CN103834999B - A kind of method of preparing gallium nitride monocrystal substrate by precrack - Google Patents

Abstract

The invention discloses a method for preparing a gallium nitride single crystal substrate by prefabricating cracks. The present invention integrates technologies such as pre-crack, MOCVD, HVPE and stress-controlled self-separation to process the edge of the heterogeneous substrate, then optimizes the MOCVD growth process, and cooperates with the specific pre-crack method. A gap is introduced at the edge of the substrate interface as a prefabricated crack; the stress control technology is used to realize the gradient change of the in-plane stress from the edge to the center; under a certain gradient stress, GaN is completely self-separated from the heterogeneous substrate, thereby obtaining a large size Complete GaN single crystal substrate. The invention obtains a self-supporting GaN single crystal substrate, the surface is smooth and crack-free, and the crystal quality is high. The present invention realizes the self-separation of in-situ GaN and heterogeneous substrates, does not require additional complicated equipment technologies such as laser stripping or depositing metal sacrificial layers, and has simple process and easy control, which greatly improves the practicability of the present invention.

Description

A method for preparing gallium nitride single crystal substrate by prefabricating cracks

technical field

The invention relates to the field of photoelectric materials and devices, in particular to a method for preparing a gallium nitride single crystal substrate by prefabricating cracks.

Background technique

Gallium nitride GaN-based III/V group nitrides are important wide-bandgap semiconductor materials with direct bandgap. It has broad application prospects in fields such as power electronic devices and other optoelectronic devices and electronic devices, as well as semiconductor devices under special conditions.

Due to the extremely high melting temperature and high nitrogen saturation vapor pressure, it is very difficult to prepare large-area GaN single crystals, and GaN-based devices have to be grown heterogeneously on sapphire or silicon carbide substrates with large mismatches. Although this heteroepitaxy technology based on buffer layer technology has achieved great success, this method cannot give full play to the superior performance of GaN-based semiconductor materials. The main problems are: 1. Due to the large gap between GaN and sapphire Lattice mismatch and thermal stress mismatch, resulting in 10 ⁹ cm ^-2 misfit dislocations, which seriously affect the crystal quality and reduce the luminous efficiency of LEDs; 2. Sapphire is an insulator, and its resistivity is greater than 10 ¹¹ Ωcm at room temperature , so that it is impossible to make a vertical structure device, usually only N-type and P-type electrodes can be made on the upper surface of the epitaxial layer, so the effective light-emitting area is reduced, and the photolithography and etching process in the device preparation is increased, so that The utilization rate of materials is reduced; 3. The thermal conductivity of sapphire is not good, and the thermal conductivity at 100°C is about 0.25W/cmK, which has a great impact on the performance of GaN-based devices, especially in large-area and high-power devices. The problem is very prominent; 4. In the production of GaN-based lasers, due to the high hardness of sapphire, and there is a 30-degree angle between the sapphire lattice and the GaN lattice, it is difficult to obtain the cleavage plane of the GaN-based LD epitaxial layer , and the cavity surface of GaN-based LD cannot be obtained by cleavage method, so GaN single crystal substrate is also of great significance for the fabrication of GaN-based lasers. Based on the above reasons, the only way to further improve and develop new GaN-based semiconductor lasers, high-power and high-brightness semiconductor lighting LEDs, and high-power microwave devices is to use GaN single crystals with low defect density and controllable optical and electrical properties. Homogeneous substrate material.

The current methods for growing GaN single crystal substrates include high temperature and high pressure method, ammonothermal method, sodium flux method and hydride vapor deposition (Hydride vapor ~ phase epitaxy) HVPE and other methods. The first three methods, high temperature and high pressure method, ammonothermal method and sodium cosolvent method, either require high temperature and high pressure equipment, or require active melts such as sodium and potassium, which are dangerous and require few research units. In the first ten years or so, only crystals with a size of 10 mm can be obtained, which basically cannot be used as a substrate, and are mainly used for the study of the basic properties of materials. Due to the advantages of relatively simple equipment, low cost, and fast growth speed, HVPE growth technology can grow uniform and large-sized GaN/Al ₂ O ₃ thick film composite substrates. Then, by removing foreign substrates such as sapphire by laser lift-off and other methods, a self-supporting GaN single crystal substrate can be obtained, which is currently the mainstream preparation technology for GaN single crystal substrates.

