Device for preparing aluminum nitride single crystal and method for stably growing aluminum nitride single crystal for long time

Abstract

The invention relates to the technical field of aluminum nitride single crystal growth, and particularly discloses a device for preparing an aluminum nitride single crystal and a method for stably growing the aluminum nitride single crystal for a long time. The device for preparing the aluminum nitride single crystal comprises a lower tungsten crucible, a tungsten wafer and an upper tungsten crucible which are sequentially distributed from bottom to top, and further comprises a heat shield covering the upper tungsten crucible, the lower tungsten crucible and the upper tungsten crucible are each provided with a containing cavity used for containing an aluminum nitride sintered material, openings of the lower tungsten crucible and the upper tungsten crucible are sealed and covered by the tungsten wafers, and the containing cavity of the lower tungsten crucible is a circular-truncated-cone-shaped cavity with the diameter gradually decreasing from top to bottom. And a heat insulation space is formed between the upper tungsten crucible and the heat insulation cover. Through the unique design of the device structure for preparing the aluminum nitride single crystal, the growth rate of the aluminum nitride single crystal is stable and controllable, and high-speed growth, expanding growth and thick crystal growth of the aluminum nitride single crystal are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum nitride single crystal growth, and particularly relates to a device for preparing aluminum nitride single crystals and a method for stably growing aluminum nitride single crystals for a long time. Background Art

[0002] The physical vapor transport (PVT) method is currently the main method for preparing high-quality aluminum nitride single crystals. The most common way to obtain high-purity and high-crystallinity aluminum nitride single crystals is to use high-quality aluminum nitride single crystals as seeds and grow them by homoepitaxy in a metal high-temperature furnace with high-purity tungsten as the thermal insulation structure. The aluminum nitride single crystals grown in the high-purity tungsten metal high-temperature furnace have low impurity content, high crystallinity quality of the aluminum nitride single crystals, good repeatability of the growth process, and the maintenance cost of the growth equipment is significantly lower than that of the graphite high-temperature furnace with graphite as the thermal insulation structure.

[0003] However, limited by the high melting point and high processing difficulty of the metal tungsten material, there are the following problems in growing aluminum nitride single crystals in a high-temperature furnace with metal tungsten as the thermal insulation structure: (1) Compared with the graphite thermal insulation material in the graphite furnace that can be machined into any complex structure, the structure of the tungsten thermal insulation material in the metal tungsten furnace is usually sheet-shaped or cylindrical. The internal temperature distribution of the metal tungsten furnace with a structure similar to that of the tungsten thermal insulation material usually shows a large radial temperature difference and a small axial temperature difference. This leads to the problem of diameter shrinkage of the powder during the growth of aluminum nitride single crystals due to the action of radial high temperature. For example, since the heater surrounds the crucible, the temperature distribution shows a decreasing trend from the outside to the inside. Therefore, the part of the aluminum nitride powder that volatilizes first is usually closest to the outside of the heater. As the growth progresses, the powder on the outside gradually volatilizes, and the diameter of the powder continuously shrinks. The resulting problems of growth rate decay and ingot diameter shrinkage have become the main obstacles restricting the high-speed growth, diameter expansion growth, and thick crystal growth of aluminum nitride single crystals. (2) In terms of the regulation of the growth rate of aluminum nitride single crystals, the conventional method is to regulate the growth rate by changing the density, particle size, and packing density of the aluminum nitride powder in the growth zone. However, the states of the above three factors will change significantly during the growth process of aluminum nitride single crystals. For example, the powder close to the inner wall of the crucible is closer to the heater of the high-temperature furnace, and the temperature in this area is significantly higher than that of the powder in the central area of the crucible. Therefore, under the action of the temperature difference driving force, the sublimated aluminum nitride gas-phase components preferentially transport and deposit into the pores between the powder particles in the central area, resulting in an increase in the density and packing density of the powder in the central area, and ultimately causing a drastic change in the growth rate of the single crystal during the growth process. Summary of the Invention

[0004] In view of the problems such as the reduction of the powder diameter and the shrinkage of the ingot diameter caused by the inability of the powder to volatilize or deposit stably for a long time and the unstable growth rate during the growth process of aluminum nitride single crystals, the present invention provides an apparatus for preparing aluminum nitride single crystals and a method for stably growing aluminum nitride single crystals for a long time. Through the design of the unique structure of the apparatus for preparing aluminum nitride single crystals, the growth rate of aluminum nitride single crystals is stable and controllable, realizing the high-speed growth, diameter expansion growth and thick crystal growth of aluminum nitride single crystals.

[0005] To solve the above technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides an apparatus for preparing aluminum nitride single crystals, which includes a lower tungsten crucible, a tungsten wafer and an upper tungsten crucible distributed in sequence from bottom to top, and further includes a heat insulation cover covering the outside of the upper tungsten crucible; the lower tungsten crucible and the upper tungsten crucible respectively have accommodation cavities for containing aluminum nitride sintered powder, and the openings of the lower tungsten crucible and the upper tungsten crucible are both covered by the tungsten wafer. The accommodation cavity of the lower tungsten crucible is a frustum-shaped chamber with a diameter gradually decreasing from top to bottom; a heat insulation space is formed between the upper tungsten crucible and the heat insulation cover.

[0006] Compared with the prior art, the apparatus for preparing aluminum nitride single crystals provided by the present invention uses a heat insulation cover to shield the radial radiant heat of the high-temperature furnace heater, thus effectively avoiding the problem of diameter reduction of the aluminum nitride sintered powder in the upper tungsten crucible during the growth process; on this basis, the lower tungsten crucible has a unique frustum-shaped chamber, which can ensure that the aluminum nitride sintered powder contained therein always keeps in contact with the inner wall of the lower tungsten crucible, so that the sublimated aluminum nitride gas components can volatilize stably and continuously. Then, the latent heat of crystallization released by sublimation can stably and continuously heat the upper tungsten crucible above the tungsten wafer, thereby realizing the stable and continuous volatilization of the aluminum nitride sintered powder contained therein, ensuring that the aluminum nitride single crystal maintains a stable and continuous growth rate, and having high market application value.

[0007] Preferably, the included angle between the inner side wall of the lower tungsten crucible and its top surface ≤ 75° (more preferably 45° - 75°).

