Aln template and preparation method thereof

Abstract

The application relates to an AlN template and a preparation method thereof, the AlN template comprising a substrate (1) and an AlN buffer layer (2) arranged on the substrate (1), wherein a SiN X masking layer (3) is arranged on the AlN buffer layer (2), the thickness of the SiN X masking layer (3) is 5-20 nm, the SiN X masking layer (3) is arranged with an AlN layer (4), the AlN layer (4) comprises a SiN X masking layer (3) and an AlN recovery layer arranged on the AlN recovery layer, the thickness of the AlN recovery layer is 400-800 nm, and the AlN flat layer has a step flow morphology and the thickness thereof is 1600-3200 nm. The AlN template has the advantages of low dislocation density, low screw dislocation and edge dislocation density, low internal stress of the AlN template after annealing, low lattice mismatch with different component aluminum gallium nitrides grown later, and low number of aluminum gallium nitride surface hills.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxial substrate preparation technology, and relates to an AlN (aluminum nitride) template and its preparation method, especially to a high-quality crack-free AlN template and its preparation method. Background Technology

[0002] Aluminum nitride (AlN) templates are the substrate materials for the epitaxial growth of aluminum gallium nitride (AlGaN)-based deep ultraviolet (DEUV) LEDs. The crystal quality of the aluminum nitride template directly determines the crystal quality of the upper AlGaN layer. High-quality aluminum nitride templates can effectively reduce the through-dislocation density (TDDs) of AlGaN, improve the radiative recombination efficiency of electrons and holes in LED structures grown based on this material, and improve the reliability and lifespan of LEDs.

[0003] AlN templates that can be used for growing deep ultraviolet LED structures include single-crystal AlN templates and heterogeneous AlN templates. Single-crystal AlN templates are expensive and have limited supply, restricting their application. Heterogeneous AlN templates are formed by fabricating AlN thin films on heterogeneous substrates. Techniques for fabricating AlN thin films on heterogeneous substrates include metal-organic chemical vapor deposition (MOCVD), magnetron sputtering, molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE).

[0004] However, existing methods all have certain drawbacks. Among them,

[0005] 1. Single-crystal AlN substrates have high manufacturing costs and low yields, making them unsuitable for large-scale applications.

[0006] 2. Molecular beam epitaxy is slow, costly, and produces oval / whisker-like defects on the surface of the grown film, and also suffers from polycrystalline growth problems.

[0007] 3. HVPE has the following defects: (1) The growth rate is fast, making it difficult to accurately control the film thickness; (2) The reaction gas corrodes the chamber, thus affecting the quality of the epitaxial film; (3) The growth rate is fast, and heteroepitaxial growth is prone to cracking.

[0008] 4. MOCVD epitaxial growth process is relatively complex. In order to control cracks and morphology, nucleation layers and coarsening layers with appropriate morphology need to be grown, and the crystal quality is relatively poor (the half-width of the rocking curve of the (102) plane is about 400 arc seconds). In addition, MOCVD equipment is relatively expensive. During the epitaxial process, a coating will be deposited around the chamber and on the top cover, which will affect the repeatability of the process.

[0009] 5. Magnetron sputtering has high production efficiency and low cost, but the thin films it grows are polycrystalline with poor crystal quality and cannot be used directly as templates. It is generally used as a nucleation layer for AlN epitaxial growth.

[0010] In high-quality AlN thin film fabrication techniques, lateral epitaxial growth (ELOG) has been shown to significantly reduce dislocation density. To achieve ELOG, one approach is to use a patterned substrate, allowing discontinuous nucleation in the initial stages of film growth. Another approach is to insert a mask material with a low adhesion coefficient after the film has grown for a period of time, thereby separating the originally continuous film. On the patterned substrate or mask surface, AlN is initially grown vertically; after reaching a certain thickness, some adjacent sidewalls will merge to form a continuous AlN film.

[0011] However, the thermal mismatch between the sapphire substrate and AlN is 78.6% (the coefficient of thermal expansion of the sapphire substrate in the

[0001] direction is 7.5 × 10⁻⁶). -6 / K, the coefficient of thermal expansion of AlN in the

[0001] direction is 4.2×10. -6 / K), because the thermal expansion coefficient of sapphire is much greater than that of AlN, AlN after high-temperature annealing will be compressed by sapphire in the

[0001] direction, the lattice constant a will decrease, resulting in a large compressive stress inside.

