Micro-LED chip array integrated with homogeneous microlens array and preparation method thereof

Abstract

The invention discloses a Micro-LED chip array integrated with a homogeneous micro-lens array and a preparation method thereof, and the method comprises the steps: carrying out the wafer-level precise bonding of a Micro-LED light-emitting pixel array and a CMOS drive circuit substrate, removing a substrate, integrating a homogeneous pixel-level GaN micro-lens array on a GaN-based pixel array through the photoetching, hot melting backflow and dry etching technologies, and carrying out the precise bonding of the micro-LED light-emitting pixel array and the CMOS drive circuit substrate. And finally, realizing the full-pixel common cathode conduction of the Micro-LED chip by adopting a metal interconnection process. According to the method, the Micro-LED pixel array and the micro-lens array are homogeneously integrated, are made of the same material and have no refractive index difference, so that no Fresnel loss exists on an interface, and the light extraction efficiency of a chip is improved. In addition, the method is simple in manufacturing process, low in cost, good in chip structure reliability, high in stability and suitable for being applied to industrial chip manufacturing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor light-emitting devices, in particular to a Micro-LED chip array integrated with a homogeneous micro-lens array and a preparation method thereof. BACKGROUND

[0002] Under the trend of lightening, high resolution and full colorization of near-eye display devices, the requirements for Micro-LED pixel unit size are becoming more and more stringent. At present, the Micro-LED pixel unit size is usually below 50 μm, and in recent years, the AR glasses on the market even require the pixel unit size to be less than 5 μm.

[0003] Under such a small pixel size condition, the traditional light extraction efficiency improvement method such as surface roughening may no longer be applicable, and the light crosstalk problem between pixels will seriously reduce the display quality. To cope with these challenges, a micro-lens array is integrated into the Micro-LED chip, which serves to improve the light extraction efficiency and reduce the beam angle (reduce light crosstalk).

[0004] However, at present, most of these micro-lenses and Micro-LED chips are integrated in a heterogeneous manner, that is, the micro-lens and the Micro-LED light-emitting material are not the same material. This integration method brings many problems: on the one hand, due to the difference in refractive index between the two, Fresnel loss will occur at the interface between the light-emitting material and the micro-lens, thereby reducing the light extraction efficiency; on the other hand, due to the difference in thermal expansion coefficient, different stresses may be generated between the two during chip manufacturing and use, which affects the stability and reliability of the device.

[0005] In addition, although homogeneous micro-lenses have appeared in the prior art, their structures are often complex, and the corresponding manufacturing methods are also relatively cumbersome, which to some extent limits their large-scale application and promotion. SUMMARY

[0006] Based on this, the present application provides a Micro-LED chip array integrated with a homogeneous micro-lens array and a preparation method thereof, which solves the problems existing in the integration of heterogeneous micro-lenses and simplifies the structure and process of the integration of homogeneous micro-lenses.

[0007] In a first aspect, the present application provides a preparation method of a Micro-LED chip array integrated with a homogeneous micro-lens array, comprising the following steps: S1, providing a GaN-based epitaxial wafer, the GaN-based epitaxial wafer comprising a substrate and a N-type GaN layer, a light-emitting layer and a P-type layer which are sequentially stacked on the substrate; S2, defining a Micro-LED light-emitting pixel array on a GaN-based epitaxial wafer, etching the P-type layer and the light-emitting layer between the Micro-LED light-emitting pixel array units until the first surface of the N-type GaN layer is exposed; S3, using wafer-level precision bonding technology, one-time bonding the Micro-LED light-emitting pixel array to the driving circuit substrate through the bonding metal; and removing the substrate to expose the second surface of the N-type GaN layer; S4, preparing a photoresist array on the second surface of the N-type GaN layer, the photoresist array corresponding to the Micro-LED light-emitting pixel array one by one; S5, through a hot reflow process, the photoresist array forms a photoresist microlens array; S6, etching part of the N-type GaN layer under the mask of the photoresist microlens array to form a GaN microlens array; the topography of the GaN microlens array is the same as that of the photoresist microlens array; S7, preparing an electrode line using a metal interconnection process, the electrode line being located on the N-type GaN layer between the GaN microlens array units, and the preparation of the Micro-LED chip array is completed.

