Preparation and separation method of LED epitaxial wafer and LED chip

Abstract

The invention provides a preparation and separation method of an LED epitaxial wafer and an LED chip. According to the LED epitaxial wafer, a first sacrificial layer and a buffer layer structure are arranged between a sapphire substrate and an epitaxial laminated layer; according to the preparation and separation method of the LED chip, an LED epitaxial wafer is etched through a chip technology to form a plurality of LED chips which are arranged at intervals through cutting channels, a part of a first sacrificial layer is exposed out of the cutting channels, then an etchant solution is adopted to dissolve the first sacrificial layer through the exposed cutting channels, lossless stripping of a sapphire substrate can be achieved efficiently at low cost, and the service life of the LED chip is prolonged. The sapphire substrate can be recycled repeatedly, the step of grinding and thinning can be omitted, the problems that the electric leakage rate is increased and the yield is low due to the fact that an epitaxial lamination layer is damaged by an existing grinding process, physical damage is generated on the side wall when LED core particles are cut through laser, and the output efficiency of light is affected are solved, and then the reliability and the yield of LED chips are improved.

Description

Technical Field

[0001] The invention belongs to the field of LEDs, and more specifically, relates to a method for preparing and separating an LED epitaxial wafer and an LED chip. Background Art

[0002] LED is a PN junction electroluminescent light-emitting device. As a new generation of solid cold light source, it has the advantages of high electro-optical conversion efficiency, low energy consumption, long life, energy saving and environmental protection, high reliability, etc. It is widely used in various places such as indoor lighting, photovoltaics, medical lighting, automobile lights, display screens, etc.

[0003] According to the chip structure, LED chips can be divided into three types: upright chips, flip chips and vertical chips. Regardless of the structure of the LED chip, there is a need to thin the substrate during the production of the LED chip. Traditional LED chips are generally sapphire substrates, which are usually ground and thinned to 100 microns or even thinner, sometimes to between 50-150 microns. In some high-precision and high-demand applications (such as micro-LEDs and flexible LEDs), the grinding and thinning thickness may be further reduced, sometimes to between 10-50 microns. However, the epitaxial wafer will inevitably produce internal stress, resulting in warping of the epitaxial wafer. It is difficult for the warped epitaxial wafer to maintain flat contact with the grinding disk during the grinding process, which will lead to uneven thinning thickness. Local areas may be over-ground or under-ground, affecting the overall thickness uniformity of the epitaxial wafer. The epitaxial structure is easily broken, cracked or damaged during the grinding process. The greater the degree of warping, the higher the risk of mechanical damage, which affects the product quality and yield. Moreover, grinding will damage the sapphire substrate and cannot be reused.

[0004] On the other hand, cutting is also an indispensable step in the LED chip manufacturing process. Cutting is the process of dividing the epitaxial wafer after grinding and thinning into single grains of the required size according to the process. Laser cutting is a new type of cutting technology that has emerged and is widely used with the development of laser technology. Laser cutting is to focus a laser beam of a certain energy density and wavelength on the surface or inside of the chip, burn a scratch on the surface or inside of the chip through the laser, and then use a chip splitter to split along the scratch. However, laser cutting itself also has some problems. The product after laser burning has caused physical damage to the side wall of the LED core grain, affecting the light output efficiency. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing and separating an LED epitaxial wafer and an LED chip, so as to solve the problem in the prior art that the LED chip grinds and thins the sapphire substrate, which easily causes damage to the epitaxial wafer and the sapphire substrate, resulting in low reliability and low yield, and the sapphire substrate cannot be reused.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An LED epitaxial wafer, characterized by comprising:

[0008] Sapphire substrate;

[0009] An epitaxial stack is arranged on one side of the sapphire substrate, and a first sacrificial layer and a buffer structure are arranged between the sapphire substrate and the epitaxial stack, wherein the first sacrificial layer is arranged on a part of the surface of the sapphire substrate, the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure at least includes an AlN nucleation layer;

[0010] The epitaxial stack at least includes a first-type semiconductor layer, an active region, and a second-type semiconductor layer sequentially stacked along a first direction, wherein the first direction is perpendicular to the sapphire substrate and points from the sapphire substrate to the epitaxial stack.

[0011] Preferably, the thickness of the first sacrificial layer is 0.1-0.4 times the thickness of the buffer structure, including the end values.

[0012] Preferably, a U-type GaN layer is provided on a surface of the first sacrificial layer facing away from the sapphire substrate, and the buffer structure covers the exposed surfaces of the first sacrificial layer and the U-type GaN layer by being stacked on the surface of the sapphire substrate.

[0013] Preferably, the first sacrificial layer comprises a water-soluble single crystal thin film, and the U-type GaN layer comprises a low-temperature U-type GaN layer.

[0014] Preferably, the thickness of the first sacrificial layer is 0.8-1 times the thickness of the U-type GaN layer, including the end values.

[0015] Preferably, a second sacrificial layer is provided between the U-type GaN layer and the buffer structure, and the buffer structure covers the exposed surfaces of the first sacrificial layer, the U-type GaN layer and the second sacrificial layer by being stacked on the surface of the sapphire substrate, wherein the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer.