[0008] Preferably, the lower tungsten crucible, the tungsten wafer, the upper tungsten crucible and the heat insulation cover are coaxially placed, and the opening of the heat insulation cover is covered by the tungsten wafer.

[0009] Preferably, the upper tungsten crucible includes a through crucible body and a tungsten substrate covering the top of the crucible body, and the tungsten substrate has a growth position for placing an aluminum nitride seed crystal.

[0010] In the upper tungsten crucible of the present invention, the crucible body and the tungsten substrate can be designed integrally or separately.

[0011] Preferably, the material of the heat insulation cover is tungsten.

[0012] Preferably, the heat shield includes a through cylindrical main body and a circular top cover covering the top of the cylindrical main body.

[0013] In the present invention, the circular top cover of the heat shield has the effect of slowing down the escape of the gaseous components of aluminum nitride from the inside of the heat shield to the outside. In the heat shield of the present invention, the cylindrical main body and the circular top cover can be integrally designed or separately designed.

[0014] The present invention has no special requirements for the diameter difference between the heat shield and the upper tungsten crucible, nor for the height of the heat shield and the upper tungsten crucible, as long as they do not contact each other. For example, the diameter difference between the heat shield and the upper tungsten crucible can be 10 mm. The heat shield can isolate the heat radiation of the heater so that it cannot directly act on the upper tungsten crucible, thereby preventing the edge temperature of the aluminum nitride sintered material in the upper tungsten crucible from being too high and volatilizing prior to the aluminum nitride sintered material in the lower tungsten crucible.

[0015] In a second aspect, the present invention provides a method for growing aluminum nitride single crystals stably for a long time by using the device for preparing aluminum nitride single crystals described above, comprising the following steps: S1. Place an aluminum nitride seed crystal in the accommodating cavity of the upper tungsten crucible and sinter it to obtain an upper tungsten crucible thermally bonded with the aluminum nitride seed crystal; the aluminum nitride seed crystal is located on the top surface of the upper tungsten crucible; S2. Place the first aluminum nitride sintered material in the accommodating cavity of the lower tungsten crucible, and sequentially place a tungsten wafer and the upper tungsten crucible thermally bonded with the aluminum nitride seed crystal on the top of the lower tungsten crucible. The upper tungsten crucible also contains a second aluminum nitride sintered material; cover the upper tungsten crucible with a heat shield to form an aluminum nitride single crystal growth structure; The first aluminum nitride sintered material is attached to the inner wall of the lower tungsten crucible; the longitudinal section of the second aluminum nitride sintered material is in an inverted U shape, and the top of the second aluminum nitride sintered material has a porous structure; S3. Place the aluminum nitride single crystal growth structure coaxially in the upper middle part of the heater of the high-temperature furnace and grow it in a nitrogen atmosphere to obtain an aluminum nitride single crystal.

[0016] The method for growing aluminum nitride single crystals with long-term stability provided by the present invention has a unique accommodation cavity in the lower tungsten crucible (the diameter gradually decreases from top to bottom). During the growth process of aluminum nitride single crystals, the first aluminum nitride sintered material always adheres to the inner wall of the lower tungsten crucible, thereby ensuring the stable and continuous volatilization of the gaseous components of aluminum nitride. The gaseous components of aluminum nitride are transported and sublimated and deposited on the bottom of the tungsten wafer under the action of the temperature difference driving force. The sublimation of the gaseous components of aluminum nitride releases a large amount of latent heat of crystallization to the tungsten wafer, achieving the effect of stably and continuously heating the tungsten wafer, so that the bottom of the second aluminum nitride sintered material located above the tungsten wafer can stably and continuously volatilize to produce gaseous components of aluminum nitride under the action of high temperature. The second aluminum nitride sintered material has a special hollow structure and pores, enabling the sublimated gaseous components of aluminum nitride to be efficiently transported to the surface of the aluminum nitride seed crystal. The gaseous components of aluminum nitride are transported to the surface of the aluminum nitride seed crystal through the pores at the top of the second aluminum nitride sintered material, completing the uniform growth of aluminum nitride single crystals. Therefore, the present invention can effectively control the sublimation rate of the second aluminum nitride sintered material and ultimately stably control the growth rate of aluminum nitride single crystals only by adjusting the density of the first aluminum nitride sintered material.

[0017] It should be noted that in the present invention, the "aluminum nitride single crystal growth structure" refers to a device for preparing aluminum nitride single crystals with a first aluminum nitride sintered material, a second aluminum nitride sintered material, and an aluminum nitride seed crystal. The aluminum nitride seed crystal is thermally bonded to the exact middle of the tungsten substrate.

[0018] Preferably, in S1, the diameter of the aluminum nitride seed crystal is 25 mm to 185 mm (more preferably 35 mm to 175 mm), and the thickness is 0.5 mm to 1 mm.

[0019] Preferably, in S1, the diameter of the tungsten substrate is 25 mm to 35 mm longer than the diameter of the aluminum nitride seed crystal.

[0020] Exemplarily, in S1, the sintering is carried out in an isostatic pressing furnace.

[0021] Preferably, in S1, the sintering temperature is 2200 °C to 2300 °C, the sintering load is 9 GPa to 11 GPa, the air pressure is 400 mbar to 1200 mbar, and the sintering time is 4.5 h to 6 h.

[0022] Preferably, in S2, the preparation method of the first aluminum nitride sintered material includes the following steps: Fill aluminum nitride powder in the lower tungsten crucible and perform the first sintering to obtain the first aluminum nitride sintered material.

[0023] Exemplarily, in S2, the purity of the aluminum nitride powder is above 99.9%.

[0024] Exemplarily, in S2, the first sintering is carried out in a closed high-temperature furnace.

[0025] Further preferably, in S2, the temperature of the first sintering is 2200° C. to 2300° C., the gas pressure is 400 mbar to 1200 mbar, and the sintering time is 9 h to 12 h.

[0026] Further preferably, in S2, the packing density of the aluminum nitride powder is 500 kg / m 3 ~2500kg / m 3 .

[0027] In the present invention, the particle size of the aluminum nitride powder affects its packing density. By adjusting the packing density of the aluminum nitride powder, the sublimation amount of the first aluminum nitride sintered material can be changed, thereby adjusting the crystallization latent heat released by its desublimation, thereby achieving the purpose of adjusting the aluminum nitride crystal growth rate.

[0028] Preferably, in S2, the height of the lower tungsten crucible is 30 mm to 80 mm.

