5 can be a chemically amplified photoresist, and the second photoresist 6 can be a phenol-formaldehyde resin-based photoresist; or the first photoresist 5 is a polymethyl methacrylate (PMMA)-based photoresist, and the second photoresist 6 is a cyclized rubber-based photoresist. After exposure and development, the photoresist mask will form a stepped "undercut" structure that is wider at the top and narrower at the bottom on the sidewalls. 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 chain scission or crosslinking characteristics to enhance the effect of the "undercut" structure. This "undercut" structure mask is one of the key innovations of the present invention and provides an important guarantee for subsequent solving the "metal fence" problem.

[0047] S4. Using the "undercut" structure mask as a template, etch 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 only adheres discontinuously at 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 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.

[0048] S5. Remove the photoresist through a developer or a stripping solution, and simultaneously strip the discontinuous metal layer 7 on the sidewalls. The developer or 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 without being affected by the "metal fence", greatly improving the performance and manufacturing yield of the product.

[0049] Example Two

[0050] A method for preparing a Micro LED includes the following steps:

[0051] S1. Epitaxial layer bonding:

[0052] Preparation of materials and equipment: Select a Micro LED epitaxial layer with a thickness of 2 μm. This epitaxial layer 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, whose surface is flat and has good electrical conductivity and thermal stability; the bonding metal layer material is gold-tin alloy, which has good soldering performance and reliability, and can ensure a firm connection between the epitaxial layer and the driving substrate; use a high-precision thermocompression bonding equipment, which can accurately control parameters such as temperature, pressure and time.

[0053] Bonding process: Place the epitaxial layer and the driving substrate on the workbench of the thermocompression bonding equipment, and adjust the position to accurately align the two; set the thermocompression bonding parameters, the temperature is 200 °C, the pressure is 10 MPa, and the bonding time is 60 s; during the bonding process, the gold-tin 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.

[0054] S2, forming a Mesa structure:

[0055] Lithography process: Select a positive photoresist, which has the advantages of high resolution and steep line edges, and is suitable for preparing high-precision Mesa masks. 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.

[0056] Etching process: Adopt a dry etching process, and the etching gas is 、 、 mixed gas, and are mainly used for etching the epitaxial layer material, It is used to remove by-products such as polymers generated during the etching process to ensure the smooth progress of the etching process; the power of the etching equipment is set to 200W, and the etching time is 10 minutes; during the etching process, by controlling parameters such as gas flow, pressure, and etching time, the etching depth and the perpendicularity of the sidewalls are precisely controlled. Finally, a Mesa structure is successfully formed on the epitaxial layer after bonding. An atomic force microscope (AFM) is used 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.

[0057] S3. Prepare a mask for the "undercut" structure:

[0058] Photoresist 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 has the characteristics of high sensitivity and high resolution and can produce obvious chemical changes during the exposure process. A spin coater is used to uniformly 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 and can maintain the integrity of the mask during subsequent processes. The spin coater is also used for coating to ensure the uniform thickness of the second photoresist layer.

[0059] 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 for forming the Mesa mask, which is deep ultraviolet light (DUV). Since the chemically amplified photoresist and the phenolic resin-based photoresist have different chain scission 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 undergo chain scission 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 mask for the "undercut" structure with a wider upper part and a narrower lower part on the sidewalls is finally formed. A scanning electron microscope (SEM) is used to observe the sidewall morphology of the "undercut" structure mask, and parameters such as the depth and angle of the "undercut" structure are measured to ensure that the "undercut" structure meets the design requirements.

[0060] S4. Metal layer etching:

[0061] Etching Equipment and Parameters: An ion beam etching (IBE) equipment is used to etch the bonded metal layer. IBE has the advantages of high etching accuracy and good anisotropy, and can precisely control 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 bonded metal layer, causing metal atoms to sputter out from the surface, realizing 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 discontinuously adheres to the top and bottom of the mask.

[0062] Etching Monitoring: During the etching process, in-situ monitoring equipment is used to monitor the progress and quality of 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, a scanning electron microscope (SEM) is used again to observe the etching effect of the bonded metal layer, measure the thickness of the etched metal layer and the deposition of sidewall metal, and verify the effectiveness of the "undercut" structure mask in preventing continuous metal deposition.

[0063] S5, Remove Photoresist and Sidewall Metal:

[0064] Photoresist Removing Solution and Conditions: An organic alkaline solution with a concentration of 3 wt% is used as the developer and photoresist remover. The organic alkaline solution can effectively dissolve the photoresist and has less corrosion to the Micro LED structure. The etched sample is placed in the photoresist removing solution, the temperature is controlled at 60 °C, and the photoresist removing time is 20 min. During the photoresist removing 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 adhesion of the sidewall metal, the sidewall metal will also be stripped synchronously during the dissolution of the photoresist.

[0065] Cleaning and Detection: After photoresist removal is completed, the sample is washed multiple times with deionized water to remove impurities such as residual photoresist removing solution and metal debris on the sample surface. Then, an optical microscope and a scanning electron microscope (SEM) are used to detect the sample to observe the surface morphology and structural integrity of the Micro LED. It is found through detection that the photoresist and sidewall metal are completely removed, the Micro LED forms an independent pixel structure, and there is no "metal fence" phenomenon. Electrical performance tests are carried out 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.

