Single crystal furnace, annealing process of crystal bar and silicon wafer

Abstract

The invention relates to the photovoltaic field, and provides a single crystal furnace, an annealing process of a crystal bar and a silicon wafer, and the single crystal furnace comprises a main furnace chamber, an auxiliary furnace chamber, an induction heating mechanism, a laser heating mechanism, a lifting device and a control mechanism. The auxiliary furnace chamber is communicated with the main furnace chamber; the induction heating mechanism comprises an induction coil, and the induction coil is arranged in the auxiliary furnace chamber and circumferentially arranged around the axis of the auxiliary furnace chamber; a laser window of the laser heating mechanism emits laser into the auxiliary furnace chamber and is located on the side, away from the main furnace chamber, of the induction heating mechanism. The lifting device is connected with the crystal bar, so that the crystal bar can move along a first direction; and the control mechanism is connected with the induction heating mechanism, the laser heating mechanism and the lifting device. The annealing efficiency and performance of the crystal bar can be improved at least.

Description

Technical Field

[0001] The present disclosure relates to the photovoltaic field, and in particular to a single crystal furnace, a crystal rod annealing process, and a silicon wafer. Background Art

[0002] As fossil fuels gradually deplete, solar energy is becoming increasingly popular as a new energy alternative. Solar cells convert sunlight into electrical energy. They utilize the photovoltaic principle to generate charge carriers, which are then extracted using electrodes, facilitating the efficient use of electrical energy.

[0003] Crystal ingots are a crucial raw material for solar cell manufacturing. The oxygen content within the ingot affects its performance. After the ingot is drawn, an annealing process is typically performed to reduce the oxygen content and improve its performance. However, the efficiency of annealing ingots in related technologies is relatively low. Summary of the Invention

[0004] The embodiments of the present disclosure provide a single crystal furnace, a crystal rod annealing process, and a silicon wafer, which are at least beneficial to improving the annealing efficiency and performance of the crystal rod.

[0005] According to some embodiments of the present disclosure, on one hand, an embodiment of the present disclosure provides a single crystal furnace, which includes: a main furnace chamber; an auxiliary furnace chamber, which is connected to the main furnace chamber; an induction heating mechanism, which includes an induction coil, which is arranged in the auxiliary furnace chamber and is circumferentially arranged around the axis of the auxiliary furnace chamber; a laser heating mechanism, which emits laser into the interior of the auxiliary furnace chamber through a laser window, and the laser window is located on the side of the induction heating mechanism away from the main furnace chamber; a pulling device, which is connected to the crystal rod so that the crystal rod can move along a first direction; a control mechanism, which is connected to the induction heating mechanism; the control mechanism is connected to the laser heating mechanism; and the control mechanism is connected to the pulling device.

[0006] In some embodiments, the auxiliary furnace chamber includes multiple groups of laser window groups circumferentially arranged around the axis of the auxiliary furnace chamber, each group of the laser window groups includes at least one laser window, and the distances between any two groups of the laser window groups in the circumferential direction are equal.

[0007] In some embodiments, each group of the laser window groups includes multiple laser windows, the distance between adjacent laser windows along the first direction is 25mm to 35mm, the length of the laser windows along the first direction is 55mm to 65mm, and the length of the laser windows along the circumferential direction is 55mm to 65mm.

[0008] In some embodiments, the crystal rod includes a target area, and the single crystal furnace also includes: a temperature sensor, which is used to detect the temperature of the target area and upload the temperature of the target area to the control mechanism; when the target area reaches a preset position, if the temperature of the target area is lower than the target temperature, the control mechanism controls the laser to irradiate the target area so that the temperature of the target area is equal to the target temperature.

[0009] According to some embodiments of the present disclosure, on the other hand, embodiments of the present disclosure further provide an annealing process for a crystal rod using the single crystal furnace described in any of the aforementioned embodiments, wherein the crystal rod is annealed, and the annealing process for the crystal rod includes: providing the crystal rod, at least a portion of the crystal rod is located in the main furnace chamber, and controlling the crystal rod to move at a first rate along a first direction; first heating the crystal rod to a preset temperature by an induction heating mechanism; and then heating the surface area of ​​the crystal rod to a target temperature by the laser heating mechanism, wherein the target temperature is higher than the preset temperature.

[0010] In some embodiments, the preset temperature is 750°C to 850°C, and the target temperature is 1150°C to 1250°C.

[0011] In some embodiments, the first rate is 1 mm / min to 1.5 mm / min.

[0012] In some embodiments, during the process of controlling the crystal ingot to move along the first direction, the crystal ingot is also controlled to rotate; the rotation rate of the crystal ingot is 5 r / min to 14 r / min.

[0013] In some embodiments, the laser heating mechanism emits a laser moving along the first direction through the laser window, and the laser forms a laser spot on the surface of the crystal rod; the moving speed of the laser spot along the first direction is 3 mm / s to 8 mm / s.

[0014] In some embodiments, after the crystal rod reaches a preset position toward the end of the main furnace chamber, the annealing process of the crystal rod further includes: continuing to move the crystal rod along the first direction for a first time; the first time is 400s to 800s.

[0015] In some embodiments, after the first time, the annealing process of the crystal rod further includes: a first cooling step, cooling the crystal rod to 750°C to 850°C at a first cooling rate; a second cooling step, cooling the crystal rod to 550°C to 610°C at a second cooling rate; and a third cooling step, cooling the crystal rod to 15°C to 30°C at a third cooling rate; wherein the first cooling rate is greater than the second cooling rate, and the second cooling rate is greater than the third cooling rate.

[0016] In some embodiments, the first cooling rate is 240°C / min to 280°C / min; the second cooling rate is 40°C / min to 55°C / min; and the third cooling rate is 10°C / min to 15°C / min.

[0017] According to some embodiments of the present disclosure, another aspect of the embodiments of the present disclosure further provides a silicon wafer, which is cut from a crystal rod obtained using the single crystal furnace described in any of the above embodiments, or cut from a crystal rod obtained by the annealing process of the crystal rod described in any of the above embodiments, wherein the oxygen content of the silicon wafer is lower than 8 ppma.

