A method of drawing large size single crystal silicon rods

Abstract

The application discloses a method for drawing large-size single crystal silicon rods, comprising the following steps: setting starting parameters according to the production environment and the size of the crystal rod to be drawn, the starting parameters including crucible rotation, crystal rotation, argon flow, furnace pressure and drawing speed; gradually increasing the crucible rotation and the drawing speed, gradually reducing the crystal rotation, maintaining the argon flow and the furnace pressure unchanged as the length of the crystal rod gradually increases; continuing to increase the length of the crystal rod to a first length, increasing the gallium concentration in the silicon melt and accelerating the resistivity attenuation of the tail of the crystal rod when the first length is reached, gradually reducing the crucible rotation, the drawing speed, the argon flow and the furnace pressure and gradually increasing the crystal rotation as the crystal rod continues to grow; starting to finish the drawing when the length of the crystal rod reaches a second length, and the remaining amount of the silicon melt is less than half of the initial amount when the second length is reached. The gallium-doped crystal rod grown by the above method has more uniform tail resistivity and longer unit growth length, and the raw material consumption is saved.

Description

Technical Field

[0001] This application relates to the field of monocrystalline silicon production, and more particularly to a method for pulling large-size monocrystalline silicon rods. Background Technology

[0002] In the field of solar energy utilization, monocrystalline silicon is an important semiconductor material used to make photovoltaic solar cells. The monocrystalline silicon rods produced need to be sliced ​​and used as the basic material for making the cells. With the continuous development of the industry, large-size monocrystalline silicon wafers have gradually become the mainstream raw material due to their advantages such as large area and high conversion efficiency, and the demand for large-size monocrystalline wafers is also increasing. The main method for producing monocrystalline silicon rods is the Czochralski method, which involves processing silicon raw materials through processes such as melting, feeding, temperature control, crystal pulling, shoulder formation, shoulder rotation, equal diameter production, and tailing. Among these processes, equal diameter production is the most important and time-consuming step in the entire monocrystalline silicon rod growth process. The effective length that can be produced in the equal diameter production process directly affects the yield and output per unit. Generally, the effective length that can be produced in the equal diameter production process depends on the resistivity distribution at the tail of the monocrystalline silicon rod. The more uniform the radial resistivity at the tail of the monocrystalline silicon rod, the longer the effective length of the entire monocrystalline silicon rod can be produced. The resistivity of the monocrystalline silicon rod is mainly determined by the gallium concentration in the silicon melt. Generally, it is necessary to control the gallium entering the monocrystalline silicon rod by controlling parameters such as crucible rotation, crystal rotation, argon flow rate, furnace pressure, and pulling speed during the equal diameter production process, thereby controlling the resistivity at the tail of the rod.

[0003] Compared to traditional boron doping in silicon ingots, gallium doping can reduce the impact of the higher light attenuation rate caused by boron doping. However, gallium has a very small segregation coefficient in silicon melt, resulting in higher resistivity at the tail of the ingot produced by existing technology. The deviation between the edge and center resistivity at the tail is significant, and the radial resistivity at the tail is uneven. Consequently, the effective length of the ingot cannot meet the requirements, forcing it to proceed to the next finishing process. This leads to low yield per unit of single-crystal silicon ingot, impacting overall production capacity. To address these issues, a method for pulling large-size single-crystal silicon ingots is needed to improve the uniformity of radial resistivity at the tail, increase the effective length of ingots produced per batch, improve production efficiency and capacity, and reduce raw material consumption and energy consumption. Summary of the Invention

[0004] This invention provides a method for pulling large-size monocrystalline silicon rods. Its main purpose is to solve the problem that the resistivity of the tail of monocrystalline silicon rods produced by existing technology is not uniform enough, which forces premature termination during production, reduces the yield per unit and affects the overall production capacity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This application provides a method for pulling large-size single-crystal silicon rods, including the following steps:

[0007] S1. Set the starting parameters according to the production environment and the required crystal rod size. The starting parameters include crucible rotation, crystal rotation, argon flow rate, furnace pressure and pulling speed.

