Device and method for reducing oxygen content of silicon single crystal

Abstract

The present invention provides a device and method for reducing the oxygen content of silicon single crystal, belonging to the technical field of single crystal silicon production, including: a single crystal furnace, a crucible is arranged inside the single crystal furnace; a heat shield, the heat shield is arranged above the crucible, the heat shield includes an upper heat shield and a lower heat shield, the upper heat shield includes an inclined section and a vertical section, the lower heat shield includes an outer side of the lower section and an inner side of the lower section, the outer side of the lower section is connected to the vertical section, and the outer side of the lower section is inclined to increase the volatilization amount of oxygen elements on the surface of the melt; a graphite central axis, the graphite central axis is arranged below the crucible, an alloy central axis is arranged at the center of the graphite central axis, a lifting device is installed below the alloy central axis, and cooling water is passed into the alloy central axis, so that the position of the alloy central axis is controlled by the lifting device during the crystal pulling process to control the temperature of the crucible and reduce the generation of oxygen elements. The present invention controls the oxygen content in the single crystal silicon rod to be below 5ppma while ensuring the stability of large-size single crystal silicon crystal growth by improving the structure of the heat shield and the central axis.

Description

Technical Field

[0001] The present invention relates to the technical field of single crystal silicon production, and in particular to a device and method for reducing the oxygen content of a silicon single crystal. Background Art

[0002] As a cornerstone device for energy conversion and transmission, insulated gate bipolar transistors (IGBTs) play a vital role in many national strategic emerging industries, including rail transit, smart grids, aerospace, electric vehicles, photovoltaics and wind power. In the production of IGBTs, the quality of semiconductor-grade single-crystal silicon wafers, as the substrate material of its chips, directly determines the overall performance of the IGBT. In particular, the oxygen content in single-crystal silicon has a significant effect on the resistivity before and after annealing in the IGBT process. In order to obtain the ideal resistivity specification, the oxygen content of single-crystal silicon must be strictly controlled.

[0003] At present, there are two main technical routes for producing IGBT substrate single crystal silicon materials: FZ method (Float Zone Method) and MCZ method (Magnetic Czochralski Method). However, the FZ method is limited by the physical properties of silicon materials, and the maximum size of single crystal silicon that can be manufactured is only 8 inches, which is stretched in the face of the growing demand for wafer fab process size. The MCZ method performs well in manufacturing 300mm large-size silicon wafers with its low cost and stability. However, large-size silicon wafers produced using the MCZ method often have a high oxygen content, which makes it difficult to meet the strict requirements of the IGBT chip process for an oxygen content of less than 5ppma. Summary of the invention

[0004] In view of this, the present invention provides a device and method for reducing the oxygen content of silicon single crystals to meet the demand for the oxygen content of large-size silicon wafers to be below 5 ppma.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A device for reducing the oxygen content of a silicon single crystal, comprising:

[0007] A single crystal furnace, wherein a crucible is arranged inside the single crystal furnace;

[0008] A heat shield, the heat shield is arranged above the crucible, the heat shield comprises an upper heat shield and a lower heat shield, the upper heat shield comprises an inclined section and a vertical section, the lower heat shield comprises an outer side of a lower section and an inner side of a lower section, the outer side of the lower section is connected to the vertical section, and the outer side of the lower section is inclined to increase the volatilization amount of oxygen elements on the surface of the melt;

[0009] A graphite center axis is arranged below the crucible, an alloy center axis is arranged at the center of the graphite center axis, a lifting device is installed below the alloy center axis, and cooling water is passed into the alloy center axis, so that the position of the alloy center axis can be controlled by the lifting device during the crystal pulling process to control the temperature of the crucible and reduce the generation of oxygen.

[0010] Preferably, the inner side of the lower section is arranged in a region of the crystal rod close to the solid-liquid interface to guide the gas flow and ensure the stability of crystal growth.

[0011] Preferably, the angle between the vertical section and the outer side of the lower section is 50-150°.

[0012] Preferably, the lifting device has a weighing function to ensure that the graphite center axis is in stable contact with the alloy center axis.

[0013] Preferably, a copper tube is arranged inside the alloy center shaft so that cooling water can be passed into the copper tube.

[0014] Preferably, the upper end of the alloy center shaft is a detachable structure.

