Apparatus and method for growing large size single crystals by pvt method

Abstract

The present application provides a device for growing large-size single crystals by PVT method, which comprises a crucible, a heat insulation structure, an induction heating unit and an infrared temperature measurement unit; the heat insulation structure is located at the top of the crucible and comprises a fixed heat insulation structure and a movable heat insulation structure; the fixed heat insulation structure is fixed at the center of the top of the crucible; the movable heat insulation structure is configured to move back and forth along the axial direction of the crucible and rotate, and when it moves to contact the top of the crucible, the movable heat insulation structure can closely fit with the fixed heat insulation structure. The present application also provides a method for growing large-size single crystals by PVT method, which uses the device of the present application. The device and method of the present application can dynamically adjust the radial temperature field of the seed crystal during the process of growing single crystals by PVT method with induction heating and cooling after growth, so that the gradient can always remain excellent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of crystal growth. Specifically, the present application relates to an apparatus and a method for growing large-size crystals by PVT method. BACKGROUND

[0002] Aluminum nitride (AlN) has a direct band gap of up to 6.2 eV, and high thermal conductivity, large surface acoustic velocity, strong corrosion resistance, and large mechanical hardness, and is an ideal material for preparing ultraviolet optoelectronic and high-power microelectronic devices. Silicon carbide (SiC) is also one of the widely concerned wide band gap semiconductor materials, which has a large band gap (at room temperature, the band gap of 4H-SiC is 3.2 eV), a high breakdown field strength, a high saturated electron mobility, a high thermal conductivity, and a good chemical stability, and is an ideal substrate material for making high-frequency, high-voltage, and high-power devices and blue light emitting diodes. Silicon carbide has important application potential in the fields of electric vehicles, rail transit, high-voltage power transmission and transformation, photovoltaic, 5G communication, etc.

[0003] The main method for growing AlN and SiC crystals at present is the physical vapor transport method (PVT method). The basic principle is to place high-purity aluminum nitride or silicon carbide powder in a crucible, heat it to 2000-2500℃, sublimate the aluminum nitride or silicon carbide powder, and transport the growth atmosphere to the aluminum nitride or silicon carbide seed crystal, and deposit and grow on the seed crystal. In the early industry, inductive heating method was generally used for crystal growth, because compared with resistance heating, the device structure of inductive heating is simple and stable, the heating efficiency is high, the heating speed is fast, and the energy saving is good. However, with the increasing size of aluminum nitride or silicon carbide, the disadvantages of inductive heating method in controlling the radial temperature field of the seed crystal gradually appear.

[0004] The inductive heating method is to heat the internal induction body through the annular induction coil outside the crucible, and the heat is generated from the crucible, especially the outer wall of the crucible. The temperature on the side of the crucible is very high, resulting in a large radial temperature gradient, and the crystal obtained by growth has a large convexity, the effective thickness is reduced and is easy to crack, which is particularly serious when growing large-size crystals. The inductive heating method cannot directly effectively control the radial temperature gradient of the seed crystal, and people can only adjust the heat preservation structure behind the seed crystal to realize the control of the radial temperature gradient of the seed crystal during growth, but this method is not real-time. In addition, if a smaller radial temperature gradient is to be achieved during crystal growth, the center of the back of the seed crystal should be increased in heat preservation. However, during the cooling process after growth, heat diffuses outward. This heat preservation structure makes the heat dissipation of the edge of the seed crystal better, and the temperature is lower, resulting in a large radial temperature gradient, which is prone to cracking, especially when growing large-size crystals.

[0005] For the problem of stress cracking in the growth of large-size single crystals by induction heating, some researchers have proposed using a double-coil independent control method to solve this problem (Yang N, Song B, Wang W, et al. Control of the temperature field by double induction coils for growth of large-sized SiC single crystals via the physical vapor transport technique[J]. 2022.). However, when multiple heating coils are added to the induction heating method, the magnetic fields may interfere with each other, causing the magnetic field and heat to be distributed in a way that deviates from the designed purpose, affecting the heating effect. Moreover, the design of multiple coils increases the difficulty of control and the cost of equipment, which is not conducive to large-scale industrial production.