The most important problem in the preparation of GaN single crystal substrates by HVPE is how to separate GaN single crystal thick films from heterogeneous substrates such as sapphire. For the separation of the GaN single crystal thick film from the substrate, there are mainly: laser lift-off method, that is, the interface between the sapphire substrate and the GaN single crystal thick film is heated by laser to separate the GaN single crystal thick film; sacrificial lining The method of Sacrificial Substrate, the main idea is to obtain a self-supporting GaN single crystal substrate by using a substrate that can be removed by chemical corrosion or etching, such as a metal, GaAs or Si substrate; self-separation technology (self- separation), the main idea is to concentrate the stress on these insertion layers through various buffer layers, insertion layers or nano-pattern layers, combined with the adjustment of growth conditions, so that the GaN single crystal thick film is spontaneously peeled off from the sapphire substrate during the cooling stage . However, these methods have disadvantages such as complicated equipment, difficult separation, easy breakage of GaN single crystal thick film, and low yield, which makes the price of GaN single crystal substrate remain high.

Contents of the invention

Aiming at the above problems in the prior art, the present invention proposes a method for preparing a large-area GaN single crystal substrate through self-separation of prefabricated cracks at a lower cost.

The purpose of the present invention is to provide a method for preparing gallium nitride single crystal substrate by prefabricating cracks.

The preparation method of the gallium nitride single crystal substrate of the present invention comprises the following steps:

1) On the heterogeneous substrate, the metal organic chemical vapor deposition MOCVD method is used to grow the GaN single crystal thin film, and cooperate with the prefabricated crack method to introduce a gap at the edge of the interface between the GaN single crystal thin film and the heterogeneous substrate as a prefabricated crack ;2) On the GaN/heterogeneous substrate with prefabricated cracks, the GaN single crystal thick film is grown by the hydride vapor deposition HVPE method. During the growth process, the stress control technology is used to control the growth of the GaN single crystal thick film to a certain thickness , to maximize the internal stress in the GaN single crystal thick film;

3) When the internal stress in the GaN single crystal thick film reaches the maximum, stop the growth and start cooling down, control the temperature gradient and temperature distribution during the cooling process, and use the thermal expansion between the GaN single crystal thick film and the heterogeneous substrate The coefficient difference makes the stress distribution in the GaN single crystal thick film gradually decrease from the edge to the center;

4) The gradually changing stress in the GaN single crystal thick film causes the interface between GaN and the heterogeneous substrate to first appear shear force at the edge, and the prefabricated crack at the edge of the interface continues to expand inward under the action of this shear force , so that GaN is automatically separated from the edge to the center, thereby obtaining a self-separated self-supporting GaN single crystal substrate.

