Differential pressure type magnetic control single crystal furnace and single crystal silicon pulling method

Abstract

The application provides a differential pressure type magnetic control single crystal furnace and a single crystal silicon pulling method, and relates to the technical field of single crystal silicon production.The single crystal furnace mainly comprises a furnace body, a quartz crucible, a heater, a crystal pulling rod, a horizontal magnetic field device and an elliptical magnetic field device; the quartz crucible comprises a center cylinder, an annular cylinder and a communicating hole to form a U-shaped communicating structure; the furnace body comprises an upper furnace shell, a lower furnace shell and a partition plate; the upper furnace shell and the center cylinder form a high-pressure cavity, and the lower furnace shell and the annular cylinder form a negative pressure cavity; the crystal pulling rod is arranged in the high-pressure cavity, and the heater is arranged in the negative pressure cavity; the horizontal magnetic field device can form a horizontal magnetic field in the annular cylinder, and the elliptical magnetic field device can form a radial magnetic field component and a vertical magnetic field component in the center cylinder.The application effectively suppresses the flow of the silicon melt at the crystal pulling interface through the pressure difference control of the high-pressure cavity and the negative pressure cavity and the cooperation of the partition magnetic field, and ensures the constant of the crystallization temperature, and is suitable for the production of small-size and high-quality single crystal silicon.

Description

Technical Field

[0001] This invention specifically relates to a differential pressure magnetically controlled single crystal furnace and a single crystal silicon pulling method, and pertains to the field of single crystal silicon production technology. Background Technology

[0002] In the production process of Czochralski (CZ) method for monocrystalline silicon, the silicon melt in the quartz crucible will generate strong thermal convection due to the temperature gradient. This thermal convection is beneficial for the curing of polycrystalline silicon raw materials and the evaporation of oxygen impurities. However, during crystal pulling, it will cause fluctuations in the melt temperature at the crystal pulling interface and uneven distribution of impurity elements such as oxygen and carbon, which seriously affects the uniformity of the resistivity of monocrystalline silicon.

[0003] To suppress unfavorable convection in molten silicon, the magnetron sputtering (MCZ) method is commonly used in existing technologies. This involves applying a magnetic field (such as a horizontal, vertical, or hook-shaped magnetic field) outside the single crystal furnace to suppress melt flow. For example, patent CN103590109B describes a magnetic field with a concave interface generated by using a first and second coil, which can suppress thermal convection at the interface. However, existing magnetic field control technologies still have the following shortcomings: 1. The melt not only exhibits thermal convection but also centrifugal eddies caused by the rotation of the crucible or crystal rod, making the situation extremely complex. It is difficult to completely suppress the melt flow using a magnetic field. Especially at the crystal pulling interface, the melt flow is still quite significant due to melt tension and capillary convection, directly affecting the quality of single-crystal silicon.

[0004] 2. Suppressing melt flow is a fundamental condition for producing high-quality monocrystalline silicon. In existing technologies, it is difficult to detect the flow rate and trajectory of the melt, and even more difficult to control the strength and distribution of the magnetic field based on the flow rate and trajectory of the melt. It is virtually impossible to completely suppress melt flow using only a magnetic field.

[0005] 3. To facilitate the growth and crystallization of single crystals, the melt at the crystallization interface needs to have a lower crystallization temperature than other parts, and this crystallization temperature must be kept constant. In existing technologies, even if the flow of the melt can be completely suppressed, it is difficult to guarantee a constant crystallization temperature. Summary of the Invention