[0016] The present invention also provides a method for preparing and separating LED chips, characterized in that the method comprises the following steps:

[0017] Step 1: preparing LED epitaxial wafers;

[0018] The preparation of the LED epitaxial wafer includes the following steps:

[0019] Step S1, providing a sapphire substrate;

[0020] Step S2, growing a first sacrificial layer on a portion of the surface of one side of the sapphire substrate;

[0021] Step S3, preparing a buffer structure on the first sacrificial layer, wherein the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure at least includes an Al N nucleation layer;

[0022] Step S4, growing an epitaxial stack on the buffer structure, wherein the epitaxial stack at least includes a first-type semiconductor layer, an active region, and a second-type semiconductor layer sequentially stacked along a growth direction;

[0023] Step 2: preparing LED chips;

[0024] By means of a chip process, the LED epitaxial wafer is etched to form a plurality of LED chips which are arranged in a spaced relationship with each other through cutting paths, wherein the cutting paths expose a portion of the first sacrificial layer and do not expose the sapphire substrate;

[0025] Step 3, separating the sapphire substrate;

[0026] Separating the sapphire substrate includes the following steps:

[0027] Step A1, fix the surface of each LED chip facing away from the sapphire substrate on the first carrier, and use a corrosive solution to dissolve the first sacrificial layer through the exposed cutting path to non-destructively separate the sapphire substrate and expose the buffer structure of each LED chip;

[0028] Step A2: fix the exposed buffer structures on the second carrier plate, and remove the first carrier plate.

[0029] Preferably, the thickness of the first sacrificial layer is 0.1-0.4 times the thickness of the buffer structure, including the end values.

[0030] Preferably, a U-type GaN layer is provided on a surface of the first sacrificial layer facing away from the sapphire substrate, and the buffer structure covers the exposed surfaces of the first sacrificial layer and the U-type GaN layer by being stacked on the surface of the sapphire substrate.

[0031] Preferably, the first sacrificial layer comprises a water-soluble single crystal film, and step A2 comprises: using deionized water to dissolve the first sacrificial layer through the exposed cutting path to non-destructively separate the sapphire substrate and expose the buffer structure of each LED chip;

[0032] When forming a water-soluble single crystal film, the following process conditions are used: a magnetron sputtering process is used to grow the water-soluble single crystal film, and the process vacuum is 2.0E -4 Pa-4.0E -4Pa, including the endpoint value; the coating temperature is 600℃-700℃, including the endpoint value; the magnetron sputtering power range is 100W-150W, including the endpoint value;

[0033] The U-type GaN layer includes a low-temperature U-type GaN layer, the U-type GaN layer is grown by a chemical vapor deposition process, and the growth temperature of the U-type GaN layer is 500° C.-600° C., including end values.

[0034] Preferably, the thickness of the first sacrificial layer is 0.8-1 times the thickness of the U-type GaN layer, including the end values.

[0035] Preferably, a second sacrificial layer is provided between the U-type GaN layer and the buffer structure, and the buffer structure covers the first sacrificial layer, the U-type GaN layer and the exposed surface of the second sacrificial layer by being stacked on the surface of the sapphire substrate, wherein the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer;

[0036] Furthermore, in the step 3, the U-type GaN layer is also separated while the sapphire substrate is separated;

[0037] Separating the sapphire substrate and the U-type GaN layer includes the following steps:

[0038] Step B1, fixing the surface of each LED chip facing away from the sapphire substrate on the first carrier, using a corrosive solution to dissolve the first sacrificial layer and the second sacrificial layer through the exposed cutting path, so as to damagelessly separate the sapphire substrate and the U-type GaN layer, and expose the buffer structure of each LED chip;

[0039] Step B2: fix the exposed buffer structures on the second carrier plate, and remove the first carrier plate.

[0040] Through the above technical solution, the following effects are achieved:

[0041] 1. The LED epitaxial wafer provided by the present invention has a first sacrificial layer and a buffer structure between a sapphire substrate and an epitaxial stack, wherein the first sacrificial layer is arranged on a part of the surface of the sapphire substrate, and the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate; based on the above arrangement, the LED chip can use a corrosive solution to dissolve the first sacrificial layer, and the sapphire substrate can be non-destructively peeled off efficiently and at low cost, so that the sapphire substrate can be recycled repeatedly, and the grinding and thinning steps can be saved, avoiding the existing grinding process from damaging the epitaxial stack and causing problems such as increased leakage rate and low yield, thereby improving the reliability and yield of the LED chip; the buffer structure can effectively alleviate the lattice mismatch between the first sacrificial layer and the epitaxial stack, and ensure that the first sacrificial layer does not react with the corrosive solution before peeling off the sapphire substrate.

[0042] 2. Furthermore, by providing a second sacrificial layer between the U-type GaN layer and the buffer structure, the LED chip can be enabled to use a corrosive solution to dissolve the second sacrificial layer according to actual needs, thereby achieving lossless stripping of the U-type GaN layer; the buffer structure covers the exposed surfaces of the first sacrificial layer, the U-type GaN layer and the second sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure can effectively alleviate the lattice mismatch between the second sacrificial layer and the epitaxial stack, and ensure that the second sacrificial layer does not react with the corrosive solution before stripping the U-type GaN layer; wherein, the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer, because the formation environment of the second sacrificial layer is slightly worse in roughness and flatness than the formation environment of the first sacrificial layer (that is, the second sacrificial layer is formed on the buffer structure, the first sacrificial layer is formed on the sapphire substrate, and the roughness and flatness of the surface of the buffer structure are slightly worse than the roughness and flatness of the surface of the sapphire substrate), the thickness of the second sacrificial layer is set to be thinner, which can improve the flatness of the film layer itself, maintain the flatness transmitted by the U-type GaN layer, and ensure the growth quality of the epitaxial stack.