[0018] The technical solution provided by the embodiments of the present disclosure has at least the following advantages:

[0019] In the technical solution of the single crystal furnace provided by the embodiments of the present disclosure, an induction heating mechanism and a laser heating mechanism can be used in the auxiliary furnace chamber to heat the crystal ingot and perform the crystal ingot annealing process. This eliminates the need to transfer the crystal ingot to other equipment for annealing after it is formed, saving time and improving the annealing efficiency of the crystal ingot.

[0020] In a single crystal furnace, a laser window is located on the side of the induction heating mechanism facing away from the main furnace chamber. The laser heating mechanism emits laser light through the laser window toward the crystal ingot. As the ingot is pulled by a pulling device, the induction heating mechanism first heats the ingot to a preset temperature. The laser heating mechanism then heats the surface of the ingot to a target temperature, which is greater than the preset temperature. This temperature increases the surface temperature above the target temperature, lowering the oxygen content within the ingot. The higher surface temperature promotes the dissociation of oxygen atoms within the surface region into free oxygen, which escapes the ingot, reducing the oxygen content within the surface. However, the lower temperature within the ingot prevents oxygen atoms from dissociating into free oxygen and escaping, resulting in a higher oxygen content within the ingot than at the surface. This creates a concentration difference between the ingot's interior and surface. This concentration difference drives oxygen atoms from the high-oxygen interior to the low-oxygen surface, ultimately escaping the ingot's surface and leaving the ingot, reducing the oxygen content and improving its performance.

[0021] In addition, the diffusion rate of oxygen atoms in the crystal rod is positively correlated with temperature. The temperature of the surface area of ​​the crystal rod is higher, which is conducive to the oxygen atoms in the surface area and the oxygen atoms that move from the inside of the crystal rod to the surface area to diffuse outward and escape from the crystal rod, which can reduce the oxygen content of the crystal rod and improve the performance of the crystal rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A schematic structural diagram of a single crystal furnace provided in an embodiment of the present disclosure;

[0024] Figure 2 A schematic diagram of a partial cross-sectional structure of a single crystal furnace provided in an embodiment of the present disclosure;

[0025] Figure 3 This is a schematic diagram of the connections of the control mechanism, laser heating mechanism, and induction heating mechanism in the single crystal furnace provided in an embodiment of the present disclosure.

[0026] Description of reference numerals:

[0027] 1. Single crystal furnace; 11. Main furnace chamber; 12. Auxiliary furnace chamber; 121. Laser window; 122. Laser window assembly; 123. Cooling pipe; 13. Induction heating mechanism; 131. Induction coil; 14. Laser heating mechanism; 15. Pulling device; 16. Control mechanism; 17. Vacuum system; 18. Cooling system. DETAILED DESCRIPTION

[0028] In the related art, after forming the crystal ingot, the crystal ingot is usually transferred to a high-temperature furnace for annealing. Transferring the crystal ingot is time-consuming, resulting in low annealing efficiency. Therefore, the annealing efficiency of the crystal ingot needs to be improved.

[0029] The disclosed embodiments provide a single crystal furnace, a crystal ingot annealing process, and a silicon wafer. In the single crystal furnace, induction heating and laser heating mechanisms can be used in a secondary furnace chamber to heat the crystal ingot for annealing. This eliminates the need to transfer the crystal ingot to other equipment for annealing after formation, saving time and improving annealing efficiency.

[0030] In a single crystal furnace, a laser window is located on the side of the induction heating mechanism facing away from the main furnace chamber, through which the laser heating mechanism emits laser light. As the crystal ingot is pulled by the pulling device, the induction heating mechanism first heats the ingot to a preset temperature. The laser heating mechanism then heats the surface of the ingot to a target temperature, which is greater than the preset temperature. This temperature increases the surface temperature, which is higher than the temperature within the ingot. The higher surface temperature favors the dissociation of oxygen atoms within the surface region into free oxygen, which escapes the ingot, reducing the oxygen content within the surface region. However, the lower temperature within the ingot prevents oxygen atoms from dissociating into free oxygen and escaping, resulting in a higher oxygen content within the ingot than at the surface. This creates a concentration difference between the ingot's interior and surface regions. This concentration difference drives oxygen atoms from the high-oxygen interior to the low-oxygen surface, ultimately escaping the ingot's surface and leaving the ingot, reducing the oxygen content and improving its performance. In addition, the diffusion rate of oxygen atoms in the crystal rod is positively correlated with temperature. The temperature of the surface area of ​​the crystal rod is higher, which is conducive to the oxygen atoms in the surface area and the oxygen atoms that move from the inside of the crystal rod to the surface area to diffuse outward and escape from the crystal rod, which can reduce the oxygen content of the crystal rod and improve the performance of the crystal rod.

[0031] In the description of the embodiments of the present disclosure, technical terms such as "first" and "second" are used solely to distinguish between different objects and should not be understood to indicate or imply relative importance or to implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present disclosure, "plurality" means more than two, unless otherwise specifically defined.

[0032] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of the present disclosure, the term "and / or" is merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0034] In the description of the embodiments of the present disclosure, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0035] In the description of the embodiments of the present disclosure, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the embodiments of the present disclosure.

[0036] In the description of the embodiments of the present disclosure, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connect," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and can refer to internal connectivity between two components or interaction between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present disclosure based on specific circumstances.

[0037] In the accompanying drawings corresponding to the embodiments of the present disclosure, the thickness and area of ​​the layers are magnified for better understanding and ease of description. When describing a component (such as a layer, film, region or substrate) on another component or on the surface of another component, the component can be "directly" located on the surface of the other component, or a third component can be present between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as being "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a partial edge of the entire surface.

[0038] In the description of the embodiments of the present disclosure, when a component “includes” another component, unless otherwise specified, other components are not excluded, and other components may be further included. In addition, when a component such as a layer, film, region, or plate is referred to as being “on / located on” another component, it can be “directly on” the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therebetween. In addition, when a component such as a layer, film, region, or plate is “directly located on” another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it means that no other components are located therebetween.

[0039] The following describes various embodiments of the present disclosure in detail with reference to the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present disclosure to facilitate a better understanding of the present disclosure. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present disclosure can still be implemented.