[0029] Preferably, in S2, the diameter of the upper plane of the first aluminum nitride sintered material is 60 mm to 210 mm, the diameter of the lower plane is 20 mm to 50 mm, and the height of the first aluminum nitride sintered material is smaller than the height of the lower tungsten crucible.

[0030] The present invention does not limit the distance between the upper surface of the first aluminum nitride sinter and the tungsten disc, as long as the two do not contact. This is because the density of the first aluminum nitride sinter is necessarily lower than the density of the sublimated aluminum nitride sinter after solidification on the tungsten disc (the density of polycrystalline is similar to that of single crystal, and the density of the sinter is even lower due to the presence of pores). Therefore, as long as the first aluminum nitride sinter and the tungsten disc do not contact, the corresponding mass and heat transfer can be achieved smoothly.

[0031] Preferably, in S2, the method for preparing the second aluminum nitride sintered material comprises the following steps: Large-particle aluminum nitride powder and small-particle aluminum nitride powder are respectively filled in the center and edge of the cylindrical tungsten crucible. After the medium-particle aluminum nitride powder is further filled on the large-particle aluminum nitride powder and the small-particle aluminum nitride powder, the cylindrical tungsten crucible is subjected to a second sintering. After the sintered material is taken out, the sintered material of the large-particle aluminum nitride powder is removed to obtain a second aluminum nitride sintered material.

[0032] It should be noted that the present invention does not limit the order of filling the large-particle aluminum nitride powder and the small-particle aluminum nitride powder.

[0033] In the present invention, the side surface of the second aluminum nitride sintered material with an inverted U-shaped longitudinal section is sintered from fine-grained aluminum nitride powder, and the top is sintered from medium-grained aluminum nitride powder. The contact area between large-grained aluminum nitride powder particles is small, and it is difficult to form a hard cake after sintering. No strong connection can be formed between the powder particles, so its sintered material is relatively easy to remove; the contact area between fine-grained aluminum nitride powder particles is large, and a stable structure with a certain strength is easily formed after sintering; the medium-grained aluminum nitride powder at the top of the inverted U-shaped structure takes into account both the sintering property and the pore structure. After sintering, the medium-grained aluminum nitride powder can form a multi-porous sintered body with a certain strength, enabling the gaseous components of aluminum nitride to be transmitted upward through these pores to complete the growth of aluminum nitride single crystals.

[0034] Further preferably, in S2, the particle size of the large-grained aluminum nitride powder is 2 μm or more.

[0035] Further preferably, in S2, the particle size of the fine-grained aluminum nitride powder is 0.2 μm to 0.5 μm.

[0036] Further preferably, in S2, the particle size of the medium-grained aluminum nitride powder is 0.5 μm to 1 μm.

[0037] Exemplarily, the purity of the large-grained aluminum nitride powder, the fine-grained aluminum nitride powder, and the medium-grained aluminum nitride powder is all above 99.9%.

[0038] Exemplarily, in S2, the second sintering is carried out in a closed high-temperature furnace.

[0039] Further preferably, in S2, the temperature of the second sintering is 2200 °C to 2300 °C, the air pressure is 400 mbar to 1200 mbar, and the sintering time is 9 h to 12 h.

[0040] Preferably, in S2, the outer diameter of the second aluminum nitride sintered material is 50 mm to 200 mm, the thickness is 8 mm to 12 mm, and the height is 20 mm to 50 mm.

[0041] It should be noted that the longitudinal section of the second aluminum nitride sintered material is in an inverted U shape, and the thickness of the second aluminum nitride sintered material represents the wall thickness of the side surface and the thickness of the top.

[0042] The present invention has no special requirements for the inner diameter of the upper tungsten crucible, as long as the second aluminum nitride sintered material can be placed in it. The second aluminum nitride sintered material can be in contact with the inner wall of the upper tungsten crucible or not.

[0043] Further preferably, in S2, the diameter of the upper plane of the first aluminum nitride sintered material is 8 mm to 12 mm larger than the outer diameter of the second aluminum nitride sintered material.

[0044] Preferably, in S2, the height of the upper tungsten crucible is 30 mm to 80 mm.

[0045] Preferably, in S2, the distance from the lower plane of the tungsten substrate to the upper plane of the second aluminum nitride sintered material is 10 mm to 50 mm.

[0046] Through a large number of experiments, the present invention found that if the above spacing is less than 10 mm, the growth space of the crystal is limited, and an aluminum nitride single crystal with a thickness greater than 10 mm cannot be obtained; the partial pressure distribution of aluminum and nitrogen gas-phase components has a large difference under the same temperature gradient condition, the nitrogen element remains basically constant, and the concentration of aluminum element gradually decreases from bottom to top. If the above spacing is greater than 50 mm, the aluminum and nitrogen elements in the aluminum nitride gas-phase components will deviate from the stoichiometric ratio due to the long-distance transmission, resulting in a decrease in the crystallization quality of the aluminum nitride crystal.

[0047] More preferably, in S2, the diameter of the aluminum nitride seed crystal is equal to the inner diameter of the second aluminum nitride sintered material.

[0048] Through a large number of experiments, the present invention found that if the diameter of the aluminum nitride seed crystal is smaller than the inner diameter of the second aluminum nitride sintered material, that is, the concentration of aluminum and nitrogen gas-phase components required for the growth of the corresponding small-sized aluminum nitride seed crystal is relatively small. In this case, the excess aluminum and nitrogen gas-phase components will be deposited on the surface and edge of the aluminum nitride seed crystal in the form of polycrystals, resulting in too high a growth rate of aluminum nitride and the appearance of parasitic polycrystals at the edge of the aluminum nitride seed crystal, causing a decrease in the crystallization quality; if the diameter of the aluminum nitride seed crystal is larger than the inner diameter of the second aluminum nitride sintered material, it will lead to the concentration of aluminum and nitrogen gas-phase components being lower than the concentration required for the growth of the aluminum nitride seed crystal, also resulting in a large number of defects on the surface of the aluminum nitride single crystal and causing a decrease in the crystallization quality.

[0049] Preferably, in S3, the growth temperature is 2200 °C to 2300 °C, the pressure is 500 mbar to 800 mbar, and the heat preservation and pressure maintenance time is 100 h to 140 h.

