A Micro LED display chip and preparation method thereof

Abstract

The present invention belongs to the technical field of LED display chips, and discloses a Micro LED display chip and a preparation method thereof. The present invention processes an MQW layer of an epitaxial wafer by ultrafast pulse laser, so that an EBL layer and a P-GaN layer that can be free of ICP etching are prepared by subsequent deposition processing, so that the preparation method of constructing a vertically distributed LED display chip is greatly simplified. At the same time, a larger current density can be achieved through a cathode shallow groove network and a deep through-hole design, and optical crosstalk can be effectively prevented.

Description

Technical Field

[0001] The present invention belongs to the technical field of LED display chips, and in particular relates to a Micro LED display chip and a preparation method thereof. Background Art

[0002] Micro light emitting diodes (Micro LED) display chips are a type of LED chip. They are a display device composed of a large number of micron-sized inorganic LED light-emitting pixels. Due to their small pixel size, small pixel pitch and excellent display effect, they have emerged in AR / VR, automotive and other applications. However, there are still many problems with Micro LED display chips at this stage. Micro LED pixel size and pixel pitch are relatively small, so it is difficult to prepare, and its luminous efficiency will also be affected by the preparation method. Therefore, it is necessary to optimize and improve its device structure and preparation method.

[0003] In the existing micro-LED manufacturing technology, ICP (Inductive Coupled Plasma) is often required to ion-etch the GaN epitaxial layer to form an independent light-emitting LED pixel unit. During this production process, ICP etching will damage the sidewalls of the micro-LED. The smaller the size, the more serious the damage, which will lead to an increase in the leakage current of the micro-LED device and a decrease in the luminous efficiency. In addition, in the existing flip-chip structure micro-LED, cathode metal needs to be made between the micro-LED pixels, resulting in a large pixel spacing between the micro-LED pixels; it requires a low-linewidth lithography machine with high manufacturing difficulty and high value for processing, which greatly increases the manufacturing cost.

[0004] Therefore, it is an urgent need to provide a micro light emitting diode manufacturing technology that can solve the above problems. Summary of the invention

[0005] In view of the limitations of the existing methods described above, the purpose of the present invention is to propose a Micro LED display chip and a method for preparing the same, so as to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0006] To achieve the above object, a first aspect of the present invention provides a method for preparing a Micro LED display chip, comprising the following steps:

[0007] (1) sequentially preparing a buffer layer, an N-GaN layer and an MQW layer on a substrate; laser processing the MQW layer using an ultrafast pulse laser at 700° C. to 800° C. to form a pixel spacing, thereby obtaining a laser-processed MQW layer;

[0008] (2) sequentially growing an EBL layer and a P-GaN layer on the laser-treated MQW layer; then preparing a first anode metal and a first protective layer on the P-GaN layer to obtain a wafer;

[0009] The wafer includes a substrate and a buffer layer, an N-GaN layer, an MQW layer, an EBL layer and a P-GaN layer prepared on the substrate, as well as a structure formed by processing the same;

[0010] (3) turning the wafer over so that the first protective layer is in contact with the driver chip, the driver chip includes a second anode metal and a second cathode metal, and the first anode metal is in contact with the second anode metal; removing the substrate and the buffer layer;

[0011] (4) depositing a second protective layer on the N-GaN layer, and making a cathode shallow groove on the second protective layer; making a cathode deep through hole, wherein the cathode shallow groove and the cathode deep through hole are connected, and the cathode shallow groove and the cathode deep through hole are used to accommodate a first cathode metal, and the first cathode metal is connected to the second cathode metal through the cathode deep through hole;

[0012] (5) Depositing a third protective layer on the second protective layer to obtain the Micro LED display chip.

[0013] The present invention proposes a small pixel pitch Micro LED display chip and a preparation method thereof that do not require ICP etching of the GaN epitaxial layer. The display chip optimizes the design of the GaN epitaxial layer structure and the preparation process. In the MicroLED display chip and the preparation method thereof provided by the present invention, there is no need for ICP etching technology to segment the pixels. Instead, after the MQW epitaxial growth, an ultrafast pulse laser is used to irradiate the MQW film layer. At this time, the irradiated GaN will absorb the laser energy and undergo a decomposition reaction, so that the GaN is decomposed into Ga droplets and N2 gas, that is, 2GaN (s) → 2Ga (l) + N2 (g). By controlling the laser irradiation area during the laser processing process, the segmentation of GaN can be achieved, thereby achieving the effect of replacing ICP etching.

