Flow guide tube apparatus for single crystal furnace, single crystal furnace and single crystal silicon rod

Abstract

A flow guide tube apparatus for a single crystal furnace, a single crystal furnace and a single crystal silicon rod; the flow guide tube apparatus comprises a bottom surface that undulates in a wave-like manner along a radial direction, thereby guiding an inert gas in a manner that increases the flow rate of the inert gas.

Description

A guide tube device for a single crystal furnace, a single crystal furnace, and a single crystal silicon rod

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310701935.1 filed in China on June 13, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments of the present application relate to the technical field of single crystal preparation, and in particular to a guide tube device for a single crystal furnace, a single crystal furnace, and a single crystal silicon rod. Background Art

[0004] Most single crystal silicon rods are manufactured using the Czochralski (CZ) method, also known as the Czochralski method. This method uses the principle of condensation crystallization driven by the melt. At the interface between the solid and the liquid, a phase change occurs from liquid to solid due to the drop in melt temperature. In this method, the solid polysilicon raw material is placed in a quartz crucible and heated by a graphite heater to melt the polysilicon raw material in the quartz crucible. After that, the polysilicon raw material goes through the processes of temperature testing, seeding, shoulder placement, shoulder rotation, equal diameter and finishing, and finally the pulling of dislocation-free single crystal silicon rods is completed.

[0005] Single crystal silicon ingots, on the other hand, can be categorized as P-type and N-type depending on the dopant. N-type ingots are typically doped with Group V elements, with red phosphorus being the primary dopant of choice for heavily doped N-type ingots. Red phosphorus is known to be volatile, flammable, and explosive, with a high segregation coefficient. Therefore, after the polysilicon raw material is melted, phosphorus doping is typically performed via vapor phase doping.

[0006] However, according to experience, when pulling N-type single crystal silicon rods, about 50% of the red phosphorus dopant will leave the liquid surface and volatilize. In addition, the volatilization of silicon oxide produced by the reaction between the silicon melt and the quartz crucible will produce a large amount of volatiles during the pulling process of N-type single crystal silicon rods. If these volatiles are not discharged from the single crystal furnace in time, they will be deposited on the surface of the upper thermal field components. In addition, when inert gas is introduced into the furnace body, these volatiles deposited on the surface of the upper thermal field components may fall into the silicon melt under the blowing effect of the inert gas, thereby causing thermal shock. When the thermal shock wave reaches the solid-liquid interface, it will cause wire breakage, thereby leading to structural changes (Structure Loss) in the single crystal silicon rod, and ultimately affecting the crystallization rate.

[0007] Summary of the Invention

[0008] In view of this, the embodiments of the present application aim to provide a guide tube device for a single crystal furnace, a single crystal furnace, and a single crystal silicon rod; the guide tube device can timely and effectively discharge volatiles during the crystal pulling process from the single crystal furnace to ensure the crystallization rate of the single crystal silicon rod and improve the quality of the single crystal silicon rod;

[0009] Secondly, it can promptly and effectively bring oxygen evenly to the solid-liquid interface, ensuring the uniformity of oxygen in the single crystal silicon rod; and it can ensure the uniformity of the temperature field in the radial direction at the solid-liquid interface, so as to effectively reduce the probability of twin formation and improve the yield of single crystal silicon rods.

[0010] The technical solution of the embodiment of the present application is implemented as follows:

[0011] In a first aspect, an embodiment of the present application provides a guide tube device for a single crystal furnace, wherein the guide tube device includes a bottom surface that undulates in a wavy manner along a radial direction, thereby guiding the inert gas in a manner that increases the flow rate of the inert gas.

[0012] Optionally, in some possible implementations, the bottom surface is configured such that the distance between the trough of the bottom surface and the liquid surface of the silicon melt decreases in a gradually decreasing manner in a radial direction from close to the end of the single crystal silicon rod to away from the end of the single crystal silicon rod.

[0013] Optionally, in some possible implementations, the maximum distance between the trough of the bottom surface and the liquid surface of the silicon melt is 65 mm to 75 mm, and the minimum distance is 35 mm to 42 mm.

[0014] Optionally, in some possible implementations, the guide tube device is made of graphite.

[0015] Optionally, in some possible implementations, a pyrolytic boron nitride coating is deposited on the surface of the flow guide tube device.