[0066] Example Three

[0067] A method for preparing Micro LED, comprising the following steps:

[0068] S1, epitaxial layer bonding:

[0069] 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 display; 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.

[0070] Bonding operation: Fix the epitaxial layer and the driving substrate on two workbenches of the flip-chip bonding device respectively, and achieve precise alignment of the two through an 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, 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 open circuits and short circuits.

[0071] S2, forming a Mesa structure:

[0072] Lithography step: Select a negative photoresist, which has high contrast and etching resistance and is suitable for preparing a mask for a complex Mesa structure. Use electron beam exposure technology for exposure. Electron beam exposure has extremely high resolution and can achieve high-precision patterning. Before exposure, evenly coat the negative photoresist on the surface of the bonded epitaxial layer, control the thickness of the photoresist by adjusting the coating process, set the exposure dose to 40 mJ / cm², and after exposure, put the sample into the developer for development. The development time is 90 s. During the development process, the unexposed part of the photoresist will be dissolved and removed, thus forming the required Mesa mask pattern.

[0073] Etching process: Adopt a wet etching process, and the etching solution is 、 、a mixed solution of HCl or a KOH and NaOH alkaline solution, which is mainly used to etch the epitaxial layer material, It plays an oxidizing role and promotes the etching reaction, while 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 the etching process, the uniformity of etching is ensured by stirring the etching solution and controlling the etching time. After the etching is completed, a profiler is used to measure the size parameters such as the height and width of the Mesa structure to ensure that the Mesa structure meets the design requirements.

[0074] S3. Prepare the mask for the "undercut" structure:

[0075] Photoresist coating process: First, a photoresist based on polymethyl methacrylate (PMMA) with a thickness of 0.3 μm is coated as the first photoresist layer; PMMA photoresist has good film-forming properties and lithography properties, and can form precise patterns in subsequent processes; a spin coater is used to uniformly coat the PMMA photoresist on the surface of the Mesa structure, and the thickness of the photoresist is controlled by adjusting the parameters of the coater. Then, a cyclized rubber-based photoresist with a thickness of 0.8 μm is coated as the second photoresist layer. The cyclized rubber-based photoresist has good anti-reflection properties and etching resistance, and can enhance the stability of the "undercut" structure. The spin coater is also used for coating to ensure the uniformity of the thickness of the second photoresist layer.

[0076] Exposure and development optimization: The sample coated with photoresist is placed in an exposure machine for exposure, and the exposure light source is an electron beam. Since the reaction characteristics of PMMA photoresist and cyclized rubber-based photoresist under electron beam exposure are different, after exposure, development is carried out. 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 cross-linking reaction and its solubility will decrease. By precisely controlling the concentration, temperature, and development time of the developer, an ideal mask for the "undercut" structure is finally formed. An atomic force microscope (AFM) is used to measure the surface topography of the mask for the "undercut" structure, and parameters such as the flatness and roughness of the "undercut" structure are analyzed to ensure that the "undercut" structure meets the process requirements.

[0077] S4. Metal layer etching:

[0078] Ion beam etching parameter setting: The bonding metal layer is etched using the ion beam etching (IBE) process; 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 mask for the "undercut" structure, the metal deposited on the sidewalls cannot form a continuous layer and only adheres discontinuously at the top and bottom of the mask.

[0079] Etching effect monitoring: During the etching process, in-situ spectroscopy monitoring technology is used to monitor the etching depth and the etching rate of the metal in real time; after the etching is completed, a scanning electron microscope (SEM) is used again to observe the etching condition 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.

[0080] S5, removing photoresist and sidewall metal:

[0081] 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 sidewall will also be peeled off as the photoresist dissolves; after the photoresist removal is completed, the sample is washed repeatedly with acetone and deionized water to remove impurities such as residual N-methylpyrrolidone and metal debris on the sample surface.

[0082] Performance detection and yield evaluation: An optical microscope and a scanning electron microscope (SEM) are used to detect the sample, and the surface morphology and structural integrity of the Micro LED are observed; comprehensive performance tests are carried out on this batch of Micro LEDs, 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 is found that the performance indicators of this batch of Micro LEDs all meet the design requirements, and there are no problems such as short circuit or open circuit caused by the "metal fence". The yield of this batch of products reaches 96%, further verifying the effectiveness and stability of the method of the present invention.

[0083] Example 4

[0084] A method for preparing Micro LED, comprising the following steps:

[0085] S1, epitaxial layer bonding:

[0086] 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 uses a silver-copper alloy, which has excellent electrical conductivity and high bonding strength.

[0087] 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 at 280 °C and the bonding time at 30 s. During the bonding process, the silver-copper alloy melts. 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 the bonding is completed, 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.

[0088] S2, Form the Mesa structure:

[0089] Lithography process: Select a negative photoresist for the lithography process. Use an extreme ultraviolet light (EUV) exposure machine for exposure. Set the exposure dose at 25 mJ / cm². Before coating the photoresist, clean the surface of the bonded sample to enhance the adhesion of the photoresist. Uniformly 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 for 45 s to form a Mesa mask pattern.