[0043] 3. The preparation and separation method of LED chips provided by the present invention comprises the following steps: firstly preparing an LED epitaxial wafer, wherein the LED epitaxial wafer comprises a sapphire substrate and a first sacrificial layer, a buffer structure and an epitaxial stack formed in sequence on the sapphire substrate, wherein the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate; then, through a chip process, the LED epitaxial wafer is etched to form a plurality of LED chips arranged at intervals through cutting paths, wherein the cutting paths expose a portion of the first sacrificial layer and do not expose the sapphire substrate to prevent the sapphire substrate from being etched and damaged; and then, a corrosive solution is used to remove the first sacrificial layer through the exposed cutting paths. The sapphire substrate can be dissolved away, and the non-destructive stripping of the sapphire substrate can be realized efficiently and at low cost, so that the sapphire substrate can be recycled repeatedly, and the grinding and thinning steps can be saved, so as to avoid the existing grinding process damaging the epitaxial stack and causing an increase in leakage rate and a low yield, and to avoid physical damage to the side wall during laser cutting of LED core particles, which affects the light output efficiency and other problems, thereby improving the reliability and yield of the LED chip. The process is simple and convenient to manufacture, and is easy to produce. The buffer structure can effectively alleviate the lattice mismatch between the first sacrificial layer and the epitaxial stack, and ensure that the first sacrificial layer does not react with the corrosive solution before stripping the sapphire substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 A schematic diagram of the structure of an LED epitaxial wafer provided by an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of another LED epitaxial wafer structure provided by an embodiment of the present invention;

[0047] Figure 3 A schematic diagram of another LED epitaxial wafer structure provided by an embodiment of the present invention;

[0048] Figures 4 to 12 The present invention provides a process cross-sectional view corresponding to each step of a method for preparing and separating an LED chip provided by an embodiment of the present invention.

[0049] Explanation of symbols in the figure:

[0050] 01. Sapphire substrate; 1. LED chip; 2. Buffer structure; 21. U-type GaN layer; 3. Epitaxial stack; 31. First-type semiconductor layer; 32. Active area; 33. Second-type semiconductor layer; 4. First-type mesa; 5. Second-type mesa; 6. First electrode; 7. Second electrode; 8. Insulating layer; 81. First through hole; 82. Second through hole; 9. First pad; 10. Second pad; 11. First sacrificial layer; 12. Second sacrificial layer; 13. First carrier; 14. Second carrier; E. Cutting path. DETAILED DESCRIPTION

[0051] To make the content of the present invention clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0053] Secondly, the present application is described in detail with reference to the schematic diagram. When describing the embodiments of the present application in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present application. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0054] The present application embodiment provides an LED epitaxial wafer, such as Figure 1 As shown, the LED epitaxial wafer includes:

[0055] Sapphire substrate 01;

[0056] An epitaxial stack 3 is provided on one side of a sapphire substrate 01, and a first sacrificial layer 11 and a buffer structure 2 are provided between the sapphire substrate 01 and the epitaxial stack 3, wherein the first sacrificial layer 11 is provided on a part of the surface of the sapphire substrate 01, and the buffer structure 2 covers the first sacrificial layer 11 by being stacked on the surface of the sapphire substrate 01, and the buffer structure 2 at least includes an AlN nucleation layer;

[0057] The epitaxial stack 3 at least includes a first-type semiconductor layer 31 , an active region 32 and a second-type semiconductor layer 33 sequentially stacked along a first direction. The first direction is perpendicular to the sapphire substrate 01 and points from the sapphire substrate 01 to the epitaxial stack 3 .

[0058] It should be noted that the present embodiment does not limit the specific doping types of the first-type semiconductor layer 31 and the second-type semiconductor layer 33. The doping types of the first-type semiconductor layer 31 and the second-type semiconductor layer 33 are opposite. The first-type semiconductor layer 31 can be a P-type semiconductor layer or an N-type semiconductor layer. The materials of the N-type semiconductor layer and the P-type semiconductor layer can be GaN or AlGaN.

[0059] Based on the above embodiments, in one embodiment of the present application, the thickness of the first sacrificial layer 11 is 0.1-0.4 times the thickness of the buffer structure 2, including the endpoint values, so that the structure of the first sacrificial layer 11 is dense and has good flatness, reducing the lattice mismatch with the buffer structure 2.

[0060] On the basis of the above-mentioned embodiments, in one embodiment of the present application, the thickness of the first sacrificial layer 11 ranges from 20 nm to 200 nm, including the end value. It is avoided that the thickness is too thin, resulting in poor compactness of the first sacrificial layer 11 and poor non-destructive stripping effect; it is avoided that the thickness is too thick, resulting in too rough surface of the first sacrificial layer 11, which affects the crystal quality of the film layer disposed on the first sacrificial layer 11.

[0061] On the basis of the above embodiments, in one embodiment of the present application, the thickness of the buffer structure 2 ranges from 70 nm to 2000 nm, including endpoint values.

[0062] On the basis of the above embodiments, in one embodiment of the present application, the buffer structure 2 further includes an Al N / Al N layer disposed on the side of the Al N nucleation layer away from the sapphire substrate 01. x Ga 1-x N superlattice structure can further alleviate the lattice mismatch between the first sacrificial layer 11 and the epitaxial stack 3 .