[0008] The preparation method of the Micro-LED chip array integrated with the homogeneous microlens array provided by the application realizes the integration of the homogeneous GaN microlens array on the Micro-LED light-emitting pixel array by etching part of the N-type GaN layer under the mask of the photoresist microlens array formed by hot reflow. The refractive index of the light-emitting layer is the same as that of the microlens array, and there is no Fresnel loss caused by reflection on the interface between the two, which can achieve higher light extraction efficiency compared to heterogeneous integration. Moreover, the thermal expansion coefficients of the light-emitting layer and the microlens array are the same, and the stress state is the same during chip manufacturing and use, which has better stability and reliability compared to heterogeneous integration. In addition, the preparation method is simple, and the integration of the microlens array is realized at the same time of the preparation of the Micro-LED chip array, which saves the complex process of separately preparing, transferring and aligning the microlens array in the prior art, and reduces the cost.

[0009] As an optional solution of the preparation method, the feature size L1 of the photoresist array unit is greater than the feature size L2 of the Micro-LED light-emitting pixel array unit; and the thickness of the photoresist array unit is less than the feature size L1 of the photoresist array unit.

[0010] As an optional solution of the preparation method, the feature size L1 of the photoresist array unit is 2 times or more than the feature size L2 of the Micro-LED light-emitting pixel array unit; and the thickness of the photoresist array unit is half of the feature size L1 of the photoresist array unit.

[0011] As an alternative of the preparation method of the present application, the material of the photoresist array is a positive photoresist or a negative photoresist.

[0012] As an alternative of the preparation method of the present application, the material of the photoresist array is 5312 positive photoresist; in the thermal reflow process, the reflow temperature is 160-260℃, and the reflow time is 60-120 minutes.

[0013] As an alternative of the preparation method of the present application, the etching of the N-type GaN layer in step S6 adopts dry etching, and the etching gas is one or more of chlorine, argon, nitrogen or boron trichloride.

[0014] As an alternative of the preparation method of the present application, the photoresist microlens array and the GaN microlens array are convex lens arrays.

[0015] As an alternative of the preparation method of the present application, the metal interconnection process is realized through a metal stripping process; or the metal interconnection process is realized through a metal wet chemical etching process; and the material of the electrode wire is one or more of chromium, titanium, aluminum, gold or platinum.

[0016] As an alternative of the preparation method of the present application, the substrate is a silicon substrate, and the method for removing the silicon substrate comprises the following steps: thinning the thickness of the silicon substrate to within 90μm through mechanical grinding and polishing by a grinding wheel; and removing the remaining silicon substrate through wet chemical etching or dry chemical etching.

[0017] In a second aspect, the present application further provides a Micro-LED chip array integrated with a homogeneous microlens array, which is prepared by the above method.

[0018] Additional aspects and advantages of the present application will be set forth in part in the following description, can be apparent from the description, and can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A cross-sectional view of a GaN-based epitaxial wafer in an embodiment of the present application.

[0020] Figure 2 A cross-sectional view after step S2 is completed in an embodiment of the present application.

[0021] Figure 3 A cross-sectional view after step S3 is completed in an embodiment of the present application.

[0022] Figure 4 A cross-sectional view after step S4 is completed in an embodiment of the present application.

[0023] Figure 5 A cross-sectional view after step S5 is completed in an embodiment of the present application.

[0024] Figure 6 This is a cross-sectional view after step S6 is completed in an embodiment of the present invention.

[0025] Figure 7 This is a cross-sectional view after step S7 is completed in an embodiment of the present invention.

[0026] Figure 8 This is a top view after step S7 is completed in an embodiment of the present invention.