[0090] Etching process: Use dry etching. Select the etching gas as and mixed gas. Adjust the etching power to 300 W and set the etching time at 8 min. During the etching process, monitor the etching rate and etching uniformity in real time. By adjusting the gas flow rate and equipment parameters, ensure that a Mesa structure that meets the requirements is accurately etched on the bonded epitaxial layer. After the etching is completed, use a scanning electron microscope (SEM) 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.

[0091] S3, Prepare the mask for the "undercut" structure:

[0092] Multi-layer 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. 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.

[0093] Exposure and development to form the structure: Expose the sample coated with the photoresist. The exposure light source is extreme ultraviolet light (EUV). Since the three-layer photoresist has different de-linking or cross-linking effects under the same exposure and development conditions, after exposure and development, a complex and stable "undercut" structure mask is formed. Analyze the surface topography of the "undercut" structure by an atomic force microscope (AFM) and measure its key parameters such as depth and slope to ensure that the "undercut" structure achieves the expected effect.

[0094] S4, Metal layer etching:

[0095] Ion beam etching parameter setting: The bonding metal layer is etched using the ion beam etching (IBE) process; the ion beam energy is set to 2000 eV, the beam current density is 5 mA / cm², and the etching time is 10 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.

[0096] 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.

[0097] S5, Remove photoresist and sidewall metal:

[0098] Photoresist removal treatment: An organic alkaline solution with a concentration of 4 wt% is selected as the developer and photoresist remover. The etched sample is immersed in the solution, the temperature is controlled at 75 °C, and the photoresist removal time is 20 min; during the photoresist removal process, the organic alkaline solution chemically reacts with the photoresist, causing the photoresist to gradually dissolve, and at the same time, the discontinuous metal layer on the sidewalls is also stripped off.

[0099] Cleaning and detection: After the photoresist removal is completed, the sample is washed multiple times with acetone, alcohol, and deionized water in sequence to remove the remaining solution and impurities; then the optical microscope and 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 carried out on this batch of Micro LEDs, including measuring parameters such as the resistance of each pixel, the current-voltage curve, etc., and luminescence performance tests are carried out to detect indicators such as luminescence intensity and luminescence uniformity; after testing, the yield rate of this batch of Micro LEDs reaches 97%, fully demonstrating the feasibility and superiority of the process of this embodiment.

[0100] A method for preparing Micro LED provided by this application, through innovative process steps, especially the design and application of the "undercut" structure mask, successfully solves the problem of "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 LED, and provides strong support for the large-scale production and application of MicroLED.

[0101] 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 multiple choices 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 broad application prospects.

[0102] 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. 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, which helps to promote the further development of Micro LED display technology.

[0103] 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, for those skilled in the art, they can still modify the technical solutions recorded 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 method for preparing Micro LED, characterized in that, It includes the following steps: S1. Bond the Micro LED epitaxial layer to the driving substrate through a metal bonding process. 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 photolithography process, and use an etching process to form a Mesa structure on the bonded epitaxial layer. S3. Form a double-layer or multi-layer photoresist structure on the surface of the Mesa structure through two or more photoresist coating processes. Among them, the thickness of the first photoresist is 0.1 - 1 μm, and the de-linking or cross-linking effects of the first photoresist and the second photoresist under the same exposure and development conditions are different, so that a lower-layer "undercut" structure is formed after exposure and development, that is, the photoresist mask forms a stepped structure with a wider top and a narrower bottom at the side wall. S4. Using the "undercut" structure mask as a template, etch the bonding metal layer. During the etching process, the metal deposited on the side wall 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. Remove the photoresist through a developer or a stripping solution, and simultaneously strip the discontinuous metal layer on the side wall to obtain a Micro LED with an independent pixel structure.

2. The method for preparing a Micro LED according to claim 1, wherein In step S1, the metal bonding process adopts one of the hot press bonding, eutectic bonding or flip chip bonding methods. Among them, the hot press 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 using 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.

3. The method for preparing a Micro LED according to claim 1, wherein, In step S2, the photoresist used in the photolithography 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.

4. A method for manufacturing a Micro LED according to claim 1, wherein, In step S2, the etching process uses dry etching or wet etching. The gas used for dry etching is , , , , , a mixture of multiple gases among Ar, 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 and NaOH alkaline solutions, the etching temperature is 20 - 50 °C, and the etching time is 2 - 10 min.

5. A method for preparing a 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. A method for preparing a 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. A method for preparing a Micro LED according to claim 1, wherein, 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 each other photoresist layer is 0.3 - 1.5 μm, and adjacent two photoresist layers cooperate with each other in terms of de-linking or cross-linking characteristics to enhance the "undercut" structure.

8. A method for preparing a 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 - 2000 eV, the beam current density is 1 - 5 mA / cm², and the etching time is 10 - 30 min.

9. A method for preparing a Micro LED according to claim 1, wherein, In step S5, the developer or the stripping solution is an organic solvent, the stripping temperature is 40 - 80 °C, and the stripping time is 10 - 30 min.

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

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