[0006] To address the above problems, there is an urgent need for a method that can dynamically adjust the radial temperature field of the seed crystal during the growth and cooling process of PVT single crystal growth, so that the radial temperature field of the seed crystal always maintains an excellent gradient, allowing the growth of high-quality, low-stress, and large-size single crystals. SUMMARY

[0007] The purpose of the present application is to provide a device and method for growing large-size single crystals by PVT induction heating. The device and method of the present application can dynamically adjust the radial temperature field of the seed crystal during the growth and cooling process of PVT single crystal growth, always maintaining an excellent gradient. The device and method provided by the present application are helpful for growing high-quality, low-stress, and large-size single crystals (including but not limited to aluminum nitride or silicon carbide single crystals), and especially when using induction heating, can effectively reduce production costs and improve production efficiency.

[0008] The above-mentioned purpose of the present application is achieved by the following technical solutions.

[0009] In one aspect, the present application provides a device for growing large-size single crystals by PVT, which includes a crucible, a heat preservation structure, an induction heating unit, and an infrared temperature measurement unit.

[0010] The heat preservation structure is located at the top of the crucible and includes a fixed heat preservation structure and a movable heat preservation structure; the fixed heat preservation structure is fixed at the center of the top of the crucible; the movable heat preservation structure is configured to move back and forth along the axial direction of the crucible and rotate, and when it moves into contact with the top of the crucible, it can tightly fit with the fixed heat preservation structure;

[0011] The infrared temperature measuring unit comprises a top center temperature measuring instrument with a temperature measuring point at the center of the top of the crucible, a top edge temperature measuring instrument with a temperature measuring point at the edge of the top of the crucible, and a bottom center temperature measuring instrument with a temperature measuring point at the center of the bottom of the crucible.

[0012] The induction heating unit is configured to provide heat to the crucible.

[0013] The combination of the fixed heat preservation structure and the movable heat preservation structure adopted in the present application can be tightly superimposed without gaps, and the best heat preservation effect can be achieved when the two are tightly superimposed.

[0014] In a specific embodiment of the present application, the movable heat preservation structure is located at a position outside the circumference of the top of the crucible and is connected to the pulling and rotating device, so as to realize vertical movement and rotation.

[0015] Preferably, in the device for growing large-size single crystals by PVT method according to the present application, a through hole as a temperature measuring channel is formed at the center of the fixed heat preservation structure.

[0016] Preferably, in the device for growing large-size single crystals by PVT method according to the present application, the aperture of the through hole is 5-20 mm.

[0017] Preferably, in the device for growing large-size single crystals by PVT method according to the present application, the fixed heat preservation structure is a circular truncated cone.

[0018] Preferably, in the device for growing large-size single crystals by PVT method according to the present application, the height of the circular truncated cone is 5-100 mm.

[0019] Preferably, in the device for growing large-size single crystals by PVT method according to the present application, the bottom diameter of the circular truncated cone is 40%-80% of the outer diameter of the crucible, and the top diameter of the circular truncated cone is 30%-60%, more preferably 30%-55%, of the outer diameter of the crucible.

[0020] In some embodiments of the present application, the fixed heat preservation structure is in the shape of a circular truncated cone, and the inner diameter gradually increases from top to bottom.

[0021] Preferably, in the device for growing large-size single crystals by PVT method of the present application, the movable heat insulation structure is annular and is divided into a first section away from the crucible and a second section close to the crucible in the axial direction; the difference between the outer diameter of the first section and the outer diameter of the crucible is 0-50 mm, the top inner diameter of the first section is 30%-100% of the outer diameter of the crucible, and the top inner diameter of the first section is greater than or equal to the bottom inner diameter of the first section; the outer diameter of the second section is the same as that of the first section. The inner annular surface of the second section is fitted with the side surface shape of the circular truncated cone of the fixed heat insulation structure.

[0022] Preferably, in the device for growing large-size single crystals by PVT method of the present application, the height of the first section is 10-150 mm.