[0008] S2. As the growth length of the crystal rod gradually increases, gradually increase the crucible rotation and pulling speed, gradually decrease the crystal rotation, and keep the argon flow rate and furnace pressure constant.

[0009] S3. The growth length of the crystal rod continues to increase to the first length. When the first length is reached, the gallium concentration in the silicon melt increases and the resistivity at the tail of the crystal rod decreases faster. At this time, as the crystal rod continues to grow, the crucible rotation, pulling speed, argon flow rate and furnace pressure are gradually reduced and the crystal rotation is gradually increased.

[0010] S4. When the crystal rod grows to the second length, the process begins to end. When the second length is reached, the remaining amount of silicon melt is less than half of the initial amount.

[0011] Preferably, in step S2, the crucible rotation is gradually increased and the crystal rotation is decreased, so that the forced convection of the silicon melt is gradually enhanced relative to the natural convection.

[0012] Preferably, in step S3, the crucible rotation is gradually reduced and the crystal rotation is increased, so that the forced convection of the silicon melt is gradually weakened relative to the natural convection.

[0013] Preferably, in step S1, the initial parameters include crucible rotation at 5 rpm, crystal rotation at 9 rpm, argon flow rate at 90 slpm, furnace pressure at 13 Torr, and pulling speed at 78 mm / hr.

[0014] Preferably, in step S2, when the growth length of the crystal rod is 800-2500 mm, the pulling speed reaches the maximum of 98 mm / hr and remains unchanged, the crucible rotation reaches the maximum of 8 rpm and remains unchanged, and the crystal rotation reaches the minimum of 7 rpm and remains unchanged.

[0015] Preferably, in step S3, the first length is 2500 mm, at which time the crucible rotation speed is reduced to 7.5 rpm, the pulling speed is reduced to 94 mm / hr, the argon flow rate is reduced to 75 slpm, the furnace pressure is reduced to 9 Torr, and the crystal rotation speed is increased to 9 rpm.

[0016] Preferably, in step S3, when the crystal rod growth length reaches 3000 mm, the pulling speed is reduced to a minimum of 90 mm / hr and kept constant, and the crystal rotation speed is increased to a maximum of 12 rpm and kept constant.

[0017] Preferably, in step S4, the second length is 3500 mm, at which time the crucible rotation speed is reduced to a minimum of 6.5 rpm and maintained, the argon flow rate is reduced to a minimum of 60 slpm and maintained, and the furnace pressure is reduced to a minimum of 5 Torr and maintained.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] This application provides a method for pulling large-size single-crystal silicon rods. By changing the crucible rotation, crystal rotation, pulling speed, argon flow rate, and furnace pressure, and adjusting these parameters at appropriate length nodes, the method alters the strength of forced convection relative to natural convection at different stages of the rod growth. Furthermore, by reducing the argon flow rate and furnace pressure in the later stages, the method better matches the parameter properties of the silicon melt in the crucible and the rod. Compared to existing technologies, this method can result in a more uniform resistivity at the tail of the gallium-doped rod, improve the rod quality pass rate, allow for the growth of longer rods beyond the existing length, increase production capacity and improve raw material utilization, and also reduce argon consumption during the rod growth process. Attached Figure Description

[0020] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0021] Figure 1 This is a flowchart of one embodiment of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0024] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] The inventors discovered that, in the field of monocrystalline silicon production technology, compared with the traditional technology of doping boron into crystal rods, doping gallium into crystal rods can reduce the impact of the high light attenuation rate caused by boron doping. However, gallium has a very small segregation coefficient in silicon melt, and the resistivity of the tail of the crystal rod produced by the existing technology is high. The deviation between the edge resistivity and the center resistivity of the tail is large, and the radial resistivity of the tail is uneven. As a result, the effective length of the crystal rod cannot reach the required length and has to be transferred to the next finishing process. The low yield of monocrystalline silicon rods affects the overall production capacity.

