A heterogeneous composite microlens micro-LED device and a preparation method thereof

Abstract

This application relates to the field of Micro-LED microdisplay technology, and in particular to a heterogeneous composite microlens Micro-LED device and its fabrication method. The method includes spin-coating a first organic material onto the surface of a device chip and curing it at high temperature to form a first organic material layer; spin-coating a second organic material layer onto the first organic material layer to form a second organic material layer; performing exposure, development, and patterning; wherein the first and second organic material layers are heterogeneous organic materials with a refractive index difference; subjecting the second organic material layer to a heating and reflow treatment to form an upper curved surface structure; introducing a first mixed atmosphere and performing a first cyclic etching stage on the first organic material layer to form a lower curved surface structure; introducing a second mixed atmosphere and performing a second cyclic etching stage to form a heterogeneous composite microlens. This method effectively controls the curvature of the top arc of the microlens, forming a microlens morphology with a superior aspect ratio. Combined with the curved surface structure of the microlens composed of heterogeneous materials, it improves the normal brightness of the device.

Description

Technical Field

[0001] This application relates to the field of Micro-LED micro-display technology, and in particular to a heterogeneous composite microlens Micro-LED device and its fabrication method. Background Technology

[0002] Micro-LED, as a next-generation display technology, has broad application prospects in AR / VR, wearable devices, automotive displays, and ultra-high-resolution displays. However, the light emission of Micro-LED chips follows a Lambertian distribution, with an emission angle exceeding 120°. This results in a large number of non-directional beams not being effectively collected and utilized, causing severe losses. Simultaneously, with the continuous improvement of display resolution requirements, Micro-LED pixel sizes have shrunk to the micrometer or even sub-micrometer level, resulting in extremely small pixel pitches. Light from adjacent pixels easily interferes with each other, leading to a decrease in contrast and clarity of the displayed image. This problem is particularly prominent in scenarios requiring small beam angles. Furthermore, GaN has a refractive index close to 2.5, while air has a refractive index of only 1. This significant difference in refractive index, influenced by Fresnel losses, causes a large amount of light to be trapped inside the chip and unable to escape effectively, further reducing the device's external quantum efficiency and luminous brightness. It also increases the difficulty of beam angle control, limiting the application of GaN-based Micro-LED devices in high-end display fields.

[0003] To achieve precise control of the beam angle of Micro-LED devices, existing technologies include microlens array integration. Microlens arrays have become the most promising technology route for industrialization due to their simple structural design, flexible optical design, and relatively mature fabrication process.

[0004] However, the microlenses used in Micro-LED devices in related technologies are mainly single-material microlenses, and their fabrication processes include hot-melt reflow, nanoimprinting, and mask-based etching. These single-material microlenses and their fabrication processes have obvious limitations: On the one hand, the traditional hot-melt reflow method can only naturally form a hemispherical structure through the surface tension of the material, which cannot achieve optical designs with a large aspect ratio, and the range of control over the divergence angle of the microlens is limited. Although the nanoimprinting process can fabricate lenses with a large aspect ratio, it must rely on a customized master mold, which is not only costly and time-consuming, but also requires high substrate flatness, making it impossible to flexibly control the geometric parameters of the microlens on the same substrate, and limiting the beam angle narrowing and normal brightness collection capabilities. On the other hand, the refractive index of single-material microlenses is fixed, and it is impossible to achieve a multi-gradient transition of refractive index from the Micro-LED chip (GaN-based chip refractive index of about 2.5) to air (refractive index 1). This results in a large refractive index abrupt change at the interface between the chip and the microlens, and between the microlens and air, which limits the improvement in light extraction efficiency and makes it difficult to meet the high brightness and high luminous efficiency requirements of high-end displays. Summary of the Invention

[0005] This application aims to propose a heterogeneous composite microlens Micro-LED device and its fabrication method, in order to solve the technical problem in the related technology of fabricating heterogeneous composite microlenses on GaN-based Micro-LEDs, where it is difficult to control the curvature of the top arc of the microlens, making it impossible to achieve a specific tilt angle surface, resulting in limited ability to improve the collimation effect and normal brightness of the microlens.

[0006] In a first aspect, this application provides a method for fabricating a heterogeneous composite microlens Micro-LED device, comprising: A GaN-based Micro-LED chip is provided, and a first organic material is spin-coated onto the surface of the GaN-based Micro-LED chip and cured at high temperature to form a first organic material layer; A second organic material is spin-coated onto the first organic material layer to form a second organic material layer, and the second organic material layer is exposed, developed, and patterned to form a square pattern array. The first organic material layer and the second organic material layer are heterogeneous organic materials, and the difference in refractive index is in the range of 0.2-0.4. The patterned second organic material layer is subjected to a heating and reflow process to form an upper curved surface structure. A first mixed atmosphere is introduced to perform a first cyclic etching stage on the first organic material layer to form a lower curved surface structure, wherein the first mixed atmosphere is CH4 and CF4, and the flow rate ratio of CH4 to CF4 is 1:7-1:3. A second mixed atmosphere is introduced to perform a second cyclic etching stage on the first organic material layer, and the etching rate is reduced to adjust the curvature of the upper curved surface structure to form a heterogeneous composite microlens. The second mixed atmosphere is CH4 and CHF3, and the flow ratio of CH4 to CHF3 is 1:3-1:1. An inert gas is introduced to purge the heterogeneous composite microlens structure, removing residual etching gas and byproducts, thus completing the fabrication of the heterogeneous composite microlens Micro-LED device.

[0007] In some embodiments, the first organic material layer is made of any one or more organic polymers such as PI, SU-8, and SOG, and its spin-coating speed range is 2000rpm-3500rpm, and its thickness range is 1.4um-2um. The second organic material layer is composed of any one or more photoresist materials, including positive photoresist and negative photoresist, and its spin coating speed range is 4000rpm-6000rpm, and its thickness range is 1.5um-2um.