[0023] Preferably, in the device for growing large-size single crystals by PVT method of the present application, the fixed heat insulation structure and the movable heat insulation structure are made of a material selected from graphite soft felt and / or graphite hard felt.

[0024] Preferably, in the device for growing large-size single crystals by PVT method of the present application, the induction heating unit comprises an induction coil.

[0025] In some embodiments of the present application, the device further comprises a pulling and rotating device, which can realize high-speed pulling (10-2000 mm / h), low-speed pulling (10-10000 μm / h) and rotation (0-100 rpm).

[0026] In some embodiments of the present application, the device further comprises a crucible tray and a motion assembly for supporting the vertical movement and rotation of the crucible. The present application does not make excessive description of the crucible tray and the motion assembly, and the person skilled in the art can select the specific structure of the crucible tray and the motion assembly according to the actual situation.

[0027] On the other hand, the present application provides a method for growing large-size single crystals by PVT method, which uses the device for growing large-size single crystals by PVT method of the present application, and comprises the following steps:

[0028] (1) placing a raw material for growing a single crystal in a crucible, fixing a seed crystal to the inside top of the crucible, placing a fixed heat insulation structure at the top center of the crucible, and connecting a movable heat insulation structure with a pulling and rotating device and moving it to an initial position;

[0029] (2) providing heat to the crucible by an induction heating unit to sublimate the raw material; monitoring the temperature at the top center of the crucible, the top edge of the crucible and the bottom center of the crucible by an infrared temperature measuring unit to obtain a radial temperature gradient and an axial temperature gradient;

[0030] (3) Adjusting the relative position of the movable heat insulation structure and the fixed heat insulation structure during the growth process to control the radial temperature gradient; adjusting the relative position of the crucible and the induction heating unit by moving the crucible to control the axial temperature gradient;

[0031] (4) Adjusting the relative position of the movable heat insulation structure and the fixed heat insulation structure during the cooling process after the growth is completed to enhance the heat insulation effect of the edge of the crucible, thereby preventing stress cracking caused by excessively low temperature of the crystal edge;

[0032] (5) Controlling the rotation of the crucible and the movable heat insulation structure during the growth process and the cooling process.

[0033] Preferably, in the method of the present application, the size of the seed crystal is 4-12 inches.

[0034] Preferably, in the method of the present application, the initial position of the movable heat insulation structure is 5-20 mm away from the top of the crucible.

[0035] Preferably, in the method of the present application, the radial temperature gradient in step (3) is 0.1-0.5°C / cm, and the axial temperature gradient is 1-10°C / cm.

[0036] Preferably, in the method of the present application, the radial temperature gradient in step (3) is 0.1-0.3°C / cm, and the axial temperature gradient is 2-5°C / cm.

[0037] Preferably, in the method of the present application, the rate of upward movement of the crucible during the growth process is 1 / 3-1 / 2 of the crystal growth rate.

[0038] Preferably, in the method of the present application, the rotation in step (5) is performed at a rotation speed of 0.1-5 rpm.

[0039] In some embodiments of the present application, the distance between the heat insulation material and the top of the crucible is adjusted by adjusting the relative position of the movable heat insulation structure and the fixed heat insulation structure during the growth process, thereby achieving a smaller radial temperature gradient with the center being cooler and the edge being slightly warmer; a relatively larger axial temperature gradient is achieved by moving the crucible to adjust the relative position of the crucible and the induction coil in the induction heating unit, so as to increase the growth rate and the utilization rate of raw materials, and the crucible is moved upward during the growth process to compensate for the decrease in the axial temperature gradient caused by the advancement of the crystal growth interface to the high-temperature material surface.

[0040] In some embodiments of the present application, the relative position of the movable heat insulation structure and the fixed heat insulation structure is adjusted during the cooling process after the growth, so as to enhance the heat insulation effect of the crucible edge, prevent the temperature of the crystal edge from being too low, realize a smaller radial temperature gradient, and prevent the crystal from cracking due to thermal stress.

[0041] In some embodiments of the present application, the crucible and the movable heat insulation structure are rotated at a low speed during the growth process and the cooling process, so as to improve the uniformity of the temperature field.