[0063] Optionally, in this embodiment, Al N / Al x Ga 1-x N superlattice structure, wherein x is between 0.65 and 0.75 and the value of x gradually increases along the first direction, can reduce the accumulation of stress and strain in the epitaxial stack 3, help to achieve better crystal quality and surface morphology, thereby improving the crystallization quality of the epitaxial stack 3.

[0064] Optionally, in this embodiment, the thickness of the Al N nucleation layer ranges from 70 nm to 500 nm, including the end value, Al N / Al x Ga 1-x The total thickness of the N superlattice structure ranges from 100 nm to 1500 nm, both inclusive.

[0065] In another embodiment of the present application, Figure 2As shown, a U-type GaN layer 21 is provided on the surface of the first sacrificial layer 11 facing away from the sapphire substrate 01 , and the buffer structure 2 covers the exposed surfaces of the first sacrificial layer 11 and the U-type GaN layer 21 by being stacked on the surface of the sapphire substrate 01 .

[0066] Optionally, in this embodiment, the first sacrificial layer 11 includes a water-soluble single crystal thin film, and the U-type GaN layer 21 includes a low-temperature U-type GaN layer.

[0067] It should be noted that the first sacrificial layer 11 of the present embodiment includes a water-soluble single crystal film, which can be dissolved by deionized water. Deionized water is obtained by removing cations and anions from water to make it nearly pure. High-purity deionized water is used to dissolve the water-soluble single crystal film, which is more environmentally friendly than other corrosive solutions.

[0068] Moreover, there is a lattice mismatch between the water-soluble single crystal film and the GaN material. In this embodiment, a low-temperature U-type GaN layer is set. The low temperature means that the growth temperature of the U-type GaN layer 21 is lower than the growth temperature of other film layers in the LED epitaxial wafer. The U-type GaN layer formed at low temperature is an amorphous structure, which can effectively alleviate the adverse effects of the lattice mismatch and avoid the high dislocation density caused by the lattice mismatch, thereby improving the flatness of the epitaxial wafer.

[0069] Optionally, in this embodiment, the material of the water-soluble single crystal thin film includes Sr3Al2O6 or Sr4Al2O7.

[0070] Optionally, in this embodiment, the growth temperature of the U-type GaN layer is 500° C.-600° C., including end points.

[0071] Optionally, in this embodiment, high-temperature annealing is performed on the low-temperature U-type GaN layer 21 , and the annealing temperature ranges from 1100° C. to 1200° C., including end points.

[0072] It should be noted that in this embodiment, the low-temperature U-type GaN layer is subjected to high-temperature annealing to transform the amorphous U-type GaN layer into a polycrystalline U-type GaN layer. Forming the polycrystalline U-type GaN layer does not affect the crystal quality of the film layer itself.

[0073] Optionally, in this embodiment, the thickness of the first sacrificial layer 11 is 0.8-1 times the thickness of the U-type GaN layer 21 , including the end value, so that the first sacrificial layer 11 has a dense structure and good flatness, and reduces the lattice mismatch with the U-type GaN layer 21 .

[0074] Optionally, in this embodiment, the thickness of the U-type GaN layer 21 ranges from 25 nm to 200 nm, including the end value. Avoid being too thin, which will result in poor compactness of the U-type GaN layer 21 and high dislocation density caused by lattice mismatch between the water-soluble single crystal film and the U-type GaN layer 21; avoid being too thick, which will reduce the flatness of the film itself.

[0075] In another embodiment of the present application, Figure 3 As shown, a second sacrificial layer 12 is provided on the surface of the U-type GaN layer 21 facing away from the first sacrificial layer 11, and the buffer structure 2 covers the exposed surfaces of the first sacrificial layer 11, the U-type GaN layer 21 and the second sacrificial layer 12 by being stacked on the surface of the sapphire substrate 01, wherein the thickness of the first sacrificial layer 11 is greater than the thickness of the second sacrificial layer 12.

[0076] Optionally, in this embodiment, the thickness of the second sacrificial layer 12 is 0.05-0.2 times the thickness of the buffer structure 2, including the end value, so that the second sacrificial layer 12 has a dense structure and good flatness, reduces the lattice mismatch with the buffer structure 2, and thus improves the crystal quality of the epitaxial stack 3.

[0077] Optionally, in this embodiment, the thickness of the second sacrificial layer 12 ranges from 10 nm to 100 nm, including the end value. Avoid being too thin, which results in poor compactness of the second sacrificial layer 12 and poor lossless separation effect; avoid being too thick, which results in the surface of the second sacrificial layer 12 being too rough and affecting the crystal quality of the epitaxial stack 3.

[0078] Optionally, in this embodiment, the second sacrificial layer 12 includes a water-soluble single crystal film.

[0079] The embodiment of the present application also provides a method for preparing and separating an LED chip, and the method for preparing and separating an LED chip comprises the following steps:

[0080] Step 1: preparing LED epitaxial wafers;

[0081] The preparation of LED epitaxial wafers includes the following steps:

[0082] Step S1: Figure 4 As shown, a sapphire substrate 01 is provided;

[0083] Optionally, in this embodiment, before the sapphire substrate 01 is placed in the reaction chamber, the sapphire substrate 01 may be organically cleaned to remove surface dirt.