[0012] Given the aforementioned technical deficiencies of existing technologies, there is an urgent need to develop a novel AlN template and its preparation method. Summary of the Invention

[0013] To overcome the shortcomings of existing technologies, this invention proposes an AlN template and its preparation method, which can obtain a high-quality AlN template with no cracks and low stress.

[0014] To achieve the above objectives, the present invention provides the following technical solution:

[0015] An AlN template includes a substrate and an AlN buffer layer disposed on the substrate, characterized in that the AlN buffer layer is provided with SiN. X Mask layer, the SiN X An AlN layer is disposed on the mask layer, the AlN layer comprising components disposed on the SiN... X An AlN recovery layer on a mask layer and an AlN planarization layer disposed on the AlN recovery layer, wherein the AlN planarization layer has a stepped flow morphology.

[0016] Preferably, the SiN X The thickness of the mask layer is 5-20nm.

[0017] Preferably, the thickness of the AlN recovery layer is 400-800 nm.

[0018] Preferably, the thickness of the AlN planarization layer is 1600–3200 nm.

[0019] Preferably, the thickness of the AlN buffer layer is 5-20 nm.

[0020] Preferably, the substrate is a sapphire planar substrate with a diameter of 2 inches.

[0021] Furthermore, the present invention also provides a method for preparing an AlN template, characterized by comprising the following steps:

[0022] 1) Grow an AlN buffer layer on the substrate;

[0023] 2) Growing SiN on the AlN buffer layer X Mask layer;

[0024] 3) In the SiN X An AlN recovery layer is grown on the mask layer;

[0025] 4) An AlN planarization layer is grown on the AlN recovery layer;

[0026] 5) Perform overall annealing treatment.

[0027] Preferably, step 2) specifically involves: introducing SiH4 and NH3 into the MOCVD equipment to deposit a SiN layer with a thickness of 5–20 nm on the surface of the AlN buffer layer. X Mask layer, the SiN X The specific growth process of the mask layer is as follows: growth temperature is 1000~1100℃, growth pressure is 60~100 torr, SiH4 flow rate is 0.3~0.6umol / min, NH3 flow rate is 1.5~3L / min, and deposition time is 60s~180s.

[0028] Preferably, step 3) specifically involves: in the MOCVD equipment, the SiN... X An AlN recovery layer with a thickness of 400–800 nm is grown on the mask layer. The specific growth process of the AlN recovery layer is as follows: growth temperature is 1180–1230 °C, growth pressure is 40–60 torr, trimethylaluminum flow rate is 250–350 μmol / min, NH3 flow rate is 200–400 sccm, propellant gas is H2 with a flow rate of 40–60 L / min, and growth time is 24–48 min.

[0029] Preferably, step 4) specifically involves: growing an AlN planarization layer with a thickness of 1600–3200 nm on the AlN recovery layer in an MOCVD device. The AlN planarization layer has a stepped flow morphology, and its specific growth process is as follows: the growth temperature is 1130–1180 °C, which is 50 °C lower than the growth temperature of the AlN recovery layer; the growth pressure is 40–60 torr; the flow rate of trimethylaluminum is 250–350 μmol / min; the flow rate of NH3 is 200–400 sccm; the propellant gas is H2, and the flow rate of the propellant gas is 40–60 L / min; and the growth time is 96–192 min.

[0030] Preferably, step 5) specifically involves: after growing the AlN planarization layer, placing the entire layer in a high-temperature annealing furnace for annealing treatment, wherein the annealing temperature is 1500–1800℃, the annealing time is 0.2–3h, the annealing atmosphere is nitrogen, the nitrogen flow rate is 100–12000 sccm, and the annealing pressure is 200–650 torr.

[0031] Preferably, step 1) specifically involves growing an AlN buffer layer (2) with a thickness of 5–20 nm using MOCVD or magnetron sputtering. The MOCVD growth process specifically involves a growth temperature of 850–950 °C, a growth pressure of 40–60 torr, an NH3 flow rate of 350–650 sccm, a trimethylaluminum flow rate of 100–160 μmol / min, and a growth time of 1–3 min. The magnetron sputtering process specifically involves a growth temperature of 550–700 °C, a sputtering power of 1000–4000 W, a nitrogen flow rate of 80–200 sccm, an oxygen flow rate of 0.1–2 sccm, an argon flow rate of 0.1–40 sccm, and a deposition time of 30–90 s.