[0026] In view of this, refer to Figure 1 This embodiment provides a method for pulling large-size single-crystal silicon rods. The method sets initial parameters that best suit the actual crystal pulling conditions based on the actual equipment, production environment, and the required rod size. Before reaching the first length, the crucible rotation and pulling speed are gradually increased, while the crystal rotation is gradually decreased, and the argon flow rate and furnace pressure are kept constant. During this process, the gallium concentration in the silicon molten material increases slowly, and the resistivity at the rod tail is relatively uniform. Adjusting the parameters stabilizes the crystal pulling environment. Increasing the crucible rotation and decreasing the crystal rotation makes the forced convection on the silicon molten material greater than the natural convection within the silicon molten material itself, making it easier for the rod to grow. Increasing the pulling speed accelerates crystal growth. After reaching the first length, the gallium concentration in the silicon molten material is already high, and the resistivity at the rod tail increases rapidly, with reduced uniformity. At this point, gradually decreasing the crucible rotation and pulling speed while increasing the crystal rotation ensures the quality of crystal growth, making natural convection greater than forced convection. The gallium in the silicon molten material is rapidly stirred up. Furthermore, reducing the argon flow rate and furnace pressure allows gallium to quickly volatilize into the rod, resulting in a more uniform radial resistivity at the rod tail. Once the crystal rod reaches the second length, less than half of the initial amount of molten silicon remains in the crucible, nearing the end of the process. The process involves finishing the crystal rod and adding more material for crystal pulling.

[0027] Example 1:

[0028] The production or verification environment is a 40-inch thermal field, and the pulled ingot size is 12 inches. The crystal pulling steps are as follows:

[0029] S1. Based on the production environment of a 40-inch hot zone and the required crystal rod size of 12 inches, the starting parameters are set as follows: starting crucible rotation is 5 rpm, crystal rotation is 9 rpm, argon flow rate is 90 slpm, furnace pressure is 13 Torr, and pulling speed is 78 mm / hr.

[0030] S2. After setting the initial parameters and starting crystal pulling, the length of the crystal rod gradually increases. As the length of the crystal rod increases, the crucible rotation and pulling speed are gradually increased, while the crystal rotation is gradually decreased, and the argon flow rate and furnace pressure are kept constant. This stage is the rapid crystal growth period from the initial insertion of the seed crystal to the start of the crystal pulling equipment. It is necessary to gradually increase the crucible rotation and decrease the crystal rotation so that the forced convection in the silicon melt in the crucible is greater than the natural convection, which promotes the silicon melt to gather towards the crystal rod during the crystal pulling process, making it easier for the crystal to grow. Maintaining a stable argon flow rate and furnace pressure in the thermal environment is beneficial for the continuous growth of the crystal rod. During this process, the gallium concentration in the silicon melt gradually increases, and the longitudinal resistivity of the crystal rod remains uniform.

[0031] It should be noted that in step S2, the parameter changes in the stages of the crystal growth process are as follows: when the crystal growth length is 500 mm, the crucible rotation speed gradually increases from 5 rpm to 8 rpm and reaches the highest speed. In the subsequent crystal pulling process, this crucible rotation speed is kept constant, and the crystal rotation speed gradually decreases from 9 rpm to 8 rpm. The pulling speed gradually increases from the initial 78 mm / hr to 93 mm / hr. The argon flow rate is kept at 90 slpm and the furnace pressure is kept at 13 Torr, which are consistent with the initial values. The crystal growth rate gradually increases, the gallium concentration in the crucible increases slowly, and the longitudinal resistivity of the crystal is relatively uniform.

[0032] When the crystal rod growth length is 800mm, the maximum rotation speed of the crucible is kept constant at 8rpm. During this process, the gallium concentration in the silicon melt increases slowly. In order to ensure the quality of crystal growth and reduce the twisting of the crystal rod, the rotation speed is reduced by 0.5rpm to 7.5rpm from 8rpm, and the pulling speed is increased to the maximum of 98mm / hr, which is the fastest crystal pulling speed. The argon flow rate and furnace pressure are also kept constant.