[0040] Figure 1 A schematic diagram of the structure of a single crystal furnace provided in an embodiment of the present disclosure is shown. Figure 2 A schematic diagram of a partial cross-sectional structure of a single crystal furnace provided in an embodiment of the present disclosure. Figure 3 This is a schematic diagram of the connection between the control mechanism, laser heating mechanism, and induction heating mechanism in the single crystal furnace provided by the embodiment of the present disclosure. Figure 2 This is a cross-sectional schematic diagram of the induction coil and laser window in the single crystal furnace.

[0041] Combined with reference Figures 1 to 3 The single crystal furnace includes a main furnace chamber 11, an auxiliary furnace chamber 12, an induction heating mechanism 13, a laser heating mechanism 14, a pulling device 15, and a control mechanism 16. The auxiliary furnace chamber 12 is connected to the main furnace chamber 11; the induction heating mechanism 13 includes an induction coil 131, which is arranged in the auxiliary furnace chamber 12 and circumferentially arranged around the axis of the auxiliary furnace chamber 12; the laser heating mechanism 14 emits laser light into the auxiliary furnace chamber 12 through a laser window 121, which is located on the side of the induction heating mechanism 13 facing away from the main furnace chamber 11; the pulling device 15 is connected to the crystal ingot, allowing the crystal ingot to move along the first direction X; the control mechanism 16 is connected to the induction heating mechanism 13, the control mechanism 16 is connected to the laser heating mechanism 14, and the control mechanism 16 is also connected to the pulling device 15.

[0042] The single crystal furnace 1 is used to form and anneal crystal ingots. The ingots are formed in the main furnace chamber 11. Specifically, raw materials are added to the furnace in the main furnace chamber 11 to melt the raw materials. The ingots are then formed through processes such as seeding, shoulder placement, shoulder rotation, diameter equalization, and finishing. Annealing of the ingots is then completed in the auxiliary furnace chamber 12.

[0043] The induction heating mechanism 13 is used to heat the crystal ingot. Specifically, it includes a power supply connected to an induction coil 131, which provides alternating current to the induction coil 131. This alternating current generates a magnetic field, which induces eddy currents in the crystal ingot. These eddy currents heat the crystal ingot through the Joule heating effect. The induction heating mechanism 13 is designed to heat both the surface and interior of the crystal ingot to a preset temperature.

[0044] The surface area is the portion of the ingot with a depth greater than zero and less than or equal to 1 mm in the direction from the surface of the ingot to the axial center of the ingot. The interior of the ingot refers to the remaining portion of the ingot excluding the surface area.

[0045] The induction coil 131 can be a copper tube water-cooled coil. The copper tube water-cooled coil uses the excellent electrical conductivity of copper to efficiently generate an alternating magnetic field to improve the induction heating efficiency. At the same time, its high thermal conductivity is used in conjunction with circulating water to quickly remove the Joule heat during the operation of the coil, thereby ensuring that the coil operates stably under high power conditions and extending its service life.

[0046] In some embodiments, the length of the induction coil 131 along the first direction X is 8 mm to 30 mm, for example, 8 mm, 10 mm, 15 mm, 20 mm, 25 mm, or 30 mm.

[0047] The heating area of ​​the induction heating mechanism 13 is defined by a first plane and a second plane within the single crystal furnace 1. Both the first plane and the second plane are perpendicular to the first direction X. The first plane is located at the end of the induction coil 131 closest to the main furnace chamber 11, and the second plane is located at the end of the induction coil 131 farther from the main furnace chamber 11. When the crystal ingot is within the heating area of ​​the induction heating mechanism 13, it can be fully heated by the induction heating mechanism 13 to a preset temperature.

[0048] It can be understood that the first plane and the second plane are artificially defined planes. In fact, the first plane and the second plane do not exist in the single crystal furnace 1.

[0049] In some embodiments, the induction heating mechanism 13 may further include a magnetic flux concentrator. The magnetic flux concentrator is disposed on the periphery of the induction coil 131 to concentrate the magnetic flux generated by the induction coil 131 and improve the heating efficiency of the induction coil 131 .

[0050] The laser heating mechanism 14 is used to heat the surface area of ​​the crystal rod with the emitted laser.

[0051] The diameter of the spot formed by the laser irradiation on the crystal rod can be 1 mm to 10 mm, for example, 1 mm, 3 mm, 5 mm, 7 mm or 10 mm.

[0052] In some embodiments, the auxiliary furnace chamber 12 includes multiple groups of laser window groups 122 circumferentially arranged around the axis of the auxiliary furnace chamber 12. Each group of laser window groups 122 includes at least one laser window 121, and any two groups of laser window groups 122 are equidistant in the circumferential direction. In other words, the laser window groups 122 are evenly distributed circumferentially, allowing the laser to simultaneously irradiate the crystal ingot from multiple directions. This ensures that all circumferential locations of the crystal ingot receive approximately equal energy, thus avoiding local overheating or insufficient heating caused by heating in a single direction.

[0053] In some embodiments, each laser window group 122 includes a plurality of laser windows 121 spaced apart along the first direction X. Compared to a solution in which each laser window group 122 includes only one laser window 121, each laser window group 121 includes at least two laser windows 121, so that each laser window group 121 can provide at least two laser beams, thereby improving the heating efficiency of the laser heating mechanism 14.

[0054] In each laser window group 122 , the multiple light spots formed on the crystal rod by the multiple laser beams emitted by the multiple laser windows 121 may completely overlap, partially overlap, or not overlap at all.

[0055] The distance between adjacent laser windows 121 along the first direction X is 25 mm to 35 mm, for example, 25 mm, 27 mm, 30 mm, 33 mm or 35 mm.

[0056] The length of the laser window 121 along the first direction X is 55 mm to 65 mm, for example, 55 mm, 57 mm, 60 mm, 63 mm, or 65 mm. The circumferential length of the laser window 121 is 55 mm to 65 mm, for example, 55 mm, 57 mm, 60 mm, 63 mm, or 65 mm. When the length of the laser window 121 is within the above range, the larger size of the laser window 121 can reduce restrictions and interference on the laser beam.

