A method for preparing a Micro-LED device

Abstract

The present application provides a method for preparing a Micro-LED device. The method improves the problem of sidewall damage caused by the use of dry etching to prepare Micro-LED grain structures. It is proposed to use a combination of tetramethylammonium hydroxide chemical corrosion and sidewall passivation to repair the sidewalls, which can completely etch the amorphous area of the Micro-LED sidewalls along the longitudinal direction, and has less destructive effect on the Micro-LED structure along the transverse direction. The sidewall lattice of the sample after etching is complete and the sidewalls are vertical. After the Micro-LED grains are formed, an optical evaluation method combining laser confocal microscopy and photoluminescence spectroscopy is used to evaluate their early performance. After packaging, the electrical performance of the Micro-LED device is tested, and the electrical performance test results are compared with the early luminescence performance evaluation. The present application can effectively process the Micro-LED sidewall damage layer, verticalize the Micro-LED sidewalls, and solve the problem of inconsistent areas of the upper and lower regions of the quantum well caused by the tilt of the sidewalls after dry etching.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor light-emitting devices, and in particular to a method for preparing a Micro-LED device. Background Art

[0002] Micro-displays based on micro-light-emitting diode (Micro-LEDs) arrays have great application prospects. Compared with traditional liquid crystal displays (LCDs) and organic light-emitting displays (OLEDs), they have the advantages of high efficiency, low power consumption, ultra-high resolution, ultra-fast response speed, and wide viewing angle. They are considered to be a "next-generation display technology."

[0003] However, there are still many problems to be solved in the development of Micro-LED, such as the sidewall damage caused by dry etching. The plasma generated during the dry etching process will inevitably introduce sidewall etching damage at the edge of the device, and at the same time produce sidewall dangling bonds. These damages easily introduce deep energy level defects to produce non-radiative recombination centers, greatly reducing the optical performance of small-sized devices. Traditional chemical etching solutions used to repair Micro-LED sidewall damage are mostly strong etching solutions such as KOH and HCl. After etching the damaged layer of the Micro-LED sidewall, there is also a certain degree of damage to intact structures such as quantum wells. Therefore, etching solutions such as KOH do not significantly improve the performance of Micro-LEDs. A chemical reagent with selective etching and relatively mild corrosiveness is particularly important for Micro-LED sidewall repair.

[0004] In addition, the Micro-LED yield issue is a key factor affecting the mass transfer of Micro-LED. Early luminous performance evaluation after the formation of Micro-LED grains can timely avoid chips of poor quality, effectively improve the yield after chip manufacturing, and reduce the difficulty of mass transfer.

[0005] Therefore, it is necessary to improve the existing process methods of Micro-LED chips and conduct early luminous performance evaluation of Micro-LED chip quality. Summary of the Invention

[0006] In order to overcome the above-mentioned defects, the purpose of this application is to provide a method for preparing Micro-LED devices, which can effectively repair the sidewall damage problem caused by dry etching, perform early quality assessment of Micro-LED chips, avoid damaged chips in time, and improve the yield.

[0007] To achieve the above objectives, the technical solutions adopted in this application are:

[0008] A method for preparing a Micro-LED device, comprising:

[0009] S1. Using a dry etching process to prepare isolation trenches on the LED epitaxial wafer to form Micro-LED grains;

[0010] The LED epitaxial wafer comprises a substrate layer, on the upper surface of which an undoped layer, an N-type layer, a quantum well layer, and a P-type layer are sequentially deposited; the depth of the isolation trench is at least as deep as the N-type layer;

[0011] S2. Place the Micro-LED die prepared in S1 in a tetramethylammonium hydroxide (TMAH) solution and heat it in a water bath to repair the sidewall damage of the isolation trench caused by the dry etching process;

[0012] S3. Evaporation of an insulating passivation layer on the edges and sidewalls of the Micro-LED crystals after treatment with tetramethylammonium hydroxide solution in S2;

[0013] S4. Use laser confocal microscopy (LSCM) to evaluate the quality of the Micro-LED die for early luminescence performance, and then use photoluminescence spectroscopy (PL) to measure the luminescence intensity at various points on the Micro-LED die surface.

[0014] S5. Using a photolithography process to etch away the insulating passivation layer on the surface of the Micro-LED die and expose the upper surface of the P-type layer, and using an evaporation process to prepare a current spreading layer on the exposed surface of the P-type layer;

[0015] S6. Using a sputtering process to prepare anode and cathode electrodes on the surface of the Micro-LED grains, thereby obtaining a Micro-LED chip;

[0016] S7. Encapsulate the Micro-LED chip produced in S6 to obtain a Micro-LED device. Then, test the electrical performance of the Micro-LED device and compare the electrical performance test results with the early luminous performance evaluation to analyze and evaluate the source of the Micro-LED chip damage (either in steps S1 to S3 or in steps S5 to S7).

