MiP packaging structure for preventing optical crosstalk and manufacturing method thereof

Abstract

The invention discloses a MiP packaging structure capable of preventing optical crosstalk and a manufacturing method thereof, and the method comprises the steps: providing a light-transmitting substrate carrying a Micro LED chip, and enabling the chip to be provided with a light-proof electrode; forming a negative shading photoresist layer on the electrode surface of the chip; light rays capable of penetrating through the substrate and a chip semiconductor layer are adopted for exposure from the back face, a light-proof electrode is used as a self-alignment mask, the light resistance layer at the gap of the chip and the back of the chip is subjected to photosensitive curing, and the light resistance layer above the electrode is kept uncured; and developing to remove the photoresist layer above the electrode. By means of the back exposure self-alignment technology, high-precision filling of exposed electrodes and pixel gaps can be achieved without high-precision photoetching alignment, light crosstalk between pixels is effectively blocked, the technological process is simplified, cost is reduced, and the yield is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor display manufacturing technology, specifically relating to a MiP (MicroLED in Package) packaging structure and its manufacturing method for preventing optical crosstalk. Background Technology

[0002] Micro LED display technology is considered a strong contender for next-generation display technology due to its advantages such as high brightness, low power consumption, and long lifespan. MiP, as an important technological approach, solves the challenges of testing and sorting after mass transfer by integrating RGB three-color Micro LED chips into a package.

[0003] However, in the MiP packaging architecture, effectively suppressing optical crosstalk between RGB subpixels is crucial for improving display contrast and color purity. Existing solutions mainly suffer from the following drawbacks: 1. Limitations of chip-level reflective layers: Although light emission efficiency can be optimized through DBR or metal reflective layers, stray light emitted from the chip sidewalls cannot be completely blocked, resulting in color crosstalk.

[0004] 2. Complex and Low-Precision Packaging-Level Processes: Currently, the industry typically uses white or black adhesive for physical isolation. This process usually relies on high-precision lithography machines for front-side alignment, exposure, and development. However, limited by the alignment precision of the lithography machine, edge errors are easily generated when removing the adhesive above the electrodes. These errors can lead to missing filler areas (light leakage) or residual adhesive on the electrodes (causing electrical connection failure), severely impacting product yield and reliability. Furthermore, high-precision lithography equipment is expensive, significantly increasing production costs.

[0005] Therefore, there is an urgent need for a fabrication method that does not require expensive photolithography alignment equipment, can achieve high-precision self-alignment, and can effectively block lateral light crosstalk. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating a Micro LED packaging structure. By using a process that combines back exposure with negative adhesive, and utilizing the self-masking principle of chip electrodes, the self-aligned preparation of the optical crosstalk barrier layer is achieved, solving the problems of severe optical crosstalk and difficult photolithography alignment in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for fabricating a MiP package structure to prevent optical crosstalk includes the following steps: Step S1: Provide a light-transmitting substrate, on one side of which a plurality of Micro LED chips are disposed. Each Micro LED chip has a light-emitting surface facing the light-transmitting substrate and an electrode surface facing away from the light-transmitting substrate. An opaque electrode layer is disposed on the electrode surface. The semiconductor material layer of the Micro LED chip is transparent to light of a specific wavelength. Step S2: A photoresist layer is formed on one side of the electrode surface of the Micro LED chip. The photoresist layer is made of a photosensitive and light-shielding material with negative photoresist properties. Step S3: Expose the light from the side of the transparent substrate facing away from the Micro LED chip using light of the specific wavelength; using the opaque electrode layer as a mask, the light penetrates the transparent substrate, the gap between the Micro LED chip and the semiconductor material layer of the Micro LED chip, causing the photoresist layer located in the gap region and the non-electrode region on the electrode surface to be photosensitive and cured. Step S4: Develop the exposed photoresist layer to remove the uncured photoresist layer above the opaque electrode layer, expose the opaque electrode layer, and form a continuous light crosstalk barrier layer between the Micro LED chips and on the electrode surface of the Micro LED chips.

[0008] In step S2, the photosensitive light-blocking material is selected from one of negative black photoresist, negative white photoresist, and light-absorbing ink with negative photoresist properties.

[0009] When the photosensitive light-shielding material is a negative black photoresist, the light crosstalk blocking layer is used to absorb stray light emitted from the sidewall of the Micro LED chip; When the photosensitive and light-shielding material is a negative white photoresist, the light crosstalk blocking layer is used to reflect the light emitted from the sidewall of the Micro LED chip.

[0010] In step S2, the photoresist layer is formed by one of the following methods: spin coating, spray coating, slot coating, or screen printing.