[0032] Preferably, steps 2)-4) are repeated 2-3 times before step 5).

[0033] Compared with the prior art, the AlN template and its preparation method of the present invention have one or more of the following beneficial technical effects:

[0034] 1. By inserting a porous mask layer, the lateral growth of AlN is increased and the dislocation density is reduced.

[0035] 2. The mask layer can be grown directly in the MOCVD equipment using the existing hydride without modifying the equipment, and it is also less expensive than using a patterned substrate for lateral growth. In addition, the growth process of the mask layer is easy to match with the subsequent growth process of the AlN recovery layer. Furthermore, the mask layer can be inserted multiple times, increasing the flexibility of the process.

[0036] 3. The high-temperature annealing process causes AlN to recrystallize, which reduces the density of screw dislocations and edge dislocations.

[0037] 4. By inserting a mask layer with a low coefficient of thermal expansion and high porosity between AlN and sapphire, the expansion and shrinkage of the sapphire substrate during the high-temperature annealing process are greatly reduced, the internal stress of AlN after annealing is reduced, the lattice mismatch with the different Al gallium nitride components grown later is reduced, and the number of hills on the Al gallium nitride surface is reduced. Attached Figure Description

[0038] Figure 1 This is a cross-sectional view after an AlN buffer layer has been grown on the substrate.

[0039] Figure 2 SiN was grown on an AlN buffer layer. X Cross-sectional view behind the mask layer;

[0040] Figure 3 It is in SiN X Cross-sectional view of the mask layer after AlN layer has been grown in the fan-shaped structure;

[0041] Figure 4 This is an exploded schematic diagram of the AlN template of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments. The content of the embodiments is not intended to limit the scope of protection of the present invention.

[0043] To overcome the problems existing in the prior art, this invention proposes an AlN template and its preparation method, which can obtain a high-quality AlN template with no cracks and low stress.

[0044] Figure 4 An exploded view of the AlN template of the present invention is shown. For example... Figure 4 As shown, the AlN template of the present invention includes a substrate 1.

[0045] The substrate 1 is preferably a sapphire substrate. For example, the substrate 1 is a sapphire planar substrate with a diameter of 2 inches. This makes the prepared AlN template suitable for fabricating deep ultraviolet LED chips.

[0046] In this invention, an AlN buffer layer 2 is provided on the substrate 1. Preferably, the thickness of the AlN buffer layer 2 is 5-20 nm.

[0047] The AlN buffer layer 2 is provided with SiN X Mask layer 3 and the SiN XThe thickness of mask layer 3 is 5-20 nm.

[0048] The SiN X The mask layer 3 is a thin film with a porous structure and a low coefficient of thermal expansion. This is achieved by inserting the SiN... X Mask layer 3 can greatly reduce the thermal expansion of the sapphire substrate during the high-temperature annealing process, thereby reducing the internal stress caused by the large thermal mismatch between sapphire and AlN.

[0049] The SiN X An AlN layer 4 is disposed on the mask layer 3. The AlN layer 4 comprises layers disposed on the SiN... X The mask layer 3 has an AlN recovery layer and an AlN planarization layer disposed on the AlN recovery layer. The thickness of the AlN recovery layer is 400-800 nm. The AlN planarization layer has a stepped flow morphology and a thickness of 1600-3200 nm.

[0050] In this invention, the AlN recovery layer can be located on the SiN... X The AlN recovery layer grows in the pores of the mask layer, which allows the AlN recovery layer to grow laterally in addition to vertical growth, thus reducing the dislocation density.

[0051] Meanwhile, the AlN leveling layer makes the surface of the AlN layer 4 smoother and gives the AlN layer 4 a stepped flow morphology, thereby releasing some of the stress generated during the production of the AlN layer 4.