[0016] In a second aspect, an embodiment of the present application provides a single crystal furnace, which includes the guide tube device as described in the first aspect.

[0017] Optionally, in some possible implementations, the single crystal furnace further includes a graphite crucible and a quartz crucible; wherein,

[0018] The quartz crucible is arranged in the graphite crucible, and the guide tube device is arranged directly above the quartz crucible.

[0019] In a third aspect, an embodiment of the present application provides a single crystal silicon rod, which is drawn using the single crystal furnace described in the second aspect.

[0020] An embodiment of the present application provides a guide tube device, a single crystal furnace, and a single crystal silicon rod for a single crystal furnace; in the embodiment of the present application, by setting the bottom surface of the guide tube device to undulate in a wave-like manner along the radial direction, the inert gas is guided in a manner that increases the flow rate of the inert gas, thereby being able to promptly remove volatiles generated during the crystal pulling process, thereby ensuring the normal progress of the crystal pulling.

[0021] In addition, the wavy bottom surface causes the distance between the guide tube device and the liquid surface to continuously change along the radial direction. It can be seen that, on the one hand, the size and change of the liquid surface distance are very important in the crystal pulling process, which directly affects the melt convection and further affects the effective oxygen content in the melt immersed in the single crystal silicon rod.

[0022] On the other hand, the fluctuation of the liquid level distance intensifies the radial convection near the liquid surface, and promptly and effectively brings oxygen evenly to the solid-liquid interface, ensuring the uniformity of oxygen in the single crystal silicon rod. At the same time, the intensification of melt convection in the radial direction ensures the uniformity of the temperature field in the radial direction of the solid-liquid interface, which not only effectively reduces the probability of twin formation, but also improves the yield of single crystal silicon rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic structural diagram of a single crystal furnace for pulling single crystal silicon rods in the related art;

[0024] FIG2 is a schematic structural diagram of a guide tube device for a single crystal furnace provided in an embodiment of the present application;

[0025] FIG3 is a schematic diagram of a change in the distance between the bottom surface of the guide tube device and the liquid surface provided in an embodiment of the present application;

[0026] FIG4 is a schematic structural diagram of a single crystal furnace provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0028] Before elaborating on the technical solution of the present application in detail, it should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present application should have the common meanings understood by persons having ordinary skills in the field to which the present application belongs.

[0029] In addition, it should be noted that the term "comprise" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, products or apparatus.

[0030] Referring to FIG1 , it shows a schematic structural diagram of a single crystal furnace 1 for manufacturing a conventional single crystal silicon rod. As shown in FIG1 , the single crystal furnace 1 includes:

[0031] A furnace body 10, wherein the furnace body 10 is used to define a furnace cavity;

[0032] a quartz crucible 20 , which is disposed at the bottom of the furnace cavity defined by the furnace body 10 and is used to contain solid polycrystalline silicon raw materials (or polycrystalline silicon melt) in the initial stage of preparing the single crystal silicon rods S;

[0033] Graphite heaters 30, the graphite heaters 30 are distributed around the quartz crucible 20;

[0034] In the specific process of manufacturing single crystal silicon rods, after a set mass of polysilicon raw materials are placed in the quartz crucible 20, the polysilicon raw materials in the quartz crucible 20 are heated by the graphite heater 30 to melt the polysilicon raw materials to form silicon melt MS;

[0035] The inverted conical guide tube 40 is mainly used to isolate the heat radiation from the graphite heater 30 to the single crystal silicon rod S, thereby ensuring the temperature gradient required for the growth of the single crystal silicon rod S and thus ensuring the crystallization rate of the single crystal silicon rod S. It is also used to guide an inert protective gas such as argon from top to bottom to the top of the silicon melt in the quartz crucible 20 to accelerate the gas flow rate at the liquid surface, thereby accelerating the removal of volatile impurities.

[0036] A gas inlet 50, which is used to introduce an inert gas, such as argon, during the crystal pulling process;

[0037] The exhaust port 60 is used to discharge volatiles generated during the crystal pulling process out of the furnace body 10 under the action of an inert gas.