[0042] Compared with the prior art, the present application has at least the following beneficial effects:

[0043] (1) The device for growing large-size single crystals by the PVT method provided by the present application can dynamically adjust the radial temperature field of the seed crystal during the growth and cooling process of the single crystal (such as an aluminum nitride or silicon carbide single crystal) by adjusting the position of the movable heat insulation structure, so that the seed crystal always maintains an excellent gradient in the radial direction. The device of the present application is suitable for inductively growing large-size single crystals. The device of the present application makes up for the disadvantage of regulating the radial temperature gradient when preparing large-size single crystals, and can grow 8-12 inch single crystals (such as aluminum nitride or silicon carbide single crystals).

[0044] Compared with a resistance heating furnace, the inductor has a simple and stable structure, high heating efficiency, fast heating speed, and is more energy-saving, and does not need to replace the heating body. Therefore, when the device of the present application is combined with the inductor, the production cost can be more effectively reduced and the production efficiency can be improved.

[0045] (2) The method for growing large-size single crystals by the PVT method provided by the present application weakens the heat insulation of the edge of the seed crystal during the growth of the crystal, and then realizes a smaller radial temperature gradient, which is beneficial to the high-quality growth of the crystal. The heat insulation of the edge of the seed crystal is enhanced during the cooling process of the crystal, so as to prevent the temperature of the edge of the seed crystal from being too low, reduce the thermal stress of the crystal, and prevent the crystal from cracking. The method of the present application is helpful to grow high-quality, low-stress, large-size single crystals (such as aluminum nitride or silicon carbide single crystals). BRIEF DESCRIPTION OF DRAWINGS

[0046] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings, in which:

[0047] Figure 1 a device schematic diagram showing one specific embodiment of the present application;

[0048] Figure 2 a connection schematic diagram of the movable heat insulation and the pulling and rotating device in one specific embodiment of the present application;

[0049] In the drawings, the reference signs are as follows:

[0050] 1 - top edge temperature gauge; 2 - movable insulation structure; 3 - fixed insulation structure; 4 - insulation material; 5 - graphite crucible; 6 - aluminum nitride or silicon carbide raw material; 7 - induction coil; 8 - crucible tray and movement assembly; 9 - bottom center temperature gauge; 10 - top center temperature gauge; 11 - pulling rotation device; 12 - aluminum nitride or silicon carbide seed crystal; 13 - aluminum nitride or silicon carbide crystal; 14 - graphite connecting frame. DETAILED DESCRIPTION

[0051] The application will be further described in conjunction with the specific embodiments given below, which are only intended to illustrate the application, and not to limit the scope of the application.

[0052] Reference Figure 1 and Figure 2 , the device and method for growing large-size single crystal by PVT method in the application are described and explained in detail.

[0053] Example 1

[0054] The growth of silicon carbide single crystal is carried out by using the device of the application, as shown in Figure 1 and Figure 2 . The size of the silicon carbide seed crystal (12) is 8 inches. The graphite crucible (5) has an outer diameter of 300 mm and is made of high-purity graphite with a purity of not less than 99.95%; the insulation material (4) is made of graphite soft felt with a purity of not less than 99.9%; the movable insulation structure (2) and the fixed insulation structure (3) are made of graphite hard felt with a purity of not less than 99.5%. The temperature data obtained by the top center temperature gauge (10) and the top edge temperature gauge (1) can be used to calculate the radial temperature gradient; the temperature data obtained by the top center temperature gauge (10) and the bottom center temperature gauge (9) can be used to calculate the axial temperature gradient.

[0055] The fixed insulation structure (3) is in the shape of a circular truncated cone with a height of 25 mm, a center temperature measuring hole diameter of 10 mm, a bottom diameter of 150 mm, and a top diameter of 100 mm.

[0056] The movable insulation structure (2) is annular and is divided into a first section and a second section from top to bottom. The first section has an outer diameter of 320 mm, a top inner diameter of 140 mm, and a height of 75 mm. The second section has an outer diameter of 320 mm and a height of 25 mm, and the inner annular surface is fitted with the side surface shape of the circular truncated cone of the fixed insulation structure (3). The movable insulation structure is bonded to the graphite connecting frame (14) and is connected to the pulling rotation device (11) by threads.