[0084] Step S2: Figure 5 As shown, a first sacrificial layer 11 is grown on a portion of the surface of one side of the sapphire substrate 01;

[0085] Step S3: Figure 6As shown, a buffer structure 2 is prepared on the first sacrificial layer 11. The buffer structure 2 covers the first sacrificial layer 11 by being stacked on the surface of the sapphire substrate 01. The buffer structure 2 at least includes an AlN nucleation layer.

[0086] Step S4: Reference Figure 1 As shown, an epitaxial stack 3 is grown on the buffer structure 2, and the epitaxial stack 3 at least includes a first-type semiconductor layer 31, an active region 32, and a second-type semiconductor layer 33 sequentially stacked along a growth direction;

[0087] It should be noted that the present embodiment does not limit the specific doping types of the first-type semiconductor layer 31 and the second-type semiconductor layer 33. The doping types of the first-type semiconductor layer 31 and the second-type semiconductor layer 33 are opposite. The first-type semiconductor layer 31 can be a P-type semiconductor layer or an N-type semiconductor layer. The materials of the N-type semiconductor layer and the P-type semiconductor layer can be GaN or AlGaN.

[0088] Step 2: preparing LED chips;

[0089] like Figure 7 As shown, through the chip process, the LED epitaxial wafer is etched to form a plurality of LED chips 1 that are spaced apart from each other through a cutting line E, and the cutting line E exposes a portion of the first sacrificial layer 11 and does not expose the sapphire substrate 01;

[0090] It should be noted that, in this embodiment, the edge region of the LED epitaxial wafer is not used for LED chip arrangement, and a cutting path E is formed in the edge region of the LED epitaxial wafer.

[0091] Optionally, in this embodiment, the cutting path E is formed by dry etching.

[0092] Optionally, in the present embodiment, each LED chip 1 has a first type mesas 4 exposing a portion of the first type semiconductor layer 31 and a second type mesas 5 exposing the second type semiconductor layer 33, a first electrode 6 is deposited on the first type mesas 4 to form contact with the first type semiconductor layer 31, and is insulated from the side wall of the epitaxial stack 3; the second electrode 7 is deposited on the second type mesas 5 to form contact with the second type semiconductor layer 33, and the first electrode 6 and the second electrode 7 are arranged far apart.

[0093] Optionally, in this embodiment, the first type of mesas 4 and the second type of mesas 5 are formed by photolithography and etching processes; and the first electrode 6 and the second electrode 7 are prepared by an electron beam evaporator.

[0094] Optionally, in this embodiment, if Figure 8 As shown, the insulating layer 8 covers the exposed surface of each LED chip 1 and exposes the first electrode 6 and the second electrode 7 , and the insulating layer 8 has a first through hole 81 exposing the first electrode 6 and a second through hole 82 exposing the second electrode 7 .

[0095] Optionally, in this embodiment, if Fig. 9 As shown, the first pad 9 is electrically connected to the first electrode 6 through the first through hole 81, the second pad 10 is electrically connected to the second electrode 7 through the second through hole 82, and the first pad 9 and the second pad 10 are spaced apart.

[0096] Optionally, in this embodiment, a PECVD evaporator is used to deposit the insulating layer 8 ; and an electron beam evaporator is used to form the first pad 9 and the second pad 10 .

[0097] Step 3: Separate the sapphire substrate 01;

[0098] Separating the sapphire substrate 01 includes the following steps:

[0099] Step A1: Fig.10 As shown, the surface of each LED chip 1 facing away from the sapphire substrate 01 is fixed on the first carrier 13, and the first sacrificial layer 11 is dissolved by a corrosive solution through the exposed cutting path E to separate the sapphire substrate 01 without damage and expose the buffer structure 2 of each LED chip 1;

[0100] Step A2: Fig.11 As shown, each exposed buffer structure 2 is fixed on the second carrier plate 14, and the first carrier plate 13 is removed.

[0101] On the basis of the above embodiment, in an embodiment of the present application, step 4 is further included after step 3, and step 4 includes the following processes:

[0102] Cleaning the surface of each LED chip 1;

[0103] Expand the second carrier board 14 to increase the distance between the LED chips 1 as required;

[0104] Each LED chip 1 is subjected to die sorting.

[0105] Based on the above embodiments, in one embodiment of the present application, the thickness of the first sacrificial layer 11 is 0.1-0.4 times the thickness of the buffer structure 2, including the end value, so that the structure of the first sacrificial layer is dense and the flatness is good, and the lattice mismatch with the buffer structure 2 is reduced.

[0106] On the basis of the above-mentioned embodiments, in one embodiment of the present application, the thickness of the first sacrificial layer 11 ranges from 20 nm to 200 nm, including the end value. It is avoided that the thickness is too thin, resulting in poor compactness of the first sacrificial layer 11 and poor non-destructive stripping effect; it is avoided that the thickness is too thick, resulting in too rough surface of the first sacrificial layer 11, which affects the crystal quality of the film layer disposed on the first sacrificial layer 11.

[0107] Optionally, in this embodiment, the thickness of the buffer structure 2 ranges from 70 nm to 2000 nm, including endpoint values.

[0108] On the basis of the above embodiments, in one embodiment of the present application, the buffer structure 2 further includes an Al N / Al N layer disposed on the side of the Al N nucleation layer away from the sapphire substrate 01. x Ga 1-x N superlattice structure can further alleviate the lattice mismatch between the first sacrificial layer 11 and the epitaxial stack 3 .