[0033] When the ingot is in the range of 800-2500mm, the gallium concentration in the silicon melt is relatively stable and the gallium concentration increases slowly. The longitudinal resistivity of the ingot is relatively uniform, which is more suitable for continuous crystal pulling and growth. During this long crystal growth process, the crucible rotation is kept at the highest of 8rpm, the crystal rotation is reduced to the lowest of 7rpm and kept constant, the pulling speed is kept at the highest of 98mm / hr, the argon flow rate and furnace pressure are also kept stable, and the crystal pulling process is relatively smooth.

[0034] S3. When the crystal rod grows to the first length, which in this embodiment is 2500 mm, the gallium concentration in the silicon melt increases, and the resistivity at the tail of the crystal rod decreases rapidly. Compared to the previous step, gallium in the silicon melt is less likely to enter the crystal rod at this point. Therefore, it is necessary to gradually reduce the crucible rotation and pulling speed, and gradually increase the crystal rotation. The increased solidification fraction in the silicon melt, reduced crucible rotation, and increased crystal rotation result in natural convection exceeding forced convection. This rapidly agitates the gallium in the silicon melt, allowing it to quickly enter the crystal rod, thus increasing the longitudinal resistivity at the tail of the crystal rod. Once the crystal rod reaches a length of approximately 2500mm, crystal formation becomes more difficult compared to the previous stages. It is necessary to gradually reduce the argon flow rate and furnace pressure to force the gallium in the molten silicon to rapidly evaporate and enter the single-crystal silicon rod. This reduces crucible rotation and pulling speed while increasing crystal rotation, resulting in a slower growth rate and ensuring the quality of the grown crystal. Furthermore, as the argon flow rate gradually decreases, the dry pump opening is maintained at approximately 50% during the crystal pulling process, preventing difficulties in crystal growth caused by pipe blockage. These steps ensure the uniformity of the longitudinal resistivity at the tail of the crystal rod.

[0035] It should be noted that in step S3, the parameter changes during the growth of the crystal rod are as follows: when the growth length of the crystal rod is 2500mm, the crucible rotation speed is reduced from 8rpm to 7.5rpm, while the crystal rotation speed is directly increased from 7rpm to 9rpm, and the pulling speed is reduced to 94mm / hr. The argon flow rate and furnace pressure are gradually reduced. The argon flow rate is gradually reduced from a maximum of 90Slpm to 75Slpm in this stage, and the furnace pressure is gradually reduced from a maximum of 13Torr to 9Torr in this stage. It should be noted that in this embodiment, the reduction of argon flow rate and furnace pressure begins to gradually decrease when the growth length of the crystal rod is about 2000mm, so that gallium can enter the crystal rod more easily. Starting from step S3, the growth rate of the crystal rod decreases, and the crystallization cross section of the crystal rod gradually changes from concave to planar. The parameters are adjusted to ensure the quality of crystal growth and avoid uneven resistivity at the tail of the crystal rod.

[0036] When the ingot growth length reaches 3000 mm, the crucible rotation is further reduced to 7 rpm, the crystal rotation is increased to a maximum of 12 rpm and maintained, the pulling speed is reduced to 90 mm / hr and maintained, the argon flow rate is reduced to 70 slpm, and the furnace pressure is reduced to 7 Torr. At this point, the crystal pulling process is nearing completion, and the crystallization interface changes from planar to convex. The gallium concentration in the silicon melt is higher. By reducing the crucible rotation and increasing the crystal rotation to the maximum, the stirring intensity in the silicon melt is increased, making natural convection greater than forced convection. Furthermore, by reducing the argon flow rate and furnace pressure, impurities in the silicon melt can more easily enter the ingot, ensuring a stable and balanced longitudinal resistivity at the tail of the ingot.

