A superconducting magnet, a magnetron-controlled single crystal pulling device and a control method

Abstract

This application discloses a superconducting magnet, a magnetron-controlled single crystal pulling device, and a control method. The superconducting magnet includes: a superconducting coil comprising two independent coil sections; a cold shield disposed outside the superconducting coil; a magnetically shielded yoke disposed outside the cold shield; a vacuum Dewar inner cylinder disposed outside the cold shield; a refrigerator disposed on the outer surface of the magnetically shielded yoke, and the refrigerator is conductively connected to both the superconducting coil and the cold shield; a set of current leads, each set electrically connected to one of the two coil sections; and a superconducting power supply electrically connected to the current leads. When the connection relationship between the current leads and the coil sections changes, the superconducting power supply inputs an excitation current to each coil section, thereby adjusting the magnetic field formed by each coil section as needed. The superconducting magnet of this application can not only generate different types of magnetic fields but also achieve adjustable magnetic field distribution, which will be of great significance for the production of high-quality single-crystal silicon.

Description

Technical Field

[0001] This application relates to the field of magnet equipment technology, and in particular to a superconducting magnet, a magnetically controlled single crystal pulling device and a control method. Background Technology

[0002] High-purity monocrystalline silicon is widely used in industries such as solar cells, integrated circuits, and semiconductors. It is one of the key materials for high-tech industries such as photovoltaic power generation and electronic information, and holds an important strategic position in ensuring energy, information, and national security. However, due to the high design, manufacturing, cost, and risk associated with the core component of magnetically pulled monocrystalline silicon technology—the large-scale superconducting strong magnet device—this technology has long been monopolized by foreign countries.

[0003] According to existing literature research, the superconducting magnet technology for magnetically controlled Czochralski (CZS) single crystal pulling is currently monopolized by foreign companies. In recent years, some domestic patents have been filed for protection. For example, in 2013, Li Chao, Yan Guo, et al. proposed "A MgB2 superconducting magnet for magnetically controlled CZS single crystal pulling" (publication number: CN103106994A); in 2019, Tang Hongming, Fu Linjian, et al. proposed "A superconducting magnet and magnetically controlled CZS single crystal pulling equipment" (publication number: CN110136915A). However, the above inventions only simply describe the superconducting magnet itself, without considering the combination of single crystal furnace and superconducting magnet, let alone how to use a single magnet to generate multiple variable magnetic field distributions to meet the complex and varied magnetic field distribution requirements of real-world single crystal pulling, and without considering cost control.

[0004] Currently, the magnetrons used in magnetically controlled single-crystal pulling superconducting magnets all use a fixed magnetic field type, such as horizontal field, CUSP (hook-shaped field), and longitudinal field (axial magnetic field). However, different types of products produced in actual crystal pulling require different magnetic field distributions. In reality, it is often necessary to purchase superconducting magnets with different magnetic field distributions, which will inevitably increase the cost for manufacturing companies significantly.

[0005] Meanwhile, since the superconducting coils in traditional superconducting designs have a fixed number of turns and are energized in series, the distribution of the magnetic field does not change when the magnetic field is energized as a whole. Only the magnetic field strength at the same location increases with the increase of current. This cannot effectively adapt to the needs of high-quality single crystal production by changing the magnetic field distribution. Summary of the Invention

[0006] This application provides a superconducting magnet, a magnetized single crystal pulling device, and a control method to solve the problem in the prior art that superconducting magnets cannot change the type and distribution of the magnetic field as needed.