[0038] It can be understood that the structure of the single crystal furnace 1 also includes: a seed crystal cable 70; wherein,

[0039] During the pulling process of the single crystal silicon rod S, a set mass of polysilicon raw material is loaded into the quartz crucible 20. After the quartz crucible 20 is heated to melt the polysilicon raw material to form silicon melt MS and the temperature of the silicon melt MS is stabilized, the seed crystal ZJ is lowered to the solid-liquid interface of the silicon melt MS through the seed crystal cable 70 and the processes of seeding, necking, shouldering, equal diameter growth and finishing are started, and finally a single crystal silicon rod S of a certain length is obtained.

[0040] It should be noted that a pulling head 80 connected to the seed cable 70 is also provided at the top of the single crystal furnace 1;

[0041] The pulling head 80 is mainly used to realize the rotation and lifting of the seed crystal ZJ, and can record data such as the displacement of the seed crystal ZJ.

[0042] It can be understood that the single crystal furnace 1 shown in FIG1 may also include other structures not shown in FIG1 , such as a crucible lifting device, etc., which are not specifically described in the embodiment of the present application.

[0043] Specifically, when using the single crystal furnace 1 to pull a single crystal silicon rod S, first, high-purity polycrystalline silicon raw material is placed in the quartz crucible 20, and while the crucible rotation mechanism (not shown in the figure) drives the quartz crucible 20 to rotate, the quartz crucible 20 is continuously heated by the graphite heater 30 to melt the polycrystalline silicon raw material contained in the quartz crucible 20 into a molten state, that is, melted into silicon melt MS.

[0044] The heating temperature is maintained at about one thousand degrees Celsius, and the gas in the furnace is usually inert gas, which melts the polysilicon raw material without producing unwanted chemical reactions.

[0045] It can be understood that during the crystal pulling process, the inert gas enters the furnace body 10 from the air inlet 50, and is blown down along the inside of the guide tube 40, passing over the surface of the single crystal silicon rod S, passing through the solid-liquid interface of the silicon melt MS, and then turns to blow the liquid surface, and then goes up along the inner wall of the quartz crucible 20 to bypass the quartz crucible 20 and go down along the outer wall of the graphite crucible (not shown in the figure) until it is blown to the exhaust port 60.

[0046] A large amount of volatiles are generated throughout the crystal pulling process. For example, when pulling N-type single crystal silicon rods, the volatiles include not only silicon oxide produced by the reaction between the silicon melt and the quartz crucible, but also volatiles from the dopant red phosphorus. These volatiles may deposit on the surface of the guide tube 40 during the entire crystal pulling process. The inert gas flow can then disperse these volatiles and carry them out of the furnace body 10. However, in some cases, due to insufficient inert gas dispersion, these volatiles may fall into the silicon melt, thereby affecting the quality of the single crystal silicon rods.

[0047] It is understandable that under normal circumstances, the inert gas flow rate at the air inlet can be increased to increase the blowing force and thus blow away the volatiles. However, when the inert gas flow rate is too large, it will cause the seed crystal pulling system and the single crystal silicon rod to shake. This shaking will cause fluctuations in the solid-liquid interface. The fluctuations in the solid-liquid interface will lead to the generation of defects such as twins in the single crystal silicon rod, and will also lead to uneven oxygen content. Violent shaking will also cause changes in the structure of the single crystal silicon rod.

[0048] Therefore, based on the above explanation, in order to avoid the shaking of the single crystal silicon rod and to remove volatiles in a timely and effective manner, thereby ensuring the normal progress of crystal pulling, the embodiment of the present application hopes to provide a guide tube with a wavy bottom surface, so that when the inert gas passes through the solid-liquid interface and passes over the liquid surface of the silicon melt, according to the Laval effect, the flow rate of the inert gas will be continuously accelerated, thereby increasing the flow rate of the inert gas, and then removing volatiles in a timely manner, thereby ensuring the normal progress of crystal pulling.

[0049] At the same time, the guide tube device provided by the present application avoids increasing the flow rate of the inert gas from the air inlet, thereby avoiding causing the single crystal silicon rod S to shake.

[0050] Specifically, referring to Figure 2, it shows a guide tube device 2 for a single crystal furnace provided in an embodiment of the present application. The guide tube device 2 includes a bottom surface 21 that undulates in a wavy manner along the radial direction, thereby guiding the inert gas in a manner that increases the flow rate of the inert gas.