[0027] Illustration: 1-Substrate, 2-Buffer layer, 3-N-type GaN layer, 4-Light-emitting layer, 5-P-type layer, 6-First bonding metal bump, 7-Second bonding metal bump, 8-Driver circuit substrate, 9-Photoresist array, 10-Photoresist microlens array, 11-GaN microlens array, 12-Electrode line, 13-Micro-LED light-emitting pixel array. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more comprehensive description of the invention will be given below with reference to the accompanying drawings.

[0029] The terminology used in the implementation section of this application is for the purpose of explaining specific embodiments of this application only, and is not intended to limit this application.

[0030] like Figures 1-8 As shown in the figure, this application provides a method for fabricating a Micro-LED chip array with an integrated homogeneous microlens array, including the following steps: S1. Provide a GaN-based epitaxial wafer, which includes a substrate 1 and a buffer layer 2, an N-type GaN layer 3, a light-emitting layer 4 and a P-type layer 5 sequentially stacked on the substrate 1.

[0031] S2. Define a Micro-LED light-emitting pixel array 13 on a GaN-based epitaxial wafer, and etch the P-type layer 5 and the light-emitting layer 4 between the Micro-LED light-emitting pixel array units until the first surface of the N-type GaN layer 3 is exposed. It should be noted that in this etching step, only the P-type layer 5 and the light-emitting layer 4 are etched to physically isolate the Micro-LED light-emitting pixel array units. The N-type GaN layer is not etched, and retaining the complete N-type GaN layer is beneficial for the morphology control of the GaN microlens array in the subsequent step S6.

[0032] S3. Using wafer-level precision bonding technology, the Micro-LED light-emitting pixel array 13 is bonded to the driving circuit substrate 8 in one step by bonding metal; and the substrate 1 and buffer layer 2 are removed to expose the second side of the N-type GaN layer 3.

[0033] S4, preparing a photoresist array 9 on the second surface of the N-type GaN layer 3, the photoresist array 9 corresponding to the Micro-LED light-emitting pixel array 13 one by one.

[0034] S5, forming a photoresist microlens array 10 by a thermal reflow process, and it is to be noted that the photoresist microlens array can be formed by the thermal reflow process, and the operation steps are relatively simple.

[0035] S6, etching part of the N-type GaN layer 3 under the mask of the photoresist microlens array 10 to form a GaN microlens array 11, and the topography of the GaN microlens array 11 is the same as that of the photoresist microlens array 10; it is to be noted that the microlens array formed by the photoresist is used as a mask, and the topography of the photoresist microlens array is accurately transferred to the N-type GaN layer by etching technology to form the GaN microlens array. This process utilizes the high-resolution characteristics of the etching process, can preserve the profile details of the photoresist microlens, and ensures the size accuracy and consistency of the microlens array.

[0036] S7, preparing an electrode line 12 by a metal interconnection process, the electrode line 12 being located on the N-type GaN layer 3 between the GaN microlens array units, and the preparation of the Micro-LED chip array is completed; it is to be noted that the electrode line is prepared on the entire Micro-LED chip array to realize the full-pixel common cathode conduction of the Micro-LED chip array.

[0037] In some embodiments, the feature size L1 of the photoresist array unit is greater than the feature size L2 of the Micro-LED light-emitting pixel array unit, and the thickness of the photoresist array unit is less than the feature size L1 of the photoresist array unit. By controlling the size of the GaN pixel array unit and the integrated homogeneous GaN microlens array unit, the light-emitting area of the pixel array unit is adjacent to the curvature center of the microlens array unit, and the GaN microlens array can exhibit a significant light collimation effect, which can significantly reduce the light cross talk between pixels and improve the display quality of the Micro-LED chip.

[0038] In some embodiments, the feature size L1 of the photoresist array unit is 2 times or more than the feature size L2 of the Micro-LED light-emitting pixel array unit, and the thickness of the photoresist array unit is half of the feature size L1 of the photoresist array unit.

[0039] In some embodiments, the thickness of the N-type GaN layer 3 is not less than 1 micrometer.

[0040] In some embodiments, the material of the photoresist array 9 is a positive photoresist or a negative photoresist.