[0015] A method for reducing the oxygen content of a silicon single crystal, using the device for reducing the oxygen content of a silicon single crystal as described above, characterized in that it includes: during the crystal pulling process, ensuring that the melt liquid level is at the same height as the center of the heater, and controlling the position of the alloy center axis according to the crystal growth stage to control the temperature of the crucible and reduce the generation of oxygen elements; wherein, in the early stage of crystal growth, the volatilization amount of the oxygen element is increased through the outer side of the upper section of the heat shield to reduce the oxygen content.

[0016] Preferably, controlling the position of the alloy center axis according to the crystal growth stage includes: in the early stage of crystal growth, closing the cooling water inside the alloy center axis, controlling the alloy center axis to descend away from the bottom of the crucible to keep the bottom of the crucible warm and ensure the quality of the crystal.

[0017] Preferably, as the single crystal silicon grows, when the R corner and the bottom of the crucible gradually enter the heating zone, cooling water is introduced into the alloy center axis, and the alloy center axis is controlled to rise so that the distance between the upper surface of the alloy center axis and the lower surface of the crucible is 5-10mm, so as to lower the temperature of the R corner and the bottom of the crucible and reduce the generation of oxygen.

[0018] Preferably, in the middle and late stages of crystal growth, when the R corner and the bottom of the crucible all enter the heating zone and are close to the main heating area, the center axis of the alloy is controlled to rise to contact the bottom of the crucible, so as to transfer heat through heat conduction, increase the cooling efficiency of the R corner and the bottom of the crucible, and reduce the generation of oxygen.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention improves the structure of the heat shield, utilizes the inclined setting of the outer side of the lower section to provide a larger oxygen volatilization area, so that more oxygen volatilizes, and utilizes the vertical section of the upper section of the heat shield to reduce its outer diameter while ensuring the growth stability of the crystal rod, increase the distance between the crucible wall and the outer side of the heat shield, and provide sufficient gas outlets before, during and after the crystal growth, so as to facilitate the oxygen to carry the volatilized oxygen element out of the crystal growth area, thereby reducing the amount of interstitial oxygen formed during the growth of single crystal silicon and reducing the oxygen content of the single crystal silicon. In addition, the present invention arranges an alloy middle axis at the center of the graphite middle axis. Since the temperature control effect of the middle axis is different at different stages of crystal growth, and the thermal conductivity of graphite is relatively weak, the heat transfer efficiency of directly introducing cooling water into the graphite middle axis is relatively low. Therefore, in order to more effectively control the temperature change of the crucible, an alloy middle axis with a better thermal conductivity coefficient is arranged at the center of the graphite middle axis, and the position of the alloy middle axis is controlled by a lifting device to control the temperature of the crucible and further reduce the generation of oxygen. Therefore, by adopting the heat shield structure and the central axis structure of the present invention, the oxygen content in the single crystal silicon rod can be stably controlled to be below 5 ppma while ensuring the stability of large-size single crystal silicon growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the device for reducing the oxygen content of silicon single crystal according to the present invention.

[0022] Figure 2 It is a cross-sectional view of the central axis of the alloy of the present invention.

[0023] Figure 3 It is a schematic diagram of the structure of the copper tube in the alloy center shaft of the present invention.

[0024] Figure 4 This is the oxygen content variation curve in Example 1.

[0025] Figure 5 This is the oxygen content change curve in Comparative Example 1.

[0026] In the figure: a single crystal furnace 10, a crucible 100, an inclined section 210, a vertical section 220, an outer side 230 of a lower section, an inner side 240 of a lower section, a graphite central axis 300, an alloy central axis 310, and a copper tube 311. DETAILED DESCRIPTION

[0027] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0028] Please see Figure 1 , a device for reducing the oxygen content of a silicon single crystal, comprising:

[0029] A single crystal furnace 10, wherein a crucible 100 is arranged inside the single crystal furnace 10;

[0030] A heat shield is arranged above the crucible 100, and includes an upper heat shield and a lower heat shield. The upper heat shield includes an inclined section 210 and a vertical section 220, and the lower heat shield includes a lower section outer side 230 and a lower section inner side 240. The lower section outer side 230 is connected to the vertical section 220, and the lower section outer side 230 is inclined to increase the volatilization amount of oxygen elements on the melt surface.