[0014] In this process, laser irradiation treatment is different from ICP etching. Since many impurities including Ar atoms will be introduced during the ICP etching process, it is easy to cause damage to the GaN lattice structure, thereby causing etching damage to the GaN crystal. This etching damage will cause a large leakage current in the final Micro LED display chip.

[0015] Moreover, some Ga droplets will remain in the area after laser processing, and the Ga droplets will remain in the pixel spacing formed after the MQW layer is processed. The Ga droplets in the pixel spacing will prevent the deposition and growth of the EBL layer and the P-GaN layer, thus achieving the effect of selective growth, thereby automatically forming a gap and avoiding subsequent processing of the EBL layer and the P-GaN layer.

[0016] Preferably, the thickness of the MQW layer is 10 nm-100 nm.

[0017] The MQW layer of appropriate thickness can ensure that the Ga droplets can stay stably at the predetermined position during the processing, so that the growth of the subsequent EBL layer and P-GaN layer can be expected, thereby improving the yield rate.

[0018] Preferably, the specific steps of the laser processing include:

[0019] Under the condition of 700° C.-800° C., the MQW layer is scanned and irradiated in a two-dimensional matrix form using an ultrafast pulse laser, so that the irradiated part is heated to 900° C.-1100° C. to form a pixel spacing.

[0020] Preferably, the ultrafast pulse laser is a picosecond ultrafast pulse laser, the laser energy is between 0.7eV-5.5eV, and the laser spot size is 10nm-500nm.

[0021] Through the laser system and optical lens system, the laser spot size can be controlled, and nanometer (10nm-500nm) scale irradiation etching can be achieved, which greatly reduces the pixel spacing and increases the effective luminous area. Ultrafast pulse lasers can precisely adjust the working conditions when processing the MQW layer due to their precisely controllable picosecond irradiation time and precise control of energy. While completing the precise and thorough segmentation of the MQW layer, a trace amount of liquid Ga is produced, which reduces the damage to the N-GaN layer during the production process while realizing the manufacturing process.

[0022] Preferably, the specific preparation method of the cathode shallow groove and the cathode deep through hole in step (4) comprises the following steps:

[0023] The substrate and the buffer layer are removed to expose the N-GaN layer, and then the second protective layer is deposited on the exposed N-GaN layer, and the cathode shallow groove is made on the second protective layer; the cathode deep through hole is made, and the cathode deep through hole penetrates the second protective layer, the N-GaN layer, the MQW layer, the EBL layer, the P-GaN layer and the first protective layer, and the cathode deep through hole is connected with the cathode shallow groove, and the first cathode metal is arranged in the cathode deep through hole and the cathode shallow groove, and the first cathode metal is connected with the second cathode metal.

[0024] A second aspect of the present invention provides a Micro LED display chip prepared using the above method.

[0025] Preferably, the structure of the Micro LED display chip is divided into a pixel area and a cathode area;

[0026] The cathode region includes, from bottom to top, a driving chip, the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer, the second protective layer and the third protective layer; the cathode region also includes the cathode deep through hole, which penetrates the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer and the second protective layer;

[0027] The pixel region includes the driving chip, the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer, the second protective layer and the third protective layer in order from bottom to top; the driving chip is provided with a second anode metal, the first protective layer is provided with the first anode metal, one end of the first anode metal is connected to the second anode metal, the other end of the first anode metal is connected to the P-GaN layer, and the second protective layer is provided with the cathode shallow groove;

[0028] The cathode deep through hole is connected to the cathode shallow groove, and the cathode deep through hole and the cathode shallow groove are used to accommodate the first cathode metal; a section of the first cathode metal is connected to the second cathode metal, and the other end of the first cathode metal (through the cathode shallow groove) is connected to the N-GaN layer.

[0029] Preferably, the first protective layer, the second protective layer and the third protective layer in the Micro LED display chip are SIO protective layers.

[0030] A third aspect of the present invention provides a display panel including the above-mentioned Micro LED display chip.

[0031] A fourth aspect of the present invention provides an electronic display screen comprising the above-mentioned display surface.

[0032] The preparation method of a Micro LED display chip provided by the present invention enables the internal structure of the LED display chip to present a vertical structure perpendicular to the driving substrate when the driving substrate is a horizontal plane, which further reduces the size of a single LED device and further reduces the pixel spacing, so that the final product has a higher pixel density.