[0008] In some embodiments, during the reflow heating process, the second organic material layer is formed into a hemispherical structure with a diameter ranging from 3.5 μm to 3.6 μm and a height ranging from 1.7 μm to 1.8 μm by reflow heating using a hot table or a constant temperature oven; and the ratio of the thickness of the first organic material layer to the height of the second organic material layer after hot melting and reflow is in the range of 1 to 1.4.

[0009] In some embodiments, during the first cyclic etching stage, the etching time for one unit cycle ranges from 60s to 100s, the etching power ranges from 150W to 300W, the number of cyclic etching cycles ranges from 4 to 6, and the etching depth ranges from 0.6um to 1.8um.

[0010] In some embodiments, during the second cyclic etching stage, the etching time for one unit cycle ranges from 60s to 80s, the etching power ranges from 120W to 200W, the number of cyclic etching cycles ranges from 6 to 10, and the etching depth ranges from 0.36um to 1.2um.

[0011] In some embodiments, during the first or second cyclic etching stage, the pressure range of the etching environment is 0.1 Pa to 1 Pa, and the temperature range of the etching environment is 40°C to 90°C.

[0012] In some embodiments, the etching rate of the first cyclic etching stage ranges from 25 Å / s to 30 Å / s; and the etching rate of the second cyclic etching stage ranges from 10 Å / s to 15 Å / s.

[0013] Compared with the prior art, the technical solution provided in the first aspect of this application has at least the following beneficial effects or advantages: The method provided in this application involves spin-coating and high-temperature curing a first organic material layer on the surface of a GaN-based Micro-LED chip, and then spin-coating a second organic material layer on top of it, the refractive index of which is controlled to be between 0.2 and 0.4. Through exposure, development, and reflow heating, the second organic material layer forms an upper curved structure under surface tension. Subsequently, a staged cyclic etching process is employed. In the first cyclic etching stage, a mixed atmosphere of CH4 and CF4 with a flow ratio of 1:7 to 1:3 is introduced. CH4 provides sidewall passivation and shape retention, while CF4 provides high-efficiency etching capability. This mixed atmosphere is used to achieve a high etching rate for the first organic material layer and a low etching rate for the second organic material layer. By controlling the etching depth to 0.6µm-1.8µm, rapid and conformal etching of the first organic material layer was achieved, constructing a microlens base structure with a large aspect ratio. In the second etching cycle, a CH4 and CHF3 mixed atmosphere with a flow ratio of 1:3 to 1:1 was switched. By reducing the overall etching rate and adjusting the etching selectivity, excess photoresist at the top was gradually and uniformly removed. This precisely corrected deviations such as a smooth top surface and sharp edges that appeared after the first etching stage, ensuring a consistent etching rate across the top region and ultimately forming a regular shape. This avoided over-etching at once, which could lead to top collapse or curvature distortion. The continuous curved surface was gradually etched to create a non-traditional ellipsoidal lens structure, effectively narrowing the beam angle and enhancing the normal brightness collection capability. Simultaneously, the bilayer microlens structure composed of two heterogeneous organic materials formed a multi-gradient refractive index transition interface from the GaN-based chip to air, significantly reducing interface reflection losses between the chip and the microlens, and between the microlens and air, thus improving the device's light extraction efficiency. The entire fabrication process does not rely on a customized master mold, which effectively reduces the fabrication cost and shortens the production cycle. At the same time, it has lower requirements for substrate flatness and has better industrial adaptability.

[0014] In a second aspect, this application provides a heterogeneous composite microlens Micro-LED device, which is fabricated by the method for fabricating a heterogeneous composite microlens Micro-LED device as described in any one of the first aspects above, including a GaN-based Micro-LED chip composed of a CMOS driving module and a GaN light-emitting module, and a heterogeneous composite microlens disposed on the light-emitting surface of the GaN-based Micro-LED chip. The CMOS driving module includes a silicon-based driving substrate and a driving substrate metal layer stacked on the silicon-based driving substrate. The GaN light-emitting module is electrically connected to the CMOS driving module through the driving substrate metal layer. The GaN light-emitting module includes: an isolation passivation layer disposed on the driving substrate metal layer, a chip bonding metal layer, a P-GaN layer, a GaN active layer and an N-GaN layer that are wrapped by the isolation passivation layer and stacked sequentially on the driving substrate metal layer, and a current spreading layer that is wrapped by an organic material layer and stacked on the N-GaN layer.

[0015] In some embodiments, the heterogeneous composite microlens includes: a lower curved surface structure for controlling the size of the microlens, and an upper curved surface structure stacked on the lower curved surface structure for controlling the contour curvature of the microlens; the upper curved surface structure and the lower curved surface structure are made of two heterogeneous materials.

[0016] In some embodiments, the heterogeneous composite microlens is a three-dimensional curved surface structure with a beam-contracting effect, and the sidewall tilt angle of the heterogeneous composite microlens is in the range of 75°-80°.