[0017] The isolation grooves set on the upper surface of the LED epitaxial wafer are in the shape of a two-dimensional grid. The isolation grooves penetrate deep into the N-type layer. The areas on the upper surface of the LED epitaxial wafer that are not divided by the isolation grooves are Micro-LED grains.

[0018] The specific operation of early luminescence performance evaluation is as follows: use a laser confocal microscope (LSCM) to test the luminescence performance of Micro-LED grains treated with tetramethylammonium hydroxide solution and sidewall passivation; the light emitted by the light source is incident on the beam splitter after passing through the collimating beam expander, and the light beam reflected by the beam splitter passes through the objective lens and forms a convergence point on the focal plane of the objective lens. The Micro-LED grain is placed at the focal plane of the objective lens, and the objective lens scans the Micro-LED grain point by point. During the scanning process, the Micro-LED grains of the sample being tested are excited to produce fluorescence, which passes through the objective lens and the beam splitter in turn and is incident on the photomultiplier tube through a small hole filter. The signal in the photomultiplier tube is processed to form an image of the Micro-LED grain being tested. By scanning each Micro-LED grain on the focal plane point by point, a complete set of Micro-LED grain confocal images is formed.

[0019] Early luminescence performance evaluation using laser confocal microscopy can analyze the damage to Micro-LED grains from steps S1 to S3.

[0020] In a preferred embodiment, the concentration of the tetramethylammonium hydroxide solution in S2 is 20%, and the solution is heated in a water bath at 80° C. for 1 hour.

[0021] In a preferred embodiment, in S4, the laser excitation wavelength of the laser confocal microscope is selected to be smaller than the emission wavelength of the micro-LED crystal. The LSCM laser excitation is uniform, and all micro-LED crystals within the observation range of the fluorescence microscope are evaluated.

[0022] The light source excitation diameter of the photoluminescence spectrum test in S4 is less than 1 micron, and the luminous intensity of each point on the surface of a single Micro-LED grain is evaluated.

[0023] In a preferred embodiment, the current spreading layer in S5 only contacts the upper surface of the P-type layer.

[0024] The current spreading layer is made of indium tin oxide (ITO). ITO has high transmittance and low resistivity. Placing the current spreading layer on the light-emitting side of the Micro-LED die ensures transmittance while reducing power loss.

[0025] In a preferred embodiment, the cathode and anode electrodes prepared in S6 are respectively connected to the N-type layer and the P-type layer of the Micro-LED crystal.

[0026] Beneficial effects

[0027] Heating in a water bath in tetramethylammonium hydroxide solution can effectively repair sidewall damage problems such as lattice mismatch and sidewall tilt of Micro-LED grains during the dry etching process.

[0028] In S2, an insulating passivation layer is provided on the Micro-LED die to perform passivation treatment, thereby further protecting the sidewalls of the Micro-LED die after being treated with the tetramethylammonium hydroxide solution;

[0029] Early luminescence performance evaluation can analyze the optical performance of each device and different Micro-LED grain points of the device.

[0030] Early luminous performance evaluation can analyze the damage of S1 to S3 Micro-LED die, while electrical performance test results of Micro-LED chips can reveal the damage of S5 to S7 Micro-LED chips. Comparison of the two can provide a reference for improving the final yield of the chip manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1a Schematic diagram of the cross-sectional structure of an LED epitaxial wafer;

[0032] Figure 1b A schematic diagram of the cross-sectional structure of S1 provided in an embodiment of the present application;

[0033] Figure 1c A schematic diagram of the cross-sectional structure of S2 provided in an embodiment of the present application;

[0034] Figure 1d A schematic diagram of the cross-sectional structure of S3 provided in an embodiment of the present application;

[0035] Figure 1e A schematic diagram of the cross-sectional structure of S5 provided in an embodiment of the present application;

[0036] Figure 1f A schematic diagram of the cross-sectional structure of S6 provided in an embodiment of the present application;

[0037] Figure 2a This is a scanning electron microscope (SEM) image of an 8-micron Micro-LED provided in an embodiment of the present application after dry etching without any processing;

[0038] Figure 2b This is an SEM image of an 8-micron Micro-LED provided in an embodiment of the present application after dry etching and chemical treatment with tetramethylammonium hydroxide solution;