[0050] More preferably, in S3, the temperature is raised to 2200 °C to 2300 °C at a heating rate of 210 °C / h to 460 °C / h (more preferably 230 °C / h to 440 °C / h), and the pressure of the high-temperature furnace is maintained at 500 mbar to 800 mbar during the heating process. Description of the Drawings

[0051] Figure 1 is a schematic structural diagram of the device for preparing aluminum nitride single crystal in the present invention; Figure 2 is a schematic diagram of the placement position of the aluminum nitride single crystal growth structure in the method for growing aluminum nitride single crystal stably for a long time in the present invention; Figure 3Schematic diagram of the filling positions of aluminum nitride powder materials with different particle sizes in the preparation method of the second aluminum nitride sintered material of the present invention; In the figure, 1 is the first aluminum nitride sintered material; 2 is the lower tungsten crucible; 3 is the tungsten wafer; 4 is the upper tungsten crucible; 5 is the heat insulation cover; 6 is the second aluminum nitride sintered material; 6-1 is the large-particle-size aluminum nitride powder material; 6-2 is the small-particle-size aluminum nitride powder material; 6-3 is the medium-particle-size aluminum nitride powder material; 7 is the aluminum nitride seed crystal; 8 is the tungsten substrate; 9 is the cylindrical tungsten crucible; 10 is the heater. Detailed implementation manners

[0052] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] Please refer to Figure 1 , the present invention provides a device for preparing aluminum nitride single crystals, which includes a lower tungsten crucible 2, a tungsten wafer 3 and an upper tungsten crucible 4 that are sequentially distributed from bottom to top, and further includes a heat insulation cover 5 covering the outside of the upper tungsten crucible 4; the lower tungsten crucible 2 and the upper tungsten crucible 4 respectively have accommodation cavities for containing aluminum nitride sintered materials (1 and 6), and the openings of the lower tungsten crucible 2 and the upper tungsten crucible 4 are both sealed by the tungsten wafer 3, and the accommodation cavity of the lower tungsten crucible 2 is a frustum-shaped cavity with a diameter gradually decreasing from top to bottom; a heat insulation space is formed between the upper tungsten crucible 4 and the heat insulation cover 5.

[0054] In some embodiments, the included angle between the inner side wall of the lower tungsten crucible 2 and its top surface ≤ 75°.

[0055] In some embodiments, the included angle between the inner side wall of the lower tungsten crucible 2 and its top surface is 45° - 75°.

[0056] In some embodiments, the lower tungsten crucible 2, the tungsten wafer 3, the upper tungsten crucible 4 and the heat insulation cover 5 are coaxially placed, and the opening of the heat insulation cover 5 is sealed by the tungsten wafer 3.

[0057] In some embodiments, the upper tungsten crucible 4 includes a through crucible body and a tungsten substrate 8 covering the top of the crucible body, and the tungsten substrate 8 has a growth position for placing an aluminum nitride seed crystal 7.

[0058] In the upper tungsten crucible of the present invention, the crucible body and the tungsten substrate can be designed integrally (such as Figure 1 ), or can be designed separately (such as Figure 2 ).

[0059] In some embodiments, the heat insulation cover 5 includes a through cylindrical main body and a circular top cover covering the top of the cylindrical main body.

[0060] In the present invention, materials without special instructions are all commercially available products.

[0061] Example 1 This example provides a method for long-term stable growth of aluminum nitride single crystals using a device for preparing aluminum nitride single crystals (please refer to Figure 2 ), including the following steps: Sa. Preparation of the first aluminum nitride sintered material 1 and the second aluminum nitride sintered material 6: The preparation method of the first aluminum nitride sintered material 1 includes the following steps: Fill aluminum nitride powder in the lower tungsten crucible 2, with a filling density of 800 kg / m 3 , place it in a sealed high-temperature furnace, and conduct the first sintering at 2200 °C and 400 mbar, holding the temperature and pressure for 12 h to obtain the first aluminum nitride sintered material 1.

[0062] The preparation method of the second aluminum nitride sintered material 6 (see Figure 3 ) includes the following steps: Fill large-particle-size aluminum nitride powder 6-1 (particle size of 1 mm) and small-particle-size aluminum nitride powder 6-2 (particle size of 0.3 μm) at the center and edge inside the cylindrical tungsten crucible 9 respectively. After continuing to fill medium-particle-size aluminum nitride powder 6-3 (particle size of 0.7 μm) on the large-particle-size aluminum nitride powder 6-1 and the small-particle-size aluminum nitride powder 6-2, place the cylindrical tungsten crucible 9 in a sealed high-temperature furnace, and conduct the second sintering at 22 °C and 400 mbar, holding the temperature and pressure for 12 h; after the high-temperature furnace cools down, take out the sintered material, and use a tungsten spoon to dig out the sintered material of the large-particle-size aluminum nitride powder 6-1 to obtain the second aluminum nitride sintered material 6.

[0063] Sb. Coaxially place the aluminum nitride seed crystal 7 in the accommodating cavity of the upper tungsten crucible 4, place it in an isostatic pressing furnace, and conduct sintering at 2200 °C, 400 mbar, and a load of 9 GPa. After holding the temperature and pressure for 6 h, obtain the upper tungsten crucible 4 thermally bonded with the aluminum nitride seed crystal 7 (the aluminum nitride seed crystal 7 is located on the lower surface of the tungsten substrate 8).

[0064] The diameter of the aluminum nitride seed crystal 7 is 40 mm and the thickness is 0.6 mm; the diameter of the tungsten substrate 8 is 28 mm longer than the diameter of the aluminum nitride seed crystal 7.

[0065] It should be noted that the order of steps Sa and Sb is not limited in this example.

[0066] Sc. Place the first aluminum nitride sintered material 1 in the accommodating cavity of the lower tungsten crucible 2, and sequentially place the tungsten wafer 3 and the upper tungsten crucible 4 thermally bonded with the aluminum nitride seed crystal 7 on the top of the lower tungsten crucible 2. The second aluminum nitride sintered material 6 is also placed in the upper tungsten crucible 4; cover the upper tungsten crucible 4 with a heat insulation cover 5 to form an aluminum nitride single crystal growth structure.

[0067] The diameter of the upper plane of the first aluminum nitride sintered material 1 is 60 mm, and the diameter of the lower plane is 25 mm; the height of the lower tungsten crucible 2 is 35 mm, and the included angle between the inner side wall and its top surface is 60°.