[0017] Compared with the prior art, the technical solution provided in the second aspect of this application has at least the following beneficial effects or advantages: The heterogeneous composite microlens Micro-LED device provided in this application adopts an integrated structure of a CMOS driving module and a GaN light-emitting module bonded together. The driving substrate metal layer on the silicon-based driving substrate provides a stable electrical connection and current transmission channel for the GaN light-emitting module. The isolation passivation layer provides comprehensive protection for the chip bonding metal layer and each semiconductor functional layer, preventing device leakage and improving reliability. The current spreading layer can uniformly disperse the injected current and improve the light emission uniformity of the GaN active layer. The heterogeneous composite microlens set on the light-emitting surface of the device is composed of two heterogeneous organic materials with a refractive index difference controlled between 0.2 and 0.4. The double-layer heterogeneous structure can form a multi-gradient refractive index transition interface from the GaN-based chip to air, forming a secondary progressive refractive index gradient distribution. A variable refractive index structure is formed inside the heterogeneous composite microlens to improve the light-gathering effect. The heterogeneous composite microlens also has a curved profile with a large aspect ratio, which can effectively narrow the beam angle and enhance the normal brightness collection capability.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the fabrication of a heterogeneous composite microlens Micro-LED device according to embodiments of this application; Figure 2 This is a schematic diagram of the structure corresponding to step S10 in the process flow method provided in the embodiments of this application; Figure 3 This is a schematic diagram of the structure corresponding to step S20 in the process flow method provided in the embodiments of this application; Figure 4 This is a schematic diagram of the structure corresponding to step S30 in the process flow method provided in the embodiments of this application; Figure 5 This is a schematic diagram of the structure corresponding to step S40 in the process flow method provided in the embodiments of this application; Figure 6 This is a schematic diagram of the structure corresponding to step S50 in the process flow method provided in the embodiments of this application; Figure 7 It is a light distribution curve corresponding to the average beam angle of the device test provided in Embodiment 2 of this application; Figure 8 It is a light distribution curve corresponding to the total luminous flux of the device tested according to Embodiment 2 of this application; Figure 9 It is a light distribution curve corresponding to the average beam angle of the device test provided in Comparative Example 1 of this application; Figure 10 It is a light distribution curve corresponding to the total luminous flux of the device provided in Comparative Example 1 of this application; Figure 11 It is a light distribution curve corresponding to the average beam angle of the device test provided in Comparative Example 2 of this application; Figure 12 It is a light distribution curve corresponding to the total luminous flux of the device provided in Comparative Example 2 of this application; Figure 13 It is a light distribution curve corresponding to the average beam angle of the device test provided in Comparative Example 3 of this application; Figure 14 It is a light distribution curve corresponding to the total luminous flux of the device provided in Comparative Example 3 of this application; Figure 15 It is a light distribution curve corresponding to the average beam angle of the device test provided in Comparative Example 4 of this application; Figure 16 It is a light distribution curve corresponding to the total luminous flux of the device provided in Comparative Example 4 of this application; Figure 17 It is a light distribution curve corresponding to the average beam angle of the device test provided in Comparative Example 5 of this application; Figure 18 It is a light distribution curve corresponding to the total luminous flux of the device provided in Comparative Example 5 of this application; Figure 19 This is a schematic diagram of the structure of a heterogeneous composite microlens Micro-LED device according to an embodiment of this application.

[0021] Figure label: 100. GaN-based Micro-LED chip; 110. CMOS driver module; 111. Silicon-based driver substrate; 112. Driver substrate metal layer; 120. GaN light-emitting module; 121. Isolation passivation layer; 122. Chip bonding metal layer; 123. P-GaN layer; 124. GaN active layer; 125. N-GaN layer; 126. Current spreading layer; 200. Heterogeneous composite microlens; 210. First organic material layer; 220. Second organic material layer; 211. Lower curved surface structure; 221. Upper curved surface structure. Detailed Implementation

[0022] The embodiments of this application are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application.

[0023] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. "Multiple" means at least two, that is, two or more; "multiple" means at least two, that is, two or more.

[0024] In this application, "and / or" is merely a way of describing the relationship between related objects, indicating that three relationships can exist; for example, a and / or b can represent three cases: a alone, a and b simultaneously, and b alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0027] Example 1 Please see Figures 1 to 6 This embodiment provides a method for fabricating a heterogeneous composite microlens Micro-LED device, wherein the fabrication method includes: Step S10: Provide a GaN-based Micro-LED chip, spin-coat a first organic material onto the surface of the GaN-based Micro-LED chip and cure it at high temperature to form a first organic material layer; In some embodiments, combined with Figure 2 The GaN-based Micro-LED chip 100 is composed of a CMOS driving module and a GaN light-emitting module. A first organic material is spin-coated onto the top surface of the GaN-based Micro-LED chip 100 and cured at high temperature to form a first organic material layer 210. The first organic material layer 210 is made of any one or more organic polymers such as PI, SU-8, and SOG. The spin-coating speed range for preparing the first organic material layer 210 is 2000rpm-3500rpm. At the same time, the total thickness of the first organic material layer 210 is controlled within the range of 1.4um-2um to ensure that the first organic material uniformly covers the surface of the GaN-based Micro-LED chip without bubbles or missed coatings.

[0028] Optionally, the high-temperature curing of the first organic material can be carried out in a constant temperature oven, cured at 180°C for 60 minutes, and then cooled to room temperature. The surface of the cured organic polymer coating is smoother, providing a flat substrate for subsequent photoresist coating and microlens molding.

[0029] It should be noted that the GaN-based Micro-LED chip 100 can be divided into a pixel region, an N-ring region, and a pad region. The fabricated heterogeneous composite microlens 200 structure is only located in the pixel region. The pixel region can include a driving substrate, a bonding metal layer, a light-emitting semiconductor layer, a semiconductor passivation layer, and a current spreading layer. The light-emitting semiconductor layer includes an N-type GaN layer, a multi-quantum-well light-emitting layer, and a P-type GaN layer. The current spreading layer is made of a Cr / Au multilayer material. The refractive index of the organic polymer material is controlled between 1.40 and 1.60 to meet the subsequent light-focusing requirements of the microlens, and the viscosity range is adjusted to 14 mPa·s-17 mPa·s to ensure uniform spin-coating.

