Preparation method of Micro-LED with high light extraction rate

Abstract

The invention relates to the field of Micro-LED efficiency optimization and display, in particular to a preparation method of a Micro-LED with high light extraction rate, which comprises the following steps of: S1, growing an etching mask layer on the top of an epitaxial wafer; s2, spin-coating a layer of photoresist on the top of the etching mask layer, and then photoetching to form a micro pattern; s3, the etching mask layer is etched; s4, the Mesa structure is etched; s5, cleaning the residual photoresist; s6, cleaning the residual etching mask layer; s7, drying for later use; s8, preparing a KOH solution, and soaking the prepared device in the KOH solution. According to the method, the side wall of the Micro-LED chip is processed through a KOH solution chemical corrosion method, so that the luminous efficiency of the Micro-LED chip is improved, the luminous efficiency of the Micro-LED chip is further improved, and the method is low in use cost, simple and convenient to operate and convenient to popularize.

Description

Technical Field

[0001] The present invention relates to the field of Micro-LED efficiency optimization and display, and in particular to a method for preparing a Micro-LED with high light extraction efficiency. Background Art

[0002] As the size of the device decreases, the efficiency of the Micro-LED chip will drop significantly, which has a huge impact on the application of the chip. Therefore, how to improve the luminous efficiency of the Micro-LED chip has become a very important scientific issue. Improving the light extraction efficiency of the Micro-LED is an important factor in improving the luminous efficiency of the Micro-LED chip. Many researchers or companies use materials such as Al2O3, SiO2, Si3N4, etc. to passivate the side walls of the Micro-LED chip, thereby repairing the side wall defects and improving the light extraction efficiency. However, this process requires the use of expensive equipment such as PECVD or ALD, and coating in a high temperature environment also causes certain secondary damage to the device itself.

[0003] Therefore, those skilled in the art are committed to developing a method for preparing Micro-LEDs with high light output efficiency. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing Micro-LED with high light output efficiency.

[0005] To achieve the above object, the present invention provides a method for preparing a Micro-LED with high light extraction efficiency, comprising the following steps:

[0006] S1, growing an etching mask layer on the top of the epitaxial wafer;

[0007] S2, spin-coating a layer of photoresist on the top of the etching mask layer, and then photolithography to form a micro pattern, and protecting the etching mask layer that needs to be retained by spin-coating the photoresist;

[0008] S3, etching the etching mask layer using ICP technology, the ICP equipment used is PlasmaPro 100Cobra, and the power parameters of the upper and lower plates are 100W / 20W respectively;

[0009] S4. Use ICP technology to etch the Mesa structure. The ICP equipment used is PlasmaPro 100Cobra, and the power parameters of the upper and lower plates are 100W / 20W respectively;

[0010] S5, cleaning residual photoresist;

[0011] S6, cleaning the residual etching mask layer;

[0012] S7, drying for standby use;

[0013] S8. Soak the prepared device in KOH solution. Since the GaN material in the epitaxial wafer has three different polarity planes, a, m, and c, the corrosion rate and effect of KOH solution on these three polarity planes are very different. This difference can be used to treat the sidewalls of the Micro-LED chip by chemical etching with KOH solution. By adjusting the inclination angle of the sidewalls of the Micro-LED chip, the light extraction efficiency of the Micro-LED chip can be improved, thereby improving the luminous efficiency of the Micro-LED chip.

[0014] Preferably, in step S1, the epitaxial wafer includes a substrate layer, a buffer layer, a U-GaN layer, an N-GaN layer, a QW layer and a P-GaN layer stacked in sequence from bottom to top.

[0015] Preferably, the thickness of the Buffer layer is 10nm-40nm, the thickness of the U-GaN layer is 3000nm-4000nm, the thickness of the N-GaN layer is 1500nm-3000nm, the thickness of the QW layer is 250nm-400nm, and the thickness of the P-GaN layer is 100nm-500nm.

[0016] Preferably, the etching mask in step S1 is made of SiO2, and the thickness of the etching mask layer is 400nm-600nm. On the one hand, the etching mask layer can protect the side walls of the chip. On the other hand, from the processing technology point of view, the shallower the etching depth, the greater the etching difficulty. The etching plane can be raised by increasing the thickness of the etching mask layer, thereby completing some shallow etching operations.

[0017] Preferably, ICP technology is used for etching in both step S3 and step S4.