[0068] The outer diameter of the second aluminum nitride sintered material 6 is 56 mm, the thickness is 8 mm, and the height is 25 mm; the height of the upper tungsten crucible 4 is 37 mm, and the distance from the lower plane of the tungsten substrate 8 to the upper plane of the second aluminum nitride sintered material 6 is 12 mm.

[0069] Sd. Place the aluminum nitride single crystal growth structure coaxially in the upper-middle part of the heater 10 of the high-temperature furnace, replace the air in the high-temperature furnace with nitrogen, raise the temperature in the high-temperature furnace from room temperature to 2200 °C within 8 h (maintaining the pressure in the high-temperature furnace at 500 mbar during the heating process) for growth. After heat preservation and pressure maintenance for 110 h, a 2-inch aluminum nitride single crystal is obtained.

[0070] By comparing the crystal thicknesses after growing for 10 h and 110 h, it can be seen that the average growth rate of the aluminum nitride single crystal in the first 10 h is 150 μm / h, and the average growth rate of the aluminum nitride single crystal within 110 h is 140 μm / h. There is no significant change in the average growth rate after growing for 10 h and 110 h, indicating that the growth rate is very stable during the growth process of the aluminum nitride single crystal.

[0071] Example 2 This example provides a method for growing aluminum nitride single crystals stably for a long time by using a device for preparing aluminum nitride single crystals (please refer to Figure 2 ), including the following steps: Sa. Preparation of the first aluminum nitride sintered material 1 and the second aluminum nitride sintered material 6: The preparation method of the first aluminum nitride sintered material 1 includes the following steps: Fill the lower tungsten crucible 2 with aluminum nitride powder, with a filling density of 1300 kg / m 3 , put it into a closed high-temperature furnace, and perform the first sintering at 2250 °C and 800 mbar, with heat preservation and pressure maintenance for 10 h to obtain the first aluminum nitride sintered material 1.

[0072] The preparation method of the second aluminum nitride sintered material 6 (see Figure 3 ) includes the following steps: At the center and the edge inside the cylindrical tungsten crucible 9, large particle size aluminum nitride powder 6-1 (particle size 1.5 mm) and small particle size aluminum nitride powder 6-2 (particle size 0.2 μm) are filled respectively. After medium particle size aluminum nitride powder 6-3 (particle size 0.5 μm) is filled continuously on the large particle size aluminum nitride powder 6-1 and the small particle size aluminum nitride powder 6-2, the cylindrical tungsten crucible 9 is placed in a sealed high-temperature furnace and second sintering is carried out at 2250 °C and 800 mbar, with heat preservation and pressure holding for 10 h. After the high-temperature furnace cools down and the sintered material is taken out, the sintered material of the large particle size aluminum nitride powder 6-1 is dug out with a tungsten spoon to obtain the second aluminum nitride sintered material 6.

[0073] Sb. An aluminum nitride seed crystal 7 is coaxially placed in the accommodating cavity of the upper tungsten crucible 4 and put into an isostatic pressing furnace. Sintering is carried out at 2250 °C, 800 mbar and a load of 10 GPa. After heat preservation and pressure holding for 5 h, the upper tungsten crucible 4 with the aluminum nitride seed crystal 7 thermally bonded (the aluminum nitride seed crystal 7 is located on the lower surface of the tungsten substrate 8) is obtained.

[0074] The diameter of the aluminum nitride seed crystal 7 is 40 mm and the thickness is 0.6 mm; the diameter of the tungsten substrate 8 is 30 mm longer than the diameter of the aluminum nitride seed crystal 7.

[0075] It should be noted that the order of steps Sa and Sb is not limited in this embodiment.

[0076] Sc. The first aluminum nitride sintered material 1 is placed in the accommodating cavity of the lower tungsten crucible 2. A tungsten wafer 3 and the upper tungsten crucible 4 with the aluminum nitride seed crystal 7 thermally bonded are sequentially placed on the top of the lower tungsten crucible 2. The second aluminum nitride sintered material 6 is also placed in the upper tungsten crucible 4. A heat insulation cover 5 is arranged outside the upper tungsten crucible 4 to form an aluminum nitride single crystal growth structure.

[0077] The diameter of the upper plane of the first aluminum nitride sintered material 1 is 60 mm and the diameter of the lower plane is 25 mm; the height of the lower tungsten crucible 2 is 45 mm, and the included angle between the inner side wall and its own top surface is 65°.

[0078] The outer diameter of the second aluminum nitride sintered material 6 is 60 mm, the thickness is 10 mm, and the height is 25 mm; the height of the upper tungsten crucible 4 is 40 mm, and the distance from the lower plane of the tungsten substrate 8 to the upper plane of the second aluminum nitride sintered material 6 is 15 mm.

[0079] Sd. The aluminum nitride single crystal growth structure is coaxially placed in the upper middle part of the heater 10 of the high-temperature furnace. The air in the high-temperature furnace is replaced with nitrogen. The temperature in the high-temperature furnace is raised from room temperature to 2250 °C within 5 h (the pressure in the high-temperature furnace is maintained at 600 mbar during the heating process) for growth. After heat preservation and pressure holding for 120 h, a 2-inch aluminum nitride single crystal is obtained.

[0080] By comparing the crystal thickness after 10 h and 120 h of growth, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 200 μm / h, and the average growth rate of aluminum nitride single crystals within 120 h is 190 μm / h. There is no significant change in the average growth rate after 10 h and 120 h of growth, indicating that the growth rate is very stable during the growth process of aluminum nitride single crystals.

[0081] Example 3 This example provides a method for long-term stable growth of aluminum nitride single crystals using a device for preparing aluminum nitride single crystals (please refer to Figure 2 ), including the following steps: Sa. Preparation of the first aluminum nitride sintered material 1 and the second aluminum nitride sintered material 6: The preparation method of the first aluminum nitride sintered material 1 includes the following steps: Fill aluminum nitride powder in the lower tungsten crucible 2, with a filling density of 2000 kg / m 3 , place it in a closed high-temperature furnace, and conduct the first sintering at 2300 °C and 1000 mbar, with heat preservation and pressure holding for 9 h to obtain the first aluminum nitride sintered material 1.