[0039] Figure 2c This is an SEM image of an 8-micron Micro-LED provided in an embodiment of the present application after dry etching with a tetramethylammonium hydroxide solution chemical treatment and SiO2 passivation;

[0040] Figure 3a A cross-sectional transmission electron microscope (TEM) image of a Micro-LED provided in an embodiment of the present application, before being processed by dry etching;

[0041] Figure 3b This is a cross-sectional TEM image of a Micro-LED provided in an embodiment of the present application after dry etching and chemical treatment with tetramethylammonium hydroxide solution and SiO2 passivation;

[0042] Figure 3c This is a high-resolution TEM image of the untreated sidewalls of the Micro-LED provided in the embodiment of the present application after dry etching;

[0043] Figure 3d This is a high-resolution TEM image of the sidewalls of a Micro-LED provided in an embodiment of the present application after dry etching and chemical treatment with tetramethylammonium hydroxide solution;

[0044] Figure 4a This is an LSCM image of a 10-micron Micro-LED provided in an embodiment of the present application after dry etching without any processing;

[0045] Figure 4b This is an LSCM image of a 10-micron Micro-LED provided in an embodiment of the present application after dry etching and chemical treatment with tetramethylammonium hydroxide solution;

[0046] Figure 4c LSCM image of a 10-micron Micro-LED provided in an embodiment of the present application after dry etching with a tetramethylammonium hydroxide solution chemical treatment and SiO2 passivation;

[0047] Figure 4d PL spectra of a 10-micron Micro-LED at 3 microns from the edge using three different treatments provided in the examples of this application. From bottom to top, the curves are the PL intensity curves for untreated, chemically treated with tetramethylammonium hydroxide solution, and chemically treated with tetramethylammonium hydroxide solution + SiO2 passivation.

[0048] Figure 5 Schematic diagram of the laser confocal microscope setup;

[0049] Among them, 1. Substrate layer, 2. Undoped layer, 3. N-type layer, 4. Quantum well layer, 5. P-type layer, 6. Isolation groove, 7. Insulation passivation layer, 8. Current spreading layer, 9. Anode and cathode electrodes, 10. Light source, 11. Spectrometer, 12. Objective lens, 13. Pinhole filter, 14. Photomultiplier tube, 15. Micro-LED grain. DETAILED DESCRIPTION

[0050] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the present application and are not intended to limit the scope of the present application. The implementation conditions used in the examples can be further adjusted according to the conditions of the specific manufacturer. The implementation conditions not specified are generally those used in routine experiments.

[0051] Next, the Micro-LED device preparation method proposed in this application is described in detail with reference to the accompanying drawings.

[0052] The preparation method implemented in this application comprises the following steps:

[0053] S1. Using a dry etching process to prepare isolation trenches on the LED epitaxial wafer to form Micro-LED grains;

[0054] In this step, the LED epitaxial wafer is as follows Figure 1a As shown, it includes a substrate layer 1, on the upper surface of which an undoped layer 2, an N-type layer 3, a quantum well layer 4 and a P-type layer 5 are sequentially deposited; the depth of the obtained isolation trench 6 is at least as deep as the N-type layer;

[0055] The dry etching process is to make the Micro-LED grain structure through the photolithography process and the inductive coupling and plasma etching process. The photolithography process includes: pretreatment, spin coating, pre-baking, exposure, development, and hardening film; Figure 1b Isolation trench and Micro-LED die array shown;

[0056] After dry etching, use acetone, isopropyl alcohol, and deionized water to clean;

[0057] S2, the Micro-LED crystals prepared in S1 were placed in a 20% concentration of tetramethylammonium hydroxide solution and heated in a water bath at 80°C for 1 hour. The tetramethylammonium hydroxide solution can completely etch the amorphous area of the Micro-LED sidewalls along the longitudinal direction, while the damage to the Micro-LED structure along the transverse direction is relatively weak. After etching, the sidewall lattice of the sample is complete and vertical, and the grain structure is bonded after etching. Figure 1c As shown;

[0058] S3, after the tetramethylammonium hydroxide solution treatment in S2, the edges and sidewalls of the Micro-LED grains are subjected to plasma chemical vapor deposition of silicon dioxide to prepare an insulating passivation layer, such as Figure 1d As shown;

[0059] S4, using LSCM to evaluate the early luminescence performance of the Micro-LED grains after chemical treatment and sidewall passivation prepared in S3;

