Crystal pulling method suitable for single heater thermal field

Abstract

The invention relates to the technical field of monocrystalline silicon crystal growth, in particular to a crystal pulling method suitable for a single heater thermal field. A crystal pulling method suitable for a single heater thermal field comprises the following steps: when material melting is completed and crystal pulling is carried out, controlling the upper edge of a heater to be above the upper edge of a crucible, and adjusting the vertical distance between the upper edge of the heater and the upper edge of the crucible to be 50-150mm; when crystal pulling enters an equal-diameter stage, along with growth of the crystal, the height of the heater is adjusted, so that the vertical height of the surface of the silicon melt and the upper edge of the heater is gradually increased. According to the crystal pulling method, a single heater is adopted, the number of heaters and matched parts are reduced, the thermal field structure is greatly simplified, and therefore the manufacturing cost of a thermal field is reduced; meanwhile, the bottom heater is omitted, so that invalid work of the bottom heater in the crystal pulling process is avoided, and the overall energy consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of single-crystal silicon crystal growth technology, and in particular to a crystal pulling method suitable for a single heater thermal field. Background Technology

[0002] In the growth of single-crystal silicon, thermal field design is a key factor determining crystal quality, production efficiency, and manufacturing costs. The widely adopted dual-heater structure, consisting of a main heater and a bottom heater, provides relatively uniform heating and reduces the risks of silicon leakage and seepage during the crystallization process to some extent. However, its inherent drawbacks are becoming increasingly apparent: First, the dual-heater system has a complex structure, requiring more thermal field components and increasing the difficulty of power wiring, significantly raising the construction and equipment investment costs. Second, the bottom heater is inactive for most of the crystal growth process, resulting in inefficient energy consumption and heat loss, and increasing the overall power demand of the equipment. With the semiconductor industry's trend towards larger crystal sizes, the structural complexity and cost issues of traditional dual-heater thermal fields are becoming increasingly prominent in meeting the demands of large-size applications. Therefore, developing a single-heater crystal pulling process that can meet the requirements of large-size thermal fields while also possessing high efficiency and energy-saving characteristics has become a pressing technological bottleneck for the industry.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a crystal pulling method suitable for a single-heater hot field, so as to solve the problems of complex structure, high cost, large heat loss and high power of traditional dual-heater hot field.

[0005] To achieve the above-mentioned objectives of the present invention, the present invention provides a crystal pulling method suitable for a single heater hot field, comprising the following steps: when the material is melted and crystal pulling is performed, the upper edge of the heater is controlled above the upper edge of the crucible, and the vertical distance between the upper edge of the heater and the upper edge of the crucible is adjusted to 50-150 mm; when the crystal pulling enters the constant diameter stage, as the crystal grows, the height of the heater is adjusted so that the vertical height between the surface of the silicon melt and the upper edge of the heater gradually increases.

[0006] In a specific embodiment of the present invention, when crystal pulling enters the constant diameter stage, as the crystal grows, the depth of the silicon melt gradually decreases, and the height of the heater gradually increases. The rate of decrease in the depth of the silicon melt is set as V1, and the rate of increase in the height of the heater is set as V2, satisfying: V2 = k·V1, where k is 0.2 to 0.3. Further, k is 0.23 to 0.27.

[0007] In a specific embodiment of the present invention, when the material is melted and crystal pulling is performed, the vertical height between the surface of the silicon melt and the bottom of the hot plate is adjusted to 20-30 mm.

[0008] In a specific embodiment of the present invention, during crystal pulling, as the crystal grows, the height of the crucible is adjusted so that the vertical height between the surface of the silicon melt and the bottom of the heat shield remains constant.

[0009] In a specific embodiment of the present invention, during the material preparation stage, the vertical distance between the center of the heater and the bottom of the crucible is adjusted to ≤100mm.

[0010] In a specific embodiment of the present invention, during the material preparation stage, the power of the heater increases from 0 to 140-160 kW within 30 minutes.