[0057] It is understandable that Figure 1 and Figure 2 Schematically shows the situation where each laser window group 122 includes two laser windows 121. In fact, the number of laser windows in the laser window group can also be a positive integer such as 3 or 4. Figure 1 and Figure 2 The figure shows that the laser window 121 is circular. In fact, the laser window 121 can also be in other shapes such as square and triangle.

[0058] The heating area of ​​the laser heating mechanism 14 is bounded by a third plane and a fourth plane within the single crystal furnace 1. Both the third plane and the fourth plane are perpendicular to the third direction. The third plane is located at the end of the laser window group 122 close to the main furnace chamber 11, and the fourth plane is located at the end of the laser window group 122 away from the main furnace chamber 11. It will be understood that the third plane and the fourth plane are artificially defined planes. In reality, the third plane and the fourth plane do not exist in the single crystal furnace 1. When the crystal ingot is within the heating area of ​​the laser heating mechanism 14, the crystal ingot within the heating area can be irradiated by the laser, causing the surface area of ​​this portion of the crystal ingot to be heated to the target temperature.

[0059] In some embodiments, the single crystal furnace 1 further includes a sapphire window embedded within the laser window 121. Sapphire has high light transmittance, can transmit high-power laser light with low loss, and is damage-resistant. Sapphire also has high melting point, thermal conductivity, and low thermal expansion properties, enabling stable operation at high temperatures, thereby improving the reliability of the single crystal furnace 1.

[0060] In some embodiments, the laser heating mechanism 14 may include a laser and a galvanometer system. The galvanometer system is connected to the laser. The laser is used to emit laser light and form a laser spot on the surface of the crystal rod. The galvanometer system adjusts the moving direction and moving speed of the laser spot on the crystal rod by adjusting the moving direction and moving speed of the laser light emitted by the laser.

[0061] In some embodiments, the galvanometer system can also adjust the size of the laser spot.

[0062] The pulling device 15 is connected to the crystal ingot, allowing it to move along a first direction X. The first direction X is the direction from the main furnace chamber 11 to the auxiliary furnace chamber 12. During the pulling process, the pulling device 15 can also control the rotation of the crystal ingot. When the laser heating mechanism 14 emits laser light through the laser window 121 to heat the surface area of ​​the crystal ingot, the rotation of the crystal ingot itself can be used to heat the circumferential surface area of ​​the crystal ingot. This eliminates the need for a complex laser scanning system. The pulling device 15 alone drives the crystal ingot to rotate, expanding the laser heating range and improving the practicality of the single crystal furnace 1.

[0063] In some embodiments, while the pulling device 15 drives the crystal ingot to rotate, under the control of the control mechanism 16, the laser light emitted by the laser heating mechanism 14 through the laser window 121 can be scanned back and forth between the third plane and the fourth plane along the first direction X. Specifically, under the control of the control mechanism 16, the galvanometer system can control the laser light emitted by the laser to move back and forth between the third plane and the fourth plane along the first direction X.

[0064] In other embodiments, the laser emitted by the laser heating may also be stationary, that is, the surface area of ​​the crystal ingot in the circumferential direction may be heated solely by the rotation of the crystal ingot itself.

[0065] The control mechanism 16 is connected to the induction heating mechanism 13 . The control mechanism 16 can control the current of the induction coil 131 in the induction heating mechanism 13 and the frequency of the alternating current of the induction coil 131 to control the heating rate of the induction heating mechanism 13 .

[0066] The control mechanism 16 is connected to the laser heating mechanism 14. The control mechanism 16 can control the wavelength and power of the laser emitted by the laser heating mechanism 14, and can also control the moving direction and moving speed of the laser spot formed by the laser on the crystal rod.

[0067] The control mechanism 16 is also connected to the pulling device 15. The control mechanism 16 can control the movement speed of the pulling device 15 in pulling the crystal ingot along the first direction X, and can also control the rotation speed of the crystal ingot.

[0068] In some embodiments, the crystal ingot includes a target area, and the single crystal furnace 1 further includes a temperature sensor. The temperature sensor is configured to detect the temperature of the target area and transmit the target area temperature to the control mechanism 16. When the target area reaches a preset position, if the temperature of the target area is less than the target temperature, the control mechanism 16 controls the laser to irradiate the target area to bring the temperature of the target area to the target temperature.

[0069] The target area is any area on the surface of the crystal ingot. The temperature sensor is used to detect the temperature of any area of ​​the crystal ingot and upload the temperature to the control mechanism 16.

[0070] The target area reaches the preset position means that the target area is located on the side of the fourth plane away from the main furnace chamber 11, that is, the target area is higher than the fourth plane, and the distance between the target area and the fourth plane along the first direction X is less than 4 mm.

[0071] When the target area reaches the preset position, the target area has been heated by the laser heating mechanism 14. Ideally, the temperature of the target area should be equal to the target temperature. Specifically, the temperature of the surface area of ​​the target area should be equal to the target temperature. If the temperature sensor detects that the temperature of the target area is lower than the target temperature, the control mechanism 16 controls the laser irradiation of the target area. Specifically, the control mechanism 16 can move the laser emission direction of at least one laser through the galvanometer system to move the laser spot to the target area and heat the target area to the target temperature. In this way, it can be ensured that the surface area of ​​the target area heated by the laser heating mechanism 14 reaches the target temperature, so that the temperature of the surface area of ​​the crystal rod is uniform, and the surface area of ​​the crystal rod can be kept at a higher target temperature. The oxygen atoms in the surface area dissociate into free oxygen and escape from the crystal rod, thereby reducing the oxygen content of the crystal rod.

[0072] It is understandable that after the moving laser heats the surface area of ​​the target area to the target temperature, the laser returns to its original working state, that is, the laser continues to scan back and forth in the first direction in the third plane and the fourth plane.

[0073] The temperature sensor may be a spectrometer.

[0074] In some embodiments, the single crystal furnace 1 further includes a position sensor connected to the control mechanism 16. The position sensor is used to detect the position of the crystal ingot and feed the position of the crystal ingot back to the control mechanism 16. Specifically, the position sensor can detect whether the target area of ​​the crystal ingot reaches the preset position.

[0075] In some embodiments, the single crystal furnace 1 further includes an observation window through which a worker can observe the moving position and annealing status of the crystal ingot.

[0076] In some embodiments, the spectrometer can detect the temperature of the crystal ingot through an observation window.