[0031] The graphite center axis 300 is arranged below the crucible 100, and an alloy center axis 310 is arranged at the center of the graphite center axis 300. A lifting device is installed below the alloy center axis 310, and cooling water is passed into the alloy center axis 310, so that the position of the alloy center axis 310 can be controlled by the lifting device during the crystal pulling process to control the temperature of the crucible 100 and reduce the generation of oxygen elements.

[0032] The present invention improves the structure of the heat shield, utilizes the inclined setting of the outer side of the lower section to provide a larger oxygen volatilization area, so that more oxygen volatilizes, and utilizes the vertical section of the upper section of the heat shield to reduce its outer diameter while ensuring the growth stability of the crystal rod, increase the distance between the crucible wall and the outer side of the heat shield, and provide sufficient gas outlets before, during and after the crystal growth, so as to facilitate the oxygen to carry the volatilized oxygen element out of the crystal growth area, thereby reducing the amount of interstitial oxygen formed during the growth of single crystal silicon and reducing the oxygen content of the single crystal silicon. In addition, the present invention arranges an alloy middle axis at the center of the graphite middle axis. Since the temperature control effect of the middle axis is different at different stages of crystal growth, and the thermal conductivity of graphite is relatively weak, the heat transfer efficiency of directly introducing cooling water into the graphite middle axis is relatively low. Therefore, in order to more effectively control the temperature change of the crucible, an alloy middle axis with a better thermal conductivity coefficient is arranged at the center of the graphite middle axis, and the position of the alloy middle axis is controlled by a lifting device to control the temperature of the crucible and further reduce the generation of oxygen. Therefore, by adopting the heat shield structure and the central axis structure of the present invention, the oxygen content in the single crystal silicon rod can be stably controlled to be below 5 ppma while ensuring the stability of large-size single crystal silicon growth.

[0033] Further, the lower inner side 240 is arranged in the region of the crystal rod close to the solid-liquid interface to guide the gas flow and ensure the stability of crystal growth. In some embodiments, the length of the lower inner side 240 is 50-100 mm, and the distance between the lower inner side and the crystal rod is 20-50 mm.

[0034] Furthermore, the angle between the vertical section 220 and the outer side 230 of the lower section is 50-150°. Among them, the inclined setting of the outer side 230 of the lower section is used to increase the volatilization amount of oxygen elements on the surface of the melt. During the growth of single crystals, more than 95% of the oxygen elements in the melt are volatilized into the gas environment through the surface of the melt. By setting the outer side 230 of the lower section at an angle, a larger oxygen volatilization area can be provided, so that more oxygen elements are volatilized, so that only fewer oxygen elements will flow to the growth front of the solid-liquid interface and grow in the single crystal silicon as interstitial oxygen, thereby reducing the oxygen content of the single crystal silicon. The vertical section of the upper heat shield can reduce its outer diameter while ensuring the growth stability of the crystal rod, increase the distance between the crucible wall and the outer side of the heat shield, and provide sufficient gas outlets before, during and after the crystal growth, so as to facilitate the argon gas to carry the volatilized oxygen elements out of the crystal growth area. In some embodiments, the length of the upper heat shield is 300-350mm, wherein the length of the vertical section is 200-250mm.

[0035] Furthermore, the lifting device has a weighing function to ensure that the graphite center axis 300 is in stable contact with the alloy center axis 310. Since the alloy center axis needs to be in contact with the crucible in a certain crystal growth stage to reduce the temperature at the bottom of the crucible, thereby controlling the oxygen content. However, during use, on the one hand, the crucible is made of graphite material, and there is a difference in the thermal expansion coefficients of graphite and alloy. Although the alloy center axis is kept at a lower temperature by cooling the circulating water, the difference in expansion will affect the contact effect between the crucible and the alloy center axis; on the other hand, the alloy center axis is deformed during long-term temperature-changing use, which will also affect the contact effect between the crucible and the alloy center axis. Through the weighing function, the weight of the alloy center axis can be obtained, thereby determining the rising speed of the alloy center axis, ensuring that the crucible and the alloy center axis are in stable contact and will not cause the crucible to shake.