[0052] In this invention, depending on the required thickness of the AlN template, there can be 1-3 layers of the SiN. X The structure consists of a mask layer, AlN recovery layers (layers 1-3), and AlN planarization layers (layers 1-3). Specifically, a SiN layer can be deposited on top of the AlN planarization layer. X Mask layer, and in the SiN X An AlN recovery layer is then applied to the mask layer, and an AlN leveling layer is then applied on top of the AlN recovery layer. This process is repeated until the thickness of the AlN template meets the requirements.

[0053] Therefore, the SiN X The mask layer can be inserted multiple times, increasing the flexibility of the process.

[0054] The preparation method of the AlN template of the present invention is described below, so that those skilled in the art can prepare the AlN template according to the description of the present invention.

[0055] The method for preparing the AlN template of the present invention includes the following steps:

[0056] 1. An AlN buffer layer 2 is grown on substrate 1.

[0057] Preferably, the substrate 1 is a sapphire substrate. For example, the substrate 1 is a sapphire planar substrate with a diameter of 2 inches. More preferably, the thickness of the AlN buffer layer 2 is 5–20 nm.

[0058] When growing the AlN buffer layer 2 on the substrate 1, either MOCVD growth process or magnetron sputtering process can be used.

[0059] The specific growth process of the AlN buffer layer 2 using MOCVD growth technology is as follows: growth temperature is 850-950℃, growth pressure is 40-60 torr, NH3 flow rate is 350 sccm-650 sccm, trimethylaluminum flow rate is 100-160 μmol / min, and growth time is 1-3 min.

[0060] The specific sputtering process for growing the AlN buffer layer 2 using magnetron sputtering is as follows: growth temperature is 550–700℃, sputtering power is 1000–4000W, nitrogen flow rate is 80–200 sccm, oxygen flow rate is 0.1–2 sccm, argon flow rate is 0.1–40 sccm, and deposition time is 30–90 s.

[0061] This step produces, as follows Figure 1 The structure shown.

[0062] II. Growing SiN on the AlN buffer layer 2 X Mask layer 3.

[0063] In this invention, the SiN can be grown on the AlN buffer layer 2 using an MOCVD growth process. X Mask layer 3. That is, SiH4 and NH3 can be introduced into the MOCVD equipment to deposit a SiN layer with a thickness of 5–20 nm on the surface of the AlN buffer layer 2. X Mask layer 3. The SiN X The specific growth process of mask layer 3 is as follows: growth temperature is 1000~1100℃, growth pressure is 60~100torr, SiH4 flow rate is 0.3~0.6umol / min, NH3 flow rate is 1.5~3L / min, and deposition time is 60s~180s.

[0064] The SiN X The mask layer 3 is a thin film with a porous structure and a small coefficient of thermal expansion. This is achieved by inserting the SiN... XMask layer 3 can greatly reduce the thermal expansion of the sapphire substrate during the high-temperature annealing process, thereby reducing the internal stress caused by the large thermal mismatch between sapphire and AlN.

[0065] Furthermore, the SiN is inserted between the AlN buffer layer 2 and the AlN layer 4. X Mask layer 3, through the mask layer with a porous structure, enables AlN to have a lateral growth mode on the surface of the mask layer, which increases the probability of dislocation annihilation and reduces the dislocation density.

[0066] Furthermore, the SiN X Mask layer 3 is grown directly in the MOCVD equipment using existing hydrides, requiring no equipment modification and also at a lower cost than using a patterned substrate for lateral growth. Furthermore, the growth process of the mask layer is easily compatible with the subsequent growth process of the AlN recovery layer.

[0067] This step produces, as follows Figure 2 The structure shown.

[0068] III. In the SiN X An AlN recovery layer is grown on mask layer 3.

[0069] In this invention, MOCVD growth process can be used to grow the SiN. X An AlN recovery layer is grown on mask layer 3. That is, in the MOCVD equipment, the SiN... X An AlN recovery layer with a thickness of 400–800 nm is grown on mask layer 3.

[0070] The specific growth process of the AlN recovery layer is as follows: the growth temperature is 1180-1230℃, the growth pressure is 40-60 torr, the flow rate of trimethylaluminum is 250-350 μmol / min, the flow rate of NH3 is 200-400 sccm, the propellant gas is H2 with a flow rate of 40-60 L / min, and the growth time is 24-48 min.