[0007] On one hand, embodiments of this application provide a superconducting magnet, comprising: A superconducting coil is a ring structure. The superconducting coil contains two independent coil parts, which are arranged vertically opposite each other along the axial direction. The cold screen is set outside the superconducting coil and has a circular cylindrical structure. The magnetic shielding yoke is set outside the cold shield, with the top, bottom and sides of the cold shield facing each other. The vacuum Dewar inner cylinder is set outside the cold shield, with the side of the vacuum Dewar inner cylinder facing the side of the cold shield near the axis. The space enclosed between the vacuum Dewar inner cylinder and the magnetic shield yoke is in a vacuum state. The refrigerator is located on the outer surface of the magnetically shielded yoke and is connected to the superconducting coil and the cold shield for heat conduction. The current leads are in sets, and each set of current leads is electrically connected to two coil sections respectively. The superconducting power supply is electrically connected to the current leads. When the connection between the current leads and the coil parts changes, the superconducting power supply inputs excitation current to each coil part so that the magnetic field formed by each coil part can be adjusted as needed.

[0008] On the other hand, this application embodiment also provides a magnetron-controlled single crystal pulling device, including a single crystal furnace and the aforementioned superconducting magnet, wherein the single crystal furnace is coaxially disposed inside the superconducting magnet.

[0009] On the other hand, embodiments of this application also provide a control method for a magnetically controlled single crystal pulling device, including: Determine the type and distribution of magnetic fields that match the requirements for single crystal pulling; Change the connection relationship between each coil section of the superconducting coil and the superconducting power source; An excitation current is input into each coil section by a superconducting power source, so that the coil section generates the required magnetic field type and distribution.

[0010] The superconducting magnet, magneto-controlled single crystal pulling device, and control method disclosed in this application have the following advantages: 1. Traditional superconducting magnets have superconducting coils with a fixed number of turns, and multiple coils are connected in series. When the magnet is energized, the distribution of the magnetic field does not change. Only the magnetic field strength at the same location increases with the increase of current. This cannot adapt to the needs of high-quality single crystal production by changing the type and distribution of the magnetic field. The asymmetric superconducting magnet proposed in this application can not only generate different types of magnetic fields, but also achieve adjustable magnetic field distribution, which will be of great significance for the production of high-quality single crystal silicon.

[0011] 2. This application adopts an improved control current design scheme, which achieves the matching between the plane in the magnetic field and the silicon solution surface through electromagnetic field adjustment, avoiding the mechanical vibration introduced by the traditional magnet through the up and down adjustment of the mechanical shaft, and helping to eliminate single crystal defects caused by vibration.

[0012] 3. This application proposes a novel current lead design scheme, which ensures that the heat leakage of the current lead does not increase compared to the traditional magnet scheme when the magnetic field generated by the superconducting magnet is variable. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the overall structure of the magnetron-controlled single crystal pulling device provided in the embodiments of this application; Figure 2 for Figure 1 Cross-sectional view of a magnetron-controlled single crystal pulling device; Figure 3 This is a 1 / 2 cross-sectional view of a superconducting magnet provided in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a cold screen provided in an embodiment of this application; Figure 5 The force conditions of the superconducting magnet provided in the embodiments of this application under different energizing modes; Figure 6 For wiring control circuits of traditional superconducting magnets; Figure 7 The CUSP magnetic field distribution under a traditional wiring control circuit; Figure 8 The axial magnetic field distribution under traditional wiring control circuits; Figure 9 The wiring control circuit for the superconducting magnet provided in the embodiments of this application; Figure 10 This is a schematic diagram of the mounting structure of the current lead provided in an embodiment of this application; Figure 11 for Figure 10 A partially enlarged schematic diagram of the medium current lead and connector; Figure 12 for Figure 11 A schematic diagram showing the state of the medium current lead after it has moved within the connector. Figure 13 CUSP magnetic field distribution 1 for the asymmetric energizing mode provided in the embodiments of this application; Figure 14 CUSP magnetic field distribution 2 for the asymmetric energizing mode provided in the embodiments of this application; Figure 15The axial magnetic field distribution of the asymmetric energizing mode provided in the embodiments of this application.