[0036] For further information, see Figure 2 and Figure 3 A copper tube 311 is disposed inside the alloy center axis 310 to allow cooling water to flow into the copper tube 311. The copper tube 311 is arranged in a spiral to increase the heat dissipation area, thereby improving the cooling effect of the alloy center axis. In some embodiments, the gap between the graphite center axis and the alloy center axis is 10 mm.

[0037] Furthermore, the upper end of the alloy center shaft 310 is a detachable structure. The alloy center shaft 310 can be divided into a cover body at the upper end and a hollow cylinder in the middle, wherein the cover body at the upper end is a detachable component. After the alloy center shaft is used for a long time, the cover body at the upper end will be deformed due to temperature change, thereby causing the alloy center shaft and the crucible to be unable to stably contact. At the same time, setting the cover body at the upper end as a detachable component can facilitate the replacement of the cover body, thereby reducing costs while ensuring the use effect of the alloy center shaft.

[0038] A method for reducing the oxygen content of a silicon single crystal, using the device for reducing the oxygen content of a silicon single crystal as described above, comprising: during the crystal pulling process, ensuring that the position of the melt level and the center position of the heater are at the same height, and controlling the position of the alloy center axis according to the crystal growth stage to control the temperature of the crucible and reduce the generation of oxygen elements; wherein, in the early stage of crystal growth, the volatilization amount of the oxygen element is increased through the outer side of the upper section of the heat shield to reduce the oxygen content.

[0039] During the crystal growth process, while the length of the single crystal silicon rod increases, the molten silicon in the crucible continues to decrease. In order to ensure the stability of the crystal growth process, the melt liquid level position and the center position of the heater are kept at the same height. Since the position of the heater is fixed, in order to ensure that the liquid level position and the center position of the heater are at the same height, the crucible height will be continuously increased. In the early stage of crystal growth, there is more melt in the crucible, and the R corner and the bottom of the quartz crucible are not in the main heating area of ​​the heater, and the temperature is relatively low. Therefore, although the oxygen element produced by the quartz crucible at this time is less per unit area because the temperature of the melt contact area is relatively low, the crucible depth is relatively large at this time, and the contact area of ​​the melt is relatively large, which increases the overall amount of oxygen element produced. At this time, the shape of the heat shield of the present invention increases the volatilization amount of oxygen element, thereby reducing the oxygen content of the single crystal silicon. At the same time, in different crystal growth stages, it is necessary to control the central axis of the alloy to be in different positions to control the temperature of the crucible and reduce the generation of oxygen elements.

[0040] Furthermore, the position of the alloy center axis is controlled according to the crystal growth stage, including: in the early stage of crystal growth, the cooling water inside the alloy center axis is turned off, and the alloy center axis is controlled to descend away from the bottom of the crucible to keep the bottom of the crucible warm and ensure the quality of the crystal.

[0041] In the early stage of crystal growth, the bottom of the crucible is not in the main heating zone, and its temperature is not high. At this time, the bottom of the crucible needs to be insulated. On the one hand, the temperature of the crucible R angle and the bottom is prevented from being too low, causing the longitudinal temperature gradient inside the melt to be too low, and the crystal grows downward in the melt, resulting in abnormal crystal growth; on the other hand, when the melt is insufficient in the later stage, the lower growth part of the melt will contact the quartz crucible to cause the crucible to break, thereby leaking silicon and causing production accidents. Therefore, in the early stage of crystal growth, it is necessary to ensure the R angle and the bottom temperature. The present invention turns off the cooling water inside the alloy center axis and controls the alloy center axis to drop away from the bottom of the crucible. Since there is a certain gap between the outside of the alloy center axis and the outside of the graphite center axis, and no flowing gas is introduced, the heat can only be transferred through the heat conduction of the graphite center axis and the heat radiation between its surface and the surface of the alloy center axis. By lowering the alloy center axis, the heat radiation efficiency can be reduced, ensuring that it has a certain good insulation effect, so that the temperature in the melt will not be too low, affecting the growth of single crystals. At the same time, it can also be ensured that the alloy center axis away from the high-temperature surface of graphite will not be deformed due to excessively high temperature. In some embodiments, the pulling length at the initial stage of crystal growth is determined according to the feed amount, mainly based on the position of the R angle of the quartz crucible and the control target of the oxygen content. In the present invention, the crystal height at the initial stage of crystal growth can be 0-1000 mm. The height of the graphite center axis is always kept in correlation with the liquid level and the heater position height.