[0071] Thus, by using high temperature (1180–1230°C), low Group V / Group III ratio (since ammonia is a Group V element and aluminum is a Group III element, the Group V / Group III ratio here refers to the ratio of ammonia to aluminum), and high propellant gas conditions to grow the AlN recovery layer, the growth temperature and the SiN can be increased. X The amount of Al source on the surface of mask layer 3 increases the surface migration ability of Al atoms, enabling AlN to be deposited on SiN. xIn the pores, AlN grows not only vertically but also to a certain extent laterally. This lateral growth mode increases the probability of dislocation annihilation and reduces the dislocation density. Furthermore, after a certain period of time, adjacent laterally grown sides will come into contact and merge, and the AlN will recombine to form a complete film.

[0072] 4. An AlN planarization layer is grown on the AlN recovery layer.

[0073] In this invention, the AlN planarization layer is still grown on the AlN recovery layer using the MOCVD growth process. That is, the AlN planarization layer with a thickness of 1600-3200 nm is grown on the AlN recovery layer in an MOCVD apparatus, and the AlN planarization layer has a stepped flow morphology.

[0074] The specific growth process of the AlN planarization layer is as follows: the growth temperature is 1130-1180℃, which is 50℃ lower than the growth temperature of the AlN recovery layer; the growth pressure is 40-60 torr; the flow rate of trimethylaluminum is 250-350 μmol / min; the flow rate of NH3 is 200-400 sccm; the propellant gas is H2 with a flow rate of 40-60 L / min; and the growth time is 96-192 min.

[0075] The growth temperature of the AlN leveling layer is 50°C lower than that of the AlN recovery layer, while other growth parameters are the same as those of the AlN recovery layer. During the growth of the AlN leveling layer, lowering the temperature makes the surface of the newly merged AlN more level, thereby enabling the fabrication of AlN with a stepped flow morphology. Furthermore, by continuing to grow AlN, some of the stress generated during the AlN production process is released.

[0076] Through the above two steps, in the SiN X A smooth AlN layer 4 is formed on the surface of mask layer 3, and its structure is as follows: Figure 3 As shown.

[0077] Meanwhile, in this invention, depending on the required thickness of the AlN template, there can be 1-3 layers of the SiN. X The mask layer, the AlN recovery layer (layers 1-3), and the AlN planarization layer (layers 1-3).

[0078] That is, a SiN layer can be grown on the AlN planar layer using the same process as in step two. X The mask layer is applied, and the same process as in step three is used on the SiN... XAn AlN recovery layer is then grown over the mask layer, and an AlN planarization layer is grown over the AlN recovery layer using the same process as in step four. This process is continued until the thickness of the AlN template meets the requirements.

[0079] 5. Perform overall annealing treatment.

[0080] After the AlN planarization layer is grown, the entire layer is placed in a high-temperature annealing furnace for annealing treatment.

[0081] In this invention, the annealing treatment is a high-temperature annealing treatment. Specifically, the annealing temperature is 1500–1800°C, the annealing time is 0.2–3 hours, the annealing atmosphere is nitrogen, the nitrogen flow rate is 100–12000 sccm, and the annealing pressure is 200–650 torr.

[0082] The high-temperature annealing process allows AlN to recrystallize. During the grain rearrangement, screw dislocations and edge dislocations climb and annihilate, reducing the dislocation density and ultimately producing a template for high-quality AlN with no cracks and low stress.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention based on the concept of the present invention, without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An AlN template comprising a substrate (1) and an AlN buffer layer (2) disposed on the substrate (1), characterized in that, The AlN buffer layer (2) is provided with SiN X Mask layer (3), the SiN X An AlN layer (4) is provided on the mask layer (3), the AlN layer (4) comprising components disposed on the SiN X An AlN recovery layer on the mask layer (3) and an AlN planarization layer disposed on the AlN recovery layer, wherein the AlN planarization layer has a stepped flow morphology; The SiN X The mask layer, AlN recovery layer, and AlN planarization layer are repeatedly applied 1 to 3 times; The SiN X The mask layer is a thin film with a porous structure and a small coefficient of thermal expansion. The SiN... X The mask layer growth process is as follows: growth temperature is 1000~1100℃, growth pressure is 60~100 torr, SiH4 flow rate is 0.3~0.6μmol / min, NH3 flow rate is 1.5~3L / min, and deposition time is 60s~180s.