[0041] In some embodiments, the material of the photoresist array 9 is 5312 positive photoresist; in the thermal reflow process, the reflow temperature is 160-260°C, and the reflow time is 60-120 minutes. In the thermal reflow process, by precisely controlling the reflow temperature and time, the photoresist can be melted to form a smooth curved surface under the action of surface tension, which is close to the ideal convex lens shape, avoiding the lens shape deviation caused by uneven etching rate in the traditional etching process. In addition, this temperature range is lower than the bonding temperature in step S3, and will not cause damage to the bonding layer.

[0042] In some embodiments, dry etching is used in step S6, and the etching gas is one or more of chlorine, argon, nitrogen, or boron trichloride. These etching gases can etch both photoresist and GaN, and the etching ratio of the two should be close to 1. The selection of these etching gases in step S6 can accurately transfer the morphology of the photoresist microlens array to the N-type GaN layer.

[0043] In some embodiments, the photoresist microlens array 10 and the GaN microlens array 11 are convex lens arrays. The light condensing property of the convex lens can improve the front light output power of the Micro-LED chip, constrain and adjust the divergent light field to improve the light collimation, reduce the crosstalk caused by sidewall light emission between chips, improve the display problems such as contrast ratio, and also suppress the total reflection and waveguide effect at the chip / air interface, and improve the external quantum efficiency.

[0044] In some embodiments, the metal interconnection process is realized by a metal stripping process; or the metal interconnection process is realized by a metal wet chemical etching process; the material of the electrode line 12 is one or more of chromium, titanium, aluminum, gold, or platinum, so as to ensure that the electrode line 12 forms a good ohmic contact with the N-type GaN layer 3, and achieves good current spreading performance, and achieves the purposes of low working voltage and high light emission uniformity.

[0045] In some embodiments, the substrate 1 is a silicon substrate, and its thickness is generally about 1 mm. The method for removing the silicon substrate 1 comprises the following steps: in the first step, the thickness of the silicon substrate 1 is thinned to within 90 μm by mechanical grinding and polishing with a grinding wheel; and in the second step, the remaining silicon substrate 1 is removed by wet chemical etching or dry chemical etching. The first step of mechanical grinding and polishing with a grinding wheel can quickly thin the silicon substrate, and after thinning, the chip surface is still covered by a silicon substrate with a thickness of several tens of microns, so the chip surface will not be damaged. In the second step, the wet chemical etching can control the composition and concentration of the etching solution, or the dry chemical etching can control the type and flow of the etching gas, so as to achieve the purpose of etching only the silicon substrate without etching other materials, thereby effectively removing the silicon substrate while ensuring that other materials are not affected.

[0046] In some embodiments, the etching in step S2 is dry etching, and the etching gas is one or more of chlorine, argon, nitrogen and boron trichloride. By reasonably controlling the flow ratio of these gases, the P-type layer 5 and the light-emitting layer 4 can be efficiently etched, and the etching product is volatile, which can be discharged from the etching cavity in time and will not cause pollution.

[0047] In some embodiments, the material of the bonding metal is one or more of gold, copper, indium, tin and silver. These materials can be diffusion bonded or eutectic bonded, with high bonding strength to ensure the stability and reliability of the chip.

[0048] In some embodiments, the feature size L1 of the photoresist array unit is in the range of 1 micrometer or above, the thickness of the photoresist array unit is in the range of 0.5 micrometer or above, the feature size L2 of the Micro-LED light-emitting pixel array unit is in the range of 0.5 micrometer or above, and the spacing between the Micro-LED light-emitting pixel array units is in the range of 1 micrometer or above.

[0049] In some embodiments, the wiring mode of the electrode line 12 is transverse wiring, longitudinal wiring or grid wiring, so that the current is well expanded, the current density of each light-emitting pixel array unit is substantially the same, the high uniformity of light emission of each light-emitting pixel array unit is ensured, and the display quality is improved. The application also provides a Micro-LED chip array integrated with a homogeneous micro-lens array, which is prepared by the above method.