[0018] Preferably, in step S4, the depth of the Mesa structure is 1 μm-3 μm, and the depth of the Mesa structure can be adjusted by adjusting the thickness of the etching mask layer.

[0019] Preferably, acetone solution is used for cleaning in step S5.

[0020] Preferably, in step S6, BOE solution is used for cleaning, and the cleaning soaking time is 3-7 minutes.

[0021] Preferably, the KOH solution in step S8 is 1-3 mol / L.

[0022] Preferably, in step S8, the temperature of the KOH solution is 70-90°C, and the immersion time is 15-45 minutes. In step S6, the side wall inclination angle of the cleaned Micro-LED chip is measured to be about 80 degrees. Such an angle will induce internal reflection, thereby reducing the light extraction efficiency of the device. In the present invention, through immersion in the KOH solution in step S8, the side wall structure of the Micro-LED chip presents a triangular prism shape, and the side wall becomes very vertical. These changes increase the relative surface area of ​​the device and increase the light extraction efficiency.

[0023] The beneficial effects of the present invention are as follows: the present invention processes the sidewalls of the Micro-LED chip by a KOH solution chemical etching method, thereby improving the light extraction efficiency of the Micro-LED chip, and further improving the luminous efficiency of the Micro-LED chip, and the method has low use cost, simple operation, and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of an epitaxial wafer in a specific implementation manner of the present invention.

[0025] Figure 2 It is a schematic diagram of the combination of an epitaxial wafer and an etching mask layer in a specific implementation manner of the present invention.

[0026] Figure 3 It is a schematic diagram of the combination of an epitaxial wafer, an etching mask layer and a photoresist in a specific implementation manner of the present invention.

[0027] Figure 4 It is a schematic diagram of etching the etching mask layer in a specific embodiment of the present invention.

[0028] Figure 5 It is a schematic diagram of etching a Mesa structure in a specific embodiment of the present invention.

[0029] Figure 6 It is a schematic diagram of the structure after cleaning the etching mask layer and the photoresist in a specific embodiment of the present invention.

[0030] Figure 7 It is a comparison diagram of immersion time and angle change in a specific embodiment of the present invention.

[0031] 1. Epitaxial wafer; 11. Substrate layer; 12. Buffer layer; 13. U-GaN layer; 14. N-GaN layer; 15. QW layer; 16. P-GaN layer; 2. Etching mask layer; 3. Photoresist. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that in the description of the present invention, the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inside", "outside", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific manner, and therefore cannot be understood as a limitation on the present invention.

[0033] First embodiment:

[0034] A method for preparing a high light-extraction efficiency Micro-LED comprises the following steps:

[0035] like Figure 1-2 As shown, S1, using PECVD to grow an etching mask layer 2 on the top of the epitaxial wafer 1, in this embodiment, the etching mask layer 2 is made of SiO2, and the thickness of the etching mask layer 2 is 400nm-600nm.

[0036] like Figure 3 As shown, S2, a layer of photoresist 3 is spin-coated on the top of the etching mask layer 2, followed by photolithography to form a micro pattern.

[0037] like Figure 4 As shown, S3, the etching mask layer 2 is etched using ICP technology.

[0038] like Figure 5 As shown, S4, using ICP technology to etch the Mesa structure, in this embodiment, the depth of the Mesa structure is 1μm-3μm.

[0039] like Figure 6 As shown, S5, the residual photoresist 3 is removed by soaking in acetone solution.

[0040] S6, using BOE solution to soak and remove the remaining etching mask layer 2, the cleaning soaking time is 3-7 minutes;

[0041] S7, drying and standby.

[0042] S8. Prepare a 1-3 mol / L KOH solution, and soak the prepared device in the KOH solution for 15-45 minutes, maintaining the temperature of the KOH solution at 70-90°C.

[0043] In this embodiment: in step S1, the epitaxial wafer 1 includes a substrate layer 11, a buffer layer 12, a U-GaN layer 13, an N-GaN layer 14, a QW layer 15 and a P-GaN layer 16 stacked in sequence from bottom to top, wherein the buffer layer 12 has a thickness of 10nm-40nm, the U-GaN layer 13 has a thickness of 3000nm-4000nm, the N-GaN layer 14 has a thickness of 1500nm-3000nm, the QW layer 15 has a thickness of 250nm-400nm, and the P-GaN layer 16 has a thickness of 100nm-500nm.