[0011] In a specific embodiment of the present invention, during the material preparation stage, after the material is added, when the area of ​​the remaining solid silicon material in the crucible is smaller than the area of ​​the bottom opening of the heat shield, the power of the heater is reduced. Further, reducing the power of the heater includes gradually reducing the power of the heater to 50-70 kW.

[0012] In a specific embodiment of the present invention, the single crystal furnace used in the crystal pulling method includes: Furnace body; A heat-insulating cylinder is installed on the inner wall of the furnace body; A heater is disposed in the inner ring of the insulation cylinder; A crucible is disposed within the inner cavity of the heater; A heat shield is disposed on the inner ring of the insulation cylinder and located above the crucible; The bottom of the crucible is provided with a first support unit, and the other end of the first support unit is connected to a first lifting unit; the bottom of the heater is provided with a second support unit, and the other end of the second support unit is connected to a second lifting unit.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The crystal pulling method of the present invention uses a single heater, which reduces the number of heaters and supporting components, greatly simplifies the thermal field structure, and thus reduces the manufacturing cost of the thermal field; at the same time, the elimination of the bottom heater avoids the ineffective operation of the bottom heater during the crystal pulling process and reduces the overall energy consumption. (2) The crystal pulling method of the present invention effectively avoids the risk of a single heater thermal field in the crystal pulling process by adjusting the relative positions of the heater and the crucible, so that the thermal field temperature distribution meets the temperature uniformity requirements of the crystal pulling process, ensuring that the crystal grows in a stable temperature environment, improving the quality of the crystal and the crystal pulling efficiency, meeting the needs of large-size crystal growth, and solving the problem of oxygen warping of the crystal rod. The oxygen content at the tail of the crystal rod can be reduced by more than 15%. (3) In the material preparation stage, the relative positions of the heater and the crucible are further adjusted so that the bottom of the crucible is in the high temperature zone, which effectively solves the problem of silicon leakage and silicon infiltration that may occur in the single heater thermal field during material preparation, improves the stability and safety of the material preparation stage, and provides a good crystal growth environment for subsequent crystal pulling. Attached Figure Description

[0014] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the structure of a single crystal furnace in the material preparation stage provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a single crystal furnace for the crystal pulling stage provided in an embodiment of the present invention.

[0016] Figure label: Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0018] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] Figure 1 This is a schematic diagram of the structure of a single crystal furnace in the material preparation stage provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a single crystal furnace for the crystal pulling stage provided in an embodiment of the present invention; as shown. Figures 1-2 As shown, the single crystal furnace with a single heater thermal field provided in this embodiment includes: Furnace body 1; Insulation cylinder 2 is installed on the inner wall of furnace body 1; Heater 3 is located in the inner ring of insulation cylinder 2; The crucible 4 is disposed inside the heater 3; Heat shield 5 is set in the inner ring of the heat preservation cylinder 2 and located above the crucible 4; The bottom of the crucible 4 is provided with a first support unit 6, and the other end of the first support unit 6 is connected to a first lifting unit (not shown in the figure); the bottom of the heater 3 is provided with a second support unit 7, and the other end of the second support unit 7 is connected to a second lifting unit (not shown in the figure).

[0021] The first support unit 6 includes, but is not limited to, a connecting rod, and the second support unit 7 includes, but is not limited to, a connecting rod. The first support unit 6 and the second support unit 7 pass through the bottom of the furnace body 1 and are connected to the first lifting unit and the second lifting unit, respectively. The structure of the first lifting unit and the second lifting unit is not limited; any structure capable of raising and lowering the crucible and the heater can be used. For example, the first lifting unit and the second lifting unit can each independently include a motor, a lead screw, and a controller. The motor is connected to the lead screw to drive the lead screw to rotate. The lead screw is connected to the first support unit 6 or the second support unit 7 to drive the crucible 4 or the heater 3 to move up and down. The heater 3 is installed on the second support unit 7 and the second lifting unit. The original lifting function of the crucible 4 is retained in the single crystal furnace, allowing the height of the heater 3 and the crucible 4 to be adjusted according to different stages of crystal growth to meet the positional requirements of different stages.