[0050] The preferred embodiments of the application are listed below. Embodiment 1

[0051] The embodiment provides a preparation method of a Micro-LED chip array integrated with a homogeneous micro-lens array, which comprises the following steps: Step S1, providing a GaN-based epitaxial wafer, as shown in the figure, the GaN-based epitaxial wafer comprises a substrate 1 and a buffer layer 2, an N-type GaN layer 3, a light-emitting layer 4 and a P-type layer 5 which are sequentially stacked on the substrate 1. The substrate 1 is a silicon substrate, the N-type GaN layer 3 is Si-doped GaN, the thickness of the N-type GaN layer 3 is 2.2 micrometers, the light-emitting layer 4 is an InGaN / GaN multi-quantum well layer, and the P-type layer 5 is Mg-doped GaN. Figure 1 Step S2, defining a Micro-LED light-emitting pixel array 13 on the GaN-based epitaxial wafer, dry etching the P-type layer 5 and the light-emitting layer 4 between the Micro-LED light-emitting pixel array units until the first surface of the N-type GaN layer 3 is exposed, and the etching gas is a combination of chlorine and boron trichloride gas. The Micro-LED light-emitting pixel array units are physically separated, as shown in the figure.

[0052] Figure 2 ​The feature size L2 of the Micro-LED light-emitting pixel array unit is 1 micrometer, and the spacing between the Micro-LED light-emitting pixel array units is 2.75 micrometers.

[0053] In step S3, a first bonding metal bump 2 is prepared on the etched P-type layer 5 by using a metal stripping process, and the material of the first bonding metal bump 2 is Cr / Au; a second bonding metal bump 3 is prepared on the driving circuit substrate 8 by using a metal stripping process, and the driving circuit substrate 8 is a CMOS driving circuit substrate, and the material of the second bonding metal bump 3 is Cr / Au. The bump size of the first bonding metal bump 2 and the second bonding metal bump 3 is 1 micrometer by 1 micrometer.

[0054] In step S3, a first bonding metal bump 2 is prepared on the etched P-type layer 5 by using a metal stripping process, and the material of the first bonding metal bump 2 is Cr / Au; a second bonding metal bump 3 is prepared on the driving circuit substrate 8 by using a metal stripping process, and the driving circuit substrate 8 is a CMOS driving circuit substrate, and the material of the second bonding metal bump 3 is Cr / Au. The bump size of the first bonding metal bump 2 and the second bonding metal bump 3 is 1 micrometer by 1 micrometer.

[0055] In step S3, a first bonding metal bump 2 is prepared on the etched P-type layer 5 by using a metal stripping process, and the material of the first bonding metal bump 2 is Cr / Au; a second bonding metal bump 3 is prepared on the driving circuit substrate 8 by using a metal stripping process, and the driving circuit substrate 8 is a CMOS driving circuit substrate, and the material of the second bonding metal bump 3 is Cr / Au. The bump size of the first bonding metal bump 2 and the second bonding metal bump 3 is 1 micrometer by 1 micrometer. Figure 3

[0056] In step S4, photoresist is coated on the second surface of the N-type GaN layer 3, the photoresist is 5312 positive photoresist, and then alignment is performed by using photoetching alignment technology, and processes such as exposure and development are performed to prepare a photoresist array 9, which corresponds to the number and position of the Micro-LED light-emitting pixel array 13, as shown in FIG. 5. Figure 4 The thickness of the photoresist array 9 is 1.5 micrometers, and the feature size L1 of the photoresist unit is 3 micrometers.