[0011] In step S3, the wavelength of the light source used for exposure is able to penetrate the light-transmitting substrate, and the wavelength of the light source is within the photosensitive wavelength range of the photosensitive shielding material.

[0012] The light-transmitting substrate is a sapphire substrate, a glass substrate, or a transparent resin substrate.

[0013] Following step S4, step S5 is also included: The structure having the optical crosstalk blocking layer is subjected to a post-curing process, which includes heat baking or ultraviolet curing, to improve the physical stability of the optical crosstalk blocking layer.

[0014] In step S2, the coating thickness of the photoresist layer is controlled so that the height of the light crosstalk barrier layer formed after development in step S4 is flush with or slightly higher than the height of the Micro LED chip.

[0015] The present invention also provides a MiP packaging structure prepared by the above-described method, comprising: Transparent substrate; Multiple Micro LED chips are spaced apart on the light-transmitting substrate; A crosstalk blocking layer is filled in the gap between adjacent Micro LED chips; The upper surface edge of the optical crosstalk blocking layer is flush with or slightly higher than the edge of the electrode layer of the Micro LED chip.

[0016] The beneficial effects of this invention are as follows: 1. Completely eliminate optical crosstalk: By filling the gaps between chips with light-shielding material, the propagation of light from the side walls is physically blocked, significantly improving the contrast and color purity of the display.

[0017] 2. High precision self-alignment process: Utilizing the chip's own metal electrodes as photomasks, it achieves "what you see is what you get" self-aligned patterning, eliminating concerns about alignment errors in the lithography machine and completely solving the problem of light leakage from electrode residue or filling gaps.

[0018] 3. Reduced costs and simplified processes: No need to use expensive high-precision lithography machines and alignment systems; micron-level patterning can be achieved with only conventional exposure equipment, significantly reducing equipment investment and manufacturing costs and improving production efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of the structure provided in step S1 of Embodiment 1 of the present invention, showing a light-transmitting substrate and a Micro LED chip that has completed mass transfer on it, wherein the electrode layer of the chip is arranged facing upwards.

[0020] Figure 2 This is a cross-sectional view of step S2 in Embodiment 1 of the present invention, showing the state after a negative black photoresist is coated on the entire electrode side of the Micro LED chip to form a photoresist layer.

[0021] Figure 3This is a schematic diagram of the process principle of step S3 in Embodiment 1 of the present invention, showing the process of exposing light of a specific wavelength from the back of the light-transmitting substrate, using an opaque electrode as a self-aligning mask.

[0022] Figure 4 This is a schematic cross-sectional view of step S4 in Embodiment 1 of the present invention, showing the state in which an optical crosstalk barrier layer is formed in the chip gap and the non-electrode area on the back side after the uncured photoresist layer above the electrode is removed by development.

[0023] Figure 5 : A microscopic photograph of the electrode area of ​​a packaging structure fabricated using conventional photolithography in the prior art, as a comparative example (showing edge errors or alignment deviations).

[0024] Figure 6 The image shows a microscopic photograph of the electrode area of ​​the MiP packaging structure prepared using the method of this invention, demonstrating the self-alignment effect of the optical crosstalk barrier layer edge being flush with the electrode edge and without residual adhesive. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] Example 1: Light-absorbing packaging structure based on negative black photoresist Figures 1 to 4 The fabrication process of the MiP packaging structure for preventing optical crosstalk of the present invention is shown in detail.

[0027] Step 1: As Figure 1 As shown, a sapphire substrate 10 is provided, and an RGB Micro LED chip array 20 is transferred onto the substrate 10 using laser lift-off and mass transfer technology. The electrode layer 30 of the chip faces upward, and the light-emitting surface faces the substrate. The electrode material is an opaque metal electrode such as Cr / Al / Ti / Ni / Au or Al / Ti / Pt / Au, typically with a thickness greater than 500 nm.

[0028] Step 2: As Figure 2 As shown, a spin coating process is used to coat the entire wafer structure surface (electrode layer) with negative black photoresist 40 (BM photoresist SN-10N).

[0029] Process parameters: Spin coating speed is controlled at 300-5000 rpm to obtain a photoresist layer with a thickness of approximately 1-10 μm.

[0030] Material characteristics: This negative black photoresist contains carbon black or titanium black pigments with an optical density (OD value) of 2 to 3 to ensure excellent light absorption performance.

[0031] Step 3: As Figure 3 As shown, a UV exposure machine is used to perform UV exposure on the back side (non-coated side) of the sapphire substrate, that is, to irradiate it with light of a specific wavelength 50.

[0032] Exposure wavelength: Select i-line 365nm or h-line 405nm to ensure that the light can penetrate the sapphire substrate.