Among them, in step 1), the pre-crack method refers to introducing a gap at the edge of the interface between the heterogeneous substrate and the GaN single crystal film by using chemical and physical methods such as photolithography, etching, masking, and corrosion to form a V-shaped or The U-shaped notch, the bottom surface of the notch is parallel to the interface, can be used as the crack source for the next step of separation. The pre-crack method includes the lateral epitaxy method, the hanging epitaxy method, the substrate patterning method and the external baffle method, and one method can be used alone or two or more methods can be used in combination. The lateral epitaxy method refers to the formation of a mask on the surrounding surface of the heterogeneous substrate by conventional plasma-enhanced chemical vapor deposition method PECVD, photolithography or etching, and the width of the mask along the edge of the heterogeneous substrate is 20-1000 Micron, height 20-500 nanometers; then, adjust the MOCVD growth process so that the GaN grown in the unmasked region of the heterogeneous substrate exceeds the thickness of the mask, and its edge grows laterally on the mask, and the width of the lateral growth is smaller than that of the mask After the MOCVD growth is completed, the mask is completely removed by etching, so that prefabricated cracks are formed at the edge of the interface between the GaN single crystal film and the heterogeneous substrate. The hanging epitaxy method refers to first growing GaN of about 0.5-2 microns by MOCVD, and then forming a mask in a large area in the center of the surface, and only having no mask in the 20-1000 micron area at the edge; using wet etching or reaction coupled plasma (Inductively Coupled Plasma) ICP etch the GaN without mask protection on the edge, etch all the way to the interface of the heterogeneous substrate, adjust the etching process to make the etching edge steep; remove the surface mask by etching, continue MOCVD to grow GaN single crystal thin film, thickness 1-10 micrometers, adjust the process to make the side wall hanging grow in an inverted triangle shape, so as to form prefabricated cracks at the edge of the interface between the GaN single crystal film and the heterogeneous substrate. The substrate patterning method refers to patterning the edge area of the heterogeneous substrate. The shape of the pattern can be a circle, a triangle, a column, a polygon, etc. The purpose is to make this part of the area difficult to grow GaN by MOCVD epitaxial growth. , the width of the patterned area is 20-1000 microns inward along the edge of the heterogeneous substrate; then MOCVD grows a GaN single crystal thin film on the patterned heterogeneous substrate with a thickness of 1-10 microns, and adjusts the process to make the growth cross-section It is in the shape of an inverted triangle, so that prefabricated cracks are formed at the edge of the interface between the GaN single crystal thin film and the heterogeneous substrate. The external baffle method refers to the use of materials capable of high temperature and corrosion resistance to make a ring-shaped baffle; place the ring-shaped baffle on a heterogeneous substrate to cover the surrounding surface of the heterogeneous substrate; epitaxially grow a certain thickness of GaN single crystal After removing the baffles from the film, a pre-crack is formed at the edge of the interface. In these methods, the MOCVD growth process needs to be adjusted according to specific conditions.

In step 2), stress control techniques include methods for reducing stress during the growth process, such as gradient modulation, periodic modulation, low-temperature insertion layer, and hydrogen chloride reverse etching. The details of gradient modulation and periodic modulation technologies can be found in Patent No. 201010527353.9. The low-temperature insertion layer is a common technology, that is, GaN is grown at a low temperature for a short time during the growth process, and then raised to a high temperature to continue the growth; the low-temperature insertion layer can be inserted in a single layer or in multiple layers. The hydrogen chloride reverse etching method is a method in which the growth of GaN is suspended during the growth process, and the HCl gas is injected separately to etch the GaN surface, and then the GaN growth is continued. The certain thickness means that the thickness of the GaN single crystal thick film reaches 0.2 to 1.5 times the thickness of the heterogeneous substrate.

In step 3), the range of temperature gradient is 10-200°C/min; the range of temperature distribution is 0.01-50°C/mm.

In step 4), the prefabricated cracks at the edge of the interface between the GaN single crystal thick film and the heterogeneous substrate continue to expand inward under the action of shear force, so that the GaN is automatically separated from the edge to the center, and a self-separated large-scale The self-supporting GaN single crystal substrate, the thickness of the separated GaN single crystal substrate is 0.1-1.0mm, and the thickness of the GaN remaining on the heterogeneous substrate is 0.01-0.3mm.

The invention proposes a self-supporting 2-inch GaN substrate preparation method that integrates methods such as prefabricated cracks, MOCVD, HVPE and stress-controlled self-separation. Through the pre-crack method, including lateral epitaxy, hanging epitaxy, substrate patterning method, external baffle method, etc., the edge of heterogeneous substrates such as sapphire is processed, and then the MOCVD growth process is optimized, which is comparable to the specific pre-crack method. Cooperate, and finally introduce a gap at the edge of the interface of GaN/heterogeneous substrate as a prefabricated crack (parallel to the interface), which is characterized in that it is easy to expand along the direction parallel to the interface when it is subjected to a large stress. This large stress mainly comes from the lattice mismatch stress of the GaN single crystal thick film grown by HVPE and the thermal stress during the cooling process. During the subsequent HVPE thick film growth and cooling process, the stress control technology is used to realize the gradient change of the in-plane stress from the edge to the center. Since the prefabricated cracks have been prepared at the edge of the interface, they can act as the source of delamination cracks, and they are easy to propagate along the parallel interface under a certain gradient stress, resulting in complete self-separation of GaN and heterogeneous substrates, thereby obtaining large-scale Complete GaN single crystal substrate. Advantages of the present invention:

The present invention adopts a lower-cost method for preparing a self-separated GaN single crystal substrate through a prefabricated crack method, and successfully obtains a self-separated 2-inch transparent self-supporting GaN single crystal substrate with a smooth surface and no cracks, and high crystal quality , the thickness reaches 320μm. The present invention realizes the self-separation of in-situ GaN and heterogeneous substrates, does not require additional complicated equipment technologies such as laser stripping or depositing metal sacrificial layers, and has simple process and easy control, which greatly improves the practicability of the present invention.

Description of drawings

Fig. 1 is the schematic diagram of the technological process of forming prefabricated cracks at the edge of the interface between heterogeneous substrate and GaN single crystal thin film by lateral epitaxy in the present invention;

Fig. 2 is the schematic diagram of the technological process of forming prefabricated cracks at the edge of the interface between heterogeneous substrate and GaN single crystal thin film by hanging epitaxy in the present invention;

3 is a schematic diagram of the process flow of the present invention to form prefabricated cracks at the edge of the interface between the heterogeneous substrate and the GaN single crystal thin film by using the external baffle method;

Fig. 4 is an effect diagram of a 2-inch self-supporting GaN single crystal substrate obtained by the pre-crack method of the present invention.

detailed description

The present invention will be further described through the embodiments below in conjunction with the accompanying drawings.

Embodiment one

In this embodiment, the method for preparing a gallium nitride single crystal substrate using the lateral epitaxy method includes the following steps:

1) On the heterogeneous substrate, the metal-organic chemical vapor deposition MOCVD method is used to grow the GaN single crystal thin film, and cooperate with the pre-crack method, the circular edge of the interface between the GaN single crystal thin film and the c-plane sapphire heterogeneous substrate A gap is introduced as a pre-crack at :

a) Form a silicon dinitride SiO ₂ mask 21 on the surrounding surface of the sapphire heterogeneous substrate 1 by conventional plasma-enhanced chemical vapor deposition method PECVD, photolithography and etching technology: first, use acetone, alcohol and Clean the surface of the commercial sapphire heterogeneous substrate with ion water, put the cleaned sapphire heterogeneous substrate into the PECVD reaction chamber to deposit SiO ₂ film with a thickness of 20-500 nanometers; then, use photolithography and etching to remove the SiO ₂ film , all other _SiO2 films on the surface except the edge area are etched away, and a _SiO2 mask 21 is formed within a certain width of the peripheral edge of the heterogeneous substrate. As shown in Figure 1(a);

b) Place it in the MOCVD reaction chamber for one growth to form a GaN single crystal thin film 3: first raise the temperature to a temperature lower than 600°C to grow a low-temperature buffer layer, and the thickness of the buffer layer is between 10 and 60 nanometers; GaN is grown at a high temperature between 900 and 1100°C. When the thickness of GaN exceeds the height of the SiO ₂ mask, the lateral growth rate of GaN is increased by controlling the V/III ratio, so that GaN grows laterally on the surface of the SiO ₂ mask to cover the edge area SiO ₂ mask to form a GaN single crystal thin film 3, as shown in Figure 1(b);

c) Etching and removing the SiO2 mask to form prefabricated cracks: After the MOCVD growth is completed, put it into HF acid, and use HF acid etching to remove all the SiO2 mask, thereby forming at the edge of the interface between GaN and sapphire heterogeneous substrate Prefabricated crack 2, as shown in Figure 1(c);

2) Surface treatment before HVPE growth, including organic cleaning and oxide layer removal; then, put it into the HVPE reaction chamber for secondary growth to form GaN single crystal thick film 4: Control the continued growth of GaN single crystal film, the growth process It is necessary to adopt the stress control technology of gradient modulation and periodic modulation method to prevent cracks in GaN single crystal thick film, and at the same time ensure high crystal quality and surface quality. The thickness of the single crystal thick film 4 reaches 0.2 to 1.5 times the thickness of the sapphire substrate, as shown in Figure 1(d);