[0060] The specific operation of early luminescence performance evaluation is as follows: using laser confocal microscopy (LSCM) to test the luminescence performance of Micro-LED grains after being treated with tetramethylammonium hydroxide solution and sidewall passivation; Figure 5 As shown, the light emitted by the light source 10 passes through the collimating beam expander and is incident on the beam splitter 11. The light beam reflected by the beam splitter passes through the objective lens 12 and forms a convergence point on the focal plane of the objective lens. The Micro-LED crystal is placed at the focal plane of the objective lens, and the objective lens scans the Micro-LED crystal point by point. During the scanning process, the sample Micro-LED crystal is excited to produce fluorescence. The fluorescence passes through the objective lens and the beam splitter in turn and is incident on the photomultiplier tube 14 through the small hole filter 13. The signal in the photomultiplier tube is processed to form an image of the Micro-LED crystal under test. By scanning each Micro-LED crystal on the focal plane, a complete set of Micro-LED crystal confocal images is formed. S5, the Micro-LED crystal after the S4 quality assessment is processed through a vapor deposition process, a photolithography process, and an etching process to prepare a current spreading layer 8 on the surface of the Micro-LED crystal. The current spreading layer uses indium tin oxide (ITO) with a thickness of about 200nm, forming an ohmic contact with the P-type layer 5, which has low resistivity and high transmittance.

[0061] S6, using the Micro-LED crystal grains prepared in S5 to prepare cathode and anode electrodes 9 through photolithography and sputtering processes, with the cathode in contact with the N-type layer 3 and the anode in contact with the current spreading layer 8 on the P-type layer 5;

[0062] S7, the prepared Micro-LED is packaged and tested, and the electrical performance test results of the Mciro-LED chip are analyzed to see the damage of the S5 to S7 Micro-LED chips, and compared with the optical performance of S1 to S3 analyzed in the early luminous performance evaluation.

[0063] Figures 2a to 2c The results of three Micro-LED sidewall treatment methods are shown: no treatment, chemical treatment with tetramethylammonium hydroxide solution, and a combination of chemical treatment with tetramethylammonium hydroxide solution and SiO2 passivation. Figure 2a 、 Figure 2b 、 Figure 2c SEM images of the 8-micron Micro-LED before and after treatment show that the chemical treatment with tetramethylammonium hydroxide solution caused obvious shallow corrosion on the sidewalls of the Micro-LED. After SiO2 passivation, the sidewalls of the device were further repaired.

[0064] Figure 3a 、 Figure 3bThis is a cross-sectional TEM image of the Micro-LED after dry etching without treatment, and after chemical treatment with tetramethylammonium hydroxide solution combined with SiO2 passivation. After chemical treatment and passivation, the slope of the Micro-LED sidewall is restored from the original 70° to a nearly steep 90°, which is conducive to the recombination of holes and electrons in the upper and lower regions of the quantum well. Figure 3c The high-resolution TEM image of the Micro-LED sidewall after dry etching is shown. Due to ion bombardment during the dry etching process, the edge of the sidewall shows a 2nm layer of disordered lattice arrangement (amorphization). After chemical treatment with tetramethylammonium hydroxide solution, the atoms on the surface of the Micro-LED sidewall show an orderly arrangement of single crystal atoms, with no obvious signs of crystal damage. Figure 3d shown.

[0065] from Figure 3d It can be seen that the combination of tetramethylammonium hydroxide solution chemical treatment and sidewall passivation can effectively repair the sidewall damage problem of Micro-LED caused by dry etching.

[0066] Figure 4a 、 Figure 4b 、 Figure 4c LSCM images of 10 micron Micro-LED after dry etching without treatment, chemical treatment with tetramethylammonium hydroxide solution, and chemical treatment with tetramethylammonium hydroxide solution + SiO2 passivation. It can be seen that compared with the untreated Figure 4a , after processing Figure 4b 、 Figure 4c Glow brighter. Figure 4d The PL intensity diagrams under three treatment methods show that after chemical treatment with tetramethylammonium hydroxide solution and SiO2 sidewall passivation, the 10-micron Micro-LED emits more uniform light, and the luminous intensity is increased by about 4.7 times.

[0067] Compared with the samples treated with chemical treatment and sidewall passivation, only the samples treated with tetramethylammonium hydroxide solution Figure 4b The samples after irradiation have uneven luminescence and the PL intensity decreases significantly. Figure 4d This is mainly due to the poor stability of the Micro-LED sidewalls after wet etching of the insulating passivation layer, and the device performance is easily degraded when exposed to air for a long time.