[0033] Exposure dosage: Adjusted according to the actual photosensitive properties and OD value of the photoresist.

[0034] Step 4: Use a developer (such as TMAH solution) to develop the surface and wash away the uncured black glue above the electrodes, exposing a clean electrode area. At the same time, retain the cured black glue walls in the chip gaps to form a light-absorbing crosstalk barrier layer.

[0035] Example 2: Reflective Packaging Structure Based on Negative White Photoresist This embodiment aims to provide a high-efficiency MiP packaging structure that utilizes reflective walls to improve light extraction efficiency.

[0036] Step 1: Provide a transparent glass substrate on which Micro LED chips are die-bonded.

[0037] Step 2: Apply a spray coating process to cover the negative white photoresist.

[0038] Reasons for choosing spraying: Spraying process provides better coverage for structures with high aspect ratios, and for white glue containing high concentrations of reflective particles (such as TiO2), spraying is less likely to cause agglomeration.

[0039] Material characteristics: This negative white photoresist contains highly reflective titanium dioxide (TiO2) particles, with a reflectivity requirement of greater than 90%.

[0040] Step 3: Expose from the back of the glass substrate. Due to the high reflectivity of the white adhesive, light has difficulty penetrating. Therefore, the exposure strategy needs to be adjusted here. A high-energy exposure wavelength should be used to ensure that the bottom (the side away from the substrate) can also be fully cured, avoiding "towering" or peeling during development.

[0041] Step 4: After development, a white reflective wall is formed around the chip.

[0042] Step 5: Add a post-curing step, baking at 150-300 ℃ for 30-60 minutes to further enhance the mechanical strength of the white reflective wall and its adhesion to the substrate.

[0043] Example 3: Based on photosensitive ink and composite curing process This embodiment explores the use of special inks with negative photolithography properties and composite curing methods.

[0044] Step 1: Provide a light-transmitting substrate and a Micro LED array.

[0045] Step 2: Apply an insulating ink with negative photosensitive properties using a slot coating method. This ink has a low viscosity, making it easy to fill tiny gaps.

[0046] Step 3: As Figure 3 As shown, UV exposure is performed on the back side (non-coated side) of the sapphire substrate using a UV exposure machine.

[0047] Exposure wavelength: Select i-line 365nm or h-line 405nm to ensure that the light can penetrate the sapphire substrate.

[0048] Exposure dosage: Adjusted according to the actual photosensitive properties and OD value of the photoresist.

[0049] Step 4: Develop the chip using a developer (such as TMAH solution) to wash away the uncured ink above the electrodes, exposing the clean electrode area, while retaining the cured ink barrier layer in the chip gaps.

[0050] This invention utilizes the metal electrodes on the surface of a Micro LED chip as a self-aligned mask. The exposure light is selected from wavelengths with high transmittance to the semiconductor material of the Micro LED chip. During exposure, the light passes through the transparent substrate, penetrating not only the gaps between the Micro LED chips but also the semiconductor material layer of the Micro LED chips. The negative photosensitive materials located in the gap regions and the non-electrode regions on the back of the chip receive light and undergo cross-linking and curing. However, the negative photosensitive material located directly above the metal electrodes, blocked by the opaque metal electrodes, does not receive light and remains uncured. After development, only the photosensitive material above the electrodes is removed, thus achieving electrode exposure while simultaneously filling the chip gaps and shielding against light leakage on the back of the chip.

[0051] Testing and Verification: To verify the superiority of the self-alignment process of this invention, the morphology of this invention was compared with that of the traditional front-side alignment photolithography process under a microscope: like Figure 5 As shown, this image displays a photograph of the Micro LED electrode area after front-side alignment, exposure, and development using a conventional lithography machine. It can be seen that, limited by the alignment precision of the lithography machine, there is a significant deviation between the edge of the barrier layer and the edge of the electrode, which can easily lead to problems such as residual colloid on the electrode or insufficient gap filling.

[0052] like Figure 6The image shows a photograph of the Micro LED electrode area fabricated using the back-side exposure self-alignment process of this invention. The photograph reveals that the electrode surface is clean and free of adhesive residue, and the edge of the optical crosstalk barrier layer is perfectly flush with the edge of the Micro LED chip's electrode layer, without any alignment deviation, achieving micron-level high-precision patterning filling.

[0053] The reliability of the packaging structure prepared by the process of Example 1 of the present invention (sapphire substrate, black glue spin coating) was tested, and the test results are shown in Table 1.