3) When the GaN single crystal thick film grows to the maximum stress thickness, start the cooling process: strictly control the temperature gradient and temperature distribution during the cooling process, so that the temperature gradient of the cooling can be controlled to 10-200 °C/min, the radial temperature The distribution is controlled to 0.01-50°C/mm, and the stress distribution in the GaN single crystal thick film is gradually reduced from the edge to the center by using the difference in thermal expansion coefficient between the GaN single crystal thick film and the heterogeneous substrate;

4) The gradually changing stress in the GaN single crystal thick film will cause the interface between GaN and the heterogeneous substrate to first appear shear force at the edge, and the prefabricated crack at the edge of the interface will continue to expand inward under the action of the shear force , so that GaN is automatically separated from the edge to the center, and a self-separated 2-inch self-supporting GaN single crystal substrate is obtained.

Using this embodiment, a self-separated 2-inch complete GaN single crystal substrate without cracks has been obtained, as shown in FIG. 4 .

Embodiment two

In this embodiment, the method for preparing a gallium nitride single crystal substrate using the hanging epitaxy method includes the following steps:

1) a) Clean the surface of the commercial sapphire heterogeneous substrate with acetone, alcohol and deionized water; put the cleaned sapphire substrate into the reaction chamber of the MOCVD equipment, and epitaxially grow nitride on the surface of the sapphire heterogeneous substrate Gallium 31, with a thickness of 0.5-2 microns, as shown in Figure 2(a);

b) Then put it into the PECVD reaction chamber to deposit SiO ₂ film with a thickness of 20-500 nanometers; then, use photolithography and HF acid to etch and remove the SiO ₂ film in the area of 20-1000 microns on the peripheral edge of the heterogeneous substrate , and keep SiO ₂ in a large area in the center of the surface to form a mask 22, as shown in Figure 2(b);

c) Use ICP to etch GaN without SiO ₂ protection on the edge, etch to the interface between GaN and sapphire, adjust the etching process to make the etching edge steep, and the width of the etched ring area is 20-1000 microns, as shown in the figure 2(c);

d) Remove the _SiO2 mask by HF acid etching, as shown in Fig. 2(d);

e) Put it into the MOCVD reaction chamber for the second growth, with a thickness of 1-10 microns, to form a GaN single crystal thin film 3, and adjust the process to make the side wall hang and grow in an inverted triangle shape, so that the difference between the GaN single crystal thin film 3 and sapphire A prefabricated crack 2 is formed at the interface boundary between the solid substrates 1, as shown in Fig. 2(e);

2) Surface treatment before HVPE growth, including organic cleaning and oxide layer removal; then, put it in the HVPE reaction chamber for HVPE growth to form GaN single crystal thick film: to control the continuous growth of GaN single crystal film, the growth process needs to use The stress control technology of gradual modulation plus periodic modulation prevents cracks in the GaN single crystal thick film, while ensuring high crystal quality and surface quality, the stress will gradually increase with the increase of thickness, and control the GaN single crystal grown by HVPE The thickness of the thick film reaches 0.2 to 1.5 times the thickness of the sapphire heterogeneous substrate, as shown in Figure 2(f);

3) When the GaN single crystal thick film grows to the maximum stress thickness, start the cooling process: strictly control the temperature gradient and temperature distribution during the cooling process, so that the temperature gradient of the cooling can be controlled to 10-200 °C/min, the radial temperature The distribution is controlled to 0.01-50°C/mm, and the stress distribution in the GaN single crystal thick film is gradually reduced from the edge to the center by using the difference in thermal expansion coefficient between the GaN single crystal thick film and the heterogeneous substrate;

4) The gradually changing stress in the GaN single crystal thick film will cause the interface between GaN and the heterogeneous substrate to first appear shear force at the edge, and the prefabricated crack at the edge of the interface will continue to expand inward under the action of the shear force , so that GaN is automatically separated from the edge to the center, and a self-separated 2-inch self-supporting GaN single crystal substrate is obtained.