[0015] Explanation of reference numerals: 1-Superconducting magnet, 2-Single crystal furnace, 3-Silicon rod assembly, 101-Refrigerator, 101A-First-stage cold head, 101B-Second-stage cold head, 102-Superconducting coil, 103-Cold shield, 103A-Slit, 104-Magnetic shielding yoke, 105-Vacuum Dewar inner cylinder, 106-Coil frame, 107-Current lead, 107A-Conventional conductor section, 107A-1-Modible part, 107A-2-Vacuum Empty sealed structure, 107A-3-plug socket, 107A-4-conductive block, 107A-5-connecting post, 107B-high temperature superconducting part, 108-pull-down rod, 109-pull-up rod, 110-superconducting power supply, 111-protection diode, 201-cavity, 202-heating element, 203-quartz crucible, 204-rotating shaft, 301-single crystal silicon rod, 302-sub-crystal, 303-pulling wire, 304-polycrystalline silicon melt. Detailed Implementation

[0016] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] This application provides a superconducting magnet, comprising: The superconducting coil 102 has a ring structure and includes two independent coil parts, which are arranged vertically opposite each other along the axial direction. A cold shield 103 is disposed outside the superconducting coil 102, and the cold shield 103 has a circular cylindrical structure. The magnetic shielding yoke 104 is disposed outside the cold shield 103, and the magnetic shielding yoke 104 faces the top surface, bottom surface and the side away from the axis of the cold shield 103. The vacuum Dewar inner cylinder 105 is set outside the cold screen 103. The vacuum Dewar inner cylinder 105 faces the side of the cold screen 103 near the axis. The space enclosed between the vacuum Dewar inner cylinder 105 and the magnetic shielding yoke 104 is in a vacuum state. The refrigerator 101 is disposed on the outer surface of the magnetically shielded yoke 104, and the refrigerator 101 is connected to the superconducting coil 102 and the cold shield 103 for heat conduction. The current leads 107 are in a set, and each set of current leads 107 is electrically connected to two coil sections respectively. The superconducting power supply 110 is electrically connected to the current lead 107. After the connection relationship between the current lead 107 and the coil section changes, the superconducting power supply 110 inputs excitation current to each coil section so that the magnetic field formed by each coil section can be adjusted as needed.

[0018] For example, such as Figure 1-15 As shown, the two coil sections are the same size and are respectively located at the top and bottom of the side of the coil frame 106 to form an up-down opposite state. Specifically, the coil frame 106 can adopt a ring-shaped cylindrical structure with a diameter between the inner and outer diameters of the cold screen 103, so that the superconducting coil 102 and the coil frame 106 can be installed as a whole inside the cold screen 103.

[0019] The cooling screen 103 is made of a material with good heat insulation properties. It can be a fully enclosed or open structure. A fully enclosed structure can minimize the heat load on the internal superconducting coil 102. In the embodiments of this application, the cooling screen 103 adopts an open structure. Specifically, the cooling screen 103 has multiple slits 103A. The slits 103A can be set on the inner or outer surface of the cooling screen 103 and extend axially to form a long strip structure. The use of slits 103A in this application can reduce the deformation of the cooling screen 103 caused by excessive eddy currents generated at the moment the superconducting coil 102 loses quench.

[0020] The magnetic shielding yoke 104 is used to confine the strong magnetic field generated by the superconducting coil 102 in the direction toward the axis, so as not to leak to the outside of the superconducting magnet 1.

[0021] When the connection between the superconducting power supply 110 and the superconducting coil 102 changes, the electromagnetic force generated will also change. To ensure that the superconducting coil 102 remains stable within the cold shield 103 after the change in electromagnetic force, the superconducting coil 102 in this application is connected to the inner bottom surface of the magnetic shielding yoke 104 via a pull rod 108, and to the inner top surface of the magnetic shielding yoke 104 via an upper pull rod 109. Furthermore, since the cold shield 103 is located outside the superconducting coil 102, the pull rods 108 and 109 need to pass through the cold shield 103. During installation, the cold shield 103 can be fixedly connected to the position through which the pull rods 108 and 109 pass, so that the cold shield 103 can also be in a stable position.