[0006] This invention provides a differential pressure magnetically controlled single crystal furnace and a single crystal silicon pulling method, the purpose of which is to solve the technical problems of existing magnetically controlled Czochralski methods that are difficult to completely suppress melt flow and difficult to ensure constant crystallization temperature.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A differential pressure magnetron-controlled single crystal furnace, comprising: The quartz crucible consists of a central cylinder, an annular cylinder, and multiple connecting holes between the two. The silicon melt forms a U-shaped connecting structure between the central cylinder and the annular cylinder. The furnace body includes an upper furnace shell, a lower furnace shell, and a partition plate. The upper furnace shell is provided with an argon inlet, and the lower furnace shell is provided with a vacuum port. The partition plate separates the upper furnace shell and the central cylinder to form a high-pressure cavity filled with argon, and the lower furnace shell and the annular cylinder to form a negative-pressure cavity. The crystal pulling rod is installed inside the high-voltage chamber; The heater is located inside the negative pressure chamber; A horizontal magnetic field device is used to generate a horizontal magnetic field inside an annular cylinder. An elliptical magnetic field device can generate radial and vertical magnetic field components within a central cylinder.

[0008] Further improvements to the technical solution: The elliptical magnetic field device is mainly composed of an energized disc-shaped spiral coil.

[0009] Further improve the technical solution: Set a feeding port on the lower furnace shell for adding polycrystalline silicon raw materials into the annular cylinder.

[0010] Further improvement of the technical solution: The quartz crucible is fitted inside the graphite crucible, and an insulation shell is provided around the heater.

[0011] Further improvement to the technical solution: A sliding sealing structure is provided between the partition plate and the annular cylinder.

[0012] A method for pulling single-crystal silicon includes the following steps: S1: Place the polycrystalline silicon raw material into the annular cylinder, vacuum and heat it until the silicon melt in the annular cylinder flows into the central cylinder. S2: Argon gas is introduced into the high-pressure chamber. By controlling the pressure difference between the high-pressure chamber and the negative-pressure chamber, the silicon melt in the central cylinder is forced into the annular cylinder. Then, the horizontal magnetic field device is turned on to suppress the thermal convection of the silicon melt in the annular cylinder through the horizontal magnetic field. S3: By controlling the pressure difference between the high-pressure chamber and the negative-pressure chamber, some of the silicon melt in the annular cylinder flows into the central cylinder and is kept at a low liquid level. Then, the elliptical magnetic field device is turned on to suppress the centrifugal eddy current and capillary convection of the silicon melt in the central cylinder. S4: Lower the crystal pulling rod into the central cylinder to pull the silicon melt.

[0013] Further improve the technical solution: In S3, maintain the liquid level of the silicon melt in the central cylinder at 40-60mm.

[0014] After implementing the above technical solution, the present invention can produce the following beneficial effects compared with the prior art: 1. The central cylinder and the annular cylinder divide the silicon melt into two parts: a small portion is located in the central cylinder, and the majority is located in the annular cylinder. The central cylinder provides a relatively ideal static and stable environment for crystal pulling. This stable environment is mainly manifested in three aspects: First, the heater is located within the negative pressure chamber, and the temperature of the annular cylinder is higher than that of the central cylinder. This not only ensures that the temperature of the silicon melt in the central cylinder is lower than that in the annular cylinder, but also effectively inhibits temperature fluctuations caused by temperature convection between the two. Second, the central cylinder is far from the heater, and its heating relies mainly on heat conduction. The small temperature difference within the cylinder provides a relatively constant crystallization temperature for pulling. Third, the radius of the annular cylinder is at least twice that of the central cylinder. When the quartz crucible rotates, the intensity of the centrifugal eddy currents experienced by the silicon melt in the central cylinder is much less than that in the annular cylinder, effectively reducing melt flow caused by centrifugal eddy currents.

[0015] 2. During crystal pulling, the silicon melt inside the central cylinder is kept at a low liquid level by pressure difference. At this time, the silicon melt inside the central cylinder is in thin layer and in contact with the bottom of the central cylinder, which reduces the space for heat convection. Its heat transfer mainly relies on heat conduction and heat diffusion, which greatly reduces the melt flow caused by heat convection.

[0016] 3. The horizontal magnetic field device has a horizontal magnetic field perpendicular to the crystal growth axis, which can suppress the thermal convection and some centrifugal eddies of the melt in the annular cylinder, reduce the oxygen content, and facilitate the uniform distribution of dopants, oxygen, carbon and other impurity elements in the melt, thus preparing the melt for homogenization before entering the central cylinder.