[0082] The preparation method of the second aluminum nitride sintered material 6 (see Figure 3 ) includes the following steps: Fill large-particle-size aluminum nitride powder 6-1 (particle size of 2 mm) and small-particle-size aluminum nitride powder 6-2 (particle size of 0.4 μm) at the center and edge inside the cylindrical tungsten crucible 9 respectively. After filling medium-particle-size aluminum nitride powder 6-3 (particle size of 0.8 μm) on the large-particle-size aluminum nitride powder 6-1 and the small-particle-size aluminum nitride powder 6-2, place the cylindrical tungsten crucible 9 in a closed high-temperature furnace, and conduct the second sintering at 2300 °C and 1000 mbar, with heat preservation and pressure holding for 9 h; after the high-temperature furnace cools down, take out the sintered material, and use a tungsten spoon to dig out the sintered material of the large-particle-size aluminum nitride powder 6-1 to obtain the second aluminum nitride sintered material 6.

[0083] Sb. Coaxially place an aluminum nitride seed crystal 7 in the accommodating cavity of the upper tungsten crucible 4, place it in an isostatic pressing furnace, and conduct sintering at 2300 °C, 1000 mbar, and a load of 10 GPa. After heat preservation and pressure holding for 4.5 h, obtain the upper tungsten crucible 4 thermally bonded with the aluminum nitride seed crystal 7 (the aluminum nitride seed crystal 7 is located on the lower surface of the tungsten substrate 8).

[0084] The diameter of the aluminum nitride seed crystal 7 is 90 mm, and the thickness is 0.8 mm; the diameter of the tungsten substrate 8 is 30 mm longer than the diameter of the aluminum nitride seed crystal 7.

[0085] It should be noted that this example does not limit the order of steps Sa and Sb.

[0086] Sc. Place the first aluminum nitride sintered material 1 in the accommodation cavity of the lower tungsten crucible 2. Sequentially place a tungsten wafer 3 and an upper tungsten crucible 4 thermally bonded with an aluminum nitride seed crystal 7 on the top of the lower tungsten crucible 2. The upper tungsten crucible 4 also contains a second aluminum nitride sintered material 6. An insulating cover 5 is arranged outside the upper tungsten crucible 4 to form an aluminum nitride single crystal growth structure.

[0087] The diameter of the upper plane of the first aluminum nitride sintered material 1 is 110 mm, and the diameter of the lower plane is 35 mm. The height of the lower tungsten crucible 2 is 60 mm, and the angle between the inner side wall and its top surface is 55°.

[0088] The outer diameter of the second aluminum nitride sintered material 6 is 110 mm, the thickness is 10 mm, and the height is 35 mm. The height of the upper tungsten crucible 4 is 75 mm, and the distance from the lower plane of the tungsten substrate 8 to the upper plane of the second aluminum nitride sintered material 6 is 40 mm.

[0089] Sd. Coaxially place the aluminum nitride single crystal growth structure in the upper middle part of the heater 10 of the high-temperature furnace. Use nitrogen to displace the air in the high-temperature furnace, and raise the temperature in the high-temperature furnace from room temperature to 2300 °C within 10 h (maintaining the pressure in the high-temperature furnace at 800 mbar during the heating process) for growth. After heat preservation and pressure maintenance for 100 h, a 4-inch aluminum nitride single crystal is obtained.

[0090] By comparing the crystal thickness after growing for 10 h and 100 h, it can be known that the average growth rate of the aluminum nitride single crystal in the first 10 h is 150 μm / h, and the average growth rate of the aluminum nitride single crystal within 100 h is 140 μm / h. The average growth rates after growing for 10 h and 100 h have no significant change, indicating that the growth rate is very stable during the growth process of the aluminum nitride single crystal.

[0091] Example 4 This example provides a method for long-term stable growth of aluminum nitride single crystals using a device for preparing aluminum nitride single crystals (please refer to Figure 2 ), including the following steps: Sa. Preparation of the first aluminum nitride sintered material 1 and the second aluminum nitride sintered material 6: The preparation method of the first aluminum nitride sintered material 1 includes the following steps: Fill the lower tungsten crucible 2 with aluminum nitride powder, with a filling density of 2500 kg / m 3 , place it in a sealed high-temperature furnace, and conduct the first sintering at 2300 °C and 1200 mbar, with heat preservation and pressure maintenance for 10 h to obtain the first aluminum nitride sintered material 1.

[0092] The preparation method of the second aluminum nitride sintered material 6 (see Figure 3 ) includes the following steps: In the center and at the edge inside the cylindrical tungsten crucible 9, large-particle-size aluminum nitride powder 6-1 (particle size: 2 mm) and small-particle-size aluminum nitride powder 6-2 (particle size: 0.5 μm) are filled respectively. After medium-particle-size aluminum nitride powder 6-3 (particle size: 1.0 μm) is filled on the large-particle-size aluminum nitride powder 6-1 and the small-particle-size aluminum nitride powder 6-2, the cylindrical tungsten crucible 9 is placed in a sealed high-temperature furnace and subjected to a second sintering at 2300 °C and 1200 mbar, with heat preservation and pressure holding for 10 h. After the high-temperature furnace cools down and the sintered material is taken out, the sintered material of the large-particle-size aluminum nitride powder 6-1 is dug out with a tungsten spoon to obtain the second aluminum nitride sintered material 6.

[0093] Sb. An aluminum nitride seed crystal 7 is coaxially placed in the accommodating cavity of the upper tungsten crucible 4 and put into an isostatic pressing furnace. Sintering is carried out at 2300 °C, 1200 mbar, and a load of 11 GPa. After heat preservation and pressure holding for 5 h, the upper tungsten crucible 4 with the aluminum nitride seed crystal 7 thermally bonded thereto is obtained (the aluminum nitride seed crystal 7 is located on the lower surface of the tungsten substrate 8).

[0094] The diameter of the aluminum nitride seed crystal 7 is 184 mm and the thickness is 1.0 mm; the diameter of the tungsten substrate 8 is 34 mm longer than the diameter of the aluminum nitride seed crystal 7.

[0095] It should be noted that the present embodiment does not limit the sequence of steps Sa and Sb.

[0096] Sc. The first aluminum nitride sintered material 1 is placed in the accommodating cavity of the lower tungsten crucible 2. A tungsten wafer 3 and the upper tungsten crucible 4 with the aluminum nitride seed crystal 7 thermally bonded thereto are sequentially placed on the top of the lower tungsten crucible 2. The second aluminum nitride sintered material 6 is also placed in the upper tungsten crucible 4. A heat insulation cover 5 is arranged outside the upper tungsten crucible 4 to form an aluminum nitride single crystal growth structure.