[0077] In some embodiments, the single crystal furnace 1 also includes a vacuum system 17, which is connected to the control mechanism 16 and to the auxiliary furnace chamber 12. Under the control of the control mechanism 16, the vacuum system 17 can adjust the vacuum degree in the auxiliary furnace chamber 12 to provide a vacuum environment for the annealing process of the crystal rod and provide an escape channel for the oxygen atoms in the crystal rod heated by the induction heating mechanism 13 and the laser heating mechanism 14 to escape.

[0078] In some embodiments, the single crystal furnace 1 further includes a cooling system 18 , which is connected to the control mechanism 16 . Under the control of the control mechanism 16 , the cooling system 18 can lower the temperature in the auxiliary furnace chamber 12 to lower the temperature of the crystal rod.

[0079] In some embodiments, the auxiliary furnace chamber 12 includes a cooling pipe 123 , and the cooling system 18 can reduce the temperature of the crystal ingot by providing a cooling medium into the auxiliary furnace chamber 12 through the cooling pipe 123 .

[0080] The cooling medium may be liquid nitrogen.

[0081] In some embodiments, the inner wall of the auxiliary furnace chamber 12 is provided with a thermal insulation coating to maintain the temperature inside the single crystal furnace 1 .

[0082] In the single crystal furnace 1 provided in the embodiment of the present disclosure, the induction heating mechanism 13 and the laser heating mechanism 14 can be used to heat the crystal ingot in the auxiliary furnace chamber 12 to perform the crystal ingot annealing process. This eliminates the need to transfer the crystal ingot to other equipment for annealing after it is formed, saving time and improving the annealing efficiency of the crystal ingot.

[0083] The induction heating mechanism 13 and the laser heating mechanism 14 can also be used to increase the temperature of the surface region of the crystal ingot to a higher temperature than the interior of the crystal ingot, creating a concentration difference between the interior and the surface regions. This concentration difference drives oxygen atoms from the high-oxygen interior to the low-oxygen surface region, ultimately escaping from the crystal ingot surface, leaving the crystal ingot, reducing the oxygen content in the crystal ingot and improving the performance of the crystal ingot. Furthermore, the diffusion rate of oxygen atoms in the crystal ingot is positively correlated with temperature. The higher temperature of the surface region of the crystal ingot facilitates the diffusion and escape of oxygen atoms in the surface region, as well as oxygen atoms that have moved from the interior of the crystal ingot to the surface region, leaving the crystal ingot. This can reduce the oxygen content in the crystal ingot and improve the performance of the crystal ingot.

[0084] According to some embodiments of the present disclosure, another aspect of the present disclosure provides an annealing process for a crystal ingot using a single crystal furnace according to any of the aforementioned embodiments. The annealing process for the crystal ingot provided by the present disclosure is described below. It should be noted that the same or corresponding parts as those in the aforementioned embodiments will not be repeated here.

[0085] Continue to refer Figures 1 to 3 The annealing process of the crystal rod includes: providing a crystal rod, at least a portion of which is located in a main furnace chamber 11, and controlling the crystal rod to move along a first direction X at a first rate; first heating the crystal rod to a preset temperature by an induction heating mechanism 13; and then heating the surface area of ​​the crystal rod to a target temperature by a laser heating mechanism 14, the target temperature being higher than the preset temperature.

[0086] This causes the temperature of the surface region of the crystal ingot to be higher than the temperature inside the crystal ingot. The higher temperature of the surface region of the crystal ingot facilitates the dissociation of oxygen atoms in the surface region into free oxygen and their escape from the crystal ingot, reducing the oxygen content in the surface region of the crystal ingot. However, the lower temperature inside the crystal ingot prevents the oxygen atoms from dissociating into free oxygen and escaping, resulting in a higher oxygen content inside the crystal ingot than in the surface region. This creates a concentration difference between the interior and surface regions of the crystal ingot. This concentration difference drives oxygen atoms from the high-oxygen interior to the low-oxygen surface region, ultimately escaping from the crystal ingot surface and leaving the crystal ingot, reducing the oxygen content in the crystal ingot and improving the performance of the crystal ingot. In addition, the diffusion rate of oxygen atoms in the crystal ingot is positively correlated with temperature. The higher temperature of the surface region of the crystal ingot facilitates the diffusion and escape of oxygen atoms in the surface region and those that have moved from the interior of the crystal ingot to the surface region, thereby reducing the oxygen content in the crystal ingot and improving the performance of the crystal ingot.

[0087] In addition, compared with the solution of directly using the laser heating mechanism 14 to heat the surface area of ​​the crystal rod to the target temperature without first heating the crystal rod to the preset temperature, heating the crystal rod to the preset temperature first can reduce the temperature difference between the surface area of ​​the crystal rod and the interior of the crystal rod, thereby avoiding the silicon lattice slip and dislocation caused by the excessive temperature difference.

[0088] It should be noted that although the temperature inside the crystal rod is low, some oxygen atoms may dissociate into free oxygen and escape. The temperature in the surface area of ​​the crystal rod is higher, and the number of oxygen atoms in the surface area dissociated into free oxygen is greater, which can still form a concentration difference such as high oxygen content inside and low oxygen content in the surface area.

[0089] In some embodiments, the crystal ingot may have an initial temperature before the annealing process. The initial temperature is 300°C to 450°C, for example, 300°C, 350°C, 380°C, 400°C, or 450°C. The initial temperature is the residual temperature of the crystal ingot after the crystal ingot has completed the seeding, shouldering, shoulder rotation, diameter equalization, finishing, and cooling processes in the main furnace chamber 11.

[0090] In some embodiments, the preset temperature is 750° C. to 850° C., for example, 750° C. to 780° C., 780° C. to 820° C., or 820° C. to 850° C. Exemplarily, the preset temperature may be 750° C., 765° C., 780° C., 800° C., 820° C., 835° C., or 850° C. Heating the crystal ingot to a preset temperature within the above range can effectively release thermal stress within the crystal ingot, preventing cracking or defects in the crystal ingot caused by excessive stress.