[0109] Optionally, in this embodiment, Al N / Al x Ga 1-x N superlattice structure, wherein x is between 0.65 and 0.75 and the value of x gradually increases along the growth direction, can reduce the accumulation of stress and strain in the epitaxial stack 3, help to achieve better crystal quality and surface morphology, thereby improving the crystallization quality of the epitaxial stack 3.

[0110] Optionally, in this embodiment, the thickness of the Al N nucleation layer ranges from 70 nm to 500 nm, including the end value, Al N / Al x Ga 1-x The total thickness of the N superlattice structure ranges from 100 nm to 1500 nm, both inclusive.

[0111] In another embodiment of the present application, reference Figure 2 As shown, a U-type GaN layer 21 is provided on the surface of the first sacrificial layer 11 facing away from the sapphire substrate 01 , and the buffer structure 2 covers the exposed surfaces of the first sacrificial layer 11 and the U-type GaN layer 21 by being stacked on the surface of the sapphire substrate 01 .

[0112] Optionally, in this embodiment, the first sacrificial layer 11 includes a water-soluble single crystal film, and step A2 includes: using deionized water to dissolve the first sacrificial layer 11 through the exposed cutting path E to non-destructively separate the sapphire substrate 01 and expose the buffer structure 2 of each LED chip 1;

[0113] When forming a water-soluble single crystal film, the following process conditions are used: a magnetron sputtering process is used to grow the water-soluble single crystal film, and the process vacuum is 2.0E -4 Pa-4.0E -4 Pa, including the endpoint value; the coating temperature is 600℃-700℃, including the endpoint value; the magnetron sputtering power range is 100W-150W, including the endpoint value;

[0114] The U-type GaN layer 21 includes a low-temperature U-type GaN layer, which is grown by a chemical vapor deposition process, and the growth temperature of the U-type GaN layer is 500° C.-600° C., including end values.

[0115] It should be noted that the first sacrificial layer 11 of the present embodiment includes a water-soluble single crystal film, which can be dissolved by deionized water. Deionized water is obtained by removing cations and anions from water to make it nearly pure. High-purity deionized water is used to dissolve the water-soluble single crystal film, which is more environmentally friendly than other corrosive solutions.

[0116] Moreover, there is a lattice mismatch between the water-soluble single crystal film and the GaN material. In this embodiment, a low-temperature U-type GaN layer is set. The low temperature means that the growth temperature of the U-type GaN layer 21 is lower than the growth temperature of other film layers in the LED epitaxial wafer. The U-type GaN layer formed at low temperature is an amorphous structure, which can effectively alleviate the adverse effects of the lattice mismatch and avoid the high dislocation density caused by the lattice mismatch, thereby improving the flatness of the epitaxial wafer.

[0117] It should also be noted that, in this embodiment, a magnetron sputtering process is used to grow a water-soluble single crystal film to form a water-soluble single crystal film with a dense structure and good flatness; a chemical vapor deposition process is used to grow a U-type GaN layer. Compared with physical vapor deposition, chemical vapor deposition has good wrapping properties and can enhance the coating effect of the U-type GaN layer on the exposed surface of the first sacrificial layer 11.

[0118] Optionally, in this embodiment, the material of the water-soluble single crystal thin film includes Sr3Al2O6 or Sr4Al2O7.

[0119] Optionally, in this embodiment, high-temperature annealing is performed on the low-temperature U-type GaN layer 21 , and the annealing temperature ranges from 1100° C. to 1200° C., including end points.

[0120] It should be noted that in this embodiment, the low-temperature U-type GaN layer is subjected to high-temperature annealing to transform the amorphous U-type GaN layer into a polycrystalline U-type GaN layer. Forming the polycrystalline U-type GaN layer does not affect the crystal quality of the film layer itself.

[0121] Optionally, in this embodiment, the thickness of the first sacrificial layer 11 is 0.8-1 times the thickness of the U-type GaN layer 21 , including the end value, so that the first sacrificial layer 11 has a dense structure and good flatness, and reduces the lattice mismatch with the U-type GaN layer 21 .

[0122] Optionally, in this embodiment, the thickness of the U-type GaN layer 21 ranges from 25 nm to 200 nm, including the end value. Avoid being too thin, which will result in poor compactness of the U-type GaN layer 21 and high dislocation density caused by lattice mismatch between the water-soluble single crystal film and the U-type GaN layer 21; avoid being too thick, which will reduce the flatness of the film itself.

[0123] In another embodiment of the present application, reference Figure 3 As shown, a second sacrificial layer 12 is provided on the surface of the U-type GaN layer 21 facing away from the first sacrificial layer 11, and the buffer structure 2 covers the exposed surfaces of the first sacrificial layer, the U-type GaN layer and the second sacrificial layer by stacking on the surface of the sapphire substrate 01, wherein the thickness of the first sacrificial layer 11 is greater than the thickness of the second sacrificial layer 12;

[0124] Furthermore, in step 3, while separating the sapphire substrate 01, the U-type GaN layer 21 is also separated;

[0125] Separating the sapphire substrate 01 and the U-type GaN layer 21 includes the following steps:

[0126] Step B1: Fig.12 As shown, the surface of each LED chip 1 facing away from the sapphire substrate 01 is fixed on the first carrier 13, and the first sacrificial layer 11 and the second sacrificial layer 12 are dissolved by a corrosive solution through the exposed cutting path E, so as to non-destructively separate the sapphire substrate 01 and the U-type GaN layer 21, and expose the buffer structure 2 of each LED chip 1;

[0127] Step B2, Reference Fig.11 As shown, each exposed buffer structure 2 is fixed on the second carrier plate 14, and the first carrier plate 13 is removed.