[0022] The refrigerator 101 has a primary cold head 101A and a secondary cold head 101B, which are respectively connected to the cold shield 103 and the superconducting coil 102 for thermal conductivity. In the embodiments of this application, the refrigerator 101 can be a GM refrigerator, whose primary and secondary cold heads cool the cold shield 103 and the superconducting coil 102 to different temperatures. Specifically, the secondary cold head 101B and the superconducting coil 102 can be connected by a high thermal conductivity secondary cold head heat-conducting plate to achieve cooling of the superconducting coil 102; similarly, the primary cold head 101A and the cold shield 103 can be connected by a high thermal conductivity primary cold head heat-conducting plate to achieve cooling of the cold shield 103. The connection can be achieved by welding or by bolting.

[0023] The current lead 107 includes a conventional conductor portion 107A and a high-temperature superconducting portion 107B. The high-temperature superconducting portion 107B is electrically connected to the superconducting coil 102. The conventional conductor portion 107A is slidably inserted into the magnetically shielded yoke 104. The high-temperature superconducting portion 107B is electrically connected to a socket 107A-3. The conventional conductor portion 107A is slidably inserted into the socket 107A-3. The connection relationship between the conventional conductor portion 107A and the superconducting coil 102 is different when the depth of insertion of the conventional conductor portion 107A into the socket 107A-3 is different.

[0024] Furthermore, such as Figure 10-12 As shown, there are two current leads 107 in a set. The two current leads 107 are electrically connected to the two ends of the superconducting power supply 110. Correspondingly, two vacuum sealing structures 107A-2 are provided on the magnetic shielding yoke 104. The conventional conductor part 107A of the two current leads 107 is inserted into the magnetic shielding yoke 104 through a vacuum sealing structure 107A-2, which also ensures that the vacuum environment inside the magnetic shielding yoke 104 is not affected.

[0025] Of the two current leads 107, the high-temperature superconducting portion 107B of one current lead 107 is electrically connected to one end of a coil portion. The connector 107A-3 has four connection points, which are electrically connected to the other end of one coil portion and both ends of the other coil portion, respectively. Two of these connection points are electrically connected to the same end of one coil portion. A conductive block 107A-4 is located at the inner bottom of the connector 107A-3. This conductive block 107A-4 can move up and down under the action of the movable portion 107A-1, allowing for different connection relationships between the two coil portions at different positions.

[0026] Specifically, the lower edge of the movable part 107A-1 has a protrusion that contacts and is electrically connected to the connection point inside the plug-in socket 107A-3. The lower end of the movable part 107A-1 has a connecting post 107A-5, which is made of the same material as the movable part 107A-1 and has threads on its outer surface. The top of the conductive post 107A-4 has a threaded hole that matches the connecting post 107A-5. When the movable part 107A-1 and the conductive block 107A-4 are in a position such as... Figure 11 In the state shown, the movable part 107A-1 is electrically connected only to connection point 2S, and not to connection point 2E. The conductive block 107A-4 connects connection points 2E and 1E together. At this time, when the superconducting power supply 110 provides current I1, Figure 10 In the middle coil section COIL1, the current flows from 1S to 1E, and in the coil section COIL2, the current flows from 2E to 2S.

[0027] When the connection needs to be changed, the movable part 107A-1 can be moved downwards. When the connecting post 107A-5 contacts the screw hole, the movable part 107A-1 also begins to rotate as it moves downwards, so that the connecting post 107A-5 is screwed into the screw hole. After the connecting post 107A-5 is fully screwed into the screw hole, the movable part 107A-1 is pulled upwards, causing the conductive block 107A-4 to move upwards inside the socket 107A-3. When the conductive block 107A-4 pushes the socket 107A-3 upwards... After connecting the two middle connection points 1E and 2S in 7A-3, rotate the movable part 107A-1 in the opposite direction to unscrew the connecting post 107A-5 from the screw hole of the conductive block 107A-4. After the connecting post 107A-5 is completely unscrewed, move the movable part 107A-1 upwards slightly to disengage the movable part 107A-1, including the connecting post 107A-5, from the conductive block 107A-4. At this point, the movable part 107A-1 is only electrically connected to connection point 2E. Figure 12 As shown, the current flowing through the coil portion COIL2 at this time is... Figure 11 The current flowing through the coil section COIL2 flows in the opposite direction, from 2S to 2E, while the current in the coil section COIL1 remains unchanged, thus changing the connection relationship.