[0057] In this embodiment, the crucible tray and movement assembly (8) for supporting the vertical movement and rotation of the graphite crucible (5) and the insulation material (4) is also included.

[0058] The method provided by the embodiment comprises the following steps:

[0059] (I) placing a silicon carbide raw material in the graphite crucible, fixing a silicon carbide seed crystal at the top of the inner side of the graphite crucible, placing a fixed heat preservation structure at the top of the graphite crucible, connecting a movable heat preservation structure with a pulling rotation device and moving to an initial position, wherein the initial position is 10 mm from the bottom of the movable heat preservation structure to the surface of the top of the graphite crucible;

[0060] (II) heating the graphite crucible by means of an induction heating device to sublimate the silicon carbide raw material, and after the growth starts, monitoring the temperature at the center of the top of the crucible, the edge of the top of the crucible and the center of the bottom of the crucible by means of an infrared temperature detector to obtain a radial temperature gradient and an axial temperature gradient;

[0061] (III) adjusting the relative position of the movable heat preservation structure and the fixed heat preservation structure to control the distance between the heat preservation material and the top of the graphite crucible, and controlling the radial temperature gradient at 0.25±0.05 ℃ / cm; adjusting the relative position of the graphite crucible and the coil by moving the graphite crucible to control the axial temperature gradient at 3.0±0.2 ℃ / cm, so as to improve the growth speed and the raw material utilization rate, and moving the crucible upward at a speed of 50 μm / h during the growth process to compensate for the decrease of the axial temperature gradient caused by the pushing of the crystal growth interface to the high-temperature material surface, so that the temperature gradient in the whole growth process is kept as consistent as possible, and stable growth conditions are created;

[0062] (IV) during the cooling process after the growth is completed, lowering the movable heat preservation structure to enhance the heat preservation effect of the edge of the crucible and prevent the temperature of the edge of the crystal from being too low, and controlling the radial temperature gradient at 0.2±0.1 ℃ / cm to prevent the crystal from cracking due to thermal stress. If the position of the movable heat preservation structure is too low to block the temperature measuring point of the temperature detector at the edge of the top of the crucible, the movable heat preservation structure can be moved upward every 0.1-1 h to expose the temperature measuring point and perform temperature measurement, and the position of the movable heat preservation structure is determined according to the radial temperature gradient obtained by calculation;

[0063] (V) because of the certain non-uniformity of the circumferential heat preservation structure and the top heat preservation structure of the crucible and the certain non-uniformity of the magnetic field generated by the induction coil, the crucible rotates at a speed of 0.3 rpm during the growth process and the cooling process, and the movable heat preservation structure rotates at a speed of 0.5 rpm, so as to improve the uniformity of the temperature field.

[0064] The method for growing a large-size single crystal by means of PVT induction heating provided by the embodiment can dynamically adjust the radial temperature field of the seed crystal during the growth and cooling process of the silicon carbide single crystal by means of PVT, which is helpful to grow a high-quality, low-stress and large-size silicon carbide single crystal.

[0065] Embodiment 2

[0066] The device of the application is used for growing the single crystal of aluminum nitride, as shown in the drawings. Figure 1 and Figure 2 The size of the aluminum nitride seed crystal (12) is 4 inches. The graphite crucible (5) has an outer diameter of 150 mm and is made of high-purity graphite with a purity of not less than 99.95%, and the inner wall of the crucible is plated with a TaC layer. The heat preservation material (4) is made of graphite soft felt with a purity of not less than 99.9%. The movable heat preservation structure (2) and the fixed heat preservation structure (3) are made of graphite hard felt with a purity of not less than 99.5%. The temperature data obtained by the top center temperature measuring instrument (10) and the top edge temperature measuring instrument (1) of the crucible can be used to calculate the radial temperature gradient; the temperature data obtained by the top center temperature measuring instrument (10) and the bottom center temperature measuring instrument (9) of the crucible can be used to calculate the axial temperature gradient.