[0091] The target temperature is 1150°C to 1250°C, for example, 1150°C to 1180°C, 1180°C to 1220°C, or 1220°C to 1250°C. Exemplarily, the target temperature can be 1150°C, 1165°C, 1180°C, 1200°C, 1220°C, 1235°C, or 1250°C. When the target temperature is within the above range, the temperature of the surface area of ​​the crystal rod is relatively high. On the one hand, it is beneficial for the oxygen atoms in the surface area to dissociate into free oxygen and escape from the crystal rod. On the other hand, the diffusion rate of oxygen atoms in the rod is positively correlated with the temperature. The higher temperature of the surface area of ​​the crystal rod is beneficial to increase the diffusion and escape rate of oxygen atoms. Both of the above aspects are beneficial to reducing the oxygen content in the surface area. In addition, when the temperature is within the above range, it is also possible to repair minor damage and holes in the surface area, reduce defects in the surface area, and improve the performance of the crystal rod. In addition, when the target temperature is within the above range, it is also possible to avoid the melting of the crystal rod in the surface area or the change of the crystal orientation due to the target temperature being too high, thereby preventing the performance of the crystal rod from being affected.

[0092] In some embodiments, when the induction heating mechanism 13 is used to heat the crystal ingot, the current of the induction coil 131 is 220 A to 280 A, such as 220 A, 240 A, 260 A, or 280 A. The frequency of the alternating current of the induction coil 131 is 18 kHz to 24 kHz, such as 18 kHz, 20 kHz, 22 kHz, or 24 kHz.

[0093] In some embodiments, when the laser heating mechanism 14 is used to heat the surface area of ​​the crystal rod, the power of the laser emitted by each laser window 121 is 50 W / cm 2 ~1000W / cm 2 , for example 50W / cm 2 ~250W / cm 2 , 250W / cm 2 ~500W / cm 2 , 500W / cm 2 ~750W / cm 2 or 500 / cm 2 ~1000W / cm 2 The laser power can be 50W / cm2 , 200W / cm 2 , 250W / cm 2 、350W / cm 2 , 500W / cm 2 、650W / cm 2 , 750W / cm 2 、850W / cm 2 or 1000W / cm 2 .

[0094] The wavelength of the laser is 1000 nm to 1100 nm, for example, 1000 nm, 1020 nm, 1040 nm, 1060 nm, 1080 nm or 1010 nm. When the wavelength of the laser is within the above range, the laser has a good penetration effect and can effectively heat the surface area of ​​the crystal ingot.

[0095] In some embodiments, the first rate is 1 mm / min to 1.5 mm / min, such as 1 mm / min, 1.1 mm / min, 1.2 mm / min, 1.3 mm / min, 1.4 mm / min, or 1.1 mm / min. When the ingot movement rate is within this range, the ingot pulling rate is slow, and the ingot stays longer in the heating area of ​​the induction heating mechanism 13 and the heating area of ​​the laser heating mechanism 14, ensuring that the ingot is fully heated.

[0096] In some embodiments, while controlling the movement of the crystal ingot in the first direction X, the crystal ingot is also controlled to rotate. This allows the laser to illuminate and heat the entire circumference of the crystal ingot without scanning along its circumference; the rotation of the crystal ingot itself ensures that the laser is irradiated and heated. Specifically, the pulling device 15 of the single crystal furnace 1 can simultaneously drive the crystal ingot to rotate while moving it in the first direction X.

[0097] The rotation rate of the crystal rod is 5 r / min to 14 r / min, for example, 5 r / min, 7 r / min, 9 r / min, 11 r / min or 14 r / min.

[0098] In some embodiments, the laser heating mechanism 14 emits a laser beam that moves along a first direction X through the laser window 121 . By utilizing the rotation of the crystal ingot itself and allowing the laser beam to move along the first direction X, the circumferential surface area of ​​the crystal ingot within the heating area of ​​the laser heating mechanism 14 is ensured to be heated.

[0099] The laser forms a laser spot on the surface of the crystal rod. The laser spot moves along the first direction X at a speed of 3 mm / s to 8 mm / s, for example, 3 mm / s, 4 mm / s, 5 mm / s, 6 mm / s, 7 mm / s or 8 mm / s.

[0100] In some embodiments, the crystal rod includes a target area, and the annealing process of the crystal rod further includes: detecting the temperature of the target area of ​​the crystal rod; when the target area reaches a preset position, if the temperature of the target area is lower than the target temperature, and when the temperature of the surface area of ​​a portion of the crystal rod after being scanned by the laser heating mechanism 14 is lower than the target temperature, controlling the laser to irradiate the target area so that the temperature of the target area is equal to the target temperature.

[0101] The position of the target area can be detected by the position sensor of the single crystal furnace 1 and uploaded to the control mechanism 16, which then determines whether the target area has reached the preset position. The temperature of the target area can also be detected by the temperature sensor of the single crystal furnace 1 and uploaded to the control mechanism 16, which then determines the relationship between the temperature of the target area and the target temperature.

[0102] When the target area reaches the preset position, the target area has passed through the heating area of ​​the laser heating mechanism 14. Ideally, the temperature of the target area should be equal to the target temperature. Specifically, the temperature of the surface area of ​​the target area should be equal to the target temperature. If the temperature sensor detects that the temperature of the target area is lower than the target temperature, the control mechanism 16 controls the irradiation of the laser target area. The control mechanism 16 can move the laser emission direction of at least one laser through the galvanometer system, so that the laser spot moves to the target area and the temperature of the target area is heated to the target temperature. In this way, it can be ensured that the surface area of ​​the target area heated by the laser heating mechanism 14 reaches the target temperature, so that the temperature of the surface area of ​​the crystal rod is uniform, and the surface area of ​​the crystal rod can be at a higher target temperature, so that the oxygen atoms in the surface area dissociate into free oxygen and escape from the crystal rod, thereby reducing the oxygen content of the crystal rod.

[0103] In some embodiments, after the end of the crystal rod toward the main furnace chamber 11 reaches a preset position, the annealing process of the crystal rod further includes: continuing to move the crystal rod along the first direction X for a first time; the first time is 400s to 800s.

