阅读说明：本技术 一种AlN薄膜及其制备方法和应用 (AlN thin film and preparation method and application thereof ) 是由 不公告发明人 于 2021-08-30 设计创作，主要内容包括：本发明提供了一种AlN薄膜及其制备方法和应用,属于半导体薄膜材料技术领域。本发明在衬底上形成掩膜后刻蚀,在衬底表面形成规则排列的凹坑；然后在凹坑中溅射沉积AlN,并通过退火的方式,在衬底表面得到了规则排列、应力小且致密的AlN籽晶。由于AlN籽晶只在凹坑中而衬底表面其他位置没有,在后续外延生长过程中,AlN籽晶为同质外延,而衬底上为异质外延,可以改善衬底和AlN层的晶格失配和热失配,又能降低位错密度,提高晶体质量。同时,由于同质和异质生长速率的差异,使后续生长的AlN层趋向于二维生长,得到表面光滑的AlN层。溅射AlN层经过退火处理后,会和衬底凹坑的最下层形成空隙层,提高深紫外LED的出光效率。(The invention provides an AlN thin film and a preparation method and application thereof, belonging to the technical field of semiconductor thin film materials. The invention forms a mask on a substrate and then etches the mask, and pits which are regularly arranged are formed on the surface of the substrate; and then, AlN is sputtered and deposited in the pits, and AlN seed crystals which are regularly arranged, have small stress and are compact are obtained on the surface of the substrate in an annealing mode. Because the AlN seed crystal is only in the pit and other positions on the surface of the substrate are not, in the subsequent epitaxial growth process, the AlN seed crystal is homoepitaxy, and the substrate is heteroepitaxy, the lattice mismatch and thermal mismatch of the substrate and the AlN layer can be improved, the dislocation density can be reduced, and the crystal quality is improved. Meanwhile, due to the difference of homogeneous growth rate and heterogeneous growth rate, the AlN layer grown subsequently tends to grow in two dimensions, and the AlN layer with a smooth surface is obtained. After annealing treatment is carried out on the sputtered AlN layer, a gap layer is formed between the sputtered AlN layer and the lowest layer of the substrate pit, and the light emitting efficiency of the deep ultraviolet LED is improved.)

1. A preparation method of an AlN thin film is characterized by comprising the following steps:

forming a mask on a substrate to obtain a substrate containing the mask;

etching the surface of the substrate containing the mask to form a pit on the surface of the substrate;

taking aluminum as a target material, sputtering and depositing AlN in the pits in the presence of nitrogen-inert mixed gas, and removing residual masks to obtain a substrate containing a sputtered AlN layer;

annealing the substrate containing the sputtering AlN layer to obtain a substrate containing a compact AlN layer;

and epitaxially growing AlN on the surface of the substrate containing the compact AlN layer to form an epitaxial AlN layer, and obtaining an AlN thin film on the surface of the substrate.

2. The production method according to claim 1, wherein the thickness of the sputtered AlN layer in the substrate containing the sputtered AlN layer is 10 to 400 nm.

3. The production method according to claim 1, wherein the annealing includes sequentially performing a first annealing and a second annealing;

the temperature of the first annealing is 1500-1800 ℃, and the heat preservation time is 0.5-5 h;

the second annealing temperature is 500-1000 ℃, and the heat preservation time is 0.5-3 h.

4. The method according to claim 1, wherein the substrate is made of sapphire, silicon carbide, zinc oxide, metal or glass.

5. The method of claim 1, wherein the mask comprises a photoresist mask, a metal mask, or a silicon dioxide mask.

6. The method of claim 1, wherein the etching comprises ion etching or chemical etching.

7. The method of claim 1, wherein the shape of the pit comprises a rectangular parallelepiped, a cube, a cone, a cylinder, or a bowl;

the pits are regularly arranged pits, the depth of each pit is 10-400 nm independently, and the width of the upper surface of each pit is 100-2000 nm independently; the distance between two adjacent pits is 1-10 μm.