[0022] The single crystal furnace of this invention uses only one heater, eliminating the need for a traditional bottom heater. This greatly simplifies the thermal field structure and significantly reduces equipment costs, making it particularly suitable for large-scale industrial production and effectively enhancing the product's market competitiveness. The elimination of the bottom heater avoids its ineffective operation during crystal pulling, improving energy efficiency and reducing overall equipment energy consumption. Crystal pulling energy consumption can be reduced by approximately 20%.

[0023] This invention provides a crystal pulling method suitable for a single heater thermal field, comprising the following steps: when the material is prepared and crystal pulling is performed, such as... Figure 2 As shown, the upper edge of heater 3 is controlled above the upper edge of crucible 4, and the vertical distance between the upper edge of heater 3 and the upper edge of crucible 4 is adjusted to 50-150 mm. When crystal pulling enters the constant diameter stage, as the crystal grows, the height of the heater is adjusted so that the vertical height between the surface of the silicon melt and the upper edge of heater 3 gradually increases.

[0024] The crystal pulling method of the present invention effectively avoids the risks of a single heater thermal field in the crystal pulling process by coordinating and adjusting the relative positions of the heater 3 and the crucible 4, so that the temperature distribution of the thermal field meets the temperature uniformity requirements of the crystal pulling process, ensuring that the crystal grows in a stable temperature environment, improving the quality of the crystal and the crystal pulling efficiency, meeting the needs of large-size crystal growth, and solving the problem of oxygen warping of the crystal rod, which can reduce the oxygen content at the tail of the crystal rod by more than 15%.

[0025] When the melting process is complete and crystal pulling begins, the crystal is slowly pulled from the molten silicon in crucible 4. The upper edge of heater 3 is positioned above the upper edge of crucible 4, and the vertical distance between the upper edge of heater 3 and the upper edge of crucible 4 is adjusted to 50–150 mm. The higher position of heater 3 provides a more uniform heat distribution throughout the thermal field, meeting the temperature uniformity requirements in the initial stage of the crystal pulling process. This ensures the temperature distribution adapts to the needs of the crystal pulling process, guaranteeing crystal growth in a stable temperature environment and effectively improving crystal quality and pulling efficiency. In different embodiments, when melting is complete and crystal pulling begins, the vertical distance between the upper edge of heater 3 and the upper edge of crucible 4 can be adjusted to a range of 50 mm, 60 mm, 80 mm, 100 mm, 120 mm, 150 mm, or any combination thereof. It is understood that the vertical distance in this invention refers to the height difference between two components or positions measured along the vertical direction of the furnace body.

[0026] During crystal pulling, as the depth of the silicon melt decreases, the position of crucible 4 is continuously raised to maintain a constant vertical distance between the surface of the silicon melt and the bottom of the heat shield 5. The inventors of this invention discovered that this leads to a gradual increase in the proportion of silicon melt in the high-temperature zone as the crystal pulling process continues, significantly enhancing the thermal convection effect. This enhanced thermal convection accelerates the flow of silicon melt from the oxygen-rich zone to the crystal growth interface, resulting in uneven oxygen content distribution in the crystal rod. Specifically, the oxygen content at the tail of the crystal rod gradually accumulates and significantly increases, even exceeding the oxygen concentration at the head, forming the so-called "oxygen warping" phenomenon. This phenomenon directly affects the uniformity of crystal quality and electrical properties. In this invention, after the crystal pulling enters the constant diameter stage, the heater 3 is gradually raised to increase the distance between the surface of the silicon melt and the upper edge of the heater 3, thereby maintaining the proportion of silicon melt in the high-temperature zone and preventing oxygen warping.

[0027] In a specific embodiment of the present invention, when crystal pulling enters the constant diameter stage, as the crystal grows, the depth of the silicon melt gradually decreases, and the height of the heater 3 gradually increases. The rate of decrease in the depth of the silicon melt is set as V1, and the rate of increase in the height of the heater 3 is set as V2, satisfying: V2 = k·V1, where k is 0.2 to 0.3, preferably 0.23 to 0.27, and can be a range of 0.2, 0.22, 0.25, 0.28, 0.3, or any combination thereof. Adjusting V1 and V2 to meet the above conditions helps to ensure that the proportion of silicon melt in the high-temperature zone during the constant diameter stage remains essentially constant, reducing the thermal convection effect and avoiding oxygen warping.