[0017] 4. The elliptical magnetic field device mainly consists of energized disc-shaped spiral coils, which can form an elliptical closed magnetic field inside the central cylinder. Each elliptical magnetic field has both a radial component pointing towards the crystal growth axis and a perpendicular component parallel to the crystal growth axis. The perpendicular component can effectively suppress the generation of capillary convection at the liquid surface, while the radial component can significantly reduce the centrifugal eddies caused by the rotation of the crystal rod and quartz crucible, making the melt surface tend to be flat.

[0018] 5. This invention, through the combination of mechanical structure and magnetic control technology, can completely suppress the flow of melt and ensure a constant crystallization temperature, laying a solid foundation for the production of high-quality monocrystalline silicon. Attached Figure Description

[0019] Figure 1 The diagram shown is a schematic of a differential pressure magneto-controlled single crystal furnace.

[0020] Figure 2 The diagram shown is a cross-sectional view of a quartz crucible.

[0021] Figure 3 The diagram shown is a schematic of an elliptical magnetic field.

[0022] Figure 4 The diagram shown is a schematic of the process before the single crystal furnace is filled with materials.

[0023] Figure 5 The diagram shown is a schematic of the material after being melted in a single crystal furnace.

[0024] Figure 6 The diagram shows the suppression of thermal convection inside the annular cylinder by a horizontal magnetic field device.

[0025] Figure 7 The diagram shows the suppression of centrifugal eddies and capillary convection within the central cylinder by the elliptical magnetic field device.

[0026] Figure 8 The diagram shown is a schematic of a single crystal furnace for crystal pulling.

[0027] In the picture: 1. Furnace body; 1.1. Upper furnace shell; 1.2. Lower furnace shell; 1.3. Partition plate; 1.4. Argon inlet; 1.5. Vacuum port; 1.6. Feed port; 1.7. High-pressure chamber; 1.8. Negative-pressure chamber; 2. Quartz crucible; 2.1. Central cylinder; 2.2. Annular cylinder; 2.3. Connecting hole; 3. Graphite crucible; 4. Heater; 5. Insulation shell; 6. Crystal pulling rod; 7. Horizontal magnetic field device; 8. Elliptical magnetic field device; 9. Shaft; 10. Crystal rods. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these preferred embodiments are merely for explaining the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that in the description of the present invention, terms such as "front," "rear," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the direction or positional relationships shown in the accompanying drawings. This is merely for ease of description and does not indicate or imply that the device or component must have a specific orientation and positional relationship, and therefore should not be construed as a limitation of the present invention. It should also be noted that in the description of the present invention, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0029] Reference Figure 1-2 The differential pressure magnetostatic single crystal furnace of the present invention mainly consists of a furnace body 1, a quartz crucible 2, a graphite crucible 3, a heater 4, a heat insulation shell 5, a crystal pulling rod 6, a horizontal magnetic field device 7, and an elliptical magnetic field device 8.

[0030] The quartz crucible 2 consists of a central cylinder 2.1, an annular cylinder 2.2, and multiple connecting holes 2.3 between them. The central cylinder 2.1 is located in the central region of the quartz crucible, and the annular cylinder 2.2 surrounds the central cylinder 2.1. The two are connected by the connecting holes 2.3, forming a U-shaped connection between the silicon melt and the central cylinder 2.1 and the annular cylinder 2. The quartz crucible 2 is housed within a graphite crucible 3, which provides heat conduction, support, and protection for the quartz crucible 2. A rotating shaft 9 is connected to the bottom of the graphite crucible 3, which drives the quartz crucible 2 and the graphite crucible 3 to rotate together.