8. The method according to claim 1, wherein the epitaxial AlN layer has a thickness of 1 to 5 μm.

9. An AlN thin film obtained by the production method according to any one of claims 1 to 8.

10. An optoelectronic device, wherein the AlN thin film of claim 9 is used.

Technical Field

The invention relates to the technical field of semiconductor thin film materials, in particular to a preparation method of an AlN thin film.

Background

Aluminum nitride (AlN), which is a wide band gap direct band gap semiconductor with a wide band gap (6.2 eV), is an important blue and ultraviolet light emitting material, and has important applications in photoelectric devices such as ultraviolet detectors, ultraviolet light emitting diodes, and ultraviolet lasers, and is particularly essential in back-incident solar blind detectors, flip-chip packaged ultraviolet LEDs.

Currently, AlN films are mainly prepared by heteroepitaxial techniques. For example, the prior art "Growth of high-quality and crack free AlN layers on sapphire substrate by multi-Growth mode modification" (see Okada N, Kato N, Sato S, et al, Growth of high-quality and crack free AlN layers on sapphire substrate by multi-Growth mode modification [ J ]. Journal of Crystal Growth, 2007, 298: 349-. However, in the process of preparing the AlN film by the above method, since the AlN epitaxial layer and the substrate have large lattice mismatch and thermal mismatch, a large amount of dislocations and stress are easily generated in the AlN crystal during the epitaxial growth process, and many dislocations may seriously reduce the light intensity, the lifetime, and other properties of the photoelectric device made of the AlN film, and a large amount of cracks may be generated due to large stress to affect the yield of the photoelectric device; meanwhile, a large amount of dislocation can be generated in the process of releasing the stress; resulting in poor quality AlN crystals.

Disclosure of Invention

In view of the above, the present invention aims to provide an AlN film, and a preparation method and an application thereof, wherein the AlN film obtained by the preparation method provided by the present invention has low dislocation density, no crack, and high quality.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of an AlN thin film, which comprises the following steps:

forming a mask on a substrate to obtain a substrate containing the mask;

etching the surface of the substrate containing the mask to form a pit on the surface of the substrate;

taking aluminum as a target material, sputtering and depositing AlN in the pits in the presence of nitrogen-inert mixed gas, and removing residual masks to obtain a substrate containing a sputtered AlN layer;

annealing the substrate containing the sputtering AlN layer to obtain a substrate containing a compact AlN layer;

and epitaxially growing AlN on the surface of the substrate containing the compact AlN layer to form an epitaxial AlN layer, and obtaining an AlN thin film on the surface of the substrate.

Preferably, the thickness of the sputtered AlN layer in the substrate containing the sputtered AlN layer is 10-400 nm.

Preferably, the annealing includes sequentially performing a first annealing and a second annealing;

the temperature of the first annealing is 1500-1800 ℃, and the heat preservation time is 0.5-5 h;

the second annealing temperature is 500-1000 ℃, and the heat preservation time is 0.5-3 h.

Preferably, the substrate is made of sapphire, silicon carbide, zinc oxide, metal or glass.

Preferably, the mask comprises a photoresist mask, a metal mask or a silicon dioxide mask.

Preferably, the etching comprises ion etching or chemical etching.

Preferably, the shape of the pit comprises a cuboid, a cube, a cone, a cylinder or a bowl;

the pits are regularly arranged pits, the depth of each pit is 10-400 nm independently, and the width of the upper surface of each pit is 100-2000 nm independently; the distance between two adjacent pits is 1-10 μm.

Preferably, the thickness of the epitaxial AlN layer is 1 to 5 μm.

The invention provides the AlN thin film obtained by the preparation method in the technical scheme.

The invention also provides the application of the AlN film in the technical scheme in photoelectric devices.