[0067] The fixed heat preservation structure (3) is in the shape of a circular truncated cone with a height of 15 mm, a center temperature measuring hole diameter of 10 mm, a bottom diameter of 75 mm, and a top diameter of 50 mm.

[0068] The movable heat preservation structure (2) is annular and is divided into a first section and a second section from top to bottom. The first section has an outer diameter of 160 mm, a top inner diameter of 80 mm, and a height of 45 mm. The second section has an outer diameter of 160 mm and a height of 15 mm, and the inner annular surface is fitted with the side surface shape of the circular truncated cone of the fixed heat preservation structure (3). The movable heat preservation structure is bonded to the graphite connecting frame (14) and is connected with the pulling and rotating device (11) through threads.

[0069] In this embodiment, the crucible tray and motion assembly (8) for supporting the vertical movement and rotation of the graphite crucible (5) and the heat preservation material (4) are also included.

[0070] The method provided in this embodiment includes the following steps:

[0071] (I) Place the aluminum nitride raw material in the graphite crucible, fix the aluminum nitride seed crystal on the inside top of the graphite crucible, place the fixed heat preservation structure on the top of the graphite crucible, connect the movable heat preservation structure with the pulling and rotating device, and move it to the initial position, which is 8 mm from the bottom of the movable heat preservation structure to the top surface of the graphite crucible;

[0072] (II) Heat the graphite crucible by the induction heating device to sublimate the aluminum nitride raw material. After the growth starts, monitor the temperatures at the top center, top edge, and bottom center of the crucible by the infrared temperature measuring instrument to obtain the radial temperature gradient and the axial temperature gradient;

[0073] (III) Adjusting the relative position of the movable heat preservation structure and the fixed heat preservation structure to control the distance between the heat preservation material and the top of the graphite crucible, and control the radial temperature gradient at 0.1±0.05℃ / cm, and by moving the graphite crucible to adjust the relative position of the graphite crucible and the induction coil, the axial temperature gradient is controlled at 2.5±0.3℃ / cm, so as to improve the growth rate and the utilization rate of raw materials, and the crucible is moved upward at a speed of 40μm / h during the growth process to compensate for the decrease of the axial temperature gradient caused by the advancement of the crystal growth interface to the high-temperature material surface, so that the temperature gradient during the whole growth process is kept as consistent as possible, and stable growth conditions are created;

[0074] (IV) During the cooling process after the growth, the movable heat preservation structure is lowered to enhance the heat preservation effect of the edge of the crucible, and the radial temperature gradient is controlled at 0.3±0.1℃ / cm to prevent the crystal from cracking due to thermal stress. If the position of the movable heat preservation structure is too low to block the temperature measuring point of the temperature measuring instrument at the edge of the top of the crucible, the movable heat preservation structure can be moved upward every 0.1-1h to expose the temperature measuring point for temperature measurement, and the position of the movable heat preservation structure is determined according to the calculated radial temperature gradient;

[0075] (V) Since the circumferential heat preservation structure and the top heat preservation structure of the crucible have certain non-uniformity, and the magnetic field generated by the induction coil also has certain non-uniformity, the crucible rotates at a speed of 0.2rpm during the growth process and the cooling process, and the movable heat preservation structure rotates at a speed of 0.3rpm, so as to improve the uniformity of the temperature field.

[0076] The method for growing large-size single crystals by PVT method and induction heating provided in the embodiment can dynamically adjust the radial temperature field of the seed crystal during the growth and cooling process of the aluminum nitride single crystal grown by the PVT method, which is helpful to grow high-quality, low-stress and large-size aluminum nitride single crystals.