[0042] Furthermore, as the single crystal silicon grows, when the R corner and the bottom of the crucible gradually enter the heating area, cooling water is introduced into the alloy center axis, and the alloy center axis is controlled to rise so that the distance between the upper surface of the alloy center axis and the lower surface of the crucible is 5-10mm, so as to lower the temperature of the R corner and the bottom of the crucible and reduce the generation of oxygen.

[0043] As the single crystal silicon grows, the crystal length gradually increases, the melt gradually decreases, and the crucible moves up continuously, so that the gap between the outside of the heat shield and the crucible gradually decreases, thereby inhibiting the volatilization of oxygen elements. At this time, the R corner and the bottom of the crucible gradually enter the heating area, and the temperature begins to rise, so that the oxygen elements inside the crucible are generated and gradually released into the melt. Therefore, at this time, cooling water begins to flow into the alloy center axis, and the alloy center axis moves up, so that the distance between the upper surface of the alloy center axis and the lower surface of the graphite crucible is continuously shortened to 5mm-10mm, so as to increase the thermal radiation effect, reduce the temperature of the bottom and R corner of the crucible, and reduce the generation of oxygen elements. In addition, although the heat transfer efficiency of thermal radiation increases, the heat transfer efficiency is still controlled at a relatively low amplitude, so that the temperature of the bottom and R corner of the crucible can be ensured to be at a relatively low amplitude, but not too low, thereby reducing the generation of oxygen elements while ensuring the normal growth of crystals.

[0044] Furthermore, in the middle and late stages of crystal growth, when the R corner and the bottom of the crucible all enter the heating zone and are close to the main heating area, the central axis of the alloy is controlled to rise to contact the bottom of the crucible, so as to transfer heat through heat conduction, increase the cooling efficiency of the R corner and the bottom of the crucible, and reduce the generation of oxygen.

[0045] In the middle and late stages of crystal growth, the gap between the crucible and the outside of the heat shield is fixed, but the bottom of the crucible and the R corner all enter the heating zone and are close to the main heating area. The temperature of the R corner and the bottom rises. At this time, the central axis of the alloy rises to contact the bottom of the crucible. By changing the heat transfer mode, the heat transfer from thermal radiation to thermal conduction, the cooling efficiency of the R corner and the bottom is increased, so that the amount of oxygen generated is reduced by controlling the crucible temperature, and the oxygen content in the single crystal silicon is controlled and reduced. In addition, the weighing function of the lifting device of the central axis of the alloy is used to keep the weighing weight at about 5kg, so that while ensuring that the central axis of the alloy is in contact with the crucible, the stability of the crucible is not affected, and the quality of the crystal is ensured. In some embodiments, the weighing function of the lifting device is associated with the rising speed. When the weighing weight is between 4kg and 6kg, the rising speed of the central axis of the alloy is kept equal to the rising speed of the central axis of the graphite. When the weighing weight is >6kg, the rising speed of the central axis of the alloy is slightly reduced. When the weighing weight is <4kg, the rising speed of the central axis of the alloy is increased; to ensure that the central axis of the alloy can be in stable contact with the crucible.

[0046] For ease of understanding, the present invention is further illustrated by the following examples and comparative examples:

[0047] Embodiment 1: A 12-inch single crystal is pulled by using the device of the present invention, wherein a heat shield is arranged above the crucible, the heat shield comprises an upper heat shield and a lower heat shield, the upper heat shield comprises an inclined section and a vertical section, wherein the length of the upper heat shield is 320 mm, and the length of the vertical section is 215 mm; the lower heat shield comprises an outer side of a lower section and an inner side of a lower section, the outer side of the lower section is connected to the vertical section, and the outer side of the lower section is inclined, wherein the inclination angle of the outer side of the lower section is 140°, the length of the inner side of the lower section is 60 mm, and the spacing between the inner side of the lower section and the crystal rod is 40 mm; the graphite central axis is arranged below the crucible, an alloy central axis is arranged at the center of the graphite central axis, a lifting device is installed below the alloy central axis, and cooling water is introduced into the alloy central axis through a copper tube. In the early stage of crystal growth, the cooling water inside the alloy center axis is turned off, and the alloy center axis is controlled to descend away from the bottom of the crucible; as the single crystal silicon grows, when the R corner and the bottom of the crucible gradually enter the heating area, cooling water is introduced into the alloy center axis, and the alloy center axis is controlled to rise, so that the distance between the upper surface of the alloy center axis and the lower surface of the crucible is 5-10mm; in the middle and late stages of crystal growth, when the R corner and the bottom of the crucible all enter the heating zone and are close to the main heating area, the alloy center axis is controlled to rise until it contacts the bottom of the crucible.