[0030] Step S20: Spin-coating a second organic material onto the first organic material layer to form a second organic material layer, and then exposing and developing the second organic material layer to form a square pattern array, wherein the first organic material layer and the second organic material layer are heterogeneous organic materials, and the difference in refractive index is in the range of 0.2-0.4. In some embodiments, combined with Figure 1 and Figure 3 A second organic material is spin-coated onto the first organic material layer 210 to form a second organic material layer 220. The second organic material layer 220 is composed of any one or more photoresist materials, such as positive photoresist and negative photoresist. Preferably, the second organic material is 5312-51 positive photoresist. The spin-coating process for preparing the second organic material layer 220 has a rotation speed range of 4000rpm-6000rpm, for example, 5500rpm. The thickness of the second organic material layer 220 ranges from 1.5um to 2um. The ICP power ranges from 100w to 300w, the RF power ranges from 20w to 50w, and the etching time ranges from 10s to 30s. ICP etching can improve the roughness of the first organic material layer 210 and enhance the adhesion of the second organic material layer 220 thereon.

[0031] Furthermore, a UV exposure machine is used for exposure processing, with an exposure time range of 200ms-400ms, to ensure accurate transfer of the photolithographic pattern to the photoresist layer. For example, a 3.4µm square photolithographic pattern size photomask can be selected. The size of the photolithographic pattern directly determines the width of the subsequent microlens contour; a larger size results in a wider microlens. After exposure, the sample is placed in a developing solution for development to remove the photoresist in unexposed areas. After development, a hot plate is used for post-baking at 115℃ for 60s to stabilize the photoresist pattern and improve the adhesion of the mask structure.

[0032] It should be noted that the first organic material layer 210 and the second organic material layer 220 are heterogeneous organic materials, and the difference in refractive index is in the range of 0.2-0.4, thereby forming a secondary progressive refractive index gradient distribution, so as to form a variable refractive index structure inside the heterogeneous composite microtransparent structure to improve the light-gathering effect.

[0033] Step S30: The patterned second organic material layer is subjected to heating and reflow treatment to form an upper curved surface structure; In some embodiments, combined with Figure 1 and Figure 4 The upper curved structure 221 is fabricated by heating and reflowing the second organic material layer 220 using a hot stage or constant temperature oven, taking advantage of the surface tension of the photoresist material. The upper curved structure 221, after sufficient reflow, is approximately hemispherical in shape, with a diameter ranging from 3.5µm to 3.6µm and a hemispherical height ranging from 1.7µm to 1.8µm. Furthermore, the ratio of the thickness of the first organic material layer 210 to the height of the second organic material layer 220 after hot reflow is between 1 and 1.4.

[0034] Optionally, during the heating and reflow process using a hot stage, the reflow temperature is 163°C and the reflow time is 10 minutes to allow the photoresist to fully reflow and solidify.

[0035] In another embodiment, a two-stage gradient reflow process can be used: the initial reflow temperature is set to 160°C to allow the photoresist to flow slightly; then the temperature is raised to 166°C for a second reflow to ensure that the photoresist is fully reflowed and to avoid excessive flow of the pattern caused by a single high temperature.

[0036] Step S40: Introduce a first mixed atmosphere to perform a first cyclic etching stage on the first organic material layer 210 to form a lower curved surface structure 211, wherein the first mixed atmosphere is CH4 and CF4, and the flow rate ratio of CH4 to CF4 is 1:7-1:3. In some embodiments, combined with Figure 1 and Figure 5 Using an inductively coupled plasma etching apparatus, the first organic material layer 210 below the upper curved structure 221 is etched under a first mixed atmosphere, so that the first organic material layer 210 can inherit the morphology of the upper curved structure 221 after etching. That is, the first organic material layer 210 forms a curved contour with a smooth transition between the circumferential contour of the first organic material layer 210 and the circumferential contour of the second organic material layer 220. The first mixed atmosphere is CH4 and CF4, and the flow ratio of CH4 to CF4 is 1:7-1:3. In the first cycle etching stage, the etching time of one unit cycle is 60s-100s, the etching power is 150W-300W, the cycle etching is 4-6 times, and the etching depth is 0.6um-1.8um.

[0037] It should be noted that when the etching power is higher than 300W, the photoresist mask is deformed by heat during the etching process, affecting the morphology of the microlens. The bottom of the lower curved surface structure 211 formed by the first stage etching does not extend directly to the top surface of the GaN-based Micro-LED chip 100. A portion of the first organic material layer 210 is reserved between the lower curved surface structure 211 and the GaN-based Micro-LED chip 100 to form a gap. If the etching depth of the first stage is less than 0.6µm, it will lead to a significant increase in the etching time of the second stage, which will make the curvature of the top of the microlens flat, resulting in a microlens structure that is not conducive to forming a small beam angle.

[0038] At the same time, the first mixing atmosphere in this stage can passivate the sidewalls of the heterogeneous composite lens and play a shape-preserving role for the lower curved surface structure.

[0039] Step S50: Introduce a second mixed atmosphere to perform a second cyclic etching stage on the first organic material layer 210, and reduce the etching rate to trim the curvature of the upper curved structure 221 to form a heterogeneous composite microlens 200. The second mixed atmosphere is CH4 and CHF3, and the flow ratio of CH4 to CHF3 is 1:3-1:1. In some embodiments, combined with Figure 1 and Figure 6 Using an inductively coupled plasma etching apparatus, the first organic material layer 210 beneath the upper curved structure 221 is further etched. Under the high aspect ratio microlens morphology obtained in the first cyclic etching stage, the top curvature is further modified by slow etching. The second mixed atmosphere is CH4 and CHF3, with a CH4 to CHF3 flow rate ratio of 1:3 to 1:1. In addition to etching the first organic material layer 210, this stage also refines the curvature of the upper curved structure 221 formed by the second organic material layer 220 by reducing the etching rate.