[0028] Wherein, the rate of decrease of the depth of the silicon melt V1 refers to the height (e.g., mm) that the surface of the silicon melt moves down per unit time (e.g., 1 min); the rate of increase of the height of the heater 3 V2 refers to the height (e.g., mm) that the upper edge of the heater 3 moves up per unit time (e.g., 1 min).

[0029] In a specific embodiment of the present invention, when the material is prepared and crystal pulling is performed, the vertical height between the surface of the silicon melt and the bottom of the hot plate 5 is adjusted to 20-30 mm, for example, it can be 20 mm, 22 mm, 25 mm, 28 mm, 30 mm or any combination thereof, which helps to control the thermal field and improve the crystal quality and oxygen content.

[0030] In a specific embodiment of the present invention, during crystal pulling, as the crystal grows, the height of the crucible 4 is adjusted so that the vertical height between the surface of the silicon melt and the bottom of the heat shield 5 remains constant. Further, the vertical height between the surface of the silicon melt and the bottom of the heat shield 5 is 20–30 mm.

[0031] In a specific embodiment of the present invention, during the material preparation stage, such as Figure 1 As shown, the vertical distance between the center of the heater 3 and the bottom of the crucible 4 is adjusted to ≤100mm, for example, it can be a range of 100mm, 80mm, 50mm, 30mm, 0 or any two of them.

[0032] Specifically, the center of heater 3 can be located above the bottom of crucible 4, below the bottom of crucible 4, or at the same level as the bottom of crucible 4. Adjusting the positions of heater 3 and crucible 4 to meet the above requirements ensures that the bottom of crucible 4 is located in the high-temperature zone, avoiding silicon leakage and seepage problems, improving the stability and safety of the material preparation stage, and providing a good crystal growth environment for subsequent crystal pulling.

[0033] In a specific embodiment of the present invention, during the material preparation stage, the power of heater 3 increases from 0 to 140-160 kW within 30 minutes. Furthermore, the increase is linear.

[0034] In a specific embodiment of the present invention, 1 / 2 to 2 / 3 of the silicon material can be added to the crucible 4 first, and the remaining silicon material can be added through a feeder. The heater is turned on, and its power is increased from 0 to 140-160 kW within 30 minutes. Then, it is observed through the observation window. When liquid can be observed and unmelted silicon material is floating on the silicon melt, it is added through the feeder. In actual operation, during the melting stage, the heat shield 5 can be adjusted to its highest position first. When adding material, the position of the crucible 4 is appropriately lowered based on whether the height of the material in the crucible 4 will touch the lower edge of the heat shield 5, to avoid the silicon material touching the lower edge of the heat shield 5.

[0035] In a specific embodiment of the present invention, during the material preparation stage, after the material is added, when the area of ​​the remaining solid silicon material in the crucible 4 is smaller than the area of ​​the bottom opening of the heat shield 5, the power of the heater 3 is reduced. Further, reducing the power of the heater 3 includes gradually reducing the power of the heater 3 to 50-70 kW, such as a range of 50 kW, 55 kW, 60 kW, 65 kW, 70 kW, or any combination thereof.

[0036] The above-mentioned material preparation steps help ensure that the bottom of crucible 4 is always in the high-temperature zone for preferential melting during the material preparation process, thus avoiding problems such as silicon leakage and silicon infiltration caused by the crystallization of the melt at the bottom.

[0037] In a specific embodiment of the present invention, the power of the heater is gradually reduced to 50-70 kW, and the rate of reduction of the heater power is 1-3 kW / min, for example, it can be a range of 1 kW / min, 1.2 kW / min, 1.5 kW / min, 1.8 kW / min, 2 kW / min, 2.2 kW / min, 2.5 kW / min, 2.8 kW / min, 3 kW / min or any combination thereof.