[0044] Second embodiment:

[0045] A method for preparing a high light-extraction efficiency Micro-LED comprises the following steps:

[0046] S1. Grow an etching mask layer 2 with a thickness of 500 nm on the top of the epitaxial wafer 1. The etching mask layer 2 is made of SiO2.

[0047] S2, spin-coating a layer of photoresist 3 on the top of the etching mask layer 2, followed by photolithography to form a micro pattern.

[0048] S3, etching the mask layer 2 using ICP technology.

[0049] S4. Use ICP technology to etch the Mesa structure, and the depth of the Mesa structure is 2μm.

[0050] S5, using acetone solution to soak and clean the residual photoresist 3.

[0051] S6, using BOE solution to soak and clean the remaining etching mask layer 2, the soaking time for cleaning is 5 minutes.

[0052] S7, drying and standby.

[0053] S8. Prepare a 2 mol / L KOH solution, and soak the prepared device in the KOH solution for 20 minutes. Keep the KOH solution temperature at 80°C. As the soaking time increases, the tilt angle of the Micro-LED chip side wall gradually approaches vertical. To further verify the relationship between the soaking time and the tilt angle of the Micro-LED chip side wall, this experiment extends the soaking time to 40 minutes. At this time, the side wall of the Micro-LED chip is close to completely vertical ( Figure 7 right image).

[0054] like Figure 7 As shown, in step S6, the sidewall inclination angle of the cleaned Micro-LED chip is measured to be approximately 80 degrees ( Figure 7The light extraction rate is 70%. The prepared Micro-LED chip is immersed in a KOH solution using the method of the present invention. As the immersion time increases, the side wall angle of the Micro-LED chip gradually approaches vertical, about 85-90 degrees, and the overall structure presents a triangular prism shape. At this time, the light extraction efficiency is increased to more than 90%.

[0055] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a high light-extraction efficiency Micro-LED, characterized in that: The following steps are involved: S1, growing an etching mask layer (2) on the top of the epitaxial wafer (1); S2, spin coating a layer of photoresist (3) on the top of the etching mask layer (2), followed by photolithography to form a micro pattern; S3, etching the etching mask layer (2); S4, etching Mesa structure; S5, cleaning the residual photoresist (3); S6, cleaning the remaining etching mask layer (2); S7, drying for standby use; S8. Soak the prepared device in KOH solution.

2. The method for preparing a high light-extraction efficiency Micro-LED according to claim 1, wherein: The epitaxial wafer in step S1 comprises a substrate layer (11), a buffer layer (12), a U-GaN layer (13), an N-GaN layer (14), a QW layer (15) and a P-GaN layer (15) which are stacked in sequence from bottom to top.

3. The method for preparing a high light-extraction efficiency Micro-LED according to claim 2, wherein: The buffer layer (12) has a thickness of 10nm-40nm, the U-GaN layer (13) has a thickness of 3000nm-4000nm, the N-GaN layer (14) has a thickness of 1500nm-3000nm, the QW layer (15) has a thickness of 250nm-400nm, and the P-GaN layer (16) has a thickness of 100nm-500nm.

4. The method for preparing a high light-extraction efficiency Micro-LED according to claim 3, characterized in that: In step S1, the etching mask layer (2) is made of S i O2, and the etching mask layer (2) has a thickness of 400nm-600nm.

5. The method for preparing a high light-extraction efficiency Micro-LED according to claim 1, wherein: In both step S3 and step S4, ICP technology is used for etching.

6. The method for preparing a high light-extraction efficiency Micro-LED according to claim 5, characterized in that: The depth of the Mesa structure in step S4 is 1 μm-3 μm.

7. The method for preparing a high light-extraction efficiency Micro-LED according to claim 1, wherein: In the step S5, acetone solution is used for cleaning.

8. The method for preparing a high light-extraction efficiency Micro-LED according to claim 1, wherein: In step S6, BOE solution is used for cleaning, and the cleaning soaking time is 3-7 minutes.

9. The method for preparing a Micro-LED with high light extraction efficiency as claimed in claim 1, characterized in that: The KOH solution in step S8 is 1-3 mol / L.

10. The method for preparing a high light-extraction efficiency Micro-LED according to claim 9, wherein: In step S8, the temperature of the KOH solution is 70-90° C., and the soaking time is 15-45 minutes.

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