The invention provides a preparation method of an AlN thin film, which comprises the following steps: forming a mask on a substrate to obtain a substrate containing the mask; etching the surface of the substrate containing the mask to form a pit on the surface of the substrate; taking aluminum as a target material, sputtering and depositing AlN in the pits in the presence of nitrogen-inert mixed gas, and removing residual masks to obtain a substrate containing a sputtered AlN layer; annealing the substrate containing the sputtering AlN layer to obtain a substrate containing a compact AlN layer; and epitaxially growing AlN on the surface of the substrate containing the compact AlN layer to form an epitaxial AlN layer, and obtaining an AlN thin film on the surface of the substrate. The method comprises the steps of preparing pits which are regularly arranged on a substrate, sputtering and depositing AlN in the pits, and sputtering AlN in an AlN layer to recrystallize after annealing treatment to form compact AlN seed crystals with small stress. Because the AlN seed crystal is only in the pit and other positions on the surface of the substrate are not, in the subsequent epitaxial growth process, the AlN seed crystal is homoepitaxy, and the substrate is heteroepitaxy, therefore, the lattice mismatch and thermal mismatch of the substrate and the AlN layer can be improved, the dislocation density can be reduced, and the crystal quality is improved. Meanwhile, due to the difference of homogeneous growth rate and heterogeneous growth rate, the AlN layer grown subsequently tends to grow in two dimensions, and the AlN layer with a smooth surface is obtained. After the sputtered AlN layer is annealed, a certain gap layer is formed with the lowest layer of the substrate pit, the difference of the refractive index of the gap layer and the AlN layer is formed, and the light emitting efficiency of the ultraviolet LED can be improved. Moreover, the preparation method provided by the invention is time-saving, labor-saving, simple and easy to implement, has a short growth period of the AlN thin film, is an effective method for realizing the high-quality and low-cost growth of the AlN epitaxial thin film, and is suitable for industrial production.

The invention provides the AlN thin film obtained by the preparation method in the technical scheme. The AlN thin film provided by the invention has the advantages of low dislocation density, no crack, smooth surface and high quality.

Drawings

FIG. 1 is a schematic cross-sectional view of a pit etched in a substrate in example 1;

FIG. 2 is a schematic cross-sectional view of a pit etched in a substrate in example 2;

FIG. 3 is a schematic cross-sectional view of a substrate containing a sputtered AlN layer in example 2;

FIG. 4 is a schematic cross-sectional view showing the structure of an AlN thin film in example 2;

in fig. 1 to 4, 1 denotes a substrate, 2 denotes a pit, 3 denotes a sputtered AlN layer, 4 denotes a void layer, and 5 denotes an epitaxial AlN layer.

Detailed Description

The invention provides a preparation method of an AlN thin film, which comprises the following steps:

forming a mask on a substrate to obtain a substrate containing the mask;

etching the surface of the substrate containing the mask to form a pit on the surface of the substrate;

taking aluminum as a target material, sputtering and depositing AlN in the pits in the presence of nitrogen-inert mixed gas, and removing residual masks to obtain a substrate containing a sputtered AlN layer;

annealing the substrate containing the sputtering AlN layer to obtain a substrate containing a compact AlN layer;

and epitaxially growing AlN on the surface of the substrate containing the compact AlN layer to form an epitaxial AlN layer, and obtaining an AlN thin film on the surface of the substrate.

In the present invention, all the raw material components are commercially available products well known to those skilled in the art unless otherwise specified.

The invention forms a mask on a substrate to obtain the substrate containing the mask. In the present invention, the substrate preferably comprises sapphire, silicon carbide, zinc oxide, metal or glass; the metal preferably comprises one or more of Al, Ag, Pt, Fe, Au and Cu. In the present invention, the mask preferably comprises a photoresist mask, a metal mask or a silicon dioxide mask; the photoresist is not particularly limited in the invention, and the photoresist known to those skilled in the art can be adopted; the thickness of the mask is not particularly limited in the present invention, and the mask can cover the substrate. In the invention, the photoresist mask is preferably obtained by spin-coating a photoresist solution on the surface of a substrate and then drying; the type of the photoresist is not particularly limited in the present invention, and a photoresist for preparing an AlN layer, which is well known to those skilled in the art, may be used. In the present invention, the metal mask is preferably obtained by self-manufacture or purchase; the homemade method preferably comprises electroplating or sputtering; the operation of preparing the metal mask by the electroplating or sputtering method is not particularly limited in the present invention, and the operation of preparing the metal mask by electroplating or sputtering known to those skilled in the art may be adopted. In the present invention, the method for preparing the silicon dioxide mask preferably includes the steps of: placing the substrate in plasma enhanced chemical vapor deposition equipment, introducing silane and nitrous oxide, and performing chemical vapor deposition on silicon dioxide on the surface of the substrate to obtain a silicon dioxide mask; in the invention, the temperature of the chemical vapor deposition is preferably 200-300 ℃, and more preferably 250 ℃; the flow ratio of silane to nitrous oxide is preferably 1: 10.