[0031] The furnace body 1 includes an upper furnace shell 1.1, a lower furnace shell 1.2, and a partition plate 1.3. The upper furnace shell 1.1 is provided with an argon inlet 1.4 for filling the furnace body with high-purity argon as a protective atmosphere. The lower furnace shell 1.2 is provided with a vacuum port 1.5 for performing vacuum operations on the furnace body. A feeding port 1.6 is provided on the lower furnace shell 1.2 for adding polycrystalline silicon raw materials into the annular cylinder 2.2.

[0032] The partition plate 1.3 is a conical rotating body installed inside the furnace body 1. Through the partition plate 1.3, the upper furnace shell 1.1 and the central cylinder 2.1 form a high-pressure chamber 1.7 filled with argon gas, and the lower furnace shell 1.2 and the annular cylinder 2.2 form a negative-pressure chamber 1.8. Since the quartz crucible 2 rotates during operation, a sliding sealing structure is provided between the partition plate 1.3 and the annular cylinder 2.2. The sliding sealing structure ensures the sealed isolation between the high-pressure chamber 1.7 and the negative-pressure chamber 1.8, while allowing the quartz crucible 2 to rotate with the rotating shaft 9.

[0033] The crystal pulling rod 6 is disposed inside the high-pressure chamber 1.7, and a seed crystal is connected to the lower end of the crystal pulling rod 6. The crystal pulling rod 6 is used to perform the crystal pulling operation of single crystal silicon inside the central cylinder 2.1, ultimately forming a crystal rod 10.

[0034] Heater 4 is located inside the negative pressure chamber 1.8 and around the annular cylinder 2.2. Heater 4 is used to heat graphite crucible 3 and quartz crucible 2. An insulation shell 5 is provided around heater 4 to reduce heat loss and improve the heating efficiency of heater 4 for graphite crucible 3 and quartz crucible 2.

[0035] The horizontal magnetic field device 7 is set outside the lower furnace shell 1.2 to form a horizontal magnetic field inside the annular cylinder 2.2, thereby suppressing the thermal convection and some centrifugal eddies of the silicon melt inside the annular cylinder 2.2.

[0036] An elliptical magnetic field device 8 is disposed at the bottom of the central cylinder 2.1 to generate an elliptical magnetic field within the central cylinder 2.1. In this embodiment, the elliptical magnetic field device 8 is mainly composed of an energized disc-shaped spiral coil.

[0037] Reference Figure 3 When the disc-shaped spiral coil is energized, it can form an elliptical closed magnetic field within the central cylinder 2.1 region. Each elliptical magnetic field has both a radial component pointing towards the crystal growth axis and a vertical component parallel to the crystal growth axis. The vertical component can effectively suppress the generation of capillary convection at the liquid surface, while the radial component can significantly reduce the centrifugal eddies caused by the relative rotation of the crystal rod 10 and the quartz crucible 2, making the silicon melt surface tend to be flat.

[0038] To illustrate the working principle of this single crystal furnace, this invention also discloses a method for pulling single crystal silicon, comprising the following steps: S1: Material Processing Stage Reference Figure 4-5Polycrystalline silicon raw material is fed into the annular cylinder 2.2 through the feeding port 1.6, and then the furnace body 1 is evacuated through the vacuum port 1.5 to achieve the predetermined vacuum level. The heater 4 is then activated to heat the polycrystalline silicon raw material in the annular cylinder 2.2 until it is completely melted into molten silicon. As the amount of molten silicon increases, it flows into the central cylinder 2.1 through the connecting hole 2.3 until the surface level of the molten silicon in the central cylinder 2.1 is approximately the same as that in the annular cylinder 2.2.