[0128] Optionally, in this embodiment, the thickness of the second sacrificial layer 12 is 0.05-0.2 times the thickness of the buffer structure 2, including the end value, so that the second sacrificial layer 12 has a dense structure and good flatness, reduces the lattice mismatch with the buffer structure 2, and thus improves the crystal quality of the epitaxial stack 3.

[0129] Optionally, in this embodiment, the thickness of the second sacrificial layer 12 ranges from 10 nm to 100 nm, including the end value. Avoid being too thin, which results in poor compactness of the second sacrificial layer 12 and poor lossless separation effect; avoid being too thick, which results in the surface of the second sacrificial layer 12 being too rough and affecting the crystal quality of the epitaxial stack 3.

[0130] Optionally, in this embodiment, the first carrier plate 13 is a UV film, and the second carrier plate 14 is a PV film, and the first carrier plate 13 can be removed by irradiating with ultraviolet light to cause the UV film to fall off;

[0131] In another embodiment of the present application, both the first carrier plate 13 and the second carrier plate 14 are PV films, and the viscosity of the second carrier plate 14 is greater than that of the first carrier plate 13 .

[0132] Optionally, in this embodiment, the second sacrificial layer 12 includes a water-soluble single crystal film, and step B1 includes: using deionized water to dissolve the first sacrificial layer 11 and the second sacrificial layer 12 through the exposed cutting line E to damagelessly separate the sapphire substrate 01 and the U-type GaN layer 21 to expose the buffer structure 2 of each LED chip 1.

[0133] In summary, through the above technical solution, the following effects are achieved:

[0134] 1. The LED epitaxial wafer provided in this embodiment has a first sacrificial layer and a buffer structure between the sapphire substrate and the epitaxial stack, wherein the first sacrificial layer is arranged on a portion of the surface of the sapphire substrate, and the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate; based on the above arrangement, the LED chip can use a corrosive solution to dissolve the first sacrificial layer, and the sapphire substrate can be non-destructively peeled off efficiently and at low cost, so that the sapphire substrate can be recycled repeatedly, and the grinding and thinning steps can be saved, avoiding the existing grinding process from damaging the epitaxial stack and causing problems such as increased leakage rate and low yield, thereby improving the reliability and yield of the LED chip; the buffer structure can effectively alleviate the lattice mismatch between the first sacrificial layer and the epitaxial stack, and ensure that the first sacrificial layer does not react with the corrosive solution before peeling off the sapphire substrate.

[0135] 2. Furthermore, by providing a second sacrificial layer between the U-type GaN layer and the buffer structure, the LED chip can be enabled to use a corrosive solution to dissolve the second sacrificial layer according to actual needs, thereby achieving lossless stripping of the U-type GaN layer; the buffer structure covers the exposed surfaces of the first sacrificial layer, the U-type GaN layer and the second sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure can effectively alleviate the lattice mismatch between the second sacrificial layer and the epitaxial stack, and ensure that the second sacrificial layer does not react with the corrosive solution before stripping the U-type GaN layer; wherein, the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer, because the formation environment of the second sacrificial layer is slightly worse in roughness and flatness than the formation environment of the first sacrificial layer (that is, the second sacrificial layer is formed on the buffer structure, the first sacrificial layer is formed on the sapphire substrate, and the roughness and flatness of the surface of the buffer structure are slightly worse than the roughness and flatness of the surface of the sapphire substrate), the thickness of the second sacrificial layer is set to be thinner, which can improve the flatness of the film layer itself, maintain the flatness transmitted by the U-type GaN layer, and ensure the growth quality of the epitaxial stack.

[0136] 3. The method for preparing and separating LED chips provided in this embodiment comprises first preparing an LED epitaxial wafer, wherein the LED epitaxial wafer comprises a sapphire substrate and a first sacrificial layer, a buffer structure and an epitaxial stack formed in sequence on the sapphire substrate, wherein the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate; then, through a chip process, the LED epitaxial wafer is etched to form a plurality of LED chips arranged at intervals through cutting paths, wherein the cutting paths expose a portion of the first sacrificial layer and do not expose the sapphire substrate to prevent the sapphire substrate from being etched and damaged; and then, a corrosive solution is used to remove the first sacrificial layer through the exposed cutting paths. The first sacrificial layer is dissolved away, and the non-destructive stripping of the sapphire substrate can be realized efficiently and at low cost, so that the sapphire substrate can be recycled repeatedly, and the grinding and thinning steps can be saved, so as to avoid the existing grinding process damaging the epitaxial stack and causing an increase in leakage rate and a low yield, and to avoid physical damage to the side wall during laser cutting of the LED core particles, which affects the light output efficiency and other problems, thereby improving the reliability and yield of the LED chip. The process is simple and convenient to manufacture, and is easy to produce; the buffer structure can effectively alleviate the lattice mismatch between the first sacrificial layer and the epitaxial stack, and ensure that the first sacrificial layer does not react with the corrosive solution before stripping the sapphire substrate.