[0057] In step S5, the sample prepared in step S4 is placed in an oven at 170 degrees Celsius for 60 minutes to heat the photoresist array 9 to above its glass transition temperature, and under the action of surface tension, the photoresist array 9 is heated to form a photoresist microlens array 10, which is a convex lens array, as shown in FIG. 6. Figure 5

[0058] In step S6, under the mask of the photoresist microlens array 10, the photoresist microlens array 10 is etched and removed by using a dry etching technology, and an etching gas composed of chlorine gas and boron trichloride gas is used to etch and remove the photoresist microlens array 10 and then etch part of the N-type GaN layer 3, so that the topography of the photoresist microlens array 10 is transferred to the N-type GaN layer 3, and a GaN microlens array 11 is etched out, realizing the integration of the GaN microlens array 11 on the GaN pixel array, as shown in FIG. 7. Figure 6

[0059] ​​​Step S7, the electrode lines 12 are prepared by a metal stripping process, and the material of the electrode lines 12 is chromium and gold. The electrode lines 12 are arranged in a grid between the GaN microlens array units on the N-type GaN layer 3, and the wiring width of the electrode lines 12 is 0.5 μm. The structure of the prepared Micro-LED chip array is shown in FIG. 1C. Figure 7 and 8 as shown.

[0060] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. Therefore, any equivalent changes or modifications made according to the principles and design ideas disclosed by the present application are within the protection scope of the present application.

Claims

1. A method for fabricating a Micro-LED chip array with an integrated homogeneous microlens array, characterized in that, Includes the following steps: S1. Provide a GaN-based epitaxial wafer, the GaN-based epitaxial wafer comprising a substrate and an N-type GaN layer, a light-emitting layer and a P-type layer sequentially stacked on the substrate; S2. Define a Micro-LED light-emitting pixel array on a GaN-based epitaxial wafer, and etch the P-type layer and light-emitting layer between the Micro-LED light-emitting pixel array units until the first surface of the N-type GaN layer is exposed; S3. Employing wafer-level precision bonding technology, the Micro-LED light-emitting pixel array is bonded to the driving circuit substrate in one step using bonding metal; The substrate was then removed to expose the second side of the N-type GaN layer; S4. A photoresist array is fabricated on the second surface of the N-type GaN layer, wherein the photoresist array corresponds one-to-one with the Micro-LED light-emitting pixel array; S5. The photoresist array is formed into a photoresist microlens array through a hot melt reflow process; S6. Under the mask of the photoresist microlens array, a portion of the N-type GaN layer is etched to form a GaN microlens array; The morphology of the GaN microlens array is the same as that of the photoresist microlens array. S7. Electrode lines are fabricated using a metal interconnect process. The electrode lines are located on the N-type GaN layer between GaN microlens array units to complete the fabrication of the Micro-LED chip array.

2. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The feature size L1 of the photoresist array unit is larger than the feature size L2 of the Micro-LED light-emitting pixel array unit; The thickness of the photoresist array unit is smaller than the feature size L1 of the photoresist unit.

3. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The feature size L1 of the photoresist array unit is twice or more than the feature size L2 of the Micro-LED light-emitting pixel array unit; the thickness of the photoresist array unit is half of the feature size L1 of the photoresist array unit.

4. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The photoresist array is made of either positive or negative photoresist.

5. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The photoresist array is made of 5312 positive photoresist; in the hot melt reflow process, the reflow temperature is 160℃-260℃ and the reflow time is 60 minutes-120 minutes.

6. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: In step S6, the etching of the N-type GaN layer is carried out by dry etching, and the etching gas is one or more of chlorine, argon, nitrogen or boron trichloride.

7. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The photoresist microlens array and the GaN microlens array are convex lens-shaped arrays.

8. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that: The metal interconnect process is achieved through a metal stripping process; or the metal interconnect process is achieved through a metal wet chemical etching process; the material of the electrode wire is one or more of chromium, titanium, aluminum, gold or platinum.

9. The method for fabricating a Micro-LED chip array according to claim 1, characterized in that, The substrate is a silicon substrate, and the method for removing the silicon substrate includes the following steps: reducing the thickness of the silicon substrate to less than 90 μm by mechanical polishing with an abrasive wheel; and removing the remaining silicon substrate by wet chemical etching or dry chemical etching.

10. A Micro-LED chip array integrating a homogeneous microlens array, characterized in that, Prepared using the method described in any one of claims 1-9.

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