Embodiment three

In this embodiment, the method for preparing a gallium nitride single crystal substrate using an external baffle method includes the following steps:

1) a) Clean the surface of the commercial sapphire heterogeneous substrate with acetone, alcohol and deionized water, put the cleaned sapphire heterogeneous substrate into the MOCVD reaction chamber, and place the circular baffle 23 on the sapphire , to cover the edge area of the sapphire, and the width of the covered ring area is 20-1000 microns, as shown in Figure 3(a);

b) Then epitaxially grow GaN single crystal film 3 on the surface of sapphire, with a thickness of 0.5-4 microns, as shown in Figure 3(b); the ring-shaped baffle can be made of metal molybdenum, quartz or graphite, which can withstand high temperature and corrosion Manufactured and composed of two semicircular rings for removal;

c) Take out the sample, and carefully take out the two semicircular baffles to form a prefabricated crack 2 at the edge of the interface between the GaN single crystal thin film and the sapphire heterogeneous substrate, as shown in Figure 3(c);

2) Surface treatment before HVPE growth, including organic cleaning and oxide layer removal; then, put it in the HVPE reaction chamber for HVPE growth to form GaN single crystal thick film: to control the continuous growth of GaN single crystal film, the growth process needs to use The stress control technology of gradual modulation plus periodic modulation prevents cracks in the GaN single crystal thick film, while ensuring high crystal quality and surface quality, the stress will gradually increase with the increase of thickness, and control the GaN single crystal grown by HVPE The thickness of the thick film reaches 0.2 to 1.5 times the thickness of the sapphire heterogeneous substrate, as shown in Figure 2(f);

3) When the GaN single crystal thick film grows to the maximum stress thickness, start the cooling process: strictly control the temperature gradient and temperature distribution during the cooling process, so that the temperature gradient of the cooling can be controlled to 10-200 °C/min, the radial temperature The distribution is controlled to 0.01-50°C/mm, and the stress distribution in the GaN single crystal thick film is gradually reduced from the edge to the center by using the difference in thermal expansion coefficient between the GaN single crystal thick film and the heterogeneous substrate;

4) The gradually changing stress in the GaN single crystal thick film will cause the interface between GaN and the heterogeneous substrate to first appear shear force at the edge, and the prefabricated crack at the edge of the interface will continue to expand inward under the action of the shear force , so that GaN is automatically separated from the edge to the center, and a self-separated 2-inch self-supporting GaN single crystal substrate is obtained.

The 2-inch self-supporting GaN single crystal substrate obtained by the above preparation method is shown in FIG. 4 .

Finally, it should be noted that the purpose of publishing the implementation is to help further understand the present invention, but those skilled in the art can understand that various replacements and modifications can be made without departing from the spirit and scope of the present invention and the appended claims. It is possible. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the protection scope of the present invention is subject to the scope defined in the claims.

Claims (10)