[0028] With the above structure, this application achieves the connection change of the coil section using only one set of current leads 107, realizing the effect that traditional wiring methods require two sets of current leads 107 to achieve. This application can generate different magnetic field types using only one superconducting magnet 1 without increasing the system's thermal load. For more specific magnetic field distribution changes, it will be achieved through... Figure 9 The independent energizing model shown can be used to perform this. Figure 10The two coil sections, COIL1 and COIL2, are separate. Each coil section is connected to its respective superconducting power supply via a set of current leads 107, allowing two superconducting power supplies 110 to energize the two coil sections independently, achieving an asymmetric magnetic field distribution. Figure 13 , 14 As shown in Figure 15, in order to meet the special requirements of single crystal growth process, the plane offset ΔH in the magnetic field achieved by the electric field will improve the mechanical vibration caused by the traditional control method of matching the plane in the magnetic field with the plane of the silicon melt by the up and down movement of the rotating shaft 204 as the growth liquid level of the single crystal drops.

[0029] Meanwhile, this application also connects a protection diode 111 in parallel across both ends of each coil section. The protection diode 111 consists of two diodes connected in reverse parallel. By setting the protection diode 111, the large current in the coil section can be quickly discharged through the protection diode 111 when the superconducting magnet 1 loses its quench, thus avoiding damage to the coil section.

[0030] This application embodiment also provides a magnetron-controlled single crystal pulling device, which includes a single crystal furnace 2 and the superconducting magnet 1 described above, with the single crystal furnace 2 coaxially disposed inside the superconducting magnet 1.

[0031] For example, the single crystal furnace 2 includes: a cavity 201; a quartz crucible 203 disposed inside the cavity 201, the quartz crucible 203 being used to hold polycrystalline silicon material; a heating element 202 disposed outside the quartz crucible 203, the heating element 202 being used to heat the polycrystalline silicon material to form polycrystalline silicon melt 304; and a rotating shaft 204 disposed at the bottom of the quartz crucible 203.

[0032] Furthermore, after the superconducting magnet 1 and the single crystal furnace 2 are installed, when the silicon rod assembly 3 is produced, a vacuum unit is first used to evacuate the superconducting magnet 1, specifically the space enclosed by the magnetically shielded yoke 104 and the vacuum Dewar inner cylinder 105, until the vacuum level reaches 10. -2At a temperature of Pa, the refrigerator 101 is turned on to cool the superconducting magnet 1, and a temperature sensor is used to monitor the temperature at key temperature detection points. When the temperature of the superconducting coil 102 inside the superconducting magnet 1 is lower than the critical temperature Tc of the superconducting wire, the superconducting coil 102 enters the superconducting state and has the ability to be energized. Then, according to the requirements of single crystal growth, a suitable magnetic field type and magnitude are selected, and the superconducting magnet 1 is energized. When the magnetic field reaches the required value, the seed crystal 302 is placed into the cavity 201 through the pulling wire 303 and immersed in the upper part of the molten polycrystalline silicon liquid surface in the quartz crucible 203. The pulling wire 303 is slowly pulled to achieve crystal pulling. During the pulling process, the quartz crucible 203 is slowly rotated by the rotating shaft 204. When it is necessary to adjust the plane position in the magnetic field, the input current of the superconducting power supply 110 can be adjusted. Finally, according to the crystal pulling process, the production of the single crystal silicon rod 301 is completed.

[0033] This application also provides a control method for a magnetically controlled single crystal pulling device, the method comprising the following steps: Determine the type and distribution of magnetic fields that match the requirements for single crystal pulling; Change the connection relationship between each coil section of the superconducting coil 102 and the superconducting power supply 110; Excitation current is input into each coil section by superconducting power supply 110, so that the coil section generates the required magnetic field type and distribution.