[0097] The diameter of the upper plane of the first aluminum nitride sintered material 1 is 190 mm and the diameter of the lower plane is 50 mm; the height of the lower tungsten crucible 2 is 80 mm, and the included angle between the inner side wall and its top surface is 45°.

[0098] The outer diameter of the second aluminum nitride sintered material 6 is 200 mm, the thickness is 12 mm, and the height is 50 mm; the height of the upper tungsten crucible 4 is 80 mm, and the distance from the lower plane of the tungsten substrate 8 to the upper plane of the second aluminum nitride sintered material 6 is 30 mm.

[0099] Sd. The aluminum nitride single crystal growth structure is coaxially placed in the upper middle part of the heater 10 of the high-temperature furnace. The air in the high-temperature furnace is replaced with nitrogen, and the temperature in the high-temperature furnace is raised from room temperature to 2250 °C within 7 h (during the heating process, the pressure in the high-temperature furnace is maintained at 700 mbar) for growth. After heat preservation and pressure holding for 135 h, an 8-inch aluminum nitride single crystal is obtained.

[0100] By comparing the crystal thickness after growing for 10 h and 135 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 120 μm / h, and the average growth rate of aluminum nitride single crystals within 135 h is 110 μm / h. There is no significant change in the average growth rate after growing for 10 h and 135 h, indicating that the growth rate is very stable during the growth process of aluminum nitride single crystals.

[0101] Comparative Example 1 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 1, except that: the first aluminum nitride sintered material 1 is replaced with a cylindrical aluminum nitride sintered material with a diameter of 60 mm, and the shape of the lower tungsten crucible 2 is also modified correspondingly. The remaining structures, dimension settings, growth conditions and steps are the same as those in Example 1 and will not be repeated.

[0102] By comparing the crystal thickness after growing for 10 h and 110 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 140 μm / h, and the average growth rate of aluminum nitride single crystals within 110 h is 70 μm / h.

[0103] Comparative Example 2 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 3, except that: the heat shield 5 is removed. The remaining structures, dimension settings, growth conditions and steps are the same as those in Example 3 and will not be repeated.

[0104] By comparing the crystal thickness after growing for 10 h and 100 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 180 μm / h, and the average growth rate of aluminum nitride single crystals within 100 h is 80 μm / h.

[0105] Comparative Example 3 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 2, except that: the lower tungsten crucible 2 containing the first aluminum nitride sintered material 1 is removed. The remaining structures, dimension settings, growth conditions and steps are the same as those in Example 2 and will not be repeated.

[0106] By comparing the crystal thickness after growing for 10 h and 120 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 180 μm / h, and the average growth rate of aluminum nitride single crystals within 120 h is 140 μm / h.

[0107] Comparative Example 4 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 2, except that: the lower tungsten crucible 2 containing the first aluminum nitride sintered material 1 is removed, and the heat shield is removed. The remaining structures, dimension settings, growth conditions and steps are the same as those in Example 2 and will not be repeated.

[0108] By comparing the crystal thickness after growing for 10 h and 120 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 220 μm / h, and the average growth rate of aluminum nitride single crystals within 120 h is 130 μm / h.

[0109] Comparative Example 5 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 4, except that: the second aluminum nitride sintered material 6 is replaced with an aluminum nitride sintered material sintered from small-particle-size aluminum nitride powder. The remaining structures, size settings, growth conditions and steps are the same as those in Example 4 and will not be elaborated.

[0110] The preparation method of the aluminum nitride sintered material sintered from small-particle-size aluminum nitride powder includes the following steps: Fill large-particle-size aluminum nitride powder 6-1 (particle size of 2 mm) and small-particle-size aluminum nitride powder 6-2 (particle size of 0.5 μm) at the center and edge inside the cylindrical tungsten crucible 9 respectively. After continuing to fill small-particle-size aluminum nitride powder 6-2 (particle size of 0.5 μm) on the large-particle-size aluminum nitride powder 6-1 and the small-particle-size aluminum nitride powder 6-2, put the cylindrical tungsten crucible 9 into a closed high-temperature furnace, and carry out the second sintering at 2300 °C and 1200 mbar, and keep the temperature and pressure for 10 h; after the high-temperature furnace cools down, take out the sintered material, and use a tungsten spoon to dig out the sintered material of the large-particle-size aluminum nitride powder 6-1 to obtain the aluminum nitride sintered material sintered from small-particle-size aluminum nitride powder.

[0111] By comparing the crystal thickness after growing for 10 h and 135 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 100 μm / h, and the average growth rate of aluminum nitride single crystals within 135 h is 70 μm / h.

[0112] Comparative Example 6 This comparative example provides a method for growing aluminum nitride single crystals, which is similar to Example 4, except that: the second aluminum nitride sintered material 6 is replaced with a solid cylindrical aluminum nitride sintered material sintered from medium-particle-size aluminum nitride powder. The remaining structures, size settings, growth conditions and steps are the same as those in Example 4 and will not be elaborated.

[0113] The preparation method of the solid cylindrical aluminum nitride sintered material includes the following steps: After filling medium-particle-size aluminum nitride powder 6-3 (particle size of 1.0 μm) in the cylindrical tungsten crucible 9, put the cylindrical tungsten crucible 9 into a closed high-temperature furnace, and carry out the second sintering at 2300 °C and 1200 mbar, and keep the temperature and pressure for 10 h; after the high-temperature furnace cools down, take it out to obtain the solid cylindrical aluminum nitride sintered material.

[0114] By comparing the crystal thickness after growing for 10 h and 135 h, it can be seen that the average growth rate of aluminum nitride single crystals in the first 10 h is 110 μm / h, and the average growth rate of aluminum nitride single crystals within 135 h is 80 μm / h.

[0115] By comparing the crystal thickness of Examples 1 to 4 and Comparative Examples 1 to 6 after growing for 10 h and during the entire growth time, the average growth rate, crystallization quality, and crystallization quality uniformity (consistency) of aluminum nitride single crystals in the first 10 h and during the entire growth time were calculated. The results are shown in Table 1. As can be seen from Table 1, after making different changes to the growth structure of aluminum nitride single crystals, the average growth rates of Comparative Examples 1 to 6 during 10 h and the entire growth time have changed significantly, indicating that the growth rate is unstable during the growth process of aluminum nitride single crystals.