[0039] The central cylinder 2.1 and the annular cylinder 2.2 divide the silicon melt into two parts: a small portion is located in the central cylinder 2.1, and the majority is located in the annular cylinder 2.2. The central cylinder 2.1 provides a relatively ideal static and stable environment for crystal pulling: First, the heater 4 is located in the negative pressure chamber 1.8, and the temperature of the annular cylinder 2.2 is higher than that of the central cylinder 2.1. This not only ensures that the temperature of the silicon melt in the central cylinder 2.1 is lower than that in the annular cylinder 2.2, but also effectively blocks the temperature fluctuations caused by the temperature difference convection between the two through the connecting hole 2.3. Second, the central cylinder 2.1 is far from the heater 4, and the heating of the central cylinder 2.1 mainly relies on heat conduction. The small temperature difference within the cylinder provides a relatively constant crystallization temperature for crystal pulling. Third, the radius of the annular cylinder 2.2 is at least twice that of the central cylinder 2.1. During crystal pulling, the intensity of the centrifugal eddy currents on the silicon melt in the central cylinder 2.1 is much smaller than that on the annular cylinder 2.2, which can effectively reduce the melt flow caused by centrifugal eddy currents.

[0040] During this stage, the silicon melt is mainly heated by thermal convection, while about 99% of oxygen impurities are discharged from the melt.

[0041] S2: Annular cylinder thermal convection suppression stage Reference Figure 6 High-purity argon gas is introduced into the high-pressure chamber 1.7 through the argon inlet 1.4, while a vacuum is continuously pumped into the negative-pressure chamber 1.8 through the vacuum port 1.5, creating a predetermined pressure difference between the high-pressure chamber 1.7 and the negative-pressure chamber 1.8. Under this pressure difference, the molten silicon in the central cylinder 2.1 is forced into the annular cylinder 2.2. Then, the horizontal magnetic field device 7 is activated, creating a horizontal magnetic field within the annular cylinder 2.2. This horizontal magnetic field suppresses thermal convection and some centrifugal eddies in the molten silicon within the annular cylinder 2.2.

[0042] During this stage, the annular cylinder 2.2 serves as the main melting and storage area. Under the influence of the horizontal magnetic field, the thermal convection of the silicon melt inside is effectively suppressed, reducing the oxygen content. This facilitates the uniform distribution of dopants, oxygen, carbon, and other impurity elements within the silicon melt, preparing it for homogenization before it enters the central cylinder.

[0043] S3: Central cylinder centrifugal vortex and capillary convection suppression stage Reference Figure 7 By precisely controlling the pressure difference between the high-pressure chamber and the negative-pressure chamber, a portion of the molten silicon within the annular cylinder 2.2 flows into the central cylinder 2.1 through the connecting hole 2.3 under the influence of the pressure difference, maintaining a low liquid level within the central cylinder 2.1. Preferably, the liquid level of the molten silicon within the central cylinder 2.1 is maintained at 40-60 mm. This low liquid level design results in the molten silicon within the central cylinder 2.1 forming a thin layer in contact with the bottom of the central cylinder 2.1, reducing the space for thermal convection. Heat transfer primarily relies on conduction and diffusion, significantly reducing melt flow caused by thermal convection.

[0044] Then, the elliptical magnetic field device 8 is activated, forming an elliptical magnetic field within the central cylinder 2.1. The elliptical magnetic field device 8 can generate numerous elliptical closed magnetic fields within the central cylinder 2.1. Each elliptical magnetic field has both a radial component pointing towards the crystal growth axis and a perpendicular component parallel to the crystal growth axis. The perpendicular component effectively suppresses capillary convection at the liquid surface, while the radial component significantly reduces centrifugal eddies caused by the rotation of the crystal rod 10 and the quartz crucible 2, making the melt surface tend to be flat. Because the pressure difference reduces the height of the silicon melt within the central cylinder 2.1 and the distance to the elliptical magnetic field device 8, the elliptical magnetic field device 8 does not require a very high magnetic field strength to suppress the flow of the silicon melt.

[0045] During this stage, the silicon melt inside the central cylinder 2.1 is in a static and stable state, which completely suppresses the flow of the melt, and the melt temperature remains constant. As long as the crystallization temperature of the silicon melt inside the central cylinder 2.1 is well controlled, crystal pulling can be carried out.