[0034] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0035] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A superconducting magnet, characterized in that, include: The superconducting coil (102) has a ring structure and includes two independent coil parts, which are arranged vertically opposite each other along the axial direction. A cold screen (103) is disposed outside the superconducting coil (102), and the cold screen (103) is a ring-shaped cylindrical structure; A magnetic shielding yoke (104) is disposed outside the cold screen (103), and the magnetic shielding yoke (104) is directly opposite the top surface, bottom surface and side away from the axis of the cold screen (103); The vacuum Dewar inner cylinder (105) is disposed outside the cold screen (103). The vacuum Dewar inner cylinder (105) faces the side of the cold screen (103) near the axis. The space enclosed between the vacuum Dewar inner cylinder (105) and the magnetic shielding yoke (104) is in a vacuum state. A refrigerator (101) is disposed on the outer surface of the magnetically shielded yoke (104), and the refrigerator (101) is connected to the superconducting coil (102) and the cold shield (103) respectively for heat conduction. The current leads (107) are in a set, and each set of the current leads (107) is electrically connected to the two coil portions respectively; A superconducting power supply (110) is electrically connected to the current lead (107). After the connection relationship between the current lead (107) and the coil part changes, the superconducting power supply (110) inputs an excitation current to each of the coil parts so that the magnetic field formed by each of the coil parts can be adjusted as needed. The current lead (107) includes a conventional conductor portion (107A) and a high-temperature superconducting portion (107B). The high-temperature superconducting portion (107B) is electrically connected to the superconducting coil (102). The conventional conductor portion (107A) is slidably inserted into the magnetic shielding yoke (104). The high-temperature superconducting portion (107B) is electrically connected to a socket (107A-3). The conventional conductor portion (107A) is slidably inserted into the socket (107A-3). The connection relationship between the conventional conductor portion (107A) and the superconducting coil (102) is different when the depth of the conventional conductor portion (107A) inserted into the socket (107A-3) is different.

2. A superconducting magnet according to claim 1, characterized in that, The cold screen (103) has multiple slits (103A).

3. A superconducting magnet according to claim 1, characterized in that, The superconducting coil (102) is connected to the inner bottom surface of the magnetic shielding yoke (104) via a pull rod (108), and the superconducting coil (102) is connected to the inner top surface of the magnetic shielding yoke (104) via an upper pull rod (109).

4. A superconducting magnet according to claim 1, characterized in that, The refrigerator (101) has a primary cold head (101A) and a secondary cold head (101B), which are respectively connected to the cold screen (103) and the superconducting coil (102) for heat conduction.

5. A superconducting magnet according to claim 1, characterized in that, The cold screen (103) has a coil frame (106) inside, and the superconducting coil (102) is disposed on the coil frame (106).

6. A superconducting magnet according to claim 1, characterized in that, Each of the coil portions has a protection diode (111) connected in parallel at both ends.

7. A magnetically controlled single crystal pulling device, characterized in that, It includes a single crystal furnace (2) and a superconducting magnet (1) according to any one of claims 1-6, wherein the single crystal furnace (2) is coaxially disposed inside the superconducting magnet (1).

8. A magnetron-controlled single crystal pulling device according to claim 7, characterized in that, The single crystal furnace (2) includes: Cavity (201); A quartz crucible (203) is disposed inside the cavity (201) and is used to hold polycrystalline silicon material; A heating element (202) is disposed outside the quartz crucible (203) and is used to heat the polycrystalline silicon material to form a polycrystalline silicon melt (304). A rotating shaft (204) is located at the bottom of the quartz crucible (203).

9. The control method for the magnetically controlled single crystal pulling device of claim 7, characterized in that, include: Determine the type and distribution of magnetic fields that match the requirements for single crystal pulling; Change the connection relationship between each coil section of the superconducting coil (102) and the superconducting power supply (110); An excitation current is input to each of the coil sections via the superconducting power source (110) to generate the required magnetic field type and distribution in the coil sections.

Images