[0068] In summary, the Micro-LED sidewall repair method proposed in the embodiments of this application can effectively repair the sidewall damage problems faced by the development of Micro-LED chips. After dry etching, a combination of chemical treatment with tetramethylammonium hydroxide solution and sidewall passivation can effectively remove sidewall damage such as lattice disorder and sidewall tilt introduced by dry etching. By combining LSCM and photoluminescence to analyze the optical properties of Micro-LED grains, early luminescence performance evaluation of device quality can be performed. This can effectively analyze quality issues of Micro-LED grains early in the process, and can be compared with final electrical testing to form a comparative analysis, which can improve the yield of Micro-LED chips to a certain extent.

[0069] The above embodiments are intended only to illustrate the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit of this application shall be included in the scope of protection of this application.

Claims

1. A method for preparing a Micro-LED device, characterized in that: The steps include: S1. Prepare isolation grooves on LED epitaxial wafers based on dry etching process to form Micro-LED grains. The LED epitaxial wafer includes a substrate layer, on the upper surface of which an undoped layer, an N-type layer, a quantum well layer, and a P-type layer are sequentially deposited; the depth of the isolation trench is at least as deep as the N-type layer; S2. Placing the Micro-LED die prepared in S1 in a tetramethylammonium hydroxide solution to repair damage to the sidewalls of the isolation trench caused by the dry etching process; S3. After the tetramethylammonium hydroxide solution treatment in S2, an insulating passivation layer is deposited on the edges and sidewalls of the Micro-LED die; S4. Use a laser confocal microscope to evaluate the quality of the Micro-LED die for early luminescence performance. Then, use photoluminescence spectroscopy to measure the luminescence intensity at various points on the surface of the Micro-LED die. S5. Using a photolithography process to etch away the insulating passivation layer on the surface of the Micro-LED die and expose the upper surface of the P-type layer, and using an evaporation process to prepare a current spreading layer on the exposed surface of the P-type layer; S6. Using a sputtering process to prepare anode and cathode electrodes on the surface of the Micro-LED grains, thereby obtaining a Micro-LED chip; S7. Encapsulating the Micro-LED chip obtained in S6 to obtain a Micro-LED device. S7 also includes testing the electrical performance of the Micro-LED device and comparing the electrical performance test results with the early luminescence performance evaluation to analyze and evaluate the source of damage to the Micro-LED chip. The early luminescence performance evaluation operation includes: Laser confocal microscopy was used to test the luminescence performance of Micro-LED grains after treatment with tetramethylammonium hydroxide solution and sidewall passivation. The light emitted by the light source is incident on the beam splitter after passing through the collimating beam expander. The light beam reflected by the beam splitter passes through the objective lens and forms a convergence point on the focal plane of the objective lens. The Micro-LED crystal is placed at the focal plane of the objective lens, which scans the Micro-LED crystal point by point. During the scanning process, the Micro-LED crystal under test is excited to produce fluorescence. The fluorescence passes through the objective lens and the beam splitter in turn and is incident on the photomultiplier tube through a small hole filter. The signal in the photomultiplier tube is processed to form an image of the Micro-LED crystal under test. By scanning each Micro-LED crystal on the focal plane point by point, a complete set of Micro-LED crystal confocal images is formed.

2. The method for preparing a Micro-LED device according to claim 1, wherein: In step S2, the concentration of the tetramethylammonium hydroxide solution is 20%, and the solution is heated in a water bath at 80° C. for 1 hour.

3. The method for preparing a Micro-LED device according to claim 1, wherein: The laser excitation wavelength band of the laser confocal microscope in step S4 is smaller than the light emission wavelength of the Micro-LED crystal.

4. The method for preparing a Micro-LED device according to claim 1, wherein: The excitation diameter of the light source in the photoluminescence spectrum test in step S4 is less than 1 micron.

5. The method for preparing a Micro-LED device according to claim 1, wherein: In step S5 , the current spreading layer is in contact with only the upper surface of the P-type layer.

6. The method for preparing a Micro-LED device according to claim 1, wherein: The current spreading layer is made of indium tin oxide.

7. The method for preparing a Micro-LED device according to claim 6, wherein: The current spreading layer has a thickness of 200 nm and forms an ohmic contact with the P-type layer.

8. The method for preparing a Micro-LED device according to claim 1, wherein: The cathode and anode electrodes prepared in step S6 are respectively connected to the N-type layer and the P-type layer of the Micro-LED crystal.

9. The method for preparing a Micro-LED device according to claim 1, wherein: Silicon dioxide was deposited by plasma chemical vapor deposition to form an insulating passivation layer.

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