[0077] The above embodiments are used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An apparatus for growing large-size single crystals by the PVT method, comprising a crucible, a heat preservation structure, an induction heating unit, and an infrared temperature measurement unit; The heat insulation structure is located at the top of the crucible and includes a fixed heat insulation structure and a movable heat insulation structure; The fixed heat insulation structure is fixed at the center of the top of the crucible; The movable insulation structure is configured to move and rotate back and forth along the axial direction of the crucible, and when it moves to contact the top of the crucible, the movable insulation structure can fit tightly against the fixed insulation structure. The infrared temperature measurement unit includes a crucible top center temperature measuring instrument with the temperature measuring point located at the center of the top of the crucible, a crucible top edge temperature measuring instrument with the temperature measuring point located at the edge of the top of the crucible, and a crucible bottom center temperature measuring instrument with the temperature measuring point located at the center of the bottom of the crucible. The induction heating unit is configured to provide heat to the crucible; The movable heat-insulating structure is ring-shaped and is divided into a first section away from the crucible and a second section close to the crucible in the axial direction; The difference between the outer diameter of the first section and the outer diameter of the crucible is 0 to 50 mm, the top inner diameter of the first section is 30% to 100% of the outer diameter of the crucible, and the top inner diameter of the first section is greater than or equal to the bottom inner diameter of the first section. The outer diameter of the second segment is the same as the outer diameter of the first segment; The fixed insulation structure is a frustum, with its inner diameter gradually increasing from top to bottom; The bottom diameter of the frustum is 40% to 80% of the outer diameter of the crucible, and the top diameter of the frustum is 30% to 60% of the outer diameter of the crucible.

2. The apparatus for growing large-size single crystals by PVT method according to claim 1, wherein, The fixed insulation structure has a through hole at its center, which serves as a temperature measurement channel.

3. The apparatus for growing large-size single crystals by PVT method according to claim 2, wherein, The diameter of the through hole is 5–20 mm.

4. The apparatus for growing large-size single crystals by PVT according to claim 1, wherein, The height of the frustum is 5–100 mm.

5. The apparatus for growing large-size single crystals by PVT according to claim 1, wherein, The height of the first section is 10 to 150 mm.

6. The apparatus for growing large-size single crystals by PVT according to claim 1, wherein, The fixed insulation structure and the movable insulation structure are made of materials selected from graphite soft felt and / or graphite hard felt.

7. A method for growing large-size single crystals by PVT, using the apparatus for growing large-size single crystals by PVT as described in any one of claims 1 to 6, comprising the following steps: (1) Place the raw material for growing single crystal in a crucible, fix the seed crystal on the top of the inner side of the crucible, place the fixed heat preservation structure at the center of the top of the crucible, and connect the movable heat preservation structure to the lifting and rotating device and move it to the initial position. (2) Heat is supplied to the crucible through an induction heating unit to sublimate the raw material; the temperature of the top center, the top edge and the bottom center of the crucible is monitored by an infrared temperature measuring unit to obtain the radial temperature gradient and the axial temperature gradient; (3) The radial temperature gradient is controlled by adjusting the relative position of the movable insulation structure and the fixed insulation structure during the growth process; the axial temperature gradient is controlled by adjusting the relative position of the crucible and the induction heating unit by moving the crucible. (4) By adjusting the relative positions of the movable insulation structure and the fixed insulation structure during the cooling process after growth, the insulation effect of the crucible edge is enhanced, thereby preventing stress cracking caused by excessively low crystal edge temperature. (5) During the growth and cooling processes, the crucible and the movable insulation structure are rotated.

8. The method according to claim 7, wherein, The seed crystal is 4 to 12 inches in size.

9. The method according to claim 7, wherein, The initial position of the movable heat-insulating structure is 5–20 mm from the top of the crucible.

10. The method according to claim 7, wherein, The radial temperature gradient in step (3) is 0.1 to 0.5℃ / cm, and the axial temperature gradient is 1 to 10℃ / cm.

11. The method according to claim 10, wherein, The radial temperature gradient in step (3) is 0.1 to 0.3℃ / cm, and the axial temperature gradient is 2 to 5℃ / cm.

12. The method according to claim 7, wherein, During the growth process, the crucible moves upward at a rate of 1 / 3 to 1 / 2 of the crystal growth rate.

13. The method according to claim 7, wherein, The rotation in step (5) is performed at a rotation speed of 0.1 to 5 rpm.

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