[0116] Table 1 Comparison table of growth rates of aluminum nitride single crystals prepared by comparative examples (μm / h)

[0117] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An apparatus for preparing single crystal aluminum nitride, characterized in that, It includes a lower tungsten crucible, a tungsten wafer, and an upper tungsten crucible that are sequentially distributed from bottom to top, and also includes a heat insulation cover covering the outside of the upper tungsten crucible; the lower tungsten crucible and the upper tungsten crucible respectively have accommodation cavities for containing aluminum nitride sintering materials, and the openings of the lower tungsten crucible and the upper tungsten crucible are both sealed by the tungsten wafer. The accommodation cavity of the lower tungsten crucible is a frustum-shaped chamber with a diameter gradually decreasing from top to bottom; a heat insulation space is formed between the upper tungsten crucible and the heat insulation cover.

2. The apparatus for preparing single crystal aluminum nitride according to claim 1, characterized in that, The included angle between the inner side wall of the lower tungsten crucible and its top surface ≤ 75°; The lower tungsten crucible, the tungsten wafer, the upper tungsten crucible, and the heat insulation cover are coaxially placed, and the opening of the heat insulation cover is sealed by the tungsten wafer.

3. The apparatus for preparing single crystal aluminum nitride according to claim 1, characterized in that, The upper tungsten crucible includes a through crucible body and a tungsten substrate covering the top of the crucible body, and the tungsten substrate has a growth position for placing aluminum nitride seeds.

4. A method for stably growing aluminum nitride single crystals for a long time by using the device for preparing aluminum nitride single crystals according to any one of claims 1 to 3, comprising the following steps: S1. Place aluminum nitride seeds in the accommodation cavity of the upper tungsten crucible and perform sintering to obtain an upper tungsten crucible thermally bonded with aluminum nitride seeds; the aluminum nitride seeds are located on the top surface of the upper tungsten crucible; S2. Place the first aluminum nitride sintering material in the accommodation cavity of the lower tungsten crucible, sequentially place the tungsten wafer and the upper tungsten crucible thermally bonded with aluminum nitride seeds on the top of the lower tungsten crucible. The upper tungsten crucible also contains a second aluminum nitride sintering material; cover the upper tungsten crucible with a heat insulation cover to form an aluminum nitride single crystal growth structure; The first aluminum nitride sintering material is attached to the inner wall of the lower tungsten crucible; the longitudinal section of the second aluminum nitride sintering material is in an inverted U shape, and the top of the second aluminum nitride sintering material has a porous structure; S3. Coaxially place the aluminum nitride single crystal growth structure in the upper middle part of the heater of the high-temperature furnace and perform growth in a nitrogen atmosphere to obtain aluminum nitride single crystals.

5. The method for growing aluminum nitride single crystals with long-term stability as described in claim 4, characterized in that, In S2, the preparation method of the first aluminum nitride sintering material includes the following steps: Fill aluminum nitride powder in the lower tungsten crucible and perform first sintering to obtain the first aluminum nitride sintering material; In S₂, the preparation method of the second aluminum nitride sintering material includes the following steps: Fill large-particle-size aluminum nitride powder and small-particle-size aluminum nitride powder at the center and edge inside a cylindrical tungsten crucible respectively. After continuing to fill medium-particle-size aluminum nitride powder on the large-particle-size aluminum nitride powder and small-particle-size aluminum nitride powder, perform second sintering on the cylindrical tungsten crucible. After taking out the sintering material, remove the sintering material of the large-particle-size aluminum nitride powder to obtain the second aluminum nitride sintering material.

6. The method for growing aluminum nitride single crystals with long-term stability as described in claim 5, characterized in that, In S2, the packing density of the aluminum nitride powder is 500 kg / m 3 ~2500 kg / m 3 ; In S2, the particle size of the large-particle-size aluminum nitride powder is above 2 μm, the particle size of the small-particle-size aluminum nitride powder is 0.2 μm to 0.5 μm, and the particle size of the medium-particle-size aluminum nitride powder is 0.5 μm to 1 μm.

7. The method for growing aluminum nitride single crystals with long-term stability as described in claim 5, characterized in that, In S1, the temperature of the sintering is 2200 °C to 2300 °C, the sintering load is 9 GPa to 11 GPa, the air pressure is 400 mbar to 1200 mbar, and the sintering time is 4.5 h to 6 h; In S2, the temperature of the first sintering is 2200°C to 2300°C, the air pressure is 400 mbar to 1200 mbar, and the sintering time is 9 h to 12 h; In S2, the temperature of the second sintering is 2200°C to 2300°C, the air pressure is 400 mbar to 1200 mbar, and the sintering time is 9 h to 12 h; In S3, the temperature of the growth is 2200°C to 2300°C, the air pressure is 500 mbar to 800 mbar, and the heat preservation and pressure maintenance time is 100 h to 140 h.

8. The method for growing aluminum nitride single crystals with long-term stability as described in claim 4, characterized in that, In S1, the diameter of the aluminum nitride seed crystal is 25 mm to 185 mm, and the thickness is 0.5 mm to 1 mm; In S1, the diameter of the tungsten substrate is 25 mm to 35 mm longer than the diameter of the aluminum nitride seed crystal.

9. The method for growing aluminum nitride single crystals with long-term stability as described in claim 5, characterized in that, In S2, the height of the lower tungsten crucible is 30 mm to 80 mm, and the height of the upper tungsten crucible is 30 mm to 80 mm; In S2, the diameter of the upper plane of the first aluminum nitride sintered material is 60 mm to 210 mm, the diameter of the lower plane is 20 mm to 50 mm, and the height of the first aluminum nitride sintered material is less than the height of the lower tungsten crucible; In S2, the outer diameter of the second aluminum nitride sintered material is 50 mm to 200 mm, the thickness is 8 mm to 12 mm, and the height is 20 mm to 50 mm.

10. The method for growing aluminum nitride single crystals with long-term stability as claimed in claim 8 or 9, characterized in that, In S2, the distance from the lower plane of the tungsten substrate to the upper plane of the second aluminum nitride sintered material is 10 mm to 50 mm; In S2, the diameter of the aluminum nitride seed crystal is equal to the inner diameter of the second aluminum nitride sintered material.

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