after the mask-containing substrate is obtained, the surface of the mask-containing substrate is etched, and pits are formed on the surface of the substrate. In the present invention, the etching preferably includes ion etching or chemical etching. In the present invention, the pits are preferably regularly arranged pits, and the formation manner of the pits is preferably determined according to the type of the mask; when the mask is a photoresist, preferably adopting a graphical transfer technology and utilizing an ion etching or chemical etching method to form pits which are regularly arranged on the surface of the substrate; the operation of the patterning transfer technology is not particularly limited, and the patterning transfer operation known to a person skilled in the art can be adopted; when the mask is made of metal, pits which are regularly arranged are preferably formed on the surface of the substrate by adopting an ion etching method; when the mask is silicon dioxide, pits which are regularly arranged are preferably formed on the surface of the substrate by adopting an ion etching or chemical etching method; the chemical etching reagent preferably comprises a hydrofluoric acid solution or a buffered oxide etching solution (BOE solution); the conditions of the ion etching and the chemical etching are not specially limited, and pits in regular arrangement can be obtained. In the invention, the shape of the pit preferably comprises a cuboid, a cube, a cone, a cylinder or a bowl; the depth of the pits is preferably 10-400 nm, more preferably 100-300 nm, and further preferably 200-250 nm; the width of the upper surface of each pit is preferably 100-2000 nm, and more preferably, the distance between two adjacent pits is preferably 1-10 mu m.

After the pits which are regularly arranged are obtained, the method takes aluminum as a target material, and removes the residual mask after AlN is sputtered and deposited in the pits in the presence of nitrogen-inert mixed gas to obtain the substrate containing the sputtered AlN layer. In the invention, the flow ratio of nitrogen to inert gas in the nitrogen-inert mixed gas is preferably 0.3-1: 1, more preferably 0.5 to 0.8: 1; the inert gas preferably comprises argon or helium. In the invention, the temperature of the sputtering deposition is preferably 400-600 ℃, and more preferably 500 ℃; the time for the sputtering deposition is not particularly limited, and the thickness of the sputtered AlN layer in the substrate containing the sputtered AlN layer can be 10-400 nm, and the thickness of the sputtered AlN layer is more preferably 50-300 nm, and even more preferably 100-200 nm. In the invention, the residual mask is preferably removed by soaking in a mask removing reagent; the soaking time is preferably 10-100 min, and more preferably 50-80 min; the mask removing agent is preferably determined according to the type of the mask; when the mask is a photoresist, the residual mask is preferably removed using NMP (N-methylpyrrolidone) or acetone; when the mask is silicon dioxide, preferably, hydrofluoric acid solution or buffered oxide etching solution (BOE solution) is adopted to remove the residual mask; when the mask is made of metal, the residual mask is removed by preferably adopting ion etching or chemical etching; the conditions of the ion etching and the chemical etching are preferably the same as those of the ion etching and the chemical etching, and are not described in detail herein.