2. The AlN template according to claim 1, characterized in that, The SiN X The thickness of the mask layer (3) is 5-20 nm.

3. The AlN template according to claim 1, characterized in that, The thickness of the AlN recovery layer is 400-800 nm.

4. The AlN template according to claim 1, characterized in that, The thickness of the AlN planarization layer is 1600~3200nm.

5. The AlN template according to claim 1, characterized in that, The thickness of the AlN buffer layer (2) is 5-20 nm.

6. The AlN template according to claim 1, characterized in that, The substrate (1) is a sapphire planar substrate with a diameter of 2 inches.

7. A method for preparing an AlN template as described in any one of claims 1-6, characterized in that, Includes the following steps: 1) An AlN buffer layer (2) is grown on a substrate (1); 2) Growing SiN on the AlN buffer layer (2) X Mask layer (3); 3) In the SiN X An AlN recovery layer is grown on the mask layer (3); 4) An AlN planarization layer is grown on the AlN recovery layer; 5) Perform overall annealing treatment.

8. The method for preparing the AlN template according to claim 7, characterized in that, Step 2) specifically involves: introducing SiH4 and NH3 into the MOCVD equipment, and depositing a SiN layer with a thickness of 5-20 nm on the surface of the AlN buffer layer (2). X Mask layer (3), the SiN X The specific growth process of the mask layer (3) is as follows: the growth temperature is 1000~1100℃, the growth pressure is 60~100 torr, the SiH4 flow rate is 0.3~0.6umol / min, the NH3 flow rate is 1.5~3L / min, and the deposition time is 60s~180s.

9. The method for preparing the AlN template according to claim 7, characterized in that, Step 3) specifically involves: in the MOCVD equipment, on the SiN... X An AlN recovery layer with a thickness of 400~800nm ​​is grown on the mask layer (3). The specific growth process of the AlN recovery layer is as follows: the growth temperature is 1180~1230℃, the growth pressure is 40~60torr, the flow rate of trimethylaluminum is 250~350umol / min, the flow rate of NH3 is 200~400sccm, the propellant gas is H2 and the flow rate of the propellant gas is 40~60L / min, and the growth time is 24min~48min.

10. The method for preparing the AlN template according to claim 9, characterized in that, Step 4) specifically involves growing an AlN planarization layer with a thickness of 1600~3200nm on the AlN recovery layer in an MOCVD device. The AlN planarization layer has a stepped flow morphology, and its specific growth process is as follows: the growth temperature is 1130~1180℃, which is 50℃ lower than the growth temperature of the AlN recovery layer; the growth pressure is 40~60 torr; the flow rate of trimethylaluminum is 250~350umol / min; the flow rate of NH3 is 200~400sccm; the propellant gas is H2, and the flow rate of the propellant gas is 40~60L / min; and the growth time is 96min~192min.

11. The method for preparing the AlN template according to claim 7, characterized in that, Step 5) specifically involves: after growing the AlN flattened layer, the entire layer is placed in a high-temperature annealing furnace for annealing treatment. The annealing temperature is 1500~1800℃, the annealing time is 0.2~3h, the annealing atmosphere is nitrogen, the nitrogen flow rate is 100~12000sccm, and the annealing pressure is 200~650torr.

12. The method for preparing the AlN template according to claim 7, characterized in that, Step 1) specifically involves growing an AlN buffer layer (2) with a thickness of 5-20 nm using MOCVD or magnetron sputtering. The MOCVD growth process specifically involves a growth temperature of 850-950℃, a growth pressure of 40-60 torr, an NH3 flow rate of 350-650 sccm, a trimethylaluminum flow rate of 100-160 μmol / min, and a growth time of 1-3 min. The magnetron sputtering process specifically involves a growth temperature of 550-700℃, a sputtering power of 1000-4000 W, a nitrogen flow rate of 80-200 sccm, an oxygen flow rate of 0.1-2 sccm, an argon flow rate of 0.1-40 sccm, and a deposition time of 30-90 s.

13. The method for preparing the AlN template according to any one of claims 7-12, characterized in that, Before step 5), repeat steps 2)-4) 2-3 times.

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