[0038] In a specific embodiment of the present invention, when the material preparation is completed and crystal pulling is performed, the power of heater 3 is adjusted to the crystal pulling power. Specifically, the crystal pulling power of this furnace, that is, the crystal pulling power corresponding to the successful crystal growth in the previous furnace, includes, but is not limited to, 55-65kW.

[0039] Example 1 This embodiment provides a crystal pulling method suitable for a single heater thermal field, employing, as follows: Figure 1 and Figure 2 The single crystal furnace shown includes the following steps: (1) Initially load 500 kg of silicon material into the crucible (36 inches), then add 480 kg of silicon material through the feeder. After loading, raise the heat shield 5 to the highest position; lower the heater 3 and raise the crucible 4 so that the vertical distance between the center of the heater 3 and the bottom of the crucible 4 is 0 (i.e., the center of the heater 3 and the bottom of the crucible 4 are at the same horizontal height). After furnace assembly and evacuation for leak detection, start heater 3 and linearly increase its power from 0 to 150kW within 30 minutes, then maintain it at 150kW. Observe through the observation window. When liquid can be observed and unmelted silicon material is floating on the silicon melt, add material through the feeder. During the addition, adjust the position of crucible 4 according to whether the height of the material in crucible 4 will touch the lower edge of the heat shield 5 to avoid the silicon material touching the lower edge of the heat shield 5, until all the silicon material is added. When the area of ​​the remaining solid silicon material in crucible 4 is smaller than the area of ​​the bottom opening of the heat shield 5, start reducing the power of heater 3 to 60kW within 30 minutes, and maintain it at 60kW until all the silicon material is melted.

[0040] (2) After the material is melted, lower the position of crucible 4 to the lower limit and the position of heat screen 5 to the lower limit. Then slowly raise crucible 4 so that the vertical height between the surface of the silicon melt in crucible 4 and the lower edge of heat screen 5 is 20-30 mm (e.g., 25 mm). Raise heater 3 so that the upper edge of heater 3 is above the upper edge of crucible 4 and the vertical distance between the upper edge of heater 3 and the upper edge of crucible 4 is 70 mm.

[0041] (3) Perform crystal pulling according to the conventional crystal pulling process, including temperature adjustment, crystal pulling, shoulder formation, and entering the equal diameter stage (furnace pressure is 7 torr, argon flow rate is 80 slpm, average production rate is set to 1.8 mm / min, crucible rotation speed is 6 r / min; other parameters not mentioned are set according to the conventional settings); during crystal pulling, as the crystal grows, adjust the height of crucible 4 so that the vertical height between the surface of the silicon melt and the bottom of the heat shield 5 remains unchanged; when entering the equal diameter stage, adjust the height of heater 3 so that the vertical height between the surface of the silicon melt and the upper edge of heater 3 gradually increases, and the rate of increase of the height of heater 3 is 0.25 times the rate of decrease of the depth of the silicon melt in crucible 4, until the crystal pulling is completed.

[0042] Example 2 This embodiment refers to the crystal pulling method of Embodiment 1, the only difference being that: in step (3), after entering the constant diameter stage, the height of heater 3 increases at a different rate.

[0043] In this embodiment, the heating rate of heater 3 is 0.15 times the rate at which the depth of the silicon melt in crucible 4 decreases.

[0044] Example 3 This embodiment refers to the crystal pulling method of Embodiment 1, the only difference being that: in step (3), after entering the constant diameter stage, the height of heater 3 increases at a different rate.

[0045] In this embodiment, the heating rate of heater 3 is 0.35 times the rate at which the depth of the silicon melt in crucible 4 decreases.

[0046] Comparative Example 1 The melting and crystal pulling processes are carried out using a conventional single-crystal furnace with a dual-heater thermal field. Both the melting and crystal pulling processes are of conventional design.

[0047] Comparative Example 2 This embodiment refers to the crystal pulling method of Embodiment 1, the only difference being that in step (3), when entering the equal diameter stage, the height of heater 3 is not adjusted.