[0033] The beneficial effects of the present invention are:

[0034] (1) The present invention can quickly segment the pixel MQW through ultrafast laser irradiation assisted by a hot stage, avoiding excessive damage caused by ICP etching in the prior art, thereby obtaining a smaller leakage current than the prior art;

[0035] (2) The present invention can produce LED devices with nanometer-level pixel pitch and pixel size through the regulation of the optical lens system, and can produce LED devices with small size and small pitch;

[0036] (3) After laser processing, the present invention can enable subsequent EBL, P-GaN and other film layers to automatically grow in selected areas without the need for etching processing;

[0037] (4) The vertical structure device design proposed in the present invention further reduces the pixel pitch and improves the pixel density;

[0038] (5) The cathode shallow groove network and cathode deep through-hole design proposed in the present invention can achieve a higher current density and prevent optical crosstalk. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Shown is a schematic diagram of the structure of the Micro LED display chip disclosed in the present invention;

[0040] Figure 2 The figure shows a schematic diagram of a Micro LED display chip structure in the prior art;

[0041] Figure 3 The figure shows a schematic diagram of the epitaxial wafer preparation structure in the Micro LED display chip preparation method disclosed in the present invention;

[0042] Figure 4 FIG. 1 is a schematic diagram of a laser processing structure in the method for preparing a Micro LED display chip disclosed in the present invention;

[0043] Figure 5 It is a schematic diagram of the structure growth after laser treatment in the method for preparing a Micro LED display chip disclosed in the present invention;

[0044] Figure 6 It is a schematic diagram of the preparation of the protective layer and the anode metal in the Micro LED display chip preparation method disclosed in the present invention;

[0045] Figure 7 The figure shows a schematic diagram of wafer inversion substrate transfer in the Micro LED display chip preparation method disclosed in the present invention;

[0046] Figure 8 It is a schematic diagram of preparing a cathode shallow groove and a cathode deep through hole in the Micro LED display chip preparation method disclosed in the present invention;

[0047] Fig. 9 Shown is a schematic diagram of the preparation of cathode metal and protective layer in the Micro LED display chip preparation method disclosed in the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the embodiments and drawings to clearly and completely describe the concept, specific structure and technical effects of the present invention, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0049] like Figure 1-Figure 9 As shown, a specific implementation method of a preparation process of a Micro LED display chip is as follows:

[0050] like Figure 3 As shown, the present invention first prepares an epitaxial wafer consisting of a substrate, a buffer layer, an N-GaN layer and an MQW layer on a substrate that serves as a carrier, wherein the epitaxial wafer on the substrate is divided into a pixel region and a cathode region, wherein the pixel region is used to prepare a light-emitting structure, and the cathode region is reserved for the subsequent preparation of a cathode deep through hole. Since the epitaxial wafer carries the crucial ultrafast pulse laser processing in the present invention, the structure of the epitaxial wafer needs to be specifically designed in terms of the composition and thickness of the epitaxial wafer.

[0051] like Figure 4As shown, the thickness of the MQW layer is 20nm (in other implementation cases, any value between 10nm and 100nm can be selected). Under this thickness, in combination with a hot stage at 800°C (in other implementation cases, any value between 700°C and 800°C can be selected), on the one hand, the MQW layer can be precisely divided into specific size areas according to specific requirements under the action of an ultrafast pulse laser, thereby obtaining a precisely divided MQW layer structure; on the other hand, since the hot stage at 800°C (in other implementation cases, any value between 700°C and 800°C can be selected) can keep the entire epitaxial wafer including the substrate and the epitaxial layer in a stable temperature state, after the ultrafast pulse laser completes the division of the MQW layer to form a pixel spacing, the exposed N-GaN layer in the cavity of the division gap is directly exposed to the irradiation of the laser. , by using ultrafast pulse laser to further irradiate the exposed N-GaN layer, so that its temperature rises to a higher GaN decomposition temperature, so that the part of N-GaN irradiated by the ultrafast pulse laser is decomposed into N2 and Ga elements according to the set requirements, and N2 will directly leave the surface of the epitaxial wafer in a gaseous state, while the melting point of Ga element is about 302.91K, that is, 29.76℃, and the boiling point is about 2476.57K, that is, 2203.42℃ under an atmospheric pressure of 101.325kPa. Therefore, when the N-GaN layer is heated to the decomposition temperature by the ultrafast pulse laser, by controlling the irradiation time of the ultrafast pulse laser, the Ga element produced after the decomposition of GaN is in a liquid state, so that the liquid Ga element remains in the cavity of the MQW layer segmentation gap formed by the ultrafast pulse laser processing.