[0040] It should be noted that in the second mixed atmosphere, if the flow ratio of CH4 to CHF3 is less than 1:3, excessive F will result in strong lateral etching, bottom shrinkage, reduced top curvature, and narrowing of the lens. If the flow ratio of CH4 to CHF3 is greater than 1:1, insufficient F and excessive carbon passivation will result in slower etching, polymer residue on the surface, incomplete etching, and abnormal surface curvature. It should also be noted that the reason why slow etching in this embodiment can modify the curvature of the top of the microlens is mainly due to the low-rate, low-power and highly controllable etching characteristics. The slow etching rate is controlled in the range of 10 Å / s-15 Å / s, which is lower than the etching rate range of 25 Å / s-30 Å / s in the first cycle etching stage. This allows for the gradual and uniform removal of excess photoresist from the top. This progressive etching can accurately correct deviations such as the top being flat and the edges being protruding after the first stage etching, making the etching rate of each area on the top as consistent as possible, and ultimately forming a regular shape. This avoids the top collapsing or curvature distortion caused by excessive etching at one time. The continuous curved surface is gradually etched to form a non-traditional ellipsoidal lens structure.

[0041] Furthermore, in the second etching cycle, the etching time for one unit cycle is 60-80 seconds, the etching power ranges from 120W to 200W, the number of etching cycles is 6-10, and the etching depth ranges from 0.36µm to 1.2µm. The 60-80 second etching time per unit cycle is important to note; an excessively long cycle time can lead to morphology deformation. A cycle length of 60-80 seconds ensures stable temperature during etching. The 0.36µm-1.2µm etching depth ensures a balance between the etching curvature and the etching depth.

[0042] In another embodiment, the pressure range within the cavity during the first and second etching cycles is 0.1 Pa to 1 Pa, and the cavity temperature is maintained between 40°C and 90°C. By controlling the pressure range to the low range of 0.1 Pa to 1 Pa, excessively low pressure leads to insufficient etching efficiency, while excessively high pressure causes high-energy ions to bombard and damage the photoresist mask, exacerbating isotropic etching. Maintaining the cavity temperature between 40°C and 90°C avoids high-temperature softening and collapse of the photoresist, thermal deformation failure, promotes the desorption of etching byproducts, and prevents excessive accumulation of passivation material at low temperatures that could hinder etching. This temperature range stabilizes the activation energy of the reaction, achieving a dynamic balance between the etching reaction and sidewall passivation, ensuring a smooth microlens surface profile and good dimensional consistency.

[0043] Step S60: Inert gas is introduced to purge the heterogeneous composite microlens 200 structure, removing residual etching gas and byproducts, thus completing the fabrication of the heterogeneous composite microlens Micro-LED device.

[0044] In some embodiments, the inert gas introduced is at least one of Ar or N2. The purging time for the heterogeneous composite microlens 200 structure ranges from 200s to 500s; the flow rate ranges from 40sccm to 100sccm, thereby removing residual etching gas and byproducts, and completing the fabrication of the heterogeneous composite microlens Micro-LED device. In the preparation method provided in this embodiment, a first organic material layer 210 is spin-coated and high-temperature cured on the surface of a GaN-based Micro-LED chip 100, and a second organic material layer 220 of heterogeneous material with a refractive index difference between the first organic material layer 210 and the first organic material layer 210 is spin-coated on it. Through exposure development and reflow heating, the second organic material layer 220 forms an upper curved surface structure 221 under surface tension. Subsequently, a staged cyclic etching process is adopted. In the first cyclic etching stage, a mixed atmosphere of CH4 and CF4 with a flow ratio of 1:7 to 1:3 is introduced. CH4 provides sidewall passivation and shape retention, while CF4 provides high-efficiency etching capability. This mixed atmosphere is used to achieve a high etching rate for the first organic material layer 210 and a high etching rate for the second organic material layer 220. The low etching selectivity of the material layer 220, controlling the etching depth to 0.6µm-1.8µm, enables rapid and conformal etching of the first organic material layer 210, constructing a microlens base structure with a large aspect ratio. The second etching cycle switches to a CH4 and CHF3 mixed atmosphere with a flow ratio of 1:3 to 1:1. By reducing the overall etching rate and adjusting the etching selectivity, excess photoresist at the top can be gradually and uniformly removed. This progressive etching precisely corrects deviations such as a smooth top surface or protruding edges that occur after the first etching stage, ensuring a consistent etching rate across the top region and ultimately forming a regular shape. This avoids over-etching at once, which could lead to top collapse or curvature distortion. The continuous curved surface is gradually etched to create a non-traditional ellipsoidal lens structure, effectively narrowing the beam angle and enhancing normal brightness collection capability. Simultaneously, the bilayer microlens structure composed of two heterogeneous organic materials forms a multi-gradient refractive index transition interface from the GaN-based chip to air, significantly reducing interface reflection losses between the chip and the microlens, and between the microlens and air, thus improving the device's light extraction efficiency. The entire fabrication process does not rely on a customized master mold, which effectively reduces the fabrication cost and shortens the production cycle. At the same time, it has lower requirements for substrate flatness and has better industrial adaptability.

[0045] Example 2 Please see Figure 7 and Figure 8This embodiment provides experiments on the average beam angle and total luminous flux of a heterogeneous composite microlens Micro-LED device prepared by the method of Example 1. In the fabrication process of the heterogeneous composite microlens Micro-LED device, a first cyclic etching stage is performed. The first mixed atmosphere is CH4 and CF4, with a CH4 to CF4 flow rate ratio of 1:4.5, a CH4 flow rate of 6.5 sccm, and a CF4 flow rate of 30 sccm. The first cyclic etching stage involves 5 etching cycles, with one cycle etching time of 100 s, an etching power range of 200 W, an etching depth of 1.5 μm, and an etching rate range of 30 Å / s. A second cyclic etching stage is then performed, with a second mixed atmosphere of CH4 and CHF. 3. The flow ratio of CH4 to CHF3 is 1:3, the flow rate of CH4 is 1 sccm, and the flow rate of CHF3 is 3 sccm. The second etching cycle consists of 10 etching passes, with one unit cycle etching time of 80 s. The etching power range is 130 W, the etching depth is 1.2 μm, and the etching rate range is 15 Å / s. A total of 15 etching passes are performed across the two etching cycles. The etching environment pressure for both cycles is 0.5 Pa, and the etching environment temperature for both cycles is 60 °C. Other parameters are selectively set according to actual needs. The heterogeneous composite microlens Micro-LED device fabricated under these process parameters is characterized by its light-emitting performance using a high-precision goniometer system. Figure 7 and Figure 8 As shown, the average beam angle (full width at half maximum, FWHM) reaches 28.3°. The polar coordinate beam distribution curve shows that the light energy is highly concentrated in the direction of the device normal, and large-angle stray light is effectively suppressed. The total luminous flux reaches 5.211 lm, achieving excellent light extraction efficiency while realizing light convergence.