[0051] It can be understood that in the embodiment of the present application, by setting the bottom surface 21 of the guide tube device 2 to fluctuate in a wave-like manner along the radial direction, the inert gas is guided in a manner that increases the flow rate of the inert gas, thereby being able to promptly remove the volatiles generated during the crystal pulling process, thereby ensuring the normal progress of the crystal pulling.

[0052] In addition, the wavy bottom surface 21 causes the distance between the guide tube device 2 and the liquid level YM in the radial direction to continuously change. It can be seen that, on the one hand, the size and change of the liquid level distance are very important in the crystal pulling process, which directly affects the melt convection and further affects the effective oxygen content in the melt immersed in the single crystal silicon rod S.

[0053] On the other hand, the fluctuation of the liquid level distance intensifies the radial convection near the liquid surface YM, and promptly and effectively brings oxygen into the solid-liquid interface uniformly, ensuring the uniformity of oxygen in the single crystal silicon rod S. At the same time, the intensification of melt convection in the radial direction ensures the uniformity of the temperature field in the radial direction of the solid-liquid interface, which not only effectively reduces the probability of twin formation, but also improves the yield of single crystal silicon rods.

[0054] Regarding the technical solution described in FIG1 , in some possible embodiments, as shown in FIG3 , the bottom surface 21 is configured such that the distance between the trough 31 of the bottom surface 21 and the liquid level YM of the silicon melt decreases in a gradually decreasing manner in a radial direction from close to the end S of the single crystal silicon rod to away from the end S of the single crystal silicon rod (indicated by the dotted arrow in the figure).

[0055] It is understood that the aforementioned involute reduction in the distance between the troughs 31 of the bottom surface 21 and the liquid surface YM refers to a continuously and gradually decreasing distance between the troughs 31 of the bottom surface 21 and the liquid surface YM. Specifically, when the inert gas enters the furnace body 10 through the gas inlet 50, it is blown down along the inner wall of the draft tube assembly 2 and sweeps across the surface of the single crystal silicon rod S, passing through the solid-liquid interface of the silicon melt MS and then across the liquid surface YM. Due to the Laval effect, when the inert gas flows through the troughs 31, the distance between the liquid surfaces there decreases, thereby reducing the pressure and increasing the flow rate of the inert gas.

[0056] That is, in the radial direction from the end S of the single crystal silicon rod to the end S away from the single crystal silicon rod, the distance between the trough 31 of the bottom surface 21 and the liquid surface YM becomes smaller and smaller, which helps to continuously accelerate the inert gas flow to quickly carry away the oxide.

[0057] It can be understood that as the distance between the trough 31 of the bottom surface 21 and the liquid surface YM becomes smaller and smaller, the pressure between the bottom surface 21 and the liquid surface YM also becomes smaller and smaller, so the flow rate of the inert gas will also become larger and larger. As the flow rate of the inert gas continues to accelerate, the volatiles in the crystal pulling process can be taken away in time to ensure the normal progress of the crystal pulling.

[0058] For the above-mentioned embodiment, in some examples, the maximum distance between the trough 31 of the bottom surface 21 and the liquid level YM of the silicon melt is 65 mm to 75 mm, and the minimum distance is 35 mm to 42 mm.

[0059] The distance between the trough 31 of the bottom surface 21 and the liquid level YM is configured to decrease in a gradually increasing manner from the end S of the single crystal silicon rod to the end S thereof, with a maximum distance of 65 mm to 75 mm and a minimum distance of 35 mm to 42 mm. Optionally, in a specific implementation, the distance between the trough 31 of the bottom surface 21 and the liquid level YM is configured to decrease in a gradually decreasing manner from the end S of the single crystal silicon rod to the end S thereof.

[0060] It should be noted that, in the radial direction from the end S of the single crystal silicon rod close to the end S of the single crystal silicon rod away from the end S, the setting of the distance between the trough 31 of the bottom surface 21 and the liquid surface YM needs to be determined according to the target requirements of the liquid surface spacing (Melt Gap). It can be understood that the size of the liquid surface spacing directly determines the axial temperature difference at the solid-liquid interface, and the axial temperature difference needs to match the crystal growth pulling rate. When the distance value between the trough 31 of the bottom surface 21 and the liquid surface YM is within the set range, the axial temperature difference can well match the crystal growth pulling rate to achieve smooth growth of the crystal.