[0052] like Figure 5 As shown, after laser processing, the EBL layer and the P-GaN layer need to be grown. During this process, due to the presence of liquid Ga single substance in the cavity of the epitaxial wafer MQW layer segmentation gap, the working condition of the cavity of the epitaxial wafer MQW layer segmentation gap during the growth of the EBL layer and the P-GaN layer is completely different from the working condition of the surrounding undivided complete MQW layer. At this time, during the deposition of the EBL layer, the complete MQW layer can grow deposited material, while the cavity of the MQW layer segmentation gap contains liquid Ga single substance, so deposited material cannot grow; using this principle, a specific epitaxial layer can be grown on the MQW layer through deposition processing, thereby avoiding multiple etching or processing of the epitaxial layer by various means in the prior art, which also makes the MQW layer segmentation gap formed during the ultra-fast pulse laser processing divide the entire epitaxial wafer into multiple micro units, and these units further deposit EBL layer and P-GaN layer during the first deposition processing, so that each unit has the basic structure of subsequent processing into an LED.

[0053] like Figure 6As shown, the epitaxial wafer after the first deposition still needs to be further processed to improve its structure. At this time, the top of the epitaxial wafer structure is the P-GaN layer. It is necessary to prepare the first anode metal and the first protective layer on the P-GaN layer at this time, so that the first anode metal is fixed by the first protective layer, one end is connected to the P-GaN, and the other end is exposed outside the first protective layer, in preparation for subsequent processing; at this time, the epitaxial wafer, while the first protective layer fixes the anode metal outside the P-GaN layer to form a connection, the first protective layer has also filled the cavity of the MQW layer segmentation gap. Filling the cavity can make the epitaxial layer more stable and ensure strength during subsequent processing.

[0054] like Figure 7 As shown, after the preparation of the anode metal connected P-GaN layer and the first protective layer is completed, the processing of the epitaxial wafer comes to an end. At this time, the epitaxial wafer needs to be reversed as a wafer as a whole, so that the epitaxial wafer substrate and the first protective layer of the epitaxial wafer currently on the outermost layer containing the exposed anode metal are swapped in relative spatial position, so that the epitaxial wafer can dock its outermost first protective layer and the anode metal exposed on the first protective layer with the corresponding anode on the subsequent driving substrate. After the position is determined and the docking is completed, due to the epitaxial wafer being reversed, the relative positions of the substrate and the buffer layer that were originally at the bottom have changed. At this time, the substrate and the buffer layer are removed, so that the N-GaN layer becomes the outermost layer exposed to the outside, which is convenient for the next processing.

[0055] like Figure 8 and Fig. 9 As shown, since the P-GaN layer has been connected to the corresponding second anode metal on the driving substrate as the anode of the driving chip through the first anode metal under the action of the first protective layer, the cathode needs to be processed to improve its structure, so a second deposition process is required at this time, wherein a cathode shallow groove needs to be prepared by depositing a second protective layer to accommodate the first cathode metal to form a connection with the N-GaN layer; a cathode deep through hole needs to be prepared to penetrate the various layers of structure located above the driving substrate until a section of the second cathode metal on the corresponding driving substrate as the cathode of the driving chip is exposed, and the other end is connected to the cathode shallow groove; then the cathode shallow groove and the cathode deep through hole are filled with the first cathode metal, so that the second cathode metal on the driving substrate and the N-GaN are connected through the first cathode metal in the cathode shallow groove and the cathode deep through hole. At this time, the driving chip on the driving substrate can control the N-GaN through the connected first cathode metal and the second cathode metal, and control the P-GaN through the anode metal; finally, the third protective layer is deposited to complete the preparation of the Micro LED display chip provided by the present invention.

[0056] Combined with the above detailed explanation of each process of the preparation process, it is not difficult to see that the present invention uses ultrafast laser and hot stage under specific conditions to quickly divide the MQW at the very beginning of the preparation method, thereby realizing rapid processing of the unit, and by regulating the optical lens system of the laser, the lattice damage caused by ICP etching in the prior art is overcome, thereby reducing the leakage current; the laser spot is controlled to a nanometer size, and an LED device unit with a nanometer pixel pitch and pixel size is constructed; during the processing, the EBL layer, P-GaN layer and other film layers do not need to be etched, and can be separated by themselves, which makes it possible to prepare small-sized and small-pitch LED devices through the technical solution provided by the present invention, while improving the processing efficiency and yield rate.

[0057] Figure 1 This is a schematic diagram of the structure of the Micro LED display chip disclosed in the present invention. After the preparation is completed, since the first protective layer and the second protective layer are fused during the preparation of the cathode deep through hole during the second deposition process, and after the cathode metal is finally prepared with the third protective layer, the third protective layer and the second protective layer are fused, the first protective layer, the second protective layer and the third protective layer are collectively referred to as protective layers in the final schematic diagram.