[0104] After the end of the crystal ingot reaches the preset position toward the main furnace chamber 11, that is, after the entire crystal ingot has been heated by the laser heating mechanism 14, the crystal ingot continues to move along the first direction X. Because an insulation layer is provided in the auxiliary furnace chamber 12, it can be assumed that the temperature of the crystal ingot remains substantially unchanged during this movement period. In other words, the first period can be considered the insulation stage in the crystal ingot annealing process.

[0105] During the holding phase, the stress inside the ingot is fully released at the preset temperature, allowing oxygen atoms to migrate to the surface area driven by concentration differences. Simultaneously, at the higher target temperature, the surface area of ​​the ingot is kept open, where oxygen atoms continue to dissociate into free oxygen and escape, reducing the oxygen content.

[0106] The first time can be 400s to 500s, 500s to 700s, or 700s to 800s. For example, the first time can be 400s, 450s, 500s, 600s, 700s, 750s, or 800s. Within the above ranges, the first time allows sufficient time for the crystal ingot to release stress and for oxygen atoms within the crystal ingot to escape and move away from the crystal ingot.

[0107] In some embodiments, the annealing process of the crystal ingot may further include shutting down the laser heating mechanism 14 and the induction heating mechanism 13 after the end of the crystal ingot facing the main furnace chamber 11 reaches a predetermined position. Once the end of the crystal ingot facing the main furnace chamber 11 reaches the predetermined position, i.e., after the entire crystal ingot has been heated by the induction heating mechanism 13 and the laser heating mechanism 14, the laser heating mechanism 14 and the induction heating mechanism 13 may be shut down to avoid wasting energy.

[0108] In some embodiments, after the first period of time, the annealing process for the crystal ingot further includes: a first cooling step, cooling the crystal ingot at a first cooling rate to a temperature of 750°C to 850°C; a second cooling step, cooling the crystal ingot at a second cooling rate to a temperature of 550°C to 610°C; and a third cooling step, cooling the crystal ingot at a third cooling rate to a temperature of 15°C to 30°C; wherein the first cooling rate is greater than the second cooling rate, and the second cooling rate is greater than the third cooling rate. The crystal ingot is first cooled to a temperature of 750°C to 850°C using the larger first cooling rate. This reduces the time the crystal ingot spends in the high-temperature range, thereby reducing the time for impurities to diffuse and defects to accumulate at high temperatures. This also prevents the crystal ingot from spending too long in the high-temperature range, as prolonged stress can induce creep damage and increase the risk of cracks. The ingot is then cooled to 550°C-610°C at the second highest cooling rate. This slows the temperature drop compared to a higher second cooling rate, allowing oxygen atoms ample time to diffuse from high-concentration areas to low-concentration areas. This reduces the likelihood of oxygen atoms concentrating in localized areas and reaching supersaturation due to temperature and concentration gradients, thereby reducing the chances of oxygen atoms nucleating and inhibiting the formation of oxygen precipitates. Finally, cooling to 15°C-30°C at a lower third cooling rate can achieve uniform temperature across the ingot, reduce temperature gradients within the ingot, and allow atoms within the ingot ample time to adjust and rearrange, maximizing the release of internal stress.

[0109] The high temperature zone refers to the temperature range from the first cooling temperature to the target temperature, and the first cooling temperature is 750°C to 850°C.

[0110] It is understandable that the crystal rod is cooled gradually from the surface area to the inside, so the first cooling stage is mainly used to cool the surface area of ​​the crystal rod, so that the temperature of the surface area of ​​the crystal rod is reduced from the target temperature to 750°C to 850°C.

[0111] In some embodiments, the first cooling rate is between 200°C / min and 280°C / min, for example, 200°C / min, 240°C / min, 240°C / min, 250°C / min, 260°C / min, 270°C / min, or 280°C / min. Within this range, the first cooling rate minimizes the time the ingot temperature remains in the high-temperature zone, reducing the time for impurity diffusion and defect accumulation at high temperatures. This also prevents the ingot from remaining in the high-temperature zone for too long, as prolonged stress can induce creep damage and increase the risk of cracks.

[0112] The second cooling rate is 40°C / min to 55°C / min, for example, 40°C / min, 45°C / min, 50°C / min, or 55°C / min. This second cooling rate allows sufficient time for oxygen atoms to diffuse within the ingot, preventing localized oversaturation and effectively suppressing the formation of oxygen precipitates. This also prevents the ingot's production annealing efficiency from being affected by an excessively slow second cooling rate.

[0113] The third cooling rate is 10°C / min to 15°C / min, for example, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, or 15°C / min. Within this range, a lower third cooling rate can ensure uniform temperature across the interior of the ingot, reduce temperature gradients within the ingot, and allow sufficient time for atoms within the ingot to adjust and rearrange, thereby maximizing the release of internal stress.

[0114] In some embodiments, the first cooling step, the second cooling step, and the third cooling step are completed by a cooling system 18 in the single crystal furnace 1. The cooling system 18 can cool the crystal ingot by providing liquid nitrogen.

[0115] In some embodiments, during the first cooling step, the flow rate of the liquid nitrogen is 80 slpm to 120 slpm, for example, 80 slpm, 90 slpm, 110 slpm, or 120 slpm. During the second cooling step, the flow rate of the liquid nitrogen is 25 slpm to 40 slpm, for example, 25 slpm, 30 slpm, 35 slpm, or 40 slpm. During the third cooling step, the flow rate of the liquid nitrogen is 8 slpm to 15 slpm, for example, 8 slpm, 10 slpm, 13 slpm, or 15 slpm.

[0116] In some embodiments, during the first cooling step, the crystal ingot moves at a rate of 2.8 mm / min to 3.5 mm / min, such as 2.8 mm / min, 3 mm / min, 3.3 mm / min, or 3.5 mm / min, along the first direction X. The relatively fast movement rate of the crystal ingot during the first cooling step facilitates reducing the distance between the crystal ingot and the cooling pipe 123 at a relatively fast rate, facilitating earlier contact of the crystal ingot with liquid nitrogen for cooling, thereby improving cooling efficiency.

[0117] In some embodiments, in the second cooling step, the crystal rod moves along the first direction X at a rate of 1.4 mm / min to 1.8 mm / min, for example, 1.4 mm / min, 1.5 mm / min, 1.6 mm / min, or 1.8 mm / min.