After the substrate containing the sputtering AlN layer is obtained, annealing is carried out on the substrate containing the sputtering AlN layer to obtain the substrate containing the compact AlN layer. In the present invention, the annealing preferably includes sequentially performing a first annealing and a second annealing; the temperature of the first annealing is preferably 1500-1800 ℃, and more preferably 1600-1700 ℃; the heating rate from room temperature to the first annealing temperature is preferably 10-20 ℃/min, and more preferably 15 ℃/min; starting timing when the temperature rises to the temperature of the first annealing, wherein the heat preservation time of the first annealing is 0.5-5 h, and more preferably 2-3 h; the purpose of the first annealing is to recrystallize the AlN obtained by sputtering to form a substrate containing a compact AlN layer; the second annealing temperature is 500-1000 ℃, and more preferably 600-800 ℃; the cooling rate of the temperature reduced to the second annealing temperature is preferably 5-10 ℃/min, and more preferably 8 ℃/min; starting timing when the temperature is reduced to the temperature of the second annealing, wherein the heat preservation time of the second annealing is 0.5-3 h, and more preferably 1-2 h; the purpose of the second annealing is to relieve stress after recrystallization of AlN; the annealing atmosphere is preferably a protective atmosphere; the protective atmosphere in the present invention is not particularly limited, and may be any protective atmosphere known to those skilled in the art, such as nitrogen or argon; the annealing is preferably performed on a graphite support of a high temperature annealing furnace.

After the substrate containing the compact AlN layer is obtained, AlN epitaxially grows on the surface of the substrate containing the compact AlN layer to form an epitaxial AlN layer, and an AlN thin film is obtained on the surface of the substrate. In the present invention, the epitaxial growth is preferably performed in an MOCVD apparatus or an MOVPE apparatus; the pressure of the gas reaction chambers of the MOCVD equipment and the MOVPE equipment is preferably 30-100 mbar independently, and more preferably 50 mbar; the atmosphere of the epitaxial growth is preferably that TMAl (trimethylaluminum) and ammonia gas are introduced; the flow ratio of the TMAl to the ammonia gas is preferably 1: 10; the temperature of the epitaxial growth is preferably 1100-1400 ℃, and more preferably 1200-1300 ℃; in the epitaxial growth process, part of AlN is in homoepitaxy, and the problems of lattice adaptation and thermal mismatch are avoided, so that the quality of AlN is improved.

In the present invention, the thickness of the epitaxial AlN layer is preferably 1 to 5 μm, more preferably 2 to 4 μm, and still more preferably 2 to 3 μm.

In the conventional heteroepitaxy technology, the difficulty of high-quality AlN epitaxial growth is high, and the following reasons mainly exist: (1) the Al-N bond energy is strong, the diffusion of Al atoms on the growth surface is limited, the lateral growth rate is low, and two-dimensional layered growth is difficult to form; (2) al source TMAl and NH in MOCVD growth₃The method has strong pre-reaction, the pre-reaction not only consumes a large amount of reactants, but also forms solid polymers which can be deposited on the surface of a sample and can not be fully decomposed, so that impurities in an epitaxial layer are doped, and even polycrystalline growth of the epitaxial layer can be caused; (3) the AlN epitaxial layer has larger lattice mismatch and thermal mismatch with the substrate, so that the AlN epitaxial layer has higher dislocation density, cracks and unsmooth surface. The invention prepares regularly arranged pits on a substrate and then sputters and sinks in the pitsAnd accumulating AlN and annealing to obtain AlN seed crystals with regular arrangement, small stress and high density on the surface of the substrate. Because the AlN seed crystal is only in the pit and other positions on the surface of the substrate are not, in the subsequent epitaxial growth process, the AlN seed crystal is homoepitaxy, and the substrate is heteroepitaxy, therefore, the lattice mismatch and thermal mismatch of the substrate and the AlN layer can be improved, the dislocation density can be reduced, and the crystal quality is improved. Meanwhile, due to the difference of homogeneous growth rate and heterogeneous growth rate, the AlN layer grown subsequently tends to grow in two dimensions, and the AlN layer with a smooth surface is obtained. And after the sputtered AlN layer is annealed, a certain gap layer is formed with the lowest layer of the substrate pit, so that the light extraction efficiency of the deep ultraviolet LED can be improved.