[0061] For example, when the guide tube device 2 provided in the embodiment of the present application is as shown in Figure 3, then considering the matching of the axial temperature difference and the crystal growth pulling speed, the distance D between each trough 31 and the liquid level YM in the radial direction from the end S of the single crystal silicon rod to the end S of the single crystal silicon rod is 75 mm, 65 mm, and 55 mm respectively. This change can enable the inert gas to flow through the guide tube device 2 and the liquid level YM. The flow rate of the inert gas continues to increase, so as to ensure that the volatiles in the crystal pulling process are removed in a timely and stable manner.

[0062] In addition, the distance between the trough 31 of the bottom surface 21 and the liquid surface YM is set to change gradually, so that the inert gas velocity increases steadily, which is also beneficial to the stable change of the melt convection during the crystal pulling process, thereby making the temperature field change uniformly during the crystal pulling process, which is more conducive to the uniform control of the oxygen content in the single crystal silicon rod.

[0063] It should be noted that in the embodiments of this application, words such as "exemplarily" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplarily" or "for example" is intended to present the relevant concepts in a concrete manner.

[0064] Regarding the technical solution described in FIG1 , in some possible implementations, the guide tube device 2 is made of graphite.

[0065] It can be understood that setting the material of the guide tube device 2 to graphite can ensure that the heat radiation of the graphite heater 30 to the single crystal silicon rod S is isolated during the crystal pulling process, ensuring the temperature gradient required for the growth of the single crystal silicon rod S, and thus ensuring the crystallization rate of the single crystal silicon rod S.

[0066] Regarding the above-mentioned embodiments, in some examples, according to the guide tube device according to claim 2, a pyrolytic boron nitride coating is deposited on the surface of the guide tube device 2. The pyrolytic boron nitride coating has good stability under high temperature conditions and high chemical stability. It will not chemically react with volatiles in the crystal pulling process. Therefore, it is very suitable for use in such a high-volatile environment and can increase the service life of the guide tube.

[0067] Next, referring to FIG. 4 , a single crystal furnace 4 according to an embodiment of the present application is shown. The single crystal furnace 4 includes the guide tube device 2 as described in the aforementioned technical solution.

[0068] Regarding the single crystal furnace 4 described in FIG4 , in some possible implementations, the single crystal furnace 4 further includes a graphite crucible 90 and a quartz crucible 20 ; wherein,

[0069] The quartz crucible 20 is disposed in the graphite crucible 90 , and the flow guide tube device 2 is disposed directly above the quartz crucible 20 .

[0070] Finally, the embodiment of the present application further provides a single crystal silicon rod, which is drawn using the single crystal furnace 4 described in the aforementioned technical solution.

[0071] It should be noted that the technical solutions described in the embodiments of this application can be combined arbitrarily without conflict.

[0072] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A guide tube device for a single crystal furnace, the guide tube device comprising a bottom surface that undulates in a wavy manner along a radial direction, so as to guide the inert gas in a manner that increases the flow rate of the inert gas.

2. The guide tube device according to claim 1, wherein: The bottom surface is configured such that the distance between the wave trough of the bottom surface and the liquid surface of the silicon melt decreases in a gradually increasing manner in a radial direction from close to the end of the single crystal silicon rod to far away from the end of the single crystal silicon rod.

3. The guide tube device according to claim 2, wherein: The maximum distance between the trough of the bottom surface and the liquid surface of the silicon melt is 65 mm to 75 mm, and the minimum distance is 35 mm to 42 mm.

4. The guide tube device according to claim 1, wherein: The guide tube device is made of graphite.

5. The guide tube device according to claim 2, wherein: A pyrolytic boron nitride coating is deposited on the surface of the guide tube device.

6. A single crystal furnace, comprising the guide tube device according to any one of claims 1 to 5.

7. The single crystal furnace according to claim 6, wherein: The single crystal furnace also includes a graphite crucible and a quartz crucible; wherein, The quartz crucible is arranged in the graphite crucible, and the guide tube device is arranged directly above the quartz crucible.

8. A single crystal silicon rod, wherein the single crystal silicon rod is drawn by the single crystal furnace according to claim 6 or 7.

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