[0118] In some embodiments, in the third cooling step, the movement rate of the crystal rod along the first direction X is 0.6 mm / min to 0.9 mm / min, for example, 0.6 mm / min, 0.7 mm / min, 0.8 mm / min, or 0.9 mm / min.

[0119] In some embodiments, the annealing process of the crystal rod further includes providing a vacuum environment to provide an escape channel for oxygen atoms in the crystal rod heated by the induction heating mechanism 13 and the laser heating mechanism 14 to escape.

[0120] Specifically, the vacuum system 17 of the single crystal furnace 1 can be used to adjust the vacuum degree in the auxiliary furnace chamber 12 so that the vacuum degree in the auxiliary furnace chamber 12 is less than 5×10 -4 The vacuum degree is within this range, which is relatively low, and can prevent oxygen impurities in the auxiliary furnace chamber 12 from entering the crystal rod.

[0121] According to some embodiments of the present disclosure, another aspect of the present disclosure further provides a silicon wafer, which is cut from a crystal ingot obtained using a single crystal furnace according to any of the above embodiments, or cut from a crystal ingot obtained by an annealing process using a crystal ingot according to any of the above embodiments. The silicon wafer provided by the present disclosure is described below. It should be noted that the parts that are identical or corresponding to the above embodiments are not repeated here.

[0122] Silicon wafers can be used to make solar cells.

[0123] The oxygen content of the silicon wafer is less than 8 ppma (Parts Per Million by Atom), such as 1 ppma, 2 ppma, 3 ppma, 4 ppma, 5 ppma, 6 ppma, and 7 ppma. The lower the oxygen content of the silicon wafer, the fewer impurities and defects it contains, resulting in higher quality silicon wafers.

[0124] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present disclosure, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present disclosure. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the scope defined in the claims.

Claims

1. A single crystal furnace, characterized in that: include: main furnace room; Auxiliary furnace chamber, the auxiliary furnace chamber is connected to the main furnace chamber; an induction heating mechanism, the induction heating mechanism comprising an induction coil, the induction coil being disposed in the auxiliary furnace chamber and circumferentially arranged around the axis of the auxiliary furnace chamber; a laser heating mechanism, the laser heating mechanism emitting laser light into the interior of the auxiliary furnace chamber through a laser window, the laser window being located on a side of the induction heating mechanism facing away from the main furnace chamber; a pulling device connected to the crystal ingot so as to enable the crystal ingot to move along a first direction; A control mechanism connected to the induction heating mechanism; the control mechanism connected to the laser heating mechanism; The control mechanism is connected to the pulling device.

2. The single crystal furnace according to claim 1, characterized in that: The auxiliary furnace chamber includes a plurality of laser window groups circumferentially arranged around the axis of the auxiliary furnace chamber, each laser window group includes at least one laser window, and the distances between any two laser window groups in the circumferential direction are equal.

3. The single crystal furnace according to claim 2, characterized in that: Each group of the laser window groups includes a plurality of the laser windows arranged at intervals along the first direction, the distance between adjacent laser windows along the first direction is 25mm to 35mm, the length of the laser windows along the first direction is 55mm to 65mm, and the length of the laser windows along the circumferential direction is 55mm to 65mm.

4. The single crystal furnace according to claim 1, characterized in that The crystal rod includes a target area, and the single crystal furnace also includes: a temperature sensor, which is used to detect the temperature of the target area and upload the temperature of the target area to the control mechanism; when the target area reaches a preset position, if the temperature of the target area is lower than the target temperature, the control mechanism controls the laser to irradiate the target area so that the temperature of the target area is equal to the target temperature.

5. A crystal rod annealing process, characterized in that: The crystal ingot is annealed using the single crystal furnace according to any one of claims 1 to 4, wherein the annealing process of the crystal ingot comprises: Providing the crystal ingot, with at least a portion of the crystal ingot located in the main furnace chamber, and controlling the crystal ingot to move along a first direction at a first speed; First, the crystal rod is heated to a preset temperature by an induction heating mechanism; The surface area of ​​the crystal rod is then heated to a target temperature by the laser heating mechanism, and the target temperature is higher than the preset temperature.

6. The annealing process for the crystal rod according to claim 5, characterized in that: The preset temperature is 750°C to 850°C, and the target temperature is 1150°C to 1250°C.

7. The annealing process for the crystal rod according to claim 5, characterized in that: The first speed is 1 mm / min to 1.5 mm / min.

8. The annealing process for the crystal rod according to claim 5, characterized in that: In the process of controlling the crystal rod to move along the first direction, the crystal rod is also controlled to rotate; the rotation rate of the crystal rod is 5 r / min to 14 r / min.

9. The annealing process for the crystal rod according to claim 8, characterized in that: The laser heating mechanism emits a laser that moves along the first direction through the laser window, and the laser forms a laser spot on the surface of the crystal rod; the moving speed of the laser spot along the first direction is 3 mm / s to 8 mm / s.

10. The annealing process for a crystal rod according to claim 6, characterized in that: After the end of the crystal ingot toward the main furnace chamber reaches a preset position, the annealing process of the crystal ingot further includes: The crystal rod continues to be moved along the first direction for a first time period; the first time period is 400s to 800s.

11. The annealing process for a crystal rod according to claim 10, characterized in that: After the first time has passed, the annealing process of the crystal rod further includes: a first cooling step of cooling the crystal ingot to 750° C. to 850° C. at a first cooling rate; a second cooling step of cooling the crystal ingot to 550° C. to 610° C. at a second cooling rate; a third cooling step of cooling the crystal ingot to a temperature of 15° C. to 30° C. at a third cooling rate; The first cooling rate is greater than the second cooling rate, and the second cooling rate is greater than the third cooling rate.

12. The annealing process for a crystal rod according to claim 11, characterized in that: The first cooling rate is 240°C / min to 280°C / min; the second cooling rate is 40°C / min to 55°C / min; and the third cooling rate is 10°C / min to 15°C / min.

13. A silicon wafer, characterized in that: The silicon wafer is cut from a crystal rod obtained using the single crystal furnace according to any one of claims 1 to 4, or cut from a crystal rod obtained by the annealing process of the crystal rod according to any one of claims 5 to 12; wherein the oxygen content of the silicon wafer is lower than 8 ppma.

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