The invention provides the AlN thin film obtained by the preparation method in the technical scheme. In the present invention, the AlN thin film preferably has a thickness of 1 to 5 μm.

The invention provides an application of the AlN film in the technical scheme in a photoelectric device. In the present invention, the optoelectronic device preferably comprises an ultraviolet detector, an ultraviolet light emitting diode or an ultraviolet laser. The surface cracks of the AlN thin film mostly influence the yield of the photoelectric device; the high dislocation density of the AlN thin film can reduce the performance (such as light intensity, service life and the like) of the photoelectric device; the surface of the AlN thin film is not smooth, and the AlN thin film can be delayed and rough in the subsequent external time, so that the antistatic capability of the photoelectric device is weaker, and even the electric leakage condition occurs, and the use of the photoelectric device is influenced. The AlN thin film provided by the invention has the advantages of low dislocation density, no crack, smooth surface and high quality, and the manufactured optical device has excellent performance and high yield.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Spin-coating photoresist on a 2-inch sapphire substrate, drying to obtain a photoresist layer, and forming regularly-arranged conical pits with the depth of 100nm and the upper surface width of 1000nm on the surface of the substrate by adopting a graphical transfer technology and an ion etching method; the schematic cross-sectional view of the pits etched on the substrate in this embodiment is shown in fig. 1, where 1 is the substrate and 2 is the pit.

Sputtering and depositing AlN in a pit by adopting physical vapor deposition equipment and taking a target material as aluminum under the conditions of argon-nitrogen mixed gas (the flow ratio of argon to nitrogen is 1: 5) and 600 ℃, and then soaking in NMP for 10-100 min to remove residual photoresist to obtain a substrate containing a sputtered AlN layer; wherein the thickness of the sputtered AlN layer is 100 nm;

placing the substrate containing the sputtered AlN layer on a graphite support of a high-temperature annealing furnace, and keeping the atmosphere in the high-temperature annealing furnace to be N₂Heating to 1750 ℃ at a heating rate of 5 ℃/min under the atmospheric pressure, then carrying out heat preservation annealing for 2h, and then cooling to 650 ℃ for carrying out heat preservation annealing for 1h to obtain a substrate containing a compact AlN layer;

and (2) placing the substrate containing the compact AlN layer in a reaction chamber of MOCVD equipment, heating to 1250 ℃, preserving the temperature for 50s, keeping the pressure in the reaction chamber at 50mbar, introducing TMAl with the flow rate of 200sccm and ammonia with the flow rate of 2000sccm, and epitaxially growing AlN to form an epitaxial AlN layer with the thickness of 2 microns to obtain the AlN thin film.

Example 2

Putting a 2-inch sapphire substrate into plasma enhanced chemical vapor deposition equipment, introducing silane and carbon dioxide gas, forming a silicon dioxide mask with the thickness of 20nm on the surface of the sapphire, etching the silicon dioxide mask to the substrate by adopting an ion etching method, and forming a cylindrical pit with the depth of 100nm and the upper surface width of 1000nm on the surface of the substrate; the schematic cross-sectional view of the pits etched on the substrate in this embodiment is shown in fig. 2, where 1 is the substrate and 2 is the pit.

Sputtering and depositing AlN in the pit by adopting physical vapor deposition equipment and taking a target material as aluminum under the conditions of argon-nitrogen mixed gas (the flow ratio of argon to nitrogen is 1: 5) and 600 ℃, and then soaking in a BOE solution for 10-100 min to remove residual photoresist to obtain a substrate containing a sputtered AlN layer; wherein the thickness of the sputtered AlN layer is 100 nm; a schematic cross-sectional structure of the substrate containing the sputtered AlN layer prepared in this example is shown in fig. 3, where 1 is the substrate, 3 is the sputtered AlN layer, and 4 is the void layer.