[0058] Figure 2 This is a schematic diagram of a Micro LED display chip structure in the prior art. Compared with the present invention, it occupies too much space and has insufficient efficiency.

[0059] Although the description of the present invention has been quite detailed and has been described in particular with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, so as to effectively cover the intended scope of the present invention. In addition, the present invention is described above with the embodiments foreseeable by the inventors, and its purpose is to provide a useful description, and those non-substantial changes to the present invention that are not currently foreseen may still represent equivalent changes of the present invention.

Claims

1. A method for preparing a Micro LED display chip, characterized in that: The following steps are involved: (1) sequentially preparing a buffer layer, an N-GaN layer and an MQW layer on a substrate; laser processing the MQW layer using an ultrafast pulse laser at 700° C. to 800° C. to form a pixel spacing, thereby obtaining a laser-processed MQW layer; (2) sequentially growing an EBL layer and a P-GaN layer on the laser-treated MQW layer; then preparing a first anode metal and a first protective layer on the P-GaN layer to obtain a wafer; (3) turning the wafer over so that the first protective layer is in contact with the driver chip, the driver chip includes a second anode metal and a second cathode metal, and the first anode metal is in contact with the second anode metal; removing the substrate and the buffer layer; (4) depositing a second protective layer on the N-GaN layer, and making a cathode shallow groove on the second protective layer; making a cathode deep through hole, wherein the cathode shallow groove and the cathode deep through hole are connected, and the cathode shallow groove and the cathode deep through hole are used to accommodate a first cathode metal, and the first cathode metal is connected to the second cathode metal through the cathode deep through hole; (5) depositing a third protective layer on the second protective layer to obtain the Micro LED display chip; The specific steps of the laser processing include: Under the condition of 700℃-800℃, the MQW layer is scanned and irradiated in a two-dimensional matrix form using an ultrafast pulse laser, so that the irradiated part is heated to 900℃-1100℃ to form a pixel spacing, and Ga droplets remain in the pixel spacing formed after the MQW layer is processed.

2. The method for preparing a Micro LED display chip according to claim 1, characterized in that: The thickness of the MQW layer is 10 nm-100 nm.

3. The method for preparing a Micro LED display chip according to claim 1, characterized in that: The ultrafast pulse laser is a picosecond ultrafast pulse laser with a laser energy between 0.7eV-5.5eV and a laser spot size of 10nm-500nm.

4. The method for preparing a Micro LED display chip according to claim 1, characterized in that: The specific preparation method of the cathode shallow groove and the cathode deep through hole in step (4) comprises the following steps: The substrate and the buffer layer are removed to expose the N-GaN layer, and then the second protective layer is deposited on the exposed N-GaN layer, and the cathode shallow groove is made on the second protective layer; the cathode deep through hole is made, and the cathode deep through hole penetrates the second protective layer, the N-GaN layer, the MQW layer, the EBL layer, the P-GaN layer and the first protective layer, and the cathode deep through hole is connected with the cathode shallow groove, and the first cathode metal is arranged in the cathode deep through hole and the cathode shallow groove, and the first cathode metal is connected with the second cathode metal.

5. A Micro LED display chip, characterized in that: Prepared by the preparation method according to any one of claims 1 to 4.

6. The Micro LED display chip according to claim 5, characterized in that: The structure of the Micro LED display chip is divided into a pixel area and a cathode area; The cathode region includes, from bottom to top, a driving chip, the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer, the second protective layer and the third protective layer; the cathode region also includes the cathode deep through hole, which penetrates the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer and the second protective layer; The pixel region includes the driving chip, the first protective layer, the P-GaN layer, the EBL layer, the MQW layer, the N-GaN layer, the second protective layer and the third protective layer in order from bottom to top; the driving chip is provided with a second anode metal, the first protective layer is provided with the first anode metal, one end of the first anode metal is connected to the second anode metal, the other end of the first anode metal is connected to the P-GaN layer, and the second protective layer is provided with the cathode shallow groove; The cathode deep through hole is connected to the cathode shallow groove, and the cathode deep through hole and the cathode shallow groove are used to accommodate the first cathode metal; a section of the first cathode metal is connected to the second cathode metal, and the other end of the first cathode metal is connected to the N-GaN layer.

7. The Micro LED display chip according to claim 6, characterized in that: The first protective layer, the second protective layer, and the third protective layer in the Micro LED display chip are SIO protective layers.

8. A display panel, characterized in that: A Micro LED display chip comprising any one of claims 5 to 7.

9. An electronic display screen, characterized in that: Comprising the display panel as claimed in claim 8.

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