[0048] Comparative Example 1: A 12-inch single crystal is pulled using the existing heat shield structure, central axis structure and existing crystal pulling method.

[0049] Oxygen content detection: The method of Example 1 was implemented three times, and the results of detecting the oxygen content of the crystal rod were as follows: Figure 4 As shown, the method of comparative example 1 was implemented 3 times, and the results of detecting the oxygen content of the crystal rod were as follows Figure 5 By comparison Figure 4 and Figure 5 It can be seen that the oxygen content of the crystal rod obtained in Example 1 is below 5 ppma.

[0050] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for reducing the oxygen content of a silicon single crystal, characterized in that: The following device is used: A single crystal furnace, wherein a crucible is arranged inside the single crystal furnace; A heat shield, the heat shield is arranged above the crucible, the heat shield comprises an upper heat shield and a lower heat shield, the upper heat shield comprises an inclined section and a vertical section, the lower heat shield comprises an outer side of a lower section and an inner side of a lower section, the outer side of the lower section is connected to the vertical section, and the outer side of the lower section is inclined to increase the volatilization amount of oxygen elements on the surface of the melt; A graphite center axis, wherein the graphite center axis is arranged below the crucible, an alloy center axis is arranged at the center of the graphite center axis, a lifting device is installed below the alloy center axis, and cooling water is passed into the alloy center axis, so that the position of the alloy center axis can be controlled by the lifting device during the crystal pulling process to control the temperature of the crucible and reduce the generation of oxygen elements; The method comprises: During the crystal pulling process, the melt level is ensured to be at the same height as the center of the heater, and the position of the alloy center axis is controlled according to the crystal growth stage to control the temperature of the crucible and reduce the generation of oxygen. In the early stage of crystal growth, the volatilization of oxygen is increased through the outer side of the upper section of the heat shield to reduce the oxygen content. Wherein, controlling the position of the central axis of the alloy according to the crystal growth stage comprises: At the beginning of crystal growth, the cooling water inside the alloy center axis is turned off, and the alloy center axis is controlled to drop away from the bottom of the crucible to keep the bottom of the crucible warm and ensure the quality of the crystal; As the single crystal silicon grows, when the R corner and the bottom of the crucible gradually enter the heating area, cooling water is introduced into the alloy center axis, and the alloy center axis is controlled to rise so that the distance between the upper surface of the alloy center axis and the lower surface of the crucible is 5-10mm, so as to reduce the temperature of the R corner and the bottom of the crucible and reduce the generation of oxygen elements; In the middle and late stages of crystal growth, when the R corner and bottom of the crucible all enter the heating zone and are close to the main heating area, the center axis of the alloy is controlled to rise to contact the bottom of the crucible to transfer heat through heat conduction, increase the cooling efficiency of the R corner and bottom of the crucible, and reduce the generation of oxygen.

2. The method for reducing the oxygen content of a silicon single crystal according to claim 1, characterized in that: The inner side of the lower section is arranged in a region of the crystal rod close to the solid-liquid interface to guide the gas flow and ensure the stability of crystal growth.

3. The method for reducing the oxygen content of a silicon single crystal according to claim 2, characterized in that: The angle between the vertical section and the outer side of the lower section is 50-150°.

4. The method for reducing the oxygen content of a silicon single crystal according to claim 1, characterized in that: The lifting device has a weighing function to ensure that the graphite center axis is in stable contact with the alloy center axis.

5. The method for reducing the oxygen content of a silicon single crystal according to claim 4, characterized in that: A copper tube is arranged inside the alloy center shaft so as to allow cooling water to flow into the copper tube.

6. The method for reducing oxygen content in silicon single crystal according to claim 4, characterized in that: The upper end of the alloy center shaft is a detachable structure.

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