[0048] The present invention employs the method of Example 1. Compared to Comparative Example 1, the crystal growth power decreased by 8 kW, a reduction of 23%. The oxygen content at the tail of the crystal rod obtained in Example 1 decreased by 2.5 ppm compared to the oxygen content at the tail of the crystal rod obtained in Comparative Example 1, a reduction of 25%. The oxygen content at the tail of the crystal rod obtained in Example 2 of the present invention increased by 1 ppm compared to the oxygen content at the tail of the crystal rod obtained in Example 1. The oxygen content at the tail of the crystal rod obtained in Example 3 of the present invention can be further reduced compared to the oxygen content of the crystal rod obtained in Example 1, but the crystallization rate is reduced (by approximately 10% compared to Example 1). The oxygen content at the tail of the crystal rod obtained in Comparative Example 2 increased by 1.5 ppm compared to the oxygen content at the tail of the crystal rod obtained in Example 1.

[0049] As can be seen from the above, the crystal pulling method of the present invention uses a single heater, which reduces the overall energy consumption; by coordinating and adjusting the relative positions of the heater and the crucible, the temperature distribution of the thermal field meets the temperature uniformity requirements of the crystal pulling process, ensuring that the crystal grows in a stable temperature environment, improving the quality of the crystal and the crystal pulling efficiency, meeting the needs of large-size crystal growth, and solving the problem of oxygen warping of the crystal rod, the oxygen content at the tail of the crystal rod can be reduced by more than 15%.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for crystal pulling suitable for a single heater hot zone, characterized in that, The method comprises the following steps: when the melting is completed and the crystal pulling is performed, the upper edge of the heater is controlled to be above the upper edge of the crucible, and the vertical distance between the upper edge of the heater and the upper edge of the crucible is adjusted to be 50-150 mm; When the crystal pulling enters the equal-diameter stage, the height of the heater is adjusted to gradually increase the vertical distance between the silicon melt surface and the upper edge of the heater as the crystal grows.

2. The method of claim 1, wherein, When the crystal pulling enters the equal-diameter stage, the depth of the silicon melt gradually decreases, the height of the heater gradually increases, the decreasing rate of the depth of the silicon melt is set to V1, the increasing rate of the height of the heater is set to V2, and V2=k*V1 is satisfied, wherein k is 0.2-0.

3.

3. The crystal pulling method according to claim 2 wherein, k is 0.23-0.

27.

4. The crystal pulling method according to claim 1, wherein When the melting is completed and the crystal pulling is performed, the vertical distance between the silicon melt surface and the bottom of the heat shield is adjusted to be 20-30 mm.

5. The method of claim 1, wherein, When the crystal pulling is performed, the height of the crucible is adjusted to keep the vertical distance between the silicon melt surface and the bottom of the heat shield unchanged as the crystal grows.

6. The crystal pulling method according to claim 1 wherein, During the melting, the vertical distance between the center of the heater and the bottom of the crucible is adjusted to be ≤100 mm.

7. The crystal pulling method according to claim 1 wherein, During the melting, the power of the heater is increased from 0 to 140-160 kW within 30 min.

8. The crystal pulling method according to claim 1 wherein, During the melting, after the melting is completed, the power of the heater is decreased when the area of the remaining solid silicon material in the crucible is less than the area of the bottom opening of the heat shield.

9. The crystal pulling method according to claim 8 wherein, The decreasing of the power of the heater comprises gradually decreasing the power of the heater to 50-70 kW.

10. The crystal pulling method according to any one of claims 1 to 9, characterized by, The single crystal furnace used in the crystal pulling method comprises: a furnace body; a heat preservation cylinder arranged on the inner wall of the furnace body; a heater arranged on the inner ring of the heat preservation cylinder; a crucible arranged in the inner cavity of the heater; a heat shield arranged on the inner ring of the heat preservation cylinder and above the crucible; the bottom of the crucible is provided with a first support unit, and the other end of the first support unit is connected with a first lifting unit; the bottom of the heater is provided with a second support unit, and the other end of the second support unit is connected with a second lifting unit.

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