[0037] S4. When the crystal rod reaches the second length, the process gradually ends. At this point, the remaining silicon molten material in the crucible is less than half of the initial value. In actual production, the decision to begin ending is generally based on approximately 40% of the initial crucible material remaining. At this point, the gallium concentration in the crucible is already high, making it unsuitable for continued crystal pulling. The process needs to be transitioned to the ending phase, with raw material added to the crucible before restarting crystal pulling. In some embodiments, this process of adding raw material and pulling crystals is typically repeated 6-7 times before the furnace is shut down. Specifically, when the second length is 3500mm, the crucible rotation speed is reduced to a minimum of 6.5rpm and maintained until the end of the process. The crystal rotation speed remains at a maximum of 12rpm, the pulling speed remains at a minimum of 90mm / hr, the argon flow rate is reduced to a minimum of 60Slpm and maintained until the end of the process, and the furnace pressure is reduced to a minimum of 5Torr and maintained until the end of the process. Maintaining high crystal rotation speed before the end of the process makes the resistivity at the center and edge of the crystal rod more consistent, resulting in a more uniform radial resistivity at the tail of the crystal rod.

[0038] The specific parameters, such as the gallium concentration in the crucible during crystal pulling in this embodiment, are shown in Table 1.

[0039] Table 1: Gallium concentration corresponding to different ingot lengths and crucible weights

[0040] 0％ 1.61E+16 0.93 5.87 1099 0％ 1.60945E+16 0.93 99.86 1083 2％ 1.63304E+16 0.92 105.74 1082 2％ 1.63453E+16 0.92 199.73 1066 3％ 1.65887E+16 0.91 205.60 1065 3％ 1.66042E+16 0.91 299.59 1049 5％ 1.68554E+16 0.89 305.46 1048 5％ 1.68713E+16 0.89 499.31 1015 8％ 1.74154E+16 0.87 505.19 1014 8％ 1.74324E+16 0.87 798.90 964 12％ 1.83292E+16 0.83 804.78 963 12％ 1.83481E+16 0.83 1198.35 896 19％ 1.97087E+16 0.78 1204.23 895 19％ 1.97305E+16 0.78 1597.80 828 25％ 2.13138E+16 0.72 1603.68 827 25％ 2.13394E+16 0.72 1997.25 760 31％ 2.32049E+16 0.67 2003.13 759 31％ 2.32353E+16 0.67 2496.57 675 39％ 2.61023E+16 0.61 2502.44 674 39％ 2.61407E+16 0.61 2995.88 590 46％ 2.98306E+16 0.54 3001.76 589 46％ 2.98809E+16 0.54 3495.20 505 54％ 3.48083E+16 0.47 3501.07 504 54％ 3.48768E+16 0.47 3994.51 420 62％ 4.17911E+16 0.41 4000.38 419 62％ 4.18901E+16 0.40

[0041] In the crystal rod growth process shown in Table 1, the gallium concentration gradually increases as the crystal rod grows. Before 2500mm, the crystal rod is easier to grow, and the gallium in the silicon melt is also easier to enter the single crystal silicon rod. At this time, the crucible rotation and pulling speed are gradually increased, and the crystal rotation is gradually decreased to keep the argon flow rate and furnace pressure in the crystal pulling environment constant. Within this range, the radial resistivity of the tail of the crystal rod is relatively uniform.

[0042] As the gallium concentration in the silicon melt continues to increase, it is necessary to gradually reduce the crucible rotation and pulling speed, and gradually increase the crystal rotation. At the same time, it is necessary to gradually reduce the argon flow rate and furnace pressure to accelerate the entry of gallium into the crystal rod and make the radial resistivity of the crystal rod tail uniform.

[0043] In this embodiment, the parameter configurations for each length of the crystal rod are shown in Table 2;

[0044] Table 2: Parameter values ​​of crucible rotation, crystal rotation, pulling speed, argon flow rate, and furnace pressure for different crystal rod lengths.