[0046] Comparative Example 1 Please see Figure 9 and Figure 10 This comparative example provides a method for fabricating a heterogeneous composite microlens Micro-LED device. The main difference from Example 2 is that the flow ratio of CH4 to CF4 in the first mixed atmosphere is greater than 1:3, the flow rate of CH4 is 15 sccm, and the flow rate of CF4 is 30 sccm. Other steps are the same as in Example 2. Simultaneously, the thicknesses of the organic material layer and the photoresist layer are reasonably set according to the atmosphere etching selectivity ratio. The heterogeneous composite microlens Micro-LED device fabricated in Comparative Example 1 is subjected to performance testing using the same testing method as in Example 2. Figure 9 and Figure 10 It can be seen that the average beam angle (full width at half maximum, FWHM) measured by the high-precision goniometer system reaches 82.8°, and the total luminous flux reaches 3.001 lm.

[0047] Comparative Example 2 Please see Figure 11 and Figure 12 This comparative example provides a method for fabricating a heterogeneous composite microlens Micro-LED device. The main difference from Example 2 is that the flow ratio of CH4 to CF4 in the first mixed atmosphere is less than 1:7, the flow rate of CH4 is 1 sccm, and the flow rate of CF4 is 30 sccm. Other steps are the same as in Example 2. The thicknesses of the organic material layer and the photoresist layer are reasonably set according to the atmosphere etching selectivity ratio. The heterogeneous composite microlens Micro-LED device fabricated in Comparative Example 2 is subjected to performance testing using the same testing method as in Example 2. Figure 11 and Figure 12 It can be seen that the average beam angle (full width at half maximum, FWHM) measured by the high-precision goniometer system reaches 101.7°, and the total luminous flux reaches 2.776 lm.

[0048] Comparative Example 3 Please see Figure 13 and Figure 14 This comparative example provides a method for fabricating a heterogeneous composite microlens Micro-LED device. The main difference from Example 2 is that the flow ratio of CH4 to CHF3 in the second mixed atmosphere is less than 1:3, the flow rate of CH4 is 1 sccm, and the flow rate of CHF3 is 6 sccm. Other steps are the same as in Example 2. The thicknesses of the organic material layer and the photoresist layer are rationally set according to the atmosphere etching selectivity ratio. The heterogeneous composite microlens Micro-LED device fabricated in Comparative Example 3 is subjected to performance testing using the same testing method as in Example 2. Figure 13 and Figure 14 It can be seen that the average beam angle (full width at half maximum, FWHM) measured by the high-precision goniometer system reaches 57.1°, and the total luminous flux reaches 2.502 lm.

[0049] Comparative Example 4 Please see Figure 15 and Figure 16 This comparative example provides a method for fabricating a heterogeneous composite microlens Micro-LED device. The main difference from Example 2 is that the flow ratio of CH4 to CHF3 in the second mixed atmosphere is greater than 1:1, the flow rate of CH4 is 6 sccm, and the flow rate of CHF3 is 3 sccm. Other steps are the same as in Example 2. The thicknesses of the organic material layer and the photoresist layer are rationally set according to the atmosphere etching selectivity ratio. The heterogeneous composite microlens Micro-LED device prepared in Comparative Example 4 is subjected to performance testing using the same testing method as in Example 2. Figure 15 and Figure 16 It can be seen that the average beam angle (full width at half maximum, FWHM) measured by the high-precision goniometer system reaches 70.4°, and the total luminous flux reaches 3.004 lm.

[0050] Comparative Example 5 Please see Figure 17 and Figure 18 This comparative example provides a method for fabricating a heterogeneous composite microlens Micro-LED device. The main difference from Example 2 is that the first mixed atmosphere in the first etching cycle is CF4 and C4F8, and the second mixed atmosphere in the second etching cycle is SF6 and CHF3. Other steps and parameters are the same as in Example 2. The heterogeneous composite microlens Micro-LED device prepared in Comparative Example 5 is then subjected to performance testing using the same method as in Example 2. Figure 17 and Figure 18 It can be seen that the average beam angle (full width at half maximum, FWHM) measured by the high-precision goniometer system reaches 64.3°, and the total luminous flux reaches 2.353 lm.

[0051] Table 1 shows the average beam angle and total luminous flux statistics for Embodiment 2 and Comparative Examples 1-5. Table 1: Average Beam Angle and Total Luminous Flux of Devices

[0052] Based on the test results in Table 1, it can be seen that, in terms of overall performance, the device prepared in Example 2 achieves a simultaneous improvement in light focusing and light extraction efficiency, with an average beam angle of only 28.3° and a total luminous flux of 5.211 lm. In contrast, the average beam angles of the devices prepared in Comparative Examples 1-5 are all higher than 57°, which is 2.0 to 3.6 times that of Example 2, and the total luminous flux is all lower than 3.004 lm, which is only 45% to 58% of that of Example 2. Among them, the total luminous flux of Example 2 is 73.5% higher than that of the best-performing Comparative Example 4 and 121.5% higher than that of the worst-performing Comparative Example 5, while the average beam angle is reduced by more than 60%.