[0046] S4: Crystal Pulling Stage Reference Figure 8 The crystal pulling rod 6 is lowered into the central cylinder 2.1, so that the seed crystal at the lower end of the crystal pulling rod 6 comes into contact with the surface of the molten silicon inside the central cylinder 2.1. The crystal pulling rod 6 rotates relative to the rotating shaft 9, and crystal pulling operations such as crystal introduction, shoulder formation, constant diameter growth, and tailing are performed on the molten silicon to finally obtain the crystal rod 10.

[0047] Throughout the crystal pulling process, the liquid level of the silicon melt in the central cylinder 2.1 is kept constant by controlling the pressure difference. Polycrystalline silicon raw materials can also be continuously supplied to the annular cylinder 2.2 through the feeding port 1.6 to achieve continuous crystal pulling production and improve production efficiency.

[0048] This invention can be widely applied in the field of monocrystalline silicon production, and is especially suitable for the Czochralski method of producing small-sized, high-quality monocrystalline silicon. Compared with existing technologies, this invention has the advantages of simple equipment structure, low magnetic field strength, low energy consumption, low cost, and high crystal pulling quality.

[0049] It is worth noting that the content not described in detail in the above embodiments is prior art. It is also worth noting that any additions, subtractions, substitutions, and improvements made by those skilled in the art based on the structure and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A differential pressure magnetostatic single crystal furnace, characterized in that: include: The quartz crucible consists of a central cylinder, an annular cylinder, and multiple connecting holes between the two. The silicon melt forms a U-shaped connecting structure between the central cylinder and the annular cylinder. The furnace body includes an upper furnace shell, a lower furnace shell, and a partition plate. The upper furnace shell is provided with an argon inlet, and the lower furnace shell is provided with a vacuum port. The partition plate separates the upper furnace shell and the central cylinder to form a high-pressure cavity filled with argon, and the lower furnace shell and the annular cylinder to form a negative-pressure cavity. The crystal pulling rod is installed inside the high-voltage chamber; The heater is located inside the negative pressure chamber; A horizontal magnetic field device is used to generate a horizontal magnetic field inside an annular cylinder. An elliptical magnetic field device can generate radial and vertical magnetic field components within a central cylinder.

2. The differential pressure magnetron-controlled single crystal furnace as described in claim 1, characterized in that: The elliptical magnetic field device is mainly composed of an energized disc-shaped spiral coil.

3. The differential pressure magnetron-controlled single crystal furnace as described in claim 1, characterized in that: A feeding port for adding polycrystalline silicon raw materials into the annular cylinder is provided on the lower furnace shell.

4. A differential pressure magnetron-controlled single crystal furnace as described in claim 1, characterized in that: The quartz crucible is fitted inside the graphite crucible, and an insulating shell is provided around the heater.

5. A differential pressure magnetron-controlled single crystal furnace as described in claim 1, characterized in that: A sliding sealing structure is provided between the partition plate and the annular cylinder.

6. A method for pulling single-crystal silicon crystals using the single-crystal furnace as described in claim 1, characterized in that: Includes the following steps: S1: Place the polycrystalline silicon raw material into the annular cylinder, vacuum and heat it until the silicon melt in the annular cylinder flows into the central cylinder. S2: Argon gas is introduced into the high-pressure chamber. By controlling the pressure difference between the high-pressure chamber and the negative-pressure chamber, the silicon melt in the central cylinder is forced into the annular cylinder. Then, the horizontal magnetic field device is turned on to suppress the thermal convection of the silicon melt in the annular cylinder. S3: By controlling the pressure difference between the high-pressure chamber and the negative-pressure chamber, some of the silicon melt in the annular cylinder flows into the central cylinder and is kept at a low liquid level. Then, the elliptical magnetic field device is turned on to suppress the centrifugal eddy current and capillary convection of the silicon melt in the central cylinder. S4: Lower the crystal pulling rod into the central cylinder to pull the silicon melt.

7. The method for pulling single-crystal silicon as described in claim 6, characterized in that: In S3, the liquid level of the silicon melt in the central cylinder is maintained at 40-60 mm.

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