1. a preparation method of gallium nitride single crystal substrate, is characterized in that, described preparation method comprises the following steps: 1) On the heterogeneous substrate, the metal organic chemical vapor deposition method is used to grow the GaN single crystal thin film, and cooperate with the prefabricated crack method to introduce a gap at the edge of the interface between the GaN single crystal thin film and the heterogeneous substrate as a prefabricated crack ; 2) On the GaN/heterogeneous substrate with prefabricated cracks, the GaN single crystal thick film is grown by the hydride vapor deposition HVPE method. During the growth process, the stress control technology is used to control the growth of the GaN single crystal thick film to a certain thickness. Maximize the internal stress in GaN single crystal thick film; 3) When the internal stress in the GaN single crystal thick film reaches the maximum, stop the growth and start cooling down, control the temperature gradient and temperature distribution during the cooling process, and use the thermal expansion between the GaN single crystal thick film and the heterogeneous substrate The coefficient difference makes the stress distribution in the GaN single crystal thick film decrease from the edge to the center gradient; 4) The gradient stress in the GaN single crystal thick film causes the interface between GaN and the heterogeneous substrate to first appear shear force at the edge, and the prefabricated crack at the edge of the interface continues to expand inward under the action of this shear force, The GaN is automatically separated from the edge to the center, thereby obtaining a self-separated self-supporting GaN single crystal substrate. 2. The preparation method according to claim 1, characterized in that, in step 1), the prefabricated crack method refers to the use of photolithography, etching, masking and corrosion chemical and physical methods, on the heterogeneous substrate and GaN single The slit is introduced into the edge of the interface of the thin film to form a V-shaped or U-shaped incision, and the bottom surface of the incision is parallel to the interface; the prefabricated crack method includes the lateral epitaxy method, the hanging epitaxy method, the substrate patterning method and the external baffle method. Each method is used alone or two or more methods are used in combination. 3. The preparation method according to claim 2, characterized in that, the lateral epitaxy method refers to the use of conventional plasma-enhanced chemical vapor deposition (PECVD), photolithography or etching methods to form Mask, the width of the mask inward along the edge of the heterogeneous substrate is 20-1000 microns, and the height is 20-500 nanometers; then, adjust the MOCVD growth process so that the GaN grown in the unmasked region of the heterogeneous substrate exceeds the thickness of the mask , its edge grows laterally on the mask, and the width of the lateral growth is smaller than the width of the mask; after the MOCVD growth is completed, the mask is completely removed by etching, so that at the edge of the interface between the GaN single crystal thin film and the heterogeneous substrate Formation of preformed cracks. 4. The preparation method according to claim 2, characterized in that, the hanging epitaxy method refers to first growing 0.5-2 micron GaN by MOCVD, and then forming a mask in the central area of the surface, and not masking in the edge 20-1000 micron area. film; use wet etching or reaction-coupled plasma ICP to etch the GaN without mask protection on the edge, etch to the interface of the heterogeneous substrate, adjust the etching process to make the etching edge steep; etch to remove the mask on the surface Film, continue to grow GaN single crystal film by MOCVD, with a thickness of 1-10 microns, adjust the process to make the side wall hang and grow in an inverted triangle shape, so as to form prefabricated cracks at the edge of the interface between the GaN single crystal film and the heterogeneous substrate. 5. The preparation method according to claim 2, wherein the substrate patterning method refers to performing patterning processing on the edge region of the heterogeneous substrate, and the shape of the pattern includes circle, triangle, column, polygon , so that this part of the region is not easy to grow GaN by MOCVD epitaxial growth, and the width of the patterned region is 20-1000 microns inward along the edge of the heterogeneous substrate; then MOCVD grows a GaN single crystal film on the patterned heterogeneous substrate, The thickness is 1-10 microns, and the process is adjusted so that the growth section is in the shape of an inverted triangle, so that prefabricated cracks are formed at the edge of the interface between the GaN single crystal film and the heterogeneous substrate. 6. The preparation method according to claim 2, wherein the method of adding an external baffle refers to making a ring-shaped baffle from a high-temperature-resistant and corrosion-resistant material; placing the ring-shaped baffle on a heterogeneous substrate above, covering the surrounding surface of the heterogeneous substrate; after the GaN single crystal thin film is epitaxially grown, the baffle is removed, and a prefabricated crack is formed at the edge of the interface. 7. The preparation method according to claim 1, characterized in that, in step 2), the stress control techniques include gradual modulation, periodic modulation, low-temperature insertion layer and methods for reducing stress during the growth process of hydrogen chloride reverse etching. 8 . The preparation method according to claim 1 , wherein in step 2), the certain thickness means that the thickness of the GaN single crystal thick film reaches 0.2-1.5 times of the thickness of the heterogeneous substrate. 9. The preparation method according to claim 1, characterized in that, in step 3), the range of temperature gradient is 10-200°C/min; the range of temperature distribution is 0.01-50°C/mm. 10. The preparation method according to claim 1, characterized in that, in step 4), the thickness of the separated GaN single crystal substrate is 0.1-1.0 mm, and the thickness of GaN remaining on the heterogeneous substrate is 0.01-1.0 mm. 0.3mm.