[0045]

[0046] As shown in Table 2, this table corresponds to the changing trends of crucible rotation, crystal rotation, pulling speed, argon flow rate, and furnace pressure when the crystal rod grows to different lengths. As the crystal rod gradually grows, the crucible rotation and pulling speed increase to the first length of the crystal rod and then decrease, while the crystal rotation decreases to the first length of the crystal rod and then increases. The argon flow rate and furnace pressure remain stable until they approach the first length of the crystal rod and then gradually decrease. It should be noted that the initial values ​​of these five parameters and the nodes at which the parameters change, namely the first and second lengths of the crystal rod, may be adjusted in some embodiments due to equipment attributes, environmental parameters, or other influencing factors. However, the trends of crucible rotation and pulling speed increasing and then decreasing, crystal rotation decreasing and then increasing, and argon flow rate and furnace pressure remaining stable and then decreasing remain unchanged. By changing these parameter trends, the parameter attributes of the silicon melt in the crucible and the crystal rod at various lengths can be better matched. This can increase the single-batch length of the crystal rod while ensuring uniform resistivity at the tail of the crystal rod, and save argon consumption, thereby improving the quality and yield of the crystal rod.

[0047] The above embodiments illustrate only one implementation of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for pulling large-size single-crystal silicon rods, characterized in that, Includes the following steps: S1. Set the starting parameters according to the production environment and the required crystal rod size. The starting parameters include crucible rotation, crystal rotation, argon flow rate, furnace pressure and pulling speed. The starting parameters include crucible rotation of 5 rpm, crystal rotation of 9 rpm, argon flow rate of 90 slpm, furnace pressure of 13 Torr and pulling speed of 78 mm / hr. S2. As the growth length of the crystal rod gradually increases, the crucible rotation and pulling speed are gradually increased, while the crystal rotation is gradually decreased, and the argon flow rate and furnace pressure are kept constant. Specifically, when the growth length of the crystal rod is 800-2500mm, the pulling speed reaches the highest 98mm / hr and is kept constant, the crucible rotation reaches the highest 8rpm and is kept constant, and the crystal rotation reaches the lowest 7rpm and is kept constant. S3. The growth length of the crystal rod continues to increase to the first length. When the first length is reached, the gallium concentration in the silicon melt increases and the resistivity at the tail of the crystal rod decreases faster. At this time, as the crystal rod continues to grow, the crucible rotation, pulling speed, argon flow rate and furnace pressure are gradually reduced, and the crystal rotation is gradually increased. Specifically, the first length is 2500mm. At this time, the crucible rotation is reduced to 7.5rpm, the pulling speed is reduced to 94mm / hr, the argon flow rate is reduced to 75Slpm, the furnace pressure is reduced to 9Torr, and the crystal rotation is increased to 9rpm. When the growth length of the crystal rod reaches 3000mm, the pulling speed is reduced to the minimum of 90mm / hr and kept unchanged, and the crystal rotation is increased to the maximum of 12rpm and kept unchanged. S4. When the crystal rod grows to the second length, the process begins to end. When the second length is reached, the remaining amount of silicon melt is less than half of the initial amount. The second length is 3500 mm. At this time, the crucible rotation speed is reduced to a minimum of 6.5 rpm and maintained, the argon flow rate is reduced to a minimum of 60 slpm and maintained, and the furnace pressure is reduced to a minimum of 5 Torr and maintained.

2. The method for pulling large-size single-crystal silicon rods as described in claim 1, characterized in that, In step S2, the crucible rotation is gradually increased and the crystal rotation is gradually decreased, so that the forced convection of the silicon melt is gradually enhanced relative to the natural convection.

3. The method for pulling large-size single-crystal silicon rods as described in claim 1, characterized in that, In step S3, the crucible rotation is gradually reduced and the crystal rotation is increased, so that the forced convection of the silicon melt is gradually weakened relative to the natural convection.

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