[0054] Table 1 Test Project Test conditions Inspection items 168h 500h 1000h 1. High-temperature storage 80°C, static 1. Transmittance change <0.5% 2. Appearance (cracking, bubbling, etc.) Pass Pass Pass 2. Thermal shock -40°C ↔ +85°C, 200 cycles 1. Transmittance change <0.5% 2. Appearance (cracking, bubbling, etc.) Pass Pass Pass 3. Low-temperature storage -40°C, static 1. Transmittance change <0.5% 2. Appearance (cracking, bubbling, etc.) Pass Pass Pass 4. High temperature and humidity 85°C / 85% RH, static 1. Transmittance change <0.5% 2. Appearance (cracking, bubbling, etc.) Pass Pass Pass 5. Strong blue light radiation 20mW / cm² @ Blue light band 1. Transmittance change <0.5% 2. Appearance (cracking, bubbling, etc.) Pass Pass Pass As shown in Table 1, the packaging structure of the present invention passed a 1000-hour test under harsh environments including high-temperature storage, thermal shock, low-temperature storage, high-temperature and high-humidity conditions, and strong blue light irradiation. The transmittance change was less than 0.5%, and no cracking or blistering was observed. This indicates that the optical crosstalk barrier layer formed by the present invention has excellent adhesion and physical stability to the substrate and chip.

Claims

1. A method for fabricating a MiP package structure to prevent optical crosstalk, characterized in that, Includes the following steps: Step S1: Provide a light-transmitting substrate, on one side of which a plurality of Micro LED chips are disposed. Each Micro LED chip has a light-emitting surface facing the light-transmitting substrate and an electrode surface facing away from the light-transmitting substrate. An opaque electrode layer is disposed on the electrode surface. The semiconductor material layer of the Micro LED chip is transparent to light of a specific wavelength. Step S2: A photoresist layer is formed on one side of the electrode surface of the Micro LED chip. The photoresist layer is made of a photosensitive and light-shielding material with negative photoresist properties. Step S3: Expose the light from the side of the transparent substrate facing away from the Micro LED chip using light of the specific wavelength; using the opaque electrode layer as a mask, the light penetrates the transparent substrate, the gap between the Micro LED chip and the semiconductor material layer of the Micro LED chip, causing the photoresist layer located in the gap region and the non-electrode region on the electrode surface to be photosensitive and cured. Step S4: Develop the exposed photoresist layer to remove the uncured photoresist layer above the opaque electrode layer, expose the opaque electrode layer, and form a continuous light crosstalk barrier layer between the Micro LED chips and on the electrode surface of the Micro LED chips.

2. The method for manufacturing the packaging structure as described in claim 1, characterized in that, In step S2, the photosensitive light-blocking material is selected from one of negative black photoresist, negative white photoresist, and light-absorbing ink with negative photoresist properties.

3. The method for manufacturing the packaging structure as described in claim 2, characterized in that, When the photosensitive light-shielding material is a negative black photoresist, the light crosstalk blocking layer is used to absorb stray light emitted from the sidewall of the Micro LED chip; When the photosensitive and light-shielding material is a negative white photoresist, the light crosstalk blocking layer is used to reflect the light emitted from the sidewall of the MicroLED chip.

4. The method for manufacturing the packaging structure as described in claim 1, characterized in that, In step S2, the photoresist layer is formed by one of the following methods: spin coating, spray coating, slot coating, or screen printing.

5. The method for manufacturing the packaging structure as described in claim 1, characterized in that, In step S3, the wavelength of the light source used for exposure is able to penetrate the light-transmitting substrate, and the wavelength of the light source is within the photosensitive wavelength range of the photosensitive shielding material.

6. The method for manufacturing the packaging structure as described in claim 1, characterized in that, The light-transmitting substrate is a sapphire substrate, a glass substrate, or a transparent resin substrate.

7. The method for manufacturing the packaging structure as described in claim 1, characterized in that, Following step S4, step S5 is also included: The structure having the optical crosstalk blocking layer is subjected to a post-curing process, which includes heat baking or ultraviolet curing, to improve the physical stability of the optical crosstalk blocking layer.

8. The method for manufacturing the packaging structure as described in claim 1, characterized in that, In step S2, the coating thickness of the photoresist layer is controlled so that the height of the light crosstalk barrier layer formed after development in step S4 is flush with or slightly higher than the height of the Micro LED chip.

9. A MiP packaging structure, characterized in that, Prepared by the manufacturing method according to any one of claims 1 to 8, comprising: Transparent substrate; Multiple Micro LED chips are spaced apart on the light-transmitting substrate; A crosstalk blocking layer is filled in the gap between adjacent Micro LED chips; The upper surface edge of the optical crosstalk blocking layer is flush with or slightly higher than the edge of the electrode layer of the Micro LED chip.

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