[0053] Meanwhile, comparing the test results of Example 2 with those of Comparative Examples 1 and 2, it can be seen that when the flow ratio of methane to carbon tetrafluoride is within the range of 1:7 to 1:3 defined in this application, the device can simultaneously obtain an extremely small beam angle and extremely high luminous flux. However, deviating from this range results in significant changes in device performance. Specifically, when the flow ratio is greater than 1:3, the average beam angle increases sharply to 82.8°, and the total luminous flux decreases by 42.4%. When the flow ratio is less than 1:7, the average beam angle further increases to 101.7°, and the total luminous flux decreases by 46.7%.

[0054] Secondly, in the second etching cycle, comparing the experimental results of Example 2 with those of Comparative Examples 3 and 4, it can be found that when the flow ratio of methane to trifluoromethane is controlled within a specific range of 1:3 to 1:1, it precisely complements the initial contour of the microlens formed in the first etching stage, thereby obtaining the ideal microlens radius of curvature and sidewall morphology. When the flow ratio is less than 1:3, the total luminous flux drops to the lowest of all samples at 2.502 lm. When the flow ratio is greater than 1:1, the average beam angle increases to 70.4°.

[0055] Furthermore, the test results from Comparative Example 2 and Comparative Example 5 show that even when using the staged cyclic etching process framework of this application, if the etching gas is replaced with the commonly used tetrafluoromethane and octafluorocyclobutane mixture or sulfur hexafluoride and trifluoromethane mixture systems for etching semiconductor materials, the performance of the fabricated device still decreases, with an average beam angle of 64.3° and a total luminous flux of only 2.353 lm. These results demonstrate that the atmosphere system of tetrafluoromethane and methane mixture in the first stage and methane and trifluoromethane mixture in the second stage, designed for the multilayer material characteristics and optical performance requirements of heterogeneous composite microlenses, can achieve high-precision control of the microlens morphology and angle while ensuring the etching rate.

[0056] Example 3 Please see Figure 19 This embodiment provides a heterogeneous composite microlens Micro-LED device, which is fabricated by the method described in Embodiment 1 above. It includes a GaN-based Micro-LED chip 100 composed of a CMOS driving module 110 and a GaN light-emitting module 120, and a heterogeneous composite microlens 200 disposed on the light-emitting surface of the GaN-based Micro-LED chip 100. The CMOS driving module 110 includes a silicon-based driving substrate 111 and a stacked... A driving substrate metal layer 112 is located on a silicon-based driving substrate 111. The GaN light-emitting module 120 is electrically connected to the CMOS driving module 110 through the driving substrate metal layer 112. The GaN light-emitting module 120 includes: an isolation passivation layer 121 disposed on the driving substrate metal layer 112; a chip bonding metal layer 122, a P-GaN layer 123, a GaN active layer 124, and an N-GaN layer 125 that are wrapped by the isolation passivation layer 121 and sequentially stacked on the driving substrate metal layer 112; and a current spreading layer 126 that is wrapped by an organic material layer and stacked on the N-GaN layer 125.

[0057] Optionally, the chip bonding metal layer 122 is made of Ni and Au stacked material, with the thickness of each metal layer being 0.1nm-1nm for Ni and 30nm-50nm for Au.

[0058] Optionally, the driving substrate metal layer 112 is made of a Cr / Au laminate. The thickness of each metal layer is: 20nm-30nm for Cr and 400nm-800nm ​​for Au.

[0059] Optionally, the semiconductor passivation layer material is SiO2 / SiN, with a thickness of 300nm-500nm, and is prepared by plasma-enhanced chemical vapor deposition at a deposition temperature of 200℃-300℃.

[0060] Optionally, the isolation passivation layer 121 material may be an organic polymer material or the same as the semiconductor passivation layer material, used to achieve electrical isolation between adjacent devices and avoid crosstalk.

[0061] Optionally, the current spreading layer 126 is made of a Cr / Au stacked material. It is prepared using an electron beam evaporation process, first evaporating Cr metal to a thickness of 10nm-30nm, and then evaporating Au metal on top to a thickness of 200nm-500nm.

[0062] Optionally, a wafer bonding machine is used to bond the driving substrate metal layer 112 to the chip bonding metal layer 122 together. The bonding conditions are: bonding pressure 5000kg-8000kg, bonding temperature 300℃-350℃, and holding time 600s-1800s.

[0063] The heterogeneous composite microlens Micro-LED device provided in this embodiment adopts an integrated structure in which a CMOS driving module 110 and a GaN light-emitting module 120 are bonded. The driving substrate metal layer 112 on the silicon-based driving substrate 111 provides a stable electrical connection and current transmission channel for the GaN light-emitting module 120. The isolation passivation layer 121 forms a complete protective envelope for the chip bonding metal layer 122 and each semiconductor functional layer, preventing device leakage and improving reliability. The current spreading layer 126 can uniformly disperse the injected current and improve the light emission uniformity of the GaN active layer 124. The heterogeneous composite microlens 200 on the light-emitting surface of the device is composed of two heterogeneous organic materials with a refractive index difference controlled between 0.2 and 0.4. The double-layer heterogeneous structure can form a multi-gradient refractive index transition interface from the GaN-based chip to the air, forming a secondary progressive refractive index gradient distribution. A variable refractive index structure is formed inside the heterogeneous composite microlens to improve the light-gathering effect. The heterogeneous composite microlens 200 also has a curved profile with a large aspect ratio, which can effectively narrow the beam angle and enhance the normal brightness collection capability.

[0064] In some embodiments, continue reading Figure 19The heterogeneous composite microlens 200 includes a lower curved surface structure 211 for controlling the size of the microlens and an upper curved surface structure 221 stacked on the lower curved surface structure 211 for controlling the contour curvature of the microlens. The upper curved surface structure 221 and the lower curved surface structure 211 are made of two heterogeneous materials. The difference in refractive index between the first organic material of the lower curved surface structure 211 and the second organic material of the upper curved surface structure 221 is 0.2-0.4, so as to form a secondary progressive refractive index gradient distribution, forming a variable refractive index structure inside the heterogeneous composite microlens to improve the light-gathering effect.