[0137] Those skilled in the art should understand that, in the disclosure of the present invention, the terms "horizontal", "vertical", "upper", "lower", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, which 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 orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0138] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0139] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An LED epitaxial wafer, characterized in that: include: Sapphire substrate; An epitaxial stack is arranged on one side of the sapphire substrate, and a first sacrificial layer and a buffer structure are arranged between the sapphire substrate and the epitaxial stack, wherein the first sacrificial layer is arranged on a part of the surface of the sapphire substrate, the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure at least includes an AlN nucleation layer; The epitaxial stack at least includes a first-type semiconductor layer, an active region, and a second-type semiconductor layer sequentially stacked along a first direction, wherein the first direction is perpendicular to the sapphire substrate and points from the sapphire substrate to the epitaxial stack.

2. The LED epitaxial wafer according to claim 1, characterized in that: The thickness of the first sacrificial layer is 0.1-0.4 times the thickness of the buffer structure, including the end values.

3. The LED epitaxial wafer according to claim 1, characterized in that: A U-type GaN layer is provided on a surface of the first sacrificial layer facing away from the sapphire substrate, and the buffer structure covers the exposed surfaces of the first sacrificial layer and the U-type GaN layer by being stacked on the surface of the sapphire substrate.

4. The LED epitaxial wafer according to claim 3, characterized in that: The first sacrificial layer includes a water-soluble single crystal thin film, and the U-type GaN layer includes a low-temperature U-type GaN layer.

5. The LED epitaxial wafer according to claim 3, characterized in that: The thickness of the first sacrificial layer is 0.8-1 times the thickness of the U-type GaN layer, including the end values.

6. The LED epitaxial wafer according to claim 3, characterized in that: A second sacrificial layer is provided between the U-type GaN layer and the buffer structure, and the buffer structure covers the exposed surfaces of the first sacrificial layer, the U-type GaN layer and the second sacrificial layer by being stacked on the surface of the sapphire substrate, wherein the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer.

7. A method for preparing and separating LED chips, characterized in that: The preparation and separation method comprises the following steps: Step 1: preparing LED epitaxial wafers; The preparation of the LED epitaxial wafer includes the following steps: Step S1, providing a sapphire substrate; Step S2, growing a first sacrificial layer on a portion of the surface of one side of the sapphire substrate; Step S3, preparing a buffer structure on the first sacrificial layer, wherein the buffer structure covers the first sacrificial layer by being stacked on the surface of the sapphire substrate, and the buffer structure at least includes an AlN nucleation layer; Step S4, growing an epitaxial stack on the buffer structure, wherein the epitaxial stack at least includes a first-type semiconductor layer, an active region, and a second-type semiconductor layer sequentially stacked along a growth direction; Step 2: preparing LED chips; By means of a chip process, the LED epitaxial wafer is etched to form a plurality of LED chips which are arranged in a spaced relationship with each other through cutting paths, wherein the cutting paths expose a portion of the first sacrificial layer and do not expose the sapphire substrate; Step 3, separating the sapphire substrate; Separating the sapphire substrate includes the following steps: Step A1, fix the surface of each LED chip facing away from the sapphire substrate on the first carrier, and use a corrosive solution to dissolve the first sacrificial layer through the exposed cutting path to non-destructively separate the sapphire substrate and expose the buffer structure of each LED chip; Step A2: fix the exposed buffer structures on the second carrier plate, and remove the first carrier plate.

8. The method for preparing and separating LED chips according to claim 7, characterized in that: The thickness of the first sacrificial layer is 0.1-0.4 times the thickness of the buffer structure, including the end values.

9. The method for preparing and separating LED chips according to claim 7, characterized in that: A U-type GaN layer is provided on a surface of the first sacrificial layer facing away from the sapphire substrate, and the buffer structure covers the exposed surfaces of the first sacrificial layer and the U-type GaN layer by being stacked on the surface of the sapphire substrate.

10. The method for preparing and separating LED chips according to claim 9, characterized in that: The first sacrificial layer includes a water-soluble single crystal thin film, and step A2 includes: using deionized water to dissolve the first sacrificial layer through the exposed cutting path to non-destructively separate the sapphire substrate and expose the buffer structure of each LED chip; When forming a water-soluble single crystal film, the following process conditions are used: a magnetron sputtering process is used to grow the water-soluble single crystal film, and the process vacuum is 2.0E -4 Pa-4.0E -4 Pa, including the endpoint value; the coating temperature is 600℃-700℃, including the endpoint value; the magnetron sputtering power range is 100W-150W, including the endpoint value; The U-type GaN layer includes a low-temperature U-type GaN layer, the U-type GaN layer is grown by a chemical vapor deposition process, and the growth temperature of the U-type GaN layer is 500° C.-600° C., including end values.

11. The method for preparing and separating LED chips according to claim 9, characterized in that: The thickness of the first sacrificial layer is 0.8-1 times the thickness of the U-type GaN layer, including the end values.

12. The method for preparing and separating LED chips according to claim 9, characterized in that: A second sacrificial layer is provided between the U-type GaN layer and the buffer structure, and the buffer structure covers the first sacrificial layer, the U-type GaN layer and the exposed surface of the second sacrificial layer by being stacked on the surface of the sapphire substrate, wherein the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer; Furthermore, in the step 3, the U-type GaN layer is also separated while the sapphire substrate is separated; Separating the sapphire substrate and the U-type GaN layer includes the following steps: Step B1, fixing the surface of each LED chip facing away from the sapphire substrate on the first carrier, using a corrosive solution to dissolve the first sacrificial layer and the second sacrificial layer through the exposed cutting path, so as to damagelessly separate the sapphire substrate and the U-type GaN layer, and expose the buffer structure of each LED chip; Step B2: fix the exposed buffer structures on the second carrier plate, and remove the first carrier plate.

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