Placing the substrate containing the sputtered AlN layer on a graphite support of a high-temperature annealing furnace, and keeping the atmosphere in the high-temperature annealing furnace to be N₂Heating to 1750 ℃ at a heating rate of 5 ℃/min under the atmospheric pressure, then carrying out heat preservation annealing for 2h, and then cooling to 650 ℃ for carrying out heat preservation annealing for 1h to obtain a substrate containing a compact AlN layer;

and (2) placing the substrate containing the compact AlN layer in a reaction chamber of MOCVD equipment, heating to 1250 ℃, preserving the temperature for 50s, keeping the pressure in the reaction chamber at 50mbar, introducing TMAl with the flow rate of 200sccm and ammonia with the flow rate of 2000sccm, and epitaxially growing AlN to form an epitaxial AlN layer with the thickness of 2 microns to obtain the AlN thin film. A schematic cross-sectional structure diagram of the AlN film prepared in this example is shown in fig. 4, where 1 is a substrate, 3 is a sputtered AlN layer, 4 is a void layer, and 5 is an epitaxial AlN layer.

Comparative example 1

Referring to Okada N, Kato N, Sato S, et al, Growth of high-quality and crack free AlN layers on sapphire substrate by multi-Growth mode modification [ J ]. Journal of Crystal Growth, 2007, 298:349-353, an AlN thin film was prepared by the following steps: controlling the temperature of the reaction chamber to be 1400 ℃, controlling the V/III ratio to be 580, 464, 348 and 232 in sequence, growing 4 AlN layers, then controlling the V/III ratio to be 116, epitaxially growing AlN, and forming an epitaxial AlN layer with the thickness of 3-4 mu m to obtain the AlN thin film.

Comparative example 2

And placing the 2-inch sapphire substrate in a reaction chamber of MOCVD equipment, heating to 1250 ℃, preserving the temperature for 50s, keeping the pressure in the reaction chamber at 50mbar, introducing TMAl and ammonia gas, and epitaxially growing AlN to obtain an AlN thin film with the thickness of 2 microns.

Comparative example 3

Spin-coating photoresist on a 2-inch sapphire substrate, drying to obtain a photoresist layer, and forming conical pits with the depth of 100nm and the upper surface width of 1000nm on the surface of the substrate by adopting a graphical transfer technology and an ion etching method;

sputtering and depositing AlN in a pit by adopting physical vapor deposition equipment and taking a target material as aluminum under the conditions of argon-nitrogen mixed gas (the flow ratio of argon to nitrogen is 1: 5) and 600 ℃, and then soaking in NMP for 10-100 min to remove residual photoresist to obtain a substrate containing a sputtered AlN layer; wherein the thickness of the sputtered AlN layer is 100 nm;

and placing the AlN layer substrate containing sputtering in a reaction chamber of MOCVD equipment, heating to 1250 ℃, preserving the temperature for 50s, keeping the pressure in the reaction chamber at 50mbar, introducing TMAl and ammonia gas, and epitaxially growing AlN to obtain an AlN thin film with the thickness of 2 mu m.

Test example

(1) And (3) optical microscope detection: the AlN thin films prepared in examples 1 to 2 were all free from cracks.

(2) And (3) atomic force microscope detection: the AlN thin films prepared in examples 1 to 2 all had atomically flat surfaces, and the surface flatness was 0.1nm or less (3 μm. times.3 μm).

(3) The results of X-ray diffractometry showing the full width at half maximum of the XRD (002) and (102) plane biaxial crystal ω rocking curves of the AlN thin films prepared in examples 1 to 2 and comparative examples 1 to 3 are shown in Table 1:

TABLE 1 results of full width at half maximum of XRD (002) and (102) plane biaxial omega rocking curves for AlN thin films prepared in examples 1 to 2 and comparative examples 1 to 3

	Half-height width of XRD (002) biaxial crystal omega rocking curve	Half-height width of XRD (102) biaxial crystal omega rocking curve
			Example 1	120	295
Example 2	135	300
			Comparative example 1	300	400
Comparative example 2	300	550
			Comparative example 3	350	600

As shown in Table 1, the method provided by the invention can greatly improve the quality of AlN crystal, and the surface is smooth and has no cracks.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.