[0065] Preferably, the first organic material of the lower curved surface structure 211 of the heterogeneous composite lens can be an SOG organic polymer composite material, and the second organic material of the upper curved surface structure 221 can be a positive photoresist 5312-51. The original heterogeneous composite lens and the GaN light-emitting module 120 main substrate are heterogeneous materials.

[0066] In some embodiments, the heterogeneous composite microlens 200 is a three-dimensional curved surface structure with a beam-converging effect, and the sidewall tilt angle of the heterogeneous composite microlens 200 is in the range of 75°-80°, forming a directional refraction constraint on the large-angle lateral light rays, effectively limiting the light-emitting angle to within 30°.

[0067] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the invention.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0069] Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The reference to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily indicate the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0070] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for fabricating a heterogeneous composite microlens Micro-LED device, characterized in that, The method includes: A GaN-based Micro-LED chip is provided, and a first organic material is spin-coated onto the surface of the GaN-based Micro-LED chip and cured at high temperature to form a first organic material layer; A second organic material is spin-coated onto the first organic material layer to form a second organic material layer, and the second organic material layer is exposed, developed, and patterned to form a square pattern array. The first organic material layer and the second organic material layer are heterogeneous organic materials, and the difference in refractive index is in the range of 0.2-0.

4. The patterned second organic material layer is subjected to a heating and reflow process to form an upper curved surface structure. A first mixed atmosphere is introduced to perform a first cyclic etching stage on the first organic material layer to form a lower curved surface structure, wherein the first mixed atmosphere is CH4 and CF4, and the flow rate ratio of CH4 to CF4 is 1:7-1:

3. A second mixed atmosphere is introduced to perform a second cyclic etching stage on the first organic material layer, and the etching rate is reduced to adjust the curvature of the upper curved surface structure to form a heterogeneous composite microlens. The second mixed atmosphere is CH4 and CHF3, and the flow ratio of CH4 to CHF3 is 1:3-1:

1. An inert gas is introduced to purge the heterogeneous composite microlens structure, removing residual etching gas and byproducts, thus completing the fabrication of the heterogeneous composite microlens Micro-LED device.

2. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 1, characterized in that, The first organic material layer is made of any one or more organic polymers such as PI, SU-8, and SOG, and its spin-coating speed range is 2000rpm-3500rpm, and its thickness range is 1.4um-2um. The second organic material layer is composed of any one or more photoresist materials, including positive photoresist and negative photoresist, and its spin coating speed range is 4000rpm-6000rpm, and its thickness range is 1.5um-2um.

3. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 1, characterized in that, In the reflow heating process, the second organic material layer is formed into a hemispherical structure with a diameter ranging from 3.5um to 3.6um and a height ranging from 1.7um to 1.8um by using a hot table or constant temperature oven for reflow heating. The ratio of the thickness of the first organic material layer to the height of the second organic material layer after hot melting and reflow is in the range of 1 to 1.

4.

4. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 1, characterized in that, In the first cyclic etching stage, the etching time for one unit cycle ranges from 60s to 100s, the etching power ranges from 150W to 300W, the number of cyclic etching cycles ranges from 4 to 6, and the etching depth ranges from 0.6um to 1.8um.

5. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 1, characterized in that, In the second cyclic etching stage, the etching time for one unit cycle ranges from 60s to 80s, the etching power ranges from 120W to 200W, the number of cyclic etching cycles ranges from 6 to 10, and the etching depth ranges from 0.36um to 1.2um.

6. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 5, characterized in that, In the first or second cyclic etching stage, the pressure range of the etching environment is 0.1 Pa to 1 Pa, and the temperature range of the etching environment is 40°C to 90°C.

7. The method for fabricating a heterogeneous composite microlens Micro-LED device according to claim 6, characterized in that, The etching rate range for the first cyclic etching stage is 25 Å / s to 30 Å / s; the etching rate range for the second cyclic etching stage is 10 Å / s to 15 Å / s.

8. A heterogeneous composite microlens Micro-LED device, characterized in that, The heterogeneous composite microlens Micro-LED device is fabricated by the method of fabricating the heterogeneous composite microlens Micro-LED device according to any one of claims 1-7, comprising a GaN-based Micro-LED chip composed of a CMOS driving module and a GaN light-emitting module, and a heterogeneous composite microlens disposed on the light-emitting surface of the GaN-based Micro-LED chip. The CMOS driving module includes a silicon-based driving substrate and a driving substrate metal layer stacked on the silicon-based driving substrate. The GaN light-emitting module is electrically connected to the CMOS driving module through the driving substrate metal layer. The GaN light-emitting module includes: an isolation passivation layer disposed on the driving substrate metal layer, a chip bonding metal layer, a P-GaN layer, a GaN active layer and an N-GaN layer that are wrapped by the isolation passivation layer and stacked sequentially on the driving substrate metal layer, and a current spreading layer that is wrapped by an organic material layer and stacked on the N-GaN layer.

9. The heterogeneous composite microlens Micro-LED device according to claim 8, characterized in that, The heterogeneous composite microlens includes: a lower curved surface structure for controlling the size of the microlens, and an upper curved surface structure stacked on the lower curved surface structure for controlling the contour curvature of the microlens; the upper curved surface structure and the lower curved surface structure are made of two heterogeneous materials.

10. The heterogeneous composite microlens Micro-LED device according to claim 9, characterized in that, The heterogeneous composite microlens is a three-dimensional curved surface structure with a beam-contracting effect, and the sidewall tilt angle of the heterogeneous composite microlens ranges from 75° to 80°.

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